CA1277415C - Elastomer membrane enhanced electrostatic transducer - Google Patents
Elastomer membrane enhanced electrostatic transducerInfo
- Publication number
- CA1277415C CA1277415C CA000506496A CA506496A CA1277415C CA 1277415 C CA1277415 C CA 1277415C CA 000506496 A CA000506496 A CA 000506496A CA 506496 A CA506496 A CA 506496A CA 1277415 C CA1277415 C CA 1277415C
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- CA
- Canada
- Prior art keywords
- plates
- transducer
- dielectric material
- gas
- elastomeric
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R19/00—Electrostatic transducers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/0292—Electrostatic transducers, e.g. electret-type
Abstract
ELASTOMER MEMBRANE ENCHANCED ELECTROSTATIC TRANSDUCER
ABSTRACT OF THE DISCLOSURE
A transducer having opposed first and second conductive plates for application of an electrical potential difference therebetween. An elastomeric dielectric material such as neoprene rubber is disposed between the plates and in contact therewith. The dielectric material has a plurality of pockets of ap-proximate average depth "d" such that, for a given gas maintained within the pockets at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage for the gas in the pockets.
Alternatively, the elastomeric dielectric material disposed between the plates may take the form of a plurality of strips or nodules which separate the plates by a distance "d" as above.
ABSTRACT OF THE DISCLOSURE
A transducer having opposed first and second conductive plates for application of an electrical potential difference therebetween. An elastomeric dielectric material such as neoprene rubber is disposed between the plates and in contact therewith. The dielectric material has a plurality of pockets of ap-proximate average depth "d" such that, for a given gas maintained within the pockets at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage for the gas in the pockets.
Alternatively, the elastomeric dielectric material disposed between the plates may take the form of a plurality of strips or nodules which separate the plates by a distance "d" as above.
Description
t~ Lrj ELASTOMER M~MBRANE ENHANCED ELECTROSTATIC TRANSDUCER
FIELD OF THE INVENTION
This application pertains to electrical-to-mechanical transducers. More particularly, the applica-tion pertains to an electrostatic transducer in which an elastomeric dielectric material is disposed between a pair of opposed conductive plates across which an elec-trical potential difference is maintained. Slight sur-face irregularities or pockets in the dielectric mater-ial facilitate dramatic increases of the electric break-down field in the microscopic gap between the plates and the dielectric material, ox in the pockets, thereby yielding extremely high electrostatic forces. Very thin deposits of dielectric material may alternatively be used to maintain a very narrow gap between the opposed plates, thereby also increasing the gap breakdown volt-age, yielding extremely high electrostatic forces and increased compliance of the device.
BACKGROUND OF THE INVENTION
A variety of electrical-to-mechanical trans-ducers exist. Familiar examples include the electro-static transducers incorporated in loudspeakers, the electromagnetic transducers incorporated in electric gauges and the piezoelectric or magnetostrictive trans-ducers used, for example, in certain narrow band under-water signalling applications. Conventional electro-static transducers typically utilize the electrostatic force generated by applying an electrical potential dif-ference between a pair of opposed metal plates separated by an air gap. In an electromagnetic transducer, an electric current causes a force to be applied to a wire 1~774~5 maintained in a magnetic field, thereby moving the wire and whatever it may contact. Piezoelectric transducers incorporate certain crystals which change their shape, and thus move slightly, in response to an applied elec-tric Eield. Magnetostrictive transducers incorporatecertain metals which change their shape, and thus move slightly, in response to an applied magnetic field.
For comparison purposes, it is useful to con-sider transducers having a volume of the order of 100 ml. Conventional electrostatic transducers of this sort have relatively low mechanical impedance (ranging from about 1 to about 100 Newton seconds per metre) and are capable of producing only relatively small forces (typically about .05 to about .5 Newtons). The mech-anical impedance range of electromagnetic transducers is about the same as that of conventional electrostatic transducers, although electromagnetic transducers are capable of producing forces of about .5 to about 10 New-tons. Piezoelectric and magnetostrictive transducers,on the other hand, have extremely high mechanical imped-ance (ranging from about 106 to about 108 Newton seconds per metre) and generate extremely high forces (on the order of about 103 to about 104 Newtons).
It can thus be seen that there is a conspicuous lack of electrical-to-mechanical transducers which, in the 100 ml. size range, would have a mechanical impedance on the order of about 103 to about 105 Newton seconds per metre and be capable of producing forces in the range of about 10 to about 103 ~ewtons. The present invention provides an electrostatic transducer which fills this gap in the prior art.
SUMMARY OF THE INVE~TIO~
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In accordance with a first embodiment, the invention provides a transducer, comprising opposed first and second conductive plates between which an electrical potential may be applied; and, an elastomeric dielectric material disposed between the plates and in contact therewith. The dielectric material has a plur-ality of pockets of approximate average depth "d" such that, for a given gas maintained within the pockets at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of the gas. The large breakdown voltages cor-respond to high electric fields and correspondingly high electrostatic forces. At the same time, the deformabil-ity of the elastomeric dielectric material, in conjunc-tion with the gas-filled pockets, enables the structure to be relatively compliant, thus achieving a mechanical impedance in the desired range.
Alternatively, in a second embodiment of the invention, the elastomeric dielectric material may take the form of small strips or nodules disposed between the plates and in contact therewith, thereby separating the plates by a distance "d" such that, for a given gas maintained between the plates at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of the gas.
Advantageously, the elastomeric dielectric material is disposed between the plates at a plurality of discrete sites, thus leaving a gas-filled gap between and in con-tact with both plates in regions not occupied by thedielectric material. In a particularly preferred embod-iment, a first plurality of strips of elastomeric dielectric material are disposed between the plates in a first direction; and, a second plurality of strips of elastomeric dielectric material are disposed between the ~ ~7741~;
plates in a second direction different from the first direcion, thereby increasing the compliance of the elas-tomeric material and decreasing the mechanical impedance of the transducer so as to facilitate large displace-ments in response to comparatively small voltages.
Another particularly preferred embodiment of the invention provides a plurality of conductive plates which may be arranged in a stack. An electrical poten-tial may be applied between each pair of opposed platescomprising the stack. An elastomeric dielectric mater-ial is disposed between and in contact with each pair of opposed plates comprising the stack. The dielectric material separates each of the pairs of opposed plates by a distance "d" such that, for a given gas maintained between the plates at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of the gas.
Advantageously, an electrical insulating material may be disposed between each of the plates and the elastomeric dielectric material so as to increase the gas breakdown voltage, and to lessen the deleterious effects of accidentally exceeding that voltage.
If the gas is air, and if "P" is normal atmos-pheric pressure, then "d" is preferably about 16 mic-rons or less.
The elastomeric dielectric material is prefer-ably neoprene rubber. The conductive plates are prefer-ably formed of aluminized mylar.
BRIEF DESCRIPTION OF THE DRAWI~GS
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Figure 1 is a graph in which force (expressed in Newtons) is plotted as the ordinate versus mechanical impedance (expressed in Newton seconds per metre) as the abscissa for various electrical-to-mechanical trans-ducers having a volume of about 100 millilitres.
