US3588381A - Transducer having spaced apart oppositely flexing piezoelectric members - Google Patents

Transducer having spaced apart oppositely flexing piezoelectric members Download PDF

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US3588381A
US3588381A US667035A US3588381DA US3588381A US 3588381 A US3588381 A US 3588381A US 667035 A US667035 A US 667035A US 3588381D A US3588381D A US 3588381DA US 3588381 A US3588381 A US 3588381A
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bimorph
bimorphs
diaphragm
flex
transducer
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Hugo W Schafft
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Motorola Solutions Inc
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Motorola Inc
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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

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  • a piezoelectric converter does not suffer the disadvantages inherent in an electromagnetic type converter such as large size, susceptibility to breakdown between windings and poor reliability.
  • Another object is to provide a piezoelectric converter to transfer energy between an electrical circuit and a diaphragm with the converter having a relatively small size.
  • the transducer comprises one or more bimorphs each having an edge portion and a central portion.
  • One of said portions is mechanically connected to the axially movable portion of a diaphragm and the other of such portions is coupled through a spacer to a reference support to preclude axial movement of such other portion with respect to the support and to permit axial movement of said one portion.
  • the transducer includes a diaphragm with an axis and an axially movable portion.
  • the transducer also includes a piezoelectric device which has first and second spaced apart bimorphs of selected polarization each of which extends transversely to the axis of the diaphragm.
  • a spacer hingedly joined to the edge portions of the bimorphs maintains the distance between such portions substantially fixed but permits independent axial movements along the individual extents of the bimorphs.
  • the bimorphs are electrically interconnected relative to their respective polarizations such that they will flex in opposite directions when stimulated.
  • the central portion of one bimorph is mechanically connected to the axially movable portion of the diaphragm for coupling mechanical stimuli therebetween and the central portion of the other bimorph is rigidly attached to a support. This will improve the response of the transducer at lower frequencies first, because the effective area is increased, and second, because its excursion over the entire frequency range to which the transducer is responsive also increases.
  • FIG. 5 is a diagrammatic and enlarged side view of a plurality of bimorphs according. to another embodiment of the invention.
  • FIG. 6 illustrates the flexure patterns of the bimorphs of FIG. 5
  • FIG. 7 illustrates a further embodiment
  • FIG. 7A illustrates the flexure patterns of the bimorphs of FIG. 7
  • FIG. 8 illustrates a mode of driving a diaphragm with a bimorph
  • FIG. 9 illustrates the flexure patterns of the bimorph of FIG.
  • FIG. 10 illustrates an alternate embodiment of the invention.
  • FIG. 11 illustrates how the embodiment of FIG. 10 may be used in a speaker.
  • FIGS. I and 2 there is shown a transducer or more specifically a speaker mounted in a housing 10 which includes a conical portion 12 and an annular slab 14 joined to the portion I2 by a pair of fasteners 16 and 18.
  • the transducer includes a compliant diaphragm 20 having an apex 22 which is movable along the axis of the diaphragm 20 when mechanically stimulated.
  • the diaphragm due to its inherent characteristics, has a number of resonances within a frequency range primarily determined by its size, with the lower the frequency range to be reproduced by the speaker, the larger the diaphragm must be. This "number of resonances causes the diaphragm to have a relatively flat response within a range of frequencies rather than the normal peaked response of a resonant circuit.
  • a piezoelectric driver 24 for converting electrical energy into mechanical energy to axially move apex 22 is shown in detail in FIG. 3 and includes bimorphs 26 and 26.
  • Bimorph 26 includes two piezoelectric wafers 28 and 30 which preferably are annular in shape to provide maximum electromechanical conversion. The wafers are joined together by epoxy or the like with an intermediate electrode 32 interposed between their innerfaces. Bimorph 26 also has a pair of outer electrodes 34 and 36 which may be plated onto the respective outer surfaces. Bimorph 26 has corresponding parts indicated by similar reference numerals which are primed. Outer electrodes 34 and 36 of bimorph 26 and outer electrodes 34 and 36' of bimorph 26' are connected together and to an input terminal 38. Intermediate electrodes 32 and 32 are connected to a second input terminal 40. An electrical signal within the audio frequency range is supplied by a source 46 (FIG. 2) to the input terminals 38 and 40.
