Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3786202 A
Publication typeGrant
Publication dateJan 15, 1974
Filing dateApr 10, 1972
Priority dateApr 10, 1972
Also published asCA991304A1, DE2318027A1, DE2318027B2, DE2318027C3, DE7313564U
Publication numberUS 3786202 A, US 3786202A, US-A-3786202, US3786202 A, US3786202A
InventorsSchafft H
Original AssigneeMotorola Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Acoustic transducer including piezoelectric driving element
US 3786202 A
Abstract
A disk shaped piezoelectric element constructed to operate in a planar mode so as to define a first overtone nodal ring on one of the major surfaces, a conically shaped diaphragm having a truncated apex defining a generally circular area affixed to a major surface of the element concentric with the nodal ring and spaced radially therefrom so as to reduce the amplitude of the output of the first overtone to approximately the amplitude of the output of the fundamental frequency, and a rubber disk affixed to the opposite major surface of the piezoelectric element to lower the fundamental resonance frequency and damp the peak output of the fundamental and first overtone resonance frequencies to provide a flat response over a desired bandwidth.
Images(1)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United stais' chafft 1 ACOUSTIC TRANSDUCER INCLUDING PIEZOELECTRIC DRIVING ELEMENT [75] Inventor: Hugo W. Schafft, Des Plaines, I11.

[73] Assignee: Motorola, Inc., Franklin Park, 111.

[22] Filed: Apr. 10, 1972 [21] Appl. No.: 242,501

151 Jan. 15, 1974 Primary Examiner-William C. Cooper Assistant Examiner-Douglas W. Olms romqx: Eug r eni [5 7 ABSTRACT A disk shaped piezoelectric element constructed to operate in a planar mode so as to define a first overtone nodal ring on one of the major surfaces, a conically shaped diaphragm having a truncated apex defining a generally circular area affixed to a major surface of the element concentric with the nodal ring and spaced radially therefrom so as to reduce the amplitude of the output of the first overtone to approximately the amplitude of the output of the fundamental frequency, and a rubber disk affixed to the opposite major surface of the piezoelectric element to lower the fundamental resonance frequency and damp the peak output of the fundamental and first overtone resonance frequencies to provide a flat response over a desired bandwidth.

15 Claims, 5 Drawing Figures [52] US. Cl. 179/110 A, 181/32 R, 310/83 [51] Int. Cl H04r 17/00 [58] Field of Search 179/110 A; 181/32 R, 181/32 A; SIG/8.6, 8.3

[56] References Cited UNITED STATES PATENTS 2,518,331 8/1950 Kalin 179/110 A 3,588,381 6/1971 Schafft 1 SIG/8.6 3,548,116 12/1970 .Schafft 179/110 A 3,654,402 4/1972 Roos 179/110 A 3,698,993 10/1972 Rauh 181/32 R UR Im 179/11011 ACOUSTIC TRANSDUCER INCLUDING PIEZOELECTRIC DRIVING ELEMENT BACKGROUND OF THE INVENTION 1. Field of the Invention Acoustic transducers are utilized to convert electrical energy to sound or acoustic energy to electrical energy. In the present embodiment a piezolectric element is utilized for a driver, which piezoelectric element bends or warps in a particular mode in response to electrical energy being applied thereacross or produces electrical energy thereacross in response to bending or warping thereof. While the present invention might be utilized in acoustic transducers for converting mechanical energy to electrical energy, it is especially useful in acoustic transducers, such as speakers and the like, converting electrical energy to acoustic energy or sound. In the speaker art, it is highly desirable to provide a transducer with a flat response over a desired bandwidth, i.e., all frequencies of sound between two desired frequencies are produced at approximately equal amplitudes. Because piezoelectric elements are mechanical vibrating devices, they have specific resonant frequency points, referred to as the fundamental, first overtone, second overtone, etc., at which points the amplitude of the output is substantially increased.

2. Description of the Prior Art In prior art acoustic transducers, any flattening of the frequency response is accomplished through design of SUMMARY OF THE INVENTION The present invention pertains to apparatus providing conversion between electrical and mechanical stimuli including a piezoelectric element constructed to operate in a planar mode and having first overtone nodal lines present on a major surface, a generally conically shaped diaphragm with truncated apex defining a circular area affixed to the major surface of the element approximately centrally within the first overtone nodal line so as to be spaced from the line sufficiently to reduce the amplitude of the output of the first overtone to approximately the amplitude of the output of the fundamental, and a resilient damping member affixed to an opposed major surface of the piezoelectric element to lower the fundamental frequency of the element and damp the fundamental and first overtone peaks.

