US2045403A - Piezoelectric device - Google Patents

Description

June 23, 1936. E. c. NlcHLlDEs 2,045,403

PIEZOELECTRIC DEVICE Filed May 24, 1933 2 Sheets-Sheet 1 lime 23, 1936- E. c. NlcHoLlDEs 2,045,403

PIEZOELEGTRIC DEVICE lFiled May 24', 1933 2 ShebS-Sheet 2` A' no. l @(659.112, um

e. c .N-Ma.. BY

5 MYM..

ATTORNEY Patented June 23,' 1936l l i 4UNITED STATES PATENT oFFics PIEZOELECTRIC DEVICE Emmanuel Christ Nicholides, New York, N. Y., 'assignon by mesne assignments, to Sonotone Corporation, New York. N. Y., a.l corporation of New York Application May 24. 1933, sei-iai No. 672.0560

' 13 claims. (ci. 1v1- 321) This invention relates to piezo-electric devices of-hearing persons suering from an` impaired and it hasv among its` objects improved acoustic outer or middle ear, but having a good inner heardevices utilizing vibrators of piezo-electric 'subing organ able to hear clearly sound vibrations stances, and particularly of Rochelle salt crystal imparted by conduction over the bones of the material.A head. Since many apparently-deaf persons have 5 A particular object of the present invention is this ability to hear well by bone conduction, nuan improved bone-conduction hearing-aid device merous eiorts have been made Iin the past to deutilizing a piezo-electric vibrator for imparting vise a hearing-aid device with an electromagnetmechanical. sound-frequency vibrations to the ically actuated bone vibrator for imparting soundbone structure of a person of impaired hearing frequency vibrations to the bone structure of the 10 and inducing sounds in his auditory center. head of such person with sufllcient power to in- The foregoing and other objects of my invenduce satisfactory hearing in his auditory center, tion `will be best understood from the following While keeping the size and shape ofthe vibrator description of exemplilcations thereof, reference small, light, and unnoticeable to permit its wear being had to the accompanying drawings, whereon the head of the user, without calling thereto 15 in a the attention of bystanders. Fig. 1 isv a perspective view" ofi` a Rochelle salt Piezo-electric vibrators made of piezo-electric crystal; f 11 f crystal members, such as quartz, tourmaline and Fig.'2 is an elevational view of a Rochelle salt Rochelle salt crystals hve'beeii kllOWn fOr many crystal plate; i years. Such piezo-electric members generate po- 20 Fig."3 is a side view of a bender vibrator unit; tential diiferences between different portions Fig. 4 is an elevational view or the vibrator unit thereof when subiected to mechanical deformaof Fig. 3; tion, and, conversely, undergo deformations when Fig. 5 is a horizontal sectional view of F'ig. 4 subjected to electric ilelds. Rochelle salt crysalong line 5 5; tal members' exhibit these piezo-electric effects 25 Fig. 6 is a vertical sectional view of a bone vito a much higher degree than the Other Similar brator unit; substances known at present, but are mechani- Fig. 7 is a cross sectional view of Fig. 6 along .cally poorer. I found that if properly used, R0- line 1 1; 'i chelle salt crystal material is best adapted for Fig. 8 is a horizontal sectional view of the bone hearing-aid bone Vibrators and, in general, for 30 vibrator along line 8,-8 of Fig. 7; audio frequency vibrators. The growth of Ro- Fig. 9 is a view of the bone vibrator unit as chelle salt crystals from which satisfactory vimounted on the head of a person; brators may be made is described in the article Fig. 10 is a circuit diagram of the hearing-aid 0f R. W- MOOTe in the Journal 0f American Chemdevice including the bone vibrator unit; ical Society of 1919, page 1060, and the literature 35 Fig. 11 is a vertical sectional view of a cone there cited, and is well established. The broad speaker; features of my present invention are, however, Fig. 12 is a vertical sectional view of a record het limited t0 Rochelle Salt Crystal Vibrators. cutting head; but are applicable to other substances exhibit- Fig. 13 is a vertical sectional view of the cutter ing Simile?l DlOpeltlee -Y 40 head of Fig. 12 along line |3-I3; In Fig. 1 is shown in perspective view a full Fig. 14 is a vertical sectional view through a glOWIi Clear Rochelle Salt erystel- Such Crystal receiver telephone; has Athree principal axes, the optical axis Z ex- Fig. i5 is a vertiea1 sectional 'view through a tending longitudinally parallel to the direction cone speaker of modified, construction; of the main faces of the crystal, the electric axis 45 Fig, 16 is a rear view of the vibrator unit. of X which lies in the direction in which an electric Fig. 15; field produces the maximum deformation, and

Fig. 17 is a horizontal cross sectional view of the transverse axis 'Y which forms with the the vibrator unit along line I1-l1 of Fig. 16; optical axis Z a plane perpendicular to the' elec- Fig. 18 is an elevational View of arecord cutting trical axis X. This nomenclature follows that 50 head; and suggested by W. G. Cady in the article Piezo- Fig, 19 is a vertical sectional view along lineI electric terminology in the Proceedings of v2in i9-I9 of Fig. 18. stitute of Radio Engineers, volume 18, page 2136,

The improvements disclosed herein are a. result 1930.

of efforts to provide a bone vibrator for hard- If a rectangular plate 20 as shown in Figs. 1 65 tentials.

and 2, cut from the crystal in a direction perpendicular to the X axis (designated as X-cut plate) with its edges in axial directions (designated as "axial X-cut plate) is subjected 'to an electric field in the direction of the X-axis, the plate undergoes its4V greatest deformations in the two dlametrical directions D1, D2 inclined 45 against the optical axis Z and the transverse axis Y, expanding, for instance, along Di-Di, and contracting along Dri-D2, the deformations reversing in character upon reversal of the direction of the electric eld. An X-cut Rochelle salt crystal bar 2| having its longitudinal edges cut under an angle of 45 to the Zand Y axes, designated 45 X-cut bar, when subjected to an alternating field in the direction ofthe X-axis will elongate during one half of each alternation and contract during the other half of each alternation, depending on the reversal of the direction of the electric field across the bar.

