Patent Publication Number: US-7211928-B2

Title: Apparatus, circuitry, signals and methods for cleaning and/or processing with sound

Description:
RELATED APPLICATIONS 
   The subject application is a continuation-in-part of commonly owned and U.S. patent application Ser. No. 10/178,751 filed Jun. 24, 2002 now U.S. Pat. No. 6,822,372 and Ser. No. 10/825,036 filed Apr. 15, 2004, each of which is expressly incorporated herein by reference. Each of these applications has a history that is detailed below. 
   History of U.S. patent application Ser. No. 10/178,751 filed Jun. 24, 2002 now U.S. Pat. No. 6,822,372: U.S. patent application Ser. No. 10/178,751 filed Jun. 24, 2002 now U.S. Pat. No. 6,822,372, entitled “Apparatus, Circuitry and Methods for Cleaning and/or Processing with Sound Waves”, still, which is a continuation in part of four U.S. patent application Ser. No. 09/370,302 filed Aug. 9, 1999 now U.S. Pat. No. 7,004,016, Ser. No. 09/609,036 filed Jun. 30, 2000 now U.S. Pat. No. 6,462,461, Ser. No. 09/678,576 filed Oct. 3, 2000 now U.S. Pat. No. 6,433,460 and Ser. No. 10/029,751 filed Oct. 29, 2001 now U.S. Pat. No. 6,538,360 the history of each is described below. 
   History of U.S. patent application Ser. No. 09/370,302 filed Aug. 9, 1999 now U.S. Pat. No. 7,004,061: U.S. patent application Ser. No. 09/370,302 filed Aug. 9, 1999 now U.S. Pat. No. 7,004,016, entitled “Probe System for Ultrasonic Processing Tank”, still pending, which is a division of U.S. patent application Ser. No. 09/097,374 filed Jun. 15, 1998 (now U.S. Pat. No. 6,016,821, granted Jan. 25, 2000); which is a continuation of U.S. patent application Ser. No. 08/718,945 filed Sep. 24, 1996 (now U.S. Pat. No. 5,834,781, granted Nov. 10, 1998) and U.S. Provisional Application No. 60/049,717 filed Jun. 16, 1997, each of which is expressly incorporated herein by reference. 
   History of U.S. patent application Ser. No. 09/609,036 filed Jun. 30, 2000 now U.S. Pat. No. 6,462,461: U.S. patent application Ser. No. 09/609,036 was filed Jun. 30, 2000, entitled “Circuitry to Modify the Operation of Ultrasonic Generators” (now U.S. Pat. No. 6,462,461, granted Oct. 8, 2002), which is expressly incorporated herein by reference. 
   History of U.S. patent application Ser. No. 09/678,576 filed Oct. 3, 2000 now U.S. Pat. No. 6,433,460: U.S. patent application Ser. No. 09/678,576 filed Oct. 3, 2000 now U.S. Pat. No. 6,433,460, entitled “Apparatus and Methods for Cleaning and/or Processing Delicate Parts”, (now U.S. Pat. No. 6,433,460, granted Aug. 13, 2002) is a Divisional Application of Continuation-in-Part application Ser. No. 09/066,158, filed Apr. 24, 1998 (now U.S. Pat. No. 6,181,051, granted Jan. 30, 2001), which is a continuation of U.S. patent application Ser. No. 08/718,945 filed on Sep. 24, 1996 (now U.S. Pat. No. 5,834,871, entitled “Apparatus And Methods For Cleaning And/Or Processing Delicate Parts”), and U.S. Provisional Patent Application Ser. No. 60/023,150, filed on Aug. 5, 1996, each of which is expressly incorporated herein by reference. 
   History of U.S. patent application Ser. No. 10/029,751 filed Oct. 29, 2001 now U.S. Pat. No. 6,538,360: U.S. patent application Ser. No. 10/029,751 filed Oct. 29, 2001, entitled “Multiple Frequency Cleaning System” (now U.S. Pat. No. 6,538,360, granted Mar. 25, 2003) is a divisional application of U.S. patent application Ser. No. 09/504,567 entitled “Multiple Frequency Cleaning System,” filed on Feb. 15, 2000 (now U.S. Pat. No. 6,313,565, granted Nov. 6, 2001), the disclosure of which is entirely incorporated herein by reference. 
   History of U.S. patent application Ser. No. 10/825,036 filed Apr. 15, 2004: U.S. patent application Ser. No. 10/825,036 filed Apr. 15, 2004 is a continuation-in-part of commonly-owned and U.S. patent application Ser. No. 09/370,302 filed Aug. 9, 1999 now U.S. Pat. No. 7,004,016, still pending; which is a division of U.S. patent application Ser. No. 09/097,374 filed Jun. 15, 1998 (now U.S. Pat. No. 6,016,821, granted Jan. 25, 2000); which is a continuation of U.S. patent application Ser. No. 08/718,945 filed Sep. 24, 1996 (now U.S. Pat. No. 5,834,871, granted Nov. 10, 1998) and U.S. Provisional Application No. 60/049,717 filed Jun. 16, 1997, each of which is expressly incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The invention relates to systems and methods for cleaning and/or processing parts. In particular, the invention relates to ultrasound systems, ultrasound generators, ultrasound transducers, ultrasound signals and methods which support or enhance the application of ultrasound energy within liquid. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to ultrasound cleaning systems, and more particularly, to systems, generators, transducers, circuitry, signals and methods that clean and/or process by coupling sound waves into a liquid. Prior art ultrasound systems lack the ability to remove a wide range of particle types and sizes without doing damage to the part being cleaned or processed. This invention improves the performance of an ultrasound system while eliminating the damage causing mechanisms. 
   SUMMARY OF THE INVENTION 
   As defined in the technical literature, “ultrasound”, “ultrasonic” and “ultrasonics” generally refer to acoustic disturbances in a frequency range above about eighteen kilohertz (khz) and which extend upwards to over four megahertz (Mhz). As is commonly used in the cleaning industry and as used herein, “ultrasonic” will generally refer to acoustic disturbances in a frequency range above about eighteen kilohertz and extending up to about 90 khz. Ultrasound and ultrasonics will be used to mean the complete range of acoustic disturbances from about 18 khz to 4 Mhz, except when they are use with terms such as “lower frequency” ultrasound, “low frequency” ultrasound, “lower frequency” ultrasonics, or “low frequency” ultrasonics, then they will mean ultrasound between about 18 khz and 90 khz. “Megasonics” or “megasonic” refer to acoustic disturbances between about 600 khz and 4 Mhz. The prior art has manufactured “low frequency” and “megasonic” ultrasound systems. Typical prior art low frequency systems, for example, operate at 25 khz, 40 khz, and as high as 90 khz. Typical prior art megasonic systems operate between 600 khz and 1 Mhz. Certain aspects of the invention apply to low frequency ultrasound and to megasonics. However, certain aspects of the invention apply to ultrasound in the 100 khz to 350 khz region, a frequency range which is sometimes denoted herein as “microsonic” or “microsonics.” The upper end of the microsonic frequency range from about 300 khz to 350 khz is called herein “higher microsonics” or “higher frequency microsonic”. 
   As used herein, “resonant transducer” means a transducer operated at a frequency or in a range of frequencies that correspond to a one-half wavelength (lambda) of sound in the transducer stack. “Harmonic transducer” means a transducer operated at a frequency or in a range of frequencies that correspond to 1 lambda, 1.5 lambda, 2 lambda or 2.5 lambda of sound, and so on, in the transducer stack. The harmonics of a practical physical structure are often not exact integer multiples of the fundamental frequency, the literature sometimes refer to these non-integer harmonics as overtones. Herein, harmonics will mean resonances higher in frequency than the fundamental resonant frequency. “Bandwidth” means the range of frequencies in a resonant or harmonic region of a transducer over which the acoustic power output of a transducer remains between 50% and 100% of the maximum value. 
   As used herein, a “delicate part” refers to those parts which are undergoing a manufacture, process, or cleaning operation within liquid subjected to ultrasound energy. By way of example, one delicate part is a semiconductor wafer which has extremely small features and which is easily damaged by cavitation implosion. Another delicate part is a modern jet engine turbine blade which can fracture if excited into resonant vibration. A delicate part often defines components in the computer industry, including disk drives, semiconductor components, and the like. 
   As used herein, “khz” refers to kilohertz and a frequency magnitude of one thousand hertz. “Mhz” refers to megahertz and a frequency magnitude of one million hertz. 
   As used herein, “successive frequencies” are two or more waveforms that are produced, one at a time, in a series fashion, where at least two different frequencies exist within the set of waveforms. At the output of a generator, these waveforms generally form an AC voltage. In an ultrasound tank, these waveforms are normally represented by an ultrasound wave in the liquid. 
   As used herein, successive frequencies are said to “sweep” when the period or the half period of two or more of the waveforms are unequal to each other. 
   Sweeping frequency generators change their output frequency through successive frequencies in a bandwidth, e.g., sweeping from the lowest frequency in a chosen bandwidth through the bandwidth to the highest frequency in the chosen bandwidth, then sweeping from this highest frequency through the bandwidth back to the lowest frequency. The function of time for these frequency changes is typically linear, but other functions of time, such as part of an exponential, are possible. As used herein, “sweep frequency” refers to the reciprocal of the time that it takes for successive frequencies to make a round trip, for example, change from one frequency through the other frequencies and back to the original frequency. Although sweep rate might technically be interpreted as the rate of change from one successive frequency to the next, the more common usage for sweep rate will be used herein; that is, “sweep rate” means the same as sweep frequency. It is generally undesirable to operate an ultrasound transducer at a fixed, single frequency because of the resonances created at that frequency. Therefore, an ultrasound generator can sweep the operational frequency through some or all of the available frequencies within the transducer&#39;s bandwidth at a “sweep rate.” Accordingly, particular frequencies have only short duration during the sweep cycle (i.e., the time period for sweeping the ultrasound frequency up and down through a range of frequencies within the bandwidth). “Sweep the sweep rate” or “double sweeping” or “dual sweep” refer to an operation of changing the sweep rate as a function of time. In accord with the invention, “sweeping the sweep rate” generally refers to the operation of sweeping the sweep rate so as to reduce or eliminate resonances generated at a single sweep frequency. “Random sweep rate” or “chaotic sweep rate” refer to sweep rates where the successive sweep rates are numbers that are described by no well defined function, i.e., random or chaotic numbers. 
   The present invention concerns the applied uses of ultrasound energy, and in particular the application and control of ultrasonics to clean and process parts within a liquid. Generally, in accord with the invention, one or more ultrasound generators drive one or more ultrasound transducers, or arrays of transducers, coupled to a liquid to clean and/or process the part. The liquid is preferably held within a tank; and the transducers mount on or within the tank to impart ultrasound into the liquid. In this context, the invention is particularly directed to one or more of the following aspects and advantages:
     (1) By utilizing harmonics of certain clamped ultrasound transducers, the invention generates, in one aspect, ultrasound within the liquid in a frequency range of between about 100 khz to 350 khz (i.e., “microsonic” frequencies). This has certain advantages over the prior art. In particular, unlike prior art ultrasonic systems which operate at less than 100 khz, the invention eliminates or greatly reduces damaging cavitation implosions within the liquid. Further, the transducers operating in this frequency range provide relatively uniform microstreaming, such as provided by megasonics; but they are also relatively rugged and reliable, unlike megasonic transducer elements. In addition, and unlike megasonics, microsonic waves are not highly collimated, or “beam-like,” within liquid; and therefore efficiently couple into the geometry of the ultrasound tank. Preferably, the application of microsonic frequencies to liquid occurs simultaneously with a sweeping of the microsonic frequency within the transducer&#39;s harmonic bandwidth. That is, microsonic transducers (clamped harmonic transducers) are most practical when there is a sweep rate of the applied microsonic frequency. This combination reduces or eliminates (a) standing waves within the liquid, (b) other resonances, (c) high energy cavitation implosions, and (d) non-uniform sound fields, each of which is undesirable for cleaning or processing semiconductor wafers and delicate parts.   (2) The ultrasound transducers or arrays of the invention typically have a finite bandwidth associated with the range of frequencies about a resonant or harmonic frequency. When driven at frequencies within the bandwidth, the transducers generate acoustic energy that is coupled into the liquid. In one aspect, the invention drives the transducers such that the frequency of applied energy has a sweep rate within the bandwidth; and that sweep rate is also varied so that the sweep rate is substantially non-constant during operation. For example, the sweep rate can change linearly, randomly, chaotically or as some other function of time. In this manner, the invention reduces or eliminates resonances which are created by transducers operating with a single sweep rate, such as provided in the prior art.   (3) At least one ultrasound generator of the invention utilizes amplitude modulation (AM). However, unlike the prior art, this AM generator operates by selectively changing the AM frequency over time. In a preferred aspect of the invention, the AM frequency is swept through a range of frequencies which reduce or eliminate low frequency resonances within the liquid and the part being processed. Accordingly, the AM frequency is swept through a range of frequencies; and this range is typically defined as about 10–40% of the optimum AM frequency. The optimum AM frequency is usually between about 1 hz and 10 khz. Therefore, for example, if the optimum AM frequency is 1 khz, then the AM frequency is swept through a frequency range of between about 850 hz and 1150 hz. In addition, the rate at which these frequencies are varied is usually less than about 1/10th of the optimum AM frequency. In this example, therefore, the AM sweep rate is about 100 hz. These operations of sweeping the AM frequency through a range of frequencies and at a defined AM sweep rate reduce or eliminate unwanted resonances which might otherwise occur at the optimum AM frequency. In another aspect of the invention, for delicate parts with very low frequency resonances, the AM frequency is changed randomly or chaotically or the AM sweep rate is swept at a function of time with a frequency about 1/10th of the AM sweep rate. This random or chaotic AM frequency in combination with the random or chaotic sweep rate of (3) provides elimination of low frequencies in a cleaning liquid, therefore, eliminating low frequency resonances. This combination is sometimes referred to as CRAM.   (4) The invention provides AM control by selecting a portion of the rectified power line frequency (e.g., 60 hz in the United States and 50 hz in Europe). In one aspect, this AM control is implemented by selecting a portion of the leading quarter sinusoid in a full wave amplitude modulation pattern that ends at the required amplitude in the zero to 90 degrees and the 180 degrees to 270 degrees regions. Another AM control is implemented by selecting a portion of the leading quarter sinusoid in a half wave amplitude modulation pattern that ends at the required amplitude in the zero to 90 degrees region.   (5) The invention can utilize several tanks, transducers and generators simultaneously to provide a wet bath of different chemistries for the delicate part. In one aspect, when two or more generators are operating at the same time, the invention synchronizes their operation to a common FM signal so that each generator can be adjusted, through AM, to control the process characteristics within the associated tank. In this manner, undesirable beating effects or cross coupling between multiple tanks are reduced or eliminated. In a preferred aspect, a master generator provides a common FM signal to the other generators, each operating as a slave generator coupled to the master generator, and each slave generator provides AM selectively. In addition, because the transducers in the several tanks are sometimes swept through the frequencies of the transducer&#39;s bandwidth, the FM control maintains overall synchronization even though varying AM is applied to the several transducers. The multi-generator FM synchronization also applies to single tank ultrasound systems. That is, the invention supports the synchronized operation of a plurality of generators that are connected to a single tank. In this case, each generator has an associated harmonic transducer array and is driven with a common FM signal and AM signal so that the frequencies within the tank are synchronized, in magnitude and phase, to reduce or eliminate unwanted resonances which might otherwise occur through beating effects between the multiple generators and transducers.   (6) In another aspect, the invention utilizes two or more transducers, in combination, to broaden the overall bandwidth of acoustical energy applied to the liquid around the primary frequency or one of the harmonics. For example, the invention of one aspect has two clamped transducers operating at their first, second third, or fourth harmonic frequency between about 100 khz and 350 khz. The center harmonic frequency of each is adjusted so as to be different from each other. However, their bandwidths are made to overlap such that an attached generator can drive the transducers, in combination, to deliver ultrasound to the liquid in a broader bandwidth. In a preferred aspect, two or more transducers, or transducer arrays, operate at unique harmonic frequencies and have finite bandwidths that overlap with each of the other transducers. If, for example, each transducer has a bandwidth of 4 khz, then two such transducers can approximately provide a 8 khz bandwidth, and three such transducers can approximately provide a 12 khz bandwidth, and so on.   (7) In one aspect, the invention provides a single tank system which selects a desired frequency, or range of frequencies, from a plurality of connected ultrasound generators. Specifically, two or more generators, each operating or optimized to generate a range of frequencies, are connected to a mux; and the system selects the desired frequency range, and hence the right generator, according to the cavitation implosion energy that is desired within the tank chemistry.   (8) The invention has additional and sometimes greater advantages in systems and methods which combine one or more of the features in the above paragraphs (1) through (7). By way of example, one particularly useful system combines two or more microsonic transducers (i.e., paragraph 1) to create broadband microsonics (i.e., paragraph 6) within liquid. Such a system can further be controlled to provide a specific amplitude modulation (i.e., paragraph 4). Examples of other systems and methods of the invention are realized with the following combinations: (2) and (4); (1), (2) and (4); and (1) and (2) with frequency sweeping of the microsonic frequency.   

