capacitive sensor

Abstract

This invention discloses a dynamic capacitive sensor configuration that applies minimal force and motion resistance to the moving electrode. The moving electrode avoids the adverse effects of large bias voltages, such as pull-in instability, regardless of any level of compliance. This configuration facilitates the introduction of highly compliant thin electrode materials that exhibit minimal potential resistance to motion. This type of material is particularly useful for sensing sound. Large bias voltages, such as 400V, can be applied without affecting its movement. The electrical sensitivity to sound is very high, for example, approximately 0.5 volts / Pascal, two orders of magnitude greater than typical sound sensors.

Description

Technical Field

[0001] This technology relates to the field of capacitive sensors. Background Technology

[0002] Sensors that rely on changes in capacitance are used in many important electronic products and systems. Capacitive sensors designed to detect motion or sound typically use a lightweight, movable electrode and a fixed electrode. A bias voltage applied between these two electrodes allows for the detection of capacitance changes caused by their relative motion. When detecting minute movements, flow rates, or sound pressure levels, the effective stiffness between the movable and fixed electrodes is typically reduced, thereby improving sensor performance. In sensitive microphones, it may be desirable to use highly compliant movable electrodes with the lowest possible mass and stiffness. In such cases, care must be taken when designing the capacitive electrodes to minimize the effects of electrostatic forces.

[0003] As is well known, the design of capacitive motion sensors using parallel-plate capacitors requires sufficiently high mechanical stiffness in the moving electrode to prevent collapse on the bias electrode. This is because electrostatic force acts as negative stiffness in minute movements around a static equilibrium position. If the bias voltage is high enough, this negative stiffness may exceed the mechanical stiffness, leading to instability. Other electrode designs result in electrostatic force acting as positive stiffness, increasing the overall system stiffness as the bias voltage increases. In this case, excessively high bias voltages can lead to a reduced response, thus decreasing sensitivity and the input / output gain of the responsiveness measurement detector system. Regardless of whether the electrostatic stiffness is positive or negative, it is almost always true that stiffness caused by electrostatic force degrades sensor performance.

[0004] If an electrostatic sensor has two electrodes, a change in the position of the moving electrode typically results in a change in electrostatic potential energy. The effective force exerted by the electric field will be equal to the derivative of this potential energy with respect to the position of the moving electrode. To minimize the electrostatic force acting on the moving electrode, an additional fixed electrode can be incorporated so that the total potential energy of the system remains approximately constant as the position of the moving electrode changes. While the total potential energy is nearly constant—leading to a smaller electrostatic force and corresponding stiffness—the two fixed electrodes will experience different charges as the position of the moving electrode changes. Sensing these two fixed electrodes separately provides the sensor with a significantly reduced effect of electrostatic force on its motion.

[0005] In addition to seeking a design that keeps the total electrostatic potential energy approximately constant as the electrodes move, it is also desirable to achieve absolute stability during large movements. This can be achieved if the electrostatic force on the moving electrode always acts to restore it to its nominal equilibrium position for all possible movements.

[0006] Extremely thin, compliant materials can be used to construct these sensing electrodes, such as graphene[1],[2]. However, these structures have very low bending stiffness, making it difficult to incorporate them into conventional microphone designs without being strongly affected by electrostatic forces; their use in acoustic sensing requires new electrode design methods.

[0007] Highly compliant materials have shown promising prospects for acoustic sensing. Fine fibers, such as spider silk, have been found to represent the movement of air in a sound field very accurately[3],[4]. The challenge of integrating highly compliant electrodes has spurred the development of microphones that integrate optical sensing[5]-[7]. While optical microphones do achieve the goal of preventing designers from having to consider the effects of sensing mechanisms on forces applied to mechanical components, they have not yet proven to be competitive in high-capacity, low-cost devices. The use of piezoelectric materials has also shown promise in avoiding the challenges of capacitive sensing on compliant microphone diaphragms[8]. It should also be mentioned that another motivation for avoiding parallel-plate capacitive sensing schemes is that viscous damping caused by flow between electrodes is a major source of thermal noise in miniature microphones[9].

[0008] Figures 1A to 1D A conventional capacitive sensing scheme is shown. Figure 1A Parallel plates separated by a gap that varies with sound pressure are shown. Figure 1B Parallel plates separated by gaps are shown, and the overlapping portion in the plane parallel to the plates varies with sound pressure. Figure 1C The diagram shows a set of three parallel plates, where the distance between the center plate and the corresponding outer plate varies with sound pressure. Figure 1D The diagram shows a set of three parallel plates, one of which moves parallel to the plane of the plate in response to sound pressure, causing the other two adjacent and coplanar plates to overlap differentially and be separated by a gap.

[0009] Of course, there can be countless electrode geometries in electrostatic induction schemes. Depending on the amount of mass, stiffness, and damping allowed in the moving electrode for a particular sensing application, existing methods can achieve varying amounts of electrostatic force and stiffness. Figure 1 shows four common configurations

[10] . Figure 1A and Figure 1B The two configurations shown on the left consist of two electrodes, while Figure 1C and Figure 1D The configuration shown on the right contains three electrodes. Figure 1A and Figure 1C In the middle, the electrode moves laterally to its parallel plane, while Figure 1B and Figure 1D In this process, the motion is parallel to the electrode plane. To date, Figure 1AThe configuration of parallel plates is the most common in acoustic sensors, with its moving electrodes comprising pressure-sensing diaphragms. Each of these can be approximated using well-known expressions for the capacitance of parallel plates. This approximation assumes that the distance between the planes is small enough relative to all other dimensions that the electric field is dominated by straight field lines orthogonal to the planes.

[0010] Considered Figures 1A to 1D Approximate expressions for the electrostatic potential energy, force, and effective stiffness of each of the four sensing configurations shown. It is assumed that the second electrode in each panel is a moving electrode, and the remaining electrodes remain stationary. Let x be the displacement of the moving electrode relative to its nominal position. Each panel is shown in a cross-section, where it is assumed that the electrodes have a constant cross-section in dimension L, which is related to... Figures 1A to 1D The planes are orthogonal. It is also assumed that electrode 2 is biased with a constant voltage V2, while the other electrodes remain at zero potential.

[0011] Figure 1A The potential energy of the configuration is:

[0012] Where ε = 8.854 pF / m is the dielectric constant of the medium. The effective electrostatic force associated with coordinate x will be V. a The derivative at x is assumed to be the equilibrium position

[11] :

[0013]

[0014] This force consistently pulls the moving electrode toward the fixed electrode. For small perturbations around the equilibrium point x, this force will be proportional to the motion, where the negative of this proportionality constant is the equivalent electrostatic stiffness k. a :

[0015]

[0016] Therefore, for the realizable values ​​of x, Figure 1A The electrostatic force in the electrode is always negative. This is the electrode configuration for almost all pressure-sensing microphones.

[0017] A similar method can be used to estimate. Figure 1B The electrostatic energy, force, and stiffness of the configuration shown are...

[0018]

[0019] The effective electrostatic force is:

[0020] In this approximation, the force is independent of x and also serves to pull the moving electrode to its nominal position. For this constant force, the effective stiffness is zero, and k b≈0. This configuration can be achieved using intersecting fingers or fins and has been successfully integrated into some acoustic pressure sensors

[12] . It should be noted that a more detailed electrostatic analysis of this configuration shows that the electrostatic stiffness becomes positive when x is not small relative to W

[13] . While avoiding instability, the electrostatic force hinders electrode movement.

[0021] Figure 1C The electrostatic potential energy is:

[0022] This expression depends on two terms, one of which increases with x, and the other decreases with x. The effective electrostatic force is:

[0023] And the effective electrostatic stiffness is:

[0024] exist Figure 1D In the above, when x = 0, we assume that electrode 2 is centered at the intersection of the two fixed electrodes, and therefore the width of the overlap with each fixed electrode is W / 2. Then, Figure 1D The electrostatic potential energy of the three electrodes in the configuration is:

[0025]

[0026] Since energy is independent of x, the effective electrostatic force and stiffness are zero, f d =0,k d =0. While this is ideal in sensors, it is difficult to achieve in condenser microphones. The electrode configuration presented below can be seen as a... Figure 1D An approximate attempt, in which the moving electrode is displaced in a direction perpendicular to its plane rather than parallel to it, such as... Figure 1D As shown. Further analysis of the system is provided in Miles, RN, “Notes on Electrostatics”, State University of New York, Binghamton, NY 13902-6000, the entire contents of which are expressly incorporated herein by reference.

[0027] See also 3931469; 3935397; 3941946; 3942029; 3944756; 3946422; 3958662; 3961202; 3980838; 3992585; 4006317; 4014091; 4034332; 4037062; 4046974; 40 63050; 4081626; 4085297; 4093884; 4122302; 4149095; 4151480; 4160882; 4170721; 4188513; 4207442; 4215249; 4225755; 4246448; 4246449; 424904 3; 4281221; 4288735; 4289936; 4302634; 4311881; 4323736; 4329547; 4360955; 4401858; 4403117; 4409441; 4414433; 4420790; 4429189; 4429191; 44 29192; 4429193; 4434327; 4436648; 4439641; 4439642; 4461931; 4489278; 4491697; 4492825; 4515997; 4524247; 4533795; 4541112; 4542264; 4558184 ;4567445;4582961;4615105;4621171;4764690;4767973;4790021;4796725;4802227;4849050;4849071;4922471;4977590;4993072;5014322;503 8459; 5054081; 5097224; 5161128; 5206914; 5208789; 5214709; 5335210; 5392358; 5452268; 5471540; 5490220; 5570428; 5573679; 5590212; 5600610 ;5712598;5745438;5802198;5854846;5862239;5870482;5978491;6075867;6125189;6145186;6175636;6178249;6188772;6201874;6218883;624 3474; 6249075; 6304662; 6308398; 6343129; 6357299; 6366678; 6376971; 6393129; 6427015; 6434245; 6441451; 6449370; 6483924; 6493288; 6504937;6510231；6535460；6535612；6543110；6545384；6580797；6583533；6584206；6600825；6628791；6630639；6661897；6664718；6667189；6677176；6724058；6731766；6741709；6744896；6756248；6760455；6781284；6785393；6788794；6788795；6804362；6806593；6812620；6812624；6818092；6819769；6829131；6842964；6870938；6870939；6911764；6940211；6944308；6978029；6987859；7003127；7019955；7023066；7034432；7039202；7040173；7049732；7054456；7062055；7064472；7074634；7095864；7107665；7132307；7142684；7146016；7152481；7158646；7193256；7194095；7199501；7208996；7215527；7218742；7221768；7224106；7233097；7233679；7256927；7259503；7269267；7269268；7292700；7295675；7298856；7305096；7317234；7320457；7327851；7329933；7346178；7352876；7359286；7362032；7362873；7368862；7377175；7386136；7394182；7400737；7425749；7447326；7461281；7466835；7468575；7489791；7493821；7570773；7579678；7585743；7595580；7607355；7608989；7620197；7642575；7668323；7697899；7702118；7702124；7710371；7715583；7756279；7761981；7769193；7781249；7804968；7804969；7804971；7805821；7812418；7829366；7835533；7848532；7855095；7856804；7860258；7880565；7884467；7888840；7889882；7894616；7898159；7899196；7903831；7907743；7911115；7912235；7912236；7916879；7923064；7923902；7925033；7925221；7932117；7940944；7948731；7949142；7951636；7953235；7970154；7974430；8000483；8004373；8005242；8009838；8018301；8023667；8036401；8041059；8042264；8045733；8045734；8047995；8054566；8059837；8059838；8059842；8064620；8072010；8073166；8073167；8073179；8080835；8081784；8085956；8085965；8090125；8093783；8094839；8094841；8094844；8098853；8098855；8103039；8104354；8107651；8111847；8111871；8114700；8126166；8126167；8126171；8130986；8134375；8138034；8139762；8139790；8139794；8165323；8170237；8175293；8175294；8183739；8184832；8188557；8194908；8196282；8199939；8218794；8229140；8242840；8243962；8243966；8254598；8259963；8265287；8284967；8295514；8295528；8300858；8300860；8327521；8327711；8335328；8345898；8345910；8369545；8369552；8374363；8379890；8385570；8385586；8389349；8391520；8401217；8401513；8405449；8406437；8411882；8416973；8433084；8438710；8447049；8448326；8456958；8467550；8467559；8468665；8497149；8502329；8503702；8508109；8509459；8515100；8519492；8526656；8542850；8542852；8542853；8546170；8548178；8553913；8559660；8562565；8565452；8565454；8582787；8588433；8588438；8588451；8590136；8594349；8600083；8605919；8611566；8618718；8625809；8625823；8625824；8625825；8630429；8630430；8637945；8638249；8643129；8643382；8644529；8664733；8666094；8666095；8666097；8670581；8673732；8675895；8686519；8692340；8698255；8698256；8699726；8699728；8699740；8705767；8705775；8710601；8718297；8723277；8724832；8731220；8737646；8742517；8744117；8755539；8755541；8755556；8758253；8760031；8767980；8774428；8783113；8787600；8787601；8790567；8792658；8803261；8804982；8811635；8818007；8824706；8824707；8824713；8831246；8836111；8837754；8842858；8847289；8848950；8855335；8855337；8860154；8861764；8873777；8885853；8897465；8913762；8921957；8929584；8942389；8942394；8958574；8958581；8962368；8965008；8965013；8965027；8975791；8975984；8976997；8983090；8983097；8983099；8988911；8995690；9001622；9002037；9002043；9008332；9008336；9008344；9031266；9042578；9056760；9059630；9061318；9071694；9078069；9083286；9083288；9084366；9085012；9094110；9094111；9094112；9094764；9096424；9107008；9111548；9113260；9113263；9124220；9128136；9131319；9133016；9139418；9143869；9143870；9143876；9148712；9148726；9148729；9148730；9154886；9161113；9167354；9170164；9179221；9181080；9181086；9197967；9204224；9210516；9212046；9214151；9215532；9216897；9219963；9221675；9226079；9232317；9236837；9241205；9242275；9247331；9250142；9253579；9258651；9258660；9264815；9266713；9270238；9271067；9277327；9277329；9281744；9282389；9282415；9287834；9288583；9290375；9294847；9301036；9301055；9319765；9319772；9321626；9327967；9332332；9332342；9332345；9337722；9338557；9338559；9340413；9342179；9344805；9344807；9344808；9344809；9344810；9350305；9351062；9351074；9351083；9357294；9357296；9363610；9369804；9369810；9382109；9392359；9402137；9403670；9407991；9408555；9413317；9414175；9419562；9420365；9420380；9420391；9426563；9428379；9438979；9439002；9444928；9445173；9445188；9451359；9455671；9456283；9462364；9462395；9466277；9467774；9470710；9470910；9479875；9488541；9491531；9497552；9499395；9502019；9503814；9503820；9503821；9503823；9510108；9510121；9516415；9516420；9516425；9516428；9518884；9520505；9521492；9525925；9537359；9538273；9540226；9544672；9544697；9548632；9548655；9554212；9554213；9559647；9560454；9571931；9575116；9578424；9584924；9584941；9590570；9591408；9591417；9596995；9602921；9602924；9609429；9609432；9609764；9611135；9615167；9628886；9628909；9628920；9634628；9635460；9641949；9648433；9654071；9658179；9661411；9661423；9667173；9668047；9668056；9668062；9673768；9673785；9674627；9676615；9676617；9681229；9681243；9685254；9686617；9686618；9692372；9693135；9695038；9706294；9706312；9706618；9708174；9712923；9716945；9722563；9723423；9729014；9729114；9729988；9736586；9736594；9738514；9743167；9743191；9743196；9743203；9756159；9756430；9762188；9769573；9774969；9778302；9781518；9787142；9790087；9791341；9793764；9794661；9794711；9800212；9800980；9809444；9809448；9809451；9812906；9813831；9815685；9820056；9825492；9828236；9828237；9831723；9832573；9838767；9843862；9854360；9854367；9860649；9866938；9866959；9866972；9877106；9878901；9893691；9894437；9900707；9906869；9919913；9921114；9929603；9930451；9936304；9941817；9942666；9944514；9947858；9949023；9949025；9949037；9955269；9955273；9961440；9961451；9966090；9967677；9967678；9967679；20010002865；20010005032；20010033670；20010046306；20020034312；20020048220；20020067663；20020076069；20020076076；20020093038；20020118850；20020122561；20020127760；20020141606；20020172387；20030016839；20030021425；20030021432；20030034536；20030057068；20030063762；20030068055；20030118203；20030123683；20030128847；20030133588；20030137021；20030174850；20030210799；20040062405；20040088851；20040113153；20040179705；20040179706；20040179709；20040184633；20040252858；20050002536；20050005421；20050013455；20050058298；20050061770；20050069164；20050094832；20050123155；20050196010；20050207596；20050254671；20050254679；20050259835；20050262947；20060008097；20060008098；20060072770；20060078137；20060078148；20060093170；20060093171；20060131163；20060177083；20060210106；20060215858；20060227984；20060230835；20060233400；20060233401；20060256981；20060280319；20060284516；20060285707；20070003082；20070009111；20070023851；20070056377；20070057603；20070058825；20070058826；20070075956；20070076904；20070108541；20070113664；20070116305；20070121967；20070121972；20070140514；20070154040；20070160248；20070182002；20070189559；20070193354；20070201709；20070201710；20070230721；20070242844；20070274544；20070284682；20070286438；20070297631；20080006093；20080019543；20080031476；20080042223；20080047128；20080075193；20080075306；20080083961；20080089536；20080104825；20080123242；20080123876；20080123878；20080164888；20080175418；20080190203；20080192962；20080203560；20080204379；20080205668；20080212807；20080229840；20080247573；20080285784；20090003629；20090003630；20090016550；20090022341；20090050989；20090060230；20090060232；20090067659；20090087002；20090087009；20090090190；20090130783；20090136064；20090154729；20090161886；20090161890；20090169035；20090185700；20090190782；20090202083；20090208037；20090214049；20090214061；20090214062；20090218642；20090232336；20090243058；20090252351；20090262958；20090278217；20090285414；20090316935；20100013501；20100072561；20100084721；20100098284；20100119088；20100142742；20100142744；20100155864；20100158279；20100158280；20100166227；20100166228；20100177846；20100177922；20100208919；20100212432；20100219839；20100254561；20100277229；20100284553；20100315272；20100328836；20100329487；20110003614；20110019845；20110026739；20110038493；20110038497；20110045616；20110073967；20110075865；20110089504；20110090009；20110108838；20110110536；20110123043；20110131794；20110135122；20110154905；20110163615；20110170714；20110170735；20110182150；20110200212；20110222713；20110228954；20110228957；20110255228；20110303994；20120014543；20120017693；20120033832；20120043974；20120056282；20120076322；20120076329；20120091544；20120091545；20120099753；20120104898；20120106769；20120121106；20120133005；20120140956；20120153771；20120170777；20120213390；20120217171；20120223770；20120224722；20120224726；20120230522；20120250897；20120250910；20120260500；20120269363；20120294464；20120299130；20120319174；20120321111；20120326249；20120328132；20130010990；20130010996；20130016859；20130028450；20130028459；20130032936；20130044899；20130051582；20130051583；20130051586；20130051587；20130062710；20130070940；20130089222；20130108074；20130109990；20130119492；20130121523；20130129117；20130129119；20130129133；20130156234；20130160554；20130170673；20130177180；20130195291；20130208915；20130221453；20130221457；20130223023；20130223654；20130230183；20130233078；20130256816；20130271307；20130277776；20130279738；20130287231；20130334627；20140003609；20140010384；20140013581；20140037113；20140037121；20140038335；20140072150；20140072152；20140079277；20140086433；20140090884；20140105428；20140109680；20140119573；20140126762；20140132294；20140133685；20140137668；20140140538；20140140560；20140145276；20140191344；20140225205；20140226846；20140233784；20140239352；20140247954；20140264652；20140266260；20140266263；20140270204；20140270271；20140270273；20140270312；20140286509；20140291781；20140294218；20140299949；20140301571；20140301572；20140307885；20140307909；20140318395；20140341402；20140369530；20140376749；20150001647；20150003643；20150003646；20150003660；20150010174；20150014797；20150016635；20150023529；20150031160；20150035091；20150049886；20150055799；20150061458；20150063608；20150071466；20150078587；20150078589；20150078592；20150082917；20150088008；20150102435；20150110333；20150125003；20150131820；20150137834；20150139453；20150162883；20150163594；20150181352；20150189443；20150189446；20150202656；20150208176；20150228265；20150230010；20150230027；20150245123；20150256913；20150256914；20150264465；20150264498；20150271586；20150289046；20150296303；20150304777；20150311870；20150318829；20150319538；20150326978；20150336790；20150341720；20150341721；20150350760；20150373446；20150380636；20150381078；20150381782；20150382091；20160014521；20160014528；20160014529；20160029110；20160029126；20160029129；20160037257；20160037263；20160041211；20160044396；20160050475；20160057532；20160065152；20160066099；20160073212；20160087606；20160091378；20160105748；20160107884；20160111954；20160134967；20160134973；20160142829；20160149542；20160155532；20160156319；20160157017；20160157022；20160157025；20160165355；20160165356；20160167946；20160173967；20160173992；20160173993；20160173994；20160176704；20160182989；20160183008；20160192084；20160192086；20160192511；20160218688；20160219374；20160219378；20160221822；20160241958；20160241965；20160255441；20160255442；20160277844；20160295333；20160304337；20160309264；20160330550；20160336013；20160337751；20160340173；20160344360；20160345097；20160352294；20160360304；20160360322；20160362292；20160373864；20160373874；20160377569；20170034634；20170041708；20170041716；20170048634；20170059433；20170064449；20170070816；20170078798；20170078801；20170094436；20170099549；20170102276；20170127189；20170135592；20170142519；20170142525；20170155365；20170156002；20170160337；20170164105；20170164119；20170166437；20170180853；20170180864；20170180900；20170195788；20170215006；20170217765；20170223450；20170230750；20170238108；20170245035；20170245059；20170245061；20170247248；20170251302；20170251303; 20170257093; 20170260044; 20170265005; 20170265009; 20170275152; 20170280237; 20170280263; 20170284825; 20170289678; 20170318385; 2 0170318393; 20170318394; 20170332178; 20170355594; 20170363493; 20170366898; 20170374469; 20180002159; 20180002160; 20180002161; 20180002167; 201 80002168; 20180007474; 20180012588; 20180027338; 20180035206; 20180035228; 20180035229; 20180044167; 20180050900; 20180059708; 20180062588; 20180 063644; 20180066980; 20180067005; 20180077499; 20180091900; 20180091903; 20180091906; 20180103325; 20180103326; and RE40860, each of which is expressly incorporated herein by reference in its entirety. Summary of the Invention