By firmly uniting to each otherthe flat faces Aof two axial-X-cut crystal plates 2U, as indicated in Fig. 3, for instance, by cementing them with shellack or Canada balsam, and applying across each of said plates potentials inducing opposite deformations in the two plates, the elongation of each plate will be restrained by the contraction of the other plate, and vice versa, causing one pair of diametrically opposed corners of the two-layer unit to bend forward of one face while the other pair of corners will be bent in opposite direction forward of the other face, twisting the unit in one direction, the actions reversing upon reversal` of the potentials applied to the two plates.

If two 45Xcut rectangular crystal plates are similarly united vto each other and proper potential is applied across each plate, inducing opposite deformations in the two plates, the elongation of one plate will be restrained by the contraction of the other plate, causing the mid-portions of one pair of opposite edges of the unit to bend forward of-one face, and the mid-portions of the other pair.of opposite edges of the unit to bend in opposite direction forward of the other face,'twisting the two-layer unit, the actions reversing on reversal of the applied potentials. These two crystal Vibratorunits are designated as twisters, the rst being a. idiametrical, the second an axial twister.

By similarly uniting the faces of two 45-X-cut bars or strips 2| yof crystal, as shown in Fig. 3, and applying across the two bars potentials inducing in one bar expansion, and in the other bar contraction, the restraint exercised by one bar on the other causes the two-layer crystal unit to bend toward one side face `0r the other depending on the direction of the applied po- Such two-layer unit is designated as bender. b

In order to impress an electric eld in the direction of the X-axis upon the two plates of a vibrator unit, electrodes in the form of sheets of conducting` material, such as tin foil, are attached to the surfaces of the plates, by Canada balsam, for instance, the junction between the electrode and the crystal surface being made very intimate to secure application of substantially the entire available potential to the body of the crystal plate, and absorb as little as possible potential in the junction layer between the electrode and the crystal surface.

To obtain the above described deformations of the two-layer crystal units, a single electric field may be applied to both plates of the u nit by providing electrode sheets only on the outer exposed faces of the unit and connecting the two sheets to the opposite poles of a source of potential. The individual crystal plates must then have opposite orientation, that is, the two plates must be placed in such relation to each other that on application of a common electric eld going in the same direction from one plate to the other, the deformations induced in the portions of one plate will be opposed to the deformations -induced in the adjacent portion of the other plate.

The deformations of the two-layer crystal units may also be produced by applying opposite po. tentials to the two plates, so that the direction of the iield in one plate is opposite to the direction of the field in the other plate, by cemcnting an additional intermediate electrode sheet at the junction between the internal surfaces of the two plates, to form a common electrode for the two plates. By connecting the two outer electrode sheets to one pole of a source of potential yand connecting the intermediate electrode sheet to the other pole of the source, oppositely directed fields will then be produced across the two plates. In this arrangement the adjacent crystal plates must be of the same orientation, that is, the

plates must be parallel to each other in their crystal formation to undergo opposite deformations on applying opposite electric fields to the two plates.

With a given potential diiference, a greater deformation of the two-layer crystal unit is obtained by separately applying to the two crystal plates the full available potential with the intermediate and outer electrode sheets. It is for this reason that in practical applications, vi-

` pendicular to its faces, its motion being simpler.

Piezo-electric twister and bender units have been found superior to single crystal plates for use as mechanical vibrators because on actuation by oscillatory potentials, they give a greater vibratory motion. Thus, a single piezo-electric crystal plate varies only slightly its length when subjected to an electric eld. When such plates are combined into a twister or a bender unit, the restraint exercised by the longitudinal deformation of one plate restrains the opposite deformation of the second plate over its entire surface, imparting to the two-layer crystal unit a bending motion of greater magnitude than the longitudinal motion of the two crystal plates could give otherwise. In the twister and bender a high degree of restraining action is obtained by cementing the entire contact surfaces of the two plates or bars to each other so that the crystal plate or bar which tends to contract opposes throughout its junction surface the expansion of the oppositely induced adjacent crystal plate or bar bringing about a resulting bending movement. A similar bending effect can also be obtained with a single strip by uniting to the surface of a crystal strip, the surface of a metal strip strong enough to resist longitudinal elongation and contraction,

to oppose the contraction and expansion of the crystal when an alternating eld is applied thereto, thereby forcing the crystal strip to execute a bending movement instead.