   The following patents, each incorporated herein by reference, provide useful background to the invention in the area of ultrasound generators: U.S. Pat. Nos. 3,152,295; 3,293,456; 3,629,726; 3,638,087; 3,648,188; 3,651,352; 3,727,112; 3,842,340; 4,044,297; 4,054,848; 4,069,444; 4,081,706; 4,109,174; 4,141,608; 4,156,157; 4,175,242; 4,275,363; and 4,418,297. Further, U.S. Pat. Nos. 4,743,789 and 4,736,130 provide particularly useful background in connection with ultrasound generators that are suitable for use with certain aspects of the invention, and are, accordingly incorporated herein by reference. 
   Clamped ultrasound transducers suitable for use with the invention are known in the art. For example, the following patents, each incorporated herein by reference, provide useful background to the invention: U.S. Pat. Nos. 3,066,232; 3,094,314; 3,113,761; 3,187,207; 3,230,403; 3,778,758; 3,804,329 and RE 25,433. 
   Techniques for mounting or affixing transducers within the tank, and of arranging the transducer and/or tank geometry are, for example, described in U.S. Pat. Nos. 4,118,649; 4,527,901; 4,543,130; and 4,836,684. Each of these patents is also incorporated by reference. 
   Single chamber ultrasound processing systems are described, for example, in U.S. Pat. Nos. 3,690,333; 4,409,999; 5,143,103; and 5,201,958. Such systems provide additional background to the invention and are, accordingly, incorporated herein by reference. 
   In one aspect, the invention provides a system for delivering broadband ultrasound to liquid. The system includes first and second ultrasound transducers. The first transducer has a first frequency and a first ultrasound bandwidth, and the second transducer has a second frequency and a second ultrasound bandwidth. The first and second bandwidths are overlapping with each other and the first frequency is different from the second frequency. An ultrasound generator drives the transducers at frequencies within the bandwidths. Together, the first and second transducers and the generator produce ultrasound within the liquid and with a combined bandwidth that is greater than either of the first and second bandwidths. 
   In another aspect, the system of the invention includes a third ultrasound transducer that has a third frequency and a third ultrasound bandwidth. The third bandwidth is overlapping with at least one of the other bandwidths, and the third frequency is different from the first and second frequencies. The generator in this aspect drives the third transducer within the third bandwidth so as to produce ultrasound within the liquid and with a combined bandwidth that is greater than either of the first, second and third bandwidths. 
   Preferably, each of the transducers are clamped so as to resist material strain and fatigue. In another aspect, each of the first and second frequencies are harmonic frequencies of the transducer&#39;s base resonant frequency. In one aspect, these harmonic frequencies are between about 100 khz and 350 khz. 
   In another aspect, the system includes at least one other synergistic ultrasound transducer that has a synergistic frequency and a synergistic ultrasound bandwidth. As above, the synergistic bandwidth is overlapping with at least one of the other bandwidths, and the synergistic frequency is different from the first and second frequencies. The generator drives the synergistic transducer within the synergistic bandwidth so as to produce ultrasound within the liquid and with a combined bandwidth that is greater than any of the other bandwidths. In one aspect, this synergistic frequency is a harmonic frequency between about 100 khz and 350 khz. 
   In other aspects, the bandwidths of combined transducers overlap so that, in combination, the transducers produce ultrasound energy at substantially all frequencies within the combined bandwidth. Preferably, the combined operation provides ultrasound with relatively equal power for any frequency in the combined bandwidth. Using the full width half maximum (FWHM) to define each bandwidth, the bandwidths preferably overlap such that the power at each frequency within the combined bandwidth is within a factor of two of ultrasound energy produced at any other frequency within the combined bandwidth. 
   In another aspect, a system is provided for delivering ultrasound to liquid. The system has an ultrasound transducer with a harmonic frequency between about 100 khz and 350 khz and within an ultrasound bandwidth. A clamp applies compression to the transducer. An ultrasound generator drives the transducer at a range of frequencies within the bandwidth so as to produce ultrasound within the liquid. 
   In still another aspect, the system can include at least one other ultrasound transducer that has a second harmonic frequency within a second bandwidth. As above, the second frequency is between about 100 khz and 350 khz, and the second bandwidth is overlapping, in frequency, with the ultrasound bandwidth. The generator drives the transducers at frequencies within the bandwidths so as to produce ultrasound within the liquid and with a combined bandwidth that is greater than the bandwidth of a single transducer. 
   Another aspect of the invention provides a system for delivering ultrasound to liquid. In such a system, one or more ultrasound transducers have an operating frequency within an ultrasound bandwidth. An ultrasound generator drives the transducers at frequencies within the bandwidth, and also changes the sweep rate of the frequency continuously so as to produce non-resonating ultrasound within the liquid. 
   Preferably, the generator of the invention changes the sweep rate frequency in one of several ways. In one aspect, for example, the sweep rate is varied as a function of time. In another aspect, the sweep rate is changed randomly or chaotically. Typically, the sweep rate frequency is changed through a range of frequencies that are between about 10–50% of the optimum sweep rate frequency. The optimum sweep rate frequency is usually between about 1 hz and 1.2 khz; and, therefore, the range of frequencies through which the sweep rate is varied can change dramatically. By way of example, if the optimum sweep rate is 500 hz, then the range of sweep rate frequencies is between about 400 hz and 600 hz; and the invention operates by varying the sweep rate within this range linearly, randomly or chaotically, or as a function of time, so as to optimize processing characteristics within the liquid. 
   The invention further provides a system for delivering ultrasound to liquid. This system includes one or more ultrasound transducers, each having an operating frequency within an ultrasound bandwidth. An amplitude modulated ultrasound generator drives the transducers at frequencies within the bandwidth. A generator subsystem also changes the modulation frequency of the AM, continually, so as to produce ultrasound within the liquid to prevent low frequency resonances at the AM frequency. 
   Preferably, the subsystem sweeps the AM frequency at a sweep rate between about 1 hz and 100 hz. For extremely sensitive parts and/or tank chemistries, the invention can further sweep the AM sweep rate as a function of time so as to eliminate possible resonances which might be generated by the AM sweep rate frequency. This sweeping of the AM sweep rate occurs for a range of AM sweep frequencies generally defined by 10–40% of the optimum AM sweep rate. For example, if the optimum AM sweep rate is 150 hz, then one aspect of the invention changes the AM sweep rate through a range of about 130 hz and 170 hz. 
   In one aspect, the invention also provides amplitude control through the power lines. Specifically, amplitude modulation is achieved by selecting a portion of a leading quarter sinusoid, in a full wave amplitude modulation pattern, that ends at a selected amplitude in a region between zero and 90 degrees and between 180 degrees and 270 degrees of the sinusoid. Alternatively, amplitude control is achieved by selecting a portion of a leading quarter sinusoid, in a half wave amplitude modulation pattern, that ends at a selected amplitude between zero and 90 degrees of the sinusoid. 
   In still another aspect, a system of the invention can include two or more ultrasound generators that are synchronized in magnitude and phase so that there is substantially zero frequency difference between signals generated by the generators. Preferably, a timing signal is generated between the generators to synchronize the signals. In one aspect, a FM generator provides a master frequency modulated signal to each generator to synchronize the signals from the generators. 
   A generator of the invention can also be frequency modulated over a range of frequencies within the bandwidth of each transducer. In another aspect, the frequency modulation occurs over a range of frequencies within the bandwidth of each transducer, and the generator is amplitude modulated over a range of frequencies within the bandwidth of each transducer. 
   The systems of the invention generally include a chamber for holding the solution or liquid which is used to clean or process objects therein. The chamber can include, for example, material such as 316L stainless steel, 304 stainless steel, polytetrafluoroethylene, fluorinated ethylene propylene, polyvinylidine fluoride, perfluoro-alkoxy, polypropylene, polyetheretherketone, tantalum, Teflon coated stainless steel, titanium, hastalloy, and mixtures thereof. 
   It is preferable that the transducers of the system include an array of ultrasound transducer elements. 
   The invention also provides a method of delivering broadband ultrasound to liquid, including the steps of: driving a first ultrasound transducer with a generator at a first frequency and within a first ultrasound bandwidth, and driving a second ultrasound transducer with the generator at a second frequency within a second ultrasound bandwidth that overlaps at least part of the first bandwidth, such that the first and second transducers, in combination with the generator, produce ultrasound within the liquid and with a combined bandwidth that is greater than any of the first and second bandwidths. 
   In other aspects, the method includes the step of compressing at least one of the transducers, and/or the step of driving the first and second transducers at harmonic frequencies between about 100 khz and 350 khz. 
   Preferably, the method includes the step of arranging the bandwidths to overlap so that the transducers and generator produce ultrasound energy, at each frequency, that is within a factor of two of ultrasound energy produced by the transducers and generator at any other frequency within the combined bandwidth. 
   The application of broadband ultrasound has certain advantages. First, it increases the useful bandwidth of multiple transducer assemblies so that the advantages to sweeping ultrasound are enhanced. The broadband ultrasound also gives more ultrasound intensity for a given power level because there are additional and different frequencies spaced further apart in the ultrasound bath at any one time. Therefore, there is less sound energy cancellation because only frequencies of the same wavelength, the same amplitude and opposite phase cancel effectively. 
   In one aspect, the method of the invention includes the step of driving an ultrasound transducer in a first bandwidth of harmonic frequencies centered about a microsonic frequency in the range of 100 khz and 350 khz. For protection, the transducer is preferably compressed to protect its integrity. 
   Another method of the invention provides the following steps: coupling one or more ultrasound transducers to the liquid, driving, with a generator, the transducers to an operating frequency within an ultrasound bandwidth, the transducers and generator generating ultrasound within the liquid, changing the frequency within the bandwidth at a sweep rate, and continuously varying the sweep rate as a function of time so as to reduce low frequency resonances. 
   In other aspects, the sweep rate is varied according to one of the following steps: sweeping the sweep rate as a function of time; linearly sweeping the sweep rate as a function of time; and randomly or chaotically sweeping the sweep rate. Usually, the optimum sweep frequency is between about 1 hz and 1.2 khz, and therefore, in other aspects, the methods of the invention change the sweep rate within a range of sweep frequencies centered about an optimum sweep frequency. Typically, this range is defined by about 10–50% of the optimum sweep frequency. For example, if the optimum sweep frequency is 800 hz, then the range of sweep frequencies is between about 720 hz and 880 hz. Further, and in another aspect, the rate at which the invention sweeps the sweep rate within this range is varied at less than about 1/10th of the optimum frequency. Therefore, in this example, the invention changes the sweep rate at a rate that is less than about 80 hz. 
   Another method of the invention provides for the steps of (a) generating a drive signal for one or more ultrasound transducers, each having an operating frequency within an ultrasound bandwidth, (b) amplitude modulating the drive signal at a modulation frequency, and (c) sweeping the modulation frequency, selectively, as to produce ultrasound within the liquid. 
   The invention is particularly useful as an ultrasound system which couples acoustic energy into a liquid for purposes of cleaning parts, developing photosensitive polymers, and stripping material from surfaces. The invention can provide many sound frequencies to the liquid by sweeping the sound through the bandwidth of the transducers. This provides at least three advantages: the standing waves causing cavitation hot spots in the liquid are reduced or eliminated; part resonances within the liquid at ultrasound frequencies are reduced or eliminated; and the ultrasound activity in the liquid builds up to a higher intensity because there is less cancellation of sound waves. 
   In one aspect, the invention provides an ultrasound bath with transducers having at least two different resonant frequencies. In one configuration, the resonant frequencies are made so that the bandwidths of the transducers overlap and so that the impedance versus frequency curve for the paralleled transducers exhibit maximum flatness in the resonant region. For example, when a 40 khz transducer with a 4.1 khz bandwidth is put in parallel—i.e., with overlapping bandwidths—with a 44 khz transducer with a 4.2 khz bandwidth, the resultant bandwidth of the multiple transducer assembly is about 8 khz. If transducers with three different frequencies are used, the bandwidth is approximately three times the bandwidth of a single transducer. 
   In another aspect, a clamped transducer array is provided with a resonant frequency of 40 khz and a bandwidth of 4 khz. The array has a second harmonic resonant frequency at 104 khz with a 4 khz harmonic bandwidth. Preferably, the bandwidth of this second harmonic frequency resonance is increased by the methods described above for the fundamental frequency of a clamped transducer array. 
   In one aspect, the invention provides a method and associated circuitry which constantly changes the sweep rate of an ultrasound transducer within a range of values that is in an optimum process range. For example, one exemplary process can have an optimum sweep rate in the range 380 hz to 530 hz. In accord with one aspect of the invention, this sweep rate constantly changes within the 380 hz to 530 hz range so that the sweep rate does not set up resonances within the tank and set up a resonance at that rate. 
   The invention provides for several methods to change the sweep rate. One of the most effective methods is to generate a random or chaotic change in sweep rate within the specified range. A simpler method is to sweep the sweep rate at some given function of time, e.g., linearly. One problem with sweeping the sweep rate is that the sweeping function of time has a specific frequency which may itself cause a resonance. Accordingly, one aspect of the invention is to sweep this time function; however, in practice, the time function has a specific frequency lower than the lowest resonant frequency of the semiconductor wafer or delicate part, so there is little need to eliminate that specific frequency. 
   Most prior art ultrasound systems are amplitude modulated at a low frequency, typically 50 hz, 60 hz, 100 hz, or 120 hz. One ultrasound generator, the proSONIK™ sold by Ney Ultrasonics Inc., and produced according to U.S. Pat. No. 4,736,130, permits the generation of a specific amplitude modulation pattern that is typically between 50 hz to 5 khz. However, the specific amplitude modulation frequency can itself be a cause of low frequency resonance in an ultrasound bath if the selected amplitude modulation frequency is a resonant frequency of the delicate part. 
   Accordingly, one aspect of the invention solves the problem of delicate part resonance at the amplitude modulation frequency by randomly or chaotically changing or sweeping the frequency of the amplitude modulation within a bandwidth of amplitude modulation frequencies that satisfy the process specifications. For cases where substantially all of the low frequencies must be eliminated, random or chaotic changes of the modulation frequency are preferred. For cases where there are no resonances in a part below a specified frequency, the amplitude modulation frequency can be swept at a frequency below the specified frequency. 
   Random or chaotic changing or sweeping of the amplitude modulation frequency inhibits low frequency resonances because there is little repetitive energy at a frequency within the resonant range of the delicate part or semiconductor wafer. Accordingly, a resonant condition does not build up, in accord with the invention, providing obvious advantages. 
   The invention also provides relatively inexpensive amplitude control as compared to the prior art. One aspect of the invention provides amplitude control with a full wave or half wave amplitude modulated ultrasound signal. For full wave, a section of the 0 degrees to 90 degrees and the 180 degrees to 270 degrees quarter sinusoid is chosen which ends at the required (desired) amplitude. For example, at the zero crossover of the half sinusoid (0 degrees and 180 degrees), a monostable multivibrator is triggered. It is set to time out before 90 degrees duration, and specifically at the required amplitude value. This timed monostable multivibrator pulse is used to select that section of the quarter sinusoid that never exceeds the required amplitude. 
   In one aspect, the invention also provides an adjustable ultrasound generator. One aspect of this generator is that the sweep rate frequency and the amplitude modulation pattern frequency are randomly or chaotically changed or swept within the optimum range for a selected process. Another aspect is that the generator drives an expanded bandwidth clamped piezoelectric transducer array at a harmonic frequency from 100 khz to 350 khz. 
   Such a generator provides several improvements in the problematic areas affecting lower frequency ultrasonics and megasonics: uncontrolled cavitation implosion, unwanted resonances, unreliable transducers, and standing waves. Instead, the system of the invention provides uniform microstreaming that is critical to semiconductor wafer and other delicate part processing and cleaning. 
   In another aspect of the invention, an array of transducers is used to transmit sound into a liquid at its fundamental frequency, e.g., 40 khz, and at each harmonic frequency, e.g., 72 khz or 104 khz. The outputs of generators which have the transducer resonant frequencies and harmonic frequencies are connected through relays to the transducer array. One generator with the output frequency that most closely producers the optimum energy in each cavitation implosion for the current process chemistry is switched to the transducer array. 
   In yet another aspect, the invention reduces or eliminates low frequency beat resonances created by multiple generators by synchronizing the sweep rates (both in magnitude and in phase) so that there is zero frequency difference between the signals coming out of multiple generators. In one aspect, the synchronization of sweep rate magnitude and phase is accomplished by sending a timing signal from one generator to each of the other generators. In another aspect, a master FM signal is generated that is sent to each “slave” power module, which amplifies the master FM signal for delivery to the transducers. At times, the master and slave aspect of the invention also provides advantages in eliminating or reducing the beat frequency created by multiple generators driving a single tank. 
   However, when multiple generators are driving different tanks in the same system, this master and slave aspect may not be acceptable because the AM of the FM signal is usually different for different processes in the different tanks. Accordingly, and in another aspect, a master control is provided which solves this problem. The master control of the invention has a single FM function generator (sweeping frequency signal) and multiple AM function generators, one for each tank. Thus, every tank in the system receives the same magnitude and phase of sweep rate, but a different AM as set on the control for each generator. 
   The invention also provides other advantages as compared to the prior art&#39;s methods for frequency sweeping ultrasound within the transducer&#39;s bandwidth. Specifically, the invention provides a sweeping of the sweep rate, within the transducer&#39;s bandwidth, such that low frequency resonances are reduced or eliminated. Prior art frequency sweep systems had a fixed sweep frequency that is selectable, once, for a given application. One problem with such prior art systems is that the single low frequency can set up a resonance in a delicate part, for example, a read-write head for a hard disk drive. 
   The invention also provides advantages in that the sweep frequency of the sweep rate can be adjusted to conditions within the tank, or to the configuration of the tank or transducer, or even to a process chemistry. 
   The invention also has certain advantages over prior art single chamber ultrasound systems. Specifically, the methods of the invention, in certain aspects, use different frequency ultrasonics for each different chemistry so that the same optimum energy in each cavitation implosion is maintained in each process or cleaning chemistry. According to other aspects of the invention, this process is enhanced by selecting the proper ultrasound generator frequency that is supplied at the fundamental or harmonic frequency of the transducers bonded to the single ultrasound chamber. 
   In another aspect, the invention provides ultrasound transducer apparatus. In the apparatus, at least one ceramic drive element is sandwiched between a front driver and a backplate. The drive element has electrical contacts or electrodes mounted on either face and is responsive to voltages applied to the contacts or electrodes so as to produce ultrasound energy. A connecting element—e.g., a bolt—connects the back plate to the front driver and compresses the drive element therebetween. In accord with the invention, the front driver and/or the backplate are shaped so that the apparatus produces substantially uniform power as a function of frequency over a range of frequencies. In another aspect, the shape of the driver and/or backplate are selected so as to provide a varying power function as a function of frequency. 
   In another aspect, a multi-frequency ultrasound generator is provided. In one aspect, the generator includes a constant power output circuit with means for switching the center frequency of the output signal selectively. The switching means operates such that little or no intermediate frequencies are output during transition between one center frequency and another. 
   Another multi-frequency generator of the invention includes two or more circuits which independently create ultrasound frequencies. By way of example, one circuit can generate 40 khz ultrasound energy; while another circuit can generate 104 khz energy. A switching network connects the plurality of circuits such that the generator is shut down and relay switching takes place in a zero voltage condition. As above, therefore, the switching occurs such that little or no intermediate frequencies are output during transition between one center frequency and another. 
   In still another aspect, a two stage ultrasound processing system is provided. The system includes (a) one or more transducers with a defined ultrasound bandwidth defined by an upper frequency and a lower frequency. The system further includes (b) a frequency generator for driving the transducers from the upper frequency to the lower frequency over a selected or variable time period and (c) a process tank connected with the transducers so as to generate ultrasound energy within the tank at frequencies defined by the generator. During a given cycle, the generator drives the transducers from the upper frequency to the lower frequency. Once the lower frequency is reached, a frequency control subsystem controls the generator so as to drive the transducers again from upper to lower frequency and without driving the transducers from lower to upper frequencies. In this manner, only decreasing frequencies—per cycle—are imparted to process chemistries. The system thus provides for removing contamination as the downward cycling frequencies cause the acoustic energy to migrate in an upwards motion inside the tank which in turn pushes contamination upwards and out of the tank. 
   In another aspect of the invention, the two stage ultrasound processing system includes means for cycling from upper-to-lower frequencies every half cycle. That is, once the transducers are driven from upper to lower frequencies over a first half cycle, the generator recycles such that the next half cycle again drives the transducers from upper to lower frequencies. Alternatively, after driving the transducers from upper to lower frequencies for a first half cycle, the system inhibits the flow of energy into the tank over a second half cycle. 
   The two stage ultrasound processing systems of the invention can be continuous or intermittent. That is, in one preferred aspect, the system cycles from upper to lower frequencies and then from lower to upper frequencies in a normal mode; and then only cycles from upper to lower frequencies in a contamination removing mode. 
   In still another aspect, the invention provides a process control probe which monitors certain process characteristics within an ultrasound process tank. The probe includes an enclosure, e.g., made from polypropylene, that transmits ultrasound energy therethrough. The enclosure houses a liquid that is responsive to the ultrasound energy in some manner such as to create free radicals and ions from which conductivity can be measured. This conductivity provides an indication as to the number of cavitation implosions per unit volume being imparted to the process chemistry within the tank. A conduit from the enclosure to a location external to the process chemistry is used to measure the characteristics of the liquid in response to the energy. In other aspects, a thermocouple is included within the enclosure and/or on an external surface of the enclosure (i.e., in contact with the process chemistry) so as to monitor temperature changes within the enclosure and/or within the process chemistry. Other characteristics within the tank and/or enclosure can be monitored over time so as to create time-varying functions that provide other useful information about the characteristics of the processes within the tank. 
   In one aspect, the invention provides an ultrasound system for moving contaminants upwards within a processing tank, which holds process liquid. An ultrasound generator produces ultrasound drive signals through a range of frequencies as defined by an upper frequency and a lower frequency. A transducer connected to the tank and the generator responds to the drive signals to impart ultrasound energy to the liquid. A controller subsystem controls the generator such that the drive signals monotonically change from the upper frequency to the lower frequency to drive contaminants upwards through the liquid. 
   In one aspect, the controller subsystem cyclically produces the drive signals such that the generator sweeps the drive signals from the upper frequency to the lower frequency over a first half cycle, and from the lower frequency to the higher frequency over a second one half cycle. The subsystem of this aspect inhibits the drive signals over the second half cycle to provide a quiet period to the liquid. 
   In other aspects, the first and second one-half cycles can have different time periods. Each successive one-half cycle can have a different time period such that a repetition rate of the first and second half cycles is non-constant. Or, the first one-half cycle can have a fixed period and the second one-half cycle can be non-constant. 
   In one aspect, the first half cycle corresponds to a first time period and the second one half cycle corresponds to a second time period, and the subsystem varies the first or second time periods between adjacent cycles. 
   Preferably, the subsystem includes means for shutting the generator off during the second one half cycle. 
   In another aspect, the subsystem includes an AM modulator for amplitude modulating the drive signals at an AM frequency. In one aspect, the AM modulator sweeps the AM frequency. In another aspect, the AM modulator sweeps the AM frequency from a high frequency to a low frequency and without sweeping the AM frequency from the low frequency to the high frequency. The subsystem can further inject a quiet or degas period before each monotonic AM frequency sweep. 
   In another aspect, there is provided an ultrasound system for moving contaminants upwards within a processing tank, including: a processing tank for holding process liquid, an ultrasound generator for generating ultrasound drive signals through a range of frequencies defined between an upper frequency and a lower frequency, at least one transducer connected to the tank and the generator, the transducer being responsive to the drive signals to impart ultrasound energy to the liquid, and a controller subsystem for controlling the generator through one or more cycles, each cycle including monotonically sweeping the drive signals from the upper frequency to the lower frequency, during a sweep period, and recycling the generator from the lower frequency to the upper frequency, during a recovery period, the sweep period being at least nine times longer than the recovery period. 
   In one aspect, the controller subsystem varies a time period for each cycle wherein the time period is non-constant. 
   In still another aspect, an ultrasound system is provided for moving contaminants upwards within a processing tank, including: a processing tank for holding process liquid; an ultrasound generator for generating ultrasound drive signals; at least one transducer connected to the tank and the generator, the transducer being responsive to the drive signals to impart ultrasound energy to the liquid; and an amplitude modulation subsystem for amplitude modulating the drive signals through a range of AM frequencies characterized by an upper frequency and a lower frequency, the subsystem monotonically changing the AM frequency from the upper frequency to the lower frequency to drive contaminants upwards through the liquid. 
   In one aspect, the generator sweeps the drive signals from upper to lower frequencies to provide additional upwards motion of contaminants within the liquid. 
   In another aspect, the AM frequencies are between about 1.2 khz and a lower frequency of 1 hz. The AM frequencies can also cover a different range, such as between about 800 hz and a lower frequency of 200 hz. 
   In another aspect, the invention provides a multi-generator system for producing ultrasound at selected different frequencies within a processing tank of the type including one or more transducers. A generator section has a first generator circuit for producing first ultrasound drive signals over a first range of frequencies and a second generator circuit for producing second ultrasound drive signals over a second range of frequencies. The generator section has an output unit connecting the drive signals to the transducers. Each generator circuit has a first relay initiated by a user-selected command wherein either the first or the second drive signals are connected to the output unit selectively. 
   In one aspect, a 24 VDC supply provides power for relay coils. 
   In another aspect, each generator circuit has a second relay for energizing the circuit. Two time delay circuits can also be included for delay purposes: the first time delay circuit delaying generator circuit operation over a first delay period from when the second relay is energized, the second time delay circuit delaying discontinuance of the first relay over a second delay period after the generator circuit is commanded to stop. The first delay period is preferably longer than the second delay period such that no two generators circuits operate simultaneously and such that all generator circuits are inactive during switching of the first relay. 
   Each relay can include a 24 VDC coil. A selecting device, e.g., a PLC, computer, or selector switch, can be used to select the operating generator circuit. At selection, 24 VDC connects to the two relays of this operating generator circuit. Preferably, each relay coil operates at a common voltage level. 
   In one aspect, a variable voltage ultrasound generator system is provided, including: an ultrasound generator; a switching regulator for regulating a 300 VDC signal to +12V and +15V lines, the generator being connected to the +12V and +15V lines; and a power factor correction circuit connected to AC power. The power factor correction circuit provides 300 VDC output to the generator and to the regulator. The generator thus being automatically operable from world voltage sources between 86 VAC and 264 VAC. 
   In another aspect, a variable voltage ultrasound generator system is provided, including: an ultrasound generator; and a universal switching regulator (known to those skilled in the art), connected to AC power, for regulating a set of DC voltages to the generator. The generator thus being automatically operable from world voltage sources between 86 VAC and 264 VAC. 
   In another aspect, a double compression transducer is provided for producing ultrasound within an ultrasound tank. The transducer has a front plate and a backplate. At least one piezoceramic is sandwiched between the front plate and backplate. A bias bolt with an elongated bias bolt body between a bias bolt head and a threaded portion extends through the front plate and the piezoceramic and is connected with the backplate (either by screwing into the backplate or by a nut screwed onto the bias bolt adjacent the backplate). The bias bolt also forms a through-hole interior that axially extends between the head and the threaded portion. A second bolt with an elongated body between a second bolt head and a threaded tip is disposed within the bias bolt. The second bolt head is rigidly attached to the tank and a nut is screwed onto the threaded tip and adjacent to the backplate. The bias bolt thus provides a first level of compression of the piezoceramic. The second bolt provides a second level of compression of the front plate and the tank, particularly when epoxy is used to bond between the front plate and the tank. 
   In still another aspect, a variable voltage ultrasound generator system is provided. The system includes an ultrasound generator and a constant peak amplitude triac circuit connected to AC power. The triac circuit converts the AC power to a 121.6 voltage peak, or less, AC signal. A bridge rectifier and filter connects to the AC signal to rectify and filter the AC signal and to generate a DC voltage less than (86)*(Square Root of 2) volts. A switching regulator regulates the DC voltage to 12 VDC and 15 VDC; and the generator connects to the DC voltage, the 12 VDC and the 15 VDC. In this manner, the generator is thus automatically operable from world voltage sources between 86 VAC and 264 VAC. 
   The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention. 
   In another aspect, the multiple frequency invention described herein is a new class of liquid cleaning and processing equipment where there is one transducer array and one generator that produces a series string of different frequencies within two or more non-overlapping continuous frequency ranges. The transducer array is capable of responding to electrical frequency signals to produce intense sound energy at any frequency within two or more distinct frequency bands. The generator is capable of supplying an electrical frequency signal at any frequency within continuous frequency ranges contained within two or more of the transducer array&#39;s frequency bands. 
   The generator and transducer array produce a series string of different frequency sound waves. The first produced frequency is typically followed by a different second frequency that is in the same frequency range as the first frequency, then this second frequency is typically followed by a different third frequency that is in the same frequency range as the first two frequencies, and this pattern continues for at least the lifetime of a sound wave in the liquid (typically 20 to 70 milliseconds). This results in multiple closely related frequencies of the same frequency range adding up within the liquid to a value of high intensity sound. This high intensity multiple frequency sound field is typically maintained long enough to accomplish a specific part of the cleaning or processing cycle, then the electrical frequency signal output of the generator is controlled to jump to a frequency in a different frequency range, typically in a different frequency band, where different frequencies are again strung together for at least the lifetime of a sound wave in the liquid. 
   This invention is an improvement over prior art multiple frequency systems because by stringing together different frequencies from the same frequency range for at least the lifetime of a sound wave in the liquid, the sound intensity of these closely related frequencies builds up to a higher value than with any of the prior art multiple frequency systems. This higher intensity sound field does the improved cleaning or processing within the frequency range and then the system jumps to another frequency range where the cleaning or processing effect is different. Again, in the second frequency range the sound intensity builds up to a higher value than with any prior art multiple frequency system and, therefore, the improvement in cleaning or processing occurs within this second frequency range. Also, by maintaining the production of sound in each frequency range for a minimum of 20 milliseconds, there is substantially no intense sound energy produced at frequencies outside of the frequency ranges, this further adds to the build up of the intensity of the sound energy. Each of these improved effects in each of the different frequency ranges adds up to a process that is superior to prior art methods. 
   A variation of the invention substitutes a fraction of a cycle of a frequency strung together with other fractions of a cycle of sound at different frequencies within a given frequency range before jumping to a different frequency range. Another variation inserts a degas time between jumps from one frequency range to another. Another variation controls the generator to cycle through the frequency ranges in different orders, i.e., several permutations of the frequency ranges are introduced into the liquid during the cleaning or processing cycle. Another variation defines each permutation of a frequency range to be a cleaning packet and the order in which these cleaning packets are delivered to the liquid is varied to produce different cleaning effects. Still other variations introduce phase lock loops, duty cycle control, amplitude control, PLC control, computer control, quiet times, active power control, series resistor VCO control, DAC VCO control, cavitation probe feedback to the generator and digital code frequency selection. In general, this invention is useful in the frequency spectrum 9 khz to 5 Mhz. 
   The foregoing and other objects of are achieved by the invention, which in one aspect comprises a system for coupling sound energy to a liquid, including at least two transducers forming a transducer array adapted for coupling to a liquid in a container. The transducer array is constructed and arranged so as to be capable of producing intense sound energy in the liquid at any frequency within at least two non-overlapping frequency bands. The system further includes a signal generator adapted for producing a driver signal for driving the transducer array at any frequency from one or more continuous frequency ranges within at least two of the frequency bands. The signal generator drives the transducer array to produce the intense sound energy characterized by a series string of different frequencies within one of the continuous frequency ranges. The generator further drives the transducer array to discontinuously jump amongst the frequency ranges, so as to generate intense sound energy characterized by a series string of different frequencies within at least one additional frequency range in at least one additional frequency band. 
   Another embodiment of the invention further includes a controller for controlling the frequency of the ultrasound energy within the series string of different frequencies. The controller also controls a duration of each frequency in the series string. 
   In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a staircase function. 
   In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a series of monotonically decreasing frequencies. 
   In another embodiment of the invention, the series of monotonically decreasing frequencies occurs for at least ninety percent of an interval during which the transducer array couples intense sound energy to the liquid. 
   In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a series of frequencies defined by a predetermined function of time. 
   In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a series of frequencies swept from a first frequency to a second frequency at a constant sweep rate. 
   In another embodiment of the invention, the series of frequencies is swept at a non-constant sweep rate. 
   In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a random or chaotic series of frequencies. 
   In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by at least a first group of frequencies from a first frequency band, and a second group of frequencies from a second frequency band, such that at least two groups of frequencies adjacent in time are from different frequency bands. 
   In another embodiment of the invention, the series string of different frequencies further includes at least one degas interval between periods of time having ultrasound energy. 
   In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by at least a first group of frequencies from a first frequency band, and a second group of frequencies also from the first frequency band, such that at least two groups of frequencies adjacent in time are from the same frequency band 
