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

The invention utilizes a multiple frequency ultrasound generator driving a multiple frequency harmonic transducer array to improve cleaning and processing effects while eliminating damage to parts being cleaned. An AC switch and circuitry to modify the output of an ultrasound generator in combination with techniques such as random AM and FM signals are used to produce ultrasound waves that have no single frequency components which eliminates exciting parts being cleaned into resonance. Generator signals that increase cavitation efficiency and that have successive time periods with predominately stable cavitation and predominantly transient cavitation further improve the performance of the cleaning or processing systems.

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'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'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'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'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's methods for frequency sweeping ultrasound within the transducer's bandwidth. Specifically, the invention provides a sweeping of the sweep rate, within the transducer'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'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 D1is illustrated. If the AC switch is a triac, the control circuitry will also supply a turn off signal D2to the generator, where D1and D2are 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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2show schematic side and top views, respectively, of an ultrasound processing system10constructed according to the invention. An ultrasound generator12electrically connects, via electrical paths14a,14b, to an ultrasound transducer16to drive the transducer16at ultrasound frequencies above about 18 khz, and usually between 40 khz and 350 khz. Though not required, the transducer16is shown inFIG. 1as an array of transducer elements18. Typically, such elements18are made from ceramic, piezoelectric, or magnetostrictive materials which expand and contract with applied voltages or current to create ultrasound. The transducer16is mounted to the bottom, to the sides, or within the ultrasound treatment tank20through conventional methods, such as known to those skilled in the art and as described above. A liquid22fills the tank to a level sufficient to cover the delicate part24to be processed and/or cleaned. In operation, the generator12drives the transducer16to create acoustic energy26that couples into the liquid22.

Although the transducer16is shown mounted to the bottom of the tank20, those skilled in the art will appreciate that other mounting configurations are possible and envisioned. The transducer elements18are of conventional design, and are preferably “clamped” so as to compress the piezoelectric transducer material.

FIG. 3illustrates a two transducer system30. Transducer32a,32bare similar to one of the elements18,FIG. 1. Transducer32aincludes two ceramic sandwiched elements34, a steel back plate38a, and a front drive plate36athat is mounted to the tank20′. Transducer32bincludes two ceramic sandwiched elements34, a steel back plate38b, and a front drive plate36bthat is mounted to the tank20′. Bolts39a,39bpass through the plates38a,38band screw into the drive plates36a,36b, respectively, to compresses the ceramics34. The transducers32are illustratively shown mounted to a tank surface20′.

The transducers32a,32bare driven by a common generator such as generator12ofFIG. 1. Alternatively, multiple generators can be used. The ceramics34are oriented with positive “+” orientations together or minus “−” orientations together to obtain cooperative expansion and contraction within each transducer32. Lead-outs42illustrate the electrical connections which connect between the generator and the transducers32so as to apply a differential voltage there-across. The bolts39a,39bprovide a conduction path between the bottoms43and tops45of the transducers32to connect the similar electrodes (here shown as −, −) of the elements34.

The thicknesses40a,40bof transducers32a,32b, respectively, determine the transducer's fundamental resonant frequency. For purposes of illustration, transducer32ahas a fundamental frequency of 40 khz, and transducer32bhas a fundamental frequency of 44 khz. Transducers32a,32beach 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 transducers32a,32bcan occur, thereby adding additional range within which to apply ultrasound26a′,26b′ to liquid22′.

The acoustic energy26′ applied to the liquid22′ by the combination of transducers32a,32bis illustrated graphically inFIG. 4. InFIG. 4, the “x” axis represents frequency, and the “y” axis represents acoustical power. The outline44represents the bandwidth of transducer32a, and outline46represents the bandwidth of transducer32b. Together, they produce a combined bandwidth43which produces a relatively flat acoustical energy profile to the liquid22′, such as illustrated by profile48. The flatness of the bandwidth43representing the acoustical profile48of the two transducers32a,32bis preferably within a factor of two of any other acoustical strength within the combined bandwidth43. That is, if the FWHM defines the bandwidth43; the non-uniformity in the profile48across the bandwidth43is typically better than this amount. In certain cases, the profile48between the two bandwidths44and46is substantially flat, such as illustrated inFIG. 4.

The generator connected to lead-outs42drives the transducers32a,32bat frequencies within the bandwidth43to obtain broadband acoustical disturbances within the liquid22′. 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 bandwidth43; 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 tank20′.

With further reference toFIGS. 1 and 2, each of the elements18can have a representative bandwidth such as illustrated inFIG. 4. Accordingly, an even larger bandwidth43can be created with three or more transducers such as illustrated by transducers32a,32b. 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 profile48ofFIG. 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 transducers18and32a,32b,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 tanks20,20′ 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 part24. 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 toFIG. 4,FIG. 5illustrates a combined bandwidth50of harmonic frequencies in the range 100–350 khz. Specifically,FIG. 5shows the combined bandwidth50that is formed by the bandwidth44′ around the second harmonic of the 40 khz frequency, and the bandwidth46′ around the second harmonic of the 41.5 khz frequency.

FIG. 6shows in block diagram embodiment of a system110constructed according to the present invention. The system110includes a signal section112which drives a power module121. The power module121powers the harmonic transducer array122. The transducer array122is coupled to a liquid123by one of several conventional means so as to generate acoustic energy within the liquid123. By way of example, the array122is similar to the array16ofFIG. 1; and the liquid123is similar to the liquid22ofFIG. 1.

The signal section112includes a triangle wave oscillator114with a frequency typically below 150 hz. The purpose of the oscillator114is to provide a signal that sweeps the sweep rate of the ultrasound frequencies generated by the transducer arrays122.

The oscillator114is fed into the input of the sweep rate VCO115(Voltage Controlled Oscillator). This causes the frequency of the output of VCO115to linearly sweep at the frequency of the oscillator114. The optimum sweep rate frequency output of VCO115is 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 VCO115output is set, for example, to sweep from 380 hz to 530 hz. If, additionally, the oscillator114is set to 37 hz, then the output of VCO115changes frequency, linearly, from 380 hz to 530 hz, and back to 380 hz at thirty seven times per second.

The output of VCO115feeds the VCO input of the 2X center frequency VCO116. The VCO116operates as follows. If, for example, the center frequency of VCO116is 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 oscillator114at the time of measurement. Since the voltage output of oscillator114is 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 oscillator114, VCO115and VCO116operate, 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 oscillator114would be replaced by a random or chaotic voltage generator to reduce the likelihood of exciting any modes within the part.

The VCO116drives a divide-by-two D flip-flop117. The purpose of the D flip-flop117is to eliminate asymmetries in the waveform from the VCO116. The output of the D flip-flop117is 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-flop117linearly 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 circuit118produces 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 multivibrator119. The timed pulse out of monostable multivibrator119is 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 multivibrator119is set to a time of 4.17 milliseconds for a 60 hz line frequency. For an amplitude that is 50% of maximum, the monostable multivibrator119is set to 1.389 milliseconds for a 60 hz line frequency. In general, the monostable multivibrator119time 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-flop117and the timed pulse output of the monostable multivibrator119feed into the synchronization logic120. The synchronization logic120performs three primary functions. First, it only allows the double sweeping square wave to pass to the output of the synchronization logic120during the time defined by the pulse from the monostable multivibrator119. Second, the synchronization logic120always allows a double sweeping square wave which starts to be completed, even if the monostable multivibrator119times out in the middle of a double sweeping square wave. And lastly, the synchronization logic120always starts a double sweeping square wave at the beginning of the ultrasound frequency, i.e., at zero degrees.

The output of synchronization logic120is a double sweeping square wave that exists only during the time defined by the monostable multivibrator119or for a fraction of a cycle past the end of the monostable multivibrator119time period. The synchronization logic120output feeds a power module121which amplifies the pulsed double sweeping square wave to an appropriate power level to drive the harmonic transducers122. The transducers122are 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 section112.

FIG. 7shows a schematic embodiment of the signal section112inFIG. 6. U1is a XR-2209 precision oscillator with a triangle wave output at pin8. The frequency of the XR-2209 is 1/(RC)=1/((27 Kohm) (1 microfarad))=37 hz. This sets the frequency of the triangle wave oscillator114,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.

U2is a XR-2209 precision oscillator with a triangle wave output at pin8. The center frequency of U2is 1/(RC)=1/((2.2 Kohm) (1 microfarad))=455 hz. The actual output frequency is proportional to the current flowing out of pin4of U2. 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 pin4must change by 16.5% in each direction, that is, by (16.5%) (2.73 milliampers)=0.45 milliampers. The triangle wave from U1causes this change. The triangle wave changes from 3 volts to 9 volts; therefore, there is 3 volts on either side of 6 volts at pin4of U2to cause the 0.45 milliampers change. By making R1=3 volts/0.45 milliampers=6.67 Kohm, the sweep rate is changed 75 hz either side of 455 hz. The actual R1used inFIG. 7is 6.65 Kohm, a commercially available value giving an actual change of 75.2 hz.

U3is 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 U3pin4flows 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 R2=3 volts/7.88 microampers=381 Kohm. InFIG. 7, however, the commercial value of 383 Kohm was used.

