US 3004177 A
Description (OCR text may contain errors)
Oct. 10, 1961 l. J. SOBEL ETAL 7 VIBRATORY PIEZOELECTRIC TRANSDUCERS Filed April 1, 1959 2 Sheets-Sheet 1 I.J.Sobel E.Lessing ATTOR NEYS United States Patent" 3,004,177 r VIBRATGRY .PIEZOELECTRIC TRANSDUCERS Ilyitch J. Sobel, 16-26 163rd St., Whitestone 57, Long Island, N.Y., and Edward Lessing, 7 Keller Lane, Dobbs Ferry, N.Y.
Filed Apr. 1, 1959, Ser. No. 803,475 4 Claims. (Cl. 310-92) This invention relates to vibratory piezoelectric transducers, such as those used in audio-frequency devices for transducing audio-frequency vibrations into corresponding electric signals or vice versa, although the invention is applicable to such transducers operating within any other frequency ranges.
In many applications, piezoelectric vibratory transducers having the form of a longitudinal beam have to be clamped at two longitudinally spacedbiasing or clamp ing regions thereof for causing them to vibrate with the desired response. Thus, for microphones designed for operation with optimum sensitivity, it is desirable to fix the resonant frequency of the piezoelectric transducerwell below the upper frequency limit of the frequency range of such microphones, such as about 1 to 1 /2 octaves below the highest frequency of its range. On the other hand, for microphones which are to operate with a flat.
frequency response over a predetermined frequency range and where the sensitivity of the microphone may be sacrificed, the resonant frequency of the transducer may be set nearer the upper limit of the desired frequency range. In the past, piezoelectric transducers of this type have been clamped at two spaced regions by distinct sets of elastic clamping members, and the assembly of such complete piezoelectric transducer devices required accurate location of the two clamping members at the accurately spaced longitudinal portions of the piezoelectric transducer. As a result, mass production of electroacoustic transducer devices operating with such piezoelectric transducers, presents difiiculties because of the non-uniformity in the operating characteristics of the completed assembled devices due to variations in the location of the two spaced clamping members along the vibratory piezoelectric transducer thereof.
An object of the invention is to simplify the manufacture of electromechanical transducer devices operating with such clamped piezoelectric transducers and to assure a materially higher degree of uniformity of their operating characteristics when manufactured on a massproduction basis.
The present invention is based on the discovery that piezoelectric transducer devices wherein a piezoelectric transducer member operates with a movable transducer region extending between two longitudinally spaced clamp regions thereof, may be manufactured with a much higher order of uniform operating characteristics than heretofore possible, by providing the piezoelectric transducer body with an integral elastomer clamping body which extends along the entire length of the movable transducer region thereof and has two spaced clamping wall sections which are held clamped to two longitudinally spaced clamping regions of the transducer member for securing the desired operating response thereof. 7
The foregoing and other objects of the invention will be best understood from the following description of examplifications thereof, reference being had to the accompanvin g drawing wherein:
FIG. 1 is a vertical cross-sectional view of a microphone transducer device exemplifying one form of the invention; 7 a V FIG. 2 is a cross-sectional view along line 2-2 of FIG. 1;
FIG. 3 is a cross-sectional view of the central region of the transducer device along line 3--3 of FIG. 1;
FIG. 4 is a vertical cross-sectional view of the internal transducer assembly of the transducer device along line 4-4 of FIG. 2;
FIG. 5 is an end view of the transducer assembly of FIG. 4 from the left end thereof;
FIG. 6is an end view of the transducer assemblyof FIG. 4 from the right end thereof; and Y FIG. 7 is an exploded view of the elements of the transducer assembly shown in FIGS. 46.
Although piezoelectric transducer devices of the invention may be used in any of the various known audiofrequency and supersonic-frequency transducer devices, and also in other applications, it will be described in connection with a high fidelity microphone of the type generally used in high fidelity audio-frequency systems operating with a uniform frequency response over thefrev quency range up to about 13,000 c.p.s.
