EP0072289A2 - Elektroakustischer Wandler mit Kondensator mit inhärent polarisiertem Dielektrikum - Google Patents

Elektroakustischer Wandler mit Kondensator mit inhärent polarisiertem Dielektrikum Download PDF

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Publication number
EP0072289A2
EP0072289A2 EP82401394A EP82401394A EP0072289A2 EP 0072289 A2 EP0072289 A2 EP 0072289A2 EP 82401394 A EP82401394 A EP 82401394A EP 82401394 A EP82401394 A EP 82401394A EP 0072289 A2 EP0072289 A2 EP 0072289A2
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EP
European Patent Office
Prior art keywords
plate
transducer according
electrodes
faces
polarization
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP82401394A
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English (en)
French (fr)
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EP0072289A3 (de
Inventor
Pierre Ravinet
François Micheron
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Thales SA
Original Assignee
Thomson CSF SA
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Filing date
Publication date
Application filed by Thomson CSF SA filed Critical Thomson CSF SA
Publication of EP0072289A2 publication Critical patent/EP0072289A2/de
Publication of EP0072289A3 publication Critical patent/EP0072289A3/de
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R17/00—Piezoelectric transducers; Electrostrictive transducers
    • H04R17/005—Piezoelectric transducers; Electrostrictive transducers using a piezoelectric polymer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
    • H04R2499/10—General applications
    • H04R2499/11—Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's