[0028] A dynamic capacitive sensor configuration is provided, designed to apply minimal force and motion resistance to the moving electrode. The aim is to enable the use of moving electrodes with arbitrary levels of compliance without suffering adverse effects from large bias voltages, such as pull-in instability. This configuration facilitates the integration of highly compliant thin electrode materials that exhibit minimal possible resistance to motion. This type of material is particularly useful for sensing sound. Measurements show that for the highly compliant acoustic sensor design examined here, a large bias voltage of 400 volts can be applied without affecting its motion. The electrical sensitivity to sound was found to be approximately 0.5 volts / Pa, two orders of magnitude larger than that of typical acoustic sensors.

[0029] One aspect of this technology seeks to provide an electrode design for capacitive sensors that minimizes the impact of electrostatic stiffness on microphone performance. If this can be achieved, the moving electrode can be designed to have optimal performance without being limited by electrostatic forces.

[0030] Another aspect of this technology seeks to provide an electrode design that is stable under all operating conditions. The electrode device described herein achieves the goal of maintaining a nearly constant potential energy and ensuring stability.

[0031] Another aspect of this technology provides a microphone design in which the movable sensing electrodes have the smallest possible mechanical stiffness and mass in order to respond appropriately to minute pressure and air velocity fluctuations in the sound field.

[0032] This approach builds upon previous work on repulsive electrostatic actuators and sensors

[14] ,

[15] . These designs employ an electrode configuration that allows the moving and sensing electrodes to move away as the bias voltage increases, rather than moving toward each other as in the more common parallel-plate configuration. Repulsive electrostatic devices avoid pull-in instability, but achieving electrode designs unaffected by electrostatic hardening remains challenging, limiting achievable performance.

[0033] The following section presents a lightweight, compliant capacitor electrode configuration designed to easily respond to sound pressure levels.

[0034] A preferred embodiment is a microphone, in which the moving element responds to changes in air pressure or airflow and senses the position of the moving element. However, the sensor design is not limited to microphones and is more generally used as an accelerometer, MEMS gyroscope, displacement sensor, vibrometer, vibration sensor, etc. Furthermore, while the basic design provides a pair of fixed electrodes held virtually ground by a negative feedback transimpedance amplifier, this is not the limit of the technology. For example, if the potential of one of the electrode surfaces is maintained at a different voltage than the other electrode surfaces, the electric field experienced by the charged moving element will be asymmetrical, and instead of a normal force acting parallel to the elongated axis of the element, a forced displacement will occur. Therefore, the charged element will act as an actuator, such as a digital mirror device, with analog control of the displacement and feedback control to maintain the position. This same implementation also generates an output in response to the displacement of the charged element from its deflected position. Since the electrostatic force on the tilting element interacts with the effective stiffness of the sensor's moving element, the resulting sensitivity of the sensor is controllable, depending on the imbalance of the electrodes and the potential of the charged element.

[0035] In another embodiment, the moving element is intentionally oscillated by a time-varying electrostatic field generated by electrodes. For example, a chemically selective sensor can be used if the diaphragm or fiber is coated with a chemically specific material. As the species of interest is absorbed onto the moving element, its mass changes, which in turn alters its response to the oscillating electric field.

[0036] In another embodiment, the moving element is thermally responsive and varies, for example, in mechanical properties or dimensions. This, in turn, alters the frequency and / or linear or nonlinear response of the charged element to disturbances, such as oscillating electric fields.

[0037] Repositioning the nominal state of a moving charged element may also affect other sensor properties. For example, the charged element may be located in a non-uniform medium, and therefore, moving the charged element will result in a different operating environment.

[0038] In some cases, more than three electrodes may interact with a single moving element. In the case of a diaphragm, this could cause or sense distortion. In the case of fibers or filaments used for other structures that are suspended along two axes, an even greater number of electrodes can detect the individual axes of movement.

[0039] In some cases, more than one moving element is provided. They can interact with electrodes and with each other in various ways. For example, they can sense movement or effects along different axes (multi-axis sensors) and detect or process spatial changes under activation conditions.

[0040] In some cases, sensors can operate in liquid media. In the case of electrostatic sensors, this typically means a high-dielectric liquid; in some cases, ionic liquids or low-dielectric liquids, including water, can be used. For example, if a device according to this technology is immersed in water and the voltage potential remains below the hydrolysis potential of water, the result will be due to the approximately 10-1 of water. -7 The natural pKa (pH) of the ionization leads to current leakage from the charged element to the electrode. This ionization level will not render this embodiment unqualified. Leakage from other liquids is less common, such as mineral oil, hydrocarbons, silicones, hydrofluorocarbons, and cryogenic liquefied gases.

[0041] In another embodiment, the presumption that the charged element does not elongate due to the potential relative to the electrode is not strictly valid. Therefore, the length of the element and its distance from the electrode will vary with the applied voltage. While sensor engagement is undesirable, in certain sensor types, this is precisely the desired effect, as it locks the moving element in place.

