Title of Invention

A MEMS BASED ELECTROSTATIC ACOUSTIC TRANSDUCER AND METHODS OF SENSING SOUND PRESSURE

Abstract

The present invention relates to an Electrostatic acoustic transducer and it comprises a Diaphragm (1),which actslike a plate, configurable to receive the sound pressure,the diaphragm is suspended on a plurality of beam(3),a back plate(2) fixed form all sides is mounter facingthe plate,a plurality of oppositely charged concentric cylinders (4)is attached to the diaphragm and the back plate(2),a Dcpower source electrically connected to the diaphragm and the plate(2);the power source is configuredto oppositely charge the cylinders on the diaphragm (1)and the back plate(2);and the read out circuitry is configured to detect change in copacitance in terem of voltage chage. The diaphragm (1) on receiving sound pressure deflects uniformly towards the back plate resulting in a uniform chage in yhe electric field and the changes in capacitance.

Full Text

3. A MEMS BASED ELECTROSTATIC ACOUSTIC TRANSDUCER AND METHODS THEREOF Field of the Invention (0001) The present invention in general relates to acoustic transducers and more particularly the present invention relates to Micro Electro-Mechanical Systems (MEMS) based electrostatic acoustic transducers and the methods of constructing the same. Background of the Invention (2) A microphone is an acoustic transducer that changes information from one form to another. The information in the form of sound energy is taken as the input and the microphone delivers it as electrical signal at the output. The main pressure sensing element in the microphone is the acoustic transducer that converts the acoustic pressure into an electrical signal. (3) A microphone typically includes a surface called a diaphragm that is configurable to vibrate in response to the sound wave inputs. The diaphragm is coupled to a circuitry, which translates the diaphragm vibrations into electrical signals, which are proportional to the sound waves. Microphones are of several types. Condenser microphone is one of the commonly encountered designs. In known designs, condenser type microphones use electrostatic capacitors, which consist of two thin parallel plates, one is movable (diaphragm) and the other fixed (backplate). The capacitance is determined by the surface area of the plates, the dielectric or the medium (air) between the plates and the distance between the plates (which changes in response to the acoustic pressure waves). The plates form a sound-pressure sensitive capacitor. (4) In condenser microphones employing electrostatic transduction, the sound waves produce a vibration of the diaphragm. The diaphragm and backplate are conductive and connected to opposite sides of a DC power supply, which provides a polarizing voltage to the capacitor. When the microphone receives a sound-pressure wave, the distance between the plates or overlap area changes resulting in change in capacitance of the circuit. The change in capacitance causes a proportional voltage change. The circuitry connected to the diaphragm then generates an output electrical signal corresponding to the variation of the capacitance. These signals are then further amplified and processed as required. The capacitor so formed between the diaphragm and the backplate is part of an RC circuit. (5) The specifications of a microphone are normally based on the factors like, sensitivity, overload characteristics, linearity or distortion, frequency and noise. Issues related to the above-mentioned factors needs to be addressed in designing the transducer and sensing element of the microphone. In general, the main focus of any proposed method should be at the most fundamental level of the sensing element, the diaphragm, which changes the entire design and hence performance as well as specifications of a microphone. (6) Following the principle mentioned above, micro elctromechanical systems (MEMS) microphones are produced where one chip serves "as the membrane/diaphragm and the other as the electrode or backplate, together forming a capacitor. Silicon micro machining and MEMS provides the means to fabricate microphones with length scales ranging from micron to millimeters. Using batch fabrication techniques, hundreds or thousands of devices can be built on a single silicon wafer. This offers a significant per-unit cost reduction relative to conventional microphone technologies. A miniature sensor enables mounting in a confined space and/or in a cluster of array of sensors. (7) The basic pressure sensing element inx a MEMS condenser microphone is a silicon membrane. The membrane is fixed at the edges. It vibrates under the applied acoustic pressure. The deflected shape of the membrane changes the electric field between the membrane and the backplate, which in turn, changes the capacitance between the two parallel plates. This change in the capacitance is used as the electrical signal generator. (8) There are several unresolved technical problems associated with the known configurations of condenser type microphone. The first problem is that the deflection field of the membrane is non-uniform and, therefore, the change in the electrical field