Abstract:
This invention generally relates to reducing electronic noise by mechanical means, in order to improve signal quality. More specifically, this invention relates to reducing small amplitude vibrations of analog electronic circuit components, which electronically respond to mechanical movements, such as vibrations. For example, in accordance with an exemplary embodiment of the present invention, a signal-to-noise ratio is improved by gravity-restoring mechanical isolation and transmission-path evasion of signal generating, processing, transmitting, broadcasting, receiving or detecting electronics.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to provisional application No. 60/215,557 filed Jun. 30, 2000. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to filtering and reducing the transmission of undesirable vibrations and signals. More specifically, this invention relates to the filtering of undesirable vibrations and signals by a mechanical means to reduce noise in signals produced by electronic components such as audio/visual components. 
     BACKGROUND OF THE INVENTION 
     Noisy music is difficult to enjoy. Similarly, it can be difficult to view a blurry picture on a television screen or video monitor. Electronic devices designed to convey information typically have inherent noise. Generally, as used herein “noise” refers to various properties such as physical vibrations, electrical signals and the like, and similarly, to any other vibrations and/or signals which are generally undesirable and interfere with the intended operation of the device. 
     Numerous commonplace electronic devices are similarly affected by vibration. For instance, record players, radios, CD players, DVD players, microphones, amplifiers, preamplifiers, power transformers, magnetic resonance imaging equipment, high-speed cameras, and high definition televisions are all susceptible to degradation in reproducing sound and/or visual images because of the interference of vibrations. When these devices are subjected to vibration, vibrational noise can become electrical noise interfering with the intended operation of the electronic device. Often manufacturers of these devices include signal processing filters in the devices to attempt to remove these unwanted signals or noise; however, these signal processing filters may not sufficiently reduce the transmission of and interference caused by undesired signals. 
     In this respect, the effectiveness of the medium carrying the information is generally proportional to its signal-to-noise ratio; typically an amplitude or a frequency ratio, expressed in percentage of noise-to-signal level or peak. For example, analog circuitry and components generate electronic noise when vibrating. Magnetic-core displacement and capacitor-bank separation movement in a common circuit are examples of electro-magnetic field and current generation or modification. Semiconductor components are also subject to mechanical vibration sensitivity. Similarly, diodes and transistors may also be noisy. 
     However, in general, analog electronics are typically the most susceptible to vibration. This is generally because noise is additive in analog circuitry. The noisier the components of the circuit, the noisier is the circuit itself is. Large-scale circuit integration, common in modern electronics, is the enemy of signal clarity. This raises the need for noise filtering, reduction, or elimination, especially in signal transmission devices. 
     Equipment use classifies signal transmission as either external or internal. Signals are externally transmitted between equipment via electrical conductors, fiber optics or other means, such as electromagnetic field, which propagates through vacuums, solids, liquids and gases. For example, one external transmission is a typical radio with a broadcasting station and a remote tuner or receiver. Television broadcasts are similar examples. 
     Undesirable vibrations can arise from both sources within the electronic device and external sources. External vibrational sources abound in our present environment. These vibrations may be transmitted through the ground and building structures from sources such as vehicles passing on nearby roads and construction. Vibrations may also be transmitted through the air in the form of sound from sources such as airplanes, motors, and other sources of sounds. Many other sources of vibrations exist in buildings, such as the air handling systems, pumps, water running in pipes, and appliances. These vibrations combine, overlap and interfere with each other. Regardless of the original source of the external vibrations, these vibrations may be transmitted through the supporting structure to the tool or electronic device that is resting on the support structure. 
     Vibrations may also originate from within the device itself Many modern-day electronic devices contain fans and other mechanical devices which can generate various amounts of vibrations. Tape players and CDs/DVDs include motors to spin the CD/DVD or turn the tape. Many people have heard the familiar hum associated with the working of electronic equipment such as power transformers or amplifiers. 