[0042] Other modifications to the basic system are also possible. The following patents and published patent applications disclose various implementation techniques and applications, and sensing technologies according to the present invention can be implemented: see 5948981; 6104492; 6312393; 6360601; 6480645; 6529652; 6544193; 6549692; 6591029; 6625399; 6642067; 6745627; 6768181; 6784500; 6798796; 6847036; 7041063; 7054519; 7091715; 7100446; 7123111; 7157712; 7159441; 7208729; 721248 7; 7214298; 7260980; 7275433; 7282709; 7284430; 7286743; 7294503; 7305880; 7308827; 7351376; 7403805; 7421898; 7448995; 7469834; 7481111; 7 482589; 7485100; 7521257; 7622081; 7640803; 7652752; 7654957; 7714278; 7756559; 7791027; 7804374; 7809417; 7818871; 7822510; 7826629; 7827 864; 7836765; 7939021; 7990539; 8022779; 8037756; 8051698; 8061201; 8129176; 8136385; 8164588; 8193869; 8220318; 8226236; 8252539; 8257666 ;8263336;8319177;8322213;8333112;8339014;8367426;8391517;8427249;8427657;8445210;8451068;8461936;8482300;8488973;8556428;85 80597; 8586918; 8592153; 8592154; 8592215; 8627511; 8650955; 8658367; 8658368; 8669771; 8677821; 8686802; 8698212; 8742469; 8742770; 87460 39; 8746048; 8748947; 8766327; 8774885; 8776573; 8787117; 8793811; 8800369; 8822205; 8822906; 8844340; 8875576; 8912580; 8914089; 8928203;8953414；8994076；8994954；9072429；9146109；9182454；9200887；9209746；9217641；9233395；9238250；9267923；9270281；9372154；9389079；9395317；9411000；9423254；9448069；9515676；9535137；9575089；9611139；9618475；9618533；9638617；9645166；9658247；9668035；9680414；9702992；9719847；9740003；9774276；9778282；9780435；9800019；9804264；9810775；9810786；9812838；9823353；9857468；9864846；9869754；9874635；9905992；9910061；9910062；9915520；9927393；9944981；9958414；9958415；9958545；9966966；20020049389；20020068370；20030033850；20030071686；20030139687；20030142934；20030179791；20030196489；20040039297；20040039298；20040060355；20040237626；20050009197；20050020926；20050068612；20050104675；20050147017；20050167508；20050199047；20050274888；20060032308；20060032309；20060033588；20060158662；20060158666；20060196266；20060233498；20070016074；20070024840；20070034005；20070115440；20070119258；20070142718；20070194239；20070287923；20070289382；20080007693；20080190198；20080190200；20080191132；20090036761；20090064781；20090174885；20090229020；20090289606；20090301193；20100000289；20100024546；20100024560；20100078564；20100137143；20100145180；20100155883；20100194374；20100213791；20100253332；20100267164；20100301398；20100308930；20100313657；20110006196；20110028807；20110040161；20110138891；20110167908；20110170108；20110194711；20110194857；20110227448；20110248320；20110275522；20110281737；20110281741；20120006114；20120009713；20120013392；20120032747；20120068776；20120086307；20120112056；20120168605；20120172256；20120187983；20120192647；20120194107；20120227498；20120261274；20120265474；20120304341；20120325683；20120326213；20120326767；20120327368；20120329043；20120329044；20120329192；20130001653；20130004948；20130004949；20130009214；20130017642；20130025368；20130064035；20130071915；20130119243；20130139285；20130180333；20130201316；20130210128；20130210182；20130217004；20130231870；20130247669；20130271123；20130302932；20140000344；20140028997；20140062619；20140093881；20140104618；20140113828；20140144230；20140147337；20140159748；20140159826；20140176958；20140185054；20140194301；20140194302；20140194303；20140224971；20140230547；20140235452；20140235463；20140251017；20140265720；20140287958；20140301167；20140324376；20140331367；20140360272；20140372057；20150029490；20150043002；20150065837；20150085249；20150091477；20150143905；20150166332；20150168344；20150171595；20150177272；20150293243；20150304741；20150308829；20150377622；20150377623；20150377916；20150377917；20150377918；20160003868；20160006414；20160033448；20160035314；20160054400；20160061772；20160062112；20160069686；20160072472；20160079953；20160087551；20160139176；20160187289；20160223319；20160298963；20160329682；20160341758；20160341761；20160341762；20160341765；20160344368；20160374703；20170003314；20170003316；20170025736；20170059530；20170067856；20170068319；20170074640；20170078400；20170126206；20170146484；20170153319；20170155225；20170164839；20170176596；20170184644；20170185954；20170194985；20170199277；20170201059；20170205223；20170219521；20170219622；20170258320；20170271610；20170272878；20170272886；20170276723；20170277125；20170277138；20170277902；20170278226；20170278447；20170278465；20170278480；20170278733；20170278874；20170278878；20170278973；20170280041；20170280265；20170281083；20170285404；20170285815；20170285871；20170286588；20170287127；20170287228；20170287293；20170287414；20170287943；20170288023；20170288125；20170288670；20170289678；20170289702；20170290097；20170293155；20170293156；20170293171；20170294543；20170295325；20170295434；20170297895；20170297899；20170299494；20170299721；20170300162；20170301391；20170301699；20170308216；20170309856；20170310743；20170316487；20170316713；20170317610；20170318388；20170318394；20170319179；20170320726；20170323481；20170323892；20170323908；20170325025；20170325081；20170328702；20170328931；20170329162；20170329439；20170331899；20170332170；20170334187；20170336205；20170336396；20170336903；20170337888；20170338107；20170338108；20170338353；20170338818；20170340396；20170343874；20170344114；20170347886；20170348095；20170352233；20170352540；20170352746；20170354031；20170355591；20170355599；20170356928；20170357113；20170357144；20170357365；20170359113；20170359536；20170359658；20170359669；20170362648；20170363493；20170363906；20170364154；20170365224；20170365234；20170365451；20170365648；20170366104；20170366235；20170366898；20170367578；20170370869；20170372114；20170372542；20170372669；20170373196；20170374441；20170374442；20170374457；20170374469；20170374473；20170374474；20180000344；20180002159；20180002160；20180002161；20180002162；20180002167；20180002168；20180004047；20180004282；20180004701；20180004702；20180005566；20180005588；20180005600；20180005946；20180006356；20180007032；20180007472；20180007473；20180007474；20180009374；20180011355；20180011447；20180011590；20180012536；20180012538；20180012912；20180013003；20180014128；20180017996；20180018014；20180018565；20180018752；20180018918；20180018934；20180019425；20180020291；20180021679；20180024241；20180024286；20180024546；20180024656；20180024680；20180025297；20180025905；20180025913；20180025918；20180026037；20180026218；20180027325；20180027339；20180029878；20180031601；20180031603；20180031943；20180032160；20180032163；20180033362；20180033399；20180033696；20180033978；20180034912；20180035190；20180035229；20180038699；20180039117；20180039302；20180039815；20180040274；20180040642；20180040722；20180041140；20180042513；20180044167；20180046004；20180046305；20180047260；20180047582；20180047609；20180048359；20180048953；20180050900；20180052274；20180052535；20180052844；20180052950；20180052951；20180053459；20180055159；20180055625；20180058967；20180059318；20180059466；20180059690；20180061344；20180061638；20180061639；20180063647；20180067005；20180067303；20180067373；20180067586；20180069064；20180069367；20180070821；20180072033；20180074592；20180075924；20180076195；20180076231；20180076232；20180076332；20180076333；20180076385；20180076394；20180076507；20180076893；20180077408；20180077497；20180077499；20180079429；20180081449；20180081536；20180082102；20180082118；20180083048；20180083074；20180084245；20180084365；20180085593；20180085859；20180086628；20180087984；20180088068；20180088236；20180088776；20180090602；20180090616；20180090621；20180091906；20180092313；20180093117；20180095127；20180095336；20180095502；20180095504；20180096177；20180096735；20180096971；20180096979；20180097040；20180097275；20180097516；20180097622；20180097983；20180098001；20180098139；20180098143；20180099867；20180099868；20180100721；20180101359；20180101388；20180101422；20180101715；20180101965；20180102086；20180102420；20180102442；20180102586；20180102667；20180102981；20180103029；20180103132；20180103320；20180103323；20180103324；20180103325；20180104407；20180105270；20180106759；20180107221；20180107280；20180107303；20180107333；20180107353；20180107382；20180107849；20180107908；20180108002；20180108172；20180108227；20180108440；20180108760；20180109061；20180109180；20180109267；20180109676；20180109710；20180109724；20180109751；20180109752；20180109835；20180109869；20180109875；20180109892；20180109947；20180110148；20180110466；20180111824；20180112837；20180112887；20180113138；20180113304；20180113305；20180113501；20180113512；20180113566；20180113607；20180114047；20180114386；20180114942；20180115116；20180115579；20180115755；20180115756；20180115811；20180115836；20180115837；20180115838；20180115864；20180115867；20180116514；20180116535；20180116561；20180116728；20180116904；20180117341；20180117436；20180118560；20180120172；20180120264；20180120265；20180120433；20180120436；20180120902；20180120930；20180120948；20180121067；20180121671；20180121703；20180121738；20180121796；20180122356；20180122506；20180122831；20180123224；20180123379；20180123402；20180123412；20180124181；20180124225；20180124230；20180124495；20180124514；20180124521；20180124564；20180124601；20180124846；20180125363；20180125366；20180125404；20180125584；20180126075；20180126273；20180127265；20180127266；20180128783；20180128851；20180128896；20180129112；20180129170；20180129290；20180129409；20180129459；20180129511；20180129831；20180129849；20180130318；20180130320；20180130434；20180130441；20180130483；20180130484；20180130539；20180130861；20180130940；20180130967；20180131091；20180131201；20180131478；20180131543；20180131664；20180131797；20180131804; 20180131858; 20180131869; 20180131873; 20180132023; 20180132024; 20180132031; 20180132043; 20180132048; 20180132116; 20180132171; 20180132192 ; 20180132815; 20180133431; 20180133504; 20180133507; 20180133583; 20180133801; 20180134385; 20180134546; 20180136321; 20180136363; 20180136712; 20180136715 ; 20180136801; 20180136819; 20180136899; 20180137467; 20180137488; 20180137498; 20180138102; 20180138155; 20180138201; 20180138283; 20180138391; 20180138416 ;20180138882;20180139389;20180139398;20180139431;20180139534;20180139536;20180139543;20180139544;20180139545; and 20180139862, each of which is expressly incorporated herein by reference in its entirety.

[0043] Various types of microelectromechanical electrostatic actuators are known. See also: 6128122; 6164134; 6201629; 6273544; 6309048; 6312114; 6353492; 6360035; 6378989; 6408878; 6424466; 6433911; 6439689; 6439699; 6443558; 6450628; 6474781; 6481835; 6491362; 6508546; 6517197; 6531668; 6538799; 6547371; 6554410; 6572220; 6575566; 6588882; 6592207; 6594057; 6 598964; 6623108; 6634735; 6641273; 6644793; 6652082; 6666548; 6698867; 6733116; 6742873; 6746108; 6786573; 6793328; 6793753; 6798729; 679 9835; 6805435; 6805454; 6808253; 6824257; 6827428; 6827429; 6832828; 6848181; 6851796; 6860590; 6863378; 6863384; 6866369; 6880235; 688092 2; 6883904; 6883906; 6886915; 6890059; 6891240; 6899137; 6899416; 6902255; 6905195; 6905620; 6913347; 6916087; 6916091; 6918655; 6921150; 6922118; 6923526; 6929030; 6929350; 6938989; 6938991; 6938994; 6949756; 6955428; 6974206; 6988785; 6988789; 6988790; 6991318; 6994424; 699 4426; 6994430; 6998278; 7001007; 7004563; 7004577; 7006720; 7014296; 7014298; 7014785; 7025324; 7028474; 7032992; 7032997; 7034854; 70403 38; 7048868; 7052114; 7052120; 7064883; 7066579; 7070256; 7070258; 7073881; 7080893; 7080895; 7083262; 7086717; 7101020; 7111924; 7132056;7134740；7144519；7144616；7147304；7147307；7152944；7152961；7152967；7155823；7159968；7160475；7168167；7169314；7175775；7178899；7182431；7182437；7183618；7184193；7188935；7188938；7189334；7198346；7207656；7210764；7216671；7216956；7219427；7219982；7226147；7227687；7229154；7233101；7234795；7249830；7250128；7258421；7258774；7264333；7273270；7278713；7282834；7284836；7290859；7293855；7322680；7328975；7331101；7331659；7334874；7338147；7347535；7347697；7350901；7350906；7354787；7359106；7360871；7370942；7375872；7380339；7380906；7380913；7384131；7387365；7387368；7393083；7396108；7399068；7401884；7401895；7401900；7401906；7410243；7410250；7413293；7416275；7419244；7419247；7419250；7431427；7434919；7441867；7442317；7447547；7448728；7457021；7467850；7468997；7472984；7475965；7494555；7506966；7517055；7524029；7524032；7527357；7528691；7537314；7537325；7549726；7553001；7556351；7556352；7556353；7556358；7556361；7562962；7562963；7569926；7578569；7578582；7585047；7585066；7588327；7591539；7591541；7597435；7601270；7611220；7615744；7616367；7625061；7625067；7625068；7628468；7637582；7654628；7654642；7658473；7661793；7661796；7661797；7669950；7669951；7669964；7669971；7673976；7677685；7677686；7699440；7703890；7708372；7708381；7717542；7731334；7731336；7731341；7735963；7735968；7740337；7746538；7748827；7753469；7753487；7753491；7753504；7754010；7758160；7758162；7758166；7758171；7762638；7766055；7771025；7771032；7775634；7780264；7784905；7784910；7794050；7815290；7815291；7835055；7864006；7874644；7891773；7893798；7896468；7896473；7901023；7905574；7905588；7914115；7918540；7918541；7931351；7934797；7934799；7934808；7938524；7939994；7946671；7950771；7950773；7950774；7960208；7967422；7971967；7971972；7971975；7973278；7976131；7987784；7992968；8002933；8011757；8021614；8025355；8047633；8057014；8061795；8066355；8079669；8079688；8087740；8087757；8104497；8104515；8104878；8110813；8124218；8167406；8220487；8226199；8226217；8231207；8251495；8264307；8282181；8282202；8288211；8323982；8336990；8376513；8382258；8382259；8393714；8398210；8398221；8398222；8419176；8440093；8444260；8455570；8459787；8465129；8465142；8468939；8469496；8480224；8485654；8506039；8517516；8523327；8523328；8529021；8530854；8534818；8550119；8562120；8585189；8585971；8602531；8602535；8604411；8629393；8632162；8633955；8641175；8646882；8646883；8651632；8651633；8652409；8656958；8657419；8659631；8668312；8668313；8684483；8695640；8696094；8714676；8717395；8736081；8770722；8783804；8784549；8791971；8802568；8806751；8845914；8846183；8847148；8916395；8929584；8932677；8936353；8936354；8939551；8991986；8992858；9010909；9017537；9103761；9151949；9162878；9174222；9174438；9234797；9508823；9653254；9696375；9799488；9897530；9953787；9956562；20010021058；20010022682；20010029983；20010033796；20010045525；20010054778；20020024569；20020029814；20020033863；20020036674；20020097300；20020101474；20020122102；20020127736；20020130931；20020144738；20020171716；20030016275；20030019833；20030020784；20030020786；20030025758；20030025761；20030042117；20030063166；20030081082；20030103106；20030132824；20030132985；20030132995；20030137567；20030142175；20030146957；20030174190；20030202055；20030202735；20030202738；20040001263；20040031150；20040032440；20040051759；20040056923；20040056924；20040075715；20040075718；20040079724；20040080556；20040085159；20040092121；20040094506；20040095434；20040095441；20040099636；20040100529；20040113983；20040118808；20040119784；20040160495；20040169697；20040169701；20040207687；20040207689；20040207690；20040207691；20040218016；20040218022；20040246305；20040246308；20040246311；20040257400；20040263551；20040263577；20050016951；20050018015；20050018016；20050018017；20050024434；20050024435；20050024436；20050024437；20050024443；20050030338；20050030339；20050030342；20050030343；20050035983；20050036002；20050037532；20050039453；20050041052；20050041055；20050041063；20050046663；20050046673；20050052497；20050052514；20050057628；20050083377；20050093933；20050093934；20050097742；20050099465；20050099466；20050104922；20050109730；20050110832；20050112882；20050116990；20050128247；20050128249；20050131490；20050134648；20050134649；20050140726；20050140728；20050144781；20050144782；20050146559；20050146562；20050146563；20050146566；20050157042；20050157081；20050157082；20050166980；20050167769；20050168532；20050168533；20050174375；20050174394；20050185021；20050189316；20050189317；20050200659；20050206684；20050215089；20050225601；20050225602；20050225604；20050226742；20050231560；20050237743；20050242058；20050243134；20050248620；20050253897；20050264607；20050264612；20050269901；20050270335；20050270338；20050275690；20050275691；20050279090；20050285901；20060007266；20060007514；20060017772；20060018005；20060033785；20060034006；20060054228；20060061628；20060072187；20060077235；20060092220；20060093753；20060098047；20060109310；20060109313；20060119661；20060152551；20060197810；20060202933；20060227156；20060227167；20060227168；20060238571；20060250448；20060268048；20060268064；20060274119；20060274121；20070002009；20070008386；20070008390；20070030315；20070030321；20070046759；20070048887；20070048898；20070052766；20070059494；20070064034；20070064037；20070064066；20070064067；20070070133；20070070161；20070080695；20070081031；20070109345；20070115316；20070120891；20070146432；20070153058；20070176967；20070176968；20070176971；20070182784；20070182785；20070183643；20070188554；20070188556；20070188557；20070188570；20070211102；20070211112；20070222807；20070222819；20070222821；20070222826；20070236313；20070257966；20070257971；20070268327；20070268343；20070291070；20070291091；20070296765；20080012913；20080012923；20080024556；20080030544；20080036821；20080050283；20080079760；20080094432；20080111853；20080111863；20080117258；20080129800；20080129809；20080141884；20080165226；20080173365；20080180778；20080192096；20080204514；20080204518；20080204519；20080210319；20080210320；20080210321；20080210322；20080211876；20080211877；20080211879；20080220216；20080220535；20080231669；20080236669；20080246817；20080252691；20080266341；20080266356；20080266361；20080273059；20080277005；20080277007；20080277258；20080278268；20080278559；20080289710；20080303866；20080303871；20080309693；20080309694；20080309695；20080309696；20080309697；20080309699；20080309720；20080309721；20080309722；20080316240；20080316241；20080316242；20080316262；20080316271；20080316276；20080318349；20090002470；20090027448；20090027459；20090085975；20090091601；20090091603；20090121156；20090122116；20090124029；20090128604；20090151422；20090153619；20090153936；20090160910；20090174014；20090185007；20090189953；20090195598；20090195614；20090201339；20090213186；20090213191；20090237433；20090237450；20090237456；20090237461；20090244193；20090244194；20090256890；20090261244；20090278897；20090289979；20090295861；20090303290；20090303297；20090303303；20090309909；20090322812；20100003772；20100026765；20100039478；20100050415；20100053268；20100053274；20100053275；20100053276；20100073441；20100110129；20100110130；20100118071；20100149268；20100149274；20100175767；20100187105；20100200782；20100201750；20100208000；20100231645；20100242765；20100253745；20100265298；20100276588；20100276606；20100277549；20100295887；20100302292；20110024923；20110025350；20110025780；20110037796；20110037797；20110037809；20110090288；20110109675；20110109677；20110109705；20110155548；20110164081；20110204018；20110205306；20110205319；20110258851；20110261123；20110261124；20110261125；20110261126；20110271857；20120026251；20120026252；20120026253；20120026259；20120026260；20120026261；20120038695；20120045615；20120056952；20120091374；20120105535；20120105548；20120105549；20120105550；20120105553；20120268525；20120268527；20120268528；20120268529；20120268530；20120268531；20120299998；20120299999；20120300000；20120300001；20120307211；20120319303；20120328834；20130059396；20130068131；20130070031；20130072614；20130199730；20130235101；20130235102；20130249982；20130249983；20130249984；20130249985；20130252234；20130257991；20130257992；20130257994；20130257996；20130257997；20130258002；20130278677；20130278689；20130280831；20130286108；20130286109；20130302785；20130328976；20130328977；20130330475；20130342597；20140009523；20140015878；20140015879；20140015880；20140015893；20140015901；20140021343；20140084390；20140126762；20140212917；20140220621；20140262972；20140273408；20140308770；20140322489；20140363678；20150043002；20150183633；20150213996; 20150266726; 20150276089; 20150294838; 20160091479; 20160103174; 20160172197; 20160173001; 20160202286; 20160243827; 20160268084; 20160324564; 20170001195; 20170146364; 20170303383; 20180075994; and 20180079640; each of which is expressly incorporated herein by reference in its entirety.

[0044] One object is to provide a sensor comprising: at least two electrodes in an electric field; and an elongated, displaceable element configured to be charged, positioned close to the at least two electrodes in the electric field, and having an aspect ratio of at least 10, the element interacting with each of the at least two electrodes to generate a composite force of at least 95% of a pulling force along an elongated axis within the element, such that displacement of the element under certain conditions causes a charge redistribution on the at least two electrodes corresponding to the magnitude of the condition, without substantially altering the responsiveness of the charge redistribution to the condition or the attraction instability.