is non-uniform. Secondly, the relationship between the capacitance and the dynamic gap between the membrane and the backplate is non-linear and, therefore, cannot be scaled linearly in designs. The third issue is that the electrical field between the two plates opposes the motion of the membrane and thus acts as an additional damper. This phenomenon couples the electrical field and the mechanical field strongly because the movement of the diaphragm is parallel to the direction of the electrical field. (9) Yet another deficiency in the known configurations is that there is not much control over the natural frequency of the structure and hence the range for flat frequency response (cut-off frequency) of the microphone. The natural frequency in the existing designs depends on the membrane geometry and the polarizing voltage. Although, the natural frequency of the membrane can be varied with polarizing voltage, there is a strong limitation on the polarizing voltage due to the critical pull-in-voltage. (10) The present invention addresses the deficiency in the prior art configurations mentioned above and discloses a novel configuration of a MEMS Microphone having miniaturized acoustic transducer and methods of constructing the same. Summary of the Invention (11) In accordance with the principal aspect of this invention, disclosed herein is an electrostatic acoustic transducer and methods of constructing the same in Micro electromechanical systems based Microphones. (12) In one preferred embodiment, disclosed herein is an electrostatic acoustic transducer that comprises a diaphragm, which acts like a plate, configurable to receive sound pressure, the diaphragm is suspended on a plurality of beams, a back plate fixed form all sides is mounted facing the plate, a plurality of oppositely charged concentric cylinders is attached to the diaphragm and the backplate, a DC power source electrically connected to the diaphragm and the backplate; the power source is configured to oppositely charge the cylinders on the diaphragm and the backplate; and a readout circuitry is configured to detect change in capacitance in terms of the voltage change. The diaphragm on receiving sound pressure deflects uniformly towards the backplate resulting in a uniform change in the electric field and therefore the changes in capacitance. (13) In one preferred embodiment, the diaphragm comprised in the acoustic transducer is a plate. The plate is suspended on plurality of beams from all sides, wherein the beams are fixed at one end. This configuration eliminates the non-uniform deflection of the main sensing part of the sensor, hence, uniform change in electric field. (14) In one another preferred embodiment, the vibrating plate comprised in the acoustic transducer suspended on plurality of beams takes sound pressure as input and deflects in the direction of propagation of the sound wave, thus translating acoustic energy into mechanical energy. V. (15) In another embodiment, disclosed herein is a acoustic transducer wherein a set of conductive concentric cylinders are attached to the vibrating plate. (16) In another embodiment, disclosed herein is a acoustic transducer wherein a set of conductive concentric cylinders are also attached to the backplate. The backplate is fixed from all sides. (17) In still another aspect, disclosed herein is an acoustic transducer wherein the radii of the plurality of concentric cylinders attached to the vibrating plate are different from the radii of the plurality of the concentric cylinders attached to the backplate. (18) In another embodiment, disclosed herein is a acoustic transducer wherein the concentric cylinders attached to the diaphragm mesh with the concentric cylinders attached to the backplate forming cylindrical combdrives. Further, an electrical field exists between the overlapping faces of the concentric cylinders of the cylindrical combdrive, forming set of cylindrical capacitors in parallel configuration.. (19) In still another aspect, disclosed herein is an acoustic transducer wherein cylindrical combdrives attached with the vibrating plate provide the basis for sensing mechanism. The change in meshed overlap of the cylindrical faces on application of sound waves changes the capacitance and, consequently the change in voltage, which can be taken as the output of an acoustic transducer. (20) In yet another preferred embodiment, disclosed herein is an acoustic transducer wherein the change in area of overlap between the faces of cylindrical combdrives changes the capacitance of the sensor thus providing a linear relationship between the change in capacitance and the mechanical displacement of the vibrating plate and thereby large displacements corresponding to higher acoustic pressure levels pose no problems. (21) In yet another preferred embodiment, disclosed herein is an acoustic transducer wherein based on a capacitive transduction scheme, incorporating three energy domains. Firstly, the incident pressure waves force the deflection of the diaphragm, inducing the displacement in the direction of sound pressure, thus translating acoustic energy to mechanical energy. One set of cylinders are attached to