  • a source 46 FIG. 2
  • the wafers 28 and 30 are each permanently electrically polarized in directions indicated by the arrows 48 and 50 respectively.
  • the electric fields in the respective wafers will be in the directions indicated by the arrows 52 and 54. Since the electric field and the polarization in wafer 28 are in the same direction, wafer 28 contracts radially inward as indicated by arrows 56. Since the polarization and the electric field in wafer 30 are in opposite directions, it will expand radially outward as indicated by the arrows 58.
  • Bimorph 26 is constructed to be relatively thin so that it will flex along its axial dimension and with the above described polarization and electric fields the bimorph 26 tends to flex at its center axis axially downward as indicated by arrow 60.
  • bimorph 26 Using the same analysis on bimorph 26' and assuming the polarization to be in the direction shown by arrows 48 and 50, it will flex in an opposing direction as indicated by arrow 62 when terminal 38 is positive with respect to terminal 40. Reversing the polarity between the terminals 38 and 40 causes a reversal in the directions of the electric fields in bimorph 26 so that wafer 28 expands radially outward and wafer 30 contracts radially inward to flex the bimorph 26 at its center in a direction indicated by arrow 64. By using similar analysis, the bimorph 26 will flex in an opposing direction indicated by arrow 65.
  • impressioning an alternating electrical signal across the input terminals 38 and 40 causes the bimorphs 26 and 26' to oscillate between simultaneous outward flexure by both bimorphs and simultaneous inward flexure thereof.
  • a variety of interconnections of the electrodes to the input terminals with respect to the polarizations of the wafers may be used of which the one shown is merely illustrative.
  • a hinge or spacer 66 schematically shown in cross section may be annular to conform to the shape of the bimorphs.
  • the spacer has annular grooved portions (schematic representation) 69 and 69' hingedly joined respectively to the circumferential edges of the bimorphs 26 and 26', and ideally maintains a fixed distance between them so that when the bimorphs flex, there is no relative motion between such edges.
  • annular grooved portions (schematic representation) 69 and 69' hingedly joined respectively to the circumferential edges of the bimorphs 26 and 26', and ideally maintains a fixed distance between them so that when the bimorphs flex, there is no relative motion between such edges.
  • such a construction permits the midpoint of the circumferential edge to be substantially stationary with the sides of such edge pivoting about the midpoint. The losses in such an arrangement would be considerably less than if the edges were rigidly clamped.
  • FIG. 3A shows a spacer composed of aluminum and having a ladder shape with a multiplicity of cross bars 67 maintaining the distance between grooved portions 69 and 69' relatively fixed.
  • the bimorphs 26 and 26 are respectively attached to these portions.
  • bimorph 26 has a rest position axis 68 and bimorph 26 has a rest position axis 68 with the circumferential edges being separated by the spacer 66 by a distance 70.
  • the flexure patterns thereof are respectively indicated by dashed lines 72 and 72 with the centers moving distances 74 and 74'.
  • the patterns are indicated by dotted lines 76 and 76' with the centers moving distances 78 and 78. Since the bimorphs are annular in shape, the motions indicated are only a representation of the actual "oil canning" or dishing" ofthe bimorphs.
  • the central portion of the upper surface of the bimorph 26 is rigidly attached to a protrusion 79 on the annular slab 14 by epoxy or the like so that when the bimorph 26 tends to flex as indicated by the dashed line 72, the circumferential edge of bimorph 26 will move downwardly from rest position axis 68 a distance 82 (as shown by the flexure pattern 80 of FIG. 48) equal to the distance 74 that the center portion of such bimorph would move if free.
  • the rest position axis of the bimorph 26 is shifted downwardly by a distance 84 equal to distance 82 to move the entire flexure pattern downwardly so that the total excursion of the central portion of the lower surface from rest position axis 68' will be a distance 86 double that of distance 74' (FIG. 4A). Since the apex 22 of the diaphragm is connected to the central portion of bimorph 26' by epoxy for example, the diaphragm generates a sound wave having a magnitude proportional to distance 86.