[0045] Another objective is to provide a sensor comprising: an element configured to be charged, positioned near at least two electrodes within an electric field, the element interacting with each of the at least two electrodes to generate a composite force of at least 95% of a pulling force within the element, such that when the element is displaced from its nominal position under certain conditions, a charge redistribution corresponding to the magnitude of the condition is induced on the at least two electrodes. The at least two electrically isolated and spaced electrodes may comprise a pair of fixed conductors separated by a linear gap, each of the pair of fixed conductors maintained at a corresponding potential, and an electric field in the space above the pair of fixed conductors is sensed based on the charge redistribution. The axis preferably has a vector component pointing along the linear gap, wherein the net force acting on the charged element in response to the sensed condition is insensitive to the displacement state of the charged element.

[0046] Another object of the present invention is to provide a method for sensing capacitance difference, the method comprising: providing a charged element in an electric field, the charged element having a movement along an axis in response to a sensed condition; providing at least two electrically isolated and spaced conductors, each conductor interacting with the electric field and having a corresponding electrode for electrically sensing a disturbance of the electric field, the net force generated on the charged element by the at least two electrically isolated and spaced conductors being perpendicular to the axis; and sensing the disturbance of the electric field caused by the movement of the charged element along the axis in response to the condition, wherein, within the range of the movement of the charged element, the position of the charged element in the electric field substantially does not change the responsiveness of the displaceable element to the condition or cause pull-in instability.

[0047] The at least two electrically isolated and spaced electrodes may include a pair of fixed conductors separated by a linear gap, each of the pair of fixed conductors being maintained at a corresponding potential to sense an electric field in the space above the pair of fixed conductors based on charge redistribution, and the axis having a vector component pointing over the gap, wherein the net force acting on the charged element in response to the sensed conditions is insensitive to the displacement state of the charged element.

[0048] The charged element can respond to acoustic vibrations, and the sensed disturbance quantitatively represents the acoustic vibrations.

[0049] The element being charged may have an elongated axis, suspended from one end, with a restoring force that tends to return the element to a nominal position, where the free end of the element is close to the at least two electrically isolated and spaced electrodes. The deviation of the vector of the net force between the element and the at least two electrically isolated and spaced electrodes from the elongated axis may be less than 5 degrees, for example, 4 degrees, 3 degrees, 2 degrees, 1 degree, etc.

[0050] A further objective is to provide a capacitive sensor comprising: at least two conductors isolated from each other by at least one spatial gap, each respective conductor interacting with an electrostatic field occupying a region near the at least two conductors and the at least one spatial gap, and electrically responding to disturbances of the electrostatic field; and a displaceable element configured to move along a displacement axis having a directional component selectively crossing the spatial gap in response to a sensed condition, and to disturb the electrostatic field corresponding to the movement, wherein, within the range of movement of the displaceable element, the electrostatic field does not substantially alter the responsiveness of the displaceable element to the sensed condition or cause attraction instability.

[0051] The at least two conductors may include a pair of fixed conductors separated by a linear spatial gap, each of the pair of fixed conductors being maintained at its respective potential to generate the electrostatic field in the space above the pair of fixed conductors depending on the difference between the respective potentials of the pair of fixed conductors, the electrostatic field having a principal field vector component pointing across the linear spatial gap, and the displaceable element may include a charged element configured with a displacement axis having a vector component pointing across the linear spatial gap, such that the force exerted on the displaceable element due to the electrostatic field is insensitive to the displacement state of the displaceable element in response to the sensed condition.

[0052] The movable element is not supported on at least one edge.

[0053] The movable element comprises at least one of the following: a metal or metallized polymer film with a thickness of less than about 10 μm; a fiber; a mesh; a carbon nanotube and a graphene sheet; and / or an electret, a thin metal sheet, polycrystalline silicon, or any doped semiconductor.

[0054] The movable element can be configured to shift along two different sensing axes, and the at least two conductors include at least three conductors.

[0055] The movable element may include a diaphragm, and the at least two conductors are configured such that a change in the potential difference between the diaphragm and any one of the at least two fixed conductors does not substantially replace or alter the effective stiffness of the diaphragm relative to the moving axis.

[0056] The capacitive sensor may also include a corresponding transimpedance amplifier configured to generate an output signal from each corresponding conductive surface.

[0057] The movable element may include a micromachined silicon diaphragm having opposite sides, the opposite sides being sufficiently isolated to maintain a pressure differential on the diaphragm, and a housing configured to selectively define at least one path for a fluid medium from a respective environmental port to a respective side of the micromachined silicon diaphragm to selectively change the pressure on the respective side of the micromachined silicon diaphragm.

[0058] The deflectable element can have a dynamic response to changes in inertial state. The deflectable element can have a dynamic response to aerodynamic influences. The deflectable element can have a dynamic response to chemical or biochemical processes.

[0059] The potential between the movable element and the at least one conductor can be at least 1V, such as 3V, 5V, 10V, 15V, 20V, 30V, 50V, 100V, 200V, 300V, 400V, or 500V. The electric field between the movable element and the at least one conductor is at least 1V / mm, such as 0.5V / mm, 1V / mm, 2V / mm, 3V / mm, 4V / mm, 5V / mm, 10V / mm, 25V / mm, 50V / mm, 75V / mm, 100V / mm, 200V / mm, 300V / mm, 400V / mm, 500V / mm, 750V / mm, 1000V / mm, 1500V / mm, 2000V / mm, 2500V / mm, etc. In some cases, the potential can be established based on the dielectric strength of the insulating medium. For example, the dielectric strength of air is approximately 3000 V / mm.

[0060] Therefore, the object of the present invention is to provide a capacitive sensor comprising: a pair of coplanar surfaces separated by a gap; a diaphragm disposed in a plane perpendicular to the coplanar surfaces and configured to move along an axis perpendicular to the gap and parallel to the coplanar surfaces, the diaphragm and the pair of coplanar surfaces being configured such that a voltage difference between the conductive diaphragm and the pair of coplanar conductive surfaces does not substantially deflect or change the effective stiffness of the diaphragm; and a set of electrodes electrically connected to each of the pair of coplanar surfaces and the diaphragm, configured to determine a differential charge induced between the pair of coplanar surfaces by the potential of the diaphragm.

[0061] The present invention also aims to provide a method for sensing vibration or sound, the method comprising: providing a pair of coplanar surfaces separated by a gap, and a diaphragm disposed in a plane perpendicular to the coplanar surfaces and configured to flex along an axis perpendicular to the gap and parallel to the coplanar surfaces; inducing a potential on the diaphragm relative to the pair of coplanar surfaces; and sensing a change in induced charge on the pair of coplanar surfaces caused by the flexure of the diaphragm along the vertical axis, wherein the diaphragm and the pair of coplanar surfaces are configured such that the voltage potential does not substantially deflect or change the effective stiffness of the diaphragm.

[0062] The sensor may also include a transimpedance amplifier configured to amplify the differential charge. The potential at each coplanar surface can be maintained at ground potential by the corresponding transimpedance amplifier, and the change in charge can be induced on the corresponding coplanar surface by the movement of the diaphragm.

[0063] The diaphragm may comprise a metallized polymer film or micromachined silicon, for example, with a thickness of <10 μm, <7.5 μm, <5 μm, <3 μm, <2 μm, or <1 μm.

[0064] The diaphragm is preferably configured to oscillate, for example, in response to acoustic vibrations (e.g., sounds produced by human speech) or changes in electric field; however, it can function as an electrometer, accelerometer, vibration sensor, flow sensor, or other type of electrical or mechanical sensor.

[0065] The sensor may also include a housing configured to selectively direct acoustic vibrations from an ambient port to one side of the diaphragm, or from each of a pair of ambient ports to a corresponding side of the diaphragm, or to provide a defined path for a fluid medium from the ambient port to one side of the deflectable element.

[0066] The diaphragm can have a movement similar to that of the air movement within the sound field.

[0067] The diaphragm has a minimum resonant frequency and can be configured to have a velocity in response to the movement of air within a sound field, the frequency of which is higher than the minimum resonant frequency that is approximately in phase with the speed of sound. For example, the minimum resonant frequency can be <250Hz, <200Hz, <150Hz, <100Hz, <80Hz, <50Hz, <35Hz, <24Hz, <20Hz, <15Hz, or <10Hz.

[0068] For example, the potential between the diaphragm and at least one of the coplanar surfaces can be >400V, >200V, >100V, >50V, >24V, >12V, >10V, >6V, or >5V.

[0069] Another object of the present invention is to provide a capacitive sensor comprising: at least two fixed conductive surfaces separated by at least one non-conductive gap, each conductive surface having an associated electrostatic field and collectively causing a composite force vector; and a deflectable element configured to move along an axis perpendicular to the composite force vector, having a movement amplitude corresponding to a sensed condition, the element being configured to have electrostatic interaction with the associated electrostatic field of each of the pair of fixed conductive surfaces, wherein, within the range of movement of the element along the axis, the composite force vector substantially does not change the deflection of the deflectable element. The capacitive sensor may be a microphone, and the sensed condition may include sound waves.

[0070] Deflectable elements may include diaphragms, such as cantilevered diaphragms, diaphragms or beams supported on opposite edges (and freely flexing between supports), perforated diaphragms, solid diaphragms, or metallized polymer diaphragms. Deflectable elements may include fibers, fiber webs, fiber pads, or metallized electrospun fibers. Deflectable elements may have solid edges, such as an inherent portion of a mechanical diaphragm, or a fiber web with solid boundary elements. Elements may include carbon nanotubes, graphene, silicon, micromachined silicon, or other materials and / or silicon nitride. Deflectable elements may be metallized, doped semiconductors, or electrets. Sensors can be fabricated using additive manufacturing processes, subtractive manufacturing processes, or aspects of each. For example, semiconductor fabrication typically employs deposition and etching. Custom manufacturing processes can be used to produce individual sensors or sensor arrays.

[0071] Movable electrodes can be provided, representing beams or plates with two free edges supported at opposite ends. These two edges can be adjacent to pairs of fixed electrodes, similar to... Figure 2 As shown. This configuration looks very much like a ribbon microphone, allowing for condenser conduction instead of motorized conduction like all ribbon microphones. Using condenser conduction allows for miniaturization, which is extremely difficult with motorized conduction.

[0072] The deflectable element can be configured to oscillate in response to acoustic vibrations.

[0073] Deflectable elements can be configured to deflect in response to vibrations or sound waves along a single axis, along two axes, or with a greater number of degrees of freedom (e.g., rotation, internal vibrations and harmonics, flexure, etc.).

[0074] The at least two fixed conductive surfaces may be coplanar or located in different planes. The at least two fixed conductive surfaces may include at least three conductive surfaces.

[0075] The deflectable element may include a diaphragm, and the at least two fixed conductive surfaces are configured together such that the voltage difference between the diaphragm and any one of the at least two fixed conductive surfaces does not substantially deflect or change the effective stiffness of the diaphragm.

[0076] The capacitive sensor may further include a set of electrodes electrically connected to each of the at least two pairs of conductive surfaces, configured to determine charge redistribution caused by movement of the deflectable element.

[0077] A corresponding transimpedance amplifier can be provided, which is configured to generate an output signal from each corresponding conductive surface.

[0078] The capacitive sensor may have a housing configured to selectively direct acoustic vibrations from an ambient port to one side of the deflectable element, or selectively direct acoustic vibrations from each of a pair of ambient ports to a corresponding side of the deflectable element. The housing may be configured to selectively provide a defined set of paths for a fluid medium from each of the pair of ambient ports to the corresponding side of the deflectable element.

[0079] The deflectable element may have a movement approximating the movement of air within the sound field surrounding the deflectable element. The deflectable element may also have a movement corresponding to its inertial state, such as acceleration, angular rotation, etc.

[0080] The deflectable element may include a film with a thickness of less than about 10 μm, 7.5 μm, 5 μm, 3 μm, or 1 μm. The deflectable element may include fibers with a diameter of about 1 μm, less than 800 nm, 750 nm, 700 nm, 600 nm, 550 nm, 500 nm, 400 nm, 300 nm, 250 nm, 225 nm, 200 nm, 175 nm, 150 nm, 125 nm, 100 nm, 80 nm, 75 nm, 60 nm, or 50 nm. The film or fiber may be metallized, for example, with a gold coating of <100 nm, 90 nm, 80 nm, 75 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 25 nm, 20 nm, 15 nm, or 10 nm.

[0081] The deflectable element has a minimum resonant shift frequency, for example, less than 250Hz, 200Hz, 175Hz, 150Hz, 125Hz, 100Hz, 80Hz, 75Hz, 70Hz, 65Hz, 60Hz, 55Hz, 50Hz, 45Hz, 40Hz, 35Hz, 30Hz, 25Hz, 20Hz, 15Hz, or 10Hz. The deflectable element can be configured to move in response to changes in air pressure corresponding to sound waves within a sound field, the frequency of which is higher than its minimum resonant frequency in phase with the speed of sound.

[0082] The potential between the deflectable element and at least one of the conductive surfaces can be at least 400V, 300V, 240V, 200V, 150V, 120V, 100V, 75V, 48V, 24V, 12V, 10V, 6V, 5V, 3.3V, 3V, 2.5V, 2V, 1.5V, 1V, or 0.5V.

[0083] The deflectable element may have a minimum resonant frequency shift of less than 250 Hz and is configured to have a speed with a phase lag of less than 90 degrees relative to air movement in response to sound waves in a sound field having frequencies higher than the minimum resonant frequency. The deflectable element may have a minimum resonant frequency shift of less than 150 Hz and is configured to have a speed with a phase lag of less than 90 degrees relative to air movement in response to sound waves in a sound field having frequencies higher than the minimum resonant frequency. The deflectable element may have a minimum resonant frequency shift of less than 80 Hz and is configured to have a speed with a phase lag of less than 90 degrees relative to air movement in response to sound waves in a sound field having frequencies higher than the minimum resonant frequency. The deflectable element may have a minimum resonant frequency shift of less than 50 Hz and is configured to have a speed with a phase lag of less than 90 degrees relative to air movement in response to sound waves in a sound field having frequencies higher than the minimum resonant frequency. The deflectable element may have a minimum resonant frequency of movement less than 25 Hz and is configured to have a speed with a phase lag of less than 90 degrees to respond to sound waves in a sound field having frequencies higher than the minimum resonant frequency. The deflectable element may have a minimum resonant frequency and move with a phase lag of less than 90 degrees to respond to changes in air pressure having frequencies higher than the minimum resonant frequency.

[0084] The potential on each conductive surface can be maintained at ground potential by a corresponding transimpedance amplifier, while the movement of the deflectable element induces a change in charge on the corresponding conductive surface.

[0085] Another objective is to provide a method for sensing vibrations, the method comprising: providing at least two separate conductive surfaces and a deflectable element, the deflection axis of the deflectable element being perpendicular to a force generated on the deflectable element by the at least two spaced conductive surfaces; inducing a potential on the deflectable element relative to the at least two conductive surfaces; and sensing a change in induced charge on the at least two conductive surfaces due to deflection of the deflectable element along the deflection axis, wherein the force generated on the deflectable element by the at least two spaced conductive surfaces substantially does not alter the deflection of the deflectable element. The change in induced charge can be sensed by at least one transimpedance amplifier. The deflectable element can move in response to sound waves in air at standard temperature and pressure and a relative humidity of 20%, approximating the movement of air within a sound field surrounding the deflectable element.

[0086] The deflectable element may have a minimum resonant frequency and move with a phase lag of less than 90 degrees to respond to sound waves in the air having frequencies higher than the minimum resonant frequency. The minimum resonant frequency is, for example, 250 Hz. The movement of the deflectable element may correspond to external forces, viscous resistance, pressure differences, etc. The movement of the deflectable element may correspond to external forces, such as changes in the stress or strain, expansion, contraction, swelling, heating, cooling, etc., of the deflectable element.

[0087] The potential on each conductive surface can be maintained at ground potential by a corresponding transimpedance amplifier, while the deflection causes the deflectable element to move to cause a change in charge on the corresponding conductive surface.