Where a relatively large bending action is desired with a small available potential, several similar twister or bender units may be united to each other in the same Way as the two plates of a twister or bender unit are united to form a unitary structure of four, six, or more crystal layers, preferably with electrode layers between adjacent junction surfaces of the crystal layers and on the outer faces of the outer crystal layers. connected to impart to one half of the crystal layers a deformation opposite to that imparted to the other half of the crystal layers on application of a potential, and thus causing bending of the entire structure. By means of such multiplelayer benders and twsters it is possible to obtain vibratory movements of substantial power with relatively low potentials.

Much more vibratory energy Can be imparted with piezo-electric vibrators at high frequencies of several thousand cycles per second than at low audible frequencies, and particularly in the range of low speech frequency. of about 500 cycles and less. The operation Aof a piezo-electric crystal is to a large degree similar to that of a condenser within the range up to its fundamental frequency. Like a condenser, piezo-electric substances -have a high impedance at lowfrequencies, the impedance decreasing with increase in frequency.

Rochelle salt crystal material has a very much greater piezo-electric eifect than quartz or other available piezo-electric substances and exhibits a much greater capacity effect at low frequencies than other piezo-electric substances. These characteristics make Rochellesalt crystal material very desirable for construction of vibrators operating in the audio frequency range and particularly in the speech range down to frequencies of about 100 cycles per second.

Rochellel salt crystal material is well suited for use in multi-layer vibrator units because the thin plates are effective in dissipating the heat and permit holding down of the crystal temperature to a value at which its piezo-electric effect remains stable during operation. V

In utilizing twisters and benders for sound production, for instance, by imparting therewith a vibratory movement to the diaphragm of a loud speaker, as practiced heretofore, a relatively large vibrator unit was clamped with one end or edge to a heavyysupport to hold it firmly in place, the other end or edge being left free to vibrate and to transmit its lvibratoryl energy to' the loud speaker diaphragm by coupling the diaphragm to the vibrating free end or edge of the vibrator unit. Relatively'large crystal vibrator units were used in such crystal drives, the mass of the crystal being large enough to have a substantial reactive inertia assisting the inertia of the heavy support of the vibrator unit in imparting the vibratory energy to the diaphragm, or other vibration receiving load.

Heretofore, most of the bone vibrators proposed for bone-conduction hearing-aids were of lthe electromagnetic type requiring a relatively complicated, large-size and heavy mechanisms. My efforts have been directed to the production of a small, light and simple hearing-aid bone vibrator by the use of a Rochelle salt crystal vibrator for converting the sound-frequency oscillations supplied to the vibrator into mechanical vibrations imparted to the bone structure.

Because of the requirement that such vibrator unit shall be small to permit its inconspicuous wear on the head of the impaired person, I constructed for this purpose a small bender of Rochelle salt crystal as shown in Figs. 3 to 5. The bender consists of two Rochelle salt crystal strips 22, 23, each 11/2 long, wide, and 11;"

thick, cemented to each other along their inner faces into a. two-layer unit 24, with a pair of tin foil electrode sheets 25, 26 secured to their outer faces and an intermediate electrode sheet 21 secured to the junction surfaces of the two crystal strips and common to the inner f faces of the two strips. The lower end of the crystal unit 24 is clamped in a clamp 28 of a rigid insulating material, such as bakelite, in which are imbedded two heavyv metallic clamping Ablocks `29 and 3|] separated from each other by an insulating barrier 3l to permit maintenance of a potential difference between the two blocks. In a cavity 32 of the clamp, the lower flat end of the crystal unit is clamped between two thin layers 33 of yieldable insulating material, like fibre -or mica. by means of a relatively rigid clamping plate 34 of insulating material, such as fibre, held down under pressure by bolts 35 screwed into the projecting sides of the metallic blocks 29 and` 30. The electrode sheet 22 on the front surface of the crystal unit and the electrode sheet 23 on the rear side of the crystal unit have resilient contact strips 36 and 31 pressed into contact with block 29, and the intermediate contact sheet 21 has a resilient contact strip 38 pressed against the block 30 within the lateral spaces of the cavity 32, thereby establishing terminal connections from ,blocks 29, 30 to. the outer electrode sheets 25, 26 and the intermediate electrode sheet 21, respectively. To supply electrical oscillations to the electrode sheets, longitudinal sleeve-like holes 4I are drilled into the clamping members 29 and 30 to receive plug pins 42 inserted from the bottom, these plug pins being connected to an insulated two-conductor cord 43 leading to a source of electric sound-frequency oscillations. The weight of the crystal unit 24 without the clamp is about 3 grams, the weight of the clamp is about grams, giving the assembled vibrator unit a "support of substantial inertia, which is, however.

relatively small compared with the inertia of the mass of the bone structure of the head of the person to which vibrator-y energy is to be applied with the vibrator unit.

This crystal vibrator unit was tested by connecting its terminal pins 42 to the output terminals of radio and phonograph amplifiers and holding its free end against the mastoid bone either with the hand. or by means of a head band, and also by holding its free end against a loud speaker cone diaphragm. The vibrator unit transmitted'satisfactorily high frequency vibrations and high musical notes, but its trans-f mission of low frequency vibrations of the speech range and the low frequencyl musical range was very poor. Its output was not satisfactory for the intended use as a hearing-aid bone vibrator which requires reproduction of enough low frequency vibrations to make speech well understood by the listener.