Figure 2 is a greatly magnified cross-section-al side view of a portion of a typical electrostatic transducer.
Figure 3 is a greatly magnified cross-sectional side view of a portion of an elastomer mem-brane enhanced electrostatic transducer constructed in accordance with a first embodiment of the invention.
Figure 4 is a greatly magnified cross-section-al side view of a portion of an alternative transducer constructed in accordance with a second embodiment of the invention.
Figure 5 is a greatly magnified cross-section-al side view of a portion of a further alternative tran-sducer constructed in accordance with the invention.
Figure 6 is a greatly magnified cross-section-al side view of a portion of a still further alternative transducer constructed in accordance with the inven-tion.
Figure 7 is a greatly magnified cross-section-al side view of a portion of yet another alternativetransducer constructed in accordance with the inven-tion.
Figure 8 is a graph in which the electrical breakdown voltage for forming a spark in a gas maintain-~774~
ed at a pressue "P" (expressed in Torr) between twometal plates across which a voltage "V" (expressed in volts) is applied is plotted as the ordinate, versus the product Pd where "d" is the distance between the plates (expressed in centimetres). The graph includes plots for various "cathodes"; the "cathode" being the lower voltage plate.
Figure 9 is an electron micrograph of a neo-prene rubber dielectric for use in constructing a trans-ducer in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 is a graph on which transducer force (expressed in Newtons) is plotted as the ordinate versus transducer mechanical impedance (expressed in Newton seconds per metre) as the abscissa for various elec-trical-to-mechanical transducers having a volume of about 100 millilitres. As indicated by region 10 on Figure 1, conventional electrostatic transducers have mechanical impedances which vary from about 1 to about 100 Newton seconds per metre and are capable of produc-ing forces of about .05 to about .5 Newtons. As shown by region 12 on Figure 1, electromagnetic transducers exhibit the same range of mechanical impedance as con-ventional electrostatic transducers, but are capable of producing forces in a range which is roughly about one order of magnitude greater than the force range of con-ventional electrostatic transducers. Piezoelectric andmagnetostrictive transducers, on the other hand, have extremely high mechanical impedance ranging from about 106 to about 108 Newton seconds per metre and are capable of producing forces in the range of about 103 to about 104 Newtons, aB illustrated by region 14 in ,:. .. , :,, .
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Figure 1.
It can thus be seen that there is a wide range of mechanical impedance and forces which existing elec-trical-to-mechanical transducers are incapable of pro-ducing. This gap, illustrated by region 16 in Figure 1, corresponds to an impedance range of about 102 to about 106 Newton seconds per metre and to a force range of about 10 to about 103 Newtons. The present invention provides an elastomer membrane enhanced elec-tro~tatic transducer which fits neatly within this gap.
That is, the transducer to be described exhibits mechan-ical impedance in the range of about .5x103 to about .5x105 Newton seconds per metre and is capable of gen-erating forces in the range of about 10 to about.5x103 Newtons. There are a wide range of practical applications for which the transducer of the invention is ideally suited. These include machine tool actuators and vibrators, alignment preserving optical components in laser systems and underwater transducers.
Figure 2 is a simplified cross-sectional side view of a conventional electrostatic transducer consist-ing of a pair of opposed metal plates 20, 22 which are separated a distance "d" by an air gap. If an A.C.
voltage source 26 is connected across plates 20, 22 to establish an electrical potential difference across the plates an electrostatic force is generated which causes the plates to oscil].ate in the directions indicated by double headed arrow 28. The magnitude of such oscilla-tion varies in proportion to the magnitude of the square of the applied voltage although, as indicated by region 10 in Figure 1, only comparatively small forces can be produced by conventional electrostatic transducers.
Moreover, there is a maximum breakdown voltage of about 1'~774~5 106 volts per metre beyond which any further increase in voltage across plates 20, 22 results in arcing be-tween the plates, in which case the transducer fails due to a large increase in the flow of electri~al current.
Figure >3 is a graph which illustrates the re-lationship between breakdown voltage "V", plate separa-tion distance "d" and pressure "P" of the gas maintained between the opposed plates of an electrostatic transduc-er like that shown in Figure 2. The graph shows thatfor a given cathode material (the "cathode" being the plate having the lower voltage) such as commercial alum-inum, the breakdown voltage V decreases as the product Pd decreases, until a minimum voltage l'Vmin" is reached; and, that the breakdown voltage V then increas-es dramatically as the product Pd continues to decrease.
It may thus be seen that if the gas pressure P is held constant, the breakdown voltage V decreases as the plate separation distance d decreases until the aforementioned minimum voltage Vmin (known as the "Paschen mini-mum") is reached, but the breakdown voltage V then in-creases dramatically as the plate separation distance d is further decreased. As Figure 8 indicates, the Pasch-en minimum voltage for air, with a commercial aluminum cathode is about 254 volts, and occurs when the product Pd is about 1.2 Torr cm. If the gas pressure P is 1 at-mosphere (i.e. 760 Torr) this corresponds to a plate separation distance d of about 1.2 Torr cm./760 Torr =
1.6x10-3 cm. or about 16 microns.
It has been recognized that an electrostatic transducer capable of measuring small displacements can be made by making d as small as possible. [See: W. B.
Gauster and M. A. Breazeale: "Detector for Measurement of Ultrasonic Strain Amplitudes in Solids", Rev. Sci.
.
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Instrum. 37, 1544-1548 (1966); and, J. H. Cantrell and J. S. Heyman: "Broadband Electrostatic Acoustic Trans-ducer for Ultrasonic Measurments in Liquids", Rev. Sci.
Instrum. 50, 31-33 (1979)]. Unfortunately however, it is very difficult to construct a practical electrostatic transducer having a plate separation gap "d" of only about 16 microns and the difficulty increases as "d" is further decreased (as it must be if an electrostatic transducer having higher breakdown voltages is to be produced). Expensive precision machining and cumbersome mounting techniques are required which preclude the use of such transducers in most practical situations.
The inventors have discovered that a practical electrostatic transducer which exploits the foregoing phenomenon may be easily constructed and operated at values of Pd which are significantly less than the value of Pd required to achieve the minumum breakdown voltage of the particular gas maintained between the transducer plates. The term "significantly" is used to imply that the breakdown voltage resulting from a particular value of Pd exceeds the minimum breakdown voltage by about 10%
or more.
In accordance with a first embodiment of the invention, an elastomeric dielectric material is placed between plates 20, 22 of the Figure 2 electrostatic transducer and is maintained in contact with both plates. It is of course well known to provide a dielec-tric materia~ between a pair of opposed plates across which a voltage potential difference is maintained (as in a conventional capacitor). However, the inventors have discovered that if the dielectric material has very slight surface irregularities or pockets, and is elasto-meric tfor example, neoprene rubber), then the desired _ g _ ~ .