   In another embodiment of the invention, the intense sound energy in each of the series string of different frequencies is characterized by at least a fraction of a cycle of the distinct frequency. 
   In another embodiment of the invention, the fraction of a cycle is one-half of a cycle, and each successive one-half cycle represents a different frequency. 
   In another embodiment of the invention, the intense sound energy includes frequencies selected from the frequency spectrum 9 khz to 5 Mhz. 
   In another embodiment of the invention, the frequency ranges are characterized by a center frequency. The center frequency of each higher frequency range is a non-integer multiple of the center frequency of the lowest frequency range, so as to prevent one or more Fourier frequencies of a periodic wave from forming in the liquid. 
   In another embodiment of the invention, the controller includes a PLC or a computer. 
   Another embodiment of the invention further includes a probe adapted for measuring one or more parameters associated with the liquid corresponding to sound-produced effects in the liquid. The controller alters the generator driver signal as both a predetermined function of the measured parameters, and according to the desired purpose of the system. 
   In another embodiment of the invention, each specific frequency range is represented by a distinct digital code. The controller initiates a transition from a first frequency range to a second frequency range in response to the digital code transitioning from a digital code representative of the first frequency range to the digital code representative of the second frequency range. 
   In another embodiment of the invention, the center frequency of each frequency range corresponds to an output of a voltage controlled oscillator. The output of the voltage controlled oscillator corresponds to an input control signal, and the input control signal is determined by a series string of resistors. The total string of resistors produces the lowest frequency range and each higher string of resistors produces each higher frequency range. 
   In another embodiment of the invention, the intense sound energy includes ultrasound energy. 
   In another embodiment of the invention, the intense sound energy in the series string of different frequencies occurs continuously for at least 20 milliseconds, within each of the continuous frequency ranges. 
   In another embodiment of the invention, the output power level of the driver signal is actively maintained by comparing an actual output power level to a specified output power level, and adjusting parameters of the driver signal to make the actual output power level substantially equal to the specified output power level. The parameters of the driver signal may be either amplitude, duty cycle, or some combination thereof. 
   In another embodiment of the invention, the intense sound energy characterized by the series string of different frequencies further includes one or more quiet time intervals characterized by a substantial absence of intense sound energy. 
   In another embodiment of the invention, the quiet time intervals are distributed periodically among the intervals of intense sound energy. In yet another embodiment, the quiet time intervals are distributed randomly or chaotically among the intervals of intense sound energy. 
   In another embodiment of the invention, the quiet time intervals are distributed among the intervals of intense sound energy according to a predetermined function of time. 
   In another embodiment of the invention, the center frequency for each frequency range is optimized by an automatic adjustment from a circuit that maintains a substantially zero phase shift between an associated output voltage and output current at the center frequency. 
   In another embodiment of the invention, the order of frequency range transitions varies such that several permutations of frequency ranges can be introduced into the liquid. In other embodiments, each permutation of frequency ranges is defined as a specific cleaning packet, and the order in which the cleaning packets are introduced into the liquid is changed such that each different order produces a different cleaning effect. 
   In another embodiment of the invention, substantially no intense sound energy is produced at frequencies outside of the frequency ranges. 
   In another embodiment of the invention, the container holding the liquid is constructed from materials resistant to detrimental effects of the liquids. These materials may include tantalum, polyetheretherketone, titanium, polypropylene, Teflon, Teflon coated stainless steel, or combinations thereof, or other similar materials known to those in the art. 
   In another embodiment of the invention, the signal generator is capable of producing an infinite number of frequencies contained within each of the unconnected continuous frequency ranges. 
   In another embodiment of the invention, the signal generator produces an output signal including the FM information for synchronizing other generators or power modules. 
   In another embodiment of the invention, the center frequency of each frequency range corresponds to an output of a voltage controlled oscillator. The output of the voltage controlled oscillator corresponds to an input control signal, and the input control signal is generated by a DAC (digital-to-analog converter). In other embodiments, the digital input to the DAC produces a stepped staircase analog output from the DAC, resulting in a stepped, staircase sweeping function within a frequency range. In yet another embodiment, the digital input to the DAC produces a random or chaotic staircase analog output from the DAC, resulting in a random or chaotic staircase sweeping function within a frequency range. 
   In another aspect, the invention comprises a system for coupling sound energy to a liquid. The system includes at least two transducers forming a transducer array adapted for coupling to a liquid in a tank, and the transducer array is constructed and arranged so as to be capable of producing intense sound energy in the liquid at any frequency within at least two non-overlapping frequency bands. The system further includes a signal generator adapted for producing a driver signal for driving the transducer array at any frequency from one or more continuous frequency ranges within at least two of the frequency bands. The signal generator drives the transducer array so as to produce intense sound energy characterized by a plurality of changing frequencies within a first frequency range, followed by a plurality of changing frequencies within a second frequency range. The system so operating reduces a strong antinode below the liquid-to-air interface. 
   In another aspect, the invention comprises a system for coupling sound energy to a liquid, that includes at least two transducers forming a transducer array adapted for coupling to a liquid in a tank. The transducer array is constructed and arranged so as to be capable of producing intense sound energy in the liquid at any frequency within at least two distinct frequency bands. The system further includes a signal generator adapted for producing a driver signal for driving the transducer array at any frequency from one or more continuous frequency ranges within the at least two frequency bands. The center frequencies of the higher frequency ranges are non-integer multiples of the center frequency of the lowest frequency range to prevent two or more Fourier frequencies of a periodic wave from forming in the liquid. The signal generator drives the transducer array to produce sound energy corresponding to a first set of frequencies from a first frequency range, then produces sound energy corresponding to a second set of frequencies from a second frequency range. The transition from the first frequency range to the second frequency range is discontinuous and occurs after a time interval at least as long as the lifetime of sound energy in the container for frequencies from the first frequency range. The sound energy corresponding to the second set of frequencies continues for a time interval at least as long as the lifetime of sound energy in the container for frequencies from the second frequency range. 
   In another aspect, the invention comprises multiple frequency generator capable of producing an output signal characterized by any frequency within two or more non-contiguous, continuous frequency ranges. The generator is controlled to change the frequency within a frequency range, and then to change frequencies from one frequency range to a second frequency range before beginning the changing of frequencies in this second frequency range. 
   In another aspect, the invention comprises a method of delivering multiple frequencies of intense sound waves to a liquid. The method includes the step of coupling to the liquid an array of transducers that are capable of producing sound energy in the liquid at an infinite number of different frequencies contained within two or more non-contiguous, continuous frequency bands. The method also includes the step of driving the transducer array with a generator capable of producing substantially all of the frequencies within continuous frequency ranges contained within two or more of the transducer array frequency bands. The method further includes the step of controlling the generator so that the produced frequencies change within the frequency ranges according to a function of time, and the frequencies jump amongst the frequency ranges. 
   In another aspect, the present invention is directed to the creation of an AC switch by electronic circuitry or electromechanical devices, such as relays. The AC switch as presented in this invention will exchange a modifying circuitry (which contains resistive, reactive, and active components) into and out of the power section of an ultrasound generator. Therefore, the output of the ultrasound generator will be modified by the modification circuitry disclosed, by way of example, herein. The AC switch is operatively connected to the modification circuitry. It switches the modification circuitry into and out of the output stage of the generator. The control circuitry is associated with the AC switch and is adapted to turn off and turn on the AC switch. The AC switch will swap resistive, reactive and active components and networks of these components into and out of the power section of ultrasound frequency generators. The present invention provides a simple and reliable manner to increase the number of parameters and diversify the capabilities of an ultrasound generator. 
   The AC switch introduces a modification circuit that is able to (1) maintain full power output from a multiple frequency ultrasound generator as the center frequency of the generator is changed, (2) step sweep the output of an ultrasound oscillator, and (3) vary the output power and amplitude of a non self-oscillating ultrasound generator. A fixed frequency oscillator can be modified to accomplish certain of these functions and to sweep frequency. This is accomplished by the step sweeping and successive AC switching in of capacitors and/or inductors (i.e. modification circuitry). 
   This patent will suggest a number of applications in which the AC switch is created by triacs. A triac is a three terminal semiconductor, which controls current in either direction. The triac is suited to create a simple and less expensive AC switch than the use of transistors. Nevertheless, it will be obvious to those skilled in the art that other circuitry can be substituted for triacs. One example of such other circuitry, which simulates a triac, is one that includes back to back silicon-controlled rectifiers. Also, a series/parallel active device configuration or bi-directional lateral insulated gate bipolar transistor, can act as the AC switch. 
   The phrase “modification circuitry” as used herein is defined as resistive, reactive and active components and networks of these components. The circuitry will have two main leads and one or more control leads available for active components or networks containing active components. One of ordinary skill in the art will readily appreciate that it is possible to introduce a different value of a resistive or reactive component through the use of a transformer; therefore, in some cases a transformer winding or tap can be the part of the modification circuitry that is switched by the AC switch. 
   The modification circuitry is placed in parallel with an AC switch when it is required that the modification circuitry be inserted into a conduction line of the ultrasound generator. The modification circuitry is placed in series with an AC switch when it is required that the modification circuitry be inserted between two nodes of the ultrasound generator. When connected in series, the modification circuitry is inserted at any time in the cycle by turning on the AC switch. In the case of a parallel connection, the modification circuitry is removed from the generator when the AC switch is on. The reverse effect will happen when the AC switch is turned off. The addition of a control circuitry to the AC switch supplies turn on and off signals to the AC switch. Where the AC switch is a triac, the control circuitry will provide (1) a turn off signal to the ultrasound generator for a period of time at least as long as the triac turn off time, (2) the turn off signal to the triac for a period of time at least as long as the triac turn off time, and (3) concurrent signals for a period of time at least as long as the triac turn off time. The use of this control circuitry is necessary due to the fact that the speed of triacs is too slow to allow them to go off when conducting an ultrasound current. 
   Another embodiment of the invention includes modification circuitry capable of modifying the following parameters of the output of an ultrasound generator: frequency; amplitude; power; impedance; and waveform. The parameter will change in accordance to the purpose of the application or generator. The modification includes at least one capacitor, one inductor, or one resistor. Finally, it can also include an active/passive network with a control circuitry adapted to control the active components in the network. 
   In another embodiment of the invention, a control circuitry capable of supplying a turn off signal to the AC switch for a duration D 1  is illustrated. If the AC switch is a triac, the control circuitry will also supply a turn off signal D 2  to the generator, where D 1  and D 2  are concurrent for a time equal to or greater than the triac turn off time. The same will apply if the AC switch is comprised of back to back silicon controlled rectifiers. In the case of the modification of the output frequency of an ultrasound oscillator, the “controller” will represent the control circuit. This controller can be further modified to selectively activate or deactivate components so as to step sweep the output frequency of an oscillator. 
   Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising two or more transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands, and one or more ultrasound generators adapted for producing driver signals for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein at least one frequency range is within the microsonic range of frequencies; and, wherein the driver signals in the microsonic range of frequencies are synchronized with a common FM signal; and, wherein the driver signals of the one or more ultrasound generators drive the transducers to produce ultrasound in the liquid characterized by a frequency that sweeps at random, chaotic or pseudo random sweep rates within at least one of the frequency ranges in one of the at least two frequency bands; and, wherein the sweep is monotonic from high frequency to low frequency with a recovery time from low frequency to high frequency that is a shorter time than the monotonic sweep; and, wherein the driver signals are amplitude modulated at a modulation frequency that changes randomly, chaotically or pseudo randomly; and, wherein the one or more ultrasound generators each have an output stage, which comprises, a) modification circuitry which modifies the output stage; b) an AC switch, operatively connected to the modification circuitry, which switches the modification circuitry into and out of the output stage of the ultrasound generator; and c) control circuitry, associated with the AC switch and with the one or more ultrasound generators, which is adapted to turn off and turn on the AC switch, wherein the control circuitry, AC switch and modification circuitry changes the one or more ultrasound generator driver signals to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by a frequency that sweeps at random, pseudo random or chaotic sweep rates within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands. In yet another embodiment of the invention, this system adds power control to the ultrasound by an amplitude modulated driver signal that has off times that vary randomly, chaotically or pseudo randomly while maintaining a specified duty cycle for power control. 
   Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising one or more transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands, and an ultrasound generator adapted for producing a driver signal for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein the driver signal of the ultrasound generator drives the transducers to produce ultrasound in the liquid characterized by successive frequencies within at least one of the frequency ranges in one of the at least two frequency bands; and, wherein the ultrasound generator has an output stage, which comprises, a) modification circuitry which modifies the output stage; b) an AC switch, operatively connected to the modification circuitry, which switches the modification circuitry into and out of the output stage of the ultrasound generator; and c) control circuitry, associated with the AC switch and with the ultrasound generator, which is adapted to turn off and turn on the AC switch, wherein the control circuitry, AC switch and modification circuitry changes the ultrasound generator driver signal to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by successive frequencies within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands. 
   Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising, two or more transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands, and, one or more ultrasound generators adapted for producing driver signals for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein at least one frequency range is within the microsonic range of frequencies; and, wherein the driver signals of the one or more ultrasound generators drive the transducers to produce ultrasound in the liquid characterized by a frequency that sweeps at random, chaotic or pseudo random sweep rates within at least one of the frequency ranges in one of the at least two frequency bands; and, wherein the driver signals are amplitude modulated at a modulation frequency that changes randomly, chaotically or pseudo randomly; and, wherein the one or more ultrasound generators each have an output stage, which comprises, a) modification circuitry which modifies the output stage; b) an AC switch, operatively connected to the modification circuitry, which switches the modification circuitry into and out of the output stage of the ultrasound generator; and c) control circuitry, associated with the AC switch and with the one or more ultrasound generators, which is adapted to turn off and turn on the AC switch, wherein the control circuitry, AC switch and modification circuitry changes the one or more ultrasound generator driver signals to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by a frequency that sweeps at random, pseudo random or chaotic sweep rates within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands. 
   Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising at least two transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands; an ultrasound generator adapted for producing a driver signal for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein at least one of the frequency ranges is in the microsonic range of frequencies; and, wherein the driver signal of the ultrasound generator drives the transducers to produce ultrasound in the liquid characterized by successive frequencies within at least one of the frequency ranges in one of the at least two frequency bands; the ultrasound generator changes the driver signal to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by successive frequencies within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands. 
   Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising two or more transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands, and, one or more ultrasound generators adapted for producing driver signals for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein the driver signals of the one or more ultrasound generators drive the transducers to produce ultrasound in the liquid characterized by a frequency that sweeps at random, chaotic or pseudo random sweep rates within at least one of the frequency ranges in one of the at least two frequency bands; and, wherein the driver signals are continuous wave; and, wherein the one or more ultrasound generators each have an output stage, which comprises a) modification circuitry which modifies the output stage; b) an AC switch, operatively connected to the modification circuitry, which switches the modification circuitry into and out of the output stage of the ultrasound generator; and c) control circuitry, associated with the AC switch and with the one or more ultrasound generators, which is adapted to turn off and turn on the AC switch, wherein the control circuitry, AC switch and modification circuitry changes the one or more ultrasound generator driver signals to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by a frequency that sweeps at random, pseudo random or chaotic sweep rates within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands. 
   Another embodiment of the invention is an ultrasound generator having an output signal that is frequency modulated with a sweeping frequency waveform and amplitude modulated with a changing frequency; wherein the sweep rate of the sweeping frequency waveform changes randomly, chaotically or pseudo randomly; and, wherein the amplitude modulation frequency changes randomly, chaotically or pseudo randomly. 
   Another embodiment of the invention is an ultrasound generator having an output signal that is frequency modulated with a sweeping frequency waveform and has continuous wave for its amplitude modulation; wherein the sweep rate of the sweeping frequency waveform changes randomly, chaotically or pseudo randomly. 
   Another embodiment of the invention is a frequency drive signal (referred to herein as the improved cavitation efficiency drive signal) where the drive signal is provided during a first defined time period and at a first frequency during a beginning portion of the first defined time period, and the drive signal is provided at a second frequency during an ending portion of the first defined time period. The frequency of the drive signal is varied from the second frequency to a third frequency; and the drive signal is provided during a second defined time period. This drive signal increases the efficiency of cavitation and can be employed with any of the generator or generator and transducer array systems described in this specification. 
   Another embodiment of the invention is for improving cleaning or processing by producing a first form of cavitation and a second form of cavitation in a liquid comprising a succession of time periods with at least one time period wherein the first form of cavitation is produced in the liquid, and, at least one of the successive time periods wherein the second form of cavitation is produced in the liquid, wherein the first form of cavitation is predominately stable cavitation, and, wherein the second form of cavitation is predominately transient cavitation. This method of improving performance with two forms of cavitation can be employed with any of the generator or generator and transducer array systems described in this specification. 
   In another embodiment of the invention the second form of cavitation is produced by the improved cavitation efficiency drive signal. A drive signal incorporating the first form of cavitation and the second form of cavitation in the form of the improved efficiency drive signal can be employed with any of the generator or generator and transducer array systems described in this specification. 
   The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the invention may be obtained by reference to the drawings, in which: 
       FIG. 1  shows a cut-away side view schematic of an ultrasound processing system constructed according to the invention; 
       FIG. 2  shows a top view schematic of the system of  FIG. 1 ; 
       FIG. 3  shows a schematic illustration of a multi-transducer system constructed according to the invention and used to generate broadband ultrasound in a combined bandwidth; 
       FIG. 4  graphically illustrates the acoustic disturbances produced by the two transducers of  FIG. 3 . 
       FIG. 5  graphically illustrates the broadband acoustic disturbances produced by harmonics of a multi-transducer system constructed according to the invention; 
       FIG. 6  shows a block diagram illustrating one embodiment of a system constructed according to the invention; 
       FIG. 7  shows a schematic embodiment of the signal section of the system of  FIG. 6 ; 
       FIGS. 8A and 8B  show a schematic embodiment of the power module section of the system of  FIG. 6 ; 
       FIG. 9  is a cross-sectional side view of a harmonic transducer constructed according to the invention and driven by the power module of  FIGS. 8A and 8B ;  FIG. 9A  is a top view of the harmonic transducer of  FIG. 9 ; 
       FIG. 10  is a schematic illustration of an amplitude control subsystem constructed according to the invention;  FIG. 10A  shows illustrative amplitude control signals generated by an amplitude control subsystem such as in  FIG. 10 ; 
       FIG. 11  shows a schematic illustration of an AM sweep subsystem constructed according to the invention;  FIG. 11A  shows a typical AM frequency generated by an AM generator;  FIG. 11B  graphically shows AM sweep frequency as a function of time for a representative sweep rate, in accord with the invention; 
       FIG. 12  illustrates a multi-generator, multi-frequency, single tank ultrasound system constructed according to the invention; 
       FIG. 13  illustrates a multi-generator, common-frequency, single tank ultrasound system constructed according to the invention; 
       FIG. 14  illustrates a multi-tank ultrasound system constructed according to the invention;  FIG. 14A  shows representative AM waveform patterns as controlled through the system of  FIG. 14 . 
       FIGS. 15A ,  15 B and  15 C graphically illustrate methods of sweeping the sweep rate in accord with the invention. 
       FIGS. 16–26  show transducer and backplate embodiments for systems, methods and transducers of the invention; and 
       FIG. 27  shows representative standing waves within one transducer of the invention; 
       FIG. 28  illustrates preferential placement and mounting of multiple transducers relative to a process tank, in accord with the invention; 
       FIG. 29  illustrates a representative standing wave relative to the process tank as formed by the arrangement of  FIG. 28 ; 
       FIG. 30  illustrates another preferential pattern of placing transducers onto a mounting surface such as an ultrasound tank, in accord with the invention; 
       FIG. 31  illustrates, in a side view, the mounting of two transducers (such as the transducers of  FIG. 30 ) to a tank, in accord with the invention; 
       FIG. 32  shows an exploded side view of further features of one transducer such as shown in  FIG. 31 ; 
       FIG. 33  illustrates a two stage ultrasound delivery system constructed according to the invention; and 
       FIGS. 34 and 35  show alternative timing cycles through which the system of  FIG. 33  applies ultrasound from upper to lower frequencies; 
       FIGS. 36–40  show alternate sweep down cyclical patterns for applying a power-up sweep pattern in accord with the invention; 
       FIGS. 41A ,  41 B and  41 C schematically illustrate ultrasound generator circuitry for providing dual sweeping power-up sweep and variable degas periods, in accord with the invention; 
       FIGS. 42 and 43  show multi-frequency ultrasound systems constructed according to the invention; 
       FIG. 44  illustrates a process control system and ultrasound probe constructed according to the invention; 
       FIGS. 45 and 46  illustrate two process tanks operating with equal input powers but having different cavitation implosion activity; 
       FIG. 47  illustrates a process probe constructed according to the invention and for monitoring process characteristics within a process chemistry such as within an ultrasound tank; 
       FIG. 48  shows a schematic view of a system incorporating the probe of  FIG. 47  and further illustrating active feedback control of energy applied to an ultrasound tank, in accord with the invention; 
       FIGS. 49–51  illustrate alternative embodiments of ultrasound generators with universal voltage input, in accord with the invention; 
       FIG. 52  graphically illustrates an AM burst pattern in accord with the invention; and 
       FIG. 53  illustrates one burst of primary frequency ultrasound within one of the non-zero AM periods; 
       FIG. 54  illustrates an AM sweep pattern, in accord with the invention; 
       FIGS. 55 ,  56  and  57  schematically show one AM power up-sweep generator circuit constructed according to the invention; 
       FIG. 58  shows a quick dump rinse (QDR) tank constructed according to the invention; 
       FIG. 59  shows an improved high frequency transducer constructed according to the invention; 
       FIG. 60  illustrates, in a side exploded view, a double compression transducer constructed according to the invention; 
       FIG. 61  shows a prior art transducer with a bias bolt threaded into the upper part of the front driver; 
       FIG. 62  shows an improved transducer, constructed according to the invention; with a bias bolt threaded into a lower part of the front plate; 
       FIG. 63  illustrates one transducer of the invention utilizing a steel threaded insert to reduce stress on the front driver; 
       FIG. 64  shows a side view of a printed circuit board coupled with transducers as a single unit, in accord with the invention; and 
       FIG. 65  shows a top view of the unit of  FIG. 64 ; 
       FIG. 66  shows an acid-resistant transducer constructed according to the invention; 
       FIG. 67  schematically shows one power up-sweep generator circuit of the invention; 
       FIG. 68  illustrates a wiring schematic that couples a common voltage supply to one generator of a system that includes multiple generators, in accord with the invention; 
       FIG. 69  shows a wiring schematic to couple the generators to a single processing tank with transducers; and 
       FIG. 70  schematically shows a circuit coupled to the rotary switch of  FIG. 68 ; and 
       FIG. 71  shows a multi-generator system constructed according to the invention. 
       FIG. 72A  shows in diagram form the multiple frequency system according to the present invention; 
       FIG. 72B  shows, in graphical form, characteristics of the transducer array of  FIG. 72A ; 
       FIG. 72C  shows, in graphical form, characteristics of the generator of  FIG. 72A ; 
       FIG. 73A  shows, in schematic form, a portion of a generator built to produce multiple frequency drive signals for an array of transducers formed from paralleled transducers of  FIG. 9 ; 
       FIG. 73B  shows, in schematic form, additional components of the generator of  FIG. 73A ; 
       FIG. 73C  shows, in schematic form, additional components of the generator of FIG.  73 A; 
       FIG. 73D  shows, in schematic form, additional components of the generator of  FIG. 73A ; 
       FIG. 73E  shows, in schematic form, additional components of the generator of  FIG. 73A ; 
       FIG. 73F  shows, in schematic form, additional components of the generator of  FIG. 73A ; 
       FIG. 74  shows, in diagram form, a multiple frequency system according to the present invention, controlled by a probe measuring sound characteristics in the liquid. 
       FIG. 75  shows the multiple frequency system of  FIG. 74 , controlled by a PLC or a computer. 
       FIG. 76  shows a typical sound profile of the system of  FIG. 74 , where quiet times are inserted into the bursts of sound energy; 
       FIG. 77  shows a block diagram of the generator according to the present invention, with phase lock loop control; 
       FIG. 78A  shows a VCO controlled by a DAC according to the present invention, to change the frequencies of the generator; 
       FIG. 78B  shows an example of a staircase function that can result from the DAC controlled VCO of  FIG. 78A ; 
       FIG. 78C  shows an example of a random staircase that can be produced by the DAC controlled VCO of  FIG. 78A ; and, 
       FIG. 79  shows a schematic of a modified PFC (power factor correction) circuit that adds amplitude control to the system according to the present invention. 
       FIG. 80  shows a schematic diagram of a conduction line of an ultrasound generator. 
       FIG. 81  shows a schematic diagram of an ultrasound generator conduction line and the AC switch and modification circuitry, in a parallel connection. The control function of the AC switch is also shown. 
       FIG. 82  shows a schematic diagram of two nodes in the power section of an ultrasound generator. 
       FIG. 83  shows a schematic diagram of the AC switch and modification circuitry connected in series between two nodes in the power section of an ultrasound generator. The control function of the AC switch is also shown. 
       FIG. 84  shows a schematic diagram of a triac circuit employing the invention as used in the output of a multiple frequency generator. 
       FIGS. 85A and 85B  show a schematic diagram of a control circuit that produces on and off signals for the gates of the triacs in  FIG. 84  and on and off signals for the frequency generation of the ultrasound generator. 
       FIG. 86  shows a schematic diagram of an ultrasound frequency oscillator with a triac network in the output to step sweep the frequency output of the oscillator. 
       FIG. 87  shows a schematic diagram of a control circuit that produces on and off signals for the gates of the triacs in  FIG. 86  and on and off signals for the oscillator in  FIG. 86 . 
       FIG. 88  shows a schematic diagram of an ultrasound frequency oscillator with a triac network in the output using inductive, capacitive and resistive modification circuits. 
       FIGS. 89A ,  89 B and  89 C show schematic diagrams of AC switches formed from various active components. 
       FIG. 90  shows a waveform of a sweeping frequency signal according to the invention. 
       FIG. 91  shows a time sequence of different forms of cavitation according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2  show schematic side and top views, respectively, of an ultrasound processing system  10  constructed according to the invention. An ultrasound generator  12  electrically connects, via electrical paths  14   a ,  14   b , to an ultrasound transducer  16  to drive the transducer  16  at ultrasound frequencies above about 18 khz, and usually between 40 khz and 350 khz. Though not required, the transducer  16  is shown in  FIG. 1  as an array of transducer elements  18 . Typically, such elements  18  are made from ceramic, piezoelectric, or magnetostrictive materials which expand and contract with applied voltages or current to create ultrasound. The transducer  16  is mounted to the bottom, to the sides, or within the ultrasound treatment tank  20  through conventional methods, such as known to those skilled in the art and as described above. A liquid  22  fills the tank to a level sufficient to cover the delicate part  24  to be processed and/or cleaned. In operation, the generator  12  drives the transducer  16  to create acoustic energy  26  that couples into the liquid  22 . 
   Although the transducer  16  is shown mounted to the bottom of the tank  20 , those skilled in the art will appreciate that other mounting configurations are possible and envisioned. The transducer elements  18  are of conventional design, and are preferably “clamped” so as to compress the piezoelectric transducer material. 
     FIG. 3  illustrates a two transducer system  30 . Transducer  32   a ,  32   b  are similar to one of the elements  18 ,  FIG. 1 . Transducer  32   a  includes two ceramic sandwiched elements  34 , a steel back plate  38   a , and a front drive plate  36   a  that is mounted to the tank  20 ′. Transducer  32   b  includes two ceramic sandwiched elements  34 , a steel back plate  38   b , and a front drive plate  36   b  that is mounted to the tank  20 ′. Bolts  39   a ,  39   b  pass through the plates  38   a ,  38   b  and screw into the drive plates  36   a ,  36   b , respectively, to compresses the ceramics  34 . The transducers  32  are illustratively shown mounted to a tank surface  20 ′. 
   The transducers  32   a ,  32   b  are driven by a common generator such as generator  12  of  FIG. 1 . Alternatively, multiple generators can be used. The ceramics  34  are oriented with positive “+” orientations together or minus “−” orientations together to obtain cooperative expansion and contraction within each transducer  32 . Lead-outs  42  illustrate the electrical connections which connect between the generator and the transducers  32  so as to apply a differential voltage there-across. The bolts  39   a ,  39   b  provide a conduction path between the bottoms  43  and tops  45  of the transducers  32  to connect the similar electrodes (here shown as −, −) of the elements  34 . 
   The thicknesses  40   a ,  40   b  of transducers  32   a ,  32   b , respectively, determine the transducer&#39;s fundamental resonant frequency. For purposes of illustration, transducer  32   a  has a fundamental frequency of 40 khz, and transducer  32   b  has a fundamental frequency of 44 khz. Transducers  32   a ,  32   b  each have a finite ultrasound bandwidth which can be adjusted, slightly, by those skilled in the art. Typically, however, the bandwidths are about 4 khz. By choosing the correct fundamental frequencies, therefore, an overlap between the bandwidths of the two transducers  32   a ,  32   b  can occur, thereby adding additional range within which to apply ultrasound  26   a ′,  26   b ′ to liquid  22 ′. 
   The acoustic energy  26 ′ applied to the liquid  22 ′ by the combination of transducers  32   a ,  32   b  is illustrated graphically in  FIG. 4 . In  FIG. 4 , the “x” axis represents frequency, and the “y” axis represents acoustical power. The outline  44  represents the bandwidth of transducer  32   a , and outline  46  represents the bandwidth of transducer  32   b . Together, they produce a combined bandwidth  43  which produces a relatively flat acoustical energy profile to the liquid  22 ′, such as illustrated by profile  48 . The flatness of the bandwidth  43  representing the acoustical profile  48  of the two transducers  32   a ,  32   b  is preferably within a factor of two of any other acoustical strength within the combined bandwidth  43 . That is, if the FWHM defines the bandwidth  43 ; the non-uniformity in the profile  48  across the bandwidth  43  is typically better than this amount. In certain cases, the profile  48  between the two bandwidths  44  and  46  is substantially flat, such as illustrated in  FIG. 4 . 
   The generator connected to lead-outs  42  drives the transducers  32   a ,  32   b  at frequencies within the bandwidth  43  to obtain broadband acoustical disturbances within the liquid  22 ′. As described herein, the manner in which these frequencies are varied to obtain the overall disturbance is important. Most preferably, the generator sweeps the frequencies through the overall bandwidth, and at the same time sweeps the rate at which those frequencies are changed. That is, one preferred generator of the invention has a “sweep rate” that sweeps through the frequencies within the bandwidth  43 ; and that sweep rate is itself varied as a function of time. In alternative embodiments of the invention, the sweep rate is varied linearly, randomly, chaotically or as some other function of time to optimize the process conditions within the tank  20 ′. 
   With further reference to  FIGS. 1 and 2 , each of the elements  18  can have a representative bandwidth such as illustrated in  FIG. 4 . Accordingly, an even larger bandwidth  43  can be created with three or more transducers such as illustrated by transducers  32   a ,  32   b . In particular, any number of combined transducers can be used. Preferably, the bandwidths of all the combined transducers overlap to provide an integrated bandwidth such as profile  48  of  FIG. 4 . As such, each transducer making up the combined bandwidth should have a unique resonant frequency. 
   Those skilled in the art understand that each of the transducers  18  and  32   a ,  32   b ,  FIGS. 2 and 3 , respectively, have harmonic frequencies which occur at higher mechanical resonances of the primary resonant frequency. It is one preferred embodiment of the invention that such transducers operate at one of these harmonics, i.e., typically the first, second, third or fourth harmonic, so as to function in the frequency range of 100 khz to 350 khz. This frequency range provides a more favorable environment for acoustic processes within the tanks  20 ,  20 ′ as compared to low frequency disturbances less than 100 khz. For example, ultrasound frequencies around the 40 khz frequency can easily cause cavitation damage in the part  24 . Further, such frequencies tend to create standing waves and other hot spots of spatial cavitation within the liquid. 
   Accordingly, the benefits of applying a broadband acoustic disturbance to the liquid also apply to the 100–350 khz microsonic frequencies. Similar to  FIG. 4 ,  FIG. 5  illustrates a combined bandwidth  50  of harmonic frequencies in the range 100–350 khz. Specifically,  FIG. 5  shows the combined bandwidth  50  that is formed by the bandwidth  44 ′ around the second harmonic of the 40 khz frequency, and the bandwidth  46 ′ around the second harmonic of the 41.5 khz frequency. 
     FIG. 6  shows in block diagram embodiment of a system  110  constructed according to the present invention. The system  110  includes a signal section  112  which drives a power module  121 . The power module  121  powers the harmonic transducer array  122 . The transducer array  122  is coupled to a liquid  123  by one of several conventional means so as to generate acoustic energy within the liquid  123 . By way of example, the array  122  is similar to the array  16  of  FIG. 1 ; and the liquid  123  is similar to the liquid  22  of  FIG. 1 . 
   The signal section  112  includes a triangle wave oscillator  114  with a frequency typically below 150 hz. The purpose of the oscillator  114  is to provide a signal that sweeps the sweep rate of the ultrasound frequencies generated by the transducer arrays  122 . 