I found that these difficulties of transmitting low frequency vibrations can be overcome by shifting the coupling point of the load to which the vibrations are to be transmitted, from the free end of the vibrator towards therpoint where the vibrator unit was clamped, near the nodal portion thereof. By holding the yfree end of the vibrator unit having maximum motion against the loud speaker cone and shifting this coupling point nearer to the clamp 28, the amount of the vlow frequencyy vibration imparted to the cone gradually increased until at a coupling point near the clamp, the cone would transmit an abundance of low frequency sound. The same experience was obtained by shifting a contact button attached to the vibrator unit and applied to the mastoid bone from a point near the lend of the vibrator area toward the clamp,` the sound gaining in low frequency tones and the speech becoming clearer as the button was brought nearer to the clamp.

I have also found that additional improvement of the transmission of low frequencies may be obtained by attaching a weight to the vibrating portion of the crystal unit. Attaching of a Weight to the vibrating crystal bar has also a very pronounced eifect in increasing the amount of low frequency oscillation energy transmitted from the crystal bar to the cone or to the bone structure. By combining the use of an additional weight attached to the vibrating crystal bar with a coupling connection lying near the4 clamp of the vibrator, there is obtained a cumu- 'lative increase of the amount of low frequency sound imparted by the crystal unit to the cone or to the bone structure, each effect contributing a share in improving the richness of the output in low frequency vibrations.

The foregoing improvements in the operation of vibrator vunits enables the construction of small bone vibrators suitable for inconspicuous wear by persons of impaired hearing and yet able to produce and impart to the bone structure of a'person of impaired hearing sufficient vibrations of the low frequency sound range to properly reproduce speech, and enough of the high frequency range to secure good reproduction of music. Such bone vibrator unit for a portable hearing-aid device embodying the foregoing improvements is shown in enlarged scale in Figs. 6 to 8 of the drawings.

The bone vibrator comprises a small flat longitudinal casing 59 closed on one side by a wall 5l and having an opening 52 on the other side. The l casing is made of an insulating molded substance,.

such as bakelite, and has imbedded in its lower part a pair of heavy metallic clamps 53, 54, insulated from each other by the body of the casing, like in the clamp shown in Figs. 3 to 5. Into a cavity provided between the two metal blocks 53 and 54 there is clamped between bre layers 55 thc lower flat end of a two-layer RochelleI salt crystal bender unit 5B by means of an insulating clamping block 5'1, the several elements being constructed and arranged like the elements shown in Figs. 3 to 5. The outer electrode sheets 59, are connected by contact strips 6I, 62 with the metallic block 53, and the intermediate elec-v trode sheet 63 is connected by a contact strip 64 with the metallic block 54, the metallic blocks 'having perforations 65 and 86 for receiving plug pins 61 of a cord 58 leading to the source of sound-frequency electric oscillations.

A short distance above the clamped lower end portion,` the crystal unit 56 has clamped thereto a button clamp 10 having two members 1I, 72 and intermediate yieldable layers 'I3 embracing thevibrating unit and held together by screws The front side of the button clamp l2 holds a bolt 'I6 over which is screwed a contact button 'VI projecting through an opening 18 in the casing the crystal vibrator wall 5| and movable within a collar 19, of rubber or similar material, lining the opening 18 of the casing. The amount of the projection of the button J1 beyond the casing wall 5| may be adjusted by interposition of one or more washers between the button and the clamp member '12.

To the free top end of the crystal vibrator unit 56 is secured a weight 84 of lead, for instance, having in the interior a cavity with a narrow portion fitting over and attached, as by cementing, to the flat sides of the upper end of the crystal vibrator unit 56, and a downward skirt-like extension for holding additional weight without clamping too much of the surface of the crystal,

and without increasing the length of the unit. An

in the direction perpendicular to its faces as in- 2 dicated by the arrows 88 in Fig. 6, sufcient spaces being left on both sides of the weight 84 to permit the crystal unit to reach its maximum amplitude without touching the walls of the casing. f

The rear wall of the casing is enclosed by a `cover sheet 90 which has clamped thereover a second sheet 9i provided with a channel 92 for receiving the flat end of a grip portion 93 attached to a head band 94 for applying the button 'I1 with pressure to the mastoid bone of a person using the instrument as shown in Fig. 9. The cover 90 and the channel sheet 9| may be firmly clamped in place by screws 95 engaging the edge of the casing wall. The conductor cord 68 carryng the conductors has its contact pins attached to the terminal blocks 53 and 54 of the vibrator unit, the cord being easily hidden in the clothing of the user.

' duce current oscillations `from the battery 99 in accordance with the sound vibrations impinging on the diaphragm of the transmitting microphone 96. The produced oscillations are amplified in the amplifier 98 and delivered through an adjustable resistor |00 to a transformer IUI from where the amplied and suitably transformed oscillations having a potential required for actuation of unit 56 are impressed upon the electrode layers of the vibrator unit 56 held with the button 'Il against vthe mastoid bone or other suitable portion of the bone structure of the head of the person. The small crystal vibrator unit constructed and arranged as described above will operate satisfactorily with `a source applying a voltage of about 10 volts to the crystal strips.

Where the available operating voltage is low,

the vibrator unit is preferably made with four crystal strips may remain of'about the same di- 'mensions as described. in connection with the vibrator of Figs. 3 and 4, the thickness of the individual strips' being reduced about one half so that the complete vibrator unit has about the same dimensions as the two-layer vibrator unit for a hearing-aid vibrator described above.