It is an object of the present invention to provide an improved piezoelectric driven acoustic transducer.

It is a further object of the present invention to provide a piezoelectric transducer having a substantially flat response over a desired bandwidth These and other objects of this invention will become apparent to those skilled in the art upon consideration of the accompanying specification, claims and drawmgs.

7 output peak in the response at approximately 1 KC,

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings, wherein like characters indicate like parts throughout the figures:

FIG. 1 is an axial sectional view of an acoustic transducer constructed in accordance with the present invention;

FIG. 2 is a view (a) in top plan of a piezoelectric driver illustrating nodal rings, (b) in side elevation of the driver illustrating the fundamental nodal ring, (0) in side elevation of the driver illustrating first overtone nodal rings, and (d) the truncated apex of a diaphragm;

FIG. 3 is a graph illustrating generally the frequency response of a transducer similar to that illustrated in FIG. 1 constructed in accordance with prior art techniques and, in dotted lines, the frequency response of a transducer similar to that illustrated in FIG. 1 constructed in accordance with the present invention;

FIG. 4 is an enlarged sectional view of a piezoelectric driving element and a resilient damping member affixed thereto, portions thereof removed; and

FIG. 5 is a greatly enlarged fragmentary view of the resilient damping member.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the figures the numeral 10 generally designates a piezoelectric transducer utilized for providing conversions between electrical and mechanical stimuli. Applications for transducers of this type are speakers, sound sensors, etc. The transducer 10 includes a housing 11 defining a generally cup shaped cavity l2, a generally conically shaped diaphragm l3 affixed within the cavity 12 by its outermost edges and having a truncated apex to which is attached a piezoelectric driver 15 with a piezoelectric element 16 and damping member 17. The operation of piezoelectric transducers wherein a piezoelectric driver is connected directly to a diaphragm and solely supported thereby is described in detail in my U. S. Pat. No. 3,548,116, entitled Acoustic Transducer Including Piezoelectric Wafer Solely Supported By A Diaphragm, 1970.

In the prior art structure of the above described patent the apex of the conically shaped diaphragm is fixedly attached to the center of a piezoelectric element and the frequency response of the transducer is approximated by the solid line graph in FIG. 3. The frequencies specified in FIG. 3 are exemplary and may vary somewhat with variations in transducers. A first designated 20, is produced primarily by a center supported resonance of the driver at 1 KC (a resonance caused by mounting the driver at the center with a relatively stiff diaphragm) which is coupled to the diaphragm by a slight axial movement of the diaphragm and driver, at the point of connection therebetween, which axial movement is present because the diaphragm is not rigid. A second output peak at approximately 5 KC, designated 21, is produced primarily by the fundamental resonance of the piezoelectric element 16. A third output peak at approximately l9 KC, designated 22, is produced primarily by the first overtone resonance of the piezoelectric element 16.

Referring to FIG. 2, the piezoelectric element 16 is illustrated in top plan in (a) and in side elevation in (b) and (c). The piezoelectric element 16, as illustrated in and issued Dec. 15,-

FIG. 2, is disk shaped, but it should be understood that substantially any flat shape might be utilized wherein the element operates in a planar bending mode, i.e., flexing or distorting along more than one axis. For example, the element 16 might be square or even irregularly shaped. However, in the present embodiment and to simplify the explanation, a disk shaped element 16 will be described and the operation thereof explained.

At the fundamental resonance frequency, the element 16 vibrates along each diameter thereof as illustrated in FIG. 2b. During the first half cycle of eachvibration the center of the element 16 flexes upwardly while the end portions turn downwardly as indicated by the dotted line 25 and during the second half cycle of each vibration the reverse occurs, as illustrated by the dotted line 26. It will be noted that two nodes are formed along the diameter, at which points no axial movement of the element 16 occurs. Because every diameter of the element 16 reacts, at the fundamental resonance frequency, as illustrated in FIG. 2b, the nodes define a nodal ring 27 on the upper and lower major surfaces of the element 16, which ring 27 is a locus of nodes or points having no axial movement at the fundamental resonance frequency.