the moving plate, the cylinders move in and out of the other set of fixed cylinders attached to the backplate, thus changing the length of overlap in the mesh. Being oppositely charged, the cylinders form into variable cylindrical capacitors in parallel. In still another embodiment, configured herein is an acoustic transducer wherein the equivalent capacitance formed is the summation of the individual capacitance of the overlapping regions between the cylindrical surfaces of each of the concentric cylinders coupled to the diaphragm and the backplate. The change in area of overlap gives change in capacitance and, consequently, a change in the output voltage, translating the mechanical energy into an electrical signal. The voltage modulation is detected by a fully active electronic circuit. (22) In yet another preferred embodiment, an acoustic transducer is configured wherein the combdrives are attached centrically on the vibrating plate thus avoiding the boundary conditions of the sensor affecting the displacement of the cylindrical combdrives . (23) It is an aspect of this invention to configure aacoustic transducer wherein the movement of the vibrating plate with the concentric cylinders is'normal to the direction of electrical field thus eliminating any additional force that opposes the deflection of the vibrating plate, towards the backplate thereby uncoupling the electrical and mechanical fields. (24) In still another preferred embodiment, disclosed herein is an acoustic transducer that comprises a sensing element and a read out circuitry, the sensing element has a beam plate assembly comprising a diaphragm configurable to receive sound pressure on one side, the other fixed at one end and the other end have been employed to suspend the diaphragm; a back plate is placed close to the diaphragm, the back plate has a plurality of concentric cylinders attached to it on the side facing the diaphragm, the placement of the back plate is such that the concentric cylinders on vibrating plate and backplate mesh to form cylindrical combdrive; thereby forming cylindrical capacitance in parallel; a DC power source is electrically connected to the diaphragm and the back plate so as to oppositely charge the concentric cylinders on the diaphragm and the back plate thus constituting a variable capacitor wherein the capacitance is changed when the diaphragm deflects towards the backplate on receiving sound pressure, the change in capacitance is detected by the read out circuitry in terms of voltage change. (0025) It is an important aspect of the invention to configure an acoustic transducer wherein the increase in the concentric cylinders results in an increase in the equivalent capacitance thus leading to better electrical sensitivity. (0026) In one another embodiment, herein disclosed is an acoustic transducer wherein the material used to construct the vibrating plate is polysilicon. (0027) In yet another embodiment, disclosed is an acoustic transducer wherein the thickness of the diaphragm and that of beams can be varied independently so as to obtain any desired natural frequency and hence, tuner the cutoff frequency of the sensor. . Also disclosed is a preferred embodiment wherein the stiffness of the beam structure can be varied to tune the mechanical sensitivity of the sensor. (0028) In one embodiment, disclosed herein is an acoustic transducer having the beam length reduced to zero and the diaphragm made to work in the membrane mode. The sensing mechanism remains as variable cylindrical capacitance. The restoring force in the membrane are the internal stresses. (29) It is another aspect of the present invention to provide for an acoustic transducer configurable for use in an array architecture where an 'n' x cn' grid of microphones can be used in place of one acoustic pressure sensor for divided narrow band of frequencies in which the corresponding acoustic pressure sensor will have absolutely flat response. (30) In a significant aspect the present invention discloses an acoustic transducer configurable to be implemented in Micro Electro Mechanical Systems based Microphones (MEMS Microphones), hearing aid applications, microphone in cellular phones, automobiles, computer peripherals, etc. (31) It is an aspect of the present invention to devise a method of sensing sound pressure employing an acoustic transducer configured according to the current invention. (32) In still an aspect the present invention discloses a method of constructing an acoustic transducer, the method comprises configuring a sensing element having a beam plate assembly comprising a diaphragm configurable to receive sound pressure on one side, the other side attached to a plurality of concentric cylinders, configuring a plurality of beams, fixed at one end and the other end configured to suspend the diaphragm; configuring a back plate placed close to the diaphragm, the back plate having a plurality of concentric cylinders attached to it on the side facing the diaphragm, the placing of the back plate providing a dynamic gap between the diaphragm and the backplate; configuring a DC power source electrically connected to the diaphragm and the back plate so