     The internal signal transfer between electronic components or units, which does not leave the equipment, is an internal source of noise. Electronic, optical and RF transmissions, both external and internal, are further classified by waveforms and bandwidth. Narrow band RF transmission is achieved by transmitting a single frequency wave, modulated either by amplitude (AM) or by frequency (FM). Digital transmission may be either AM or FM. Digital data however are more efficiently transmitted in ultra wide band (UWB) as pulse or wavelet train, which is modulated by the pulse separation time, which is analogous to FM, but referenced as PM or pulse modulation.. 
     The modulation frequency to base frequency ratio is noise level limited. For example, one can fit more channels into a given broadcasting bandwidth if the signal-to-noise ratio of the channels are smaller. UWB broadcast is less limited by bandwidth, than by noise level to pulse amplitude ratio itself. AM, FM or PM applied in different fields based on their characteristic power need, propagation path or penetration capability. For example, AM waves can travel around the globe, but are easily distorted and decay fast. The FM transmitting and receiving antennas need to “see” each other, since FM wave travels straight, remains strong and less prone for distortion. 
     In contrast, PM waves thus need very little energy to penetrate solids, and therefore can penetrate structure such as walls. However, its transmitter and receiver are bulky and cumbersome. PM technology is emerging quickly, because it needs no precious bandwidth sharing. Regardless of its nature and type though, to be efficient, the transmissions are preferably noiseless. One way to achieve that goal is to eliminate, or at least reduce, the noise generated or strongly affected by mechanical vibrations. 
     Micro vibrations also affect semiconductor tool operations in unique ways. For example, roentgen or deep ultra violet (UV) lithographic tools mask or etch nanometer wide wires onto complementary metal oxide (CMOS), silicon, germanium or other semiconductor wafer surface. The printed integrated circuit (IC) quality is strongly affected by direct vibration of the tool&#39;s optics but also by the signal-to-noise ratio of the very fine picture. Scanning electron microscopy (SEM) and probing tools in semiconductor fabs are other examples of common micro- or nano-vibration sensitivity. Similar noise-vibration problems arise in modern biotechnology, where tweezers need to manipulate microorganisms, cells and molecules. In these, last category of complex equipment, sometimes it s hard to separate the effects of mechanical noise from electronic, optical and signal transmission noises. Nonetheless, mechanical noise reduction, however, invariably improves performance. 
     In an effort to reduce electronic and mechanical vibration within equipment, isolation of electronic devices with rubber feet, air bearings, rigid cone legs and high damping elastomeric or felt or cork pads has been attempted. Some of these vibration or noise mitigation techniques intend to reduce noise propagation pathway by cross section or by length. Some form dead-end wave-guides or echo-aside chambers. Others attempt to absorb, dissipate, convert to heat, or otherwise attenuate vibration. Still others simply provide elastic support to the chassis to limit equipment-housing resonance. 
     While these earlier attempts to reduce equipment vibrations are somewhat successful, they fall short in efficiency and even more in reducing electronic noise. They mostly damp and attenuate (shift the phase of) mechanical vibration without evading it. Unfortunately, however, they often add their own signal to the noise at characteristic frequencies. 
     Therefore, it has long been recognized that a need exists to prevent external vibrations from interfering with the operation of sensitive devices such as those mentioned above. It is well known that it is desirable to isolate the various components that make up, for example, an audio system, so that the vibrations of one component of the audio system do not interfere with the operation of other components of the audio system. Furthermore, it is desirable to reduce the vibrations that are generated internally by the electronic devices. 