Referring to the drawings, FIGS. 1-3 show a microphone adapted to pick up acoustically transmitted sound signals and transduce them into corresponding electric signals. However, the electro-acoustic transducer of such microphone will also transduce electric signals impressed on the electrodes of its piezoelectric transducer into corresponding acoustic output.
The microphone shown operates with a conventional piezoelectric transducer 21 (FIGS. 4-7) having an elongated axis. The transducer 21 may be formed of two strip-like ceramic piezoelectric transducer elements soldered to opposite sides of a central metal sheet element faces 22, with the underlying two ceramic body sections being electrically polarized in differential relation for generating aiding voltages when the transducer 21 is subjected to bending or'strains in a direction transverse to its electrode surfaces, such as disclosed in Koren et al. Patent 2,863,076. The piezoelectric transducer 21 shown has metallic surface electrodes on its external electrode surfaces 22.
A microphone of the type herein described may be designedto operate with substantially uniform response over a wide range of audio frequencies, for instance, between 30 c.p.s. and 13,000 c.p.s. This in turn requires that the ceramic transducer 21 should resonate or have a resonant frequency at about 4500 c.p.s. This necessitates that the two spaced clamping regions of the elongated transducer 21 be held clamped by two spaced clamping bodies so that the vibratory regions of the piezoelectric transducer extending between and beyond the two clamped regions thereof shall vibrate with the desired high resonant frequency.
In accordance with the invention, piezoelectric mechano-electric transducer devices are manufactured on a mass-production basis with a higher order of uniform operating characteristics than heretofore possible, by providing their vibratory piezoelectric transducer with an integral clamping body of elastomer material having two sets of spaced integral elastomer clamping sections which are held clamped against longitudinally spaced outer surface portions of two spaced clamping regions of the piezoelectric transducer for restraining movement of the clamped transducer regions while the intermediate and any other vibratory regions thereof remain free from clamping engagement and are free to vibrate .with the desired high resonant frequency.
In the device shown, the" transducer 21 forms part of a transducer 'as'ser'nbly generally designated 29, comprising an elastomer clamping body 3% and a rigid mounting structure 4t) which serve to hold the transducer 21 in'its operative vibratory position Within the rigid mountingstructure. The elastomer bodylsil may be made of elastic rubber-like organic solid material such as a vinyl chloridecompou'rid,"or the like,"which embodies sufficient plasticizer substance to serve as a solid elastic elastomer body, portions of which may be clamped against opposite surface portionsof the piezoelectric transducer 21 for 'restraining'motion thereof without causing fracture of the relatively fragile piezoelectric body of such transducer. In the form shown,th'e' elastomer clamping body 3%) has a hollow interior space 31 within which a substantial axial length of the transducer 21 is 'free'to vibrate. The integral elastomer clamping body 39 has an intermediate junction body portion which is free from clamping engagement with the intermediate vibratory transducer region 25, and at each of its two opposite ends two sets of two opposite elastomer clamping wall sections 32, 33 respectively, held in clamping engagement with the two clamped transducer regions 24 embraced thereby for restraining their vibration motion, while the intermediate vibratory region 25 of the transducer remains free to vibrate. Proper clearance spacing 'is' thus provided between the inwardly facing surfaces of the intermediate junction body portion of the elastomer clamping body 36 and the facing surfaces 22, as well as the side edges of the freely vibrating intermediate transducer region 25 extending along the major length of the hollow space 31 of the transducer-clamping elastomer body 3-9. i
"The rigid mounting structure so may be made of any hard, rigid material. In the form shown, the mounting structure 40 is of hard synthetic resin material, as by molding, and has sutiicie'nt rigidity to resist deforma-V t'i'on and provide strong mounting forces whereby the transducer 21 with its elastomer clamping body 30 are held in their operative positions relatively to the other elements of the'microphone. The rigid mounting structure this shown formedwith a'hollow interior mounting space 41 shaped to receive and hold fixed therein in proper operative position the elongated elastomer clamp ing body 39 with its transducer 21. At one end of its hollow interior space 41 the mounting structure 41 has one set of opposite rigid clamping walls 42 which are spaced fromeach other'by a clamping space of sufii c'iently small height for holding the embraced elastomer clamping wall sections 32 compressed and clamped against one embraced, clamped transducer region 2'4 for restraining vibratory motion thereof. At the opposite end of its hollow interior space 41, the integral mount ing structure 40 has a further set of opposite rigid clamping walls 42 which arespaced from 'each' other by a clamping space which is of sufficiently small height for holding the embraced elastomer clamping wall sections 32 compressed and clamped against the other embraced, clamped transducer region 24 for restraining vibratory motion thereof.