U3pin7has 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 U1.

U4is a D flip-flop in a standard divide by two configuration. It squares up any non 50% duty cycle from U3and provides a frequency range of 102 khz to 106 khz from the 204 khz to 212 khz U3signal.

The output of U4feeds 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 U5, the edge triggered 4538 monostable multivibrator wired in a trailing edge trigger/retriggerable configuration. The output of U5goes high for a period determined by the setting on the 500 Kohm potentiometer. At the end of this period, the output of U5goes 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 U4.

The timed pulse U5feeds the D input of U6, a 4013 D-type flip flop. The square wave from U4is invented by U7aand feeds the clock input of U6. U6only transfers the signal on the D input to the output Q at the rise of a pulse on the clock input, Pin3. Therefore, the Q output of U6on Pin1is high when the D input of U6on Pin3is high and the clock input of U6on Pin3transitions high. This change in the Q output of U6is therefore synchronized with the change in the square wave from U4.

The synchronized high Q output of U6feeds U8Pin13, a 4093 Schmidt trigger NAND gate. The high level on Pin13of U8allows the square wave signal to pass from U8Pin12to the output of U8at Pin11.

In a similar way, U8synchronizes the falling output from U5with the square wave from U4. Therefore, only complete square waves pass to U8Pin11and only during the time period as chosen by monostable multivibrator U5. The 4049 buffer driver U7binverts the output at U8Pin11so it has the same phase as the square wave output from U4. This signal, U7bPin2is now the proper signal to be amplified to drive the transducers.

FIGS. 8A and 8Brepresent a circuit that increases the signal from U7bPin2inFIG. 7to a power level for driving the transducers122,FIG. 6. There are three isolated power supplies. The first one, including a T1, a bridge, C19, VR1and C22, produces +12 VDC for the input logic. The second and third isolated power supplies produce +15 VDC at VR2Pin3and VR3Pin3for gate drive to the IGBTs (insulated gate bipolar transistors).

The signal input toFIGS. 8A and 8Bhave its edges sharpened by the 40106 Schmidt trigger U9a. The output of U9afeeds the 4049 buffer drivers U10cand U10dwhich drive optical isolator and IGBT driver U12, a Hewlett Packard HCPL3120. Also, the output of U9ais inverted by U9band feeds buffer drivers U10aand U10bwhich drive U11, another HCPL3120.

This results in an isolated drive signal on the output of U11and the same signal on the output of U12, only 180 degrees out of phase. Therefore, U11drives Q1on while U12drives Q2off. In this condition, a power half sinusoid of current flows from the high voltage full wave DC at B1through D1and Q1and L1into C1. Current cannot reverse because it is blocked by D1and the off Q2. When the input signal changes state, U11turns off Q1and U12turns on Q2, a half sinusoid of current flow out of C1through L2and D2and Q2back into C1in the opposite polarity. This ends a complete cycle.

The power signal across C1couples through the high frequency isolation transformer T4. The output of T4is connected to the transducer or transducer array.

FIG. 9shows a cross-sectional side view of one clamped microsonic transducer128constructed according to the invention; whileFIG. 9Ashows a top view of the microsonic transducer128. The microsonic transducer128has a second harmonic resonant frequency of 104 khz with a 4 khz bandwidth (i.e., from 102 khz to 106 khz). The cone-shaped backplate139flattens the impedance verses frequency curve to broaden the frequency bandwidth of the microsonic transducer128. Specifically, the backplate thickness along the “T” direction changes for translational positions along direction “X.” Since the harmonic resonance of the microsonic transducer128changes as a function of backplate thickness, the conical plate139broadens and flattens the microsonic transducer's operational bandwidth.

The ceramic134of microsonic transducer128is driven through oscillatory voltages transmitted across the electrodes136. The electrodes136connect to an ultrasound generator (not shown), such as described above, by insulated electrical connections138. The ceramic134is held under compression through operation of the bolt132. Specifically, the bolt132provides 5,000 pounds of compressive force on the piezoelectric ceramic134. 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 inFIGS. 10 and 10A. Specifically,FIG. 10shows an amplitude control subsystem140that provides amplitude control by selecting a portion of the rectified line voltage145which drives the ultrasound generator amplitude select section146. The signal section112,FIG. 6, and particularly the monostable multivibrator119and synchronization logic120, provide similar functionality. InFIG. 10, the amplitude control subsystem140operates with the ultrasound generator142and connects with the power line voltage138. The rectification section144changes the ac to dc so as to provide the rectified signal145.

The amplitude select section146selects a portion of the leading quarter sinusoid of rectified signal145that ends at the desired amplitude, here shown as amplitude “A,” in a region148between zero and 90 degrees and in a region150between 180 degrees and 270 degrees of the signal145. In this manner, the amplitude modulation152is selectable in a controlled manner as applied to the signal154driving the transducers156from the generator142, such as discussed in connection withFIGS. 3 and 4.

FIG. 10Ashows illustrative selections of amplitude control in accord with the invention. The AC line158is first converted to a full wave signal160by the rectifier144. Thereafter, the amplitude select section146acquires 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 signal162is provided. Similarly, a one-half amplitude signal164is generated by choosing the 30 degrees and 210 degrees locations of the same sinusoids. By way of a further example, a one-third amplitude signal166is 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 section144can also be a half-wave rectifier. As such, the signal145will 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 inFIGS. 3,4,10and10A, 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. 11illustrates an AM sweep subsystem170constructed according to the invention. The AM sweep subsystem170operates as part of, or in conjunction with, the ultrasound generator172. The AM generator174provides an AM signal175with a selectable frequency. The increment/decrement section176commands the AM generator174over command line177to change its frequency over a preselected time period so as to “sweep” the AM frequency in the output signal178which drives the transducers180.

U.S. Pat. No. 4,736,130 describes one AM generator56,FIG. 1, that is suitable for use as the generator174ofFIG. 11. By way of example,FIG. 11Aillustrates one selectable AM frequency signal182formed 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 inFIG. 11, then the frequency is commanded to vary between 1.25 khz+250 hz and 1.25 khz−250 hz, such as illustrated inFIG. 11B.FIG. 11Billustrates a graph of AM frequency versus time for this example.

FIG. 12schematically illustrates a multi-generator, single tank system200constructed according to the invention. In many instances, it is desirable to select an ultrasound frequency201that most closely achieves the cavitation implosion energy which cleans, but does not damage, the delicate part202. In a single tank system such as inFIG. 12, the chemistries within the tank210are 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 system200has multiple generators206and transducers208that provide different frequencies. By way of example, generator206acan provide a 40 khz primary resonant frequency; while generator206bcan provide the first harmonic 72 khz frequency. Generator206ccan provide, for example, 104 khz microsonic operation. In the illustrated example, therefore, the generators206a,206b,206coperate, respectively, at 40 khz, 72 khz, and 104 khz. Each transducer208responds at each of these frequencies so that, in tandem, the transducers generate ultrasound201at the same frequency to fill the tank210with the proper frequency for the particular chemistry.

In addition, each of the generators206a–206ccan and do preferably sweep the frequencies about the transducers' 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 tank210is filled with a new chemistry, the operator selects the optimum frequency through the mux select section212. The mux select section connects to the analog multiplexer (“mux”)214which connects to each generator206. Specifically, each generator206couples through the mux214in a switching network that permits only one active signal line216to the transducers208. For example, if the operator at mux select section212chooses microsonic operation to optimize the particular chemistry in the tank210, generator206cis connected through the mux214and drives each transducer208a–208cto generate microsonic ultrasound201which fills the tank210. If, however, generator206ais selected, then each of the transducers208are driven with 40 khz ultrasound.

FIG. 13illustrates a multi-generator, common frequency ultrasound system230constructed according to the invention. InFIG. 13, a plurality of generators232(232a–232c) connect through signal lines234(234a–234c) to drive associated transducers238(238a–238c) in a common tank236. Each of the transducers238and generators232operate 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 tank236(and within the part242).

In order to eliminate “beating” between ultrasound energies240a–240cof the several transducers238a–238cand generators232a–232c, the generators232are each driven by a common FM signal250such as generated by the master signal generator244. The FM signal is coupled to each generator through signal divider251.

In operation, system230permits the coupling of identical frequencies, in magnitude and phase, into the tank236by the several transducers238. Accordingly, unwanted beating effects are eliminated. The signal250is swept with FM control through the desired ultrasound bandwidth of the several transducers to eliminate resonances within the tank236; 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 system230ofFIG. 13can additionally include or employ other features such as described herein, such as AM modulation and sweep, AM control, and broadband transducer.

FIG. 14illustrates a multi-tank system260constructed according to the invention. One or more generators262drive each tank264(here illustrated, generators262aand262bdrive tank264a; and generators264cand264ddrive tank264b). Each of the generators262connects to an associated ultrasound transducer266a–dso as to produce ultrasound268a–din the associated tanks264a–b.