   The oscillator  114  is fed into the input of the sweep rate VCO  115  (Voltage Controlled Oscillator). This causes the frequency of the output of VCO  115  to linearly sweep at the frequency of the oscillator  114 . The optimum sweep rate frequency output of VCO  115  is typically from about 10 hz, for magnetostrictive elements, to about 1.2 khz, for piezoelectrics. Therefore, the optimum center sweep rate frequency can be anywhere within the range of about 10 hz to 1.2 khz, and that sweep rate is varied within a finite range of frequencies about the center sweep frequency. This finite range is typically set to about 10–50% of the center sweep rate frequency. For example, the center sweep rate frequency for one process might be 455 hz, so the VCO  115  output is set, for example, to sweep from 380 hz to 530 hz. If, additionally, the oscillator  114  is set to 37 hz, then the output of VCO  115  changes frequency, linearly, from 380 hz to 530 hz, and back to 380 hz at thirty seven times per second. 
   The output of VCO  115  feeds the VCO input of the 2X center frequency VCO  116 . The VCO  116  operates as follows. If, for example, the center frequency of VCO  116  is set to 208 khz and the bandwidth is set to 8 khz, the center frequency linearly changes from 204 khz to 212 khz and back to 204 khz in a time of 1.9 milliseconds (i.e., 1/530 hz) to 2.63 milliseconds (i.e., 1/380 hz). The specific time is determined by the voltage output of the oscillator  114  at the time of measurement. Since the voltage output of oscillator  114  is constantly changing, the time it takes to linearly sweep the center frequency from 204 khz to 212 khz and back to 204 khz is also constantly changing. In this example, the time changes linearly from 1.9 milliseconds to 2.63 milliseconds and back to 1.9 milliseconds at thirty seven times per second. 
   The oscillator  114 , VCO  115  and VCO  116  operate, in combination, to eliminate the repetition of a single sweep rate frequency in the range of 10 hz to 1.2 khz. For example, the highest single frequency that exists in the stated example system is 37 hz. If an unusual application or process were found whereby a very low frequency resonance around 37 hz exists, then the oscillator  114  would be replaced by a random or chaotic voltage generator to reduce the likelihood of exciting any modes within the part. 
   The VCO  116  drives a divide-by-two D flip-flop  117 . The purpose of the D flip-flop  117  is to eliminate asymmetries in the waveform from the VCO  116 . The output of the D flip-flop  117  is thus a square wave that has the desired frequency which changes at a sweep rate that is itself sweeping. In the stated example, the output square wave from D flip-flop  117  linearly changes from 102 khz to 106 khz and back to 102 khz at different times in the range of 1.9 milliseconds to 2.63 milliseconds. This sweeping of the sweep rate is sometimes referred to herein as “double sweep” or “double sweeping.” 
   The AC line zero-crossover detection circuit  118  produces a signal with a rise time or narrow pulse at or near the time that the AC line voltage is at zero or at a low voltage, i.e., at or near zero degrees. This signal triggers the adjustable monostable multivibrator  119 . The timed pulse out of monostable multivibrator  119  is set to a value between zero degrees and ninety degrees, which corresponds to a time from zero to 4.17 milliseconds for a 60 hz line frequency. 
   If the maximum amplitude were desired, for example, the monostable multivibrator  119  is set to a time of 4.17 milliseconds for a 60 hz line frequency. For an amplitude that is 50% of maximum, the monostable multivibrator  119  is set to 1.389 milliseconds for a 60 hz line frequency. In general, the monostable multivibrator  119  time is set to the arcsine of the amplitude percent times the period of the line frequency divided by 360 degrees. 
   The double sweeping square wave output of the D flip-flop  117  and the timed pulse output of the monostable multivibrator  119  feed into the synchronization logic  120 . The synchronization logic  120  performs three primary functions. First, it only allows the double sweeping square wave to pass to the output of the synchronization logic  120  during the time defined by the pulse from the monostable multivibrator  119 . Second, the synchronization logic  120  always allows a double sweeping square wave which starts to be completed, even if the monostable multivibrator  119  times out in the middle of a double sweeping square wave. And lastly, the synchronization logic  120  always starts a double sweeping square wave at the beginning of the ultrasound frequency, i.e., at zero degrees. 
   The output of synchronization logic  120  is a double sweeping square wave that exists only during the time defined by the monostable multivibrator  119  or for a fraction of a cycle past the end of the monostable multivibrator  119  time period. The synchronization logic  120  output feeds a power module  121  which amplifies the pulsed double sweeping square wave to an appropriate power level to drive the harmonic transducers  122 . The transducers  122  are typically bonded to a tank and deliver sound waves into the liquid within the tank. These sound waves duplicate the pulsed double sweeping characteristics of the output of the signal section  112 . 
     FIG. 7  shows a schematic embodiment of the signal section  112  in  FIG. 6 . U 1  is a XR-2209 precision oscillator with a triangle wave output at pin  8 . The frequency of the XR-2209 is 1/(RC)=1/((27 Kohm) (1 microfarad))=37 hz. This sets the frequency of the triangle wave oscillator  114 ,  FIG. 6 , to sweep the sweep rate at 37 hz. The other components associated with the XR-2209 are the standard configuration for single supply operation of this integrated circuit. 
   U 2  is a XR-2209 precision oscillator with a triangle wave output at pin 8 . The center frequency of U 2  is 1/(RC)=1/((2.2 Kohm) (1 microfarad))=455 hz. The actual output frequency is proportional to the current flowing out of pin 4  of U 2 . At 455 hz, this current is 6 volts/2.2 Kohm=2.73 milliampers. It is generally desirable, according to the invention, to sweep the 455 hz sweep rate through a total change of 150 hz, i.e., 75 hz either side of 455 hz. Since 75 hz/455 hz=16.5%, the current flowing out of pin  4  must change by 16.5% in each direction, that is, by (16.5%) (2.73 milliampers)=0.45 milliampers. The triangle wave from U 1  causes this change. The triangle wave changes from 3 volts to 9 volts; therefore, there is 3 volts on either side of 6 volts at pin 4  of U 2  to cause the 0.45 milliampers change. By making R 1 =3 volts/0.45 milliampers=6.67 Kohm, the sweep rate is changed 75 hz either side of 455 hz. The actual R 1  used in  FIG. 7  is 6.65 Kohm, a commercially available value giving an actual change of 75.2 hz. 
   U 3  is an XR-2209 precision oscillator with a center frequency of approximately 1/(RC)=1/((12 Kohm+2.5 Kohm) (330 microfarad))=209 khz with the potentiometer set to its center position of 2.5 Kohm. In the actual circuit, the potentiometer is adjusted to about 100 ohms higher to give the desired 208 khz center frequency. Out of U 3  pin 4  flows 6 volts/(12 Kohm+2.5 Kohm+100 ohms)=0.41 milliampers. To change the center frequency a total of 8 khz, the 0.41 milliampers is changed by 4 khz/208 khz=1.92%, or 7.88 microampers. This means that R 2 =3 volts/7.88 microampers=381 Kohm. In  FIG. 7 , however, the commercial value of 383 Kohm was used. 
   U 3  pin 7  has a square wave output that is changing from 204 khz to 212 khz and back to 204 khz at a rate between 380 hz and 530 hz. The actual rate is constantly changing thirty seven times a second as determined by U 1 . 
   U 4  is a D flip-flop in a standard divide by two configuration. It squares up any non 50% duty cycle from U 3  and provides a frequency range of 102 khz to 106 khz from the 204 khz to 212 khz U 3  signal. 
   The output of U 4  feeds the synchronization logic which is described below and after the description of the generation of the amplitude control signal. 
   The two 1N4002 diodes in conjunction with the bridge rectifier form a full wave half sinusoid signal at the input to the 40106 Schmidt trigger inverter. This inverter triggers when the half sinusoid reaches about 7 volts, which on a half sinusoid with an amplitude of 16 times the square root of two is close enough to the zero crossover for a trigger point in a practical circuit. The output of the 40106 Schmidt trigger falls which triggers U 5 , the edge triggered 4538 monostable multivibrator wired in a trailing edge trigger/retriggerable configuration. The output of U 5  goes high for a period determined by the setting on the 500 Kohm potentiometer. At the end of this period, the output of U 5  goes low. The period is chosen by setting the 500 Kohm potentiometer to select that portion of the leading one-quarter sinusoid that ends at the required amplitude to give amplitude control. This timed positive pulse feeds into the synchronization logic along with the square wave output of U 4 . 
   The timed pulse U 5  feeds the D input of U 6 , a 4013 D-type flip flop. The square wave from U 4  is invented by U 7   a  and feeds the clock input of U 6 . U 6  only transfers the signal on the D input to the output Q at the rise of a pulse on the clock input, Pin 3 . Therefore, the Q output of U 6  on Pin 1  is high when the D input of U 6  on Pin 3  is high and the clock input of U 6  on Pin 3  transitions high. This change in the Q output of U 6  is therefore synchronized with the change in the square wave from U 4 . 
   The synchronized high Q output of U 6  feeds U 8  Pin 13 , a 4093 Schmidt trigger NAND gate. The high level on Pin 13  of U 8  allows the square wave signal to pass from U 8  Pin 12  to the output of U 8  at Pin 11 . 
   In a similar way, U 8  synchronizes the falling output from U 5  with the square wave from U 4 . Therefore, only complete square waves pass to U 8  Pin 11  and only during the time period as chosen by monostable multivibrator U 5 . The 4049 buffer driver U 7   b  inverts the output at U 8  Pin 11  so it has the same phase as the square wave output from U 4 . This signal, U 7   b  Pin 2  is now the proper signal to be amplified to drive the transducers. 
     FIGS. 8A and 8B  represent a circuit that increases the signal from U 7   b  Pin 2  in  FIG. 7  to a power level for driving the transducers  122 ,  FIG. 6 . There are three isolated power supplies. The first one, including a T 1 , a bridge, C 19 , VR 1  and C 22 , produces +12 VDC for the input logic. The second and third isolated power supplies produce +15 VDC at VR 2  Pin 3  and VR 3  Pin 3  for gate drive to the IGBTs (insulated gate bipolar transistors). 
   The signal input to  FIGS. 8A and 8B  have its edges sharpened by the 40106 Schmidt trigger U 9   a . The output of U 9   a  feeds the 4049 buffer drivers U 10   c  and U 10   d  which drive optical isolator and IGBT driver U 12 , a Hewlett Packard HCPL3120. Also, the output of U 9   a  is inverted by U 9   b  and feeds buffer drivers U 10   a  and U 10   b  which drive U 11 , another HCPL3120. 
   This results in an isolated drive signal on the output of U 11  and the same signal on the output of U 12 , only 180 degrees out of phase. Therefore, U 11  drives Q 1  on while U 12  drives Q 2  off. In this condition, a power half sinusoid of current flows from the high voltage full wave DC at B 1  through D 1  and Q 1  and L 1  into C 1 . Current cannot reverse because it is blocked by D 1  and the off Q 2 . When the input signal changes state, U 11  turns off Q 1  and U 12  turns on Q 2 , a half sinusoid of current flow out of C 1  through L 2  and D 2  and Q 2  back into C 1  in the opposite polarity. This ends a complete cycle. 
   The power signal across C 1  couples through the high frequency isolation transformer T 4 . The output of T 4  is connected to the transducer or transducer array. 
     FIG. 9  shows a cross-sectional side view of one clamped microsonic transducer  128  constructed according to the invention; while  FIG. 9A  shows a top view of the microsonic transducer  128 . The microsonic transducer  128  has a second harmonic resonant frequency of 104 khz with a 4 khz bandwidth (i.e., from 102 khz to 106 khz). The cone-shaped backplate  139  flattens the impedance verses frequency curve to broaden the frequency bandwidth of the microsonic transducer  128 . Specifically, the backplate thickness along the “T” direction changes for translational positions along direction “X.” Since the harmonic resonance of the microsonic transducer  128  changes as a function of backplate thickness, the conical plate  139  broadens and flattens the microsonic transducer&#39;s operational bandwidth. 
   The ceramic  134  of microsonic transducer  128  is driven through oscillatory voltages transmitted across the electrodes  136 . The electrodes  136  connect to an ultrasound generator (not shown), such as described above, by insulated electrical connections  138 . The ceramic  134  is held under compression through operation of the bolt  132 . Specifically, the bolt  132  provides 5,000 pounds of compressive force on the piezoelectric ceramic  134 . This transducer invention will be referred to herein as the “reverse bolt construction” transducer. 
   Amplitude control according to one embodiment of the invention is illustrated in  FIGS. 10 and 10A . Specifically,  FIG. 10  shows an amplitude control subsystem  140  that provides amplitude control by selecting a portion of the rectified line voltage  145  which drives the ultrasound generator amplitude select section  146 . The signal section  112 ,  FIG. 6 , and particularly the monostable multivibrator  119  and synchronization logic  120 , provide similar functionality. In  FIG. 10 , the amplitude control subsystem  140  operates with the ultrasound generator  142  and connects with the power line voltage  138 . The rectification section  144  changes the ac to dc so as to provide the rectified signal  145 . 
   The amplitude select section  146  selects a portion of the leading quarter sinusoid of rectified signal  145  that ends at the desired amplitude, here shown as amplitude “A,” in a region  148  between zero and 90 degrees and in a region  150  between 180 degrees and 270 degrees of the signal  145 . In this manner, the amplitude modulation  152  is selectable in a controlled manner as applied to the signal  154  driving the transducers  156  from the generator  142 , such as discussed in connection with  FIGS. 3 and 4 . 
     FIG. 10A  shows illustrative selections of amplitude control in accord with the invention. The AC line  158  is first converted to a full wave signal  160  by the rectifier  144 . Thereafter, the amplitude select section  146  acquires the signal amplitude selectively. For example, by selecting the maximum amplitude of 90 degrees in the first quarter sinusoid, and 270 degrees in the third quarter sinusoid, a maximum amplitude signal  162  is provided. Similarly, a one-half amplitude signal  164  is generated by choosing the 30 degrees and 210 degrees locations of the same sinusoids. By way of a further example, a one-third amplitude signal  166  is generated by choosing 19.5 degrees and 199.5 degrees, respectively, of the same sinusoids. 
   Those skilled in the art will appreciate that the rectification section  144  can also be a half-wave rectifier. As such, the signal  145  will only have a response every other one-half cycle. In this case, amplitude control is achieved by selecting a portion of the leading quarter sinusoid that ends at a selected amplitude between zero and 90 degrees of the sinusoid. 
   The ultrasound generator of the invention is preferably amplitude modulated. Through AM control, various process characteristics within the tank can be optimized. The AM control can be implemented such as described in  FIGS. 3 ,  4 ,  10  and  10 A, or through other prior art techniques such as disclosed in U.S. Pat. No. 4,736,130. 
   This “sweeping” of the AM frequency is accomplished in a manner that is similar to ultrasound generators which sweep the frequency within the bandwidth of an ultrasound transducer. By way of example, U.S. Pat. No. 4,736,130 describes one ultrasound generator which provides variable selection of the AM frequency through sequential “power burst” generation and “quiet time” during a power train time. In accord with the invention, the AM frequency is changed to “sweep” the frequency in a pattern so as to provide an AM sweep rate pattern. 
     FIG. 11  illustrates an AM sweep subsystem  170  constructed according to the invention. The AM sweep subsystem  170  operates as part of, or in conjunction with, the ultrasound generator  172 . The AM generator  174  provides an AM signal  175  with a selectable frequency. The increment/decrement section  176  commands the AM generator  174  over command line  177  to change its frequency over a preselected time period so as to “sweep” the AM frequency in the output signal  178  which drives the transducers  180 . 
   U.S. Pat. No. 4,736,130 describes one AM generator  56 ,  FIG. 1 , that is suitable for use as the generator  174  of  FIG. 11 . By way of example,  FIG. 11A  illustrates one selectable AM frequency signal  182  formed through successive 500 μs power bursts and 300 μs quiet times to generate a 1.25 khz signal (e.g., 1/(300 μs+500 μs)=1.25 khz). If, for example, the AM frequency is swept at 500 hz about a center frequency of 1.25 khz, such as shown in  FIG. 11 , then the frequency is commanded to vary between 1.25 khz+250 hz and 1.25 khz−250 hz, such as illustrated in  FIG. 11B .  FIG. 11B  illustrates a graph of AM frequency versus time for this example. 
     FIG. 12  schematically illustrates a multi-generator, single tank system  200  constructed according to the invention. In many instances, it is desirable to select an ultrasound frequency  201  that most closely achieves the cavitation implosion energy which cleans, but does not damage, the delicate part  202 . In a single tank system such as in  FIG. 12 , the chemistries within the tank  210  are changed, from time to time, so that the desired or optimum ultrasound frequency changes. The transducers and generators of the prior art do not operate or function at all frequencies, so system  200  has multiple generators  206  and transducers  208  that provide different frequencies. By way of example, generator  206   a  can provide a 40 khz primary resonant frequency; while generator  206   b  can provide the first harmonic 72 khz frequency. Generator  206   c  can provide, for example, 104 khz microsonic operation. In the illustrated example, therefore, the generators  206   a ,  206   b ,  206   c  operate, respectively, at 40 khz, 72 khz, and 104 khz. Each transducer  208  responds at each of these frequencies so that, in tandem, the transducers generate ultrasound  201  at the same frequency to fill the tank  210  with the proper frequency for the particular chemistry. 
   In addition, each of the generators  206   a – 206   c  can and do preferably sweep the frequencies about the transducers&#39; bandwidth centered about the frequencies 40 khz, 72 khz and 104 khz, respectively; and they further sweep the sweep rate within these bandwidths to reduce or eliminate resonances which might occur at the optimum sweep rate. 
   When the tank  210  is filled with a new chemistry, the operator selects the optimum frequency through the mux select section  212 . The mux select section connects to the analog multiplexer (“mux”)  214  which connects to each generator  206 . Specifically, each generator  206  couples through the mux  214  in a switching network that permits only one active signal line  216  to the transducers  208 . For example, if the operator at mux select section  212  chooses microsonic operation to optimize the particular chemistry in the tank  210 , generator  206   c  is connected through the mux  214  and drives each transducer  208   a – 208   c  to generate microsonic ultrasound  201  which fills the tank  210 . If, however, generator  206   a  is selected, then each of the transducers  208  are driven with 40 khz ultrasound. 
     FIG. 13  illustrates a multi-generator, common frequency ultrasound system  230  constructed according to the invention. In  FIG. 13 , a plurality of generators  232  ( 232   a – 232   c ) connect through signal lines  234  ( 234   a – 234   c ) to drive associated transducers  238  ( 238   a – 238   c ) in a common tank  236 . Each of the transducers  238  and generators  232  operate at the same frequency, and are preferably swept through a range of frequencies such as described above so as to reduce or eliminate resonances within the tank  236  (and within the part  242 ). 
   In order to eliminate “beating” between ultrasound energies  240   a – 240   c  of the several transducers  238   a – 238   c  and generators  232   a – 232   c , the generators  232  are each driven by a common FM signal  250  such as generated by the master signal generator  244 . The FM signal is coupled to each generator through signal divider  251 . 
   In operation, system  230  permits the coupling of identical frequencies, in magnitude and phase, into the tank  236  by the several transducers  238 . Accordingly, unwanted beating effects are eliminated. The signal  250  is swept with FM control through the desired ultrasound bandwidth of the several transducers to eliminate resonances within the tank  236 ; and that sweep rate frequency is preferably swept to eliminate any low frequency resonances which can result from the primary sweep frequency. 
   Those skilled in the art should appreciate that system  230  of  FIG. 13  can additionally include or employ other features such as described herein, such as AM modulation and sweep, AM control, and broadband transducer. 
     FIG. 14  illustrates a multi-tank system  260  constructed according to the invention. One or more generators  262  drive each tank  264  (here illustrated, generators  262   a  and  262   b  drive tank  264   a ; and generators  264   c  and  264   d  drive tank  264   b ). Each of the generators  262  connects to an associated ultrasound transducer  266   a–d  so as to produce ultrasound  268   a–d  in the associated tanks  264   a–b.    
   The common master signal generator  270  provides a common FM signal  272  for each of the generators  262 . Thereafter, ultrasound generators  262   a–b  generate ultrasound  268   a–b  that is identical in amplitude and phase, such as described above. Similarly, generators  262   c–d  generate ultrasound  268   c–d  that is identical in amplitude and phase. However, unlike above, the generators  262  each have an AM generator  274  that functions as part of the generator  262  so as to select an optimum AM frequency within the tanks  264 . In addition, the AM generators  274  preferably sweep through the AM frequencies so as to eliminate resonances at the AM frequency. 
   More particularly, generators  274   a–b  generate and/or sweep through identical frequencies of the AM in tank  264   a ; while generators  274   c–d  generate and/or sweep through identical frequencies of AM in tank  264   b . However, the AM frequency and/or AM sweep of the paired generators  274   a–b  need not be the same as the AM frequency and/or AM sweep of the paired generators  274   c–d . Each of the generators  274  operate at the same carrier frequency as determined by the FM signal  270 ; however each paired generator set  274   a–b  and  274   c–d  operates independently from the other set so as to create the desired process characteristics within the associated tank  264 . 
   Accordingly, the system  260  eliminates or prevents undesirable cross-talk or resonances between the two tanks  264   a–b . Since the generators within all tanks  264  operate at the same signal frequency  270 , there is no effective beating between tanks which could upset or destroy the desired cleaning and/or processing characteristics within the tanks  264 . As such, the system  260  reduces the likelihood of creating damaging resonances within the parts  280   a–b . It is apparent to those skilled in the art that the FM control  270  can contain the four AM controls  274   a–d  instead of the illustrated configuration. 
     FIG. 14A  shows two AM patterns  300   a ,  300   b  that illustrate ultrasound delivered to multiple tanks such as shown in  FIG. 14 . For example, AM pattern  300   a  represents the ultrasound  268   a  of  FIG. 14 ; while AM pattern  300   b  represents the ultrasound  268   c  of  FIG. 14 . With a common FM carrier  302 , as provided by the master generator  270 ,  FIG. 14 , the ultrasound frequencies  302  can be synchronized so as to eliminate beating between tanks  264   a ,  264   b . Further, the separate AM generators  274   a  and  274   c  provide capability so as to select the magnitude of the AM frequency shown by the envelope waveform  306 . As illustrated, for example, waveform  306   a  has a different magnitude  308  as compared to the magnitude  310  of waveform  306   b . Further, generators  374   a ,  374   c  can change the periods  310   a ,  310   b , respectively, of each of the waveforms  306   a ,  306   b  selectively so as to change the AM frequency within each tank. 
     FIGS. 15A ,  15 B and  15 C graphically illustrate the methods of sweeping the sweep rate, in accord with the invention. In particular,  FIG. 15A  shows an illustrative condition of a waveform  350  that has a center frequency of 40 khz and that is varied about the center frequency so as to “sweep” the frequency as a function of time along the time axis  352 .  FIG. 15B  illustrates FM control of the waveform  354  which has a varying period  356  specified in terms of time. For example, a 42 khz period occurs in 23.8 microseconds while a 40 khz period occurs in 25 microseconds. The regions  358   a ,  358   b  are shown for ease of illustration and represent, respectively, compressed periods of time within which the system sweeps the waveform  354  through many frequencies from 42 khz to 40 khz, and through many frequencies from 40 khz to 38 khz. 
     FIG. 15C  graphically shows a triangle pattern  360  which illustrates the variation of sweep rate frequency along a time axis  362 . 
   The invention thus attains the objects set forth above, among those apparent from preceding description. Since certain changes may be made in the above apparatus and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing be interpreted as illustrative and not in a limiting sense. 
   It is also to be understood that the following claims are to cover all generic and specific features of the invention described herein, and all statements of the scope of the invention which, as a matter of language, might be said to fall there between. 
     FIGS. 16–20  illustrate alternative backplate configurations according to the invention. Unlike the configuration of  FIG. 3 , the backplates of  FIGS. 16–20  are shaped to flatten or modify the power output from the entire transducer when driven over a range of frequencies such as shown in  FIG. 4 . Specifically,  FIG. 16  includes a backplate  58  that, for example, replaces the backplate  38  of  FIG. 3 . A portion of the bolt  39  is also shown. As illustrated, the backplate  58  has a cut-away section  60  that changes the overall acoustic resonance of the transducer over frequency. Similarly, the backplate  58   a  of  FIG. 17  has a curved section  60   a  that also changes the overall acoustic resonance of the transducer over frequency.  FIGS. 18 ,  19  and  20  similarly have other sloped or curved sections  60   b ,  60   c , and  60   d , within backplates  58   b ,  58   c  and  58   d , respectively, that also change the overall acoustic resonance of the transducer. 
   The exact configuration of the backplate depends upon the processing needs of the ultrasound being delivered to a tank. For example, it is typically desirable to have a flat or constant power over frequency, such as shown in  FIG. 4 . Accordingly, for example, the backplate and/or front driver can be cut or shaped so as to help maintain a constant power output such that the energy generated by the transducer at any given frequency is relatively flat over that bandwidth. Alternatively, the backplate can be cut or shaped so as to provide a varying power output, over frequency, such as to compensate for other non-linearities within a given ultrasound system. 
     FIG. 27  illustratively shows how standing waves are formed within one transducer  69  of the invention over various frequencies  61 ,  62 ,  63 . Because of the shaped surface  70  of the backplate  59 , there are no preferred resonant frequencies of the transducer  69  as standing waves can form relative to various transverse dimensions of the transducer  69 . By way of example, frequency  62  can represent 38 khz and frequency  63  can represent 42 khz. 
     FIG. 21  illustrates still another transducer  80  of the invention that provides for changing the power output as a function of frequency. The front driver  82  and the backplate  84  are connected together by a bolt  86  that, in combination with the driver  82  and backplate  84 , compress the ceramics  88   a ,  88   b . The configuration of  FIG. 21  saves cost since the front driver  82  has a form fit aperture-sink  90  (the bolt head  86   a  within the sink  90  are shown in a top view in  FIG. 22 ) that accommodates the bolt head  86   a . A nut  86   b  is then screwed onto the other end of the bolt  86  and adjacent to the backplate  84  such that a user can easily access and remove separate elements of the transducer  80 . 
   The front driver  82  and/or backplate  84  (the “backplate” also known as “back mass” herein) are preferably made from steel. The front driver  82  is however often made from aluminum. Other materials for the front driver  82  and/or the backplate  84  can be used to acquire desired performance characteristics and/or transducer integrity. 
     FIG. 23  shows another transducer  92  that includes a backplate  94  and a front driver  96 . A bolt  98  clamps two ceramic elements  97   a ,  97   b  together and between the backplate  94  and driver  96 ; and that bolt  98  has a bolt head  100  that is approximately the same size as the diameter “D” of the transducer  92 . The bolt head  100  assists the overall operation of the transducer  92  since there is no composite interface of the bolt  98  and the driver  96  connected to the tank. That is, the bond between the tank and the transducer  92  is made entirely with the bolt head  100 . By way of comparison, the bond between the tank and the transducer  80 ,  FIG. 21 , occurs between both the bolt  86  and the driver  82 . A sloped region  99  provides for varying the power output over frequency such as described herein. 
     FIG. 24  illustrates one end  102  of a transducer of the invention that is similar to  FIG. 23  except that there is no slope region  99 ; and therefore there is little or no modification of the power output from the transducer (at least from the transducer end  102 ). 
     FIGS. 15 and 16  show further transducer embodiments of the invention.  FIG. 25  shows a transducer  110  that includes a driver  112 , backplate  114 , bolt  116 , ceramic elements  118   a ,  118   b , and electrical lead-outs  120 . The backplate is shaped so as to modify the transducer power output as a function of frequency. The driver  112  is preferably made from aluminum. 
     FIG. 26  illustrates an alternative transducer  120  that includes a backplate  122 , driver  124 , bolt  126 , ceramic elements  128   a ,  128   b , and lead outs  130 . One or both of the backplate and driver  122 ,  124  are made from steel. However, the front driver  124  is preferably made from aluminum. The bolt head  126   a  is fixed within the driver  124 ; and a nut  126   b  is screwed onto the bolt  126  to reside within a cut-out  122   a  of the backplate  122 . The backplate  122  and front driver  129  are sealed at the displacement node by an O-ring  123  to protect the electrical sections (i.e., the piezoelectric ceramics and electrodes) of the transducer  120  under adverse environmental conditions. 
   The designs of  FIGS. 23–24  have advantages over prior art transducers in that the front plate in each design is substantially flush with the tank when mounted to the tank. That is, the front plates have a substantially continuous front face (e.g., the face  112   a  of  FIG. 25 ) that mounts firmly with the tank surface. Accordingly, such designs support the tank surface, without gap, to reduce the chance of creating cavitation implosions that might otherwise eat away the tank surface and create unwanted contaminants. 
     FIG. 28  shows one preferred arrangement (in a bottom view) for mounting multiple transducers  140  to the bottom  142   a  of a process tank  142 . Specifically, the lateral spacing between transducers  140 —each with a diameter X—is set to 2X to reduce the cavitation implosions around the transducers  140  (which might erode the generally expensive tank surface  142   a ). By way of example, if the transducer  140  has a two inch diameter (i.e., X=2″), then the spacing between adjacent transducers  140  is four inches. Other sizes can of course be used and scaled to user needs and requirements.  FIG. 29  illustrates, in a cross sectional schematic view, a standing wave  144  that is preferentially created between adjacent transducers  140 ′ with diameters X and a center to center spacing of 2X. The standing wave  144  tends to reduce cavitation and erosion of the tank  142 ′ surface. 
   Surface cavitation is intense cavitation that occurs at the interface between the solution within the tank and the radiating surface upon which the ultrasound transducers are mounted. There are several problems associated with surface cavitation damage. First, it is often intense enough to erode the material of the radiating surface. This can eventually create a hole in the radiation surface, destroying the tank. The erosion is also undesirable because it introduces foreign materials into the cleaning solution. Surface cavitation further generates cavitation implosions with higher energy in each cavitation implosion than exists in the cavitation implosions in the process chemistry. If the cavitation implosions in the process chemistry are at the proper energy level, than there is the possibility that the higher energy cavitation implosions at the surface cavitation will cause pitting or craters in the parts under process. In addition, the energy that goes into creating the surface cavitation is wasted energy that is better used in creating bulk cavitation. 
     FIG. 30  illustrates a closed hex spacing pattern  149  of transducer elements  150  that causes the radiating membrane  151  (i.e., the surface of the tank to which the elements are bonded to) to vibrate in a sinusoidal pattern such that surface cavitation is prevented or reduced. In a side view,  FIG. 31  illustrates a G-10 isolator  153  bonded between two of the transducers  150 ′ (and specifically the front driver  150   a ) and the radiating surface  151 ′, i.e., the wall of the tank  154  holding the process chemistry  156 . The G-10  153  operates to further reduce unwanted surface cavitation, often times even when the closed hex spacing pattern of  FIG. 30  is not possible. Piezoelectric elements  155  are sandwiched between the front plate  150   a  and backplate  154 .  FIG. 32  shows an exploded side view of one of the G-10 mounted transducer  150 ″ of  FIG. 31 . Layers of epoxy  160  preferably separate the G-10 isolator  153  from the transducer  150 ″ and from the surface  152 ′. 
   Most ultrasound processes, including cleaning, have two distinct stages. The first stage is usually preparation of the liquid and the second stage is the actual process. The system  200  of  FIGS. 33–35  reduces the time for liquid preparation and accomplishes the task to a degree where shorter process times are possible. 
   The invention of  FIG. 33  utilizes the sound fields as an upward driving force to quickly move contaminants to the surface  207   a  of the liquid  207 . This phenomenon is referred to herein as “power up-sweep” and generally cleans the liquid more quickly and thoroughly so that part processing can be done with less residual contamination. 
   More particularly,  FIG. 33  shows a system  200  constructed according to the invention. A generator  202  drives a plurality of transducers  204  connected to a process tank  206 , which holds a process chemistry  207 . The generator  202  drives the transducers  204  from an upper frequency (f upper ) to a lower frequency (f lower ), a shown in  FIG. 35 . Once f lower  is reached, a frequency control subsystem  208  controls the generator  202  so as to drive the transducers  204  again from f upper  to f lower  and without driving the transducers from f lower  to f upper . In this manner, only decreasing frequencies are imparted to the process chemistry  207 ; and acoustic energy  210  migrates upwards (along direction  217 ), pushing contamination  211  upwards and out of the tank  206 . 
   As shown in  FIG. 34 , the two stage ultrasound processing system  200  can alternatively cycle the transducers  204  from f upper  to f lower  every other half cycle, with a degas, quiet or off half cycle  222  between each power burst. The control subsystem  208  of this embodiment thus includes means for inhibiting the flow of energy into the tank  206  over a second half cycle so that the quiet period  222  is realized. It is not necessary that the time periods of the first and second one-half cycles  222   a ,  222   b , respectively, be equal. 
     FIGS. 34 and 35  also show that the rate at which the frequencies are swept from f upper  to f lower  can vary, as shown by the shorter or longer periods and slope of the power bursts, defined by the frequency function  220 . 
   The generator  202  preferably produces frequencies throughout the bandwidth of the transducers  204 . The generator  202  is thus preferably a sweep frequency generator (described in U.S. Pat. Nos. 4,736,130 and 4,743,789) or a dual sweep generator (described in International Patent Application PCT/US97/12853) that will linearly or non-linearly change frequency from the lowest frequency in the bandwidth to the highest frequency in the bandwidth; and that will thereafter reverse direction and sweep down in frequency through the bandwidth. The invention of  FIG. 35  has an initial stage where the sweeping frequency only moves from the highest bandwidth frequency to the lowest bandwidth frequency. Once the lowest frequency is reached, the next half cycle is the highest frequency and the sweep starts again toward the lowest frequency. An alternative ( FIG. 34 ) is to shut the ultrasonics off when the lowest frequency is reached and reset the sweep to the highest frequency. After an ultrasonics quiet period  222 , another sweep cycle from high frequency to low frequency occurs. This “off” period followed by one directional sweep is repeated until contamination removal is complete; and then the processing can start in a normal way. Alternatively, a power up-sweep mode can be utilized for improved contamination removal during processing. 
   The reason that contamination is forced to the surface  207   a  of the process chemistry  207  in the system of  FIG. 33  is because the nodal regions move upward as frequency is swept downward. Contamination trapped in nodal regions are forced upward toward the surface as nodes move upward. Generally, the system of  FIG. 33  incorporates a type of frequency modulation (FM) where frequency changes are monotonic from higher to lower frequencies. Transducers  204  mounted to the bottom of the process tank  206  generate an ever expanding acoustic wavelength in the upward direction  217  (i.e., toward the surface  207   a  of the process chemistry  207 ). This produces an acoustic force  210  which pushes contamination  211  to the surface  207   a  where the contamination  211  overflows the weirs  213  for removal from the tank  206 . 
   Those skilled in the art should appreciate that methods and systems exist for sweeping the applied ultrasound energy through a range of frequencies so as to reduce resonances which might adversely affect parts within the process chemistry. See, e.g., U.S. Pat. Nos. 4,736,130 and 4,743,789 by the inventor hereof and incorporated by reference. It is further known in ultrasound generators to “sweep the sweep rate” so that the sweep frequency rate is changed (intermittently, randomly, with a ramp function, or by another function) to reduce other resonances which might occur at the sweep rate. By way of example, the inventor of this application describes such systems and methods in connection with  FIGS. 3 ,  4 ,  5 A,  5 B,  22 A,  22 B and  22 C of International Application No. PCT/US97/12853, which is herein incorporated by reference. 
   The variable slope of the frequency function  220  of  FIGS. 34 and 35  illustrates that the time period between successive power up sweeps, from f upper  to f lower , preferably changes so as to “sweep the sweep rate” of the power up sweep. Accordingly, the power up-sweep preferably has a non-constant sweep rate. There are several ways to produce a non-constant power up-sweep rate, including:
         (a) As illustrated in  FIG. 36 , sweep down in frequency (i.e., from f upper  to f lower ) at a relatively slow rate, typically in the range of 1 hz to 1.2 khz, and sweep up in frequency (i.e., from f lower  to f upper ) during the recovery time at a rate about ten times higher than the sweep down frequency rate. Vary the rate for each cycle. This cycle is repeated during processing.   (b) As illustrated in  FIG. 37 , sweep down in frequency at a relatively slow rate and shut the generator  202  off (such as through the control subsystem  208 ) at periods  225 ′ when the lowest frequency f lower  in the bandwidth (bandwidth=f upper −f lower ) is reached. During the off time  225 ′, a degassing period  222  can occur as in  FIG. 34  due to buoyancy of the gas bubbles; and the subsystem  208  resets the generator  202  to the highest frequency for another relatively slow rate of sweeping from f upper  to f lower , each time reducing contaminants. Vary the time of the degas period. Repeat this cycle during processing.   (c) As a function of time, change or “sweep” the power up-sweep rate at optimum values (1 hz to 1.2 khz) of the rate, as shown in  FIG. 38 . The change in the upward sweep rate and the change in the downward sweep rate can be synchronized or they can be random or chaotic with respect to one another.   (d) For the case where there is a degas period, such as in  FIGS. 34 and 39  (i.e. the recovery period when the generator is off or unconnected while resetting from low frequency to high frequency), vary the length of the degas period  222  ( FIG. 34 ),  225 ′ ( FIG. 39 ) randomly or as a function of time such as through a linear sweep rate time function. This technique has an advantage for cases where there is one optimum power up-sweep rate (i.e., the rate of frequency change between f upper  and f lower ) and, accordingly, low frequency resonances are eliminated by changing the overall rate. In such a technique, the slope of the frequency function  220 ′ in  FIG. 39 , is constant, though the period of each degas period  225 ′ changes according to some predefined function.   (e) As shown in  FIG. 40 , sweep the rate with a combination of (c) and (d) techniques above.       