In accordance with the invention, the height of the clamping space between the set of rigid clamping walls 42 is greater than the height of the clamping space between the other set of clamping wall sections 43." In addition, the entire length of the hollow mounting space 41 of the mounting structure extending to the right of clamping wall sections 43 (as seen in FIG. 4), is made sufiieiently "wider than the thickness of the elastomer body extending to the left of its elastomer clamping wall sections 32, for permitting free entry and insertion of the narrower end of elastomer clamping body'30 into' the clamping space 41 until the narrower left end of the elastomer clamping wall section 33 reaches the'clamp ing space between the rigid clamping wall sections 43 of mounting structure 40. This arrangement enables free and ready insertion of the narrower end of elaso- Wain d mer body 30 with the transducer 21 and its terminal members 51, 51, held assembled tliiereon, into the hollow mounting structure 4% through the wider spacing between its rigid clamping wall sections 42, and free inward movement of the elastomer body assembly toward the narrower spacing of the other set of rigid clamping wallsections 43' of" the rigid mounting structure 4%). Thereupon, the closer-spaced forward elastomer'clamp ing wall sections 33 are forced into their" operative clamped position between the closer-spaced rigid clamping wall sections 43 of the mounting structure 4t), while the other set of the wider-spaced elastomer clamping wall sections 33' are forced intenam in engagement under the wider-spaced rigid clamping wall sections .42 of the rigid mounting "member 41),"therebji completing the operative assembly of transducer 2i and elastomer clamping body 30' in precisely accurate clamping positions thereof within the rigid mounting 'st'ructuredt 'In accordance with the inventioii,"the self-supporting transducer assembly of the type described above, is combined with two strip-like metallic terminal members arranged to be held clamped to the electrodes of the piezoelectric transducer, and having exposed external terminal portions through whichexternal circuits are connected to electrodes of the transducer structure 21. In the form shown, the transducer assembly 20' has two ter.- minal members 51, SS'made, for instance, of electrically conductive sheet material which is also elastic, such as brass. Each of the terminal members 51, 55 has a mounting arm 52 and 57, respectively, bounded by tapered edges to fit between the tapered inward surfaces of the mounting compartment 41 of'th'e rigid mounting structure 40; The two terminal'mounting arms 52,57 are arranged to'be'retained iri'fixed position between the sidewise facing exterior surfaces of the side walls 35 of the'elastotner'clamping body 36 (FIGS. EH7), and the inwardly facing "surfaces of. the side walls of the integraL'rigid mounting 's'tructurefeii. Each terminal arm 52, 57 has a laterally extending flat contact tongue portion 5358, respectively, formed out of a portion of'therespectiveimounting arm 52,52, as by cutting and bending. The two terminal contact ton tea 53, 5e are held clamped in their operative po' between the underlying outer electrode surface port ns 22 of the endr'egions of the piezoelectric transducer and the overlying'el'asto mer clamping wall portions 33 which are held clamped thereto by the overlying rigid clamping "wall portions '45 of the rigid clamping structur'e ltl. i i h "The side walls 35 of the elastomer clamping body 39 are provided with cut-outs 36' (FIGS. 5, 7) through which the laterally bent contact portions 53, 53 of the two terminal members 51, 55 pass into engagement with the underlying'electrode'surface portions 22 of ti piezo electric transducer 21. "Each of the two terminal strips 51, 55 also has a laterally projecting terminal prong arm 54, 59 exposed to engagement with a suitable socket terminal element of the cooperating external electric circuit to which it is'to be detachably connected.
