US1788405A - Composite piezo-electric acoustic device - Google Patents

Description

|| I J1 I INVENTOR LEXRNDER MclEAN NIEGLSON.

y kd; ATTRNEY A. MCL. NlcoLsoN COMPOSITE Enzo-ELECTRIC AcousTIc DEVICE Filed Jan.

Jan. 13, 1931.v

Patented Jan. 13, 193i UNETED STATE maaar ortica i ALEXANDER MCLEAN NIGOLSON, F NEW YORK, N. Y., ASSIGNOR, BY MESNE ASSIGN- MEN TS, T0 FEDERAL TELEGRAPH COMPAN, A, CGRPORATION Ole"` CAJliIE'RlW11Al COPQSITE PIEZO-ELE'CTRIC ACOUSTIC DEVICE Application filed January 11, 1927.. Serial No. 160,358.

This invention relates to a piezo-electric crystal device, and more particularly, to an acoustic device, adapted for `the conversion of liuctuating electromotive forces into sound @y Waves, and vice versa. 1t has been known for some time that crystals of certain substances, such as Rochelle' salt, quartz, tourmaline, and the like, produce anelectromotive force if subjected to physical stress or l@ movement, and conversely, produce physical stresses or movement in response to the impression of an electromotive force upon them. In my copending application, Serial No.

155,899, filed Dec. 20th, 1926, entitled Composite piezo-electric torsion device, I have shown and described a composite piezo-electric crystal device, comprising a lmultiplicity of chemically and optically similar heterogeneou piezo-electric crystals physically secured is to a single entity, and arranged so that the piezo-electric eiects of the individual component crystals may be integrated.

I have discovered that such a composite piezo-electric device as I have described'in the said application may be utilized in connection With an acoustic diaphragm to produce an acoustic device such as a loud speaker, ora microphone, and as a matter-of fact, when properly constructed and arranged, will produce results never before obtained. y

' It is an object of this invention to provide a piezo-electricacoustic device of high quality and high sensitivity.

It is still a further object of this invention to provide a piezo-electric acoustic device of high yQuality and high sensitivity at a relatively low cost.

It is still a further object of this invention to provide a piezo-electric acoustic device of highv quality and high sensitivity and characterized by extreme simplicity and re liability, at a relatively, low cost. i

It is still a further object of'this invention to provide a piezo-electric acoustic device of high quality and of high sensitivity, in which a piezo-electric element ot any desired size and shape may beprovided without the exv pense and Wastage involved in the cutting or grinding of crystals to the desired size and shape.

It is still a further object of this invention I to provide a generally improved device of the class described. Still further objects of this -invention will 'be apparent from the specification. i

,forth with particularity in the appended claims. My invention itself, however, both as to its fundamental principles and as to its practical application, will be best understood by reference to the specification and'accompanying drawing, in which:

Fig. l is a front elevation of one form o piezo-electric 4acoustic device according t9 my invention, showing the cover removed and the diaphragm inplace.

Fig. 2 is a top plan view of another form thereof.

Fig. 3 is a front elevation thereof showing the cover in place. 4

Fig. 4 i-s a diagrammatic view of the crystal structure, which may be utilized in the piezoelectric element, and,

i Figs. 5-8 arediagrammatic views normal to the c-axis, of additional forms of crystal structure which may be utilizedrin the piezoelectric crystal element.

Fig. 9 is a detail showing one method ot mounting the diaphragm on the cover.

In accordance with my invention, ll select a multiplicity of piezo-electric crystals to be assembled into a composite device, in the manner shown and described in my copending ap'- plication referred to above. rlhe selection, as therein statedyis preferably made by choosing crystals which are chemically yand opti-l cally similar. For example, 'I may selecta number of quartz crystals, being careful to 'separate the crystals of deXtro-asymmetry was In the case of other hemihedral crystals, which occur only in right-handed or lefthanded forms as the case may be, such for ex- I ample as Rochelle salt, it is not necessary to separate the forms, because they do not occur concurrently.