1 ~774~
increase in gap breakdown voltage may be achieved,thereby Eacilitating production of transducers having mechanical impedance/force characteristics falling with-in region 16 depicted in Figure 1, as a result of the deformability of the elastomeric dielectric material.
Figure 3 is a greatly magnified cross-sectional side view of an electrostatic transducer 30 according to the first embodiment of the invention.
Transducer 30 comprises a pair of thin aluminium plates 32, 34 across which an electrical potential difference is maintained by a voltage source (not shown). A com-pressible neoprene rubber dielectric 36 having a break-down voltage of about 2x107 volts per metre is dispos-ed between plates 32, 34 and in contact therewith. Thesurfaces of dielectric 36 adjacent plates 32, 34 are very slightly irregular such that, when viewed on the microscopic scale shown in the electron micrograph of Figure 9, the surfaces exhibit a large plurality of poc-kets having an approximate average depth "d" of about 10microns each. Accordingly, when dielectric 36 is dis-posed between plates 32, 34 there is a corresponding large plurality of discrete gaps on the order of about 10 microns between each of plates 32, 34 and the adjac-ent surfaces of dielectric 36. The aforementioned poc-kets would ordinarily be distributed throughout dielec-tric 36, and need not be confined to (or even present on) the surface of dielectric 36.
The slight surface irregularities of dielec-tric 36 provide, in effect, a gap of approximately 10 microns between each of plates 32, 34 and the adjacent faces of dielectric material 36. Alternatively, the pockets distributed throughout dielectric 36 constitute a large number of discrete, localized gaps of about 10 1 ~774~5 microns each. As discussed above with reference to Fig-ure 8, small gaps of this order of magnitude are capable of sustaining relatively high voltages before breakdown occurs. Moreover, because the dielectric material is elastomeric, plates 32,34 may oscillate significantly in response to the large electrostatic force corresponding to the large voltages sustainable by the slight surface irregularities or pockets of the dielectric. Dielectric material 36 thus facilitates the production of electro-static forces on the order of the range of forces andmechanical impedances indicated by region 16 in Figure 1.
The first embodiment of the invention describ-ed above and illustrated in Figure 3 is subject to a number of shortcomings. For example, if dielectric mat-erial 36 is relatively thick in comparison to the aver-age depth d of the dielectric surface irregularities or pockets, and if transducer 30 is operated with an A.C.
voltage, then the effective efficiency of the device is decreased. This decrease arises because of the extra power consumed in the process of charging and discharg-ing the relatively large volume of the dielectric mater-ial. Secondly, if the device is connected across a con-stant voltage source, small currents flowing through thedielectric surface irregularity or pocket gaps could, after a time, short out the electric field in the gaps, thereby reducing the electrostatic force to zero. A
further shortcoming of such a device is that it could be difficult to manufacture inexpensively in large quanti-ties. The foregoing shortcomings are overcome by the second and further alternative embodiments of the inven-tion illustrated in Figures 4, 5, 6 and 7 which will now be described.
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Figure 4 illustrates a transducer 40 having a pair of opposed metal pla~es 42, 44 across which an electrical potential difference is maintained by a volt-age source (not shown~. A plurality of strips, beads or nodules 46a, 46b, 46c, etc. of elastomeric dielectric material are disposed between plates 42 and 44 in con-tact therewith, thereby separating plates 42, 44 by a distance "d" such that, for a given gas maintained be-tween plates 42, 44 at a pressure "P", the product Pd is significantly less than the value required to achieve the Paschen minimum breakdown voltage of the gas. There are known techniques for rapid application of thin strips or small beads of elastomeric material to sur-faces, which may be adapted to construct the second em-bodiment of the invention illustrated in Figure 4. Notethat in the embodiment of Figure 4 the thickness of the dielectric material is reduced to equal the desired min-imum displacement "d" between plates 42, 44; thereby facilitating operation of the device at direct current voltages (i.e. because the gas is in contact with both plates 42 and 44, small leakage currents cannot short out the field across the gas-filled gap).
Figure 5 illustrates a further alternative em-bodiment of the invention comprising a transducer 50 having a pair of opposed metal plates 52, 54 across which an electrical potential difference is maintained by a voltage source (not shown). A first plurality of strips 56a, 56b, 56c, etc. of elastomeric dielectric material are disposed between plates 52, 54 in a first direction. That is, strips 56a, 56b and 56c have long-itudinal axes perpendicular to the plane of the paper.
A second plurality of strips of elastomeric dielectric material, only one of which; namely, strip 58a is visi-ble in Figure 5, are disposed between plates 52, 54 in a ~774~5 second direction which is different than the first dir-ection. That is, strip s8a and the other strips com-prising the second plurality of strips have longitudinal axes which are closer to the plane of the paper. The embodiment of Figure 5 may be fabricated by utilizing known techniques to rapidly apply thin elastomeric beads to each of plates 52 and 54, following which the plates may be aligned with the axes of the beads so applied at an angle to each other. This minimizes the contact area between the dielectric material on the two pl~tes 52, 54. The compliance of the elastomeric material is thus increased, resulting in reduced mechanical impedance.
This feature is desirable when large displacements are needed in response to comparatively small voltages across plates 52, 54-Figure 6 illustrates a still further embodi-ment of the invention comprising a transducer 60 having a pair of opposed metal plates 62, 64 across which an electrical potential difference is maintained by a volt-age source (not shown). An electrical insulating mater-ial 66 such as Mylar~ or metal oxide is applied over each of the opposed surfaces of plates 62, 64. A plurality of strips, beads or nodules 68a, 68b, 68c, etc. of elas-tomeric dielectric material are then disposed betweenthe opposed layers of insulating material. (Figure 6 illustrates the use of beads or nodules of elastomeric material as shown in Figure 4, but overlapping strips of elastomeric material could also be used as shown in Fig-ure 5.) Insulating material 66 serves to increase thebreakdown voltage of the gasfilled gap maintained be-tween insulating layers 66 by the elastomeric dielectric material. Since the gap is bounded by insulating mater-ial, electrical breakdown occurs in accordance with a process known as "electrodeless breakdown" or "external ~ ~ - 13 -~'~774~5 electrode bre~kdown". There is some evidence that the minimum breakdown voltage of a gas obtained via elec-trodeless breakdown exceeds that which is obtained when the gas is allowed to contact the electrodes [see: D.
Friedmann, F~ L. Curzon and J. Young: "A New Electrical Breakdown Phenomenon in Gas-Filled Insulating Bulbs", Appl. Phys. Lett. 38, 414-415 (1981)]. Increased break-down voltage is desirable because transducer 60 could then produce larger electrostatic forces than those attainable in the absence of insulating material 66.
Moreover, this reduces the risk of transducer failure by preventing arcing between plates 62, 64. Also, by en-suring that the average conductivity of insulating materiai 66 exceeds that of the gas, one can still main-tain operation at constant voltages, without leakagethrough the air gap reducing the resulting electrostatic force.