In the form shown, the rigid clamping wall sections 42, 43, which'underlie the lower wall of the integral elastomer clamping body 3%, form part of a rigid base wall 44 held seated agaihst'a 'wall of casing 60 and provided with a thicker base wall section 45 shaped to lit and to be fixed within an opening'ol of the casing 69, in which the transducer assembly 26 isoperatively mounted' In the form shown, the thicker base wall section 45 is of'cir'cular' shape, aiiditha's a polarizing ridge 45-]. arranged to fit in an oriented position in'the corre spondingly shaped casing opening 61. The circular casing openingol hasa polarizing recess into which the polarii With this arrangement the transducer assembly 20 is readily mounted in its operative position along the wall of itscasing 60 by dropping its base wall projection 45 with its polarizing aligning ridge 45-1 into the seating opening 61 of its casing 60, with the aligning recess of the casing opening engaging the aligning ridge 45-1 of the base wall projection 45. The transducer assembly is secured into its operative position along the casing opens ing 61, in which it is shown in FIGS. 1-3, by applying a coating of a known good cement to the base wall, its wall projection 45, and the seating surfaces of the walls of the casing 60 and its opening 61 engaged thereby before placing the mounting structure 40 of the transducer assembly 20 in its operative position within the casing 60;
A feature of the invention involves an arrangement which makes possible the automatically aligned positioning of the elements of a transducer assembly of the type described above, for assuring that the elastomer clamping body is automatically fixed in its accurately aligned position within the mounting structure 40 in the manner described above, notwithstanding the fact thatthe two metallic terminal members have external terminal projections extending in a direction transverse to the direction of the movement of the elongated elastomer body 30 into its coaxial mounting space 41. To this end, the base wall 44 of the transducer mounting structure 40 is provided on the side of its greater-spacing clamping wall sections 42 (FIGS. 3-7) with two elongated slots 47 extending from the wall edge thereof toward its interior region through which the outwardly projecting terminal arms or terminal prongs 54, 59 project in laterally outward direction. This makes it possible to move the elongated elastomer body 30 with the transducer 21 held assembled therein, in the way shown in detail in FIGS. 47, with the contact tongues 53, 58 of the two terminal members 51, 55 held in the assembled position along and partially within the elastomer body, into the interior mounting space 41 of the mounting structure 40, in the way described above, while the two terminal prongs 54, 59 which project laterally beyond the elongated elastomer body 30 move along the slots 47 of the mounting structure base wall 44 into their final inward position within the base wall slots 47 in which they are shown in FIGS 1, 3 and 4-6.
With such arrangement, the inward boundary edge surface 48 of the prong-receiving slots 47 of the mounting base wall 44 serve as automatic stops which automatically stop the inward movement of the assembly of the transducer 21, the elastomer body 30, and the two terminal members 51, 55, when they reach the inward operative position between the two sets of clamping wall sections of the mounting structure 40 by the automatic assembling and aligning operating described above. I
In the transducer device the abutment between the terminal prongs 54, 59 of the transducer assembly of elastomer body 30 and the stop edge surface 48 in the terminal slots 47 of rigid mounting structure 40 fixes their final aligned assembly position.
With such arrangement for automatically stopping the inward movement of the sub-assembly of the transducer elements which are combined with the elastomer body when they reach their operative position within the interior of the rigid mounting structure 49, the two interior wall surfaces of the mounting structure overlying the facing surfaces of the elastomer body 30 extending over the wide transducer electrode surfaces, may be given an inwardly tapering shape as indicated in FIG. 7.
However, if the transducer assembly of the type described above is provided with externally exposed terminal portions (corresponding to terminal prongs 54, 59 described above), which extend in the same axial direction as the piezoelectric transducer 21, such sub-assembly of the elastomer body 30 is providedwith a different type of stop elements cooperating with stops of the mounting structure 40 for automatically stopping inward movement of the sub-assembly of elastomer body 30 when it reaches the inward operative position. Byway of example, the inward surfaces of the mounting structure 40, near its rightward end, as seen in FIG. 4, may have inwardly extending stop shoulders or stops 49 adjoining its two wider-spaced clamping wall portions 42, which mounting wall stops 49 are arranged to engage stop surfaces 39 formed on the facing side surfaces of the outward regions of the two elastorner clamping wall regions 32. The stop surfaces 49 and 39 of the mounting structure 40 and the elastomer body 30 are so arranged that when the sub-assembly of the elastomer body 30, of the type described above, is moved inwardly into mounting space 41 of mounting structure 40, thesub-assembly of elastomer body 30 is automatically stopped at the end of its inward movement when'the elastomer clamping regions 32, 33 reach the inward position in which they are forced into clamping engagement with the clamped transducer regions 44 overlying clamping wall portions 42, 43 of the mounting structure 40.