The common master signal generator270provides a common FM signal272for each of the generators262. Thereafter, ultrasound generators262a–bgenerate ultrasound268a–bthat is identical in amplitude and phase, such as described above. Similarly, generators262c–dgenerate ultrasound268c–dthat is identical in amplitude and phase. However, unlike above, the generators262each have an AM generator274that functions as part of the generator262so as to select an optimum AM frequency within the tanks264. In addition, the AM generators274preferably sweep through the AM frequencies so as to eliminate resonances at the AM frequency.

More particularly, generators274a–bgenerate and/or sweep through identical frequencies of the AM in tank264a; while generators274c–dgenerate and/or sweep through identical frequencies of AM in tank264b. However, the AM frequency and/or AM sweep of the paired generators274a–bneed not be the same as the AM frequency and/or AM sweep of the paired generators274c–d. Each of the generators274operate at the same carrier frequency as determined by the FM signal270; however each paired generator set274a–band274c–doperates independently from the other set so as to create the desired process characteristics within the associated tank264.

Accordingly, the system260eliminates or prevents undesirable cross-talk or resonances between the two tanks264a–b. Since the generators within all tanks264operate at the same signal frequency270, there is no effective beating between tanks which could upset or destroy the desired cleaning and/or processing characteristics within the tanks264. As such, the system260reduces the likelihood of creating damaging resonances within the parts280a–b. It is apparent to those skilled in the art that the FM control270can contain the four AM controls274a–dinstead of the illustrated configuration.

FIG. 14Ashows two AM patterns300a,300bthat illustrate ultrasound delivered to multiple tanks such as shown inFIG. 14. For example, AM pattern300arepresents the ultrasound268aofFIG. 14; while AM pattern300brepresents the ultrasound268cofFIG. 14. With a common FM carrier302, as provided by the master generator270,FIG. 14, the ultrasound frequencies302can be synchronized so as to eliminate beating between tanks264a,264b. Further, the separate AM generators274aand274cprovide capability so as to select the magnitude of the AM frequency shown by the envelope waveform306. As illustrated, for example, waveform306ahas a different magnitude308as compared to the magnitude310of waveform306b. Further, generators374a,374ccan change the periods310a,310b, respectively, of each of the waveforms306a,306bselectively so as to change the AM frequency within each tank.

FIGS. 15A,15B and15C graphically illustrate the methods of sweeping the sweep rate, in accord with the invention. In particular,FIG. 15Ashows an illustrative condition of a waveform350that 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 axis352.FIG. 15Billustrates FM control of the waveform354which has a varying period356specified 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 regions358a,358bare shown for ease of illustration and represent, respectively, compressed periods of time within which the system sweeps the waveform354through many frequencies from 42 khz to 40 khz, and through many frequencies from 40 khz to 38 khz.

FIG. 15Cgraphically shows a triangle pattern360which illustrates the variation of sweep rate frequency along a time axis362.

FIGS. 16–20illustrate alternative backplate configurations according to the invention. Unlike the configuration ofFIG. 3, the backplates ofFIGS. 16–20are shaped to flatten or modify the power output from the entire transducer when driven over a range of frequencies such as shown inFIG. 4. Specifically,FIG. 16includes a backplate58that, for example, replaces the backplate38ofFIG. 3. A portion of the bolt39is also shown. As illustrated, the backplate58has a cut-away section60that changes the overall acoustic resonance of the transducer over frequency. Similarly, the backplate58aofFIG. 17has a curved section60athat also changes the overall acoustic resonance of the transducer over frequency.FIGS. 18,19and20similarly have other sloped or curved sections60b,60c, and60d, within backplates58b,58cand58d, 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 inFIG. 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. 27illustratively shows how standing waves are formed within one transducer69of the invention over various frequencies61,62,63. Because of the shaped surface70of the backplate59, there are no preferred resonant frequencies of the transducer69as standing waves can form relative to various transverse dimensions of the transducer69. By way of example, frequency62can represent 38 khz and frequency63can represent 42 khz.

FIG. 21illustrates still another transducer80of the invention that provides for changing the power output as a function of frequency. The front driver82and the backplate84are connected together by a bolt86that, in combination with the driver82and backplate84, compress the ceramics88a,88b. The configuration ofFIG. 21saves cost since the front driver82has a form fit aperture-sink90(the bolt head86awithin the sink90are shown in a top view inFIG. 22) that accommodates the bolt head86a. A nut86bis then screwed onto the other end of the bolt86and adjacent to the backplate84such that a user can easily access and remove separate elements of the transducer80.

The front driver82and/or backplate84(the “backplate” also known as “back mass” herein) are preferably made from steel. The front driver82is however often made from aluminum. Other materials for the front driver82and/or the backplate84can be used to acquire desired performance characteristics and/or transducer integrity.

FIG. 23shows another transducer92that includes a backplate94and a front driver96. A bolt98clamps two ceramic elements97a,97btogether and between the backplate94and driver96; and that bolt98has a bolt head100that is approximately the same size as the diameter “D” of the transducer92. The bolt head100assists the overall operation of the transducer92since there is no composite interface of the bolt98and the driver96connected to the tank. That is, the bond between the tank and the transducer92is made entirely with the bolt head100. By way of comparison, the bond between the tank and the transducer80,FIG. 21, occurs between both the bolt86and the driver82. A sloped region99provides for varying the power output over frequency such as described herein.

FIG. 24illustrates one end102of a transducer of the invention that is similar toFIG. 23except that there is no slope region99; and therefore there is little or no modification of the power output from the transducer (at least from the transducer end102).

FIGS. 15 and 16show further transducer embodiments of the invention.FIG. 25shows a transducer110that includes a driver112, backplate114, bolt116, ceramic elements118a,118b, and electrical lead-outs120. The backplate is shaped so as to modify the transducer power output as a function of frequency. The driver112is preferably made from aluminum.

FIG. 26illustrates an alternative transducer120that includes a backplate122, driver124, bolt126, ceramic elements128a,128b, and lead outs130. One or both of the backplate and driver122,124are made from steel. However, the front driver124is preferably made from aluminum. The bolt head126ais fixed within the driver124; and a nut126bis screwed onto the bolt126to reside within a cut-out122aof the backplate122. The backplate122and front driver129are sealed at the displacement node by an O-ring123to protect the electrical sections (i.e., the piezoelectric ceramics and electrodes) of the transducer120under adverse environmental conditions.

The designs ofFIGS. 23–24have 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 face112aofFIG. 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. 28shows one preferred arrangement (in a bottom view) for mounting multiple transducers140to the bottom142aof a process tank142. Specifically, the lateral spacing between transducers140—each with a diameter X—is set to 2X to reduce the cavitation implosions around the transducers140(which might erode the generally expensive tank surface142a). By way of example, if the transducer140has a two inch diameter (i.e., X=2″), then the spacing between adjacent transducers140is four inches. Other sizes can of course be used and scaled to user needs and requirements.FIG. 29illustrates, in a cross sectional schematic view, a standing wave144that is preferentially created between adjacent transducers140′ with diameters X and a center to center spacing of 2X. The standing wave144tends to reduce cavitation and erosion of the tank142′ 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. 30illustrates a closed hex spacing pattern149of transducer elements150that causes the radiating membrane151(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. 31illustrates a G-10 isolator153bonded between two of the transducers150′ (and specifically the front driver150a) and the radiating surface151′, i.e., the wall of the tank154holding the process chemistry156. The G-10153operates to further reduce unwanted surface cavitation, often times even when the closed hex spacing pattern ofFIG. 30is not possible. Piezoelectric elements155are sandwiched between the front plate150aand backplate154.FIG. 32shows an exploded side view of one of the G-10 mounted transducer150″ ofFIG. 31. Layers of epoxy160preferably separate the G-10 isolator153from the transducer150″ and from the surface152′.

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 system200ofFIGS. 33–35reduces the time for liquid preparation and accomplishes the task to a degree where shorter process times are possible.

The invention ofFIG. 33utilizes the sound fields as an upward driving force to quickly move contaminants to the surface207aof the liquid207. 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. 33shows a system200constructed according to the invention. A generator202drives a plurality of transducers204connected to a process tank206, which holds a process chemistry207. The generator202drives the transducers204from an upper frequency (fupper) to a lower frequency (flower), a shown inFIG. 35. Once floweris reached, a frequency control subsystem208controls the generator202so as to drive the transducers204again from fupperto flowerand without driving the transducers from flowerto fupper. In this manner, only decreasing frequencies are imparted to the process chemistry207; and acoustic energy210migrates upwards (along direction217), pushing contamination211upwards and out of the tank206.

As shown inFIG. 34, the two stage ultrasound processing system200can alternatively cycle the transducers204from fupperto flowerevery other half cycle, with a degas, quiet or off half cycle222between each power burst. The control subsystem208of this embodiment thus includes means for inhibiting the flow of energy into the tank206over a second half cycle so that the quiet period222is realized. It is not necessary that the time periods of the first and second one-half cycles222a,222b, respectively, be equal.

FIGS. 34 and 35also show that the rate at which the frequencies are swept from fupperto flowercan vary, as shown by the shorter or longer periods and slope of the power bursts, defined by the frequency function220.