Definitions

  • the invention relates to microphones and hydrophones in which the acoustic pressure acts directly on a vibrating structure of the electrically polarized solid dielectric capacitor type.
  • Condenser microphones using an electrically polarized solid dielectric generally consist of one or more dielectric films coated with electrodes.
  • electric charges are created by piezoelectric effect or by excess electric charge.
  • the induced electric charge must vary exactly like the incident sound pressure.
  • the mechanical compliance of a vibrating microphone structure intervenes in the operation, because it fixes the resonance frequency and therefore the upper limit of the frequency band reproduced at constant level.
  • care must be taken to ensure that the rear face of the diaphragm is not subjected to sound pressure and for this purpose, the diaphragm is mounted in a rigid case so as to make it compress a certain amount. air volume.
  • the rigidity of the vibrating structure is therefore reinforced by the presence of the volume of air, but as the deformation work is partly stored in an environment devoid of transducing properties, the sensitivity of the microphone is less than if its membrane was the only organ resistant to acoustic pressure.
  • the influence of an air cushion loading a membrane is predominant when it is very flexible, when its surface is large and when the volume of compressed air is reduced.
  • the piezoelectricity phenomena have been the subject of numerous studies showing that parallel to the intrinsic piezoelectricity defined as is known by a tensor of rank three and implying that the material considered would not laugh at the centrosymmetric structure, there exists a bending piezoelectricity.
  • the electric polarization induced by the bending piezoelectricity is determined by the piezoelectric coefficients of a tensor of rank four and manifests itself when there is a stress gradient within the material subjected to deformation.
  • bending piezoelectricity does not imply a prior structural or electrical anisotropy of the mechanically stressed material because it is the inhomogeneous stress which creates the structural defect giving rise macroscopically to the induced electric polarization. Nevertheless, experience shows that the manifestations of bending piezoelectricity are appreciably increased when the material considered has received an electrical anisotropy of the polar type or by excess charge.
  • the present invention aims to apply flexural piezoelectricity to a polarized solid dielectric condenser microphone structure.
  • the subject of the invention is an electroacoustic transducer with a polarized solid dielectric capacitor comprising at least two collecting electrodes, a vibrating structure made of said dielectric and subjected to the incident acoustic pressure and a support to which said vibrating structure is attached by its edges. ; said collector electrodes being carried by said vibrating structure and connected respectively to two output terminals, characterized in that said vibrating structure is a flat structure in the form of a plate sufficiently thick so that the mean sheet does not undergo any significant deformation during the bending of said plate.
  • a piezoelectric ceramic material of the PZT type twenty times more rigid than the PVF 2 leads to a minimum thickness that is half as small according to the same criterion.
  • the permittivity of the PZI ceramic is a hundred times higher than that of PVF 2 , which means that the open circuit voltage of a ceramic microphone capsule is, all other things being equal, a hundred times lower .
  • Piezoelectric ceramics and intrinsically piezoelectric crystals are rather reserved for microphonic detection of very high acoustic pressures or at ultrasonic frequency.
  • Piezoelectricity can manifest itself in two distinct forms which are intrinsic piezoelectricity and bending piezoelectricity.
  • Intrinsic piezoelectricity implies that the material subjected to deformation has properties comparable to that of a crystalline body of a non-centrosymmetric class. This is the case of polar polymeric materials such as polarized polyvinylidene fluoride.
  • bending piezoelectricity can exist in any dielectric body, because it is attributable to the formation of dipole moments in the presence of a gradient of mechanical tension. The intensity with which bending piezoelectricity can manifest is notably increased when the material is electrically polarized by excess charge (electret) or by creation of a polar phase on the macroscopic scale.
  • This device comprises a beam 6 with a prismatic section, for example made of polyvinylidene fluoride polarized parallel to the axis Z.
  • This beam is carried at one end by an embedding 2 and can be made to flex by applying a force to it at the other end.
  • F direction parallel to the axis Z.
  • the longitudinal axis of the beam OX forms with an axis OY and the axis OZ a triangular trihedron; the figures in parentheses designate these axes according to usage in crystallography.
  • the faces of the beam 6 normal to the Z axis carry two electrodes 7 and 8 forming a capacitor.
  • Electrodes are connected to terminals 9 and 10 between which an electric voltage V appears.
  • the voltage state in the straight section 13 of the beam is represented by a triangular distribution with zero center 12 which represents the bending voltages.
  • the non-zero components of the stress tensor are:
  • X 1 describes the distribution 12 at zero average over the 2h height of the beam and X 5 describes the distribution 11 whose average X 5 on the height 2h of the beam is necessarily equal to - No tension of expansion according to OX exists since the force F is perpendicular to the axis of the beam.
  • d 35 . X 5 represents the charge density relative to the intrinsic piezoelectricity of which it is known that the induced polarization P i is given by the tensorial expression: where d iik are the piezoelectric modules belonging to a tensor of rank three.
  • the term varies as a function of the abscissa of the electrodes and represents the charge density relative to the bending piezoelectricity of which it is known that the induced polarization P i 'is given by the tensorial expression: where f ijke are the piezoelectric modules belonging to a tensor of rank 4 and xl la l coordinate. Knowing that the coordinates are three in number, the tensor expressing the bending piezoelectricity contains 81 piezoelectric modules not all zero whatever the dielectric material considered.