as to oppositely charge the concentric cylinders on the diaphragm and the back plate thus constituting a variable capacitor wherein the capacitance is changed when the diaphragm deflects towards the backplate on receiving sound pressure and the change in capacitance being detected by the electronic circuitry in terms of voltage change. Brief Description of the Drawing Figures (33) Fig. 1 shows the basic configuration of a condenser microphone based on electrostatic transduction scheme. (34) Fig. 2 shows the diaphragm of the microphone with the concentric cylinders. (35) Fig. 3(a) shows the overlapping of the concentric cylinders of the diaphragm and the backplate of the microphone. (36) Fig. 3(b) and 3(c) shows the sectional view of the overlapping of the concentric cylinders forming cylindrical combdrives and the equivalent capacitance of the configuration. (37) Fig 4(a) and 4(b) show the static and deflected positions of the diaphragm with respect to the applied acoustic pressure. Fig 4(c) shows the electric field between the overlapped cylindrical faces and the movement of the diaphragm perpendicular to the direction of electric field. (38) Fig 5 shows the mode shape in the first mode of vibration of sensing element. (0039) • Fig 6 shows the design of the sensing element in membrane mode with concentric cylinders having the beam length reduced to zero. (0040) Fig.7 (a) & 7(b) show the variation of design in terms of achieving high cut-off frequency with respect to the first resonant frequency. (0041) Fig. 8 shows the linearity in design with tttp application at different sound pressure levels. The response is plotted against the sound pressure level on a logarithmic scale. Detailed Description of the Preferred Embodiments (42) Fig 1 shows the basic configuration of a condenser microphone based on electrostatic acoustic transduction mechanism. The basic elements of the condenser microphone include the transducer elements in the form of a diaphragm 110 which is placed close to the backplate 120, a DC power source 130 connected to the diaphragm 110 and the backplate 120 and produces the electric potential between them and an amplifier 140. The backplate 120 is fixed. The arrangement of the diaphragm and the backplate acts as the parallel plate capacitor. With the application of the acoustic pressure waves 100 as an input, the diaphragm 110 deflects and moves towards the fixed backplate 120. The deflection of the diaphragm 110 changes the gap between the diaphragm 110 and the backplate 120 and thereby changing the electric field. Consequently the change in capacitance of the circuit is read out through an electronic circuitry in terms of the voltage change. (43) Fig 2 shows the diaphragm (vibrating plate) 110 with a plurality of concentric cylinders 150a, 150b, ..150n attached with the diaphragm 110 of the acoustic pressure sensor. The diaphragm 110 is suspended on a plurality of beams 160 at one end and the other end of the beams 160 is fixed. The diaphragm is exposed to acoustic pressure 100 in the direction shown and the diaphragm 110 deflects in the direction of application of the acoustic pressure 100. (44) Fig. 3(a) shows the overlapping of the concentric cylinders 150a> 150b, »150n on the diaphragm 110 and the concentric cylinders 170a, 170bl-170n on the fixed backplate 120. (0045) Fig 3 (b) shows the sectional view of the meshed overlapping of the concentric cylinders 150a, 150b, »150n on the diaphragm 110 and the concentric cylinders 170a, 170b,~170n of the backplate 120. The set of conductive cylinders 150a, 150b,~150nand 170a> 170b,~170n forms the cylindrical combdrives. lc is the length of the cylinders attached with the plates 110 and 120. The length of overlap 180 of the cylindrical faces 150 and 170 in meshed configurations forms the cylindrical capacitance. (0046) Fig 3(c) shows for a given number of concentric cylinders on the moving diaphragm 110 and the fixed backplate 120, the equivalent capacitance is the summation of the individual capacitances, which are in parallel configurations. (0047) For a cylindrical geometry such as coaxial cylinders, the capacitance is given by: where 'a' is the inner radius, 'b' the outer radius, 7' the length of cylinder, and e0 is the permittivity of free space between the two cylindrical surfaces. (0048) Let the initial overlap between the fixed and the moving cylindrical combdrives be lQ 180. The length of overlap of combdrives is determined by cylindrical capacitance arid is given by, where, l0 ~ initial overlap of cylindrical combdrives attached to the diaphragm 110 and the backplate 120, l(t) = overlap at some instant *t\ x(t) = deflection of the plate on application of acoustic pressure. (0049) For the given number of cylinders in xne comoanves on ine moving diaphragm 110 and the fixed backplate 120, the equivalent capacitance can be calculated as follows: j = 1, 2, 3, ...,n, No of cylinders; v\ = inner radius of the cylindrical combdrives; r0= outer radius of the cylindrical combdrives; fj = fixed cylinders attached with backplate of the microphone m, = moving cylinders attached with diaphragm of microphone CI, C2, ....C6 = Cylindrical capacitors formed between