[0088] A further objective is to provide a capacitance sensing method comprising: providing a sensor including at least two electrically isolated electrodes having a correlated electric field, and a charged element within the correlated electric field having a movement axis responsive to a sensed condition, the movement axis being orthogonal to the electrostatic force between the charged element and the at least two electrically isolated electrodes, and having no mechanical response to the magnitude of the electrostatic force between the charged element and the at least two electrically isolated electrodes; causing movement of the charged element relative to the at least two electrically isolated electrodes along the movement axis; sensing an induced charge on each of the at least two electrically isolated electrodes due to the movement of the charged element; and generating a signal corresponding to the movement. The sensed condition may be sound.

[0089] The element being charged is suspended from one end and has an elongated axis and a restoring force that tends to return the element to a nominal position, where the free end of the element being charged is close to the at least two electrically isolating electrodes, and the electrostatic force between the element being charged and the at least two electrically isolating electrodes is parallel to the elongated axis.

[0090] The charged element has an elongated axis and is supported by a flexible cantilever, the elongated axis being parallel to the electrostatic force and pointing toward the gap between the at least two electrically isolating electrodes.

[0091] Each of the at least two electrically isolating electrodes applies a force component to the element being charged along the moving axis, wherein the superposition of the force components applied to the element being charged along the moving axis eliminates the net force along the moving axis.

[0092] The charged element comprises a filament with a diameter of less than about 1 micrometer. The charged element may also comprise a filament or conductive wire with a diameter of less than about 550 nm. Movement in the air can be a response to acoustic vibrations at frequencies above 250 Hz, dominated by viscous drag.

[0093] The element being charged may include a conductive perforated plate with cantilever support, the cantilever support supporting movement of the conductive perforated plate only along the axis of movement. The element being charged may move in the air in response to acoustic vibrations at frequencies above 100 Hz dominated by viscous resistance.

[0094] The charged element may have an elongated profile and an elongated axis, the elongated axis having an angle of less than about 3 degrees, less than 2 degrees, less than 1 degree, or less than 0.5 degrees relative to the vector of the electrostatic force.

[0095] The element being charged may have an elongated profile and an elongated axis perpendicular to the axis of movement, and the force component of the electrostatic force along the axis of movement is -18dB, -20dB, -24dB, -28dB, -30dB, -33dB, -36dB, or -40dB lower than the force component of the electrostatic force along the elongated axis.

[0096] The element being charged may have an elongated axis parallel to the electrostatic force and have tensile stiffness, wherein the element being charged is not attracted by the electrostatic force until the electrostatic force exceeds the tensile stiffness.

[0097] The at least two electrically isolated electrodes may be symmetrical with respect to the element being charged, and a signal is generated by providing a transimpedance amplifier for each corresponding electrode and determining the movement of the element being charged based on the voltage difference of the output of the respective transimpedance amplifier.

[0098] Another objective is to provide a directional microphone or sensor comprising: at least two electrically isolated electrodes having an associated electric field; a charged element having a movement axis about a fixed position within the associated electric field, the charged element being configured to move along a movement axis orthogonal to the electrostatic force between the charged element and the at least two electrically isolated electrodes; and electronic circuitry configured to generate an output dependent on the movement (e.g., in response to sound) and to generate a deflection force on the charged element thereby altering the movement axis of the charged element. An input may be received that defines a desired movement axis of the charged element.

[0099] Another object of the present invention is to provide a method for determining the propagation vector of a wave (e.g., sound or vibration), comprising: providing at least two electrically isolated electrodes having an associated electric field; and a charged element within the associated electric field, the charged element having a movable axis about a fixed position, the charged element being configured to move about the movable axis, the movable axis being orthogonal to the electrostatic force between the charged element and the at least two electrically isolated electrodes; generating a first output depending on the movement along the axis; receiving a signal for changing the associated electric field and thereby deflecting the charged element, thereby changing the movable axis to a second movable axis; generating a second output depending on the movement along the second axis; and analyzing the first output and the second output to determine the vector propagation characteristics of the vibration.

[0100] Another objective is to provide a sensor comprising a charged (or rechargeable) element configured to be placed within an electric field having at least two electrodes, the charged or rechargeable element interacting with each of the at least two electrodes to generate a composite force within the charged element that is only tensile and has no tendency to deflect from the nominal position of the charged element, such that when the charged element deflects from the nominal position, it causes a senseable redistribution of charge on the at least two electrodes.

[0101] Deflection can be caused by a variety of effects. For example, in a microphone implementation, sound can act on the charged element to cause it to shift in a movement pattern corresponding to pressure changes or overall flow patterns (e.g., viscous resistance).

[0102] In an implementation of an accelerometer, the element being charged may be, or may have, a movement corresponding to the test mass or inertial mass.

[0103] In vibration sensors, the inertial mass has a mechanical integral over time, or the output has an electrical integral over time, to determine the pulse amplitude.

[0104] Similarly, in a gyroscope (e.g., a MEMS gyroscope), the charged element can respond directly or indirectly to the Coriolis force or the gyroscope reaction force.

[0105] The element being charged can be a microcantilever beam, for example, capable of sensing asymmetrical bending effects. For instance, if one side of the beam is coated with a chemically responsive material while the other side is not, or if one side is selectively exposed to a chemical that it responds to, deflection can be measured. Typically, the low-frequency response of the device (<1Hz or 0.1Hz) may be poor or susceptible to noise, so the element being charged may vibrate. In this case, the vibration will act as frequency modulation of the offset position of the element being charged.

[0106] Microcantilever beams can also be coated with selective chemisorbents, which alter the mass of the charged element based on exposure to a specific type of chemical. In this case, it is often very useful to sense mass changes by vibrating the microcantilever beam and sensing its dynamic characteristics. For example, the microcantilever may have an elastic mount, and the resonant frequency at which the charged element moves will depend on its mass. In a non-resonant system, the induced mass of the charged element in response to a defined force will vary with the mass of the charged element.

[0107] In some cases, the mounting components of the charged element possess relevant physical properties that vary with sensed conditions. For example, the mounting components may be thermally responsive materials. Therefore, as the temperature of the mounting components changes, the mechanical properties of the mounting components of the charged element can also be sensed. This could be deflection, damping coefficient, elasticity, etc.

[0108] The charged element can also act as a sensor of the hydrodynamic properties of the medium it is immersed in. For example, instead of fibers (e.g., submicron fibers) that provide the dominant factor in response to overall flow as fluid resistance, larger fibers are provided within a transition region. Therefore, the movement of the fiber in the medium in response to standard vibrations will vary based on the properties of the medium. If the medium is homogeneous and the temperature and pressure are constant, changes in mass and / or viscosity will be reflected in the response of the charged element.

[0109] In some cases, a sensor array may be provided. For example, this array can sense spatial or volumetric differences in conditions such as sound waves. It should be noted that the charged elements may be directional, so spatial and volumetric sensors can generate information related to propagation vectors, scattering, and other effects. In other cases, the sensor array is configured or processed to invalidate or eliminate unwanted signal components and select or respond to desired signal components.

[0110] Another objective is to provide a sensor comprising a charged element configured to be placed within an electric field having at least two electrodes, the element interacting with each of the at least two electrodes to generate a composite force within the element that is only tensile, without a tendency to deflect from a nominal position, such that the element causes charge redistribution on the at least two electrodes when deflected from the nominal position.

[0111] The element may have movement or deflection in response to acceleration, Coriolis force, asymmetric bending force, chemical interaction between the medium and the surface of the element, biological interaction between the medium and the surface of the element, or chemisorption interaction between the medium and the surface of the element. For example, the sensor may also include a mechanical integrator, wherein the element has movement in response to impact.

[0112] The composite force may be oscillating, and the element has a deflection responsive to at least the oscillating composite force.

[0113] The sensor may also include an electronic amplifier configured to generate a signal corresponding to the deflection of the element.

[0114] The sensor may also include electronic equipment configured to determine the time response of the deflection of the element.

[0115] The time response may include vibration frequency, resonant frequency, or phase delay.

[0116] For example, the deflection of the element can be in response to the temperature, pressure, illumination, and / or viscosity of the fluid surrounding the element.

[0117] The sensor may further include a resilient mount for the element, the resilient mount pivotally supporting the element. Deflection of the element may respond to changes in the physical properties of the resilient mount. Deflection of the element may also respond to chemical interactions of the resilient mount with the surrounding medium.

[0118] The element may have an associated catalyst, wherein the deflection of the element is responsive to the amount of the associated catalyst on the substrate.

[0119] Another objective is to provide a sensor array comprising a plurality of elements arranged in a spatial array, the plurality of elements being configured to be charged, each corresponding element of the space being disposed within an electric field controlled by at least two corresponding electrodes, the corresponding element interacting with each of the at least two corresponding electrodes to generate a compound pull within the corresponding element, which, due to the compound force, has essentially no tendency to deflect from its nominal position, such that the corresponding element, upon deflection, causes a redistribution of charge on the at least two corresponding electrodes. The spatial array can provide a three-dimensional array of the plurality of elements. The sensor array may further include an external condition gradient surrounding the plurality of elements. The sensor array may further include a thermal control element configured to form a thermal gradient among the plurality of elements. The sensor array may further include an optical system configured to project an image onto the spatial array. The corresponding elements may have a plurality of corresponding, distinct selective chemical responses.

[0120] An array can also be provided in which the environment of the sensor is controlled to provide differential conditions, typically a state of gradual change within a certain range. For example, a linear array of sensors can be provided, maintained at different temperatures. A simple approach is to provide a temperature gradient induced by a heat source at one end of the array. The array can then sense the properties of the medium within the temperature range. Similarly, other gradients can be applied, such as illumination or other electromagnetic radiation, field of view, distance from the axis of rotation, etc.

[0121] As described above, a chemical sensor can be used, and the array can have the characteristic of incremental (or other) changes in the sensor, the sensed environment, or the medium to be sensed.

[0122] The sensor may include, for example, a catalyst (inorganic, organic, enzyme, etc.) that selectively interacts with the analyte in the medium. This can produce various effects, but typically generates heat (thermal energy) or a change in redox potential. To sense the heat, static characteristics (deflection position) or dynamic characteristics (vibration frequency, vibration amplitude, etc.) can be measured.

[0123] Redox changes are particularly interesting because they can be used to alter the voltage (charge) of the charged element, thus producing an output dependent on the modulated charge. Redox changes can also alter conductivity and other properties. For example, redox changes can be measured using a colorimetric redox indicator that can interact with an optical system, such as a laser or a light-emitting diode (semiconductor or organic semiconductor). The result may be a temperature change. However, in pulsed illumination systems, the coupling of the charged element to the pulse may vary depending on its light absorption, allowing for the measurement of the dynamic response even when there is no significant change in overall temperature.

[0124] In certain situations, sensors can provide fluid sensing. Typically, the presence of liquid between the sensing electrodes and the element being charged is problematic because many liquids are conductive and will drain charge from the element, although some are dielectric and non-conductive. However, given aqueous solutions and bioanalytes, spaces in which the associated electric field is typically impractical for sensing can be problematic, and even high humidity in such areas can hinder reliable sensing. One solution is to fabricate a sensor operating at <1.23V (the hydrolytic potential of water) and supply current to the element being charged to replenish the drained charge. It should be noted that this sensor can function as a conductive sensor, where the current distribution between the electrodes depends on location. However, in some cases, the attractive force between the electrodes and the element being charged may still be relevant, as the force depends on the charge and distance regardless of the current.

[0125] Another alternative is to provide the analyte in a fluid space with walls, and mount the charged element outside the fluid space on the opposite side of the walls. Changes in the fluid space that alter electrical or thermodynamic factors can be sensed by the walls and reflected in changes in the electrical (charge) or mechanical properties of the charged element. For example, a glucose sensor can be implemented using glucose oxidase immobilized in the fluid space. After glucose oxidase catalyzes the conversion of glucose to gluconolactone, FAD is reduced to FADH2, which is oxidized back to FAD by a redox mediator and then oxidized by an electrode reaction (this potential can, of course, be measured directly). The electrode is coupled to the charged element in this case, and the charge on the charged element depends on glucose oxidation. If the charged element is sensed to move, the amplitude of the signal will depend on the charge induced on the charged element by glucose oxidation. Other enzyme-coupled reactions can be sensed similarly. One advantage of this implementation is that it achieves electrical isolation between the aqueous medium and the electronics. Another advantage is that it can respond to intermediate conditions and superposition effects. For example, if two enzymes are involved in competing or parallel reactions, their reaction outputs can be added to or subtracted.

[0126] The charged element can directly sense motion through sensing effects, or indirectly sense motion by coupling with another mechanical element. Similarly, the modulation of motion caused by sensing effects can be a direct effect of sensing interactions, or indirectly through intermediate elements.

[0127] This can be achieved by: imaging sensors, such as spatial arrays of elements, whose displacement or vibration is modulated by illumination with ultraviolet, visible, infrared, far-infrared, terahertz radiation, etc.; and optical systems that can project images onto the array for sensing. Long-wavelength sensing, which is relatively difficult in semiconductor CCD or photodiode imagers, is a particularly attractive application. It should be noted that the sensing electrodes are designed to have an electric field aligned with the elongated axis of the moving element within its range of motion, thus avoiding a pull-in effect; however, this can be implemented to allow “backside” illumination, i.e., the image is projected onto the array (or individual element sensor) through the electrode side of the device. Vibrations of the moving element can be sensed by providing a time-varying electric field around the moving element, for example, by modulating the sensing electrodes or providing an additional “drive” electrode system. In any case, if the electric field is modulated, the electronics typically filter or compensate for the modulation while demodulating the applied signal.

[0128] Systems employing the aforementioned sensor can be mobile phones (smartphones) or other consumer electronic devices, automobiles or their components, flying objects or drones, telephones, computers, display devices, weaponry, toys, etc. The sensor can replace traditional types of sensors in a variety of applications, and its advantage lies in allowing for new applications.