   Note that in each of  FIGS. 34–40 , the x-axis represents time (t) and the y-axis represents frequency f. 
     FIG. 41  shows a schematic  250  illustrating the most general form of generator circuitry providing both non-constant power up-sweep rate and non-constant degas period, as described above. 
     FIG. 42  shows a system  300  including a generator  302  and transducers  304  that can be switched, for example, to either 72 khz or 104 khz operation. The transducers  304  operate to inject sonic energy  305  to the process chemistry  307  within the tank  306 . Because of the impedance characteristics at these frequencies, the generator  302  includes a constant power output circuit  306  that changes the center frequency output from the generator  302  while maintaining constant output power. The circuit  306  includes a switch section  308  that switches the output frequency from one frequency to the next with no intermediate frequencies generated at the output (i.e., to the transducers  304 ). 
   A similar system  310  is shown in  FIG. 43 , where switching between frequencies does not utilize the same power circuit. In  FIG. 43 , the generator  312  includes at least two drive circuits for producing selected frequencies f 1  and f 2  (these circuits are illustratively shown as circuit (f 1 ), item  314 , and circuit (f 2 ), item  316 ). Before the reactive components in either of the circuits  314 ,  316  can be switched to different values, the output circuit  318  shuts down the generator  312  so that stored energy is used up and the relay switching occurs in a zero voltage condition. 
   From the above, one skilled in the art should appreciate that the system  310  can be made for more than two frequencies, such as for 40 khz, 72 khz and 104 khz. Such a system is advantageous in that a single transducer array can be used for each of the multiple frequencies, where, for example, its fundamental frequency is 40 khz, and its first two harmonics are 72 khz and 104 khz. 
   An alternative system is described in connection with  FIG. 71 . 
     FIG. 44  illustrates a system  400  and process probe  402  constructed according to the invention. A generator  404  connects to transducers  406  to impart ultrasound energy  403  to the process chemistry  407  within the tank  408 . The probe  402  includes an enclosure  410  that houses a liquid  412  that is responsive to ultrasound energy within the liquid  407 . The enclosure  410  is made from a material (e.g., polypropylene) that transmits the energy  403  therethrough. In response to the energy  403 , changes in or energy created from liquid  412  are sensed by the analysis subsystem  414 . By way of example, the liquid  412  can emit spectral energy or free radicals, and these characteristics can be measured by the subsystem  414 . Alternatively, the conduit  416  can communicate electrical energy that indicates the conductivity within the enclosure. This conductivity provides an indication as to the number of cavitation implosions per unit volume within the process chemistry  407 . The conduit  416  thus provides a means for monitoring the liquid  412 . A thermocouple  420  is preferably included within the enclosure  410  and/or on the enclosure  410  (i.e., in contact with the process chemistry  407 ) so as to monitor temperature changes within the enclosure  410  and/or within the process chemistry  407 . Other characteristics within the tank  408  and/or enclosure  410  can be monitored by the subsystem  414  over time so as to create time-varying functions that provide other useful information about the characteristics of the processes within the tank  408 . For example, by monitoring the conductivity and temperature over time, the amount of energy in each cavitation explosion may be deduced within the analysis subsystem  414 , which preferably is microprocessor-controlled. 
   The prior art is familiar with certain meters which measure sound characteristics and cavitations within an ultrasound tank. Each of the meters gives one number, usually in units of watts per gallon, and sometimes in undefined units such as cavities. However, the activity in a cavitating ultrasound tank is very complex and no single number adequately describes this activity. For example, as shown in  FIGS. 45 and 46 , it is possible to have two ultrasound tanks  420 ,  422 , both having the same input power (i.e. watts per gallon) but each having very different ultrasound activity characteristics. The first tank  420  might have relatively few high energy cavitation implosions  420   a  while the second tank  422  has many low energy cavitation implosions  422   a  (specifically,  FIGS. 45 and 46  show cavitation implosions  420   a ,  422   a  during a fixed time period in the two tanks  420 ,  422  having equal input energies). At least two numbers are thus necessary to describe this situation: the energy in each cavitation implosion and the cavitation density. The energy in each cavitation implosion is defined as the total energy released in calories from a single cavitation event; and the cavitation density is defined as the number of cavitation events in one cubic centimeter of volume during a 8.33 millisecond time period. Note, in Europe and other countries with fifty hz power lines, the cavitation events in one cubic centimeter are counted over a ten millisecond time period and multiplied by 0.833. This technique provides the most accurate measurement for the common ultrasound systems that have their amplitude modulation pattern synchronized by two times the power line frequency. 
   In most ultrasound systems, the cavitation density also varies as a function of time. Accordingly, this is a third characteristic that should be measured when measuring ultrasound activity in a tank. 
     FIG. 47  thus illustrates one probe  650  of the invention which permits the calculation of these important parameters. Specifically, the probe  650  measures average conductivity, conductivity as a function of time, and change in temperature. 
   A characteristic of ultrasound cavitation in aqueous solutions is the production of free radicals, ions and super oxides. These by-products of the cavitation increase the conductivity of the aqueous solution. A measure of the conductivity is thus a function of the number of cavitation implosions present in the aqueous sample, and the time variation of this conductivity is a measure of how the cavitation density varies as a function of time. 
   Another characteristic of cavitation is that it heats the aqueous solution. This is because all the energy released during each cavitation implosion becomes heat energy. By measuring the change in temperature of the aqueous sample, therefore, and by knowing its mass and specific heat, one can calculate the total energy released from the cavitation by the following formula: energy (calories) equals specific heat (no units, i.e., a ratio) times mass (grams) times the change in temperature (degrees C.). When the amount of energy released is known, as well as the number of cavitation implosions that released this energy, a division of the quantities gives the energy in each cavitation implosion. 
   The probe  650  is similar in operation to the probe  402  of  FIG. 44  and includes a fixed sample volume of aqueous solution  652  (or other chemistry that changes conductivity in an ultrasound field) contained in the probe tip  650   a . The probe tip  650   a  is designed to cause minimal disturbance to the ultrasound field (e.g., the field  403  of  FIG. 44 ). Accordingly, the probe tip  650   a  is preferably made of a material that has nearly the same acoustic impedance as the liquid being measured and that has low thermoconductivity. Polypropylene works well since it and water have nearly the same acoustic impedance. 
   The probe  650  thus includes, within the probe tip  650   a , two electrodes  654 ,  656  to measure conductivity, and a temperature measuring probe (e.g., a thermocouple)  658  to monitor the temperature of the fixed mass of aqueous solution  652 . These transducers  654 ,  656  and  658  are connected to data wires for sampling of the transducer responses. A data collection instrument (e.g., an A/D sensor interface board and a computer) connects to the wires  670  out of the probe  650  to measure temperature rise as a function of time, Delta T=g(t), and to evaluate this quantity over a specific time period t′, in seconds, i.e., Delta T=g(t′). The data collection instrument also measures the initial conductivity, C 0 , without ultrasonics, and the conductivity as a function of time, C=h(t), within the ultrasound field. Fixed constants associated with the probe should also be stored, including the specific heat (p) of the liquid  652 , the volume (V) of the liquid  652  (in cubic centimeters), the mass (m) of the liquid  652  (in grams), and the functional relationship n=f(C,C 0 ) between conductivity and the number of cavitation implosions occurring in the probe tip  650   a  in 8.33 milliseconds determined by counting the sonoluminescence emissions over a 8.33 millisecond period and plotting this versus the conductivity measurement. The instrument then calculates the ultrasound parameters from this information according to the following formulas:
 