the fixed and moving combdrives C = Equivalent capacitance C(t) = Cl+C2+C3+ 'n' no. of cylinders on the moving plate (diaphragm 110) create '2n' gaps among the overlapping surfaces. This accounts for '2w' cylindrical capacitors in parallel. The calculations shown above forC(/) for 3 cylindrical combs on the diaphragm which gives rise to 6 cylindrical capacitances in parallel. The same can be extended to cn' no. of cylindrical combdrives and forming '2n' cylindrical capacitances, increase in number of cylindrical combdrives gives higher capacitance change and hence, better electrical sensitivity. (0050) Fig 4(a) shows the suspension of the plate 110 with plurality of beams 160 fixed at one end. The sensing part 190 is configured in such a manner that it is not affected with the boundary condition of the beams 160. Further in fig 4(b) it can be seen that there is uniform displacement of the sensing part 190 of the microphone due to sound pressure waves 100. Due to this particular configuration and uniform displacement of the sensing part, the change in electric field is also uniform. (51) Fig 4(b) shows the deflected position of the diaphragm 110 on application of sound pressure waves 100. Deflection of sensing part 190 i.e. concentric cylinders 150a, 150b, »150n on 110 with respect to the applied acoustic pressure 100 is shown. The set of cylindrical capacitors 150 and 170 on 110 and 120 respectively forms the cylindrical comb drive, which is used as an electrostatic capacitive sensing element. The change in capacitance is due to the change in the area of overlap 180 between two concentric cylindrical faces. First, the incident acoustic pressure waves 100 force the bending of the diaphragm 110, inducing displacement normal to the z-direction, thus translating the acoustic energy to mechanical energy. Since one set of the cylindrical combdrives are attached to the moving diaphragm 110, the concentric cylinders move in and out of the other set of fixed cylindrical combdrives attached to the backplate 120, thus changing the length of overlap. Consequently, the change in area of overlap changes the capacitance. This change in capacitance causes a change in the output voltage, translating the mechanical energy into an electrical signal. The voltage modulation is detected through a fully active electronic circuit. (52) Fig 4(c) shows the electric field between overlapped faces of the cylinders in meshed configuration. It can also be observed that the change in electric field due to deflection of the diaphragm is uniform. The electrostatic field is limited between the concentric cylindrical faces of the combdrives" 150 and 170 because there is no charge on the moving flat plates, the diaphragm 110 and the backplate 120. The displacement of the moving combs on the plate 110 that affects this electrostatic field is normal to the direction of the electric field 200 and therefore, the changes induced in the electrostatic field are only due to the much weaker fringing field effects. Thus, the electrostatic field remains nearly constant. Moreover, there is no additional force of opposition due to the electrical field in the direction parallel to the mechanical motion. This phenomenon uncouples the electrical and mechanical fields in the proposed invention. (53) The change in capacitance is calculated due to change in area of overlap or the length of overlap between a set of cylindrical capacitor. The calculation of capacitance explained earlier shows a linear relationship between change in capacitance and deflection of the sensing element 110. One of the advantages due to this linear relationship is that larger mechanical displacement of the diaphragm 110 corresponding to higher acoustic pressure levels poses no problems. (54) Fig 5 shows the mode shape in the first mode of vibration of the diaphragm 110. This particular method of configuring an acoustic transducer provides a range of variation in design. The natural frequency of the proposed structural configuration depends only on the mechanical properties and not on the bias voltage. The plates 110 and beams 160 can be designed in numerous ways to place the natural frequencies at any desired location without resorting to optimization, because the beam 160 and the plate 110 combination can almost decouple the mass and stiffness properties of the structure. The ability to place the natural frequency at any location gives a direct control over the flat response of the device. The desired flexibility can be obtained to tune the stiffness of the structure and hence, can get the desired sensitivity. This particular aspect is extremely helpful in designing a system of microphone array where each sensor can be tuned to respond to a narrow bandwidth of the acoustic spectrum with extremely high flatness and high sensitivity. (55) Fig 6 illustrates further the design of the sensing element in membrane mode with cylindrical combdrives with the beam length reduced to zero. Apart from a beam-diaphragm combination, the sensing element can also be made as a complete membrane 110 by reducing the beam length to zero. It can be modeled as a membrane considering the same cylindrical combdrives 