US1583417A - Piezo-electric device and method of producing it - Google Patents

Description

May 4 ,1926. 1,583,417

I A. M. NICOLSQN PIEZO ELECTRIC DEVICE AND METHOD (DP PRODUCING IT Filed Feb. 4, 1925 hue/rial": A/examerM Mao/son Patented May 4, 1926. I

qumrnn STAT ALEXANDER M. NICOLSON,

MENTS, T0 WESTERN NEW YORK.

IPIEZO-ELECTRIC DEVICE AND METHOD, OF PRODUCING IT.

Application filed February 4, 1925. Serial. No. 6,862.

To allwhom it may concern:

Be it known that I, ALEXANDER M. Nioon SON, a subject of the King of Great Britain, residing at New York, in the county ofNew York and State of New York, have invented certain new and useful Improvements in Piezo-Electric Devices and Methodsof Producing Them, of which the following is a full, clear, concise and exact description.

This invention relates to vices and method of producing the same, and aims to provide sensitive, eflicient, simple and durable devices of that character, for translating electrical Variations into mechanical force variations, and vice versa, such devices being useful, for instance, in the transmission and reception of telephone currents and the phonographic recording and reproduction of sound waves.

In accordance with the invention a piezoelectric crystal, preferably a Rochelle salt crystal having the composite or hour-glass structure and having orthogonal electric poles, such as is described in my article on Thepiezo-electric effect in the composite Rochelle salt crystal, published in the Proceedings of the American Institute of Electrical Engineers, November, 1919, is provided with electrodes or electrically 'conducting, charge collecting means in contact with the parts of the crystal which are oppositely electrified when the crystal is stressed, one of the charge collecting means being preferably in intimate contact with the interior of the crystal. For example, the means for collecting the charges from the pyramidal poles or hour-glass shaped portions of the crystal may be an electrical conductor 0r conductors within or passing through those portions and cutting various imaginary planes perpendicular to the principal axis of the crystal, that is, planes parallel toand of the crystal, as shown in my copending application, Serial No. 655,800, filed August 16, 1923.

At the place where. this interior electrode or the lead for connecting it in circuit passes through the surface of the'crystal it may occupy a very small portion of that surface, and therefore it is easy to insure that the leakage resistance along the sur-.

face of the crystal from this interior electrode to the charge collecting conductor of piezo-electric delying between the basal planes opposite sign will be maintained high, as for instance, by bringing the interior conductor, or its lead, through the surface of the crystal at a point distant from the conductor of opposite sign, or by bringing the interior conductor or its lead through the surface in an ,insulating tube or covering, or by employing both of these features.

Further, by reason of' the fact that this electrode is within the crystal, intimate contact may be maintained between the electrode and the crystal without any necessity of employing means to make the electrode integral with the crystal.

A better understanding of the invention will be had from the following detailed description in connection with the accompanying drawings in which:

Fig. 1 is a side elevation of a loud speaking telephone receiver embodying one form of the invention;

i Fig. 2 is a front elevation of the structure of Fig. 1; a

Fig. 3. is a cross-sectional view in side elevation along the line 3-3 of. Fig. 2;

Fig. 4. is a perspective of a piezo-electrie crystal of Rochelle salt showing the axes of. the crystal;

Fig. 5 is a front elevation of a crystal having an interior electrode of a different.

form from that shown in Fig. 1;

Fig. 6 is a side elevation of Fig. 5.

Referring especially to Figs. 1 and 2, a piezo-electric crystal 10 having the. composite structure referred to above is mounted n a base 11. The crystal may be produce by methods such as, for instance, those described in the above mentioned A. I. E. E. Patents No. 1,414,370, May 2, 1922, method of making piezo-electrical crystals, and No. 1,438,965, December 19, devices and method of producing the same, or in my copending application Serial No. 756,390, filed December 17. 192A.

Attached to the upper end or upper basal plane of the crystal is an arm .12 which carries a diaphragm 13 to be in response to twisting of the crystal about its principal, or vertical axis. The crystal may be caused to twist by applying anelec-v tromotive force to girdle electrode, 14 and OF NEW YORK, N. Y., 'ASSIGNOR, BY MESNE ASSIGN- ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF publication, in my 1922, piezo-electrie vibrated by arm 12 1 an electrode which is imbeddedin the crystal. Conversely, '-.e1 ectromot1ve" forcemay be generated between these electrodes by twisting the crystal, as for instance by causing sound waves to impinge upon the diapragm 13.