cavitation density= D=n/V=f ( C,C   0 )/ V   (a)
 
energy in each cavitation implosion= E =(0.00833)( p )( m )( g ( t ′)) V/f ( C,C   0 )/ t′   (b)
 
cavitation density as a function of time= f ( h ( t )) V   (c)
 
   These three measured parameters are then fed back to the generator to continuously control the output of the generator to optimum conditions.  FIG. 48  shows a complete system  675  for monitoring and processing data from such a probe  650 ′ and for modifying applied ultrasound energy  676  applied to the process chemistry  678 . Specifically, the system  675  monitors the parameters discussed above and, in real time, controls the generator  680  to adjust its output drive signals to the transducers  682  at the tank  684 . The data collection instrument  685  connects to the wiring  670 ′ which couples directly to the transducers within the probe tip  650 ′. The instrument  685  generates three output signal lines corresponding to measured parameters: the “A” signal line corresponds to the energy in each cavitation implosion, the “B” signal line corresponds to the cavitation density output, and the “C” signal line corresponds to the cavitation density as a function of time. These signal lines A–C are input to separate comparators  686   a ,  686   b  and  686   c . The comparators  686   a–c  are coupled to signal lines D–F, respectively, so that the input signal lines A–C are compared to user selected optimum values for each of the parameters. Typically, the user employs empirical experimentation to arrive at the optimum values for a particular tank  684  and chemistry  678 . The results from the comparators  686  are input to the control system  690 , which controls the generator  680  (those skilled in the art should appreciate that the controller  690  and generator  680  can be, and preferably are, coupled as a single unit). 
   The energy in each cavitation implosion decreases as the frequency of the ultrasonics  676  increases and as the temperature of the solution  678  increases. The energy in each cavitation implosion is measured and compared to the optimum value (set by signal lines D–F) for the process, and if the measured value has a higher energy value than the optimum value, as determined by the comparators  686 , the center frequency of the generator  680  is increased (by the controller  690  receiving data at the “center frequency input control”) until the values are equal. If there is not enough range in the center frequency adjustment to reach the optimum value, then the temperature of the solution  678  is increased by the control system  690  until the optimum value is reached. An alternative is to utilize a switchable frequency generator, as described above, so as to change the drive frequency to one where the energy in each cavitation implosion is not greater than the optimum value, and without changing the solution temperature. 
   The cavitation density increases as the ultrasound power into the tank  684  increases. Therefore, the cavitation density measurement fed back to the generator  680  is compared against the optimum value of cavitation density for the process; and if the measured value is lower than the optimum value, the generator output power is increased (by the controller  690  receiving data at the “power control”) until the two values are equal. If the measured value is greater than the optimum value, the generator output power is decreased until the values are equal. 
   Cavitation density as a function of time is controlled by the amplitude modulation (AM) pattern of the generator output  692 . Therefore the measured cavitation density as a function of time is measured and the generator&#39;s AM pattern is adjusted (via the controller  690  receiving data at the “AM Control”) until the measured function equals the optimum function. 
     FIG. 49–51  illustrate separate embodiments of universal voltage input ultrasound generators, in accord with the invention. These embodiments are made to solve the present day problems associated with separate designs made for countries with differing power requirements (in volts A–C, or “VAC”), such as:
     100 VAC Japan, and intermittently during brown-outs in the U.S.   120 VAC U.S.   200 VAC Japan   208 VAC U.S.   220 VAC Most of Europe except Scandinavia and U.K.   240 VAC U.S., U.K., Norway, Sweden and Denmark   “Z” VAC Corresponding to unusual voltages found in France and other world locations   
   These voltages are obviously problematic for industry suppliers of ultrasound generators, who must supply the world markets. The invention of  FIGS. 49–51  eliminates the chance that a particular world consumer receives an incorrect generator by providing universal voltage generators that operate, for example, between 86 VAC and 264 VAC. 
   In  FIG. 49 , an ultrasound generator  500  is shown connected to a 300 VDC source  501 . A power factor correction (PFC) circuit  502  connects to the front end of the generator  500  to produce a regulated 300 VDC. A switching regulator  504  regulates the 300 VDC to +12V and +15V. The generator  500  can be represented, for example, as the circuit of  FIG. 41 , except that the “high voltage supply” is replaced by the PFC circuit  502  and the +12V and +15V are replaced with control voltages from the regulator  504 . 
     FIG. 50  illustrates a generator  510  connected to a universal input switching regulator  512 . The regulator  512  generates a set  513  of DC voltages for the generator  510 . The generator  510  includes circuitry  514  that operates with the set  513 . The generator  510  can be represented, for example, as the circuit of  FIG. 41 , except that the “high voltage supply” and the +12V and +15V are replaced with output voltages from the regulator  512 . 
   Those skilled in the art should appreciate that methods and systems exist for utilizing the power line to acquire amplitude control for ultrasound generators. By way of example, the inventor of this application describes such systems and methods in connection with  FIGS. 3 ,  4 ,  5 A,  5 B and  7  of International Application No. PCT/US97/12853. Specifically, an amplitude control subsystem is achieved by rectifying the AC power line and selecting a portion of the rectified line voltage that ends at the desired amplitude (such as between zero and 90 degrees or between 180 degrees and 270 degrees of the signal). In this manner, amplitude modulation is selectable in a controlled manner as applied to the signal driving the transducers from the generator. For example, by selecting the maximum amplitude of 90 degrees in the first quarter sinusoid, and 270 degrees in the third quarter sinusoid, a maximum amplitude signal is provided. Similarly, a one-half amplitude signal is generated by choosing the 30 degrees and 210 degrees locations of the same sinusoids. By way of a further example, a one-third amplitude signal is generated by choosing 19.5 degrees and 199.5 degrees, respectively, of the same sinusoids. 
     FIG. 51  illustrates a generator  530  which operates at a DC voltage less than or equal to (86)(√2) volts. As in amplitude control, a triac  532  is used to select that portion of the power line voltage with an amplitude equal to the generator DC voltage requirements. The signal  534  is rectified and filtered by the bridge rectifier and filter  536  to obtain the constant DC voltage  538  in the range less than or equal to (86)*(Square Root 2) volts. The generator  530  can be represented, for example, as the circuit of  FIG. 41 , except that the “high voltage supply” is replaced by the voltage from the bridge rectifier and filter  536  and the +12V and +15V are replaced with output voltages from the regulator  540 , as above. 
   In another embodiment, the selected AC voltage angle can be reduced to lower the DC voltage to reduce the amplitude of the ultrasound drive signal. 
   The “power up sweep” features of the invention also apply to amplitude modulation, where an AM pattern of the AM frequency varies according to the power up-sweep techniques discussed above, and preferably at the same time with the techniques of “sweep the sweep rate”, as discussed herein. With power up-sweep AM, the AM pattern modulation creates an additional upward force on contamination while eliminating low frequency resonances. 
     FIG. 52  illustrates an AM (amplitude modulation) pattern  600  of the invention, where the frequency of the AM is constantly decreasing with increasing time t. More particularly, ultrasound bursts of energy (as shown in  FIG. 53 , with a frequency f) are contained within each of the non-zero portions  600   a  of the pattern  600 . As time increases, longer and longer bursts of energy are applied to the associated transducers. In the optimum case, the ultrasound frequency within each burst of  FIG. 53  varies with a power up sweep, from f upper  to f lower , as discussed above. 
     FIG. 54  shows a plot  610  of AM frequency verses time t. As shown, the AM frequency monotonically changes from a high frequency, f high , to a low frequency, f low . When f low  is reached, a degas or quiet period  612  is typically introduced before the cycle  614  repeats. 
   Note that the sweep rate of the change of the AM frequency along the slope  616  can and preferably does change at a non constant sweep rate. The rate of AM frequency change can thus be non-constant. The degas period  612  can also be non constant. The degas period  612  can also be substantially “0”, so that no time is permitted for degas. 
   Generally, there are three ways to change the AM frequency. The burst length “L” ( FIG. 53 ) can be changed, the time between bursts can be changed (e.g., the periods  600   b ,  FIG. 52 , where the amplitude is zero); or both parameters can be changed simultaneously. 
     FIGS. 55 ,  56  and  57  schematically illustrate electronics for one ultrasound generator with AM power up-sweep capability, in accord with the invention. 
   A common feature in prior art tanks (ultrasound and non-ultrasonic) is a quick dump rinse feature (QDR) where a large valve in the bottom of the tank opens to allow the solution in the tank to quickly drain out of the tank. This QDR feature reduces the contamination residing on the parts under process as compared to the contamination that would reside if the liquid were removed more slowly from the tank, or if the parts were pulled out of the tank. 
     FIG. 58  illustrates a QDR tank  800  modified in accord with the invention to speed up the rate of liquid removal from the tank. The large valve output  802  is connected to a vacuum reservoir  804  that is evacuated to a pressure below atmospheric pressure during the cleaning cycle. When the valve  802  is opened to dump the liquid  702 ″, the difference between atmospheric pressure and the pressure in the vacuum vessel  806  forces the liquid  702 ″ out of the tank  800 , thus shortening the drain time and further reducing the residual contamination. 
   The conventional stacked transducer consists of a front driver, active piezoelectric elements and a back mass. The length “L” of the transducer (from front plate to backplate) basically determines the transducer&#39;s primary and harmonic frequencies. As the fundamental frequency of the transducer becomes higher, the thickness of each of the transducer elements is reduced until they become impractical.  FIG. 59  shows a transducer  850  constructed according to the invention which reduces this impracticality. 
   In  FIG. 59 , the transducer  850  is shown connected to an ultrasound processing tank  852 , which holds process chemistry  854 . The transducer includes two piezoelectric elements  856  that are compressed between the backplate  858  and the tank  852 . Specifically, a bias bolt  860  connects through the transducer  850  and connects directly into a weld  861  at the tank  852 . Accordingly, there is no front plate; and thus the transducer length “L” can be divided between the piezoelectric elements  856  and the back mass  858 . This division makes it possible to make a stacked transducer  850  with a higher fundamental frequency (and higher harmonics too). 
   Another configuration of the transducer in  FIG. 59  uses one piezoelectric element  856  in the center of the stack and an insulating ceramic front driver or quartz front driver between the piezoelectric element and the tank  852 . Another configuration of  FIG. 59  also replaces back mass  850  with a ceramic back mass. These transducers of the  FIG. 59  type are referred to herein as the “welded stud type construction” transducers. 
   Most transducers discussed herein are longitudinal vibrators with elements sandwiched by a center bolt that holds the transducer assembly together and that provides a compressive bias to the active piezoelectric components (i.e., sandwiched between the a front plate and back mass or backplate). Since piezoelectric ceramic is strong under compression, but weak in tension, the constant compressive force provided by the spring constant of the bolt greatly improves the reliability of this transducer over other configurations. 
   The longitudinal vibrating transducer is normally connected to the tank or other surface that is to receive the sound energy by epoxy or brazing, or by a mechanical stud, or by a combination of these schemes. 
   The invention of  FIG. 60  illustrates a transducer  900  constructed according to the invention and shown in an exploded view. The transducer  900  has “double compression”, as discussed below, to increase its reliability over the prior art. Specifically, the bias bolt  904  has a through-hole  902  in its center. The center hole  902  receives a second bolt  906  that is welded to the surface of the tank  908  (illustrated by weld joint  910 ). When integrated, the second bolt  906  protrudes out past the tail mass  927  (i.e., the backplate) of the transducer  900  by way of a Belleville disc spring washer  912  and nut  914 , which screws onto bolt  906 . 
   As in other transducers herein, the transducer  900  includes piezoelectric ceramics  916 , associated electrodes  918 , and lead-outs  920  for the electrodes  918 . 
   The bias bolt  904  thus provides the first compressive force similar to other transducers herein. That is, the bolt  904  slides through the front driver  922  via the through-hole  924 , and continues on through the ceramics  916 . The back mass  910  has threads  910   a  which mate with the bolt  904 ; and thus the bolt  904  screws into the back mass  910 . By tightening the bolt  904  into the back mass  910 , the bolt  904  firmly seats into the counter-sink  922   a  of the front plate  922  and compression is applied to the ceramics  916 . 
   As an alternative, the threads in the back mass  910  can be thru-holed; and a nut against the back mass can replace the threads to support compression bias on the piezoceramic  916 . 
   The second compressive force derives from the operation of the second bolt  906 , which compresses the epoxy  926  after seating within the counter-sink  904   a  of the first bolt  904  and after tightening the nut  914  onto the bolt  906 . The front driver  922  is then bonded to the tank  908  via an epoxy layer  926 . The second compressive force keeps a compressive bias on the epoxy  926  bond between the front driver  922  and the tank surface  908 . 
   As an alternative, it is possible to eliminate the Belleville disc spring washer  912  and rely entirely on the spring tension in the second bolt  906 ; but the added feature of the Belleville disc spring washer  912  provides a larger displacement before tension goes to zero. 
   The second compressive bias of transducer  900  provides at least three improvements over the prior art. First, during the epoxy curing process, the bias keeps force on the epoxy bond  926  (even if the epoxy layer thickness changes during a liquid state) resulting in a superior bond. Second, during operation of the transducer  900 , the reliability of the bond  926  is enhanced because of the constant mechanical compressive force. That is, epoxy bonds are weakest in shear forces, and reasonably strong in tension but superior in compression. Third, during abnormal conditions (e.g., a mechanical jar to the bonding surface) that might dislodge a conventionally bonded transducer, the second compression force with its spring characteristics absorbs the mechanical shock and protects the epoxy bond. 
   Those skilled in the art should appreciate that the double compression transducer  900  provides increased reliability when mounted with most any surface, and not simply an ultrasound tank  908 . 
     FIG. 61  shows a cross-sectional view of a conventional stacked transducer  1000  with a bias bolt  1002  that screws into threads  1004  in the aluminum front driver  1006 . The threads  1004  are only within the top portion  1006   a  of the front driver  1006 . The transducer includes the normal piezo-ceramics  1007 , electrodes  1008 , and rear mass  1009 . 
     FIG. 62  shows an alternative transducer  1010  constructed according to the invention. In transducer  1010 , the threads  1012  within the front driver  1014  are at bottom portion  1014   a  so that bias pressure is not concentrated on the top threads (as in  FIG. 61 ) where the surface of the aluminum can be deformed in operation, decreasing bias pressure. The elements  1002 ′,  1007 ′,  1008 ′ and  1009 ′ have similar function as in  FIG. 61 ; except that they are sized and shaped appropriately to accommodate the thread repositioning at the bottom  1014   a  of the driver  1014 . 
     FIG. 63  illustrates a transducer  1020  that is similar to the transducer  1010 ,  FIG. 62 , except that a helical insert  1022  is used instead of the threads  1012 . The helical insert  1022  is preferably made from steel and will not plastically deform under normal transducer stresses. The helical insert  1022  thus prevents distortion of the aluminum driver  1014 ′ under the normal stresses of the transducer  1020 . Note that the helical insert can similarly replace the threads  1004  of the prior art transducer  1000  to provide similar advantages in preventing distortion. 
     FIG. 64  illustrates a side view of one embodiment of the invention including a printed circuit board (PCB)  1030  connected with ultrasound transducers  1032  such as described herein (including, for example, piezoelectric ceramics  1034 ). The PCB  1030  contains circuitry and wiring so as to function as an ultrasound generator and for the electrodes of the transducers  1032 . As such, the PCB  1030  can drive the transducers  1032  to produce ultrasound  1036  when powered. By way of example, the PCB  1030  can include the circuitry of  FIGS. 41A ,  41 B and  41 C. 
   The PCB  1030  and transducers  1032  are also substantially “integral” in construction so as to be a single unit. This provides structural integrity, and reduces the cost and size of the system. 
     FIG. 65  shows a top view of the PCB  1030  of  FIG. 64 . For purposes of illustration, the top surface  1030   a  of the PCB  1030  is shown with electrodes  1038  for the positive side of the piezoelectric ceramic  1034 . The electrodes  1038  are preferably connected by wiring  1048  (e.g., circuit board land patterns) to provide for common voltage input to the transducers  1032 . There is a similar electrode pattern on the bottom side (not shown) of the PCB  1030  that makes contact with the transducer&#39;s front driver  1032   b , which is in electrical contact with the bias bolt  1032   a  ( FIG. 64 ). The bolt  1032   a  connects through the transducer  1032  and into the back mass  1032   c , providing electrical feedthrough to the negative electrode of the piezoelectric ceramic  1034 . The PCB  1030  thus provides two electrodes for each transducer  1032  and all the interconnect wiring for the transducers  1032  such as by etching the PCB pattern. The ultrasound generator is also provided with the PCB  1030  circuitry (illustrated by circuit board components  1040 ) with its output connected into the transducer electrodes as part of the PCB artwork. 
     FIG. 66  illustrates an acid resistant transducer  1050  with internal piezoelectric compression. By way of background, the above description has described certain transducers that utilize metal masses to lower the resonant frequency of the piezoelectric ceramics and a bolt to keep a compressive bias on the piezoelectric elements. In harsh environments, e.g., sulfuric acid process tanks, the metallic elements of the transducer are prone to acid attack and therefore are a reliability risk. The transducer  1050  of  FIG. 66  resolves this problem by eliminating the metal masses and the bolt. The compressive force on the piezoelectric ceramic  1058  is obtained by an epoxy  1052  that contracts upon curing. The metal “back mass” and the metal “front driver” such as described above are replaced by a non-metallic material  1060 . In  FIG. 66 , the front driver  1060   a  and back mass  1060   b  are thus both made from a non-metallic material such as quartz. 
   The internal piezoceramics  1058  connect to wiring to drive the elements  1058  in the normal way. To protect the wiring and ceramics, it can be made from Teflon which is soldered to the ceramic  1058  by known methods, such as illustrated by solder joint  1064 . This transducer will be referred to herein as the “acid transducer type construction”. 
     FIG. 67  illustrates a generator circuit  2000  used to implement power up-sweep such as described herein (e.g., such as described in connection with  FIGS. 41A ,  41 B and  41 C, except that  FIGS. 41A ,  41 B and  41 C uses IGBTs as the switching devices and  FIG. 67  uses MOSFETs). In  FIG. 67 , circuit  2000  includes a capacitive element  2012  with terminal  2012   a  connected to earth ground  2015   a . The other terminal  2012   b  connects to terminal  2040   b  of inductor  2040 . Terminal  2040   a  of inductor  2040  connects to terminal  2013   a  of the secondary  2013   c  of transformer  2013 . Terminal  2013   b  of secondary  2013   c  connects to earth ground  2015   b . The circuit  2000  includes two drive networks  2018  and  2020 , and a controller  2022 . 
   Drive network  2018  includes a blocking network  2028  and a multi-state power switch network  2030 , which is coupled to the controller  2022  by way of line  2022   a . The drive network  2020  includes a blocking network  2032  and a multi-state power switch network  2034 , which is coupled to the controller  2022  by way of line  2022   b.    
   In drive network  2018 , the blocking network  2028  and switch network  2030  provide a unidirectional current flow path characterized by a first impedance from the potential +V through the first primary winding  2013   d   1  of center-tapped primary winding  2013   d  of transformer  2013  when the switch network  2030  is in a first (conductive) state. The networks  2028  and  2030  provide an oppositely directed current flow path characterized by a second impedance from circuit ground  2023   a  through  2013   d   1  to the potential +V when the switch network  2030  is in a second (non-conductive) state. The first impedance of the flow path established when network  2030  is in its first state is lower than the second impedance of the flow path established when the network  2030  is in its second state. 
   In drive network  2020 , the blocking network  2032  and switch network  2034  provide a unidirectional current flow path characterized by a third impedance from the potential +V through the second primary winding  2013   d   2  of center-tapped primary winding  2013   d  of transformer  2013  when the switch network  2032  is in a first (conductive) state. The networks  2032  and  2034  provide an oppositely directed current flow path characterized by a fourth impedance from circuit ground  2023   b  through  2013   d   2  to the potential +V when the switch network  2034  is in a second (non-conductive) state. The third impedance of the flow path established when network  2034  is in its first state is lower than the fourth impedance of the flow path established when the network  2030  is in its second state. 
   The impedance (Z) of drive network  2018  when switch network  2030  is in its second state may be primarily determined by resistor  2028   b  (of value “R”), in which case Z has a value substantially equal to R for current flow in a direction toward +V, and a “near-infinity” value (i.e. relatively high) for current flow away from +V. In other embodiments, Z may be non-linear, normally lower at the beginning of operation in the second state and higher at times after the second state begins. For example, a metal oxide varistor (MOV) in parallel with a resistor (R) may be the primary determining factor for Z. In this case, at the beginning of operation in the second state when the voltage across Z is high, the low impedance of the on MOV primarily determines Z and later in the second state, as the voltage drops below the MOVs breakdown potential, Z is primarily determined by R. 
   A similar situation occurs for the impedance of drive network  2020  when switch network  2034  is in its second state. 
   Where the circuit  2000  is adapted to drive an ultrasound transducer, the capacitive element  2012  may be an electrostrictive device suitable for use as an ultrasound transducer. With such a configuration, for example, the controller  2022  may effectively control the circuit  2000  to drive such ultrasound transducers at a selectively controlled frequency. In various forms of the invention, the controller  2022  may be adaptively controlled so as to track variations in the resonant frequency for the respective ultrasound transducers, or to frequency modulate the frequency with a function such as a power up-sweep function, described above. 
   In operation, the controller  2022  cyclically switches the switch network  2030  between its first and second states at a frequency f (f=1/T), where f is less than or equal to f r  (f r =1/T r ), where f r  is the resonant frequency of the series LC network formed by  2012  and  2040 , approximately equal to 1/(2*PI*Square Root(LC)), where PI is approximately 3.14159. During each cycle, network  2030  is controlled to be in its first state for a period greater than or equal to T r /2, but less than or equal to T/2, at the beginning of each cycle. Network  2030  is controlled to be in its second state for the remainder of each cycle. 
   Similarly, the controller  2022  also cyclically switches the switch network  2032  between its first and second states at the frequency f (f=1/T). During each cycle, network  2032  is controlled to be in its first state for a period greater than or equal to T r /2, but less than or equal to T/2, at the beginning of each cycle. Network  2032  is controlled to be in its second state for the remainder of each cycle. In the presently described embodiment, the start time for each cycle of the switching of network  2030  is offset by T/2 from the start time for each cycle of the switching of network  2034 . In other forms, the start time for the cycle of the switching network  2030  may be offset by at least T r /2 and less than T r /2+D, where D equals T−T r . 
   An AC voltage waveform (V 0 ) at frequency f is impressed across the capacitive element  2012 . Generally, this voltage waveform V 0  passes from low to high and from high to low with a sinusoidal waveshape (at frequency f r ). After rising from its low peak level to its high peak level, the voltage waveform stays substantially at its high peak level (except for droop due to resistive losses) for a period ½ (T−T r ), or D/2, before passing from that high peak level to its low peak level. Similarly, upon returning to the low peak level, the voltage waveform V 0  remains at that level (except for droop due to resistive losses) for a period ½(T−T r ), or D/2, before again passing to the high peak level. 
   Thus, the voltage impressed across capacitive element  2012  rises and falls at the resonant frequency f r  with the capacitive element  2012  being maintained in its fully charged state for a “dead” time which is adjustably dependent upon the switching frequency f of the controller  2022 . Accordingly, the drive frequency to the element  2012  may be adjustably controlled. 
   Where the element  2012  is an ultrasound transducer, circuit  2000  is used to drive that transducer at a frequency adjusted to match the optimal drive frequency. In various embodiments, variations in that optimal drive frequency may be detected and the controller may be adjusted in closed loop fashion to adaptively track such variations. 
   Blocking network  2028  includes a diode  2028   a  in parallel with a resistor  2028   b , and the blocking network  2032  includes a diode  2032   a  and a resistor  2032   b . The single inductor (L)  2040  operates in resonance with the element  2012 . 
   Circuit  2000  is particularly useful with “fast” switching devices (such as bipolar, MOS and IGBT transistors) which do not require an extended turn-off time. In operation, the capacitive element  2012  and transformer  2013  function like the circuit of  FIG. 41 , except that circuit  2000  utilizes FETs instead of IGBTs (insulated gate bipolar transistors) for the terminal power switching devices. The power devices  2030 ,  2034  are also connected to circuit ground, eliminating the need for separate isolated power supplies, reducing the cost of the generator. 
   In another implementation of circuit  2000 ,  FIG. 67 , the inductor  2040  is not a separate component, but rather is incorporated into the transformer  2013  by way of leakage inductance. This leakage inductance performs the same function as inductor  2040  and the leakage inductance is controlled by the coupling of transformer  2013 , e.g., by setting a gap in the transformer&#39;s core as is known in the art. This circuit of the  FIG. 67  type is referred to herein as the “zero current switching inverter circuit”. 
   With further reference to  FIG. 43 , one embodiment of the invention couples multiple generator frequencies to a common tank  306 ′ and transducers  304 ′.  FIG. 68  schematically shows additional switch circuitry corresponding and connecting to a different generator frequency, e.g.,  2104   a  for 40 khz,  2104   b  for 72 khz,  2104   c  for 104 khz, and  2104   d  for 170 khz). Which ever generator thus connects to the 24 VDC supply between pins “1” and “2” on its corresponding remote connector  2104  will drive the common process tank, as shown in  FIG. 69 . The generators can have a remote on/off relay in the form of  FIG. 70 , which illustrates coupling between a Deltrol relay and the remove relay. The connector-to-tank wiring is further illustrated in  FIG. 69 . In  FIG. 69 , each generator within the system connects to each of the plurality of transducers  2106  within the tank; though only one generator actively drives the transducers  2106  depending upon the position of the switch  2102 . 
   In operation, power is applied to one generator (e.g., the 40 khz generator coupled to remote connector  2104   a ) via the 24 VDC signal from the rotary switch  2102 . The following sequence then occurs with respect to  FIGS. 58–60 :  2098  compatible with this embodiment. In  FIG. 68 , a common 24 VDC supply  2100  couples to a user-selectable switch  2102  (e.g., a rotary switch) to provide drive energy to remote connectors  2104   a–d  (each connector  2104   
   
     
       
         
             
             
           
             
                 
             
             
               Time 
               Event 
             
             
                 
             
           
          
             
                 7 milliseconds 
               Remote relay #1 energizes starting 
             
             
                 
               the 1/2 sec. timer #1 
             
             
                10 milliseconds 
               Deltrol relay #1 connects the tank to the 40 khz 
             
             
                 
               generator 
             
             
               0.5 seconds 
               1/2 sec. timer #1 starts the 40 khz generator, 
             
             
                 
               the tank runs at 40 khz 
             
             
                 
             
          
         
       
     
   
   If the rotary switch  2102  is turned to the next position, e.g., to the 72 khz generator position, the following sequence occurs (assuming, worst case, that the rotary switch is moved very fast so there is zero time between the 40 khz position and the 72 khz position): 
   
     
       
         
             
             
           
             
                 
             
             
               Time 
               Event 
             
             
                 
             
           
          
             
                0 milliseconds 
               24VDC is removed from remote relay #1 
             
             
                0 milliseconds 
               24VDC is removed from Deltrol relay #1 
             
             
                5 milliseconds 
               40 khz generator turns off 
             
             
                7 milliseconds 
               72 khz remote relay #2 energizes starting 
             
             
                 
               the 1/2 sec. timer #2 
             
             
                10 milliseconds 
               Deltrol relay #2 connects tank to 72 khz generator 
             
             
               250 milliseconds 
               Deltrol relay #1 disconnects 40 khz generator from 
             
             
                 
               the tank 
             
             
                0.5 seconds 
               1/2 sec. timer #2 starts the 72 khz generator, 
             
             
                 
               the tank runs at 72 khz 
             
             
                 
             
          
         
       
     
   
   To avoid this “worst case” scenario, extra margin is provided by providing an off position between each rotary switch generator position. That is, the rotary switch can be labeled as follows:
 
OFF-40 khz-OFF-72 khz-OFF-104 khz-OFF-170 khz
 
   Generators connected within this system preferably have a four socket reverse sex square flange AMP CPC receptacle with arrangement 11-4 (AMP part number 206430-1) installed on the rear of the generator. The mating four pin plug (AMP part number 206429-1) has the following pin connections: 
   
     
       
         
             
             
           