The minimum breakdown voltage may also be in-creased by maintaining an electronegative gas such as carbon dioxide, sulphur hexafluoride or oxygen in the gap between plates 62, 64. Mixtures of electronegative and non-electronegative gases are expected to be partic-ularly useful because the high breakdown voltage char-acteristics of electronegative gases could then be ex-ploited in combination with the larger Pd values which characterize the Paschen minimum voltages of non-elec-tronegative gases, which in turn implies that rougher surfaced dielectric materials (i.e. materials having surface pockets deeper than about 16 microns) could be used. The following table provides the Paschen minimum voltage texpressed in volts) and corresponding Pd values (expressed in Torr cm.) for three electronegative gases (carbon dioxide, sulphur hexafluoride and oxygen) and for one non-electronegative gas (air):
774~5 Paschen Min.
Voltage Pd carbon dioxide 488 .45 sulphur hexafluoride 507 .24 oxygen 446 .8 air 260 .6 Figure 7 illustrates yet another embodiment of the invention which, like the embodiment of Figure 6, may be constructed by using alumininized mylar in con-tinuous sheet form. The thin layer of aluminium deposi-ted on the mylar serves as electrically conductive plate material for construction of transducers generally simi-lar to those shown in Figures 4, 5 or 6. Thin beads,strips or nodules of elastomeric material may be applied to the aluminized mylar surface as explained above. The sheet of aluminized mylar may then be cut into a large number of individual plates which may then be stacked one on top of the other to construct a multilayer trans-ducer 70 as shown in Figure 7. As may be seen, trans-ducer 70 includes a plurality of plates 72a, 72b, 72c, etc., each separated by a layer 74a, 74b, etc. of elec-trically insulating mylar. An electrical potential dif-ference is maintained across the plates by a voltagesource (not shown). The elastomeric material applied to the aluminized mylar serves as a compressible dielectric disposed between and in contact with each pair of oppos-ed plates comprising the stack. Although Figure 7 il-lustrates the use of overlapping strips 76a, 76b, 76c,etc. of elastomeric material as shown in Figure 5, those skilled in the art will understand that strips, beads or nodules of elastomeric material could also be used as shown in Figure 4. Furthermore, a layer of insulating material could also be disposed between each pair of ' ~,~X774~.~
opposed plates and the elastomeric dielectric material which separates the plates, as described above with ref-erence to Figure 6.
As in the embodiment of Figure 5, the dielec-tric material 76a, 76b, 76c, etc. separates each of the pairs of opposed plates 72a, 72b, etc. comprising the stack by a distance "d" such that, for a given gas main-tained between the plates at a pressure "P", the product Pd is significantly less than the value required to achieve the Paschen minimum breakdown voltage of the gas. The resultant transducer is capable of generating very large displacements, due to the cumulative effect of the displacements generated by each of the opposed pairs of plates comprising transducer 70.
There are a wide variety of practical applica-tions for elastomer membrane enhanced electrostatic transducers constructed in accordance with the inven-tion. As one example, the invention facilitates theproduction of an inexpensive, highly controllable device for generating small scale motions at forces falling within region 16 shown in Figure 1. This may have ap-plication for example, in the control of machine tools in which fast, accurate, minute movements of a cutting tool are required. This is conventionally done with large, expensive hydraulic controls which are typically not very accurate when dimensions measured in thou-sandths of inches are to be accommodated.
The geometry of the transducer is readily ad-justed to match its acoustic impedance to that of water.
Therefore, transducers constructed in accordance with the invention may be directly coupled to water and are well suited for use in sonar underwater signalling ap-~, ~774~5 plications, over a wide frequency band. Conventionally, in comparison, piezoe]ectric transducers are used in underwater sonar signalling applications but they are only capable of accommodating a very narrow band of frequencies centered on the resonant frequency of the particular piezoelectric crystal material utilized.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the prac-tice in this invention without departing from the spirit or scope thereof. For example, in order to increase the available range of suitable dielectric materials, elas-tomeric materials may be combined with other essentially rigid (i.e. non-elastomeric) dielectric materials to produce composite dielectric structures which retain much of the deformability of elastomers and are thus still capable of exploiting the phenomenon outlined above to yield transducers exhibiting force and mechani-cal impedance characteristics falling within, or evenbeyond, region 16 shown in Figure 1. The rigid dielec-tric portion could be applied to the conductive plates by painting, spraying, vacuum deposition, or other known techniques. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
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FIELD OF THE INVENTION
This application pertains to electrical-to-mechanical transducers. More particularly, the applica-tion pertains to an electrostatic transducer in which an elastomeric dielectric material is disposed between a pair of opposed conductive plates across which an elec-trical potential difference is maintained. Slight sur-face irregularities or pockets in the dielectric mater-ial facilitate dramatic increases of the electric break-down field in the microscopic gap between the plates and the dielectric material, ox in the pockets, thereby yielding extremely high electrostatic forces. Very thin deposits of dielectric material may alternatively be used to maintain a very narrow gap between the opposed plates, thereby also increasing the gap breakdown volt-age, yielding extremely high electrostatic forces and increased compliance of the device.
BACKGROUND OF THE INVENTION
A variety of electrical-to-mechanical trans-ducers exist. Familiar examples include the electro-static transducers incorporated in loudspeakers, the electromagnetic transducers incorporated in electric gauges and the piezoelectric or magnetostrictive trans-ducers used, for example, in certain narrow band under-water signalling applications. Conventional electro-static transducers typically utilize the electrostatic force generated by applying an electrical potential dif-ference between a pair of opposed metal plates separated by an air gap. In an electromagnetic transducer, an electric current causes a force to be applied to a wire 1~774~5 maintained in a magnetic field, thereby moving the wire and whatever it may contact. Piezoelectric transducers incorporate certain crystals which change their shape, and thus move slightly, in response to an applied elec-tric Eield. Magnetostrictive transducers incorporatecertain metals which change their shape, and thus move slightly, in response to an applied magnetic field.
For comparison purposes, it is useful to con-sider transducers having a volume of the order of 100 ml. Conventional electrostatic transducers of this sort have relatively low mechanical impedance (ranging from about 1 to about 100 Newton seconds per metre) and are capable of producing only relatively small forces (typically about .05 to about .5 Newtons). The mech-anical impedance range of electromagnetic transducers is about the same as that of conventional electrostatic transducers, although electromagnetic transducers are capable of producing forces of about .5 to about 10 New-tons. Piezoelectric and magnetostrictive transducers,on the other hand, have extremely high mechanical imped-ance (ranging from about 106 to about 108 Newton seconds per metre) and generate extremely high forces (on the order of about 103 to about 104 Newtons).
It can thus be seen that there is a conspicuous lack of electrical-to-mechanical transducers which, in the 100 ml. size range, would have a mechanical impedance on the order of about 103 to about 105 Newton seconds per metre and be capable of producing forces in the range of about 10 to about 103 ~ewtons. The present invention provides an electrostatic transducer which fills this gap in the prior art.