After the component crystals have been selected, I may then proceed to build up a composite structure by arranging the crystals in the desired fashion, being careful to orient each crystal properly with respect to the 0-aXis so that the piezo-electric effects of the various component crystals may be integrated, as more particularly described and claimed in my copending applications entitled Composite piezo-electric crystal de vice, Serial N o. 155,898, and Orientation of component crystals in composite piezo-electric devices, Serial No. 155,902. crystals of like chemical and optical form are always analogous to either a right-handed screw thread, or a left-handed screw thread, depending on whether the crystals are dextro or laevo asymmetrical, it suffices merely to arrange the crystals with their c-axes parallel and with symmetrical electrodes, for applying or drawing electricity of the proper sign from the component crystals.`

The electrodes may comprise plates of lmetal foil secured to the crystals at proper points forming mechanically and electrically opposite poles. For example, one electrode may comprise an equatorial belt of conducting material forming a loop around the crystal in a plane normal to the c-axis, and the other electrode may be attached to the basal plane of the crystal, as more par'- ticularly described in the applications referred to above.

Observing this requirement, the component crystals may be assembled into a composite structure in a number of ways. Referring i now more particularly to Fig. 1, I have shown a number of crystals 1, 2, 3, 4, etc., assembled into a composite cylindrical structure, in which there are arranged a number of crystals in line with the c-axis, which is shown as -a dot `and dash line. The component crystals herein shown are arranged 1n any desired manner so as to build up a composite structure of the desired dimensions, and various sized crystals may be juxtaposed in a manner more or less analogous to that of a stone mason in fashioning a wall from stones of different size and shape.

Thevarious component crystals ma be secured together,l physically into a smgle entity in any desired manner, but I prefer to use a. cement of the, same elastic properties as those of the component crystals, so' that stress Waves `will be transmitted to all of the components. In the case of Rochelle salt crystals, I prefer to use what I termA Rochelle salt cement or a melt of Rochelle salt which has been melted ata temperature conby melt or cement if desired. A cap or stress distributing member 32, adapted to embrace the other end, is suiliciently rigidly secured thereto so that an acoustic diaphragm may be attached thereto so as -to be vibrated by torsional vibration of the device, or so as to impart vibrations or stresses to the device. In addition, a plurality of mechanical clamping means, such as tie rods 50 and 51, may be provided passing through the base and cap, threaded to receive nuts 52 and 53 by which the crystal structure may be put under compression.

The stress plate 32 may include a metal strap 58 adapted to snugly embrace the upper end of the composite crystal device, and to it is secured an acoustic diaphragm such as a cone 54, although it will be understood 'that any other suitable type of diaphragm may be substitutedv if desired.

A modified arrangement is shown in Figs. 2 and 3, in which` a `cover 55 is provided for the purpose of sealing the crystal 'device 31 in the base 30, and be sealed therein by suitable packing. The end and sides, if' desired,

of the composite crystal are preferably sealed to the inner side of the cover 50, in any suitable way, as for instance by Rochelle salt cement or melt, in such manner that torsional vibration of the composite crystal carries with it the cover. v

Suitable means for exerting compression on the crystals may be provided, such as tie rods '50 and 51, which may be passed through extensions 60 and 61 provided on the cover, and threaded nuts 52 and 53, by which the desired compression may be obtained.

The acoustic diaphragm 54 will preferably be clamped or otherwise firmly secured to the cover in such a manner that torsional vibration of the cover Acauses substantially recip- .rocatory vibration of the diaphra mand vice more regular'arrangement of thecoi'n' onent crystals. In this instance one row o crystals may consist of crystals 10, 11, 12, and 13',

all arranged with their c-axes parallel, and being arranged in lines normal to the c-aXes.

It Will be understood that a pluralityl of crystals may be arranged also in the same plane with crystals 10, l1, 12, and 13, but normal to the line of those crystals, thereby forming a solid structure in which there are a plurality of crystals arr'anged in lines normal to the c-axis and normal to each other. A-

second layer of crystals 14, 15, and 16 may be disposed above the first layer, and an .additional layer of crystals 17, 18, 19 and 20may be arranged. More layers may be added as desired, with the object oi bringing the composite structure to the dimensions desired,

,corresponding electrodes (shown diagrammatically) being provided whereby corresponding poles on the component crystals may be connected together, as for example by means of leads 21, 22, 23 and 24 connected to main lead 28, on the one hand, and leads 25, 26, and 27, connected to main lead 29.