In a similar fashion FIG. illustrates movement of the element 16 at the first overtone resonance frequency. Because of the first overtone being a higher frequency, two concentric nodal rings 28 and 29 are defined on the major surfaces of the element 16. The nodal ring 29 is concentric with the nodal ring 27 defined by the fundamental frequency and spaced radially inwardly therefrom. It will be noted from a comparison of FIG. 2b and c that the output, or amount of axial movement, of the element 16 at the fundamental resonance frequency is substantially constant throughout the area encircled by the nodal ring 29. Further, since the amount of movement of the element 15 determines the amount of movement of the diaphragm l3, and hence, the output or conversion between stimuli), connecting the diaphragm at a point concentric to the nodal rings 27, 28 and 29, as in the prior art, will provide the maximum output of all frequencies and result in the frequency response illustrated in full lines in FIG. 3.

In FIG. 2d a portion of the diaphragm 13 is illustrated with the apex thereof truncated to define a generally circular area having a diameter smaller than the diameter of the nodal ring 29. If the diameter of the truncated apex of diaphragm 13 is equal to the diameter of the nodal ring 29 the first overtone will be substantially eliminated, since the output or axial movement of the element 16 at the nodal ring 29 for the first overtone is zero. Thus, by forming the diaphragm 13 so that the truncated apex has a diameter greater than a point and less than the diameter of the nodal ring 29, the output of the first overtone (peak 22 in FIG. 3) can be diminished to approximately the amplitude of the fundamental (peak 21 in FIG. 3). Since the second overtone is substantially above the first overtone and beyond the desired frequency response in acoustic transducers, it is not necessary to consider overtones beyond the first.

Referring more specifically to FIG. 4, the piezoelectric driver 15 is illustrated in enlarged cross section, with a portion thereof removed. The piezoelectric element 16 includes first and second piezoelectric wafers 40 and 41 having an electrode 42 sandwiched therebetween and electrodes 43 and 44 fixedly engaged in overlying relationship on opposed major surfaces thereof. The operation of the element 16 is well known to those skilled in the art and, as previously mentioned, is described in detail in U. S. Pat. No. 3,548,l 16. It is, therefore, sufficient to state at this time that the electrodes 42, 43 and 44 drive the element 16 in a planar mode of operation. The element 16 has resilient damping member 17 affixed to the major surface thereof op posite the major surface having the diaphragm l3 affixed thereto. In the present embodiment, since the element 16 is generally disk shaped, the damping member 17 is also disk shaped, and as illustrated, has a slightly larger diameter than the element 16. The damping member 17 damps or loads the movement of the element 16 to reduce the fundamental peak 21 and to further reduce the first overtone peak 22 so that the frequency response of the driver 15 approaches the dotted line curve 50 in FIG. 3.

The damping member 17 is formed of a resilient material, such as rubber (the term rubber being understood to include natural and synthetic materials) or other elastomers. Elastomers generally have a frequency dependent shear modulus which varies directly with the frequency of stresses applied thereto, i.e., the shear modulus increases with the frequency of stresses applied thereto. At static or slowly occurring stresses the elastomeric material operates in a rubbery region in which it appears elastic to the forces operating upon it. However, as higher frequency dynamic stresses are applied the shear modulus is increased and the elastomer goes through a glassy transition region into a glassy region where it appears metallic or hard. At the lower frequencies, around the peaks 20 and 21 of FIG. 3, the damping member 45 is preferably operating in the glassy transition region and introduces hysteresis losses which substantially remove the peaks 20 and 21. However, at the upper frequencies, around the peak 22, the material of the damping member 17 may begin to approach the glassy region and the hysteresis losses are substantially reduced. Thus, the damping effect of the member 17 at the peak 22 is greatly reduced.

To compensate for the reduction in hysteresis losses small particles 46 of a relatively heavy material, such as iron or lead, are intermixed with the resilient material of the clamping member 17 during the formation of the disk. These particles 46 add additional weight to the member 17 and introduce a coulomb type damping which is caused by internal friction between the metal particles and their enclosing rubber walls. This internal friction is caused by a relative movement due to a difference in inertia of the heavy particles and the surrounding resilient material of the clamping member 17. This frictional or coulomb type damping increases with the number of particles and the size of the particles. It has been found, for example, that lead particles having approximately a I00 mesh size mixed with rubber in a 3 to 1 ratio, by weight, provide a desired amount of damping for the frequency response illustrated in FIG. 3. Small amounts of a lubricant, such as graphite, may also be added to the damping member 17, as illustrated in FIG. 5 by the numeral 47, to increase the relative movement between the heavy particles 46 and the elastomeric or rubber material and, therefore, increase the damping action.