  • the volume of the sound emanated by diaphragm 20, as previously stated, is directly proportional to such excursion so that if a 400 hertz (resonant frequency) bimorph is used, the volume of sound, in response to a 400 hertz signal, will be substantially greater than the response to a hertz signal.
  • the area of the bimorph may be increased according to the inverse proportional relationship between the resonant frequency and area (diameter squared) of a piezoelectric bimorph driver.
  • a 2 inch diameter disc has a resonant frequency of 400 hertz and thus has an excursion of a given magnitude when an electrical signal at 400 hertz is applied, doubling its diameter to 4 inches (multiplying area by four) reduces the resonant frequency of the bimorph to I00 hertz.
  • a 4 inch driver in addition to being too large to be usable in a conventional size speaker housing, would be flimsy to therefore introduce losses into the converter.
  • This problem is solved by the use of two smaller diameter bimorphs 26 and 26' connected to the spacer 66 to have the effect of doubling the area and thus halving the resonant frequency.
  • the resonant frequency of the combination is 200 hertz.
  • there would be a negligible response of a 400 hertz bimorph to a 200 hertz signal the response of a 200 hertz pair of bimorphs to such signal is substantial.
  • the excursion is doubled over the entire frequency range to which the driver 24 is response (above its resonant frequency) that is, 200 hertz and up.
  • the area of each bimorph is doubled so that each has a diameter of 2.8 inches (2wt 2inches) which is substantially less than the 4 inches required of a single bimorph.
  • the spacer 66 used to connect the bimorphs 26 and 26 will not provide zero relative motion between the circumferential edges of the bimorphs, and yet provide complete freedom for rectilinear motion at the center portions so that some loss may be introduced, although practical constructions have minimized losses quite satisfactorily.
  • the bimorphs had a diameter of 1.7 inches and a thickness of 0.019 inches, and when mounted to a diaphragm, the assembly had a lower cutoff frequency or resonant frequency of 200 hertz.
  • a further embodiment of the invention shown in FIG. 5 includes a pair of piezoelectric drivers 98 and 100 each ofwhich in driver 100 have their circumferential edges hingedly joined to a further spacer 112.
  • the center portion of the upper surface of bimorph 102 is rigidly attached to the protrusion 79 of the slab 14.
  • the center portion of the lower surface of bimorph 110 is attached to the apex 22 of the diaphragm 20.
  • the center portions on the opposite outer surfaces of the bimorphs 104 and 108 are attached by a spacer 113 to maintain the distance between such portions fixed.
  • Each bimorph has a pair of outer electrodes plated onto the respective outer surfaces all of which are connected together and to one of the input terminals 38.
  • the intermediate electrodes of the four bimorphs are also joined together and to the other of the input terminals 40 with the bimorphs being polarized in the directions indicated by the arrows.
  • An electrical signal applied between input terminals 38 and 40 will cause the bimorphs in driver 98 to flex in opposite directions and similarly will cause the bimorphs in driver 100 to flex in opposite directions and further the bimorphs 102 and 108 will flex in the same direction as will the bimorphs 104 and 110.
  • the circumferential edge of bimorph 102 will move downwardly from its rest position axis 114 a distance 116 as shown by the the flexure pattern 118 of FIG. 6A. Since the spacer 106 maintains the distance 120 between the circumferential edges fixed, the rest position axis 122 of the bimorph 104 is shifted downwardly by a distance equal to distance 116 to move the entire flexure pattern 123 downwardly. Since the distance between the bimorphs 104 and 108 is fixed by the spacers 113, the flexing of the bimorph 104 in effect displaces the rest position axis 124 of the bimorph 108 which itself bends according to the flexure pattern 126.
  • the flexure pattern 130 of bimorph 110 moves downwardly so that the center portion of the lower surface of bimorph 110 moves a distance 130 from its rest position axis 131.
  • the dashed line 132 represents the flexure pattern of a single bimorph with its excursion at its center being a distance 134 which is about one-quarter that of distance 130.