  • the measuring device of FIG. 1 allows the two forms of piezoelectricity to be deducted from each other.
  • any structure made of an insulating material and in a state of inhomogeneous stresses is capable of delivering an electrical signal between electrodes which is a measurement of stress experienced by this structure.
  • FIG. 3 represents an elementary volume dx, dy, dz of plate at rest (cubic form) and under pure bending stresses.
  • the volume 15 of thickness e comprises at mid-height a neutral sheet 16 whose surface does not vary between the rest state and the deformed state.
  • FIG. 4 represents the deformation in a spherical cap of radius p of a flat circular plate undergoing at its periphery a uniform bending torque M.
  • the arc Ab has the length the diameter 2a of the plate and its highest point corresponds to arrow 6. This is true if we assume that the middle sheet does not undergo any meridian deformation. We can therefore calculate the radius a 1 of the circular arrow undergoing the greatest circumferential shortening. This radius is worth: the circumferential expansion is therefore equal to: either approximately
  • Curve 18 of the diagram in FIG. 6 gives the values of the expression where k is given by the expression X ⁇ is the circumferential stress in a system of cylindrical coordinates ( ⁇ , r, z).
  • Curve 19 of the diagram in FIG. 6 gives the values of the expression X is the meridian constraint.
  • Figure 7 we can see a meridian section of a microphone capsule according to the invention in which it has given up embedding the vibrating plate.
  • the plate 1 completely coated on its two faces of electrodes 7 and 8 is simply pressed instead of being embedded.
  • the simple support of Figure 7 does not generate bending torque at the point of attachment of the plate bent by the acoustic pressure p.
  • the deformation shown in dotted lines in FIG. 7 has a simply convex shape devoid of the point of inflection. This results in a state of mechanical tension very different from that of FIG. 6, but which remains governed by the resistance to bending.
  • the charges globally collected by the electrodes 7 and 8 do not exactly compensate each other and the sensitivity of the microphone capsule is substantially increased.
  • the section in FIG. 7 shows that the bottom of the housing 21 has an annular collar in which a bearing 22 with a pointed top has been formed on which the plate assembly 1, 7, 8 rests.
  • the application of this assembly against the bearing surface 22 is ensured by a seal 23 of compressible insulating material which lines the crown 20 fitted on the bottom of the housing 21.
  • This pivoting causes the bearing face of the seal 23 to tip over, but to avoid creating a resistant torque, this seal is made of polymer or elastomer foam.
  • This joint can be made conductive, in order to make contact with the electrode 7.
  • the electrode 7 plays the role of ground electrode connected to the metal parts 20 and 21 of the housing and the electrode 8 is stopped at low distance from the bearing surface 22.
  • the parts 21 and 22 are made of an insulating material and making the electrostatic shielding by crimping in a metallic outer casing as illustrated for example in FIG. 14.
  • a significant gain in sensitivity of the device of FIG. 5 can be obtained by subdivision of one of the electrodes 7 or 8 according to a circular cut of radius R '.
  • FIG. 8 This alternative embodiment is illustrated by the partial isometric view of FIG. 8.
  • the bottom of the case 21 and the flange 20 here form a flat recess pinching a flat plate 1.
  • the electrode 27 completely covers the face of the plate 1 facing towards outside.
  • the inner face of the plate 1 carries two concentric electrodes 26 and 25.
  • the central electrode is a disc 25 whose radius is close to the value R 'defined above.
  • the peripheral electrode 26 is a ring with an inner radius close to R '.
  • the circular cut-off which separates the two electrodes 25 and 26 is located at the radius R ', that is to say at 70% of the center with respect to the non-embedded area of the plate 1.
  • the microphone voltages delivered by the electrodes 25 and 26 are of opposite signs and greater than the voltage which would be delivered by the electrodes 25 and 26 joined together.
  • Several modes of operation can be envisaged - voltages supplied by the electrodes. The simplest solution consists in providing on the internal face of the plate 1 only one of the electrodes 25 and 26. In this case an adapter circuit single input impedance is appropriate.
  • Microphonic sensitivity where v is the no-load voltage delivered and p the acoustic pressure can be deduced from the expression where c is the inter-electrode capacity given by and Q ' F the collected charge calculated by integrating expression (d) of the charge Q F between the integration limits O and R' / R.
  • this voltage sensitivity can be evaluated in the case of a polarized polyvinylidene fluoride plate.
  • the inerelectrode capacity is the same for the central electrode 25 and for the annular electrode 26, the same sensitivity is obtained in both cases. It goes without saying that the electrode 27 does not need to extend beyond the zone opposite that of the electrodes 25 and 26 which serves to collect the induced charge.
  • the sensitivity of the microphone capsule can be doubled by using the electrodes 25 and 26 as output terminals.
  • the electrode 27 covers the entire plate 1 and it must be shielded effectively against external electrostatic influences, because it is floating.
  • the electrical assembly of FIG. 9 illustrates this mode of connection in connection with a differential amplifier comprising two unipolar transistors with insulated gate T 1 and T 2 .
  • the sources of the transistors T 1 and T 2 are connected to the negative pole 30 of a symmetrical power supply having as pole the pole 29.
  • the drain of the transistor T is connected directly to the positive pole 28 of the power supply while the drain of the transistor T 2 is connected to it via a load resistor R I at the terminals of which the amplified voltage appears.