The effect of the reduction in hysteresis losses at the higher frequencies can also be reduced or eliminated by selecting an elastomeric material with a glass transition region above the highest frequency desired for the frequency response of the transducer 10. It has been found for example that neoprene has a relatively high glass transition region and may, in many instances, provide sufficient damping at high frequencies so that the addition of particles 46 is not required. It should be understood that the type of materials utilized and the frequency response desired dictate the ultimate construction of the transducer 10.

In addition to providing the damping function described above, the damping member 17 increases the mass of the driver 15 and, therefore, improves the weight ratio of the driver 15 over the diaphragm 13. This improved weight ratio results in a tighter coupling between the driver 15 and the diaphragm 13 at the lower frequencies. Thus, in some instances, although the material selected for the damping member 17 provides sufficient damping at the higher frequencies, it may be desirable to add relatively heavy particles 46 to the member 17 to increase the mass of the driver 15.

The addition of the clamping member 17 to the driver 15 (and the diaphragm 13 to a much smaller extent) lower the fundamental resonance frequency of the driver 15. Referring to FIG. 3, it can be seen that the knee 51 of the flattened response curve 50 (illustrated in dotted lines) occurs slightly below the peak 21 for the fundamental resonance frequency. The diameter and thickness of the damping member 17 should be adjusted to lower the resonance frequency of the combined piezoelectric element 16 and damping member .17 to a point below the fundamental resonance frequency of the piezoelectric element 16 (peak 21) such that the curve 50 falls away sharply at the lower frequencies (as illustrated in FIG. 3). If the resonance fre quency of the driver 15 is too high it will add to the peak 21 and produce too high an output at the lower frequencies while not extending the frequency response sufficiently into the lower frequency range. If the resonance frequency of the driver 15 is lowered too much the curve 50 will not fall away sharply at the lower frequencies but will rise at a much lower rate. Thus, through careful selection of the diameter thickness and mass of the clamping member 17 the desired flat response of the transducer can be extended somewhat into the lower frequency range. Further, through careful selection of the type and thickness of material and the amount and particle size of particles 46 the degree of damping can be adjusted to provide a substantially flat response over a desired band of frequencies. It should be noted that the damping member 17 might be constructed with an annular configuration, in which case high frequency damping is controlled by adjusting the size of the inside diameter, since high frequency damping is most effective in the center of the driver 15.

The cavity 12 in the housing 11 has a resonant frequency which, in many instances appears in the desired frequency response of the transducer 10. At the cavity resonance there is a tendency to absorb output power from the transducer 10 and, thus, a notch (not shown) will appear in the output curve 50 of HO. 3. To prevent the power output loss and the resulting distortions, acoustic absorbing material, in the present embodiment an annularly shaped member 55 of foam rubber or the like, is placed in the cavity 12 between the housing 11 and the diaphragm 13. The member 55 alters the cavity resonance, or lowers the Q of the cavity 12, to

substantially eliminate the absorbing of power and consequent notch in the output curve 50. It should be understood that the acoustic absorbing material is only utilized when the cavity resonance falls within the desired frequency response and, in some instances, it may be possible to eliminate the material through design of the transducer components.

Thus, an improved piezoelectric transducer is disclosed having an output which is substantially flat throughout a desired band of frequencies. The transducer output has been referred to throughout the specification and it should be understood that this refers to either mechanical or electrical output in response to either electrical or mechanical input, respectively. Further, in addition to a flat response and improved coupling at the lower frequencies, the critically damped element 16 has an improved transient response over known electrodynamic drive systems for transducers. While I have shown and described a specific embodiment of this invention, further modifications and improvements will occur to those skilled in the art. I desire it to be understood, therefore, that this invention is not limited to the particular form shown and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of this invention.

I claim:

1. Apparatus providing conversions between electrical and mechanical stimuli comprising:

a. a piezoelectric element having a generally flat major surface, electrodes attached to said element for driving said element in a planar bending mode when said electrodes are properly energized, and first overtone nodal lines present on said major surface during planar bending mode operation of said element;

b. a generally conically shaped diaphragm having a truncated apex defining a generally circular area with a diameter larger than a point and sufficiently less than the distance between nodes of the first overtone to reduce the amplitude of the output of the first overtone to approximately the amplitude of the output of the fundamental; and

c. means fixedly attaching the truncated apex of said diaphragm to said piezoelectric element with the circular area defined by said apex generally encircled by and substantially centered within the first overtone nodal lines.