In the particular embodiment of the invention shown, the piezoelectric transducer 21 is connected to a vibratory diaphragm 64 through a motion-transmitting member or link 65. Although the intermediate vibratory transducer region 25 extending between its two clamped regions 24 may be coupled through such link to the diaphragm 64, the transducer device shown operates with a transducer 21 which has a further vibratory transducer region 26 coaxial with the intermediate vibratory transdncer region 25 thereof, and extending coaxially therewith beyond one of its clamped regions 24, for instance to the right, as seen in FIG. 4. The vibratory diaphragm is very light, and may be formed, for instance, of thin aluminum foil. In the particular device shown, the diaphragm 64 is of circular shape, and its rim is secured, as by cement, to the underlying edge of easing rim 63 of the circular casing 60. The motion'transmitting link 65 has two inward grip arms 66 embracing with their notched end portions an end portion of the outer vibratory region 26 of transducer 21, for'transmitting vibratory motionbetween it and the diaphragm 64. The outer end of the link 65 passes through the center of the conically shaped vibratory diaphragm 64, and is secured to the adjoining diaphragm portions in a conventional way, as by wax or cement.
To protect the delicate vibratory diaphragm 64 against disturbance from the exterior, it is covered by a protective cover wall 70, having slit openings through which acoustic signals are transmitted between the surrounding space and the diaphragm 64 for causing the diaphragm 64 to vibrate in accordance with the, sound propagated in the surrounding space, or to cause the diaphragm to transmit acoustic energy or sound to the surrounding space when vibrated by the vibratory transducer 21. In the form shown, the periphery of the protective cover wall is held clamped against the underlying casing rim 6?. by an overlying inward rim projection or flange 68 of a casing cover 69 secured to the exterior of the relatively rigid transducer casing 60. In the form shown, the casing cover 69 is formed of a relatively thick layer of elastomer or rubber-like material which is retained on the exterior of the casing 60 by elastic forces and/or a layer of cement, and also by the overlapping engagement of the cover regions overlapping the upward and downward sides of the microphone 6t as shown in FIG. 1.
The desired flatness of the response is achieved by damping means which suppress excessive acoustic motion in the region of the resonantfrequency of the transducer.
In accordance with the sole invention of the applicant Sobel, the damping fabric and the separate hard and strong protective cover generally used with high quality acoustic diaphragm transducers, is replaced by a hard cover wall overlying and protecting the vibratory diaphragm, the hard cover wall having one or more slits of minute width and depth, which have negligible acoustic inertance while 7 7 providing the desired'acousticdamping resistance which dissipates excessive acoustic motion without appreciable sacrifice in over-all sensitivity. This s'ole invention constitutes the subject-matter claimed in the co-pending application Serial No. 825,083, filed July 6, 1959, by Li. Sobel, as sole inventor thereof. I
Without thereby in any way limiting the scope of the invention, but toenable more ready fpractic'e thereof, there will now be given by way of example, design data of embodiments of the invention:
I A microphone which has a substantially fiat open-circuit response over the frequency range of 30 to about 13,000 c.p.s., has a diaphragm of aluminum foil 1.2 inches in diameter. It has a piezoelectric ceramic transducer body .026" thick, .063" wide, and .425" long, formed of lead zirconate and lead titanate ceramic known as PZT. The clamped length of the ceramic transducer including its free vibratory portion is 300". 'The clamping width (along its axis) between its metal terminal contact 58 is .40". The clamping width at the opposite end .of the elastomer body is .050. The thickness of the uncompressed elastomer body atits wider end is .160", and at its opposite narrower end, .130". The overhang of the outwardly projectingportion of the transducer to the point of its engagementwith the diaphragm drive rod is .100". The volume of the casing'compartrnent underlying the diaphragm is large enoughto assure that its acoustic stiffness has only negligible effect on the microphone response. A conventional minute leak opening from the compartment space provides pressure equalization on both sides of the diaphragm. The clamped piezoelectric transducer, without its link connection, resonates between 4000 and 4500 c.p.s. It operates with a sensitivityof 63 decibelsbelow 1 voltfor-acoustic pressure of l dyne/cm. square.