[0129] Various sensors that can be modified to employ the technology of this invention, and the use of such sensors, are known. See also 6199575; 6621134; 6670809; 6749568; 6848317; 6889555; 6926670; 6935165; 6994672; 7036372; 7046002; 7073397; 7077010; 7078796; 7093494; 7109859; 7143652; 7164117; 7169106; 7204162; 7205173; 7260980; 7260993; 7340941; 7368312; 7397421; 7402449; 7425749; 7451647; 747487 2; 7518493; 7518504; 7539532; 7539533; 7543502; 7558622; 7562573; 7663502; 7677099; 7689159; 7694346; 7732302; 7733224; 7748272; 7775215; 7775966; 7784344; 7786738; 7795695; 7810394; 7849745; 7878075; 7915891; 7923999; 7950281; 7977635; 7984648; 8000789; 8016744; 8020440 ; 8037757; 8061201; 8103333; 8108036; 8118751; 8121673; 8121687; 8129802; 8130986; 8136385; 8143576; 8146424; 8171794; 8187795; 8215168; 8235055; 8268630; 8278919; 8323188; 8323189; 8328718; 8338896; 8344322; 8347717; 8352030; 8368154; 8371166; 8390916; 8397579; 8418556 ;8425415;8427177;8434160;8434161;8449471;8461988;8464571;8467133;8472120;8475368;8477425;8477983;8482859;8488246;8500636;8516905;8525673;8525687;8531291;8534127;8542365;8578775;8615374;8646308;8652038;8669814;8677821;8680991;8684253;8684900;8684922；8708903；8713711；8717046；8719960；8727978；8742944；8747313；8747336；8750971；8764651；8787600；8814691；8831705；8833171；8833175；8845557；8848197；8850893；8875578；8878528；8924166；8939154；8963262；8964298；8968195；9000833；9007119；9020766；9028405；9034764；9046547；9052194；9052335；9060683；9074985；9086302；9094027；9096424；9097890；9097891；9107586；9118338；9128136；9128281；9129295；9134534；9151723；9159710；9182596；9190937；9194704；9199201；9204796；9215980；9222867；9223134；9228916；9229227；9237211；9238580；9250113；9252707；9285589；9291638；9307319；9322685；9329689；9335271；9341843；9351640；9359188；9364362；9366862；9389077；9389215；9400233；9404954；9423254；9441940；9444404；9459100；9459673；9465064；9473831；9476975；9494477；9518886；9522276；9528831；9534974；9541464；9549691；9557345；9568461；9575089；9582072；9584931；9588190；9596988；9628919；9631996；9644963；9651538；9658179；9683844；9689889；9695038；9696222；9708176；9722561；9733230；9733268；9759917；9775520；9778302；9781521；9801542；9814425；9820657；9820658；9835647；9838767；9839103；9843858；9843862；9844335；9846097；9856133；9863769；9865176；9866066；9867263；9875406；9897460；9897504；9901252；9903718；9907473；9910061；9910062；9938133；9945746；9945884；9958348；9970958；9976924；20020151816；20020177768；20020193674；20040007051；20040119591；20040207808；20040260470；20050001316；20050001324；20050046584；20050066728；20050072231；20050104207；20050139871；20050199071；20050199072；20050265124；20060056860；20060081054；20060081057；20060107768；20060178586；20060205106；20060208169；20060211912；20060211913；20060211914；20060248950；20070023851；20070029629；20070089512；20070089513；20070125161；20070129623；20070209437；20070230721；20070241635；20070265533；20070273504；20070276270；20080001735；20080004904；20080021336；20080079444；20080081958；20080149832；20080163687；20080169921；20080188059；20080202237；20080281212；20080294019；20090022505；20090024042；20090049911；20090064781；20090064785；20090072840；20090078044；20090114016；20090133508；20090140356；20090227876；20090227877；20090255336；20090282916；20090318779；20090320591；20100039106；20100049063；20100083756；20100100079；20100132466；20100147073；20100186510；20100238454；20100242606；20100244160；20100251800；20100271003；20100275675；20100308690；20110010107；20110049653；20110061460；20110062956；20110073447；20110089324；20110100126；20110115624；20110120221；20110138902；20110181422；20110192226；20110192229；20110226065；20110254107；20110267212；20110295270；20110317245；20120004564；20120025277；20120032286；20120034954；20120043203；20120075168；20120092156；20120092157；20120095352；20120095357；20120133245；20120192647；20120194418；20120194419；20120194420；20120194549；20120194550；20120194551；20120194552；20120194553；20120200488；20120200499；20120200601；20120206134；20120206322；20120206323；20120206334；20120206335；20120206485；20120212398；20120212399；20120212400；20120212406；20120212414；20120212484；20120212499；20120218172；20120218301；20120235847；20120235883；20120235884；20120235885；20120235886；20120235887；20120235900；20120235969；20120236030；20120236031；20120242501；20120242678；20120242697；20120242698；20120245464；20120249797；20120291549；20120313711；20120330109；20130002244；20130009783；20130023794；20130023795；20130047746；20130050155；20130050226；20130050227；20130050228；20130069780；20130072807；20130080085；20130095459；20130104656；20130127980；20130133396；20130156615；20130170681；20130172691；20130172869；20130178718；20130186171；20130191513；20130197322；20130201316；20130204488；20130211291；20130215931；20130221457；20130226034；20130226035；20130226036；20130231574；20130263665；20130276510；20130278631；20130279717；20130297330；20130314303；20130317753；20130328109；20130330232；20130340524；20140011697；20140026686；20140031263；20140041452；20140047921；20140049256；20140053651；20140055284；20140063054；20140063055；20140077946；20140090469；20140094715；20140104059；20140111019；20140111154；20140121476；20140130587；20140142398；20140143064；20140163425；20140176251；20140188404；20140188407；20140192061；20140192836；20140194702；20140217929；20140225250；20140235965；20140249429；20140250969；20140253219；20140257141；20140260608；20140266065；20140266263；20140266787；20140296687；20140299949；20140306623；20140319630；20140321682；20140330256；20140352446；20150019135；20150068069；20150082872；20150096377；20150099941；20150105631；20150125003；20150125832；20150126900；20150141772；20150154364；20150163568；20150171885；20150176992；20150211853；20150220199；20150226558；20150250393；20150260751；20150268060；20150268284；20150269825；20150276529；20150309316；20150309563；20150323466；20150323560；20150323694；20150338217；20150351648；20150359467；20150374378；20150377662；20150377916；20150377917；20150377918；20160000431；20160000437；20160002026；20160003698；20160006414；20160030683；20160041211；20160066788；20160076962；20160130133；20160131480；20160137486；20160139173；20160140834；20160161256；20160176704；20160187654；20160202755；20160209648；20160213934；20160223579；20160231792；20160232807；20160235494；20160241961；20160274141；20160287166；20160305780；20160305835；20160305838；20160305997；20160310020；20160320426；20160327446；20160327523；20160334439；20160338644; 20160341761; 20160347605; 20160349056; 20160360304; 20160360965; 20160363575; 20160370362; 20160377569; 20170003314; 20170023429; 20170025904; 20170041708; 20170051884; 20170052083; 20170074853; 20170078400; 20170086281; 20 170086672; 20170121173; 20170135633; 20170142525; 20170146364; 20170152135; 20170160308; 20170164878; 20170167945; 20170167946; 20170168084; 20170168085; 20170168566; 20170191894; 20170199035; 20170201192; 20170217765; 20170223450; 20170 254831; 20170257093; 20170258386; 20170258585; 20170260044; 20170265287; 20170284882; 20170295434; 20170297895; 20170318385; 20170318393; 20170331899; 20170336205; 20170343350; 20170344114; 20170347886; 20180000545; 20180002162; 2018000 8356; 20180008357; 20180017385; 20180034912; 20180035206; 20180035228; 20180035229; 20180035888; 20180038746; 20180080954; 20180085605; 20180086625; 20180092313; 20180108440; 20180124181; 20180124521; and 20180134544, each of which is expressly incorporated herein by reference in its entirety.

[0130] The moving element can be used in actuation mode, for example, to define a carrier excitation, based on which the sensed effect is modulated by changing the amplitude of a defined frequency or by altering the frequency or time delay (phase) characteristics. This is particularly useful when shifting the baseband (DC) signal into a range where the sensor exhibits better characteristics, such as higher sensitivity, lower noise, etc.

[0131] By altering the electric field around the moving element, the intentional movement of the moving element can be used for various purposes. In one case, it might be desirable to employ an attraction response to protect the sensor from harsh environmental conditions; therefore, the moving element is intentionally moved out of a harmful path. In another case, the space in which the moving element operates may be non-uniform, and the movement of the moving element allows for exploration of that space.

[0132] As described above, the sensor can exhibit high directivity, for example, a cardioid response pattern. By deflecting the moving element from its nominal position, information about the vector direction of the effect can be determined. Furthermore, this deflection can distinguish between excitations with directional components and non-directional excitations or noise. The deflection does not have to be binary, and in the case of fiber optic sensors, three or more electrodes can be used to sense two axes. Other configurations with a larger number of electrodes are also possible. For example, instead of aligning the elongated axis of the moving element with the gap between the electrodes (the nominal design in a two-electrode symmetric sensor), a third electrode positioned between the two lateral electrodes can smooth the gradient (i.e., linearize the transition, thereby linearizing the response of the moving electrode) when the two lateral electrodes are maintained at different potentials and the central electrode is maintained at an intermediate potential.

[0133] For the medium surrounding the element, the moving element can act as a valve or flow control vane, and its position is controlled by the potential on the electrode.

[0134] In a medium where the fluid is close to the turbulence threshold, the location of one or more components

[0135] The deflection of a moving element, especially a significant deflection, can alter the effective stiffness of a sensor, thereby changing the amplitude of the response and the resonant frequency. Each of these can be useful in various types of sensors. Attached Figure Description

[0136] Figures 1A to 1D A conventional capacitive sensing scheme is shown.

[0137] Figure 2 A compatible electrostatic sensor is shown.

[0138] Figure 3 It shows according to Figure 2 Photos of the physical setup.

[0139] Figures 4A to 4C It shows that for Figure 2 The first and second derivatives of the electrode configuration, potential energy, and charge sensitivity estimates are given as functions of the tip displacement of the moving electrode.

[0140] Figure 5 A schematic diagram of the characterization settings is shown.

[0141] Figures 6A to 6D It shows Figure 2 The measurement results of the electrode configuration.

[0142] Figures 7A to 7B It shows Figure 2 Measurement results and frequency of electrode configuration.

[0143] Figure 8A An embodiment of the perforated plate diaphragm of the present invention is shown.

[0144] Figure 8B An embodiment of the fiber web moving element of the present invention is shown. Detailed Implementation

[0145] Figure 2 A compliant electrostatic sensor according to the present invention is shown.

[0146] The movable electrode according to the preferred embodiment studied herein is constructed of a thin sheet of material that is highly flexible in a direction perpendicular to its plane. It is supported along one edge, thus allowing it to easily rotate or bend around this support line, such as... Figure 2 As shown in the figure, this diagram represents a two-dimensional cross-section of the system, which remains constant along its entire dimension perpendicular to this portion. The moving electrode consists of a thin, flexible element of length L2 and thickness H2, with the included angle α relative to the horizontal orientation shown in the figure. The moving electrode is shown as a straight, solid body that can pivot about its attachment point. It could also consist of a flexible beam or chord suspended at one end, with sufficiently small bending stiffness to resemble... Figure 2 It can rotate freely as shown.

[0147] The fixed electrode is oriented such that it forms a planar surface orthogonal to the plane of the moving electrode. Orienting the fixed and moving electrodes so that their surfaces are orthogonal helps to minimize the net electrostatic force on the moving electrode, since the electric field will always be perpendicular to the conductor surface. By properly arranging the position and orientation of these electrodes, the electrostatic force acting on the planar surface of the moving electrode can be effectively canceled out, while a relatively small force is applied perpendicularly to the free edge.

[0148] According to an exemplary embodiment, the movable electrode consists of a thin, flexible element with a length of L2 = 6.2 mm and a thickness of H2 = 5 μm. The flexible element shown in the figure is deflected by an angle α relative to the horizontal orientation. Two vertically fixed electrodes are shown to the right of the movable electrode, with lengths L1 = L3 = 2.5 mm and thicknesses H1 = H3 = 200 μm. The horizontal gap between the movable electrode and the two fixed electrodes is g = 300 μm. They are in g... y They are separated by a gap in the vertical direction of 50 μm and maintained at the same potential.

[0149] By dividing the fixed electrode into two surfaces, denoted as electrodes 1 and 3 respectively, and maintaining both electrodes at the same voltage, the position of the moving electrode is sensed. The charge on these two fixed electrodes will change with the position of the moving electrode. For electrodes of practical size, it was found that the electrostatic force is negligible compared to those associated with the elastic properties of the electrodes.

[0150] exist Figure 2 In the diagram, two vertically fixed electrodes with lengths L1 and L3 and thicknesses H1 and H3 are shown to the right of the moving electrode. As the moving electrode rotates, it changes the charge distribution and net capacitance on this set of electrodes. The voltage applied to the moving electrode is set by a voltage source V2. The voltages on the two fixed electrodes are set to V = 0. In this embodiment, for the sake of simplicity, we assume that the moving electrode maintains a straight shape, allowing it to move as a rigid pendulum that can pivot freely about its attachment point. Minor deviations from this straight shape due to bending will not significantly change the results. The length L2 of the moving electrode is 6.2 mm and the thickness H2 is 5 μm to ensure electrode height compliance. These values ​​are chosen to correspond to the measurement configuration described below.

[0151] Photos of the manufactured equipment, such as Figure 3 As shown. Three electrodes are supported on an insulating block attached to a micromanipulator, thereby bringing electrode 2 close to the line separating electrodes 1 and 3. The distances between the electrodes and the overall dimensions were determined optically using a microscope.

[0152] To very roughly estimate the mechanical stiffness of a feasible moving electrode, we can consider the stiffness of a cantilever beam supported by fixed boundaries. Assume the electrode has a Young's modulus E = 2 × 10⁻⁶. 9 N / m 2 The electrode is composed of a polymer. To make the electrode conductive, a very thin layer of aluminum is coated on it; this layer must be thin enough not to significantly increase stiffness. Considering a force applied uniformly along the length, the equivalent mechanical stiffness per unit width can be approximated as k≈8EI / L. 3 / 2 Where I = H 3 / 2 / 12. Since L2 = 6.2 × 10 -3 m and H2 = 5 × 10-6 The mechanical stiffness per unit width is k≈0.7N / m. 2 Although this is a very approximate estimate, the following results indicate that the effective stiffness due to electrostatic forces is significantly smaller than this mechanical stiffness, and therefore its effect on movement can be ignored.

[0153] Figure 3 The following diagram illustrates the implementation. Figure 2 The photograph shows the physical setup of the concept. Electrodes 1 and 3 are formed using thin copper strips aligned perpendicular to the free end of electrode 2 on its left side. Electrode 2 is clamped and fixed to its right side. As shown, the sound field is incident from a direction perpendicular to the plane of electrode 2.

[0154] Although Figure 2 Unlike parallel-plate capacitive sensors, the electrode configuration of these sensors is not readily analyzed through simple design equations, but the charge distribution can be estimated digitally for a given set of applied electrode voltages. The boundary element method is used here, which provides a numerical solution to the following integral equation:

[0155]

[0156] in

[0157]

[0158] yes and The distance between them represents any two points on the electrode surface. It is in each position The given surface voltage specified at the location. The surface charge density is unknown. ∈=8.854pF / m is the dielectric constant of the medium. When the domain is two-dimensional, equation (10) becomes

[16] .

[0159]

[0160] Discretizing the surface into a finite number of regions allows us to solve for the charge distribution of any given electrode geometry. Knowing the charge density at various locations of the moving electrode enables the calculation of the electrostatic potential energy based on the electrode position. These data can then be numerically differentiated to estimate the first and second derivatives that provide the electrostatic force and effective stiffness associated with a given motion.

[0161] Figures 4A to 4C It shows that for Figure 2 The electrode configuration, the first and second derivatives of the potential energy estimate as a function of the tip displacement of the moving electrode, and the effective electrostatic force are... Figure 4A The first derivative of the potential energy shown is proportional, and the electrostatic stiffness is... Figure 4BThe negative values ​​of the second derivatives shown are proportional. The estimated force is always attractive and stiffens because it always acts to return the electrodes to the equilibrium position of x = 0. Assume that the bias voltage applied to the moving electrode is V = 400 volts, and the two stationary electrodes are at zero volts. Figure 4C The maximum amplitude of the charge sensitivity shown is approximately 4 × 10⁻⁶. -8 Coulombs / meter.

[0162] Because the domain is two-dimensional, the result is along the perpendicular to Figure 2 The unit length in the direction of the plane. Figure 2 This shows that the force consistently exhibits attractive properties, restoring the electrode to a single equilibrium position at x=0. The second derivative of the electrostatic energy provides effective electrostatic stiffness at the equilibrium position. This electrostatic stiffness can be compared with the estimated mechanical stiffness of the cantilever beam described above. The electrostatic stiffness is found to be approximately 0.4 N / m. 2 The estimated mechanical stiffness above is k≈0.7N / m. 2 Note that this electrostatic stiffness was estimated using a large bias voltage of 400 volts applied to the moving electrode. This bias voltage was expected to have little significant effect on electrode movement. This voltage exceeds the practical voltages used in miniature microphone designs. However, precision microphones (such as the Bruel and Kjaer 4138 used below) typically employ a 200-volt bias voltage. Using such a rather extreme voltage provides evidence that the electrode design is not adversely affected by the bias voltages that might actually be used.

[0163] Given all surfaces S i The charge density ρ on the electrode can be used to calculate the total charge Q on each of the three electrodes. i where i = 1, 2, 3

[0164]

[0165] The sensor output will be considered as the charge difference between electrodes 1 and 3.

[0166] Figure 4C The predicted charge sensitivity of the device is shown, which is calculated based on the known difference between Q1 and Q3 within the displacement range of the moving electrode 2.

[0167] Then calculate the derivative of the charge difference with respect to the displacement of the tip of electrode 2, and give the sensitivity in coulombs per meter, such as... Figure 4C As shown.