It will be uderstood that if mechanical stresses be applied to these structures, so as to `torsionally stress the crystals about the c-axis, an electromotive force will manifest itself upon leads 28 and 29, andconversely, the application of an electromotive force to these leads will cause a corresponding stress of the composite crystal, wherebyit will be understood that the structure may operate either as' a motor or generator, and that in either case, the electrical oscillations impressed upon or derived from the crystal device may be amplified, as by thermionic amplitiers, to the extent necessary or desirable.

Referring now to' Figs. 5 8 which are diagrammatic views taken on planes normal to .the c-axis of the component crystals, I have shown additional ways of arranging the various component crystals so that the piezoelectric eiiects of the component crystals may be integrated'. In Fig. 5, it will be noted, the crystals 33 and 34 are arranged in a symmetrical arrangement, the remaining space i being partially or completely lled by the binder such as cement or melt 35.

The arrangement in Figp is symmetrical, comprising` crystals 36--43, and the remaining space being taken by the binder 35 as before. In the arrangement shown in Figf?, the various vcrystals 451, 452, -45n are arranged in a ring, which may be partially or completely filled by the binder 35. The arrangement shown in Fig. 8 is a heterogeneous varrangement of crystals 461, 462, 46,1, o

varying sizes and shapes, the interstices being occupied by the binder 35.

It will be understood that leads may be carried to the individual crystals through the container in any suitable way. For instance, a pair' of terminals may be provided on the base,'such as 60 and 61", and the leads may be .taken ltherefrom internally therethrough in j a manner such as to be entirely contained Within the cover 55, when thesame 'is placed upon the composite device.

Also, WhileI have referred toRochelle salt cement or melt as the binder, it 'will be understood that other substances' such as hard wax, etc., may be used as described in my application referred to above.

lVhile Ihave shown and described certain preferred embodiments of my invention, it 'will be understood that modifications and changes may be made 'Without departingy from the spirit and scope of my invention, as

will be understood by those skilled in the art.

y I claim y l. In piezo-electric acoustic-apparatus hav- -ing a substantially uniformp-frequency'respense characteristic, in combination, a composite piezo-electric devicecomprising a multiplicity .of chemically and optically similar component piezo-electric crystals physically secured into a single entity, said crysf' tals being so arranged that piezo-electric torsional vibration.. of said individual componentsmay be integrated, and an acoustic diaphragm,va band circumscribing said composite device at a point of maximum torsional vibration thereof and means 'for attaching said band to said diaphragm, in a manner such that torsional vibration of said composite piego-electric device effects vibration'` of said diaphragm. v

2. In piezo-electric acoustic apparatus hav- Aing a substantially uniform frequency response characteristic, in combination, a com'` posite'piezo-electric device comprising a multiplicity of chemically and opticall similar component piezo-electric crystals physically ing so arranged that-piezo-electric torsional vcemented into a' single entity, said crystals bev vibration of said individual components may V be integrated, an acoustic diaphragm, and means comprising a band' circumscribing said piezo` ectric device for securing said diaphragm to said device ink such manner thattorsional vibration of'said device causes reciprocatory vibration of said diaphragm.

3. In piezo-electric acoustic apparatus having a substantially uniformv frequency rei sponse characteristic, in combination, a composite piezo-electric crystal device comprising a plurality oi'chemically and optically tion of said diaphragm, and means for applying compression to said device.

4. In a linkage system for mechanically connecting an acoustic diaphragm to a piezoelectric device, a band circumscribing said piezo-electric device at a point of torsional vibration thereof, and means for attaching said band to said diaphragm.

5. In a linkage vs stem for mechanically connecting an acoustic diaphragm to a piezoelectric device comprising a multiplicity of chemically and optially similar component piezo-electric crystals .physically cemented into a single entity, said crystals being so ar- `ranged that piezo-electric torsional vibration of said individual components may be integrated, a band circumscribing said piezo-electric device in a plane of torsional vibrationr thereof and means for attaching said band to said diaphragm.'

6. In a linkage system for mechanically connecting an acoustic diaphragm to a piezoelectric device mounted in a casing in such manner that mechanical vibrations of said piezo-electric device are transmitted to said casing, a band passing around the periphery of said casing, andmeans for attaching said band to said diaphragm.

In testimony whereof I hereunto affix my signature.A

ALEXANDER MGLEAN NICOLSON.

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