  • Additional bimorphs could be connected to increase the excursion of the bimorph 110 in response to a given amplitude signal by attaching the center portion of the first bimorph to a given amplitude signal by attaching the center portion of the first bimorph to the housing 10, attaching the center portion of the last of the bimorphs to the diaphragm and attaching spacers between succeeding ones of the intermediate bimorphs.
  • the method of interconnecting the electrodes and the directions of polarization of the respective papers in each bimorph is merely exemplary and other methods could be utilized with the criteria being that the bimorphs in each driver simultaneously flex in opposite directions while corresponding bimorphs in all the drivers flex simultaneously in the same direction.
  • a further embodiment of the invention shown in FIG. 7 includes a pair of piezoelectric drivers 138 and 140 each of which is similar in construction to that shown in FIG. 3.
  • the edges of the bimorph 138 are hingedly connected to the housing (schematically indicated as a support) and the edge of the bimorph 140 is hingedly connected to an axially movable portion of the diaphragm 20.
  • the central portions of the respective bimorphs are connected together by a spacer 142 to maintain the distance between such portions fixed. Again the electrical interconnections between the bimorphs 138 and 140 with respect to their polarization are such as to cause them to flex in opposite directions.
  • bimorphs could be connected in series in which case the edge of a third bimorph would be hingedly connected to the edge of bimorph 140 and a spacer would be connected between the center of the third bimorph and the center of the fourth bimorph with the edge of the fourth bimorph being hingedly connected to the axially movable portion of the diaphragm 20.
  • FIG. 8 there is shown a single annular bimorph wafer 150 similar in construction to the bimorph 26 of FIGS. 1 and 3. It is mounted at its center to the apex 22 of diaphragm 20. Such a construction is shown and described in US Pat. application Ser. No. 557,120 assigned to the assignee of the present invention.
  • the bimorph wafer 150 has a pair of outer electrodes plated on to the respective outer surfaces which are connected to one of the input terminals 38.
  • the intermediate electrode is connected to the input terminal 40. With no additional mechanical connections to the wafer 150, an electrical signal applied to such input terminals will cause the wafer to flex as indicated in the edge view of the wafer shown in FIG. 9.
  • the dotted line 152 represents the flexure pattern resulting from one polarity electrical signal and the dashed line 154 represents the pattern resulting from an opposite polarity electrical signal.
  • the axis 156 represents zero motion of the wafer. It is to be understood that at any instant of time, the mass above the axis 156 equals the mass below the axis. In other words, the mass inwardly of a null circle represented by the points 158 and 160 equals the mass outwardly of such circle. As is known, the lower the frequency of sound a speaker is to reproduce, the larger in size (and thus mass) the diaphragm must be.
  • Ring 162 serves to decrease the resonant frequency of wafer 150, permits a heavier diaphragm 20, but increases mechanical losses.
  • the clips 164 form a hinge somewhat similar to the hinge 69 of FIG. 3A.
  • the notches 166 in each of the clips 150 correspond generally to the grooved portion 69' of the hinge 66, that is, the bimorph wafer 150 is retained in position by these notches.
  • the elongated portion 168 of the clips 164 correspond to the cross bars 67 of the hinge 66.
  • the top of the elongated portions 168 are connected to a mass in the form of ring 162.
  • Such a construction is particularly useful in the speaker of FIG. 11 where components corresponding to those of FIG. 1 are given the same reference numeral.
  • the tops of the elongated portions 168 are attached to the annular slab 14 which is the top of the housing 10 to provide the mass represented by the ring 162 of FIG. 10.
  • the circumferential edge of the wafer 150 is hingedly joined to the notches 166 in the clips 164.
  • the center portion of wafer 150 is attached to the apex 22 of the diaphragm 20.