     SUMMARY 
     This invention generally relates to reducing electronic noise by mechanical means, in order to improve signal quality. More specifically, this invention relates to reducing small amplitude vibrations of electronic circuit components, which electronically respond to mechanical movements, such as vibrations. For example, in accordance with an exemplary embodiment of the present invention, a signal-to-noise ratio is improved by gravity-restoring mechanical isolation and transmission-path evasion of signal generating, processing, transmitting, broadcasting, receiving or detecting electronics. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Additional aspects of the present invention will become evident upon reviewing the non-limiting embodiments described in the specification and the claims taken in conjunction with the accompanying figures, wherein like numerals designate like elements, and: 
     FIG. 1 is a cross-sectional view of an exemplary embodiment of a filter in accordance with the present invention; 
     FIG. 2 is a cross-sectional view of an alternative embodiment of a filter in accordance with the present invention; 
     FIG. 3 is a cross-sectional view of another alternative embodiment of a filter in accordance with the present invention; and 
     FIG. 4 is a cross-sectional view of still another alternative embodiment of a filter in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In accordance with the present invention, a mechanical signal filter  100  is provided to filter vibrations and reduce noise in devices supported by filter  100 . It should be appreciated by one skilled in the art, that the following description is of exemplary embodiments only and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description merely provides convenient illustrations for implementing various embodiments of the invention. For example, various changes may be made in the design and arrangement of the elements described in the exemplary embodiments herein without departing from the scope of the invention as set forth in the appended claims. 
     Thus, in accordance with an exemplary embodiment of the present invention and with reference to FIG. 1, mechanical signal filter  100  comprises a rolling bearing  150  in contact with at least two surfaces such that rolling bearing  150  may translate between the surfaces in a manner which assists in filtering noise between the surfaces. In accordance with various aspects of the present invention, the invention achieves its objectives by providing a plurality of rigid balls  150  between similarly hard and rigid corresponding circular raceways  113  in a base plate  110  and a top plate  120 . In the preferred embodiment, three balls  150  are provided. Additionally, in accordance with various embodiments of the present invention, an optional spacer  130  retains balls  150  within filter  100 . For example, with continuing reference to the non-limiting embodiment of FIG. 1, roller bearing  150  comprises a ball bearing manufactured from 440 Rc60 stainless steel. Of course, as mentioned above, other materials having similarly desirable properties now known or as yet unknown may likewise be substituted and still fall within the ambit of the appended claims. Additionally, other modifications of bearing  150  may be useful. For example, a ceramic coated or carbide bearing  150  may be mated with steel raceways  113  having ceramic linings or inserts. 
     Additionally, although rolling bearing  150  is described in various embodiments herein as a ball bearing  150  with a substantially spherical shape, in accordance with various alternative embodiments, various other configurations of rolling bearing  150  may be used. Thus, it should be appreciated that any rolling bearing that allows the two structures to translate with a substantially reduced area of contact between the touching components is within the ambit of the present invention. 
     In the presently described embodiment, signal filter  100  comprises base plate  110  and top plate  120  both of a substantially rigid nature in contact with bearings  150  such that bearing  150  may translate between base and top plates  110 ,  120 . Base plate  110  and top plate  120  each have corresponding circular and conical raceways  113   a,b  oriented around a center  101  of filter  100 . Bearings  150  reside in raceways  113   a,b . As mentioned above, spacer  130  for retaining balls  150  within filter  100  may be provided. Generally, spacer  130  is configured from Delrin® and takes the form of a circular “washer” shape around filter  100 . Of course it should be appreciated that spacer  130  may be configured from any material and the Delrin® is merely exemplary. 
     In accordance with various aspects of the present invention, base and top plates  110 ,  120  are suitably secured together during use. For example, in the present exemplary embodiment, plates  110 ,  120  are held together using a large shoulder assembly screw  140 . Additionally, a setscrew  141  may be used to stop large shoulder screw  140  at an appropriate distance to clear top plate  120  before bearing  150  hits screw  140  when filter  100  is displaced during use. Moreover, set screw  141  counter locks, securing filter  100  for shipping. Optionally, a counter bore  122  for screw  140  is provided for clearance and/or to act as a stroke limiter on the displacement of filter  100 . Similarly, a bore  131  may be provided in spacer  130  for clearing and retaining bearing  150 . 