A completely assembled bone vibrator as shown in Figs. '6 to 8 is about 1%" long, '3/4" wide, and thick, being small and suitable for inconspicuous wear back of the ear of the user, with the button held underv slight pressure against the mastoid bone to permit transmission of vi- I brations from the vibrator arm in the interior to the bone structure. This pressure does not materially displace the vibrating unit inside the .casing vfrom its neutral position and does not disturb its free vibrations. The Weight of the crystal portions of the vibrator is about 21/2 grams, the Weight of the additional weight attached to the vibrator bar is about 31/2 grams, and the total vibrator with'the casing weighs about 18 grams, being thus light and pleasant to wear.

Upon excitation of the electrode sheets with electric sound-frequency oscillations of about 10 volts produced by speech or music, the piezo-electric forces impart to the projecting crystal bar a vigorous vibratory bending action causing the weighted end-of the bar to vibrate with a substantial` amplitude, the amplitude of the vibrations decreasing in the direction toward the clamped nodal portion of the bar. The contact button carried by the lower portion of the bar is thus actuated by the vibration of the portion of the bar on which it is held, and imparts to the bone structure, with which its outer surface is in contact, vibratory energy corresponding to the vibrations of the crystal bar. The coupling of the bone structure to a point of Athe vibrating crystal bar relatively remote from its free end, and disposed riear to the nodal region, secures a better match between the impedance ofthe bone structure and the impedance of the part of the bar coupled to the bone structure for low frequency vibrations than could be obtained by coupling the bone structure tothe end portion of the vibrating crystal bar. -By locating the button at a portion of the bar at which the most effective impedance match for low frequency vibrations is obtained between the bone structure and the vibrator unit, an optimum condition of energy transfer from the bar to the bone structure is obtained, enabling imparting of sufficient vibratory energy, including ample low frequency energy, to secure good reproduction of, sounds of the speech and musical range. The transfer of low frequency vibrations is further increased by the additional weight attached to the crystal vibrator bar, materially supplementing the improved ability of the vibrator unit to impart low frequency vibrations to the bone structure.

The advantageous features of coupling the load that is tobe vibrated to a portion of the vibrating crystal unit having a smaller vibrating amplitude than the vibrating end portions of the 'vibrator unit, and ,the weighting of the vibrating portion part of the piezo-electric crystal vibrator unit are of great practical importance not only in order toenable construction of miniature vibrator devices capable of imparting sufficient low frequency vibrations, sch asare required in connection with bone-conduction hearing-aids, but are also of. great advantage" in' other flelds using piezo-electric vibrators for driving loud speaker f er of low frequency sound vibrations. A coupling' Aby connecting diaphragms, telephones, phonograph recorders, and like devices.

1n Fig. 11 is shown a loud speaker driven by a piezo-electric vibrator unit and arranged in accordance with the broad principles of the inven- 5 tion described above. It comprises a heavy vibrator housing held on the top of a heavy conical base The front wall of the casing has a circular opening ||2 over which is attached l the flange ||3 of a cone bracket ||4 carrying on a circular rim ||5 the forward end ||6 of a cone diaphragm ||1 by means of a flexible annular fabric strip ||8v permitting forward and backward movement of the cone during vibrations. Within the casing I I0 back of the opening l2 is mounted a vibrator unit in the form of a bender of Rochelle salt crystal material constructed like the bender shown in Figs. 3 to 5, but considerably larger in' size. It may, for instance, Acomprise two crystal bars |2| and |22, 20 each about 5" long, 11/2" wide, and 1/8" thick' assembled with two outer electrode sheets |23 and an intermediate electrode. sheet |24,l and clamped at the lower end within a. clamp |25 constructed like the smaller clamp of Figs. 3 to 5. 'I'he clamp |25 is attached to the bottom wall |26 of the casing by bolts |21, or in some other suitable way, so that the weight of the ,clamp |25 and the weight of the. casing attached to it act as a heavy mass definitely fixing in space .the clamped lower end of the bender unit |20. A weight |28 is attached to the upper end of the bender unit |20, being constructed like the corl projecting bender unit |20 at a point lying a small distance above the clamp |25 at, which a good impedance match is obtained with cone for transrod |30 extending from the coupling clamp |20 is attached to the center of the cone ||1 and couples the cone to the bender. l

Electrical oscillations are supplied to the benderl the electrode sheets |23 and |24 thereof, like in the arrangement shown in Figs. 3 to 5, to leads |3| extending from an electric sound-frequency oscillation source, such as the output circuit of an audio frequency ampler. By coupling the cone to an intermediate point of the crystal vibrator bar and the addition of weight to it, a much smaller vibrator unit than required in the prior art constructions will produce ix such speaker a large outputv rich -in low frequency vibrations and securing natural reproduction of speech and music. y

In' Figs. 12 and 13 is shown a phonograph recorder head made in accordance with my invention. At the end of a horizontally mounted recording arm |40, carrying in its interior the 60 y conductor leads |4| from a source' of, sound#v plying oscillation to its electrode sheets. At an intermediate point of the bender bar, not far from the clamp |44, there is provided a coupling clamp |46 similar to the coupling clamp 10 and y.|29 of Figs. 8 and 11. One of the clamping members has on its lower side a mounting for re-` ceiving and clamping a stylus carrier |48 to cut 75 is connected to the center of the diaphragm |53 supporting member of metal a groove in a phonograph recording disc |49. A housing |50 in the form of a tube with an opening |5| for permitting downward projection of the stylus |48 encloses the bender unit. In operation, the record disc |49is rotated4 and the sound-frequency oscillations are impressed upon the bender crystal by means of the leads |4|, imparting to the bender a vibratory motion. By using a weight |45 on the end of the vibrator and coupling the stylus |48 to an intermediate portion of the crystal bar having a good irnpedance match with the cutting stylus load |48, the bender imparts to the cutting stylus |48 a much larger amount of Ilow frequency energy than possible otherwise, enabling the construction of small record cutters capable of cutting records of low frequency sounds.