SUMMARY OF THE INVE~TIO~
~'~774~
In accordance with a first embodiment, the invention provides a transducer, comprising opposed first and second conductive plates between which an electrical potential may be applied; and, an elastomeric dielectric material disposed between the plates and in contact therewith. The dielectric material has a plur-ality of pockets of approximate average depth "d" such that, for a given gas maintained within the pockets at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of the gas. The large breakdown voltages cor-respond to high electric fields and correspondingly high electrostatic forces. At the same time, the deformabil-ity of the elastomeric dielectric material, in conjunc-tion with the gas-filled pockets, enables the structure to be relatively compliant, thus achieving a mechanical impedance in the desired range.
Alternatively, in a second embodiment of the invention, the elastomeric dielectric material may take the form of small strips or nodules disposed between the plates and in contact therewith, thereby separating the plates by a distance "d" such that, for a given gas maintained between the plates at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of the gas.
Advantageously, the elastomeric dielectric material is disposed between the plates at a plurality of discrete sites, thus leaving a gas-filled gap between and in con-tact with both plates in regions not occupied by thedielectric material. In a particularly preferred embod-iment, a first plurality of strips of elastomeric dielectric material are disposed between the plates in a first direction; and, a second plurality of strips of elastomeric dielectric material are disposed between the ~ ~7741~;
plates in a second direction different from the first direcion, thereby increasing the compliance of the elas-tomeric material and decreasing the mechanical impedance of the transducer so as to facilitate large displace-ments in response to comparatively small voltages.
Another particularly preferred embodiment of the invention provides a plurality of conductive plates which may be arranged in a stack. An electrical poten-tial may be applied between each pair of opposed platescomprising the stack. An elastomeric dielectric mater-ial is disposed between and in contact with each pair of opposed plates comprising the stack. The dielectric material separates each of the pairs of opposed plates by a distance "d" such that, for a given gas maintained between the plates at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of the gas.
Advantageously, an electrical insulating material may be disposed between each of the plates and the elastomeric dielectric material so as to increase the gas breakdown voltage, and to lessen the deleterious effects of accidentally exceeding that voltage.
If the gas is air, and if "P" is normal atmos-pheric pressure, then "d" is preferably about 16 mic-rons or less.
The elastomeric dielectric material is prefer-ably neoprene rubber. The conductive plates are prefer-ably formed of aluminized mylar.
BRIEF DESCRIPTION OF THE DRAWI~GS
-.
~'~7741S
Figure 1 is a graph in which force (expressed in Newtons) is plotted as the ordinate versus mechanical impedance (expressed in Newton seconds per metre) as the abscissa for various electrical-to-mechanical trans-ducers having a volume of about 100 millilitres.
Figure 2 is a greatly magnified cross-section-al side view of a portion of a typical electrostatic transducer.
Figure 3 is a greatly magnified cross-sectional side view of a portion of an elastomer mem-brane enhanced electrostatic transducer constructed in accordance with a first embodiment of the invention.
Figure 4 is a greatly magnified cross-section-al side view of a portion of an alternative transducer constructed in accordance with a second embodiment of the invention.
Figure 5 is a greatly magnified cross-section-al side view of a portion of a further alternative tran-sducer constructed in accordance with the invention.
Figure 6 is a greatly magnified cross-section-al side view of a portion of a still further alternative transducer constructed in accordance with the inven-tion.
Figure 7 is a greatly magnified cross-section-al side view of a portion of yet another alternativetransducer constructed in accordance with the inven-tion.
Figure 8 is a graph in which the electrical breakdown voltage for forming a spark in a gas maintain-~774~
ed at a pressue "P" (expressed in Torr) between twometal plates across which a voltage "V" (expressed in volts) is applied is plotted as the ordinate, versus the product Pd where "d" is the distance between the plates (expressed in centimetres). The graph includes plots for various "cathodes"; the "cathode" being the lower voltage plate.
Figure 9 is an electron micrograph of a neo-prene rubber dielectric for use in constructing a trans-ducer in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 is a graph on which transducer force (expressed in Newtons) is plotted as the ordinate versus transducer mechanical impedance (expressed in Newton seconds per metre) as the abscissa for various elec-trical-to-mechanical transducers having a volume of about 100 millilitres. As indicated by region 10 on Figure 1, conventional electrostatic transducers have mechanical impedances which vary from about 1 to about 100 Newton seconds per metre and are capable of produc-ing forces of about .05 to about .5 Newtons. As shown by region 12 on Figure 1, electromagnetic transducers exhibit the same range of mechanical impedance as con-ventional electrostatic transducers, but are capable of producing forces in a range which is roughly about one order of magnitude greater than the force range of con-ventional electrostatic transducers. Piezoelectric andmagnetostrictive transducers, on the other hand, have extremely high mechanical impedance ranging from about 106 to about 108 Newton seconds per metre and are capable of producing forces in the range of about 103 to about 104 Newtons, aB illustrated by region 14 in ,:. .. , :,, .
1~774~
Figure 1.
It can thus be seen that there is a wide range of mechanical impedance and forces which existing elec-trical-to-mechanical transducers are incapable of pro-ducing. This gap, illustrated by region 16 in Figure 1, corresponds to an impedance range of about 102 to about 106 Newton seconds per metre and to a force range of about 10 to about 103 Newtons. The present invention provides an elastomer membrane enhanced elec-tro~tatic transducer which fits neatly within this gap.
That is, the transducer to be described exhibits mechan-ical impedance in the range of about .5x103 to about .5x105 Newton seconds per metre and is capable of gen-erating forces in the range of about 10 to about.5x103 Newtons. There are a wide range of practical applications for which the transducer of the invention is ideally suited. These include machine tool actuators and vibrators, alignment preserving optical components in laser systems and underwater transducers.
Figure 2 is a simplified cross-sectional side view of a conventional electrostatic transducer consist-ing of a pair of opposed metal plates 20, 22 which are separated a distance "d" by an air gap. If an A.C.
voltage source 26 is connected across plates 20, 22 to establish an electrical potential difference across the plates an electrostatic force is generated which causes the plates to oscil].ate in the directions indicated by double headed arrow 28. The magnitude of such oscilla-tion varies in proportion to the magnitude of the square of the applied voltage although, as indicated by region 10 in Figure 1, only comparatively small forces can be produced by conventional electrostatic transducers.
Moreover, there is a maximum breakdown voltage of about 1'~774~5 106 volts per metre beyond which any further increase in voltage across plates 20, 22 results in arcing be-tween the plates, in which case the transducer fails due to a large increase in the flow of electri~al current.
Figure >3 is a graph which illustrates the re-lationship between breakdown voltage "V", plate separa-tion distance "d" and pressure "P" of the gas maintained between the opposed plates of an electrostatic transduc-er like that shown in Figure 2. The graph shows thatfor a given cathode material (the "cathode" being the plate having the lower voltage) such as commercial alum-inum, the breakdown voltage V decreases as the product Pd decreases, until a minimum voltage l'Vmin" is reached; and, that the breakdown voltage V then increas-es dramatically as the product Pd continues to decrease.