     In accordance with the present invention, means for returning bearing  150  to a starting point within raceways  113   a,b  is also provided. That is, when no external forces are being applied to filter  100 , bearings  150  return to a rest state or starting point  102 . Although many different methods could be used to return bearing  150  to starting point  102 , in accordance with various embodiments of the present invention, the circular or conical shape of raceways  113   a,b  suitably allow gravity to return bearing  150  to starting point  102 . In these embodiments, starting point  102  is the position of lowest potential energy; i.e., the lowest point on raceways  113   a,b.    
     Additionally, as described in additional detail below, in accordance with various aspects of the present invention, bearings  150  are in substantially constant contact with raceways  113  at contact points  151 ,  152 . When a load is placed on filter  100 , bearings  150  and raceways  113  slightly indent at contact points  151 ,  152 , expanding the contact area between bearing  150  and raceways  113 , but are generally very small relative to the size of bearing  150 . 
     In accordance with various aspects of the present invention a lower raised perimeter  111  is provided on base plate  110  to aid in reducing the contact area between filter  100  and the structure upon which it rests. Similarly, an upper raised perimeter  112  may be provided on top plate  120  to aid in reducing the contact area between filter  100  and the structure which rests upon filter  100 . 
     With reference now to FIG. 2, an alternative embodiment of the present invention is illustrated. Generally, this embodiment of filter  100  is similar to that of FIG. 1, but is capable of being secured to support equipment rigidly. This exemplary embodiment is particularly suited to small equipment or for internal signal filtering in equipment, for example, to isolate electronic printed circuit boards and breadboards. 
     The present exemplary embodiment has a threaded stud  210  to attach filter  100  to the base of the equipment it is supporting. Filter  100  again generally comprises top plate  120 , base plate  110 , bearings  150  and spacer  130 . Additionally, in accordance with this exemplary embodiment, a locking screw  260  is provided for securing filter  100  to its base (e.g., a floor or table). 
     With reference now to FIG. 3, another alternative embodiment of the present invention is illustrated. Again, this embodiment of filter  100  is similar to that of FIGS. 1 and 2, but is for floor mounting and has additional dust and debris protection. This exemplary embodiment is particularly suited to carpet floor mounting and also provides echo chambers  370  for enhancing filter  100  performance. Filter  100  again generally comprises top plate  120 , base plate  110 , bearings  150  and spacer  130 . This embodiment also includes assembly screw  350  for retaining plates  110 , 120  together. Additionally, a threaded hole  360  for attachment to equipment is provided. In accordance with another aspect of the this non-limiting embodiment, a dust cap  380  for keeping the internal portion of filter  100  clear is provided. Dust cap  380  may comprise any material, and, in the present embodiment comprises  304  stainless steel. 
     With reference now to FIG. 4, still another alternative embodiment of the present invention is illustrated. Again, this embodiment of filter  100  is similar to that of FIGS. 1-3, but is modified to include an optional dust bell/kick cover  410  and wide base support plate for carpet mounting. Filter  100  again generally comprises top plate  120 , base plate  110 , bearings  150  and spacer  130 . This embodiment also has echo chambers  470 , though in this particular embodiment, echo chambers  470  are vented  415 . This embodiment is also suited to distributing a payload to larger floor area on soft floor, such as carpet or soil (also called the concert leg) because of the addition of a spreader plate  460 . This embodiment also includes a mounting surface  414 , which optionally has a raised perimeter to reduce contact area and/or may be lined with elastomer or felt or cork or other soft material to aid in effectiveness of filter  100 . 
     Thus, in accordance with the present invention, due to ambient and equipment vibrations, bearings  150  are in a constant oscillation of small, variable amplitude in random directions. Body waves  170 , for example, in the form of dynamic pressure variations or sound, pass through bearing  150  only at contact points  151 ,  152 . As mentioned above, the contact areas at contact points  151 ,  152  are very small, allowing only a narrow clear passage pathway for waves  170  passing through filter  100 . Accordingly, a sound wave  171  beginning to pass through filter  100  which does not align with contact points  151 ,  152  center will refract and disperse in multiple reflections inside bearing  150 , without leaving bearing  150 . The dispersed wave energy is thus dissipated (largely through heat), and most of wave  171  will never pass through filter  100 . This is largely because by the time an exiting wave  172  would have a chance to realign so as to pass through contact point  152 , it will likely interfere with other oncoming waves and bearing will have already moved from a position which would allow it to escape bearing  150 . Herein, this is called wave return path evasion or transmission path evasion and filter  100  functioning this way can be referred to as an evader. 