In Fig. 14 is shown a telephone receiver having a diaphragm |53 for reproducing sound and driven by a Rochelle salt crystal bender |54 in accordance with my invention. The diaphragm |53 may be in the form of a circular thin metal sheet held at its edges between two washers |55 which are clamped to a shoulder |51 of an enclosing casing |58 by an inward projection |59 of the cover |60. The bender |54 is made of two crystal strips |62, |63 united to each other and clamped at the lower end by a clamp |64 like the bender of Figs. 3 tc 5. The bender unit may be very small, for instance, about long, 1A" Wide, and 115 thick. The clamp |64 is at-A tached to a heavy metal plate |65, that is secured to the telephone casing by means of screws |61. The bender has attached to its free end a weight |68, and at its intermediate portion it has attached to it a coupling clamp |69 which by a coupling rod |10, the several elements being constructed similar to the loud speaker of Fig. 11. By impressing oscillatory sound-frequency electric oscillations'on the crystal electrodes through conductors of a cord 1| connected to the electrode sheets as described before, the little bender |54 is set into vibration to vibrate in accordance with the impressed oscillations. By reason of the coupling of the diaphragm to an intermediate point of the bender bar, the impedance of which is wellxmatched to the impedance of the diaphragm, and the weighting of the vibrating crystal bar, this small and simple'vibrating structure will readily supply 'enough low frequency vibratory energy as well as suircient high frequencyenergy to secure good reproduction of speech and music.

The improved utilization of piezo-electric vibrator units by matched coupling to the vibrating piezo-electric member and by weighting the member is not conned to bender type vibrators, but is applicable to other types of piezo-electric vibrating units. In Figs. 15 and 16 there is shown a loud speaker cone driven by an axial twister unit in accordance with my invention. A twister unit |15, made of two rectangular crystal plates |16, |11 cut from a Rochelle salt crystal like the plate 20 of Figs. 1 and 2, and united' to each other, is provided with exterior electrode sheets |1 8 and an. intermediate electrode sheet 19 at their junction surface, as described before. The crystal unit may measure; for instance, 41/2 X 41/2" x One corner |80 ofv the crystal unit has its edges clamped between a heavy |8| and a clamping block |82 engaging the edges of the corner of the lcrystal unit for a substantial length to x the position of the corner portion in the space and prevent its vibration when excited by potentials appliedto the electrode sheets. To secure uni-A form compression of the clamped portion of the crystal, strips |83 of yieldable insulating material are interposed at the clamping surfaces. The' weight attached to the end of the bender unit 56 of Figs. 6 and 7. -The supporting clamping member |8| is provided at its bottom with a heavy base plate |81which is secured by bolts |88 to the bottom side |89-of a casing |90 enclosing the vibrator unit. Cords 9| imbedded in channels within the supporting member |8| provide insulated connections to the pair of outer electrode sheets |18 and theintermediate electrode sheets/|19, respectively, to permit excitation of the crystal plates of the twister.

Like in Fig. 11, the casing |90 has an opening |93 against which is mounted a flange |94 of a cone bracket |95 supporting the front edge of cone |96.

To transmit the vibrations from the twister unit |15 to the cone |96, there is provided a clamping frame |91, showniin cross section in Fig. 17, comprising a pair of bars |98 held on opposite sides of the twister by spacers |99 and secured to each other by bolts 200, the bars |98 carrying at their center clamping blocks 20| engaging from opposite sides an intermediateportion of the twister 202, with intermediate resilient layers 203 of libre, for instance, serving to uniformly distribute the pressure 'of the clamping blocks over the crystal surface. The front i bar of the clamping frame |91 has mounted thereon a coupling rod 204, the other end of which is adjustably attached to the center of the cone |96. A

To operate the loud speaker, sound-frequency oscillations from an audio frequency amplifier are impressed through cords |9| on the electrode sheets |18 and |19 of the two crystal plates. Because of the clamping of one corner portion of the twister, a strong vibratory bending movement is imparted to the upwardly .projecting portion 2|0 of the twister lying opposite the clamped corner and, to a lesser degree, to the two lateral corners 2| of the twister. Through the use of the weights attached to the three vibrating corners 2|0 and 2| the twister vibrates with a substantial amount of low frequency vibrations-which it would not have without the additional weights. By coupling the cone to a point of the twister lying at a distance from the freely vibrating end portion of the crystal plates, and near to the nodal portions, the impedance of the conc may be matched to a good degree with the impedance of the effective twister portion to secure a higher transfer of low frequency vibrations to the cone and production of more low frequency sound vibrations by the cone than would be possible if the outer vibrating edges of the twister y' plate were used for coupling the twister to the cone.