It may thus be seen that if the gas pressure P is held constant, the breakdown voltage V decreases as the plate separation distance d decreases until the aforementioned minimum voltage Vmin (known as the "Paschen mini-mum") is reached, but the breakdown voltage V then in-creases dramatically as the plate separation distance d is further decreased. As Figure 8 indicates, the Pasch-en minimum voltage for air, with a commercial aluminum cathode is about 254 volts, and occurs when the product Pd is about 1.2 Torr cm. If the gas pressure P is 1 at-mosphere (i.e. 760 Torr) this corresponds to a plate separation distance d of about 1.2 Torr cm./760 Torr =
1.6x10-3 cm. or about 16 microns.
It has been recognized that an electrostatic transducer capable of measuring small displacements can be made by making d as small as possible. [See: W. B.
Gauster and M. A. Breazeale: "Detector for Measurement of Ultrasonic Strain Amplitudes in Solids", Rev. Sci.
.
~:~77~
Instrum. 37, 1544-1548 (1966); and, J. H. Cantrell and J. S. Heyman: "Broadband Electrostatic Acoustic Trans-ducer for Ultrasonic Measurments in Liquids", Rev. Sci.
Instrum. 50, 31-33 (1979)]. Unfortunately however, it is very difficult to construct a practical electrostatic transducer having a plate separation gap "d" of only about 16 microns and the difficulty increases as "d" is further decreased (as it must be if an electrostatic transducer having higher breakdown voltages is to be produced). Expensive precision machining and cumbersome mounting techniques are required which preclude the use of such transducers in most practical situations.
The inventors have discovered that a practical electrostatic transducer which exploits the foregoing phenomenon may be easily constructed and operated at values of Pd which are significantly less than the value of Pd required to achieve the minumum breakdown voltage of the particular gas maintained between the transducer plates. The term "significantly" is used to imply that the breakdown voltage resulting from a particular value of Pd exceeds the minimum breakdown voltage by about 10%
or more.
In accordance with a first embodiment of the invention, an elastomeric dielectric material is placed between plates 20, 22 of the Figure 2 electrostatic transducer and is maintained in contact with both plates. It is of course well known to provide a dielec-tric materia~ between a pair of opposed plates across which a voltage potential difference is maintained (as in a conventional capacitor). However, the inventors have discovered that if the dielectric material has very slight surface irregularities or pockets, and is elasto-meric tfor example, neoprene rubber), then the desired _ g _ ~ .
1 ~774~
increase in gap breakdown voltage may be achieved,thereby Eacilitating production of transducers having mechanical impedance/force characteristics falling with-in region 16 depicted in Figure 1, as a result of the deformability of the elastomeric dielectric material.
Figure 3 is a greatly magnified cross-sectional side view of an electrostatic transducer 30 according to the first embodiment of the invention.
Transducer 30 comprises a pair of thin aluminium plates 32, 34 across which an electrical potential difference is maintained by a voltage source (not shown). A com-pressible neoprene rubber dielectric 36 having a break-down voltage of about 2x107 volts per metre is dispos-ed between plates 32, 34 and in contact therewith. Thesurfaces of dielectric 36 adjacent plates 32, 34 are very slightly irregular such that, when viewed on the microscopic scale shown in the electron micrograph of Figure 9, the surfaces exhibit a large plurality of poc-kets having an approximate average depth "d" of about 10microns each. Accordingly, when dielectric 36 is dis-posed between plates 32, 34 there is a corresponding large plurality of discrete gaps on the order of about 10 microns between each of plates 32, 34 and the adjac-ent surfaces of dielectric 36. The aforementioned poc-kets would ordinarily be distributed throughout dielec-tric 36, and need not be confined to (or even present on) the surface of dielectric 36.
The slight surface irregularities of dielec-tric 36 provide, in effect, a gap of approximately 10 microns between each of plates 32, 34 and the adjacent faces of dielectric material 36. Alternatively, the pockets distributed throughout dielectric 36 constitute a large number of discrete, localized gaps of about 10 1 ~774~5 microns each. As discussed above with reference to Fig-ure 8, small gaps of this order of magnitude are capable of sustaining relatively high voltages before breakdown occurs. Moreover, because the dielectric material is elastomeric, plates 32,34 may oscillate significantly in response to the large electrostatic force corresponding to the large voltages sustainable by the slight surface irregularities or pockets of the dielectric. Dielectric material 36 thus facilitates the production of electro-static forces on the order of the range of forces andmechanical impedances indicated by region 16 in Figure 1.
The first embodiment of the invention describ-ed above and illustrated in Figure 3 is subject to a number of shortcomings. For example, if dielectric mat-erial 36 is relatively thick in comparison to the aver-age depth d of the dielectric surface irregularities or pockets, and if transducer 30 is operated with an A.C.
voltage, then the effective efficiency of the device is decreased. This decrease arises because of the extra power consumed in the process of charging and discharg-ing the relatively large volume of the dielectric mater-ial. Secondly, if the device is connected across a con-stant voltage source, small currents flowing through thedielectric surface irregularity or pocket gaps could, after a time, short out the electric field in the gaps, thereby reducing the electrostatic force to zero. A
further shortcoming of such a device is that it could be difficult to manufacture inexpensively in large quanti-ties. The foregoing shortcomings are overcome by the second and further alternative embodiments of the inven-tion illustrated in Figures 4, 5, 6 and 7 which will now be described.
~ ~7'741~
Figure 4 illustrates a transducer 40 having a pair of opposed metal pla~es 42, 44 across which an electrical potential difference is maintained by a volt-age source (not shown~. A plurality of strips, beads or nodules 46a, 46b, 46c, etc. of elastomeric dielectric material are disposed between plates 42 and 44 in con-tact therewith, thereby separating plates 42, 44 by a distance "d" such that, for a given gas maintained be-tween plates 42, 44 at a pressure "P", the product Pd is significantly less than the value required to achieve the Paschen minimum breakdown voltage of the gas. There are known techniques for rapid application of thin strips or small beads of elastomeric material to sur-faces, which may be adapted to construct the second em-bodiment of the invention illustrated in Figure 4. Notethat in the embodiment of Figure 4 the thickness of the dielectric material is reduced to equal the desired min-imum displacement "d" between plates 42, 44; thereby facilitating operation of the device at direct current voltages (i.e. because the gas is in contact with both plates 42 and 44, small leakage currents cannot short out the field across the gas-filled gap).
Figure 5 illustrates a further alternative em-bodiment of the invention comprising a transducer 50 having a pair of opposed metal plates 52, 54 across which an electrical potential difference is maintained by a voltage source (not shown). A first plurality of strips 56a, 56b, 56c, etc. of elastomeric dielectric material are disposed between plates 52, 54 in a first direction. That is, strips 56a, 56b and 56c have long-itudinal axes perpendicular to the plane of the paper.
A second plurality of strips of elastomeric dielectric material, only one of which; namely, strip 58a is visi-ble in Figure 5, are disposed between plates 52, 54 in a ~774~5 second direction which is different than the first dir-ection. That is, strip s8a and the other strips com-prising the second plurality of strips have longitudinal axes which are closer to the plane of the paper. The embodiment of Figure 5 may be fabricated by utilizing known techniques to rapidly apply thin elastomeric beads to each of plates 52 and 54, following which the plates may be aligned with the axes of the beads so applied at an angle to each other. This minimizes the contact area between the dielectric material on the two pl~tes 52, 54. The compliance of the elastomeric material is thus increased, resulting in reduced mechanical impedance.