The generator202preferably produces frequencies throughout the bandwidth of the transducers204. The generator202is 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 ofFIG. 35has 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 period222, 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 surface207aof the process chemistry207in the system ofFIG. 33is 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 ofFIG. 33incorporates a type of frequency modulation (FM) where frequency changes are monotonic from higher to lower frequencies. Transducers204mounted to the bottom of the process tank206generate an ever expanding acoustic wavelength in the upward direction217(i.e., toward the surface207aof the process chemistry207). This produces an acoustic force210which pushes contamination211to the surface207awhere the contamination211overflows the weirs213for removal from the tank206.

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 withFIGS. 3,4,5A,5B,22A,22B and22C of International Application No. PCT/US97/12853, which is herein incorporated by reference.

The variable slope of the frequency function220ofFIGS. 34 and 35illustrates that the time period between successive power up sweeps, from fupperto flower, 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 inFIG. 36, sweep down in frequency (i.e., from fupperto flower) at a relatively slow rate, typically in the range of 1 hz to 1.2 khz, and sweep up in frequency (i.e., from flowerto fupper) 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 inFIG. 37, sweep down in frequency at a relatively slow rate and shut the generator202off (such as through the control subsystem208) at periods225′ when the lowest frequency flowerin the bandwidth (bandwidth=fupper−flower) is reached. During the off time225′, a degassing period222can occur as inFIG. 34due to buoyancy of the gas bubbles; and the subsystem208resets the generator202to the highest frequency for another relatively slow rate of sweeping from fupperto flower, 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 inFIG. 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 inFIGS. 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 period222(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 fupperand flower) and, accordingly, low frequency resonances are eliminated by changing the overall rate. In such a technique, the slope of the frequency function220′ inFIG. 39, is constant, though the period of each degas period225′ changes according to some predefined function.(e) As shown inFIG. 40, sweep the rate with a combination of (c) and (d) techniques above.

Note that in each ofFIGS. 34–40, the x-axis represents time (t) and the y-axis represents frequency f.

FIG. 41shows a schematic250illustrating the most general form of generator circuitry providing both non-constant power up-sweep rate and non-constant degas period, as described above.

FIG. 42shows a system300including a generator302and transducers304that can be switched, for example, to either 72 khz or 104 khz operation. The transducers304operate to inject sonic energy305to the process chemistry307within the tank306. Because of the impedance characteristics at these frequencies, the generator302includes a constant power output circuit306that changes the center frequency output from the generator302while maintaining constant output power. The circuit306includes a switch section308that switches the output frequency from one frequency to the next with no intermediate frequencies generated at the output (i.e., to the transducers304).

A similar system310is shown inFIG. 43, where switching between frequencies does not utilize the same power circuit. InFIG. 43, the generator312includes at least two drive circuits for producing selected frequencies f1and f2(these circuits are illustratively shown as circuit (f1), item314, and circuit (f2), item316). Before the reactive components in either of the circuits314,316can be switched to different values, the output circuit318shuts down the generator312so 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 system310can 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 withFIG. 71.

FIG. 44illustrates a system400and process probe402constructed according to the invention. A generator404connects to transducers406to impart ultrasound energy403to the process chemistry407within the tank408. The probe402includes an enclosure410that houses a liquid412that is responsive to ultrasound energy within the liquid407. The enclosure410is made from a material (e.g., polypropylene) that transmits the energy403therethrough. In response to the energy403, changes in or energy created from liquid412are sensed by the analysis subsystem414. By way of example, the liquid412can emit spectral energy or free radicals, and these characteristics can be measured by the subsystem414. Alternatively, the conduit416can 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 chemistry407. The conduit416thus provides a means for monitoring the liquid412. A thermocouple420is preferably included within the enclosure410and/or on the enclosure410(i.e., in contact with the process chemistry407) so as to monitor temperature changes within the enclosure410and/or within the process chemistry407. Other characteristics within the tank408and/or enclosure410can be monitored by the subsystem414over time so as to create time-varying functions that provide other useful information about the characteristics of the processes within the tank408. For example, by monitoring the conductivity and temperature over time, the amount of energy in each cavitation explosion may be deduced within the analysis subsystem414, 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 inFIGS. 45 and 46, it is possible to have two ultrasound tanks420,422, both having the same input power (i.e. watts per gallon) but each having very different ultrasound activity characteristics. The first tank420might have relatively few high energy cavitation implosions420awhile the second tank422has many low energy cavitation implosions422a(specifically,FIGS. 45 and 46show cavitation implosions420a,422aduring a fixed time period in the two tanks420,422having 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. 47thus illustrates one probe650of the invention which permits the calculation of these important parameters. Specifically, the probe650measures 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 probe650is similar in operation to the probe402ofFIG. 44and includes a fixed sample volume of aqueous solution652(or other chemistry that changes conductivity in an ultrasound field) contained in the probe tip650a. The probe tip650ais designed to cause minimal disturbance to the ultrasound field (e.g., the field403ofFIG. 44). Accordingly, the probe tip650ais 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 probe650thus includes, within the probe tip650a, two electrodes654,656to measure conductivity, and a temperature measuring probe (e.g., a thermocouple)658to monitor the temperature of the fixed mass of aqueous solution652. These transducers654,656and658are 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 wires670out of the probe650to 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, C0, 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 liquid652, the volume (V) of the liquid652(in cubic centimeters), the mass (m) of the liquid652(in grams), and the functional relationship n=f(C,C0) between conductivity and the number of cavitation implosions occurring in the probe tip650ain 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,C0)/V(a)
energy in each cavitation implosion=E=(0.00833)(p)(m)(g(t′))V/f(C,C0)/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. 48shows a complete system675for monitoring and processing data from such a probe650′ and for modifying applied ultrasound energy676applied to the process chemistry678. Specifically, the system675monitors the parameters discussed above and, in real time, controls the generator680to adjust its output drive signals to the transducers682at the tank684. The data collection instrument685connects to the wiring670′ which couples directly to the transducers within the probe tip650′. The instrument685generates 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 comparators686a,686band686c. The comparators686a–care 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 tank684and chemistry678. The results from the comparators686are input to the control system690, which controls the generator680(those skilled in the art should appreciate that the controller690and generator680can be, and preferably are, coupled as a single unit).

The energy in each cavitation implosion decreases as the frequency of the ultrasonics676increases and as the temperature of the solution678increases. 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 comparators686, the center frequency of the generator680is increased (by the controller690receiving 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 solution678is increased by the control system690until 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 tank684increases. Therefore, the cavitation density measurement fed back to the generator680is 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 controller690receiving 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 output692. Therefore the measured cavitation density as a function of time is measured and the generator's AM pattern is adjusted (via the controller690receiving data at the “AM Control”) until the measured function equals the optimum function.

FIG. 49–51illustrate 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 Japan208 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 ofFIGS. 49–51eliminates 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.

InFIG. 49, an ultrasound generator500is shown connected to a 300 VDC source501. A power factor correction (PFC) circuit502connects to the front end of the generator500to produce a regulated 300 VDC. A switching regulator504regulates the 300 VDC to +12V and +15V. The generator500can be represented, for example, as the circuit ofFIG. 41, except that the “high voltage supply” is replaced by the PFC circuit502and the +12V and +15V are replaced with control voltages from the regulator504.

FIG. 50illustrates a generator510connected to a universal input switching regulator512. The regulator512generates a set513of DC voltages for the generator510. The generator510includes circuitry514that operates with the set513. The generator510can be represented, for example, as the circuit ofFIG. 41, except that the “high voltage supply” and the +12V and +15V are replaced with output voltages from the regulator512.

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 withFIGS. 3,4,5A,5B and7of 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. 51illustrates a generator530which operates at a DC voltage less than or equal to (86)(√2) volts. As in amplitude control, a triac532is used to select that portion of the power line voltage with an amplitude equal to the generator DC voltage requirements. The signal534is rectified and filtered by the bridge rectifier and filter536to obtain the constant DC voltage538in the range less than or equal to (86)*(Square Root 2) volts. The generator530can be represented, for example, as the circuit ofFIG. 41, except that the “high voltage supply” is replaced by the voltage from the bridge rectifier and filter536and the +12V and +15V are replaced with output voltages from the regulator540, 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. 52illustrates an AM (amplitude modulation) pattern600of the invention, where the frequency of the AM is constantly decreasing with increasing time t. More particularly, ultrasound bursts of energy (as shown inFIG. 53, with a frequency f) are contained within each of the non-zero portions600aof the pattern600. 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 ofFIG. 53varies with a power up sweep, from fupperto flower, as discussed above.

FIG. 54shows a plot610of AM frequency verses time t. As shown, the AM frequency monotonically changes from a high frequency, fhigh, to a low frequency, flow. When flowis reached, a degas or quiet period612is typically introduced before the cycle614repeats.

Note that the sweep rate of the change of the AM frequency along the slope616can and preferably does change at a non constant sweep rate. The rate of AM frequency change can thus be non-constant. The degas period612can also be non constant. The degas period612can 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 periods600b,FIG. 52, where the amplitude is zero); or both parameters can be changed simultaneously.