Another application of the principles of the present invention in connection with a twister drive is shown in Figs. 18 and 19 in connection with a phonograph record cutter. At the end of a horizontally mounted cutter arm 220 is provided a relatively heavy supporting member 22| against which a twister unit 222 similar to that described in connection with Figs. 15 and 16, but smaller in size, is clamped along the two edges of one of its corners by means of a clamping plate 223 secured to the clamping support by screws 224, resilient layers 225of nbre or rubber, being interposed at the clamping surfaces. The electrode sheets 226 and 221 of opposite polarity are connected to a pair of conductor leads 228, leading lthrough a hollow channel in the supporting member 220 to a sound frequency source of electric sound-frequency oscillations for imparting a vibratory bending movement to the unclamped exposed portion of the twister, the biggest amplitude of the twister being at the corner Iportion 229 opposite the clamped corner portion thereof. By attaching a weight 230 of lead or the like, as described before, to the corner 229 of the twister, its vibrations are increased in the low frequency range.

A coupling frame 23| made similar to the coupling frame |91 has two of its contact members 232 clamped through intermediate flexible layers to an intermediate portion 233 of the twister between its free vibrating corner 229 and its clamped corner, the clamping frame carrying on two rigid arms 234 a cutter mounting 235 to which a cutter 23B acting on a record 231 may be secured. The clamping frame may be additionally supported by two resilient strips 238 which are attached at their ends to the twister clamp 22| and to the clamping frame 23| and arranged to permit lateral vibration ofthe frame 23| when actuated by the vibration of the twister through the clamping contacts 232.

Upon energization of the electrode sheets 22.6 and 221 of the twister 222 Vfrom a source of electrical sound-frequency oscillations through the lead 228, a vibratory motion having an abundance of low frequency vibrations will be imparted to the twister plate by the action of the weighted corner 229 of the twister unit, and by matched coupling of the cutter head to an intermediate portion of the vibrating twister unit will be secured effective transmission of the low frequency vibrations from the twister unit to the cutter en abling the cutter to produce a record that will give good reproduction of the low frequency range of speech and music. Y

The invention described in connection with the exemplications described above enable utilization of piezo-electric crystal vibrators to produce and deliver substantial amounts of low frequency vi- `bratory energy to sound producing devices in a much simpler way and to a much greater extent than heretofore thought possible. This is achieved by coupling the load to which the vibrations are to be imparted to va portion of the vibrating crystal unit that matches the impedance of the load to a much larger extent than the portions of the vibrator having the maximum vibration amplitude, and by adding weight to the vibrating portions of the vibrating crystal unit which causes an increase of the low frequency vibration output of the vibrating unit, compared to its output when it vibrates under the same conditions without-the additional weight, and to a still greater degree by the combined use of the l two effects.

of the invention.

I claim: 1. In a piezo-electric broad construction commensurate with the scope vibrator device for supplying mechanical vibratory energy to a vibratory load comprising a vibrator member of piezoelectric substance having a nodal portion undergoing negligible movement during vibration, electrode means for impressing an electric oscillatory field on said substance for imparting to said vibrator member a vibratory motion lrelative to a portion thereof, means actuated by a portion of reduced amplitude on said member lying intermediate a nodal portion and the portion of maximum amplitude thereof for imparting vibratory energy from said member to a vibratory load, and a weight of a substance of greater specic weight than said piezo-electric substance attached to the vibrating portion of said member.

2. In a piezo-electric vibrator device for supplying vibratory energy to a vibratory load, a vibrator member of piezo-electric substance having a nodal portion undergoing negligible movement during vibration,l electrode means for impressing an electric oscillatory field on said sub. stance -for imparting to said vibrator member a vibratory motion relative to a portion thereof, means for coupling to a vibratory load an intermediate portion of said vibrator member lying closer to the nodal portion than the portion of maximum amplitude of said member, and a weight greater than the weight of the piez'oelectric substance of said member attached to the vibrating portion of said member having -greatest amplitude.

3. In a piezo-electric vibrator device, one or more pairs of layersl of piezo-electric crystal substance united to each other along their faces to constitute an integral crystal unit, electrode layers in contact with the faces of said crystal layers for impressing oscillatory electric fields across a pair of layers alternatelyl inducing in each layer an expanding force restrained by a contracting force induced in the adjacent layer impartling to the unit a vibratory bending movement,

means confining a nodal portion of said unit against vibratory movement, means mechanically coupled to an intermediate vibrating portion of said crystal unit lying closer to said nodal portion than the portions of maximum amplitudeof said unit'to derive vibratory energy from said unit and impart said energy to an external load, and a weight of a substance of greater specific weight than said piezo-electric substance attached to the vibrating portion of said unit.

4. In a piezo-electric vibrator device for supplying vibratory energy to a vibratory load, one

or more pairs of layers of piezo-electric Rochelle salt crystal substance united to each other along their faces to constitute an integral crystal unit, electrode layers in contactwith the faces of said crystal layers for impressing oscillatory electric fields across a pair of layers alternately inducing in each layer an expanding force restrained by a contracting force induced in the adjacent layer imparting to the unit a vibratory bending movement, means mechanically coupled to an intermediate vibrating portion of said crystal unit lying closer to said nodal portion than the portions of maximum amplitude of said unit to derive vibratory energy from said unit and impart said energy to a load, and a. weight of a substance of greater specific weight than said piezo-electric substance attached to the vibrating portion of said unit.