             
                 
             
           
          
             
               Pin#1 
               +24 VDC referenced to Pin #2 connects the 
             
             
                 
               generator or power module to the 
             
             
                 
               transducers and turns the generator on 
             
             
               Pin#2 
               return for 24 VDC signal, can be grounded 
             
             
               Pin#3 
               anode of LED to indicate RF current flow 
             
             
               Pin#4 
               cathode of LED to indicate RF current flow 
             
             
                 
             
          
         
       
     
   
   The cable from the AMP plug is for example a Manhattan/Cot PIN M39025 control cable with four #24 AWG wires, with the following color codes: Pin# 1  red; Pin# 2  green; Pin# 3  blue; and Pin# 4  white. 
   Generators within this system can have a nine socket reverse sex square flange AMP CPC receptacle with arrangement 17-9 (AMP part number 211769-1) installed on the rear of the generator according to the following connections.
         Socket # 1 : +RF output   Socket # 2 : not used   Socket # 3 : +RF output   Socket # 4 : −DC test point   Socket # 5 : −RF output, ground   Socket # 6 : cable shield, ground   Socket # 7 : +DC output interlock   Socket # 8 : +DC input interlock   Socket # 9 : waveform test point       

   The mating nine pin plug (AMP part number 211768-1) can have the following pin outs and color code when supplied with a three wire RF cable.
     Pin# 1 : +RF output red   Pin# 3 : +RF output red   Pin# 5 : −RF output green/yellow   

   All pin# 5 s can for example be wired together and connected to the −RF transducer lead. All pin # 1 &#39;s are then connected together and connected to the +RF transducer lead coming from one-half of the transducers. All pin # 3 &#39;s are then connected together to the +RF transducer lead coming from the other one-half of the transducers. The only exception to this is when the generators do not all drive the same number of transducers. 
     FIG. 71  schematically shows a multi-generator system  3000  used to drive common transducers  3002 . One advantage of the system  3000  is that multiple generators  3004  can alternatively drive the transducer  3002 ; and it is assured that no two generators operate simultaneously. Each generator  3004  preferably represents a different drive frequency. Generator  3004   a  represents, for example, the generator set forth by circuitry of  FIG. 41  (except that preferably, a ½ second delay is installed into circuit  250  by adjusting capacitor  3006  to one microfarad instead of 1/10 microfarad, which provides only 50 milliseconds delay). The relays  3008   a ,  3008   b  for example can be implemented similar to the relay schematic of  FIG. 70 . 
   The rotary switch  3010  (e.g., similar to the switch  2102 ,  FIG. 68 ) permits user selection between any of the generators  3004 . Generator  3004   b  can thus be switched in to drive the transducer  3002  with a different frequency. Those skilled in the art should appreciate that additional generators  3004   c ,  3004   d , can be installed into the system  3000  as desired, with additional frequencies. Those skilled in the art should appreciate that the rotary switch  3010  can be replaced by a PLC or computer control to provide similar generator selection. 
   As used herein, “lifetime” of a sound wave in a liquid contained in a tank or other container is defined as the time for the sound wave to decay from 90% to 10% of its intensity value after the sound energy input to the tank or container is stopped. Lifetime is a function of the sound frequency, type of liquid, shape and material of the container, and loading of the container. 
   As used herein, “degas time”, “quiet time”, “transition time” and “off time” are periods of time when the generator is supplying no electrical frequency drive signal to the array of transducers. 
   As used herein, “permutations of frequency ranges” means different orders of supplying the frequency ranges to the liquid. For example, if there are four frequency ranges, there are twenty-four permutations of these four frequency ranges. 
   As used herein, “cleaning packet” is defined as a permutation of frequency ranges. 
   As used herein, “intense” sound energy is defined as sound energy having amplitude suitable for cleaning and processing components; such amplitudes typically produce cavitation as is well known to those in the art. 
   As used herein, “frequency band” is defined as a continuous set of frequencies over which a transducer array can generate intense sound energy. These frequency bands are typically located around the fundamental frequency and the harmonics of the transducer array. 
     FIG. 72A  shows a diagram of a multiple frequency cleaning system  10  constructed according to the present invention. A signal generator  12  (also referred to herein as ‘generator’) connects via electrical paths  14 ,  15 ,  16  to a transducer array consisting of paralleled transducers  17 ,  18 ,  19 . The transducer array is driven by the generator  12  to produce multiple frequency sound waves  26  in liquid  22  which is contained in tank  20 . Tank  20  is typically constructed of 316L stainless steel, but other tanks or containers such as those constructed of tantalum, polyetheretherketone, titanium, polypropylene, Teflon, Teflon coated stainless steel, or other material or combination of materials can be used. These alternate materials are most appropriate when the liquid  22  is an aggressive chemistry that will degrade or erode 316L stainless steel. 
     FIG. 72B  shows a graph of the sound intensity produced by the transducer array verses the frequency of the sound. BW 1   21  is a first frequency band of frequencies produced by the transducer array and BW 2   23  is a second frequency band of frequencies produced by the transducer array. Since these frequency bands are continuous along the frequency axis, there are an infinite number of frequencies contained in each frequency band that can be excited by the generator. The first frequency band typically occurs around the fundamental frequency of the transducer and the other frequency bands typically occur around the transducer harmonics. It is possible to not use the frequency band around the fundamental frequency and to select two or more of the frequency bands around harmonic resonances for the operating areas of the transducer array. 
     FIG. 72C  shows a graph of the generator output voltage verses frequency. R 1   25  is a first range of frequencies produced by the generator, with R 1   25  being a frequency subset of BW 1   21 . R 2   27  is a second range of frequencies produced by the generator, with R 2   27  being a frequency subset of BW 2   23 . 
     FIG. 9  shows a cross-sectional view of one transducer  128  constructed according to the invention; while  FIG. 9A  shows a top view of the transducer  128 . Two or more transducers are connected in parallel to form an array of transducers. The parallel array of transducers formed from transducers  128  exhibit frequency bands that are centered on 39.75 khz, 71.5 khz, 104 khz, 131.7 khz, 167.2 khz and 250.3 khz. 
   In  FIGS. 9 and 9A , the ceramic  134  of transducer  128  is driven through oscillatory voltages transmitted across the electrodes  136 . The electrodes  136  connect to a generator (not shown), such as described above, by insulated electrical connections  138 . The ceramic  134  is held under compression through operation of the bolt  132  providing compressive force by way of the front driver  130  and the back mass  139 . 
     FIG. 73A  shows the basic schematic for a generator  29  built according to the invention, with  FIGS. 73B ,  73 C,  73 D,  73 E and  73 F showing the component details of the circuit blocks in  FIG. 73A . The generator  29  receives AC power from the power line into filter  30 , the purpose of filter  30  is to prevent high frequency noise voltages produced by the generator from entering the AC power lines. Switch  31  controls the AC power to generator  29  and fuses  32  protect the system from over current conditions. Bridge diode  33  in combination with filter capacitor  34  converts the AC line voltage to a DC voltage. The power module  35  converts the DC voltage to the needed frequencies to drive the transducer array (not shown) as described above. The control  37  supplies the frequency modulation (FM) and the amplitude modulation (AM) information to the power module  35 . The output power circuit  38  measures the power delivered to the transducer array and supplies this information to the output power regulator  39 . The output power regulator  39  compares the signal from output power circuit  38  with the desired output power supplied through pin  5  of remote connector  43  and supplies the difference information to control  37  so the AM can be adjusted to make the actual output power substantially equal to the desired output power. 
   In  FIG. 73A  BNC connector  44  supplies the FM information to other generators (often called power modules) that need to be synchronized with this generator  29  for the purpose of eliminating beat frequencies. Terminal  41  serves as a junction connection for the power output lines. Transformer  40  isolates the generator  29  from the transducer array and output connector  42  supplies the output drive signals to the transducer array. 
     FIGS. 73B and 73C  show in schematic form the component details of control  37 . VCO (voltage controlled oscillator) U 13  produces a triangle wave at output pin  8  that sweeps the sweep rate signal generated by VCO U 8 . Besides generating the sweep rate signal, U 8  also makes this sweep rate signal non-symmetrical so that most of the time (greater than 90%) the sweep rate is from high frequency to low frequency so the transducers substantially respond to a monotonic frequency change direction. VCO U 14  generates two times the needed drive frequency from the sweeping information produced by U 13  and U 8  and from the binary code supplied to P 3  and P 4  in  FIG. 73C . The specific binary code and center frequencies (after the U 11 :B divide by two flip flop) for the component values shown in  FIGS. 73B and 73C  are when P 3 ,P 4  are 1,1 the center frequency is 39.75 khz, when P 3 ,P 4  are 0,1 the center frequency is 71.5 khz, when P 3 ,P 4  are 1,0 the center frequency is 104 khz and when P 3 ,P 4  are 0,0 the center frequency is 167.2 khz. The series string of resistors consisting of RV 40 , R 40 , RV 72 , R 73 , RV 104 , R 105 , RV 170  and R 171  determine the center frequency of the signal from pin  7  of U 14  by responding to the binary code. For example, when P 3 ,P 4  are 1,1 output pin  3  of gate U 10 :A is an open circuit, output pin  5  of gate U 9 :B is an open circuit and output pin  3  of gate U 9 :A is an open circuit. This results in the total series string of resistors RV 40 , R 40 , RV 72 , R 73 , RV 104 , R 105 , RV 170  and R 171  being connected to pin  4  of U 14  and this produces the center frequency two times 39.75 khz. As a second example, when P 3 ,P 4  are 0,1 output pin  3  of gate U 10 :A is an open circuit, output pin  5  of gate U 9 :B is an open circuit and output pin  3  of gate U 9 :A is a short circuit. This results in the resistors RV 40  and R 40  being shorted out and now the series string of resistors RV 72 , R 73 , RV 104 , R 105 , RV 170  and R 171  are connected to pin  4  of U 14  and this produces the center frequency two times 71.5 khz. As a third example, when P 3 ,P 4  are 1,0 output pin  3  of gate U 10 :A is an open circuit, output pin  5  of gate U 9 :B is a short circuit and output pin  3  of gate U 9 :A is a open circuit. This results in the resistors RV 40 , R 40 , RV 72  and R 73  being shorted out and now the series string of resistors RV 104 , R 105 , RV 170  and R 171  are connected to pin  4  of U 14  and this produces the center frequency two times 104 khz. And lastly as a forth example, when P 3 ,P 4  are 0,0 output pin  3  of gate U 10 :A is a short circuit, output pin  5  of gate U 9 :B is a open circuit and output pin  3  of gate U 9 :A is a open circuit. This results in the resistors RV 40 , R 40 , RV 72 , R 73 , RV 104  and R 105 , being shorted out and now the series string of resistors RV 170  and R 171  are connected to pin  4  of U 14  and this produces the center frequency two times 167.2 khz. The frequency is continually changing around the chosen center frequency by the current input from R 31  which is connected to U 14  pin  4 . The current into R 31  is a result of the sweeping of the sweep rate signal produced by VCOs U 13  and U 8  as described above. U 11 :B divides by two the frequencies produced by U 14  and this is inverted by U 6 D, U 6 E and U 6 F before being output to J 6 C for connection to the power module  35  as shown in  FIG. 73A . 
   It should be noted that the center frequencies of this design are not integer multiples of the lowest (fundamental) frequency. The integer multiples of 39.75 khz are 79.5 khz, 119.25 khz, 159 khz, 198.75 khz, 238.5 khz, 278.25 khz, etc. None of these integer multiples are equal to the center frequencies of this design or the complete set of center frequencies possible with the transducer design in  FIGS. 9 and 9A , i.e., 39.75 khz, 71.5 khz, 104 khz, 131.7 khz, 167.2 khz and 250.3 khz. This eliminates the possibility of generating the components of a Fourier series and therefore prevents the possibility of a periodic wave that can damage a part by exciting it into resonance. 
   It should also be noted that rather than a binary code to specify the frequency ranges, it is possible to use a BCD code or any other digital code to specify the frequency ranges. It is also possible to accomplish the same selection function with an analog level, for example, the analog level could be put into an ADC (analog to digital converter) and the ADC output could be used to drive the binary selection circuitry. 
     FIG. 73B  (sheet 1 of 2) is a schematic of that part of control  37  that generates an AM signal on J 6 D which is output to the power module  35  for the following purposes: to control the output power of the generator; to allow the insertion of quiet times, degas times, transition times and off times into the generator output; to shut the generator off in the event of a fault condition such as low voltage or over temperature; and to start the generator up safely in the correct logic states. The power is controlled by a zero to five-volt level on P 5 . This voltage feeds the plus input to operational amplifier U 16  that compares this voltage to the ramp voltage on the operational amplifier&#39;s minus input. The ramp is formed by RV 1 , R 18  and C 5  and it is reset by U 10 B. When the ramp voltage exceeds the voltage level on P 5 , the output of the operational amplifier U 16  changes from +12 VDC to zero, this ripples through four gates that invert the signal four times and therefore a zero is on J 6 D which terminates the sound burst at the correct time to control the power to the level specified by the voltage on P 5 . The insertion of quiet times, degas times, transition times and off times into the generator output are accomplished by setting the appropriate input to NAND gate U 12  to a zero. A change in the binary code to P 3  or P 4  in  FIG. 73C  causes a transition time zero to occur on input pin  3  of U 12 . A 12 to 50 VDC signal on P 7  causes a zero on pin  11  of U 12  for the insertion of a quiet time, degas time or off time. Zero inputs to the appropriate inputs of U 12  are also the way fault signals shut down the generator. A low voltage on the power lines causes Schmitt trigger U 1 A pin  1  to go low which results in a zero on pin  10  of U 12 . An over temperature condition is sensed by U 3  and it puts out a zero to pin  4  of U 12  when this over temperature condition occurs. The generator is allowed to assume all the correct logic states by the delayed start hold off caused by R 20  and C 26 . 
     FIG. 73C  has four monostable multivibrators that introduce a degas time or off time between discontinuous jumps from one frequency range to the next frequency range. These degas times allow the sound waves from the prior frequency range to decay before sound waves from the new frequency range are introduced into the liquid. This is accomplished in the  FIG. 73C  schematic section of control  37  by any transition on the binary input lines P 3  and/or P 4  causing a transition on at least one of the monostable multivibrators U 22 A, U 22 B, U 23 A or U 23 B producing an output pulse the length of the degas time. This pulse travels through U 7  and feeds pin  3  of U 12  in  FIG. 73B  (sheet 1 of 2) where the AM is shut down for the length of the degas pulse. 
     FIG. 73D  is a schematic of the power module  35 . The front end logic consisting of U 5 , U 6 , U 7  and U 11  accepts and synchronizes the FM and AM signals from the control  37 . The power section of power module  35  converts the synchronized FM and AM signals to levels appropriate for driving the transducers. This power section will respond to the infinite number of different frequencies that are possible with this multiple frequency system. The power circuit is well known to people skilled in the art and is described in U.S. Pat. No. 4,743,789. 
     FIG. 73E  is a schematic of the circuit that measures the output power of the generator  29 . This output power circuit  38  senses the time function of the generators output voltage (Vt) and senses the time function of the generators output current (It). These functions Vt and It are multiplied, averaged over time and scaled to get the output power of the generator which is supplied to J 6 R as a voltage signal scaled to 100 watts per volt. 
     FIG. 73F  is a schematic of the output power regulator  39 . A voltage (Vd) representing the desired output power is input to P 5 C. This is compared to the voltage (Va) representing the actual output power on JR 6  (which came from the output of the output power circuit  38  as shown in  FIG. 73A ). If Vd is higher than Va, the voltage output on P 5  increases which increases the actual output power of the generator until Va is substantially equal to Vd. If Vd is less than Va, then the output voltage on P 5  is decreased until the actual output power becomes substantially equal to the desired output power. 
     FIG. 74  is the system  10  in  FIG. 72A  with a probe  51  sensing the sound characteristics in the tank to form the feedback system  50  of  FIG. 74 . The probe can be of the form disclosed in U.S. application Ser. No. 09/370,302 filed Aug. 9, 1999, entitled “Probe System for Ultrasonic Processing Tank” and after proper interfacing  52  signals are sent to the remote connector on generator  53  to modify the output drive to transducer array  54 . In the most sophisticated applications, the interface  52  is a PLC (programmable logic controller) or a computer that is properly programmed. 
   The system  70  in  FIG. 75  has a PLC or a computer  71  that is programmed to control and set the parameters for generator  72 . The programmed parameters are output by the generator  72  to drive the transducers  74  which put sound with the programmed characteristics into tank  73 . 
     FIG. 76  shows the addition of quiet times  81  into a typical AM pattern  80  of this invention. The invention produces continuously changing sound at frequencies in a first range of frequencies  82  before jumping to frequencies in a second range of frequencies  83 . Quiet times  81  are inserted into the continuously changing signal produced by the generator within a frequency range to break up the signal into smaller bursts of sound  85  for the purpose of optimizing certain processes such as the development of photosensitive polymers. 
     FIG. 77  shows the addition of a PLL  96  (phase lock loop) to the generator  95  for the purpose of making adjustments to the center frequency of each frequency range to track changes in the resonance of the transducer array  97 . The PLL  96  senses the current between line  98  and line  99  and the PLL senses the voltage between line  99  and ground  93 . The PLL generates a frequency on line  94  that feeds the generator  95  VCO so that the sensed current becomes in phase with the sensed voltage at the center frequency of the range. 
   A further advantage of this multiple frequency system is that it can reduce the intense cavitation region that occurs just below the liquid air interface. The location of this region is frequency dependent, therefore, by jumping from one frequency range to another, the intense region changes position and is averaged over a larger area. 
   An alternate way to control the frequency changes of this invention is shown in  FIG. 78A . The method consists of specifying changing digital numbers into a DAC  90  (digital to analog converter) and then driving a VCO  91  with the output of the DAC. The VCO  91  produces the changing frequencies in response to the changing digital numbers.  FIG. 78B  shows a typical staircase sweeping frequency output that can result from this circuitry. If the time at each level  92  is less than the period of the frequency being produced, then the changing frequency will be a different frequency each cycle or each fraction of a cycle. If the time at each level  92  is more than the period of the frequency being produced, then there can be two or more cycles of one frequency before the frequency changes to the next frequency.  FIG. 78C  shows an example of a random staircase function that can be produced by the circuitry represented in  FIG. 78A  by inputting random or chaotic digital numbers into the DAC  90 .  FIGS. 78A ,  78 B and  78 C represent the frequency changes in a single range. It is clear to someone skilled in the art that larger frequency changes are possible with this circuitry and therefore the jumping from one range to another range can also be done. It is also clear to someone skilled in the art that a separate DAC can be used for each frequency range to increase the resolution of the frequency changes. A hybrid system is also possible, i.e., using the DAC and VCO of  FIG. 78A  for the changes in the frequency range and using the digital number input to the series string of resistors as shown in  FIG. 73B  to select the specific frequency range. 
   It should be noted that the changing of frequency within a frequency range or amongst frequency ranges could be done with digital circuitry, analog circuitry or a hybrid combination of analog and digital circuitry. In the case of pure analog control, frequency changes within a range are normally high resolution, e.g., a different frequency every one half of a cycle, every one-quarter of a cycle or lesser fraction of a cycle. In the case of digital circuitry or hybrid analog digital circuitry, the resolution of changes depends on the speed at which the digital number is changed. This causes the staircase type of function when the resolution is low, e.g., several cycles of one frequency before several cycles of a different frequency are produced. In the purest sense, all changes can be considered a staircase function because, for example, the one half cycle changes can be considered stairs with a width equal to the time of the one half cycle. 
     FIG. 78B  is drawn to show a constant sweep rate of the staircase function. A non constant sweep rate to eliminate resonances that can occur at a constant sweep rate or a monotonic sweep function to help remove contamination from the tank are other variations to the function shown in  FIG. 78B . The non-constant sweep rate and the monotonic changing frequency are best combined to give both of the advantages. It is often most practical to simulate the monotonic function by sweeping in the high to low frequency direction for about 90% of the time and to recover from the low frequency point to the high frequency point during the remaining time. However, experimental evidence shows that any recovery time that is shorter than the time of the monotonic sweeping from high frequency to low frequency will give some benefit of moving contamination upwards in the tank. 
   The above designs adjust the duty cycle of the generator output to regulate and/or control the output power of the system. It is sometimes advantageous to regulate and/or control the output power of the system by adjusting the amplitude of the generator&#39;s output voltage instead of the duty cycle. One way to accomplish this is by replacing the DC power supply in  FIG. 73A  consisting of bridge diode  33  and capacitor  34  with a modified PFC (power factor correction) circuit  100  as shown in  FIG. 79 . The operation of PFC circuits is well known to people skilled in the art, the modification to the PFC circuit  100  consists of the addition of R 1 , R 2 , R 3  and Q 1  to form an input that will allow the adjustment of the regulated output voltage of the PFC circuit  100 . In operation, the control line P 5  from the output power regulator  39  in  FIG. 73A  is connected to the input of PFC circuit  100  in  FIG. 79 . If more power is needed, the control line rises in voltage causing the PFC circuit  100  to regulate at a higher output voltage causing the generator  29  to increase its output power. The opposite occurs in the lower power direction. A stable condition occurs when the actual output power substantially equals the specified output power. It is clear to someone skilled in the art that both duty cycle and amplitude can be used to adjust the output power of the system. For example, the system could be set so the duty cycle stayed at maximum while the amplitude was used to do the adjusting of the output power, however, if the amplitude reached its lowest point, then the duty cycle would begin to decrease to maintain the control and/or regulation. Another configuration could use amplitude for regulation and duty cycle for control. 
   It is well known in the cleaning industry that each different frequency best removes a specific type and size of contamination. The inventor of this system has observed that the order in which the different frequencies are delivered to the liquid produces a new cleaning effect that best removes a specific type and size of contamination. For example, if the system produces three frequency ranges, say centered on 71.5 khz, 104 khz and 167.2 khz, then there are six different orders or permutations of the frequency ranges that can be delivered to the liquid. They are (71.5, 104, 167.2); (71.5, 167.2, 104); (104, 71.5, 167.2); (104, 167.2, 71.5); (167.2, 71.5, 104) and (167.2, 104, 71.5). Since contamination typically occurs in many different types and sizes, the more new cleaning effects that the contamination is exposed to, the more contamination that will be removed. An additional advantage is obtained by changing the order in which the different permutations of frequency ranges are delivered to the liquid. If in the example, each permutation is considered a cleaning packet, then there are six cleaning packets. 
   There are 720 different ways these cleaning packets can be ordered, each producing a useful cleaning effect that can be supplied in a practical manner with this inventive system. 
   The generator detailed in  FIGS. 73A to 73F  is a highly integrated system. It should be noted that the function of this generator can be simulated in many ways that are more primitive by those skilled in the art and these other implementations are considered within the scope of this invention. 
   Referring now to the drawings in detail, for the ease of the reader, like reference numerals designate identical or corresponding parts throughout the views depicted in the drawings. It should be noted that each embodiment of the present invention is not depicted by a drawing; nor are each of the notable applications of the present invention depicted by a drawing.  FIG. 80  shows a schematic representation of a view of a conduction line  20  from a power section of an ultrasound generator.  FIG. 81  shows a box representation of a “parallel structure”. As used herein, a parallel structure refers to a modification circuitry  26  and an AC switch  25  with a control  23  where the two leads of the modification circuitry  26  are connected in parallel to the AC switch  25 . The “parallel structure” is connected into the conduction line  20  of the power section of an ultrasound generator. As used herein, “power section of an ultrasound generator”, “ultrasound generator power section” or “output of an ultrasound generator” is defined as that output circuitry of an ultrasound generator where the ultrasound frequency is present. Where AC switch  25  is comprised of a triac, lead number  1  of the modification circuitry  26  is connected to triac terminal MT 1 . Lead number  2  of the modification circuitry  26  is connected to triac terminal MT 2 . The triac gate is connected to the control  23 . In cases where the modification circuitry  26  contains active components, the additional control leads of these active components are also connected into the control  23 . In cases where the AC switch  25  is a configuration containing more than one active component, the leads of each of the active components are driven by control  23 , with proper isolation between the separate control lines where necessary. 
     FIG. 82  shows a schematic view of two nodes  27  and  28  in the power section of an ultrasound generator.  FIG. 83  illustrates a “series structure”. As used herein, a “series structure” refers to a modification circuitry  33  and an AC switch  34  in which the two leads of the modification circuitry  33  are connected in series with the leads of an AC switch  34 . This series structure is connected between two nodes in the power section of an ultrasound generator as shown in  FIG. 83 . A control  29  is present to turn on and off the AC switch  34 . When the AC switch  34  is comprised of a triac, the leads are the MT 1  and MT 2  terminals of the triac. The third lead is the gate of the triac or AC switch  34  and is connected with the control system  29 . In cases where the modification circuitry  33  contains active components, the additional control leads of these active components are also connected into the control circuitry  29 . In cases where the AC switch  34  is a configuration containing more than one active component, the leads of each of the active components are driven by control  29 , with proper isolation between the separate control lines where necessary. 
     FIG. 84  illustrates the use of a triac circuit in a preferred embodiment of the invention as depicted in  FIGS. 80 and 81 . The triac circuit, of  FIG. 84 , is used to modify the output of a multiple frequency ultrasound generator. In particular, the modification circuitry is comprised of five capacitor passive components  19 ,  36 ,  38 ,  40 , and  42  and associated triacs  35 ,  37 ,  39 ,  41 , and  43 . The triacs switch the modification circuitry into and out of the output stage of a multiple frequency ultrasound generator. In a typical application, the output of an ultrasound generator is connected between the +RF and −RF terminals, as shown in  FIG. 84 . The ultrasound transducer array is connected between the +RF and GND terminals.  FIG. 84  also contains a more complex parallel structure defined by the modification circuitry formed by capacitors  19  and  36  and triac  37  in parallel with the AC switch, triac  35 . 
   The first structure  44  defined in  FIG. 84  is formed by capacitor  19  and triac  35 . This first structure  44  is a parallel structure and is connected in the conduction line that typically connects −RF to GND. Thus, when triac  35  is off, the capacitor  19  is inserted between −RF and GND. When triac  35  is on, capacitor  19  is shorted out which effectively connects −RF to GND. The practical effect of this first structure  44  is to place capacitor  19  in series with the transducer array when triac  35  is off and to connect the transducer array directly to the ultrasound generator when triac  35  is on. This arrangement is useful when generating the highest frequency in a multiple frequency ultrasound generator. 
   Capacitor  36  and triac  37  demarcate the second structure  45  in  FIG. 84 . This second structure  45  is a series structure and is connected between the nodes labeled −RF and GND. Thus, when triac  37  is on, capacitor  36  is inserted between −RF and GND. The reverse effect can be seen when triac  37  is off. When capacitor  36  is open circuited, capacitor  36  is effectively removed from the circuit. The practical effect of this second structure  45  is to place capacitor  36  in series with the transducer array when triac  37  is on. Assuming triac  35  is off, it will increase the capacitance, in series with the transducer array, to capacitors  19  and  36 . This is useful when generating the second frequency (counting down from the highest) in a multiple frequency ultrasound generator. 
   The above two structures can form a more complex structure  46  which is an active/passive modification circuitry comprising capacitors  19 ,  36  and triac  37 . This modification circuitry is in parallel with triac  35  to form the third structure  46 , which is a parallel structure. The practical effect of this third structure  46  is to connect the ultrasound generator output directly to the transducer array when triac  35  is on. When triac  35  is off, it will place a capacitance in series with the transducer array (either capacitor  19  or  19  plus  36  depending on the state of triac  37 ) when triac  35  is off. This is useful when generating lower frequencies in a multiple frequency ultrasound generator, because when triac  35  is on, it eliminates the higher frequency structures from the system. 
   The fourth structure  47  present, as shown in  FIG. 84 , is comprised of capacitor  38  and triac  39 , which form a series structure. When triac  39  is on, capacitor  38  is inserted between +RF and GND. In the case of triac  39  being off, capacitor  38  is open circuited, which effectively removes capacitor  38  from the circuit. The practical effect of this fourth structure  47  is to place capacitor  38  in parallel with the transducer array when triac  39  is on. The effect of this is to increase the capacitance in parallel with the transducer array. This is useful when generating the second frequency in a multiple frequency ultrasound generator. It allows for the addition of the appropriate capacitance, making the power delivered at the second frequency equal to the power at the first frequency. 
   The fifth structure  48 , as shown in  FIG. 84 , comprises capacitor  40  and triac  41 . The fifth structure  48  has the same effect as the fourth structure, (i.e., it increases or decreases the amount of capacitance in parallel with the transducer array depending on the state of triac  41 ). This is useful when generating the third frequency in a multiple frequency ultrasound generator. The power is kept equal to the first two frequencies by the increase or decrease of capacitance at the third frequency. 
   The sixth structure  49 , as shown in  FIG. 84 , is comprised of capacitor  42  and triac  43 . The sixth structure  49  is another series structure, which increases or decreases the capacitance in parallel with the transducer array depending of the state of triac  43 . This is useful when generating the fourth frequency in a multiple frequency ultrasound generator. It adds sufficient capacitance to make the power at the fourth frequency equal to the first three frequencies. 
   The five gates of triacs  35  to  43  can be controlled individually, as are the gates as depicted in  FIG. 86 . However, as shown in  FIG. 84 , the gates for triacs  35  and  41  are controlled by the same signal  50 . Similarly, the gates for triacs  37  and  39  are controlled by the same signal  51 . Finally, the gate for triac  43  is controlled independently by signal  52 . The reason for the mixture of dependent and independent control of the various gates is that, in the logic design of this particular circuit, the truth table for the gates of triacs  35  and  41  are identical. The same is true for the gates of triacs  37  and  39 . The signals from  50 ,  51  and  52  come from the control circuitry as depicted in  FIGS. 85A and 85B . 
   The  FIGS. 85A and 85B  illustrate a control circuit for the circuits in  FIG. 84 . In  FIG. 85A , the inputs  54  and  55  accept a binary code to determine the state of the triacs in  FIG. 84 . The logic in  FIG. 85B  decodes the binary code to generate the gate drive signals for the triacs in  FIG. 84 . The drive signal can be a positive voltage to the gate that will turn on the triac allowing the triac to conduct. The turn off signal is more complicated. To keep a triac conducting or in the on state, a current above a minimum current or the threshold current is sufficient. Therefore, to turn off a triac, the current flow has to be zero or less than the threshold current. The gates of the triac also need an off signal, usually zero volts. The “triac turn off time” as used herein is defined as the time required to accomplish the turn off of the triac with the gate at zero and with no current flow in the triac. The generator control line  63  in  FIG. 85A  goes low when the generator must be turned off to allow a triac to turn off (that is, when the generator is turned off, the output current decays to zero which lowers the current through the triac to below its threshold current, thus allowing the triac to turn off). The controller functions as follows. When the signal to inputs  54  or  55  is changed, one or more of the monostable multivibrators  56 ,  57 ,  58  or  59  triggers a high level output for approximately 37 milliseconds. These outputs proceed into NOR gate  60  and lower the voltage to the generator control line  63  for 37 milliseconds. The time the generator control line  63  is lowered depends on the time required for the energy stored in reactive components to decay, as well as on the application energy feedback. For example, in the case of a cleaning tank, the sound energy in the tank feeds back into the transducer, which will generate an AC ultrasound voltage on the output stage of the generator. This feedback will typically take about 20 milliseconds to decay below the threshold of the triac. It is for this reason than the monostable multivibrators  56 ,  57 ,  58 , or  59  will output a signal for approximately 37 milliseconds, allowing for the above-mentioned conditions to be met. This 37 millisecond signal has the effect of turning the generator off and therefore stops the ultrasound current from flowing through the “on” triacs. The signal change representing the new binary code is delayed about 50 microseconds. This delay is accomplished by either a resistor and capacitor combination  61  or by resistor and capacitor combination  62  or by both. The purpose of this delay is to make sure that the generator has accomplished its turn off sequence before the binary code is decoded into the new set of triac gate signals. It is acceptable to have the zero gate signal to the triac applied at any time with respect to the generator off signal. The only mandatory condition for the generator off signal is that the triac current be below the threshold (referred to herein as D 2 ) and that it and the triac zero gate signal (referred to herein as D 1 ) be concurrent for a time equal to or greater than the triac turn off time. The logic in  FIG. 85B  decodes the signals in a way that is well known to those familiars with NAND and invert logic. The gate signals are output onto  50 ,  51  and  52 , as shown in  FIG. 84 . The high level outputs provide the on signal for the respective triacs, which will be turned on, and a low level output on the gates of the other triacs. 
   The binary code for the logic in  FIGS. 85A and 85B  is (P 1 , P 2 )=(0,0) for the highest frequency, (P 1 , P 2 )=(1,0) for the second frequency, (P 1 , P 2 )=(0,1) for the third frequency, and (P 1 , P 2 )=(1,1) for the fourth frequency. 
     FIG. 86  depicts another preferred embodiment of this invention. The output frequency of an ultrasound oscillator  10  is changed by the addition of three series structures ( 78 ,  79 , and  80 ) to the output of the oscillator. The first series structure  78  consists of capacitor  83   a  and triac  83   b . The second series structure  79  consists of capacitor  84   a  and triac  84   b . Finally, the third series structure  80  consists of capacitor  85   a  and triac  85   b . A controller  12  turns the oscillator  10  on and off by way of isolated lines  72  and  73 . The turn off and turn on signals are applied according to the circuit being a short circuit or an open circuit. The short circuit turns the oscillator off and the open circuit turns the oscillator on. The controller  12  also turns the triacs,  83   b ,  84   b  and  85   b , on and off by way of lines  74 ,  75  and  76 . Lines  74 ,  75 ,  76  are functionally similar to  50 ,  51  and  52  from  FIG. 85B  of this application. The controller  12  can contain circuitry similar to  FIGS. 85A and 85B , so as to provide the turn off and on signal to the triacs, as shown in  FIG. 86 . An alternative to control function  12  of  FIG. 86  is depicted in  FIG. 87 . 
   When the capacitance of the transducer  77  is defined to be a capacitance value  77 , then with all the triacs in their off state, oscillator  10  produces a frequency approximately equal to f 1  where 
   