FIGS. 55,56and57schematically 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. 58illustrates a QDR tank800modified in accord with the invention to speed up the rate of liquid removal from the tank. The large valve output802is connected to a vacuum reservoir804that is evacuated to a pressure below atmospheric pressure during the cleaning cycle. When the valve802is opened to dump the liquid702″, the difference between atmospheric pressure and the pressure in the vacuum vessel806forces the liquid702″ out of the tank800, 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'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. 59shows a transducer850constructed according to the invention which reduces this impracticality.

InFIG. 59, the transducer850is shown connected to an ultrasound processing tank852, which holds process chemistry854. The transducer includes two piezoelectric elements856that are compressed between the backplate858and the tank852. Specifically, a bias bolt860connects through the transducer850and connects directly into a weld861at the tank852. Accordingly, there is no front plate; and thus the transducer length “L” can be divided between the piezoelectric elements856and the back mass858. This division makes it possible to make a stacked transducer850with a higher fundamental frequency (and higher harmonics too).

Another configuration of the transducer inFIG. 59uses one piezoelectric element856in the center of the stack and an insulating ceramic front driver or quartz front driver between the piezoelectric element and the tank852. Another configuration ofFIG. 59also replaces back mass850with a ceramic back mass. These transducers of theFIG. 59type 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 ofFIG. 60illustrates a transducer900constructed according to the invention and shown in an exploded view. The transducer900has “double compression”, as discussed below, to increase its reliability over the prior art. Specifically, the bias bolt904has a through-hole902in its center. The center hole902receives a second bolt906that is welded to the surface of the tank908(illustrated by weld joint910). When integrated, the second bolt906protrudes out past the tail mass927(i.e., the backplate) of the transducer900by way of a Belleville disc spring washer912and nut914, which screws onto bolt906.

As in other transducers herein, the transducer900includes piezoelectric ceramics916, associated electrodes918, and lead-outs920for the electrodes918.

The bias bolt904thus provides the first compressive force similar to other transducers herein. That is, the bolt904slides through the front driver922via the through-hole924, and continues on through the ceramics916. The back mass910has threads910awhich mate with the bolt904; and thus the bolt904screws into the back mass910. By tightening the bolt904into the back mass910, the bolt904firmly seats into the counter-sink922aof the front plate922and compression is applied to the ceramics916.

As an alternative, the threads in the back mass910can be thru-holed; and a nut against the back mass can replace the threads to support compression bias on the piezoceramic916.

The second compressive force derives from the operation of the second bolt906, which compresses the epoxy926after seating within the counter-sink904aof the first bolt904and after tightening the nut914onto the bolt906. The front driver922is then bonded to the tank908via an epoxy layer926. The second compressive force keeps a compressive bias on the epoxy926bond between the front driver922and the tank surface908.

As an alternative, it is possible to eliminate the Belleville disc spring washer912and rely entirely on the spring tension in the second bolt906; but the added feature of the Belleville disc spring washer912provides a larger displacement before tension goes to zero.

The second compressive bias of transducer900provides at least three improvements over the prior art. First, during the epoxy curing process, the bias keeps force on the epoxy bond926(even if the epoxy layer thickness changes during a liquid state) resulting in a superior bond. Second, during operation of the transducer900, the reliability of the bond926is 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 transducer900provides increased reliability when mounted with most any surface, and not simply an ultrasound tank908.

FIG. 61shows a cross-sectional view of a conventional stacked transducer1000with a bias bolt1002that screws into threads1004in the aluminum front driver1006. The threads1004are only within the top portion1006aof the front driver1006. The transducer includes the normal piezo-ceramics1007, electrodes1008, and rear mass1009.

FIG. 62shows an alternative transducer1010constructed according to the invention. In transducer1010, the threads1012within the front driver1014are at bottom portion1014aso that bias pressure is not concentrated on the top threads (as inFIG. 61) where the surface of the aluminum can be deformed in operation, decreasing bias pressure. The elements1002′,1007′,1008′ and1009′ have similar function as inFIG. 61; except that they are sized and shaped appropriately to accommodate the thread repositioning at the bottom1014aof the driver1014.

FIG. 63illustrates a transducer1020that is similar to the transducer1010,FIG. 62, except that a helical insert1022is used instead of the threads1012. The helical insert1022is preferably made from steel and will not plastically deform under normal transducer stresses. The helical insert1022thus prevents distortion of the aluminum driver1014′ under the normal stresses of the transducer1020. Note that the helical insert can similarly replace the threads1004of the prior art transducer1000to provide similar advantages in preventing distortion.

FIG. 64illustrates a side view of one embodiment of the invention including a printed circuit board (PCB)1030connected with ultrasound transducers1032such as described herein (including, for example, piezoelectric ceramics1034). The PCB1030contains circuitry and wiring so as to function as an ultrasound generator and for the electrodes of the transducers1032. As such, the PCB1030can drive the transducers1032to produce ultrasound1036when powered. By way of example, the PCB1030can include the circuitry ofFIGS. 41A,41B and41C.

The PCB1030and transducers1032are 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. 65shows a top view of the PCB1030ofFIG. 64. For purposes of illustration, the top surface1030aof the PCB1030is shown with electrodes1038for the positive side of the piezoelectric ceramic1034. The electrodes1038are preferably connected by wiring1048(e.g., circuit board land patterns) to provide for common voltage input to the transducers1032. There is a similar electrode pattern on the bottom side (not shown) of the PCB1030that makes contact with the transducer's front driver1032b, which is in electrical contact with the bias bolt1032a(FIG. 64). The bolt1032aconnects through the transducer1032and into the back mass1032c, providing electrical feedthrough to the negative electrode of the piezoelectric ceramic1034. The PCB1030thus provides two electrodes for each transducer1032and all the interconnect wiring for the transducers1032such as by etching the PCB pattern. The ultrasound generator is also provided with the PCB1030circuitry (illustrated by circuit board components1040) with its output connected into the transducer electrodes as part of the PCB artwork.

FIG. 66illustrates an acid resistant transducer1050with 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 transducer1050ofFIG. 66resolves this problem by eliminating the metal masses and the bolt. The compressive force on the piezoelectric ceramic1058is obtained by an epoxy1052that contracts upon curing. The metal “back mass” and the metal “front driver” such as described above are replaced by a non-metallic material1060. InFIG. 66, the front driver1060aand back mass1060bare thus both made from a non-metallic material such as quartz.

The internal piezoceramics1058connect to wiring to drive the elements1058in the normal way. To protect the wiring and ceramics, it can be made from Teflon which is soldered to the ceramic1058by known methods, such as illustrated by solder joint1064. This transducer will be referred to herein as the “acid transducer type construction”.

FIG. 67illustrates a generator circuit2000used to implement power up-sweep such as described herein (e.g., such as described in connection withFIGS. 41A,41B and41C, except thatFIGS. 41A,41B and41C uses IGBTs as the switching devices andFIG. 67uses MOSFETs). InFIG. 67, circuit2000includes a capacitive element2012with terminal2012aconnected to earth ground2015a. The other terminal2012bconnects to terminal2040bof inductor2040. Terminal2040aof inductor2040connects to terminal2013aof the secondary2013cof transformer2013. Terminal2013bof secondary2013cconnects to earth ground2015b. The circuit2000includes two drive networks2018and2020, and a controller2022.

Drive network2018includes a blocking network2028and a multi-state power switch network2030, which is coupled to the controller2022by way of line2022a. The drive network2020includes a blocking network2032and a multi-state power switch network2034, which is coupled to the controller2022by way of line2022b.

In drive network2018, the blocking network2028and switch network2030provide a unidirectional current flow path characterized by a first impedance from the potential +V through the first primary winding2013d1of center-tapped primary winding2013dof transformer2013when the switch network2030is in a first (conductive) state. The networks2028and2030provide an oppositely directed current flow path characterized by a second impedance from circuit ground2023athrough2013d1to the potential +V when the switch network2030is in a second (non-conductive) state. The first impedance of the flow path established when network2030is in its first state is lower than the second impedance of the flow path established when the network2030is in its second state.

In drive network2020, the blocking network2032and switch network2034provide a unidirectional current flow path characterized by a third impedance from the potential +V through the second primary winding2013d2of center-tapped primary winding2013dof transformer2013when the switch network2032is in a first (conductive) state. The networks2032and2034provide an oppositely directed current flow path characterized by a fourth impedance from circuit ground2023bthrough2013d2to the potential +V when the switch network2034is in a second (non-conductive) state. The third impedance of the flow path established when network2034is in its first state is lower than the fourth impedance of the flow path established when the network2030is in its second state.

The impedance (Z) of drive network2018when switch network2030is in its second state may be primarily determined by resistor2028b(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 network2020when switch network2034is in its second state.