A similar microphone which has a substantially fiat, open-circuit response between 13,000 and 16,000 c.p.s.,at a lower sensitivity of 68db below 1 volt, for the same air pressure, has a shorter piezoelectric ceramic transducer of .390" length,"and otherwise similar dimensions.
*A similar microphone which has a higher sensitivity of 5 8 db below 1 volt for the same acoustic pressure and a substantially flat response over the frequency range from 30 to 8000 c.p.s., has a longer ceramic piezoelectric transducer of -.450"-length,'and the same other dimensions. The clamped piezoelectric transducer without its drive link connection resonates between 2700 and 3000 c.p.s.
It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in com nection with the specific exemplifications thereof will suggest various other modifications and applications of the same. It is accordingly desired that in'construing the breadth of the appended claims, they shall not be limited to the specific exemplifications of the invention described above.
1. In a mechano-electric transducer device, an elongated piezoelectric transducer body with two opposite, relatively large, outer transducer surfaces and having an intermediate elongated vibratory transducer region extending between two clamped transducer regions thereof, an integr'al, hollow elongated elastomer body coextensive with and surrounding the over-all length of said clamped and intermediate transducer regions, said elastomer body having two spaced sets of two spaced, generally parallel restraining walls engaging with their inner elastomer sur faces the outer surfaces of said two clamped transducer regions, respectively, an integral, relatively rigid hollow mounting structure coextensive with said elastomer body and having two corresponding spaced sets of two spacedi opposite clamping walls engaging and clamping with their" inner clamping surfaces the outer surfaces of said two sets of restraining walls for suppressing vibratory motion of said two clamped transducer regions, said intermediate vibratory transducer region being relatively free for vibratory transducer motion in a direction transverse to said transducer surfaces.
2. In a transducer device as claimed in claim 1, the height of one clamping space between one of said two sets of clamping walls being greater than the height of the further clamping space between the other set of clamping walls, the two sets of elastomer restraining walls being of a height corresponding and complementary to the greater and smaller heights of said two clamping spaces of the mounting structure, whereby the transducer assembly comprising said elongated elastomer body with said piezoelectric transducer body mounted therein may be freely moved with its smaller-height restraining walls throughthe greater-height clamping space of said mounting structure into its operative position within said mounting strnc ture.
'3. In atransducer device as claimed in claim 2, an-
exposed electrode surface on eachof said two opposite transducer surfaces along at least one clamped transducer region, two L-shaped metallic terminal strips extending with their strip surfaces transversely to said transducer surfaces, one mounting arm of each terminal strip being held clamped by opposite side wall portions of one set of said clamping walls to opposite side wall surfaces of the correspondingset ofelastomer restraining walls, and the other terminal arm of each terminal strip extending in the same general direction transversely to said electrode surfaces, the mounting arm of each of said terminal strips having a laterally extending contact portion held in clamping contact engagement with a difierent one of the two oppoiste electrode surfaces of the transducer body by overlying clamping walls of said one set or" clamping walls.
4. In a transducer device as claimed in claim' 3, one clamping wall of said mounting structure extending along said clamping space having openings through which the terminal strips project, respectively, beyond the exterior of said two walls for contact engagement with external contact members, said one clamping wall having two slits extending from said two openings, respectively, to the edge of said mounting wall, whereby said transducer assembly including said two terminal strips may he moved jointly into said operative position within said mounting structure.
References Cited in the file of this patent UNITED STATES PATENTS