     
       
         
           f1 
           = 
           
             1 
             
               2 
               ⁢ 
               π 
               ⁢ 
               
                 
                   ( 
                   
                     L1 
                     ⁡ 
                     
                       ( 
                       
                         81 
                         + 
                         77 
                       
                       ) 
                     
                   
                   ) 
                 
               
             
           
         
       
     
   
   When triac  83   b  is turned on by the controller  12 , thereby putting a high level on line  74  during operation of the oscillator (while maintaining the high level on line  74  or while 
           f2   =     1     2   ⁢   π   ⁢       (     L1   ⁡     (       83   ⁢   a     +   81   +   77     )       )                 
maintaining the current flow through triac  83   b  or maintaining both of these conditions, i.e., maintaining the on state of triac  83   b ), the oscillator changes frequency from the above value to approximately f 2 , where
 
Therefore, the oscillator frequency made a step change from frequency f 1  to a lower frequency f 2 .
 
   In a similar fashion, when triac  84   b  is then turned on by the controller  12 , thereby putting a high level on line  75  during operation of the oscillator (while maintaining the on state of triacs  83   b  and  84   b ), the oscillator changes frequency from the above value to approximately f 3 , where 
           f3   =     1     2   ⁢   π   ⁢       (     L1   ⁡     (       83   ⁢   a     +     84   ⁢   a     +   81   +   77     )       )                 
Therefore, the oscillator frequency made a step change from frequency f 2  to a lower frequency f 3 .
 
   In a similar fashion, when triac  85   b  is then turned on by the controller  12 , thereby putting a high level on line  76  during operation of the oscillator, the oscillator changes frequency from the above value to approximately f 4 , where 
           f4   =     1     2   ⁢   π   ⁢       (     L1   ⁡     (       83   ⁢   a     +     84   ⁢   a     +     85   ⁢   a     +   81   +   77     )       )                 
Therefore, the oscillator frequency made a step change from frequency f 3  to a lower frequency f 4 .
 
   The above examples show a method to step sweep the output frequency of an oscillator from a high frequency to a lower frequency by successively turning on additional series structures comprising a capacitor modification circuitry and a triac. According to the invention, it is then necessary for the controller  12  to output a short circuit between lines  72  and  73  to turn the oscillator  10  off before the triacs  83   b ,  84   b  and  85   b  can be turned off. In a preferred embodiment, the controller  12  turns off all the triacs during this generator off time. The generator off time is timed to be at least as long as the triac turn off time plus the decay time of the sound field. Then the cycle of turning on the triacs one at a time to step sweep from the highest frequency f 1  to the lowest frequency f 4  can occur again. The controller then starts another oscillator off time where all the triacs are turned off and the cycle repeats. This step swinging operation can be accomplished with the control circuit, as shown in  FIG. 87 . 
   It is clear to those skilled in the art that the circuit in  FIG. 86  can produce other frequency cycles. With three series structures ( 78 ,  79 ,  80 ) having unequal values for capacitors  83   a ,  84   a  and  85   a , a total of eight different frequencies are possible. The three listed above and 
   
     
       
         
           
             
               
                 f5 
                 = 
                 
                   1 
                   
                     2 
                     ⁢ 
                     π 
                     ⁢ 
                     
                       
                         ( 
                         
                           L1 
                           ⁡ 
                           
                             ( 
                             
                               
                                 84 
                                 ⁢ 
                                 a 
                               
                               + 
                               81 
                               + 
                               77 
                             
                             ) 
                           
                         
                         ) 
                       
                     
                   
                 
               
             
           
           
             
               
                 f6 
                 = 
                 
                   1 
                   
                     2 
                     ⁢ 
                     π 
                     ⁢ 
                     
                       
                         ( 
                         
                           L1 
                           ⁡ 
                           
                             ( 
                             
                               
                                 83 
                                 ⁢ 
                                 a 
                               
                               + 
                               
                                 85 
                                 ⁢ 
                                 a 
                               
                               + 
                               81 
                               + 
                               77 
                             
                             ) 
                           
                         
                         ) 
                       
                     
                   
                 
               
             
           
           
             
               
                 f7 
                 = 
                 
                   1 
                   
                     2 
                     ⁢ 
                     π 
                     ⁢ 
                     
                       
                         ( 
                         
                           L1 
                           ⁡ 
                           
                             ( 
                             
                               
                                 84 
                                 ⁢ 
                                 a 
                               
                               + 
                               
                                 85 
                                 ⁢ 
                                 a 
                               
                               + 
                               81 
                               + 
                               77 
                             
                             ) 
                           
                         
                         ) 
                       
                     
                   
                 
               
             
           
           
             
               
                 f8 
                 = 
                 
                   1 
                   
                     2 
                     ⁢ 
                     π 
                     ⁢ 
                     
                       
                         ( 
                         
                           L1 
                           ⁡ 
                           
                             ( 
                             
                               
                                 85 
                                 ⁢ 
                                 a 
                               
                               + 
                               81 
                               + 
                               77 
                             
                             ) 
                           
                         
                         ) 
                       
                     
                   
                 
               
             
           
         
       
     
   
   Any permutation of these eight frequencies (8! or 40,320 permutations) can be organized into a cycle by the controller  12  and supplied to the transducer. It should be noted that for any frequency change that does not require a triac to be turned off, the frequency change can be accomplished without the controller  12  turning off the oscillator. However, if any frequency change occurs where one or more triacs have to be turned off, then the controller  12  concurrently turns off the oscillator for a time at least as long as the turn off time of the triacs plus the decay time of the sound field. 
     FIG. 87  shows a schematic diagram of a control circuit representing the controller  12  of  FIG. 86 . Since in the discussion of  FIG. 86  above the main functional characteristics of  FIG. 87  were mentioned, only a brief description of the main elements will be discussed herein below. The controller  12  (or  101  from  FIG. 88 ) produces on/off signals for the gates of the triacs and on/off signals for the oscillator. The signal to turn on/off the oscillator  10  is sent by way of lines  116  and  117  (these lines are equivalent to lines  72  and  73  in  FIG. 86 ). This on/off signal is generated by element  115  when the output is a short circuit, thereby turning off oscillator  10 . The component  118  decodes the signal to be output onto  119 ,  120  and  121  (these lines are equivalent to lines  74 ,  75  and  76  of  FIG. 86 ) which is the signal sent into the triacs ( 83   b ,  84   b , and  85   b ). The element  122  is in charge of sending the signals to be interpreted by  118  and  115 . 
     FIG. 88  shows that an inductive modification circuit, a resistive modification circuit and a parallel structure can also modify an oscillator  10 . The operation of  FIG. 88  is similar to that described for  FIG. 86 . The control  101  for  FIG. 88  can be similar to the control shown in  FIG. 87 . 
   With reference to  FIG. 88 , the series structure  107 , comprising inductor  110   a  and triac  110   b , will increase the frequency of the oscillator when triac  110   b  is turned on. The series structure  108  comprising resistor  111   a  and triac  111   b  will decrease the output amplitude and power when triac  111   b  is turned on. The parallel structure  109  comprising capacitor  112   a  and triac  112   b  will increase the frequency when triac  112   b  is turned on. 
   Another application of the present invention is to change the output power and amplitude of an ultrasound generator. With some ultrasound generators that are not of the self-oscillating type ( FIG. 86  is an example of a self-oscillating type, U.S. Pat. No. 4,743,789 is an example of a non self-oscillating type) their output power and amplitude are dependent on the total amount of capacitance connected to their outputs. Connecting series structures, comprising a capacitor and a triac, as shown, for example, in  FIG. 86 , to the output of these non self-oscillating generators allows the power and amplitude to be changed by controlling the state of the triacs. With n series structures, 2 raised to the power n power levels and amplitude levels can be programmed into the controller. 
     FIGS. 84 through 88  illustrate triacs utilized as the AC switch. However, as one skilled in the are will readily appreciate, any AC switch can be used (not just triacs). There are many ways to build AC switches, such as from transistors, including bipolar junction transistors (BJTs), metal oxide semiconductor field effect transistors (MOSFETs), and insulated gate bipolar transistors (IGBTs). Additionally, suitable AC switches can be constructed from thyristors, such as gate turn-off thyristors (GTOs), silicon controlled rectifiers (SCRs), MOS controlled thyristors (MCTs), and asymmetrical silicon controlled rectifiers (ASCRs). Other AC switches or devices with forced turn off and turn on capability, such as a bi-directional lateral insulated gate bipolar transistor or a relay, can be used. Such a transistor is described in U.S. Pat. No. 5,977,569. Triacs are preferred because they are inexpensive and have only one gate lead. As is well know in the art, most of the other AC switches, including transistors and thyristors, require more than one control lead to be driven. Often these multiple drives have to be isolated from one another. Gate turn off thyristors (GTOs) can make suitable AC switch, particularly if the cost of two control leads can be justified, because GTOs can be forced off by their gate leads. 
     FIG. 89A  shows an AC switch in a series transistor configuration where BJTs (one N channel BJT and one P channel BJT) are used.  FIG. 89B  shows an AC switch made in a parallel thyristor configuration where SCRs are used. This  FIG. 89B  circuit is commonly known as back to back SCRs. Those skilled in the art can readily appreciate the use any active components (i.e., active components that can function as a switch) either in a parallel configuration or in a series configuration to form an AC switch. Typically, diodes are needed in the series or parallel configuration to pass current or to protect the active device.  FIG. 89C  shows a transistor parallel configuration using IGBTs where the AC switch comprises four diodes. As used herein, the phrase “series/parallel active device configuration” mean active components either in series or in parallel. The active components can be a transistor configuration or a thyristor configuration or a combination of active devices and zero or more diodes. The active devices in series or parallel configuration will form an AC switch where one active device conducts current during one half of an AC cycle and the other active device conducts current during the other half of the AC cycle. 
   In an ultrasonic or microsonic cleaning or processing liquid, it is known that a particular frequency or a set of closely spaced frequencies will resonate a certain size population of bubbles or voids within the liquid. A conventional sweeping frequency ultrasonic or microsonic cleaning or processing signal produces a particular frequency or a set of closely spaced frequencies followed by the next particular frequency or set of closely spaced frequencies adjacent to the first particular frequency or set of closely spaced frequencies. 
   Unfortunately, cavitation efficiency suffers with this type of conventional sweeping frequency ultrasonic or microsonic cleaning or processing signal because the first particular frequency or set of closely spaced frequencies depletes members of that certain size population of bubbles or voids within the liquid leaving a smaller population for the second adjacent particular frequency or set of closely spaced frequencies to resonate. 
   There is shown in  FIG. 90 , a sweeping frequency drive signal  3100  that overcomes the above-described cavitation efficiency limitation of the prior art. When a certain size population of bubbles or voids within the liquid begins to be depleted causing a loss in cavitation efficiency, drive signal  3100  jumps, changes or rapidly sweeps to a non adjacent frequency within the bandwidth of the transducer array, such that the process continues with improved cavitation allowed by the new bubble population associated with this new non adjacent particular frequency or set of closely spaced frequencies. 
   In a preferred embodiment, drive signal  3100  can be maintained in the upper half of a bandwidth. The bandwidth is typically 10% of the center frequency (unless the system employs a special design/procedure, e.g., overlapping transducers frequency ranges). Therefore, for a center frequency at the high end of the microsonic frequency range (350 khz), the bandwidth is typically 35 khz. For 40 khz ultrasonic transducers, the bandwidth is typically about 4 khz. After a defined period of time (i.e., before cavitation efficiency suffers) at point  3102 , the frequency is changed to a new frequency that is typically one half bandwidth lower than the current frequency. This change in frequency may occur by sweeping the frequency to the new lower frequency (not shown; wherein the sweep time is typically less than 25% of the defined period of time), or stepping the frequency to the new lower frequency, as shown in  FIG. 90 . The length of this “defined period of time” is dependent on the frequency, power density, sweep rate, type of chemistry and chemistry conditions such as temperature. “Defined periods of time” vary inversely with respect to frequency and span the range from ten microseconds to two milliseconds. At point  3104 , this sweeping frequency continues from this new lower frequency. After the defined period of time (described above) at point  3106 , the frequency jumps to a new higher frequency (point  3108 ) that is typically one half bandwidth higher than the current frequency. 
   While a one half bandwidth frequency jump is typical, other amounts are possible. For example, the frequency may be jumped by a much larger percentage of the bandwidth, e.g., from a frequency proximate the lower limit of the bandwidth to a frequency proximate the upper limit of the bandwidth, such as from point  3110  to point  3112 . Less than one-half bandwidth changes can also be used and are an improvement over the prior art; however, they are not as optimum an improvement as the preferred embodiment described herein. 
   Further, while the system is described above as sweeping the frequency between points  3104  and  3106 , other configurations are possible. For example, the frequency may be maintained constant (not shown) during the defined period of time. Alternatively, the frequency may be changed (between points  3104  and  3106 ) via one or more frequency steps (shown in phantom); or the set of closely spaced frequencies between points  3104  and  3106  may be random frequencies (not shown). 
   This frequency sweeping and frequency jumping continues until striking the lowest frequency in the bandwidth (at point  3110 ). At this point, the frequency jumps to the highest frequency in the bandwidth (to point  3112 ), and the sweeping and jumping process is repeated until the lowest frequency in the bandwidth is reached again (not shown). This high cavitation efficiency process is repeated and continued for the time needed in that particular bandwidth. 
   If a multiple frequency generator is driving a multiple frequency transducer array with a set of defined bandwidths (e.g., multiple harmonic or overtone bandwidths), then after the time needed in a particular bandwidth has elapsed, the drive signal may change to a different bandwidth and may produce a similar high cavitation efficiency signal in that different bandwidth. Also, in the case of a multiple frequency generator driving a multiple frequency transducer array with a set of defined bandwidths, the change or jump (upon the depletion of a certain size population of bubbles or voids within the liquid) can be to a frequency in another bandwidth. This has the added advantage that besides a new bubble population for increased cavitation efficiency, the cavitation in the prior bandwidth typically produced bubbles that are resonant in the new bandwidth to which the signal changed or jumped. 
   In the prior art generator and transducer array systems, it is typical to have amplitude modulation of a frequency modulated waveform as the output signal from the generator and driving the transducer array. A typical amplitude modulation pattern is full wave modulation and a typical frequency modulation pattern is a triangular sweeping frequency waveform. The inventor has found that the cleaning or processing efficiency when using this type of waveform drops off as the process continues because the single form of cavitation produced by the given waveform can not do all aspects of the process efficiently. The inventor has found that using two forms of cavitation, where the first form is predominately stable cavitation and the second form is predominately transient cavitation, allows the process to proceed to a more complete level, for example, in the case of a cleaning process, the two forms of cavitation applied in succession over a given time span result is a lower percentage of particles left on the part being cleaned than will occur with one form of cavitation being applied over the same time span. 
   There is shown in  FIG. 91 , a diagram  4100  that shows a succession of time periods with different forms of cavitation in successive time periods. In the first time period shown between points  4101  and  4102 , there exists a first form of cavitation where the cavitation is predominately stable cavitation. The stable cavitation can be produced by one or more of the techniques described below. In the second time period shown between points  4103  and  4104 , there exists a second form of cavitation where the cavitation is predominately transient cavitation. The transient cavitation can be produced as described below. In the third time period shown between points  4105  and  4106 , there exists a cavitation region called “none”. This is typically an off period of the generator, where no acoustic energy is delivered to the transducer array. The term “none” will also mean a condition where there is acoustic energy in the liquid but that acoustic energy is below the threshold of cavitation or so low that the cavitation produced is below that which is practical to accomplish the cleaning or processing. This “none” condition can also be achieved by excess gas in the liquid, absorption of acoustic energy by the part being cleaned or by contamination in the liquid. In  FIG. 91  point  4107  to point  4108  is a time period of predominately transient cavitation followed by a successive time period of predominately stable cavitation from points  4109  to  4110 , demonstrating that different order to the forms of cavitation will have a beneficial effect on the process.  FIG. 91  ends showing between points  4110  and  4111   a  time period of predominately transient cavitation, but it is clear to one skilled in the art that any succession of time periods where at least one time period has predominately stable cavitation and at least one of the successive time periods has predominately transient cavitation, or the reverse order of this, will produce the increased cleaning or processing efficiency described herein. 
   The following waveforms are used to produce predominately stable cavitation and the existence of any one or combination at the output of a generator supplements the classical definition of stable cavitation for the purposes of this invention. (1) Rapidly changing frequencies (sweep rates) where the frequency change (df/dt) is greater than (0.106)*(fc) Mhz per second, where fc is the average of the highest frequency in khz and the lowest frequency in khz in the set of rapidly changing frequencies (typically, this set of frequencies is within a bandwidth of operation of the transducer array) and the delivered power is in the range of 25 to 60 watts per transducer. (2) Narrow rectangular pulse width amplitude modulation where the pulse width is less than 24/Pp milliseconds, where Pp is the peak power of the pulse in watts and the frequency change (df/dt) ranges from zero to less than (0.106)*(fc) Mhz per second. (3) Irregular shaped amplitude modulation where the area under the power versus time curve for each pulse is less than 24 milliwatt-seconds per transducer in the array. (4) Changing to a new frequency set or bandwidth before the onset of imploding cavitations, this is typically before 24 milliwatt-seconds per transducer of acoustic power is delivered at the current frequency set or bandwidth. (5) Sweeping a full wave modulated waveform at a rate below (0.106)*(fc) Mhz per second while chopping the amplitude into pulses that change in width to maintain an area under each pulse curve that is less than 24 milliwatt-seconds per transducer. 
   Waveforms to produce transient cavitation are well known to those skilled in the art of ultrasonic cleaning. Optimum sweep rates, typically in the range of 120 to 550 hz combined with wide pulses or full wave modulation (typically repetitive every 8.33 milliseconds or every 10 milliseconds) produce the best state of the art cavitation. Improved transient cavitation efficiency as described above and shown in  FIG. 90  is a preferred embodiment for use in the time periods where transient cavitation is employed. 
   The invention thus attains the objects set forth above, among those apparent in the preceding description. Since certain changes may be made in the above description without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are to cover all generic and specific features of the invention described herein, and all statements of the scope of the invention which, as a matter of language, might be said.