Where the circuit2000is adapted to drive an ultrasound transducer, the capacitive element2012may be an electrostrictive device suitable for use as an ultrasound transducer. With such a configuration, for example, the controller2022may effectively control the circuit2000to drive such ultrasound transducers at a selectively controlled frequency. In various forms of the invention, the controller2022may 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 controller2022cyclically switches the switch network2030between its first and second states at a frequency f (f=1/T), where f is less than or equal to fr(fr=1/Tr), where fris the resonant frequency of the series LC network formed by2012and2040, approximately equal to 1/(2*PI*Square Root(LC)), where PI is approximately 3.14159. During each cycle, network2030is controlled to be in its first state for a period greater than or equal to Tr/2, but less than or equal to T/2, at the beginning of each cycle. Network2030is controlled to be in its second state for the remainder of each cycle.

Similarly, the controller2022also cyclically switches the switch network2032between its first and second states at the frequency f (f=1/T). During each cycle, network2032is controlled to be in its first state for a period greater than or equal to Tr/2, but less than or equal to T/2, at the beginning of each cycle. Network2032is 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 network2030is offset by T/2 from the start time for each cycle of the switching of network2034. In other forms, the start time for the cycle of the switching network2030may be offset by at least Tr/2 and less than Tr/2+D, where D equals T−Tr.

An AC voltage waveform (V0) at frequency f is impressed across the capacitive element2012. Generally, this voltage waveform V0passes from low to high and from high to low with a sinusoidal waveshape (at frequency fr). 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−Tr), 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 V0remains at that level (except for droop due to resistive losses) for a period ½(T−Tr), or D/2, before again passing to the high peak level.

Thus, the voltage impressed across capacitive element2012rises and falls at the resonant frequency frwith the capacitive element2012being maintained in its fully charged state for a “dead” time which is adjustably dependent upon the switching frequency f of the controller2022. Accordingly, the drive frequency to the element2012may be adjustably controlled.

Where the element2012is an ultrasound transducer, circuit2000is 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 network2028includes a diode2028ain parallel with a resistor2028b, and the blocking network2032includes a diode2032aand a resistor2032b. The single inductor (L)2040operates in resonance with the element2012.

Circuit2000is 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 element2012and transformer2013function like the circuit ofFIG. 41, except that circuit2000utilizes FETs instead of IGBTs (insulated gate bipolar transistors) for the terminal power switching devices. The power devices2030,2034are also connected to circuit ground, eliminating the need for separate isolated power supplies, reducing the cost of the generator.

In another implementation of circuit2000,FIG. 67, the inductor2040is not a separate component, but rather is incorporated into the transformer2013by way of leakage inductance. This leakage inductance performs the same function as inductor2040and the leakage inductance is controlled by the coupling of transformer2013, e.g., by setting a gap in the transformer's core as is known in the art. This circuit of theFIG. 67type is referred to herein as the “zero current switching inverter circuit”.

With further reference toFIG. 43, one embodiment of the invention couples multiple generator frequencies to a common tank306′ and transducers304′.FIG. 68schematically shows additional switch circuitry corresponding and connecting to a different generator frequency, e.g.,2104afor 40 khz,2104bfor 72 khz,2104cfor 104 khz, and2104dfor 170 khz). Which ever generator thus connects to the 24 VDC supply between pins “1” and “2” on its corresponding remote connector2104will drive the common process tank, as shown inFIG. 69. The generators can have a remote on/off relay in the form ofFIG. 70, which illustrates coupling between a Deltrol relay and the remove relay. The connector-to-tank wiring is further illustrated inFIG. 69. InFIG. 69, each generator within the system connects to each of the plurality of transducers2106within the tank; though only one generator actively drives the transducers2106depending upon the position of the switch2102.

In operation, power is applied to one generator (e.g., the 40 khz generator coupled to remote connector2104a) via the 24 VDC signal from the rotary switch2102. The following sequence then occurs with respect toFIGS. 58–60:2098compatible with this embodiment. InFIG. 68, a common 24 VDC supply2100couples to a user-selectable switch2102(e.g., a rotary switch) to provide drive energy to remote connectors2104a–d(each connector2104

If the rotary switch2102is 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):

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 thegenerator or power module to thetransducers and turns the generator onPin#2return for 24 VDC signal, can be groundedPin#3anode of LED to indicate RF current flowPin#4cathode 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#1red; Pin#2green; Pin#3blue; and Pin#4white.

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 outputSocket #2: not usedSocket #3: +RF outputSocket #4: −DC test pointSocket #5: −RF output, groundSocket #6: cable shield, groundSocket #7: +DC output interlockSocket #8: +DC input interlockSocket #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 redPin#3: +RF output redPin#5: −RF output green/yellow

All pin#5s can for example be wired together and connected to the −RF transducer lead. All pin #1's are then connected together and connected to the +RF transducer lead coming from one-half of the transducers. All pin #3'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. 71schematically shows a multi-generator system3000used to drive common transducers3002. One advantage of the system3000is that multiple generators3004can alternatively drive the transducer3002; and it is assured that no two generators operate simultaneously. Each generator3004preferably represents a different drive frequency. Generator3004arepresents, for example, the generator set forth by circuitry ofFIG. 41(except that preferably, a ½ second delay is installed into circuit250by adjusting capacitor3006to one microfarad instead of 1/10 microfarad, which provides only 50 milliseconds delay). The relays3008a,3008bfor example can be implemented similar to the relay schematic ofFIG. 70.

The rotary switch3010(e.g., similar to the switch2102,FIG. 68) permits user selection between any of the generators3004. Generator3004bcan thus be switched in to drive the transducer3002with a different frequency. Those skilled in the art should appreciate that additional generators3004c,3004d, can be installed into the system3000as desired, with additional frequencies. Those skilled in the art should appreciate that the rotary switch3010can 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. 72Ashows a diagram of a multiple frequency cleaning system10constructed according to the present invention. A signal generator12(also referred to herein as ‘generator’) connects via electrical paths14,15,16to a transducer array consisting of paralleled transducers17,18,19. The transducer array is driven by the generator12to produce multiple frequency sound waves26in liquid22which is contained in tank20. Tank20is 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 liquid22is an aggressive chemistry that will degrade or erode 316L stainless steel.

FIG. 72Bshows a graph of the sound intensity produced by the transducer array verses the frequency of the sound. BW121is a first frequency band of frequencies produced by the transducer array and BW223is 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. 72Cshows a graph of the generator output voltage verses frequency. R125is a first range of frequencies produced by the generator, with R125being a frequency subset of BW121. R227is a second range of frequencies produced by the generator, with R227being a frequency subset of BW223.

FIG. 9shows a cross-sectional view of one transducer128constructed according to the invention; whileFIG. 9Ashows a top view of the transducer128. Two or more transducers are connected in parallel to form an array of transducers. The parallel array of transducers formed from transducers128exhibit frequency bands that are centered on 39.75 khz, 71.5 khz, 104 khz, 131.7 khz, 167.2 khz and 250.3 khz.

InFIGS. 9 and 9A, the ceramic134of transducer128is driven through oscillatory voltages transmitted across the electrodes136. The electrodes136connect to a generator (not shown), such as described above, by insulated electrical connections138. The ceramic134is held under compression through operation of the bolt132providing compressive force by way of the front driver130and the back mass139.

FIG. 73Ashows the basic schematic for a generator29built according to the invention, withFIGS. 73B,73C,73D,73E and73F showing the component details of the circuit blocks inFIG. 73A. The generator29receives AC power from the power line into filter30, the purpose of filter30is to prevent high frequency noise voltages produced by the generator from entering the AC power lines. Switch31controls the AC power to generator29and fuses32protect the system from over current conditions. Bridge diode33in combination with filter capacitor34converts the AC line voltage to a DC voltage. The power module35converts the DC voltage to the needed frequencies to drive the transducer array (not shown) as described above. The control37supplies the frequency modulation (FM) and the amplitude modulation (AM) information to the power module35. The output power circuit38measures the power delivered to the transducer array and supplies this information to the output power regulator39. The output power regulator39compares the signal from output power circuit38with the desired output power supplied through pin5of remote connector43and supplies the difference information to control37so the AM can be adjusted to make the actual output power substantially equal to the desired output power.

InFIG. 73ABNC connector44supplies the FM information to other generators (often called power modules) that need to be synchronized with this generator29for the purpose of eliminating beat frequencies. Terminal41serves as a junction connection for the power output lines. Transformer40isolates the generator29from the transducer array and output connector42supplies the output drive signals to the transducer array.