[0168] The overall sensor sensitivity can be expressed as charge sensitivity (in coulombs per meter, S). Q (represented by), electrical sensitivity (in volts per coulomb, S) e) and mechanical sensitivity (S in meters per pascal) m The combination of ) will result in the overall sensitivity being:

[0169] S = S Q ×S e ×S m Volt / Pascal (14)

[0170] In the experimental results shown below, a transimpedance or charge amplifier was used to obtain the electronic output. This was accomplished using a general-purpose operational amplifier, where the gain is primarily achieved through the effective feedback capacitor C. f Configure the settings. Then, the electrical sensitivity can be estimated using the following methods:

[0171]

[0172] Of course, mechanical sensitivity S m It will depend on the mechanical properties of the moving electrode 2. As a rough approximation, in the hypothetical “ideal” sensor, the average motion of electrode 2 is very close to the average motion of air in the sound field, as demonstrated in [3]. Assuming the sound field consists of plane waves propagating in one direction, the velocity of the sound particles is given by U = P / (ρ0c), where ρ0 is the nominal air density and c is the propagation speed of the sound wave. The quantity ρ0c is the characteristic acoustic impedance of the medium

[17] . Since it is assumed that the electrode rotates about its fixed end, the free end that is sensed will move at approximately twice the average displacement, which will occur at the center. For harmonics of frequency ω, in this ideal case, the mechanical sensitivity of the displacement of the free end of the electrode can be approximated as:

[0173]

[0174] In order to obtain Figure 2 The experimental results of the electrode system were used to fabricate electrode 2 (Goodfellow.com part number ES301855) using a 5 μm thick polyethylene terephthalate film (metallized with an aluminum thin layer). Fixed electrodes 1 and 3 were constructed using two 2.5 mm wide copper strips. This assembly was supported on a micromanipulator to allow adjustment of the nominal position of the moving electrode relative to the fixed electrode. A loudspeaker placed approximately 1 meter away acoustically actuated the moving electrode. Measurements were taken in an anechoic chamber. Figure 5 A schematic diagram of the characterization settings is shown.

[0175] Electronic output is obtained by using transimpedance circuits connected to electrodes 1 and 3. These circuits are not optimized for performance and use a general-purpose TL074 quad operational amplifier with a 1 GΩ feedback resistor. It should be noted that parasitic capacitances in parallel with the resistors typically significantly affect the impedance of such high-value resistors; parasitic capacitances are typically around C. f=1pF, which dominates the impedance over a wide frequency range. The circuit was implemented using via components on a prototype circuit board, which also affects the parasitic capacitance.

[0176] Figure 5 A schematic diagram of the characterization setup is shown. Electrode movement was detected using a laser vibrometer. The sound field formed by the loudspeaker was measured using a Bruel and Kjaer 4138 reference microphone. The electronic output was measured using a charge / transimpedance amplifier. All signals were recorded using a National Instruments PXI-1033 data acquisition system.

[0177] The velocity of the moving electrode was also measured using a Polytec laser vibrometer consisting of a Polytec OFV-534 compact sensor head and a Polytec OFV-5000 vibrometer controller. Sound pressure levels near the moving electrode were measured using a Bruel and Kjaer 4138 precision microphone with a 1 / 8-inch diameter pressure-sensitive diaphragm. A bias voltage of V2 = 400 volts was applied to electrode 2 using an American Power Designs M5-1000 DC-DC converter.

[0178] Figures 6A to 6D It shows Figure 2 The measurement results were obtained from the electrode configuration. A bias voltage of V = 400 volts was applied to the moving electrode, while the two stationary electrodes were at zero volts. The moving electrode was driven by a sound field consisting of 250 Hz tones produced by a loudspeaker with an amplitude of approximately 1 Pascal. Figure 6A The measured sound pressure (Pascals) at the location of the moving electrode is shown, measured by the Bruel and Kjaer 4138 reference microphone. Figure 6B The image shows the velocity (mm / s) measured midway between the clamped and free ends of the moving electrode, obtained using a laser vibrometer. When the sound field propagates as a plane wave, the velocity is almost proportional to and in phase with the pressure. This design can be employed using a beam response higher than its first resonant frequency. Because the beam is then “highly compliant,” i.e., mass-dominated rather than stiffness-dominated, it is desirable for the beam velocity to be in phase with the speed of sound.

[0179] Figure 6C and 6D The output voltage generated by the detection circuit, which employs a simple transimpedance amplifier, is shown, responding to the charges on electrodes 1 and 3. As expected, these signals are observed to be approximately out of phase with each other if the moving electrode moves away from the other as it moves toward one of the fixed electrodes. The two outputs can then be subtracted to obtain improved detection with increased sensitivity. The amplitude of the output voltage is approximately 250 mV, therefore the sensitivity of the differential output is approximately 0.5 volts / Pa. Figures 6A to 6D The data shown indicates that the DC bias voltage applied to electrode 2 is 400 volts.

[0180] For a sound pressure of approximately 1 Pa, corresponding to Figures 6A to 6D The displacement of the velocity shown is approximately 2.5 micrometers. It should be noted that this displacement was measured at the midpoint between the clamping end and the free end of the electrode. We can then estimate that for a 1 Pascal sound field, the displacement of the free end will be approximately 5 micrometers. The effective mechanical sensitivity can then be considered as S... m ≈5×10 -6 Meters per pascal. This measurement can be compared with the rough estimate provided in equation (16), where ρ c ≈415 Pascals per second / meter, ω=2π250. Then, formula (16) yields S. m ≈3×10 -6 The value per meter (m / Pa) is in reasonable agreement with the measurement results.

[0181] Figure 4C The estimated charge sensitivity shown is approximately S Q ≈40 nanocoulombs / meter. The electrical sensitivity given in formula (15) depends on the effective capacitance C. f As mentioned above, the capacitance is estimated to be Cf≈1pF. The terms in formula (14) are calculated as follows:

[0182] S = S Q ×S e ×S m ≈(40×10 -9 )×10 12 ×3×10 -6 ≈0.12 volts / pascal (17)

[0183] The measured electrical output can be regarded as Figure 6C and 6D The difference in the signals shown, i.e. for a 1 Pascal sound field, results in a measured peak voltage of approximately 0.5 volts, which is greater than the rough approximation of 0.12 volts but within a reasonable range.

[0184] Figures 6A to 6D The data indicates that the sensor is able to generate a considerable electronic output due to acoustic excitation. This is due to the use of a large bias voltage of 400 volts applied to the moving electrode. It is generally expected that using such a large bias voltage on a highly compliant electrode would have a significant effect on its movement.

[0185] Figure 7A and Figure 7B It shows Figure 2 Measurement results and frequency of electrode configuration. These results indicate that the effect of bias voltage on electrode movement is negligible, while the electrosensitivity depends on... Figure 7A The amplitude of the measured electrode displacement is approximately proportional to the bias voltage over a wide frequency range. For bias voltages of zero, 200 volts, and 400 volts, the amplitude of the measured electrode displacement as a function of frequency is independent of the bias voltage. The predicted air displacement amplitude for a 1 Pa plane acoustic wave is also shown. This indicates that, according to Figure 7B The electrodes move at least as much in a plane wave as in air. Electrosensitivity is considered to be the difference between the output voltage obtained from electrodes 1 and 3 and the sound pressure level at the point of electrode movement. This indicates that, as expected, the sensitivity approximately doubles for double the bias voltage.

[0186] Despite using a fairly large bias voltage, Figures 7A to 7B The results show that the electric field does not cause the motion of the moving electrode to stiffen (or soften). The figure illustrates the relationship between the measured electrode displacement amplitude and frequency. Figure 7A ) and the measured electrical sensitivity, which is defined as the electrical sensitivity measured from electrodes 1 and 3 (e.g. Figure 2 The difference between the output voltage and the incident sound pressure obtained (as shown) Figure 7B The results are shown for bias voltages of zero, 200 volts, and 400 volts. Although the response as a function of frequency is not ideal (i.e., not flat) due to sound reflections caused by the resonance of the stationary and moving electrodes, it is clear that the measured electrode velocity is essentially unaffected by significant changes in the bias voltage. This indicates that the electrostatic force is negligible relative to other mechanical forces acting on the electrodes, such as from... Figures 4A to 4C The data is as expected.

[0187] Figures 7A to 7B The predicted amplitude of airflow displacement in a plane wave sound field is also shown. This indicates that the electrode displacement measured due to sound is generally higher than the predicted value for plane sound waves. This also indicates that the electrode is highly compliant and its motion is unaffected by electrostatic or mechanical forces or stiffness.

[0188] The observation that such thin electrodes can move in a sound field with displacements similar to those in air is consistent with predictions of acoustically induced motion of thin, flexible walls

[18] . Although many other effects can affect the motion of the electrodes studied here, and are not quite similar to the problem of predicting sound transmission through walls, it is clear that thin, light membranes can move with air in a sound field. If we consider the incident sound to be a harmonic propagating perpendicular to the membrane plane at frequency ω, the complex amplitude p of the sound wave propagating through the membrane can be calculated. t The ratio to the incident pressure p1

[18] ,

[0189]

[0190] Where ρ wHere, ρ0 is the mass density of the membrane material, h is the membrane thickness, and ρ0c ≈ 415 pascal-s / m is the product of the nominal air density ρ0 and the speed of sound c. In plane sound waves, the ratio of pressure to the velocity of sound particles is equal to ρ0c, which leads to:

[0191]

[0192] Where u1 is the complex amplitude of the acoustic particle velocity of the incident plane wave. Equations (18) and (19) give the ratio of the membrane velocity to the acoustic medium velocity when the membrane is absent.

[0193]

[0194] Because of the speed U w Both U1 and U1 are in the same factor Since it is related to the corresponding displacement, the ratio in equation (20) will also be equal to the ratio of displacements. This ratio depends only on the factor (ρ). w hω / 2ρ0c). For the metallized polymer electrode used here, its density is estimated to be ρ. w ≈1380kg / m 3 The thickness is h≈5μm. Figures 7A to 7B Within the frequency range shown, this factor varies from approximately 0.003 at 50 Hz to 1 at 20 kHz. Therefore, within this frequency range, the thin electrode can be considered to move in the sound field with displacement similar to that in air.

[0195] The high compliance of the electrodes is, of course, the main reason why their movement can be easily detected by this capacitive sensing scheme. Highly compliant electrodes can be used as long as the sensing configuration itself does not introduce significant electrostatic forces that would affect movement.

[0196] The measured electrical sensitivity is Figure 7B As shown in the figure. Similarly, the frequency response is not ideal due to mechanical resonance, but the sensitivity is in the range of 0.1 to 1 volt / pascal in the lower frequency range shown. Optimized electrode design and improved readout circuitry would undoubtedly provide improved results for these measurements.

[0197] Compare Figure 7A and 7B This indicates that increasing the bias voltage proportionally increases the sensitivity at almost all frequencies, with no significant effect on the movement of the measurement. Therefore, the electrode configuration studied here allows for decoupling of the sensing method from the mechanical design of the electrodes; the electrodes can withstand the forces applied by the electric field without requiring specific electrode design. Designers are free to construct the desired moving electrodes to achieve a given sensitivity without worrying about electrostatic forces causing instability or hindering movement.

[0198] In the preceding text, it was assumed that the movable electrode consisted of a flat planar component. However, in some cases, it may be advantageous for its free edges to be curved. Furthermore, the plane of the movable component could also be oriented such that it is not parallel to the gap between the fixed electrodes. In this case, the movement of the electrode will result in an increase in its overlap area with one fixed electrode and a decrease in its overlap area with the other fixed electrode. This will lead to its function being similar to... Figure 1D In the illustrated embodiment, the charge on the fixed electrode depends on the overlap region rather than as shown. Figure 1C The distance in the middle. However, in this case, the overlapping area is formed only by the free edge of the moving electrode, not its planar surface. The direction of motion is usually orthogonal to the fixed electrode, rather than as... Figure 1D As shown, parallel. As previously mentioned, in other cases, larger movements cause a reduced force to return to the equilibrium position, stabilizing the system as a whole. Alternatively, the electrodes can be moved using a flat plane and the gap between the fixed electrodes can be made non-parallel to the electrodes or parallel to the plane. Figure 2 This effect is achieved by making the plane not perfectly straight in the direction perpendicular to it.

[0199] review Figure 3 The free end of the prototype implementation of electrode 2 is not perfectly straight, which may result in a lack of electrostatic stiffness in the data.

[0200] In many sensing applications, it is desirable for moving elements to be driven with minimal force, and therefore must be as lightweight and compliant as possible to provide minimal potential resistance and subsequently, maximum possible displacement response. If the moving element is an electrode in a capacitive sensor, care must be taken to ensure that forces associated with the electric field do not adversely affect motion and subsequent sensor performance. Current electrode geometries minimize electrostatic forces acting in the direction of motion.

[0201] In the electrode design studied here, electrostatic potential energy is considered as a function of electrode movement. If the potential energy remains approximately constant as the electrode moves, the force will tend to be smaller because, for this conservative force, the force equals the derivative of the potential energy. By dividing the fixed electrode into two parts, the potential energy can be kept insensitive to electrode displacement while allowing the difference in charge on the two fixed electrodes to be sensed. The result is the ability to sense motion without applying a significant electrostatic force that affects the motion.

[0202] Besides designing the sensor to maintain a nearly constant potential energy within the range of motion of interest, this is due to the fact that the moving electrode is thin and orthogonal to the stationary electrode because the electric field is orthogonal to the surface of the conductor. The forces between them are small. By maintaining geometric symmetry around the nominal position of the moving electrode, the electrostatic forces applied perpendicularly to its surface will roughly cancel each other out. This makes it possible to design the moving electrode to have completely negligible mechanical stiffness in its primary direction of movement. Negligible stiffness can be achieved by supporting the moving electrode with hinges that have virtually no rotational resistance, or by making the moving electrode from an extremely thin material with weak resistance to bending. If the material is thin enough, it can be configured like a cantilever beam, completely fixed to a supporting structure and free at the other end. The mechanical restoring stiffness only needs to be sufficient to resist any other environmental forces that may act on it, such as gravity.

[0203] Since electrostatic force does not affect movement, a higher bias voltage can be applied to the moving electrode, thereby improving the overall electrosensitivity. In the results presented here, a highly compliant moving electrode was used, which moves easily in response to sound pressure. The electrode configuration allows for a relatively large 400-volt bias voltage with negligible effect on electrode movement. This results in an output electrosensitivity of approximately 0.5 volts / pa.

[0204] Another desirable characteristic of capacitive sensors is their ability to ensure stability across the entire range of possible shift and bias voltages. For example... Figures 4A to 4C As shown, when the moving electrode is subjected to large movement, although it has little resistance to small offsets from the equilibrium position, the restoring force will always come into play to restore it to the equilibrium position, thus ensuring overall stability.

[0205] The movement of the moving electrode is largely unaffected by changes in the bias voltage, while the overall electrical output sensitivity to sound is improved as expected.

[0206] The sensor can be designed as a microphone, achieving an equivalent sound pressure level of 20 dBA and maintaining a frequency response of ±3 dB within the 20 Hz to 20 kHz frequency range.

[0207] Although the cantilevered plate element has been described above as a transducer for the mechanical movement of a charge by sound waves in the air, one or more fibers can also be used, which have the advantage of high aerodynamic mass drag. According to this technique, since the electrostatic interaction between the sensing plate and the moving element does not substantially deflect the element or substantially change its stiffness, this technique allows sensing approximate particle movement in the air surrounding the fiber via viscous drag. The sensor is not limited to a single fiber compared to the more commonly measured deflection of the plate caused by a pressure difference; therefore, multiple fibers can be provided, or independently moving parallel elements, each interacting with a glass fiber. Sensing electrodes, or a loose pad or mesh, can be formed to allow all fibers to move together. See [4, 30, 41, 42, 3]. For example, the fiber can be spider silk coated with 80 nm gold or electrospun polymethyl methacrylate.

[0208] The operation of a viscous drag moving element can be analyzed based on the pressure difference of the planar traveling sound waves acting on its two planes. An approximate qualitative model can be constructed by treating the moving element as an elastic beam. In the response at a single frequency ω, the beam deflection w(x,t) at a point along its length x at time t can be calculated by solving the following standard partial differential equation.

[0209]

[0210] Where E is Young's modulus, I is the area moment of inertia, ρ is the material density, b is the width, h is the thickness, P is the plane wave sound pressure amplitude, k = ω / c is the wave number, c is the wave propagation speed, d is the effective distance the sound travels between the two planes of the beam, C is the viscous damping coefficient, and U is the complex amplitude of the sound particle velocity.

[0211] As the beam becomes sufficiently narrow (i.e., when h and b become smaller), the viscous damping force... In contrast, all terms in equation (21) can be neglected. This is because C's dependence on h and b is much weaker than that of all other terms. Furthermore, for isolated fibers or bundles, the effective separation distance d is approximately equal to b, thus the sound pressure difference term (the first term on the right-hand side) also becomes smaller. Therefore, in this limiting case where the viscous term dominates, the relative movement between the fiber and the air becomes negligible, leading to Therefore, if the sensing element is properly designed so that viscous forces dominate, the sensing element will move together with the acoustic medium.