2. Apparatus as set forth in claim 1 wherein the piezoelectric element is generally disk shaped and the nodal line for the first overtone defines a generally circular area concentric with the truncated apex of the diaphragm.

3. Apparatus as set forth in claim 1 wherein the piezoelectric element includes two piezoelectric wafers affixed together in parallel contiguous relationship with electrodes on each side of each wafer.

4. Apparatus as set forth in claim 1 having in addition a resilient clamping member affixed to the piezoelectric element on the side opposite the diaphragm for lowering the fundamental resonance frequency and damping the resonance peak thereof to extend the range of the speaker to lower frequencies and to provide a relative flat response over the entire range.

5. Apparatus as set forth in claim 4 wherein the damping member is formed from a material including rubber.

6. Apparatus as set forth in claim wherein the rubber has a glass transition region approximately including the frequency of the first overtone.

7. Apparatus as set forth in claim 5 wherein the rubber includes neoprene.

8. Apparatus as set forth in claim 5 wherein the clamping member includes particles of a relatively heavy material intermixed with the rubber for providing frictional damping at the higher frequencies of operation.

9. Apparatus as set forth in claim 8 wherein the particles include lead of approximately 100 mesh size and three parts by weight of lead to one part by weight of rubber.

10. Apparatus as set forth in. claim 8 wherein the damping member further includes particles of dry lubricant intermixed with the particles of relatively heavy material for increasing relative motion between the particles of relatively heavy material and the rubber at the higher frequencies of operation.

11. Apparatus as set forth in claim 4 wherein the damping member extends outwardly beyond the edges of the piezoelectric element for further damping the lower frequencies of operation.

12. Apparatus as set forth in claim 4 wherein the combined mass of the piezoelectric element and the damping member is substantially heavier than the mass of the diaphragm.

13. An improved acoustic transducer comprising:

a. a housing defining a cavity therein;

b. a generally disk shaped piezoelectric element having opposed generally flat major surfaces and defining thereon a nodal ring for a first overtone frequency, said element having electrodes attached thereto for driving said element in a planar bending mode when said electrodes are properly energized;

c. a generally conically shaped diaphragm having a truncated apex defining a generally circular area with a diameter larger than a point and sufficiently different from the diameter of the first overtone nodal ring to reduce the amplitude of the output of the first overtone to approximately the amplitude of the output of the fundamental;

d. means fixedly attaching the truncated apex of said diaphragm to one of said major surfaces of said piezoelectric element with the circular area defined by said apex generally concentric with the first overtone nodal ring; and

e. means operatively mounting said diaphragm within the cavity of said housing.

14. An improved acoustic transducer as set forth in claim 13 having in addition a generally disk shaped resilient damping member affixed to the major surface of said piezo-electric element opposite the major surface having the diaphragm affixed thereto.