FIGS. 73B and 73Cshow in schematic form the component details of control37. VCO (voltage controlled oscillator) U13produces a triangle wave at output pin8that sweeps the sweep rate signal generated by VCO U8. Besides generating the sweep rate signal, U8also 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 U14generates two times the needed drive frequency from the sweeping information produced by U13and U8and from the binary code supplied to P3and P4inFIG. 73C. The specific binary code and center frequencies (after the U11:B divide by two flip flop) for the component values shown inFIGS. 73B and 73Care when P3,P4are 1,1 the center frequency is 39.75 khz, when P3,P4are 0,1 the center frequency is 71.5 khz, when P3,P4are 1,0 the center frequency is 104 khz and when P3,P4are 0,0 the center frequency is 167.2 khz. The series string of resistors consisting of RV40, R40, RV72, R73, RV104, R105, RV170and R171determine the center frequency of the signal from pin7of U14by responding to the binary code. For example, when P3,P4are 1,1 output pin3of gate U10:A is an open circuit, output pin5of gate U9:B is an open circuit and output pin3of gate U9:A is an open circuit. This results in the total series string of resistors RV40, R40, RV72, R73, RV104, R105, RV170and R171being connected to pin4of U14and this produces the center frequency two times 39.75 khz. As a second example, when P3,P4are 0,1 output pin3of gate U10:A is an open circuit, output pin5of gate U9:B is an open circuit and output pin3of gate U9:A is a short circuit. This results in the resistors RV40and R40being shorted out and now the series string of resistors RV72, R73, RV104, R105, RV170and R171are connected to pin4of U14and this produces the center frequency two times 71.5 khz. As a third example, when P3,P4are 1,0 output pin3of gate U10:A is an open circuit, output pin5of gate U9:B is a short circuit and output pin3of gate U9:A is a open circuit. This results in the resistors RV40, R40, RV72and R73being shorted out and now the series string of resistors RV104, R105, RV170and R171are connected to pin4of U14and this produces the center frequency two times 104 khz. And lastly as a forth example, when P3,P4are 0,0 output pin3of gate U10:A is a short circuit, output pin5of gate U9:B is a open circuit and output pin3of gate U9:A is a open circuit. This results in the resistors RV40, R40, RV72, R73, RV104and R105, being shorted out and now the series string of resistors RV170and R171are connected to pin4of U14and 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 R31which is connected to U14pin4. The current into R31is a result of the sweeping of the sweep rate signal produced by VCOs U13and U8as described above. U11:B divides by two the frequencies produced by U14and this is inverted by U6D, U6E and U6F before being output to J6C for connection to the power module35as shown inFIG. 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 inFIGS. 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 control37that generates an AM signal on J6D which is output to the power module35for 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 P5. This voltage feeds the plus input to operational amplifier U16that compares this voltage to the ramp voltage on the operational amplifier's minus input. The ramp is formed by RV1, R18and C5and it is reset by U10B. When the ramp voltage exceeds the voltage level on P5, the output of the operational amplifier U16changes from +12 VDC to zero, this ripples through four gates that invert the signal four times and therefore a zero is on J6D which terminates the sound burst at the correct time to control the power to the level specified by the voltage on P5. 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 U12to a zero. A change in the binary code to P3or P4inFIG. 73Ccauses a transition time zero to occur on input pin3of U12. A 12 to 50 VDC signal on P7causes a zero on pin11of U12for the insertion of a quiet time, degas time or off time. Zero inputs to the appropriate inputs of U12are also the way fault signals shut down the generator. A low voltage on the power lines causes Schmitt trigger U1A pin1to go low which results in a zero on pin10of U12. An over temperature condition is sensed by U3and it puts out a zero to pin4of U12when this over temperature condition occurs. The generator is allowed to assume all the correct logic states by the delayed start hold off caused by R20and C26.

FIG. 73Chas 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 theFIG. 73Cschematic section of control37by any transition on the binary input lines P3and/or P4causing a transition on at least one of the monostable multivibrators U22A, U22B, U23A or U23B producing an output pulse the length of the degas time. This pulse travels through U7and feeds pin3of U12inFIG. 73B(sheet 1 of 2) where the AM is shut down for the length of the degas pulse.

FIG. 73Dis a schematic of the power module35. The front end logic consisting of U5, U6, U7and U11accepts and synchronizes the FM and AM signals from the control37. The power section of power module35converts 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. 73Eis a schematic of the circuit that measures the output power of the generator29. This output power circuit38senses 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 J6R as a voltage signal scaled to 100 watts per volt.

FIG. 73Fis a schematic of the output power regulator39. A voltage (Vd) representing the desired output power is input to P5C. This is compared to the voltage (Va) representing the actual output power on JR6(which came from the output of the output power circuit38as shown inFIG. 73A). If Vd is higher than Va, the voltage output on P5increases 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 P5is decreased until the actual output power becomes substantially equal to the desired output power.

FIG. 74is the system10inFIG. 72Awith a probe51sensing the sound characteristics in the tank to form the feedback system50ofFIG. 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 interfacing52signals are sent to the remote connector on generator53to modify the output drive to transducer array54. In the most sophisticated applications, the interface52is a PLC (programmable logic controller) or a computer that is properly programmed.

The system70inFIG. 75has a PLC or a computer71that is programmed to control and set the parameters for generator72. The programmed parameters are output by the generator72to drive the transducers74which put sound with the programmed characteristics into tank73.

FIG. 76shows the addition of quiet times81into a typical AM pattern80of this invention. The invention produces continuously changing sound at frequencies in a first range of frequencies82before jumping to frequencies in a second range of frequencies83. Quiet times81are inserted into the continuously changing signal produced by the generator within a frequency range to break up the signal into smaller bursts of sound85for the purpose of optimizing certain processes such as the development of photosensitive polymers.

FIG. 77shows the addition of a PLL96(phase lock loop) to the generator95for the purpose of making adjustments to the center frequency of each frequency range to track changes in the resonance of the transducer array97. The PLL96senses the current between line98and line99and the PLL senses the voltage between line99and ground93. The PLL generates a frequency on line94that feeds the generator95VCO 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 inFIG. 78A. The method consists of specifying changing digital numbers into a DAC90(digital to analog converter) and then driving a VCO91with the output of the DAC. The VCO91produces the changing frequencies in response to the changing digital numbers.FIG. 78Bshows a typical staircase sweeping frequency output that can result from this circuitry. If the time at each level92is 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 level92is 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. 78Cshows an example of a random staircase function that can be produced by the circuitry represented inFIG. 78Aby inputting random or chaotic digital numbers into the DAC90.FIGS. 78A,78B and78C 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 ofFIG. 78Afor the changes in the frequency range and using the digital number input to the series string of resistors as shown inFIG. 73Bto 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. 78Bis 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 inFIG. 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's output voltage instead of the duty cycle. One way to accomplish this is by replacing the DC power supply inFIG. 73Aconsisting of bridge diode33and capacitor34with a modified PFC (power factor correction) circuit100as shown inFIG. 79. The operation of PFC circuits is well known to people skilled in the art, the modification to the PFC circuit100consists of the addition of R1, R2, R3and Q1to form an input that will allow the adjustment of the regulated output voltage of the PFC circuit100. In operation, the control line P5from the output power regulator39inFIG. 73Ais connected to the input of PFC circuit100inFIG. 79. If more power is needed, the control line rises in voltage causing the PFC circuit100to regulate at a higher output voltage causing the generator29to 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 inFIGS. 73A to 73Fis 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. 80shows a schematic representation of a view of a conduction line20from a power section of an ultrasound generator.FIG. 81shows a box representation of a “parallel structure”. As used herein, a parallel structure refers to a modification circuitry26and an AC switch25with a control23where the two leads of the modification circuitry26are connected in parallel to the AC switch25. The “parallel structure” is connected into the conduction line20of 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 switch25is comprised of a triac, lead number1of the modification circuitry26is connected to triac terminal MT1. Lead number2of the modification circuitry26is connected to triac terminal MT2. The triac gate is connected to the control23. In cases where the modification circuitry26contains active components, the additional control leads of these active components are also connected into the control23. In cases where the AC switch25is a configuration containing more than one active component, the leads of each of the active components are driven by control23, with proper isolation between the separate control lines where necessary.

FIG. 82shows a schematic view of two nodes27and28in the power section of an ultrasound generator.FIG. 83illustrates a “series structure”. As used herein, a “series structure” refers to a modification circuitry33and an AC switch34in which the two leads of the modification circuitry33are connected in series with the leads of an AC switch34. This series structure is connected between two nodes in the power section of an ultrasound generator as shown inFIG. 83. A control29is present to turn on and off the AC switch34. When the AC switch34is comprised of a triac, the leads are the MT1and MT2terminals of the triac. The third lead is the gate of the triac or AC switch34and is connected with the control system29. In cases where the modification circuitry33contains active components, the additional control leads of these active components are also connected into the control circuitry29. In cases where the AC switch34is a configuration containing more than one active component, the leads of each of the active components are driven by control29, with proper isolation between the separate control lines where necessary.

FIG. 84illustrates the use of a triac circuit in a preferred embodiment of the invention as depicted inFIGS. 80 and 81. The triac circuit, ofFIG. 84, is used to modify the output of a multiple frequency ultrasound generator. In particular, the modification circuitry is comprised of five capacitor passive components19,36,38,40, and42and associated triacs35,37,39,41, and43. 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 inFIG. 84. The ultrasound transducer array is connected between the +RF and GND terminals.FIG. 84also contains a more complex parallel structure defined by the modification circuitry formed by capacitors19and36and triac37in parallel with the AC switch, triac35.

The first structure44defined inFIG. 84is formed by capacitor19and triac35. This first structure44is a parallel structure and is connected in the conduction line that typically connects −RF to GND. Thus, when triac35is off, the capacitor19is inserted between −RF and GND. When triac35is on, capacitor19is shorted out which effectively connects −RF to GND. The practical effect of this first structure44is to place capacitor19in series with the transducer array when triac35is off and to connect the transducer array directly to the ultrasound generator when triac35is on. This arrangement is useful when generating the highest frequency in a multiple frequency ultrasound generator.