[0212] Extremely thin, compliant materials are widely used to construct these sensing electrodes, such as graphene [1, 2] and carbon nanotubes or nanotube yarns. Electrospun polymer fibers can also be used for flow sensing

[41] . These very thin structures have extremely low bending stiffness, but they are not feasible to incorporate into conventional condenser microphone designs unless their movement is subjected to a strong electrostatic force perpendicular to their long axis. Figure 8A The planar vibrating diaphragm design is shown. This design senses the resistance of air passing through the diaphragm, but this design has significant stiffness and therefore generally cannot satisfy the assumption that all terms of equation (21) are entirely dominated by viscous resistance terms. However, in some cases, porous diaphragms are acceptable sensors. In one example, the diaphragm can be made of multilayer graphene; in microelectromechanical systems (MEMS) designs, the diaphragm can also be formed of polycrystalline silicon or silicon nitride. The diaphragm can be inherently conductive or metallized, for example, having a layer of gold. The diaphragm, or more generally, the moving element, can be formed of electret materials.

[0213] A typical silicon micromachining process for forming a thin velocity-sensing film begins with a bare silicon wafer on which a one-micron oxide layer is grown via wet oxidation. This oxide layer provides an etch stop layer for wafer-through etching, creating an open air space behind the film. A silicon nitride film approximately 0.5 microns thick is then deposited using a low-pressure chemical vapor deposition (LPCVD) furnace. The silicon nitride is patterned using photolithography to define pores for achieving porosity and to define electrode edges. A portion of the nitride film is made conductive by depositing and patterning a thin layer (approximately 80 nm) of phosphorus-doped silicon using an LPCVD process. The film is then annealed to form polycrystalline silicon. Reactive ion etching (RIE) is performed on the wafer back side to expose the back side of the silicon electrodes. The electrodes are released by removing the hot oxide using buffered hydrofluoric acid. Fabrication of the sensing electrodes is accomplished by depositing a conductive film around the moving electrodes.

[0214] Figure 8B A fiber web element is shown, forming a loose sheet that is typically moved as a whole by the viscous drag of fibers by moving air. The mesh is designed to have high stiffness due to forces applied in the mesh plane and high flexibility when out-of-plane forces are applied, such as those caused by acoustic flow. Because the mesh consists of a large number of loosely arranged individual fibers, it is difficult to ensure dimensional accuracy and in-plane stiffness at the edges closest to the sensing electrode to ensure that the fibers near the sensing electrode are not free. This, in turn, reduces repeatable sensitivity and resistance to in-plane electrostatic attraction. Therefore, a thin solid frame or binding tape can be attached to the mesh near the edges of the sensing electrode. Suitable fibers include metallized electrospun PMMA and carbon nanotubes, or a combination of both.

[0215] The fibers can be less than 1 μm in size and, for example, can be about 500 nm in diameter.

[0216] The device according to this technology can be used not only as a sensor but also as an actuator. In this case, for example, a small time-varying differential voltage can be applied to the electrodes, which will effectively adjust the equilibrium position of the system. The voltage applied to the moving element electrodes can be set to a value that adjusts the electrostatic stiffness to almost any desired value, so that movement is limited only by the mechanical stiffness and mass of the moving electrodes.

[0217] Using highly compliant and lightweight moving electrode materials (such as graphene) enables actuation with very small drive voltages. This configuration allows for adjustment of the equilibrium position over a wide range based on minute variations in the drive voltage. The moving electrode's response to voltage changes is linear, rather than quadratic, which may be desirable for parallel plate actuators. Furthermore, in a four-electrode implementation, three static electrodes can be used instead of the two static electrodes described above. In this case, the additional electrodes provide extra capability to adjust the effective electrostatic stiffness of the moving electrode. As discussed in the various embodiments above, the "repulsion" may be repulsive rather than attractive.

[0218] The various embodiments described above can be combined to provide other embodiments. These and other changes can be made to the embodiments based on the detailed description above. Generally, the terminology used in the following claims should not be construed as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted to include all possible embodiments and the full scope of equivalents. Claims are valid. Therefore, the claims are not limited by the disclosure.

[0219] References

[0220] Each of the following references is explicitly incorporated herein by reference in its entirety:

[0221] [1] Y.-M.Chen, S.-M.He, C.-H.Huang, C.-C.Huang, W.-P.Shih, C.-L.Chu, J.Kong, J.Li and C.-Y.Su, “Ultra-large suspended graphene as a highly elastic membrane for capacitive pressure sensors”, Nanoscale, vol.8, no.6, pp.3555-3564, 2016.

[0222] [2] C. Berger, R. Phillips, A. Centeno, A. Zurutuza and A. Vijayaraghavan, “Capacitive pressure sensing with suspended graphene-polymer heterostructure membranes”, Nanoscale, vol. 9, no. 44, pp. 17439-17449, 2017.

[0223] [3] J. Zhou and R. N. Miles, “Sensing fluctuating airflow with spider silk”, Proceedings of the National Academy of Sciences, p. 201710559, 2017.

[0224] [4] R. Miles and J. Zhou, “Sound-induced motion of a nanoscale fiber”, Journal of Vibration and Acoustics, vol. 140, no. 1, p. 011009, 2018.

[0225] [5] R. Miles and F. Degertekin, “Optical sensing in a directional memsmicrophone”, November 2, 2010, US Patent 7,826,629.

[0226] [6] B. Bicen, S. Jolly, K. Jeelani, C.T. Garcia, N.A. Hall, F.F. Degertekin, Q. Su, W. Cui, and R.N. Miles, “Integrated Optical Displacement Detection and Electrostatic Actuation for Directional Optical Microphones With Micromachined Biomimetic Diaphragms,” IEEE Sensors Journal, vol.9, no.12, pp.1933-1941, December 2009.

[0227] [7] R. N. Miles, Q. Su, W. Cui, M. Shetye, F. F. Degertekin, B. Bicen, C. Garcia, S. Jones and N. Hall, “A low-noise differential microphone inspired by the ears of the parasitoid fly Ormia ochracea,” Journal of the Acoustical Society of America, vol. 125, no. 4, Part 1, pp. 2013-2026, April 2009.

[0228] [8]ML Kuntzman, NN Hewa-Kasakarage, A. Rocha, D. Kim and NA Hall, “Micromachined in-plane pressure-gradient piezoelectric microphones”, IEEE Sensors Journal, vol.15, no.3, pp.1347-1357, 2015.

[0229] [9] B.-H. Kim and H.-S. Lee, “Acoustical-thermal noise in a capacitive memmicrophone”, IEEE Sensors Journal, vol.15, no.12, pp.6853-6860, 2015.

[0230]

[10] LKBaxter, “Capacitive sensors”, Ann Arbor, vol. 1001, p. 48109, 2000.

[0231]

[11] DKMiu, Mechatronics: electromechanics and controlmechanics. Springer Science & Business Media, 2012.

[0232]

[12] R. Miles, “Comb sense microphone”, June 9, 2009, US Patent 7,545,945.

[0233]

[13] R. N. Miles, W. Cui, Q. T. Su and D. Homentcovschi, “Amems low-noise soundpressure gradient microphone with capacitive sensing” Journal of Microelectromechanical Systems, vol. 24, no. 1, pp. 241-248, 2015.

[0234]

[14] S. Towfighian, S. He and RBMrad, “A low voltage electrostatic microactuator for large out-of-plane displacement” in ASME 2014 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, American Society of Mechanical Engineers, pp. V004T09A015-V004T09A015.

[0235]

[15] S. He, RBMrad and J. Chang, “Development of a high-performance microelectrostatic repulsive-force rotation actuator” Journal of Microelectromechanical Systems, vol.19, no.3, pp.561-569, 2010.

[0236]

[16] D. Poljak and CA. Brebbia, Boundary element methods for electrical engineers. WIT Press, 2005, vol.4.

[0237]

[17] P. Morse and K. Ingard, Theoretical Acoustics. Princeton University Press, 1986.

[0238]

[18] A. London, “Transmission of reverberant sound through single walls” J. Research Nat. Bur. of Stand, vol. 42, no. 605, p. 2, 1949.

[0239]

[19] R. N. Miles, W. Cui, Q. T. Su and D. Homentcovschi, “A mems low-noise soundpressure gradient microphone with capacitive sensing,” Journal of Microelectromechanical Systems, vol. 24, no. 1, pp. 241-248, 2015.

[0240]

[20] T.T. Bringley. Analysis of the immersed boundary method for Stokesflow. Doctoral dissertation, New York University, 2008.

[0241]

[21] KK Charaziak and CAShera. Compensating for ear-canal acoustics when measuring otoacoustic emissions. The Journal of the Acoustical Society of America, 141(1):515-531, 2017.

[0242]

[22] R. Cox. The motion of long slender bodies in a viscous fluid part 1. General theory. Journal of Fluid mechanics, 44(4):791-810, 1970.

[0243]

[23] W. Cui, B. Bicen, N. Hall, S. Jones, F. Degertekin and R. Miles. Optical sensing in a directional MEMS microphone inspired by the ears of the parasitoid fly, Ormia ochracea. In MEMS 2006: 19th IEEE International Conference on MicroElectro Mechanical Systems, Technical Digest, Proceedings: IEEE Micro ElectroMechanical Systems Workshop, pages 614-617, Istanbul, Turkey, January 22-26, 2006.

[0244]

[24] H. Droogendijk, J. Casas, T. Steinmann and G. Krijnen. Performance assessment of bio-inspired systems: flow sensing mems hairs. Bioinspiration & biomimetics, 10(1):016001, 2014.

[0245]

[25] T. Interactions of fibers and flow: asymptotics, theory, and numerics. Doctoral dissertation, Technical University of Kaiserslautern, 2000.

[0246]

[26] K. Grosh and RJ Littrell. Piezoelectric MEMS microphone, December 26, 2017. US 9,853,201.

[0247]

[27] D. Homentcovschi, R. Miles, P. Loeppert and A. Zuckerwar. A microacoustic analysis including viscosity and thermal conductivity to model the effect of the protective cap on the acoustic response of a mems microphone. Microsystem Technologies, 20(2):265-272, 2014.

[0248]

[27] W.-X. Huang, SJShin and HJSung. Simulation of flexible filaments in a uniform flow by the immersed boundary method. Journal of Computational Physics, 226(2):2206-2228, 2007.

[0249]

[28] G. H.-U. Kleindienst. Oscillation of cricket sensory hairs in a low-frequency sound field. Journal of Comparative Physiology A, 167(2):193-200, 1990.

[0250]

[29] R. Miles. Comb sense capacitive microphone, June 9, 2009. U.S. Patent Application 2009 / 0262958.

[0251]

[30] RNMiles. "A Compliant Capacitive Sensor for Acoustics: Avoiding Electrostatic Forces at High Bias Voltages." IEEE Sensors Journal 18, no. 14 (2018): 5691-5698.

[0252]

[31] C. Motchenbacher and J. Connelly. Low-Noise Electronic System Design. John Wiley & Sons, Inc., 1993.

[0253]

[32] L. Rosenhead. Laminar Boundary Layers: An Account of the Development, Structure, and Stability of Laminar Boundary Layers in Incompressible Fluids, Together with a Description of the Associated Experimental Techniques. Clarendon Press, 1963.

[0254]

[33] MJ Shellley and T. Ueda. The stokesian hydrodynamics of flexing, stretching filaments. Physica D: Nonlinear Phenomena, 146(1):221-245, 2000.

[0255]

[34] R. Sisto, L. Cerini, F. Sanjust and A. Moletti. Intensimetric detection of distortion product otoacoustic emissions with ear canal calibration. The Journal of the Acoustical Society of America, 142(1): EL13-EL17, 2017.

[0256]

[35] G. G. Stokes. On the effect of the internal friction of fluids on the motion of pendulums, volume 9. Pitt Press, 1851.

[0257]

[36] A.-K. Tornberg and K. Gustavsson. A numerical method for simulations of rigid fiber suspensions. Journal of Computational Physics, 215(1):172-196, 2006.

[0258]

[37] A.-K. Tornberg and MJ Shelley. Simulating the dynamics and interactions of flexible fibers in stokes flows. Journal of Computational Physics, 196(1):8-40, 2004.

[0259]

[38] S. Towfighian and R.N. Miles. A new approach to capacitive sensing: Repulsive sensors, September 1, 2016. NSF Grant 1608692.

[0260]

[39] B. Varanda, R. Miles and D. Warren. Characterization of the dominant structural vibration of hearing aid receivers. Journal of Vibration and Acoustics, 138(6):061009, 2016.

[0261]

[40] E. Wente. A condenser transmitter as a uniformly sensitive instrument for the absolute measurement of sound intensity. Physical Review, 10(1):39, 1917.

[0262]

[41] J. Zhou, B. Li, J. Liu, W. Jones Jr. and R. Miles. Highly-damped nanofibermesh for ultrasensitive broadband acoustic flow detection, 2018. to appear in Journal of Micromechanics and Microengineering.

[0263]

[42] J. Zhou and R. Miles. Directional sound detection by sensing acousticflow, 2018. to appear in IEEE Sensors.

[0264]

[43] J.M. Crowley, Fundamentals of applied electrostatics. John Wiley & Sons, 1986.

[0265]

[44] N. Jonassen, Electrostatics. Springer Science & Business Media, 2013.

[0266]

[45] T. F. E. and V. Hansen, “On the calculation of potential integrals for linear source distributions on triangular domains,” IEEE Transactions on Antennas and Propagation, vol.43, no.12, pp.1499-1502, 1995.

[0267]

[46] J. Zhou, R. N. Miles and S. Towfighian, “A novel capacitive sensing principle for microdevices” in ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2015, pp. V004T09A024-V004T09A024.

Claims

1. A capacitive sensor, comprising: At least two conductors, each of the at least two conductors having a planar surface, the at least two conductors being isolated from each other by at least one spatial gap, each respective conductor interacting with an electrostatic field, the electrostatic field occupying a region near the at least two conductors and the at least one spatial gap, and providing an electrical response to disturbances of the electrostatic field; and A deflectable element is configured to move along a displacement axis having a directional component that selectively crosses the spatial gap in response to a sensed condition, and to perturb the electrostatic field corresponding to the movement, wherein within the deflection range of the deflectable element, the electrostatic field does not substantially alter the responsiveness of the deflectable element to the sensed condition or cause attraction instability. The deflectable element has a thickness along the displacement axis and a length in a direction orthogonal to the displacement axis. Wherein, the at least two conductors and the deflectable element are oriented such that the length of the deflectable element is orthogonal to the planar surfaces of the at least two conductors; and The deflectable element is configured to deflect in response to a sound wave.

2. The capacitive sensor according to claim 1, wherein: The at least two conductors include a pair of fixed conductors separated by a linear spatial gap. Each of the fixed conductors is maintained at its respective potential to generate an electrostatic field in the space above the pair of fixed conductors, depending on the difference between the potentials of the fixed conductors. The electrostatic field has a principal field vector component pointing across the linear spatial gap. The deflectable element includes a chargeable element configured with a displacement axis having a vector component pointing across the linear spatial gap, such that the force applied to the deflectable element due to the electrostatic field is insensitive to the displacement state of the deflectable element in response to the sensed conditions.

3. The capacitive sensor according to any one of claims 1 and 2, wherein, The deflectable element includes a cantilevered diaphragm.

4. The capacitive sensor according to any one of claims 1 to 2, wherein, The deflectable element includes at least one of a perforated membrane, a fiber web, a fiber pad, a metallized electrospun fiber, a carbon nanotube, and graphene.

5. The capacitive sensor according to any one of claims 1 to 2, wherein, The potential at each of the at least two conductors is maintained at a predetermined potential by a corresponding transimpedance amplifier, while the movement of the deflectable element causes a change in charge on the corresponding conductive surface.

6. The capacitive sensor according to any one of claims 1 to 2, wherein, The capacitive sensor includes a microphone, and the deflectable element has a movement amplitude corresponding to the sound wave.

7. A method for sensing vibration using a capacitive sensor according to any one of claims 1 to 5, comprising: A voltage potential is induced on the deflectable element relative to the at least two conductors; as well as Sensing changes in induced charge on the at least two conductors caused by the deflection of the deflectable element along the displacement axis, wherein the force generated by the at least two conductors on the deflectable element does not substantially change the deflection of the deflectable element.

Images