5. In 'a piezo-electric vibrator device, a layer of piezo-electric crystal substance, electrode means for impressing oscillatory electric fields constitute an integral brator of substantial said piezo-electric substance across the thickness of said layer imparting thereto alternating forces tending to longitudinally deform said layer, means restraining said layer against longitudinal deformation and imparting under the action of said forces a vibratory bending movement to said layer relatively to a nodal portion thereof, and a weight o1 a substance of greater specific weight than said piezoelectric substance and greater weight than about half the weight of said layer attached to the vibrating portion of said crystal layer.

6. In a piezo-electric vibrator device, one or more pairs of layers of piezo-electric crystal substance united to each other along their faces to crystal unit, electrode layers in contact with the faces of said crystal layers for impressing oscillatory electric ields across a pairof crystal layers inducing alternately in each of said layers opposite mutually restraining forces imparting to said unit a vibratory movement, and a weight greater than the weight of the piezo-electric substance of said unit attached to the vibrating portion of said unit.

7. In a piezo-electric vibrator device, one o r more pairs of bars of piezo-electric crystal substance united to each other along their faces to constitute an integral crystal unit, electrode layers in contact with the faces of said crystal bars for impressing oscillatory electric elds across a pair of bars alternately inducing in each bar an expanding force restrained by a contracting force induced in the adjacent bar imparting to the unit a vibratory bending movement, and a weight of a substance of greater specific weight than said piezo-electric substance having a weight greater than half the Weight of said substance attached to the vibrating portion of said unit.

8, In a piezo-electric device for imparting mechanical vibrations to a load, a vibrator comprising a member of piezo-electric substance, supporting means restraining one `part of said Vibrator and supporting' another part of said vimass in a oating vibrating condition, electrode means for impressing electrical oscillations of said substance to produce a vibratory motion between the restrained an'd the oating parts of said vibrator, and coupling means for coupling an intermediateportion of said vibrator disposed between the restrained and oating parts ofthe vibrator to a load, the floating parts of thevibrator extending beyond said coumass forces transmitting vibratory energy to said load.

9. In a piezo-electric device for imparting mechanical vibrations to a load, a vibrator comprising a member of piezo-electric substance, supporting means restraining one part of said vibrator and supporting another part of said vibrator in a oating condition, electrode means for impressing electrical oscillations of said substance to produce a vibratory motion between the restrained and the floating parts/of said vibrator, and means for coupling an intermediate portion of said vibrator disposed between the restrained and iioating parts of the vibrator to a load, the floating part of the vibrator extending beyond said coupling portion having a substantial mass including a body of greater specic weight than for producing forces ytransmitting vibratory energy to said load.

10. In a piezo-electric device for imparting mechanical vibrations to a load, a vibrator comprising a layer of piezo-electric substance, supporting means restraining one part of said vibrator and supporting another a floating vibrating condition, means including' electrodes for impressing on said layer electric oscillations inducing in said layer longitudinal deformation forces producing a vibratory bending motion between the restrained and floating parts of said vibrator. and coupling means for coupling to a vibratory load an intermediate portion of said vibrator disposed between the restrained and floating parts of the vibrator to a load, the floating part of the vibrator extending beyond said coupling portion having a substantial mass for producing by the vibratory action of its mass forces transmitting vibratory energy to said load.

1l. In a piezo-electric device for imparting mechanical vibrations to a load, a vibrator comprising a layer of piezo-electric substance, supporting means restraining one part of said vibrator and supporting another part of said vibrator in a oatingcondition, means including electrodes for impressing on said layer electric oscillations inducing in said layer longitudinal deformation forces producing a vibratory bending motion between the restrained and floating parts of said vibrator, and means for coupling an intermediate portion of said vibrator disposed between the restrained and floating parts of the vibrator to a load, theloating part of the vibrator extending beyond said coupling portion having a substantial mass including a body of greater specic weight than said piezo-electric substance for producing forces transmitting vibratory energy to said load. v

12. In a piezo-electric device for imparting mechanical vibrations to a load, a vibrator comprising a member of piezo-electric Rochelle salt crystal substance, supporting means restraining one part of said vibrator and supporting another part of said vibrator in a floating vibrating condition, electrode means for impressing electrical oscillations of said substance to produce a vibratory motion between the restrained and the floating parts of said vibrator, and coupling means for coupling an intermediate portion of said vibrator disposed between the restrained and oating parts of the vibratorto a load, the oating part of the vibrator extending beyond said coupling portion having a substantial mass for producing by the vibratoryV action of its mass forces transmitting vibratory energy to said load.

13. In a piezo-electric device for imparting mechanical vibrations to a load, a vibrato;l comprising a member of piezo-electric Rochelle salt crystal substance, supporting means restraining one part of said vibrator and supporting another part of said vibrator in a floating condition, electrode means for impressing electrical oscillations of said substance to produce a vibratory. motion between the restrained and the oating parts of said vibrator, and means for coupling an intermediate portion of said vibrator disposed between the restrained' and,fioating parts of the vibrator to a load, the oating part of the vibrator extending beyond said coupling portion having aisubstantial mass including a body of greater specic Weight l than said piezo-electric substance for producing.

forces transmitting vibratory energy to said load. f

EMMANUEL CHRIST NICHOLIDES.

part of said vibrator in

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