150, where the restoring forces in a membrane are the internal 1 e> stresses. The diaphragm deflection fw' in this case can be approximated by the following differential equation: (0056) Fig.7 (a) & 7(b) show the variation in configuration of the sensing element in terms of achieving high cut-off frequency with respect to the first resonant frequency. It can be observed from the figure that by varying the plate thickness (mass) and beam thickness (stiffness) independently, the desired resonant frequency can be achieved. (57) Fig. 8 shows the linearity in design with the application at different sound pressure levels. The response is plotted against the sound pressure level on a logarithmic scale. (58) While this invention has been described in detail with reference to certain preferred embodiments, it should be appreciated that the present,invention is not limited to those precise embodiments. Rather, in view of the present disclosure, which describes the current best mode for practicing the invention, many modifications and variations would present themselves to those skilled in the art without departing from the scope and spirit of this invention. -w WE CLAIM: 1. An electrostatic acoustic transducer comprising: a diaphragm suspended on a plurality of beams, a back plate mounted close to the diaphragm; a plurality of oppositely charged concentric cylinders attached to the diaphragm and the backplate; a sensing mechanism based on electrostatic transduction with linear relationship between the capacitance and the deflection of the diaphragm due to the sound pressure; a power source electrically connected to the diaphragm and the backplate; the power source configurable to oppositely charge the concentric cylinders on the diaphragm and the backplate; and a readout circuitry configurable to detect change in capacitance in terms of voltage change wherein the diaphragm on receiving sound pressure deflects uniformly towards the backplate resulting in uniform electric field. 2. An electrostatic acoustic transducer according to claim 1 wherein the diaphragm is a plate, the plate being suspended by a plurality of beams. 3. An electrostatic acoustic transducer as claimed in claim 2 wherein the diaphragm is a plate suspended on one end of the plurality of beams, said beams fixed at the other end. 4. An electrostatic acoustic transducer according to claim 1 wherein the diaphragm is a membrane. 5. An electrostatic acoustic transducer according to claim 1 wherein the concentric cylinders attached to the vibrating plate mesh with the concentric cylinders attached to the backplate, forming cylindrical combdrives. 6. An electrostatic acoustic transducer according to claim 5 wherein an electrical field exists between the overlapping faces of the concentric cylinders attached to the vibrating plate and the backplate, forming the basis for sensing mechanism. 7. An electrostatic acoustic transducer according to claim 6 wherein an electrical field between the opposite faces of the transducer is uniform. 8. An electrostatic acoustic transducer according to claim 6 wherein the change in capacitance is calculated based on variable cylindrical capacitance. 9. An electrostatic acoustic transducer according to claim 6 wherein the movement of the plate is normal to the direction of electrical field thus eliminating any additional force that opposes the deflection of the plate towards the backplate. 10. An electrostatic acoustic transducer according to claim 1 wherein the radii of the plurality of concentric cylinders attached to the plate are different from the radii of the plurality of the concentric cylinders attached to the backplate. 11. An electrostatic acoustic transducer according to claim 1 wherein the electrostatic field is limited between the concentric cylindrical faces of the combdrives because there is no charge on the moving fiat plate. 12. An electrostatic acoustic transducer according to claim 1 wherein the power source is a DC source. 13. An electrostatic acoustic transducer according to any of claims 1, 5, 6, 11, or 12 wherein the number of concentric cylinders attached to the diaphragm and the backplate is increasable. 14. An electrostatic acoustic transducer as claimed in claim-1 comprising: a sensing element; the sensing element having a beam plate assembly comprising a diaphragm configurable to receive sound pressure on one side, the other side attached to a plurality of concentric cylinders, a plurality of beams, fixed at one end and the other end configured to suspend the diaphragm; a back plate placed close to the diaphragm, the back plate having a plurality of concentric cylinders attached to it on the side facing the diaphragm; a power source electrically connected to the diaphragm and the back plate so as to oppositely charge the concentric cylinders on the diaphragm and the back plate thus constituting a variable capacitor wherein the capacitance is changed when the diaphragm deflects towards the backplate on receiving sound pressure, the change in capacitance being detected by the read out circuitry in terms of voltage change, said electro static acoustic transducer characterized in the electrostatic capacitive