Capacitor36and triac37demarcate the second structure45inFIG. 84. This second structure45is a series structure and is connected between the nodes labeled −RF and GND. Thus, when triac37is on, capacitor36is inserted between −RF and GND. The reverse effect can be seen when triac37is off. When capacitor36is open circuited, capacitor36is effectively removed from the circuit. The practical effect of this second structure45is to place capacitor36in series with the transducer array when triac37is on. Assuming triac35is off, it will increase the capacitance, in series with the transducer array, to capacitors19and36. 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 structure46which is an active/passive modification circuitry comprising capacitors19,36and triac37. This modification circuitry is in parallel with triac35to form the third structure46, which is a parallel structure. The practical effect of this third structure46is to connect the ultrasound generator output directly to the transducer array when triac35is on. When triac35is off, it will place a capacitance in series with the transducer array (either capacitor19or19plus36depending on the state of triac37) when triac35is off. This is useful when generating lower frequencies in a multiple frequency ultrasound generator, because when triac35is on, it eliminates the higher frequency structures from the system.

The fourth structure47present, as shown inFIG. 84, is comprised of capacitor38and triac39, which form a series structure. When triac39is on, capacitor38is inserted between +RF and GND. In the case of triac39being off, capacitor38is open circuited, which effectively removes capacitor38from the circuit. The practical effect of this fourth structure47is to place capacitor38in parallel with the transducer array when triac39is 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 structure48, as shown inFIG. 84, comprises capacitor40and triac41. The fifth structure48has 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 triac41). 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 structure49, as shown inFIG. 84, is comprised of capacitor42and triac43. The sixth structure49is another series structure, which increases or decreases the capacitance in parallel with the transducer array depending of the state of triac43. 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 triacs35to43can be controlled individually, as are the gates as depicted inFIG. 86. However, as shown inFIG. 84, the gates for triacs35and41are controlled by the same signal50. Similarly, the gates for triacs37and39are controlled by the same signal51. Finally, the gate for triac43is controlled independently by signal52. 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 triacs35and41are identical. The same is true for the gates of triacs37and39. The signals from50,51and52come from the control circuitry as depicted inFIGS. 85A and 85B.

TheFIGS. 85A and 85Billustrate a control circuit for the circuits inFIG. 84. InFIG. 85A, the inputs54and55accept a binary code to determine the state of the triacs inFIG. 84. The logic inFIG. 85Bdecodes the binary code to generate the gate drive signals for the triacs inFIG. 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 line63inFIG. 85Agoes 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 inputs54or55is changed, one or more of the monostable multivibrators56,57,58or59triggers a high level output for approximately 37 milliseconds. These outputs proceed into NOR gate60and lower the voltage to the generator control line63for 37 milliseconds. The time the generator control line63is 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 multivibrators56,57,58, or59will 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 combination61or by resistor and capacitor combination62or 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 D2) and that it and the triac zero gate signal (referred to herein as D1) be concurrent for a time equal to or greater than the triac turn off time. The logic inFIG. 85Bdecodes the signals in a way that is well known to those familiars with NAND and invert logic. The gate signals are output onto50,51and52, as shown inFIG. 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 inFIGS. 85A and 85Bis (P1, P2)=(0,0) for the highest frequency, (P1, P2)=(1,0) for the second frequency, (P1, P2)=(0,1) for the third frequency, and (P1, P2)=(1,1) for the fourth frequency.

FIG. 86depicts another preferred embodiment of this invention. The output frequency of an ultrasound oscillator10is changed by the addition of three series structures (78,79, and80) to the output of the oscillator. The first series structure78consists of capacitor83aand triac83b. The second series structure79consists of capacitor84aand triac84b. Finally, the third series structure80consists of capacitor85aand triac85b. A controller12turns the oscillator10on and off by way of isolated lines72and73. 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 controller12also turns the triacs,83b,84band85b, on and off by way of lines74,75and76. Lines74,75,76are functionally similar to50,51and52fromFIG. 85Bof this application. The controller12can contain circuitry similar toFIGS. 85A and 85B, so as to provide the turn off and on signal to the triacs, as shown inFIG. 86. An alternative to control function12ofFIG. 86is depicted inFIG. 87.

When the capacitance of the transducer77is defined to be a capacitance value77, then with all the triacs in their off state, oscillator10produces a frequency approximately equal to f1where

When triac83bis turned on by the controller12, thereby putting a high level on line74during operation of the oscillator (while maintaining the high level on line74or while

f2=12⁢π⁢(L1⁡(83⁢a+81+77))
maintaining the current flow through triac83bor maintaining both of these conditions, i.e., maintaining the on state of triac83b), the oscillator changes frequency from the above value to approximately f2, where
Therefore, the oscillator frequency made a step change from frequency f1to a lower frequency f2.

In a similar fashion, when triac84bis then turned on by the controller12, thereby putting a high level on line75during operation of the oscillator (while maintaining the on state of triacs83band84b), the oscillator changes frequency from the above value to approximately f3, where

f3=12⁢π⁢(L1⁡(83⁢a+84⁢a+81+77))
Therefore, the oscillator frequency made a step change from frequency f2to a lower frequency f3.

In a similar fashion, when triac85bis then turned on by the controller12, thereby putting a high level on line76during operation of the oscillator, the oscillator changes frequency from the above value to approximately f4, where

f4=12⁢π⁢(L1⁡(83⁢a+84⁢a+85⁢a+81+77))
Therefore, the oscillator frequency made a step change from frequency f3to a lower frequency f4.

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 controller12to output a short circuit between lines72and73to turn the oscillator10off before the triacs83b,84band85bcan be turned off. In a preferred embodiment, the controller12turns 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 f1to the lowest frequency f4can 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 inFIG. 87.

It is clear to those skilled in the art that the circuit inFIG. 86can produce other frequency cycles. With three series structures (78,79,80) having unequal values for capacitors83a,84aand85a, a total of eight different frequencies are possible. The three listed above and

Any permutation of these eight frequencies (8! or 40,320 permutations) can be organized into a cycle by the controller12and 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 controller12turning off the oscillator. However, if any frequency change occurs where one or more triacs have to be turned off, then the controller12concurrently 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. 87shows a schematic diagram of a control circuit representing the controller12ofFIG. 86. Since in the discussion ofFIG. 86above the main functional characteristics ofFIG. 87were mentioned, only a brief description of the main elements will be discussed herein below. The controller12(or101fromFIG. 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 oscillator10is sent by way of lines116and117(these lines are equivalent to lines72and73inFIG. 86). This on/off signal is generated by element115when the output is a short circuit, thereby turning off oscillator10. The component118decodes the signal to be output onto119,120and121(these lines are equivalent to lines74,75and76ofFIG. 86) which is the signal sent into the triacs (83b,84b, and85b). The element122is in charge of sending the signals to be interpreted by118and115.

FIG. 88shows that an inductive modification circuit, a resistive modification circuit and a parallel structure can also modify an oscillator10. The operation ofFIG. 88is similar to that described forFIG. 86. The control101forFIG. 88can be similar to the control shown inFIG. 87.

With reference toFIG. 88, the series structure107, comprising inductor110aand triac110b, will increase the frequency of the oscillator when triac110bis turned on. The series structure108comprising resistor111aand triac111bwill decrease the output amplitude and power when triac111bis turned on. The parallel structure109comprising capacitor112aand triac112bwill increase the frequency when triac112bis 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. 86is 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, inFIG. 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 88illustrate 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. 89Ashows an AC switch in a series transistor configuration where BJTs (one N channel BJT and one P channel BJT) are used.FIG. 89Bshows an AC switch made in a parallel thyristor configuration where SCRs are used. ThisFIG. 89Bcircuit 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. 89Cshows 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 inFIG. 90, a sweeping frequency drive signal3100that 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 signal3100jumps, 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 signal3100can 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 point3102, 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 inFIG. 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 point3104, this sweeping frequency continues from this new lower frequency. After the defined period of time (described above) at point3106, the frequency jumps to a new higher frequency (point3108) 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 point3110to point3112. 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 points3104and3106, 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 points3104and3106) via one or more frequency steps (shown in phantom); or the set of closely spaced frequencies between points3104and3106may be random frequencies (not shown).

This frequency sweeping and frequency jumping continues until striking the lowest frequency in the bandwidth (at point3110). At this point, the frequency jumps to the highest frequency in the bandwidth (to point3112), 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 inFIG. 91, a diagram4100that shows a succession of time periods with different forms of cavitation in successive time periods. In the first time period shown between points4101and4102, 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 points4103and4104, 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 points4105and4106, 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. InFIG. 91point4107to point4108is a time period of predominately transient cavitation followed by a successive time period of predominately stable cavitation from points4109to4110, demonstrating that different order to the forms of cavitation will have a beneficial effect on the process.FIG. 91ends showing between points4110and4111atime 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 inFIG. 90is 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.