  • a transducer including in combination; support means, a diaphragm having an axis and an axially movable portion, piezoelectric means'including first and second spaced apart bimorphs of selected polarization each extending transversely to the axis of the diaphragm and each having an edge portion and a central portion, said piezoelectric means further including spacer means connecting one of said portions of said first bimorph to the corresponding portion of said second bimorph, means electrically interconnecting said bimorphs relative to their respective polarizations such that said bimorphs tend to flex in opposite directions, first means mechanically coupling the other portion of said first bimorph to the axially movable portion of said diaphragm for coupling mechanical stimuli therebetween, and second means rigidly attaching said support means to the portion of said second bimorph corresponding to the portion of said first bimorph which is coupled to said diaphragm.
  • said first means includes further piezoelectric means, said further piezoelectric means having third and fourth spaced apart bimorphs of selected polarization each extending transversely to the axis of the diaphragm and each having an edge portion and a central portion, said further piezoelectric means having spacer means hingedly connected to the edge portions of said third and fourth bimorphs, means electrically interconnecting said first, second, third and fourth bimorphs relative to their respective polarizations such that: said first and second bimorphs simultaneously tend to flex in opposite directions with respect to each other, said third and fourth bimorphs simultaneously tend to flex in opposite directions with respect to each other, said first and third bimorphs simultaneously tend to flex in the same direction, and said second and fourth bimorphs simultaneously tend to flex in the same direction, third means connecting the central portion of said third bimorph to the axially movable portion of said diaphragm, and fourth means connecting the central portion of said fourth bimorph to the central portion ofsaid
  • a loudspeaker including in combination; a support means, a diaphragm having an axis and an axially movable portion capable of receiving mechanical stimuli thereat and converting the same into sound waves, piezoelectric means having a pair of input terminals for receiving an electrical signal and converting the same into mechanical stimuli, said piezoelectric means including first 'and second spaced apart bimorphs of selected polarization and each extending transversely to the axis of the diaphragm, and each having an edge portion and a central portion, said piezoelectric means further including spacer means hingedly connected to the edge portions of said bimorphs and having a construction to maintain the distance between said edges substantially fixed and yet permit independent axial movements along the individual extents of said bimorphs, means electrically interconnecting said bimorphs to said input terminals relative to their respective polarizations such that when the electrical signal is applied to said terminals said bimorphs tend to flex in opposite directions, first means mechanically coupling the central portion of said first bimorph to the
  • said first means includes further piezoelectric means, said further piezoelectric means having third and fourth spaced apart bimorphs of selected polarization each extending transversely to the axis of the diaphragm and each having an edge portion and a central portion, said further piezoelectric means having spacer means hingedly connected to the edge portions of said third and fourth bimorphs and having a construction to maintain a substantially fixed distance between such edge portions and yet permit independent axial movements along the individual extents of said third and fourth bimorphs, means electrically interconnecting said first, second, third and fourth bimorphs relative to the respective polarizations such that: said first and second bimorphs simultaneously tend to flex in opposite directions, said third and fourth bimorphs simultaneously tend to flex in opposite directions, said first and third bimorphs simultaneously tend to flex in the same direction, and such that said second and fourth bimorphs simultaneously tend to flex in the same direction, third means connecting the central portion of said third bimorph to the axially mov