  • the electrodes 25 and 26 are respectively connected to the gates of the transistors T 2 and T 1 . Thanks to the differential mounting, you can drawback connect the electrode 27 to the common pole 29 by the connection 31. Of course, other amplifier circuits and / or impedance adapters can be envisaged, for example those which use bipolar transistors.
  • the limitation of the response on the side of the low frequencies is obtained by a high-value resistor put in parallel on the active capacitors 25, 27 or 26, 27. This resistor can be integrated into the plate 1 or better achieved by making the conductor dielectric constituting the plate 1.
  • the vibrating plate is uniformly polarized from the center to the point of attachment with the housing.
  • the charge induced by a determined stress depends on the magnitude and as a sign of the excess charge or of the dipole polarization permanently created in the dielectric forming the vibrating plate. We can therefore play on this factor to increase the microphonic sensitivity of a flat mounting plate such as that shown in FIG. 5.
  • FIG. 10 is a meridian section of a microphone capsule using a plate 1 with inhomogeneous polarization.
  • This plate 1 is coated on its two faces with electrodes 7 and 8 going from the center to the plane embedding of the case 34.
  • the dipolar polarization P created in the crown of radius greater than R ' is equal and in the opposite direction to the polarization P 'created in the central disc of radius less than or equal to R'.
  • the voltage delivered v is greater than that which the microphone capsule would provide if only one of the two polarizations existed, a solution which also appears in the context of the present invention, but it is not twice what the capsule of the microphone provides.
  • the short-circuit current with constant induced load is a function proportional to the acoustic frequency and that if a current amplifier is used with low input impedance and high output impedance a capacitive load at the output must be provided to straighten the response curve.
  • Figure 11 is a partial sectional view of a laminated vibrating plate comprising a layer 35 inert from the piezoelectric point of view to which adheres a layer 34 piezoelectrically active but having identical elastic properties.
  • the diagram of the bending tensions retains the triangular shape with a vertex on the middle fiber 36, but only the tensions existing in the layer 34 contribute to developing an induced load on the surface. Intrinsic piezoelectricity can therefore provide a non-zero contribution to which is added the contribution of bending piezoelectricity.
  • Figure 12 is a partial sectional view of a laminated vibrating plate comprising a piezoelectric inert layer 38 which adheres to a piezoelectrically active layer 34 having higher compliance.
  • the deflection of the layer 38 results in a fairly uniform stretching of the layer 34 which is represented by the stress diagram 39.
  • the plate of Figure 11 can be constituted for example by two layers of PVF 2 only one being electrically polarized.
  • the laminated plate of FIG. 12 can be constituted for example by a layer 34 of polarized PVF 2 glued or grafted onto a metal blade 38 of greater rigidity. In this case, the metal blade acts as an electrode.
  • electronic bombardment technology can be used which allows, with an energy of a few tens of keV, to penetrate to a depth of a few tens of microns in a polymer material.
  • a conductivity profile can also be obtained by diffusion of alkaline ions carried by a solvent.
  • the planar vibrating plate 1 is clamped in a peripheral recess formed by the flat edges of a metallic cover 44 and of a bottom of the case 45 also metallic.
  • the face of the plate 1 facing the cover 44 is completely covered with an electrode 7 grounded to the case, which occurs at the end of assembly by crimping a metal casing 43.
  • the bottom of the cover 44 is pierced with orifices 48 forming a grid permeable to sound; the inside of the cover is lined with a textile covering 47 which is also permeable to sound.
  • the cover 44 and the plate 1 define a first acoustic cavity 46.
  • a second acoustic cavity is formed by an upper recess in the bottom of the case 45 which has an inner wall pierced with an orifice 50.
  • a lower recess in the bottom of the case 45 forms a third acoustic cavity 53 with a printed circuit board 54.
  • the communication orifice 50 between the second acoustic cavity and the third acoustic cavity is closed by a damping textile pad 49.
  • the underside of the plate 1 carries an annular electrode 8 electrically connected to an amplifier circuit 51 carried by the center of the plate 1.
  • Supply circuits 55 carried by the printed circuit 54 are connected by dotted connections to the circuit 51.
  • Output terminals 56 carried by the printed circuit 54 are also connected to the impedance adapter circuit 51.
  • a leakage resistance 52 is produced between the electrode 7 and the electrode 8 by plugging in with a conductive paste, a hole made through the plate 1 This resistance serves to limit the electroacoustic response towards the low frequencies.
  • the damping means 47 and 49 contribute to damping the resonance frequency of the plate 1.
  • FIG. 14 shows that the use of a flat plate is relatively easy to implement and that it makes it possible to achieve a high degree of integration of the electronic components while retaining simple shapes for the parts. mounting.
  • the stability over time of the electroacoustic characteristics is remarkable and the compactness of the microphone capsule does not in any way affect its electroacoustic performance.
  • the device of FIG. 14 more particularly illustrates a pressure microphone receiving the acoustic pressure on one of the faces of the plate.
  • the invention also applies to microphones with a pressure gradient which prove to be particularly effective in noisy atmospheres in favoring close sound sources.
  • the plates can be produced not only from polyvinylidene fluoride, but also from one of its copolymers.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Multimedia (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
EP82401394A 1981-08-11 1982-07-27 Elektroakustischer Wandler mit Kondensator mit inhärent polarisiertem Dielektrikum Withdrawn EP0072289A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8115507A FR2511571A1 (fr) 1981-08-11 1981-08-11 Transducteur electroacoustique a condensateur a dielectrique solide polarise
FR8115507 1981-08-11