sensing element comprising first set of concentric cylinder attached to moving diaphragm, second set of concentric cylinders attached to fixed back plate, such that first set of the said concentric cylinder is movable into and out of second set of concentric cylinders, said two sets of cylinders charged oppositely, such that the length of the cylindrical faces of the two sets in meshed condition forming the cylindrical capacitance with plurality of cylinders in each set. 15. An electrostatic acoustic transducer according to claim 14 characterized in the cylindrical capacitor comprising two sets of concentric cylinders one set attached to moving diaphragm and second set attached to fixed back plate, said first set of cylinders movable into and out of second set of cylinders thereby the two sets of cylinders meshed for an overlap length to form cylindrical combdrives. 16. An electrostatic acoustic transducer according to claim 14 wherein the plurality of concentric cylinders attached to the moving diaphragm and the plurality of the concentric cylinders attached to the fixed back plate are oppositely charged, on meshing form a set of cylindrical capacitors in parallel configuration. 17. An electrostatic acoustic transducer according to claim 14 wherein the concentric cylinders on moving diaphragm and fixed back plate mesh to form concentric combdrive, characterized in the combdrive attached centrally on the moving diaphragm. 18. An electrostatic acoustic transducer according to claim 17 wherein the equivalent capacitance formed is the summation of the individual capacitance due to overlapped regions between the cylindrical surfaces of each of the concentric cylinders attached to the moving diaphragm and the fixed backplate. 19. An electrostatic acoustic transducer according to any of claims 14 through to 19 wherein the number of concentric cylinders attached to the diaphragm and the backplate is increasable. 20. An electrostatic acoustic transducer according to any of claims 1 though to 19 wherein the increase in the concentric cylinders results in an increase in the equivalent capacitance thus leading to better electrical sensitivity. 21. An electrostatic acoustic transducer according to any of claims 1 through to 20 wherein the material used to construct the vibrating plate is polysilicon. 22. An electrostatic acoustic transducer according to any of claims 1 through to 21 wherein the configuration of the diaphragm and the beam structure can be varied to place the natural frequencies at any desired location, the beam and plate combination being enabled to decouple the mass and stiffness properties of the structure thus providing a direct control over the flatness of frequency response of the device. 23. An electrostatic acoustic transducer according to any of claims 1 through to 22 wherein the natural frequency of the structure is not limited to pull-in voltage. 24. An electrostatic acoustic transducer according to any of claims 1 through to 23 wherein the stiffness of the beam structure is variable to tune the mechanical sensitivity of the sensor. 25. An electrostatic acoustic transducer according to any of claims 15 though to 24 wherein the beam length is reduced to zero. 26. An electrostatic acoustic transducer according to any of claims 15 though to 25 wherein the diaphragm also acts as a membrane. 27. An electrostatic acoustic transducer according to any of claims 1 through to 26 configurable for use in an array architecture where an *n' x 'n' grid of acoustic transducers can be used in place of one acoustic transducer for divided narrow band of frequencies in which the corresponding acoustic transducer will have a flat response, for use in Micro electromechanical systems, audio Microphones, hearing aids, microphones in cellular phones and computer peripherals. 28. A method of sensing sound pressure employing the acoustic transducer comprising: forming a deflecting member diaphragm with a set of charged cylinders, forming a fixed member back plate with a set of charged cylinders, applying sound pressure on the deflecting member, and translating the acoustic energy into mechanical energy by movement of charged cylinders of diaphragm towards the charged cylinders of back plate, which mesh together to form cylindrical capacitors in parallel configuration. 29. A method of constructing an electrostatic acoustic transducer comprising: a. forming a deflectable member diaphragm, b. fixing a fixed member back plate, c. connecting oppositely charged concentric cylinders on the diaphragm and the adjacent back plate, and d. applying sound pressure to deflect the diaphragm towards the back plate allowing the concentric cylinders to overlap to form a cylindrical capacitors in parallel configuration.

Documents:

924-mas-2002-abstract.pdf

924-mas-2002-claims duplicate.pdf

924-mas-2002-claims original.pdf

924-mas-2002-correspondance others.pdf

924-mas-2002-correspondance po.pdf

924-mas-2002-description complete duplicate.pdf

924-mas-2002-description complete original.pdf

924-mas-2002-drawings.pdf

924-mas-2002-form 1.pdf

924-mas-2002-form 19.pdf

924-mas-2002-form 26.pdf

924-mas-2002-form 3.pdf

924-mas-2002-form 5.pdf