     In this regard, mechanical signal filter  100  suitably allows a supported device (such as a DVD player) to float and roll in response to vibrations either internal to the device or from the structure supporting the device. Vibrations in the supporting structure cause filter  100  to vibrate in all three directions. Vibrations in the two horizontal directions (perpendicular to gravity) cause bearing  150  to displace from  152  starting point and roll up the incline of raceways  113 , increasing bearings  150  potential energy and reducing the kinetic energy that otherwise would have been transmitted to the supported device resting on top plate  120 . Eventually, gravity returns bearing  150  to starting point  152  and bearing  150  returns to its lowest state of potential energy. In this manner, a reduced amount of energy in the horizontal component of the external vibrations is transmitted to the supported device as vibrations. Similarly, as bearing  150  moves in raceways  113 , friction dissipates the energy that has been transmitted to filter  100  and, if the external vibrations cease, bearing  150  will eventually come to rest. 
     The vibrations which this invention is designed to filter and keep from reaching the supported device supply a harmonic-like force and cause bearing  150  to oscillate and continuously roll within its confined parameters. The rolling motion makes it even more difficult for signals to communicate back and forth between the supported device and the supporting structure. As the vertical vibration component enters bearing  150 , bearing  150  is already in motion and corresponding contact points  151 ,  152  on opposite sides of bearing  150  are shifting out of contact. Therefore, there is no straight path of constant communication between the supported structure and the supporting structure from one moment to the next. And furthermore, a vibration from the supported device that is transmitted to the supporting structure will be less likely to be able to reflect back along the same path to return to the supported device. The frequency of the vibrations correspond to the frequency of oscillation of bearing  150 , and therefore bearing  150  is likely to be moving fast enough to interrupt the transmission path of the vibrations. 
     In this manner, the supported structure and the supporting structure are effectively decoupled and noise from the surrounding environment can be efficiently filtered before reaching the supported structure. This noise can be removed at a very high efficiency and has been tested to remove between 95% and 99.9% of noise and vibration. 
     In accordance with various aspects of the present invention, some embodiments make evader more efficient than others. For instance, a harder bearing and/or raceway is typically more efficient than softer one. Additionally, the bearing radius to raceway radius ratio and other geometrical and material property conditions can change the performance. 
     Descriptive Examples 
     As mentioned above, in operation, when filter  100  is in use, bearings  150  displace (oscillate) within raceways  113 . A pseudo natural period of the oscillation is equal to the natural period of a pendulum of length L is: 
     
       
         4(R−r)  
       
     
     where R is the radius of the curvature of raceway  113  and r is half the distance between contact points (in the various exemplary embodiments, herein, the radius of bearing). Pendulums can be in resonance forced by vibration of a period matching the pendulum period. Therefore, the pendulum&#39;s period (equal to the inverse frequency) is natural. However, nonlinear pendulums have no real or natural periods. They oscillate around a frequency, but generally not in resonance. Therefore, the frequency around which a nonlinear pendulum oscillates is called pseudo natural frequency. 
     Three or more bearings  150  in “doughnut shape” raceways  113  act like a nonlinear pendulum. The pendulum frequencies are independent of the pendulum&#39;s bob weight (mass). Thus, the pseudo frequency of filter  100  is also independent of the support load or payload, the equipment weight, placed upon said assembly. However, since the evasion condition calls for the indentation diameter, which is a function of the payload, the evader is load dependent. Thus, the same distinguishes filter  100  in accordance with the present invention from an isolator, which would be non-load dependent. 