  • a transducer including in combination; support means, a diaphragm having an axis and an axially movable portion, a plurality of piezoelectric means and a corresponding plurality of spacer means individually associated with said piezoelectric means, each of said piezoelectric means including first and second spaced apart bimorphs of selected polarization, each of said bimorphs extending transversely to the axis and having an edge portion and a central portion, each spacer means hingedly connected to the edge portions of associated first and second bimorphs, means electrically interconnecting all of said bimorphs relative to said polarizations such that said first and second bimorphs in each of said piezoelectric means simultaneously tend to flex in opposite directions, and such that all of said first bimorphs simultaneously tend to flex in the same direction, and such that all of said second bimorphs simultaneously tend to flex in the same direction, means connecting the central portion of said first bimorph of the first of said piezoelectric means to the axially movable portion of said di
  • a transducer including in combination, support means, a diaphragm having a portion which is movable along an axis, first and second piezoelectric members of selected polarization which extend transversely to said axis and each member having an edge portion and a central portion, spacer means connecting one of said portions of said first member to the corresponding portion of said second member, means electrically interconnecting said first and second members such that they flex in opposite directions in response to an electrical potential of a given polarity, first means mechanically coupling the other portion of said first member to the movable portion of said diaphragm for intercoupling mechanical stimuli therebetween, and second means mechanically coupling said support member to the portion of said second member corresponding to the portion of said first member which is coupled to said diaphragm.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Piezo-Electric Transducers For Audible Bands (AREA)
US667035A 1967-08-28 1967-08-28 Transducer having spaced apart oppositely flexing piezoelectric members Expired - Lifetime US3588381A (en)

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3786202A (en) * 1972-04-10 1974-01-15 Motorola Inc Acoustic transducer including piezoelectric driving element
US4386241A (en) * 1979-08-16 1983-05-31 Seikosha Co., Ltd. Piezoelectric loudspeaker
US4461930A (en) * 1982-09-23 1984-07-24 Pioneer Speaker Components, Inc. Acoustic transducer with honeycomb diaphragm
WO1988003739A1 (en) * 1986-11-07 1988-05-19 Plessey Australia Pty. Limited A composite sonar transducer for operation as a low frequency underwater acoustic source
AU594852B2 (en) * 1986-11-07 1990-03-15 Gec Marconi Systems Pty Limited A composite sonar transducer for operation as a low frequency underwater acoustic source
US4996713A (en) * 1989-09-25 1991-02-26 S. Eletro-Acustica S.A. Electroacoustic piezoelectric transducer having a broad operating range
US20170295423A1 (en) * 2014-12-02 2017-10-12 Sony Corporation Speaker apparatus
RU2649041C2 (ru) * 2016-09-21 2018-03-29 Владимир Борисович Комиссаренко Электроакустический пьезокерамический преобразователь
US20200389739A1 (en) * 2019-06-04 2020-12-10 uBeam Inc. Piezoelectric transducer

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3009048C2 (de) * 1980-03-08 1983-04-21 Kuttruff, Heinrich, Prof. Dr., 5100 Aachen Piezoelektrischer Mehrschichtwandler für Ultraschall
JPS60134700A (ja) * 1983-12-23 1985-07-17 Nippon Denso Co Ltd 発音装置

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3786202A (en) * 1972-04-10 1974-01-15 Motorola Inc Acoustic transducer including piezoelectric driving element
US4386241A (en) * 1979-08-16 1983-05-31 Seikosha Co., Ltd. Piezoelectric loudspeaker
US4461930A (en) * 1982-09-23 1984-07-24 Pioneer Speaker Components, Inc. Acoustic transducer with honeycomb diaphragm
WO1988003739A1 (en) * 1986-11-07 1988-05-19 Plessey Australia Pty. Limited A composite sonar transducer for operation as a low frequency underwater acoustic source
US4878207A (en) * 1986-11-07 1989-10-31 Plessey Australia Pty. Ltd. Composite sonar transducer for operation as a low frequency underwater acoustic source
AU594852B2 (en) * 1986-11-07 1990-03-15 Gec Marconi Systems Pty Limited A composite sonar transducer for operation as a low frequency underwater acoustic source
US4996713A (en) * 1989-09-25 1991-02-26 S. Eletro-Acustica S.A. Electroacoustic piezoelectric transducer having a broad operating range
US20170295423A1 (en) * 2014-12-02 2017-10-12 Sony Corporation Speaker apparatus
US10154336B2 (en) * 2014-12-02 2018-12-11 Sony Corporation Speaker apparatus
RU2649041C2 (ru) * 2016-09-21 2018-03-29 Владимир Борисович Комиссаренко Электроакустический пьезокерамический преобразователь
US20200389739A1 (en) * 2019-06-04 2020-12-10 uBeam Inc. Piezoelectric transducer
US11190881B2 (en) * 2019-06-04 2021-11-30 uBeam Inc. Piezoelectric transducer
US20220086568A1 (en) * 2019-06-04 2022-03-17 uBeam Inc. Piezoelectric transducer

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DE6609583U (de) 1972-07-13
DE1762509A1 (de) 1970-10-29
FR1578513A (enrdf_load_stackoverflow) 1969-08-14

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