15. An improved acoustic transducer as set forth in claim 14 having in addition acoustic absorbing material positioned in the cavity of said housing generally between said housing and said diaphragm.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2518331 *May 6, 1948Aug 8, 1950Bell Telephone Labor IncPiezoelectric crystal mounting
US3548116 *Aug 22, 1969Dec 15, 1970Motorola IncAcoustic transducer including piezoelectric wafer solely supported by a diaphragm
US3588381 *Aug 28, 1967Jun 28, 1971Motorola IncTransducer having spaced apart oppositely flexing piezoelectric members
US3654402 *Sep 25, 1969Apr 4, 1972Philips CorpTransducer for converting acoustic vibrations into electrical oscillations, and vice versa, in the form of a diaphragm coated with at least one layer of a piezo-electric material
US3698993 *Mar 29, 1971Oct 17, 1972Sonix IncSound deadening sheet material
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4035672 *Feb 6, 1975Jul 12, 1977Cts CorporationAcoustic transducer with a dual purpose piezoelectric element
US4283605 *Apr 2, 1979Aug 11, 1981Matsushita Electric Industrial Co., Ltd.Piezoelectric speaker
US4368401 *Jan 22, 1981Jan 11, 1983Siemens AktiengesellschaftTransducer plate for piezo-electrical transducers
US4414436 *Apr 19, 1982Nov 8, 1983Pioneer Speaker Components, Inc.Narrow-frequency band acoustic transducer
US4418248 *Dec 11, 1981Nov 29, 1983Koss CorporationDual element headphone
US4456849 *Sep 16, 1982Jun 26, 1984Matsushita Electric Industrial Co., Ltd.Piezoelectric ultrasonic transducer with damped suspension
US4458170 *Dec 8, 1981Jul 3, 1984Matsushita Electric Industrial Co., Ltd.Ultrasonic transmitter-receiver
US4461930 *Sep 23, 1982Jul 24, 1984Pioneer Speaker Components, Inc.Acoustic transducer with honeycomb diaphragm
US4607186 *Nov 5, 1982Aug 19, 1986Matsushita Electric Industrial Co. Ltd.Ultrasonic transducer with a piezoelectric element
US4705981 *Jan 28, 1987Nov 10, 1987Murata Manufacturing Co., Ltd.Ultrasonic transducer
US5193119 *Apr 27, 1990Mar 9, 1993Franco TontiniMultiple loudspeaker
US5444324 *Jul 25, 1994Aug 22, 1995Western Atlas International, Inc.Mechanically amplified piezoelectric acoustic transducer
US5446332 *Jul 28, 1992Aug 29, 1995Robert Bosch GmbhUltrasonic transducer
US5638456 *Jul 6, 1994Jun 10, 1997Noise Cancellation Technologies, Inc.Piezo speaker and installation method for laptop personal computer and other multimedia applications
US5652801 *Aug 5, 1994Jul 29, 1997Aura Systems, Inc.Resonance damper for piezoelectric transducer
US5828768 *May 11, 1994Oct 27, 1998Noise Cancellation Technologies, Inc.Multimedia personal computer with active noise reduction and piezo speakers
US6087760 *Dec 3, 1997Jul 11, 2000Matsushita Electric Industrial Co., Ltd.Ultrasonic transmitter-receiver
US6181797Jan 9, 1999Jan 30, 2001Noise Cancellation Technologies, Inc.Piezo speaker for improved passenger cabin audio systems
US6215884Dec 9, 1998Apr 10, 2001Noise Cancellation Technologies, Inc.Piezo speaker for improved passenger cabin audio system
US7415121 *Oct 29, 2004Aug 19, 2008Sonion Nederland B.V.Microphone with internal damping
US7494210 *Jul 13, 2005Feb 24, 2009Ricoh Printing Systems, Ltd.Inkjet recording head having dynamic vibration absorber
US8058774 *Jan 11, 2011Nov 15, 2011Murata Manufacturing Co., Ltd.Vibrating plate piezoelectric generator
US8264124 *May 26, 2011Sep 11, 2012Murata Manufacturing Co., Ltd.Ultrasonic transducer
US8354773 *Aug 22, 2003Jan 15, 2013Siemens Medical Solutions Usa, Inc.Composite acoustic absorber for ultrasound transducer backing material
US8487513 *Feb 2, 2011Jul 16, 2013Samsung Electro-Mechanics Co., Ltd.Piezoelectric actuator
US20050043625 *Aug 22, 2003Feb 24, 2005Siemens Medical Solutions Usa, Inc.Composite acoustic absorber for ultrasound transducer backing material and method of manufacture
US20110221304 *May 26, 2011Sep 15, 2011Murata Manufacturing Co., Ltd.Ultrasonic Transducer
US20120153775 *Feb 2, 2011Jun 21, 2012Samsung Electro-Mechanics Co., Ltd.Piezoelectric actuator
CN1856811BAug 6, 2004Oct 27, 2010音速时代有限公司Electro-acoustic device for creating patterns of particulate matter
DE3531325A1 *Sep 2, 1985May 7, 1986Sawafuji Dynameca Co LtdPiezoelektrische schwingkoerper und mit denselben ausgestatteter lautsprecher
EP0053947A1 *Dec 10, 1981Jun 16, 1982Matsushita Electric Industrial Co., Ltd.Ultrasonic transducer
WO1982000543A1 *Jun 29, 1981Feb 18, 1982Motorola IncApparatus and method for enhancing the frequency response of a loudspeaker
WO1992002795A2 *Jul 23, 1991Feb 20, 1992Bosch Gmbh RobertUltrasonic transducer
Classifications
U.S. Classification310/324, 310/330, 181/166, 310/334, 381/190, 381/354, 310/326
International ClassificationH04R17/00
Cooperative ClassificationH04R17/00
European ClassificationH04R17/00