This feature is desirable when large displacements are needed in response to comparatively small voltages across plates 52, 54-Figure 6 illustrates a still further embodi-ment of the invention comprising a transducer 60 having a pair of opposed metal plates 62, 64 across which an electrical potential difference is maintained by a volt-age source (not shown). An electrical insulating mater-ial 66 such as Mylar~ or metal oxide is applied over each of the opposed surfaces of plates 62, 64. A plurality of strips, beads or nodules 68a, 68b, 68c, etc. of elas-tomeric dielectric material are then disposed betweenthe opposed layers of insulating material. (Figure 6 illustrates the use of beads or nodules of elastomeric material as shown in Figure 4, but overlapping strips of elastomeric material could also be used as shown in Fig-ure 5.) Insulating material 66 serves to increase thebreakdown voltage of the gasfilled gap maintained be-tween insulating layers 66 by the elastomeric dielectric material. Since the gap is bounded by insulating mater-ial, electrical breakdown occurs in accordance with a process known as "electrodeless breakdown" or "external ~ ~ - 13 -~'~774~5 electrode bre~kdown". There is some evidence that the minimum breakdown voltage of a gas obtained via elec-trodeless breakdown exceeds that which is obtained when the gas is allowed to contact the electrodes [see: D.
Friedmann, F~ L. Curzon and J. Young: "A New Electrical Breakdown Phenomenon in Gas-Filled Insulating Bulbs", Appl. Phys. Lett. 38, 414-415 (1981)]. Increased break-down voltage is desirable because transducer 60 could then produce larger electrostatic forces than those attainable in the absence of insulating material 66.
Moreover, this reduces the risk of transducer failure by preventing arcing between plates 62, 64. Also, by en-suring that the average conductivity of insulating materiai 66 exceeds that of the gas, one can still main-tain operation at constant voltages, without leakagethrough the air gap reducing the resulting electrostatic force.
The minimum breakdown voltage may also be in-creased by maintaining an electronegative gas such as carbon dioxide, sulphur hexafluoride or oxygen in the gap between plates 62, 64. Mixtures of electronegative and non-electronegative gases are expected to be partic-ularly useful because the high breakdown voltage char-acteristics of electronegative gases could then be ex-ploited in combination with the larger Pd values which characterize the Paschen minimum voltages of non-elec-tronegative gases, which in turn implies that rougher surfaced dielectric materials (i.e. materials having surface pockets deeper than about 16 microns) could be used. The following table provides the Paschen minimum voltage texpressed in volts) and corresponding Pd values (expressed in Torr cm.) for three electronegative gases (carbon dioxide, sulphur hexafluoride and oxygen) and for one non-electronegative gas (air):
774~5 Paschen Min.
Voltage Pd carbon dioxide 488 .45 sulphur hexafluoride 507 .24 oxygen 446 .8 air 260 .6 Figure 7 illustrates yet another embodiment of the invention which, like the embodiment of Figure 6, may be constructed by using alumininized mylar in con-tinuous sheet form. The thin layer of aluminium deposi-ted on the mylar serves as electrically conductive plate material for construction of transducers generally simi-lar to those shown in Figures 4, 5 or 6. Thin beads,strips or nodules of elastomeric material may be applied to the aluminized mylar surface as explained above. The sheet of aluminized mylar may then be cut into a large number of individual plates which may then be stacked one on top of the other to construct a multilayer trans-ducer 70 as shown in Figure 7. As may be seen, trans-ducer 70 includes a plurality of plates 72a, 72b, 72c, etc., each separated by a layer 74a, 74b, etc. of elec-trically insulating mylar. An electrical potential dif-ference is maintained across the plates by a voltagesource (not shown). The elastomeric material applied to the aluminized mylar serves as a compressible dielectric disposed between and in contact with each pair of oppos-ed plates comprising the stack. Although Figure 7 il-lustrates the use of overlapping strips 76a, 76b, 76c,etc. of elastomeric material as shown in Figure 5, those skilled in the art will understand that strips, beads or nodules of elastomeric material could also be used as shown in Figure 4. Furthermore, a layer of insulating material could also be disposed between each pair of ' ~,~X774~.~
opposed plates and the elastomeric dielectric material which separates the plates, as described above with ref-erence to Figure 6.
As in the embodiment of Figure 5, the dielec-tric material 76a, 76b, 76c, etc. separates each of the pairs of opposed plates 72a, 72b, etc. comprising the stack by a distance "d" such that, for a given gas main-tained between the plates at a pressure "P", the product Pd is significantly less than the value required to achieve the Paschen minimum breakdown voltage of the gas. The resultant transducer is capable of generating very large displacements, due to the cumulative effect of the displacements generated by each of the opposed pairs of plates comprising transducer 70.
There are a wide variety of practical applica-tions for elastomer membrane enhanced electrostatic transducers constructed in accordance with the inven-tion. As one example, the invention facilitates theproduction of an inexpensive, highly controllable device for generating small scale motions at forces falling within region 16 shown in Figure 1. This may have ap-plication for example, in the control of machine tools in which fast, accurate, minute movements of a cutting tool are required. This is conventionally done with large, expensive hydraulic controls which are typically not very accurate when dimensions measured in thou-sandths of inches are to be accommodated.
The geometry of the transducer is readily ad-justed to match its acoustic impedance to that of water.
Therefore, transducers constructed in accordance with the invention may be directly coupled to water and are well suited for use in sonar underwater signalling ap-~, ~774~5 plications, over a wide frequency band. Conventionally, in comparison, piezoe]ectric transducers are used in underwater sonar signalling applications but they are only capable of accommodating a very narrow band of frequencies centered on the resonant frequency of the particular piezoelectric crystal material utilized.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the prac-tice in this invention without departing from the spirit or scope thereof. For example, in order to increase the available range of suitable dielectric materials, elas-tomeric materials may be combined with other essentially rigid (i.e. non-elastomeric) dielectric materials to produce composite dielectric structures which retain much of the deformability of elastomers and are thus still capable of exploiting the phenomenon outlined above to yield transducers exhibiting force and mechani-cal impedance characteristics falling within, or evenbeyond, region 16 shown in Figure 1. The rigid dielec-tric portion could be applied to the conductive plates by painting, spraying, vacuum deposition, or other known techniques. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
~, .
~ ' .
Claims (12)
1. A transducer, comprising:
(a) opposed first and second conductive plates for application of an electrical potential therebetween; and, (b) an elastomeric dielectric material dis-posed between said plates and in contact therewith;
said dielectric material having a plurality of pockets of approximate average depth "d" such that, for a given gas maintained within said pockets at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of said gas.