     An optimally performing filter  100  in accordance with the present invention satisfies a transmission evasion condition where a sound propagation constant is greater than a circular frequency constant, or:            2      d     v     &gt;     s     ω                 L                              
     where d is the distance between contact points (in the various exemplary embodiments, herein, the bearing diameter), v is the sound propagation velocity of the bearing material, s is the indentation diameter of the ball at contact, and ω is the circular frequency of the filter as a gravity restoring isolator of equivalent pendulum of length L, and, as mentioned above, L is four times the difference of the raceway cavity radius R and the bearing radius r. This inequality is in time units (e.g., seconds). It states that the time needed for a sound wave to enter into the bearing and return to an entry location is longer than the time needed for the sound wave to travel across the passage line—the line connecting the two contact points—by the mechanical oscillation of the bearing. 
     1. Embodiment 1 
     In a first embodiment, filter  100  has an overall diameter of about 1 ⅝ inch and is made of 440 stainless steel. This embodiment has bearings  150  of the same material and have a diameter of {fraction (5/16)} inch [d], with a sound propagation velocity of 318 mile/sec [v]. This same embodiment with a load ranging from 5 lbs. to 100 lbs. has an indentation diameter of 34 micro-inch [s] and a circular frequency of 18 Hz [ω]. For this embodiment, the curvature of raceways  113  is ⅝ inch [R]. 
     Thus, the sound propagation constant:          2      d     v                          
     is 311 nanoseconds (ns) 
     and the circular frequency constant:        s     ω                 L                            
     is 156 ns 
     and therefore the inequality is satisfied. 
     2. Embodiment 2 
     In a second embodiment, filter  100  has an overall diameter of about ⅞ inch and is made of 440 stainless steel. This embodiment has bearings  150  of the same material and have a diameter of {fraction (3/16)} inch [d], with a sound propagation velocity of 318 mile/sec [v]. This same embodiment with a load ranging from 2 lbs. to 33 lbs. has an indentation diameter of 0.47 micro-inch [s] and a circular frequency of 9 Hz [ω]. For this embodiment, the curvature of raceways  113  is 1.4 inch [R]. 
     Thus, the sound propagation constant:          2      d     v                          
     is 19 ns 
     and the circular frequency constant:        s     ω                 L                            
     is 11 ns 
     and therefore the inequality is satisfied. 
     3. Embodiment 3 
     In a third embodiment, filter  100  has an overall diameter of about 3 ⅜ inch and is made of 440 stainless steel. This embodiment has bearings  150  of the same material and have a diameter of ⅜ inch [d], with a sound propagation velocity of 318 mile/sec [v]. This same embodiment with a load ranging from 9 lbs. to 330 lbs. has an indentation diameter of 45 micro-inch [s] and a circular frequency of Hz [ω]. For this embodiment, the curvature of raceways  113  is ¾ inch [R]. 
     Thus, the sound propagation constant:          2      d     v                          
     is 37 ns 
     and the circular frequency constant:        s     ω                 L                            
     is 19 ns 
     and therefore the inequality is satisfied. 
     4. Embodiment 4 
     In a fourth embodiment, filter  100  has an overall diameter of about 3 ⅝ inch and is made of 440 stainless steel. This embodiment has bearings  150  of the same material and have a diameter of ¼ inch [d], with a sound propagation velocity of 318 mile/sec [v]. This same embodiment with a load ranging from 5 lbs. to 100 lbs. has an indentation diameter of 52 micro-inch [s] and a circular frequency of 8.8 Hz [ω]. For this embodiment, the curvature of raceways  113  is 1 ½ inch [R]. 
     Thus, the sound propagation constant:          2      d     v                          
     is 24 ns 
     and the circular frequency constant:        s     ω                 L                            
     is 12 ns 
     and therefore the inequality is satisfied. 
     Lastly, while the principles of the invention have been described in illustrative embodiments, many combinations and modifications of the structures described above, as well as arrangements, proportions, elements, materials and components, used in the practice of the invention—in addition to those not specifically described—may be varied and particularly adapted for specific environment or operating equipment, without departing from those principles.