Publications (2)

Publication Number Publication Date
EP0072289A2 true EP0072289A2 (de) 1983-02-16
EP0072289A3 EP0072289A3 (de) 1983-04-06

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EP82401394A Withdrawn EP0072289A3 (de) 1981-08-11 1982-07-27 Elektroakustischer Wandler mit Kondensator mit inhärent polarisiertem Dielektrikum

Country Status (5)

Country Link
EP (1) EP0072289A3 (de)
JP (1) JPS5841000A (de)
KR (1) KR840001425A (de)
FR (1) FR2511571A1 (de)
GB (1) GB2111799A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4607145A (en) * 1983-03-07 1986-08-19 Thomson-Csf Electroacoustic transducer with a piezoelectric diaphragm
DE3825973A1 (de) * 1988-07-29 1990-02-01 Siemens Ag Elektroakustischer einheitswandler

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3425176A1 (de) * 1984-07-09 1986-02-20 Fernsprech Und Signalbau Kg Sc Piezoelektrische fernsprechkapsel
DE3425175A1 (de) * 1984-07-09 1986-03-27 Fernsprech- und Signalbau KG Schüler & Vershoven, 4300 Essen Piezoelektrischer, akustischer wandler
DE10297066B4 (de) 2002-04-11 2006-08-31 Rion Co., Ltd. Elektroakustischer Wandler
DE102010021157A1 (de) * 2010-05-21 2011-11-24 Daniela Manger 3D-Stereospaltmikrofon
KR101781551B1 (ko) * 2011-07-20 2017-09-27 삼성전자주식회사 전기에너지 발생 소자 및 그 구동방법

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1131741B (de) * 1961-02-03 1962-06-20 Siemens Ag Elektrostriktive Membran fuer einen elektroakustischen Wandler
FR1334235A (fr) * 1961-09-29 1963-08-02 Siemens Ag Transformateur électro-acoustique
DE2714709A1 (de) * 1976-04-02 1977-10-06 Matsushita Electric Ind Co Ltd Elektroakustischer wandler mit einer hochpolymeren piezoelektrischen membran
US4064375A (en) * 1975-08-11 1977-12-20 The Rank Organisation Limited Vacuum stressed polymer film piezoelectric transducer
US4170742A (en) * 1974-07-15 1979-10-09 Pioneer Electronic Corporation Piezoelectric transducer with multiple electrode areas

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1131741B (de) * 1961-02-03 1962-06-20 Siemens Ag Elektrostriktive Membran fuer einen elektroakustischen Wandler
FR1334235A (fr) * 1961-09-29 1963-08-02 Siemens Ag Transformateur électro-acoustique
US4170742A (en) * 1974-07-15 1979-10-09 Pioneer Electronic Corporation Piezoelectric transducer with multiple electrode areas
US4064375A (en) * 1975-08-11 1977-12-20 The Rank Organisation Limited Vacuum stressed polymer film piezoelectric transducer
DE2714709A1 (de) * 1976-04-02 1977-10-06 Matsushita Electric Ind Co Ltd Elektroakustischer wandler mit einer hochpolymeren piezoelektrischen membran

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
ELECTRONICS LETTERS, vol. 11, no. 22, 30 octobre 1975, pages 532,533, Londres (GB); J.F. SEAR et al.: "Noise cancelling microphone using a piezoelectric plastics transducing element *
JAPANESE JOURNAL OF APPLIED PHYSICS, vol. 15, no. 11, 1976, pages 2239-2240, Tokyo (JP); L. BREGER et al.: "Banding piezoelectricity in polyvinilidene fluoride" *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4607145A (en) * 1983-03-07 1986-08-19 Thomson-Csf Electroacoustic transducer with a piezoelectric diaphragm
DE3825973A1 (de) * 1988-07-29 1990-02-01 Siemens Ag Elektroakustischer einheitswandler

Also Published As

Publication number Publication date
GB2111799A (en) 1983-07-06
FR2511571B1 (de) 1983-12-02
FR2511571A1 (fr) 1983-02-18
EP0072289A3 (de) 1983-04-06
JPS5841000A (ja) 1983-03-10
KR840001425A (ko) 1984-04-30

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