(a) opposed first and second conductive plates for application of an electrical potential therebetween; and, (b) an elastomeric dielectric material dis-posed between said plates and in contact therewith;
said dielectric material having a plurality of pockets of approximate average depth "d" such that, for a given gas maintained within said pockets at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of said gas.
2. A transducer, comprising:
(a) opposed first and second conductive plates for application of an electrical potential therebetween; and, (b) an elastomeric dielectric material dis-posed between said plates and in contact therewith, thereby separating said plates by a distance "d" such that, for a given gas maintained between said plates at a pressure "P", the product Pd is signifi-cantly less than the value required to achieve the minimum breakdown voltage of said gas.
(a) opposed first and second conductive plates for application of an electrical potential therebetween; and, (b) an elastomeric dielectric material dis-posed between said plates and in contact therewith, thereby separating said plates by a distance "d" such that, for a given gas maintained between said plates at a pressure "P", the product Pd is signifi-cantly less than the value required to achieve the minimum breakdown voltage of said gas.
3. A transducer, comprising:
(a) a plurality of conductive plates arranged in a stack for application of an electri-cal potential between each pair of op-- Page 1 of Claims -posed plates comprising said stack; and, (b) an elastomeric dielectric material dis-posed between and in contact with each pair of opposed plates comprising said stack;
said dielectric material separating each of said pairs of opposed plates by a distance "d" such that, for a given gas maintained between said plates at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of said gas.
(a) a plurality of conductive plates arranged in a stack for application of an electri-cal potential between each pair of op-- Page 1 of Claims -posed plates comprising said stack; and, (b) an elastomeric dielectric material dis-posed between and in contact with each pair of opposed plates comprising said stack;
said dielectric material separating each of said pairs of opposed plates by a distance "d" such that, for a given gas maintained between said plates at a pressure "P", the product Pd is significantly less than the value required to achieve the minimum breakdown voltage of said gas.
4. A transducer as defined in claim 1, 2 or 3, further comprising an electrical insulating material disposed between each of said plates and said elastomer-ic dielectric material.
5. A transducer as defined in claim 1, 2 or 3 wherein said gas is air, "P" is normal atmospheric pres-sure, and "d" is less than about 16 microns.
6. A transducer is defined in claim 1, 2 or 3 wherein said dielectric material is neoprene rubber.
7. A transducer as defined in claim 1, 2 or 3 wherein said gas is an electronegative gas, "P" is nor-mal atmospheric pressure and "d" is less than about 10 microns.
8. A transducer as defined in claim 1, 2 or 3 wherein said gas is a mixture of electronegative and non-electronegative gases.
9. A transducer as defined in claim 1, 2 or 3 wherein said plates are formed of aluminized mylar.
- Page 2 of Claims -
- Page 2 of Claims -
10. A transducer as defined in claim 1, 2 or 3, wherein said dielectric material is disposed at a plur-ality of sites between said plates, leaving said gas be-tween and in contact with said plates at regions other than said sites.
11. A transducer as defined in claim 2 or 3, wherein:
(a) a first plurality of strips of elastomer-ic dielectric material are disposed be-tween said plates in a first direction;
and, (b) a second plurality of strips of elasto-meric dielectric material are disposed between said plates in a second direction different than said first direction.
(a) a first plurality of strips of elastomer-ic dielectric material are disposed be-tween said plates in a first direction;
and, (b) a second plurality of strips of elasto-meric dielectric material are disposed between said plates in a second direction different than said first direction.
12. A transducer as defined in claim 1, 2 or 3, wherein said dielectric material is a composite struc-ture of elastomeric and non-elastomeric material.
- Page 3 of Claims -
- Page 3 of Claims -
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000506496A CA1277415C (en) | 1986-04-11 | 1986-04-11 | Elastomer membrane enhanced electrostatic transducer |
| US07/037,265 US4885783A (en) | 1986-04-11 | 1987-04-10 | Elastomer membrane enhanced electrostatic transducer |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000506496A CA1277415C (en) | 1986-04-11 | 1986-04-11 | Elastomer membrane enhanced electrostatic transducer |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1277415C true CA1277415C (en) | 1990-12-04 |
Family
ID=4132870
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000506496A Expired - Lifetime CA1277415C (en) | 1986-04-11 | 1986-04-11 | Elastomer membrane enhanced electrostatic transducer |
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| Country | Link |
|---|---|
| US (1) | US4885783A (en) |
| CA (1) | CA1277415C (en) |
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| US2221671A (en) * | 1938-07-09 | 1940-11-12 | Gen Electric | Gas dielectric media |
| US2796467A (en) * | 1951-12-12 | 1957-06-18 | Bell Telephone Labor Inc | Directional transducer |
| BE540809A (en) * | 1954-08-26 | |||
| NL281794A (en) * | 1961-08-07 | |||
| US3373251A (en) * | 1965-02-23 | 1968-03-12 | Shure Bros | Electrostatic transducer |
| FR2123070B1 (en) * | 1970-11-06 | 1977-07-08 | ||
| FR2114999B1 (en) * | 1970-11-20 | 1973-11-23 | Anvar | |
| FR2144933A5 (en) * | 1971-07-02 | 1973-02-16 | Anvar | |
| US3787642A (en) * | 1971-09-27 | 1974-01-22 | Gte Automatic Electric Lab Inc | Electrostatic transducer having resilient electrode |
| US3736436A (en) * | 1971-11-04 | 1973-05-29 | Mc Donnell Douglas Corp | Electret pressure transducer |
| US3742152A (en) * | 1971-11-22 | 1973-06-26 | Anvar | Ultrasonic transducers |
| US3821491A (en) * | 1972-05-15 | 1974-06-28 | Amperex Electronic Corp | Microphone construction |
| US3890511A (en) * | 1974-04-15 | 1975-06-17 | Gte Laboratories Inc | Electret pulse generator |
| US3978446A (en) * | 1975-08-25 | 1976-08-31 | Gte Sylvania Incorporated | Electret cable hydrophone array |
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| US4105877A (en) * | 1977-04-25 | 1978-08-08 | Peters Bernardus Gradus | Electrostatic loudspeaker having elastic diaphragm spacer elements cured in situ |
| FR2397120A1 (en) * | 1977-07-04 | 1979-02-02 | Lewiner Jacques | IMPROVEMENTS IN ELECTROMECHANICAL TRANSDUCERS |
| US4151378A (en) * | 1978-05-08 | 1979-04-24 | Electro-Voice, Incorporated | Electrostatic microphone with damping to improve omnidirectionality, flatten frequency response, reduce wind noise |
| US4246449A (en) * | 1979-04-24 | 1981-01-20 | Polaroid Corporation | Electrostatic transducer having optimum sensitivity and damping |
| US4620262A (en) * | 1984-09-13 | 1986-10-28 | Olsen Randall B | Pyroelectric energy converter element comprising vinylidene fluoride-trifluoroethylene copolymer |
-
1986
- 1986-04-11 CA CA000506496A patent/CA1277415C/en not_active Expired - Lifetime
-
1987
- 1987-04-10 US US07/037,265 patent/US4885783A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| US4885783A (en) | 1989-12-05 |
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