The girdle electrode shown is of the character described in the A. I. E. E publication mentioned above, and also described intheabove mentioned Patent No. 1,438,965.

In aco-rdance with the invention the in ternal electrode 15 preferably comprises a plate conductor, as a metal sheet for example, lying in a plane cutting approximately the middle of the crystal along the a axis and lying parallel to the I) and 0 axes, and extending substantially the whole length and width of the crystal so that it will cover imaginary planes passed perpendicular to the surface and lying between the apexes of the pyramids and-points near the ends of the crystal. The portion of the pyramidal pole lying between any one of these planes and the apex I of the pyramidal pole may be regarded as a pyramidal pole having that plane as its basal plane, and electrode 15' passes through and contacts with a great number of such planes thus collecting the electrical charges appearing on them when the crystal is stressed and conducting such charges to the outside of the crystal by means of the lead 16 connected to or forming a part of the conductor 15, it being understood, of course, that lead 16 may be connected to one terminal of a receiving apparatus (not shown) the other terminal of which may be connected to a lead 17 brought from the girdle electrode 14 of the crystal. When the crystal device is used as a receiver, the source of electromotive force (not shown) from which it is to be operated is connected between leads 16 and 17, and the conductor 15 then acts as a charging means instead of as a collector of electrical charges.

The electrode 15 comprises in accordance with the invention, a flat conductor of area preferably of the same magnitude as that of the back 39, of the crystal. The combination of electrodes covering a large portion of the area of the crystal along a plane parallel to the b and c axes with the crystal per se have been found to form articularly efficient structures for translating electrical variations into mechanical force vibrations and vice versa. This electrode is further preferably of some form designed to have intimate contact with the adjoining crystal surfaces.

One method of imbedding the internal electrode 15 in the crystal 10 might be to separate the crystal, as by sawing for example, along a plane near the middle of the (1 axis of the crystal and parallel to the]; and ,0 axes. After the internal electrode elements 18 and 19 have been secured in place and the lead elements 22 and 23 secured to the electrode elements, in the manner. hereinbefore described, the crystal may be made integral by joining the halves 28 and 29 with a suitable adhesive applied to the edges of the crystal. One cement composition which has been found satisfactory is the Rochelle salt cement disclosed in my copending application, Serial N o. 7 10,? 46, filed September 3.0, 1924:.

The thickness and composition of the particular internal electrode or conductor employed may be considerably varied. Examples of electrodes which have been found satisfactory are thin sheets of metal foil, a layer of mercury, saturated Rochelle salt solution and graphite. -Actual practice has shown that thin metal foil or sheets are especially satisfactory in that they both make intimate contact with the crystal surfaces and are in a solid form in contrast to granular and liquid electrodes. By actual test, it has been found, for example, that lead foil having a thickness of approximately ten mils forms a satisfactory form of internal electrode.

When applying sheets of metal foil, it has been found desirable to apply individual sheets or conductors to each of the separated surfaces of the crystal. Referring to Fig, 3

of the drawings there are shown sheets of metal foil 18 and 19, composed of lead, for example, in intimatecontact with the internal surfaces 20 and 21 of the crystal 10. There is also represented a lead 16 leading outside the crystal which is composed of two sets of conductors 22 and 23, one set, 22, being connected to plate 18 and the other set, 23, being connected to the other plate 19, so that intimate contact can be made with the entire internal electrode surfaces.

Each of these metal foil sheets is prcfer. ably supplied with a thin coating of some material which will act as an adhering medium between the crystal and conductor.

A thin coating of wax, such as beeswax, for example, has been found satisfactory, but it is evident that other material might be used to replace the beeswax.

One means of securing the separte elements 22 and 23 of the lead 16 might be to insert a mass of low melting point metal, such as Woods metal, for example, in a hole 24in the crystal surface and then melting the metal globule 25 around the conductor, as around conductor 22, for example. In this method, it has been found desirable to add additional sheets of metal foil 26 and'27 to cover each of the conductors at the point at which they are sealed or soldered to the crystal.

Another means of securing a connection between a lead and an electrode might be a mass of pliable elastic material, such as softrubher, covered with a pliable electrical conducting material, as lead foil for example, p aced between the individual electrode elements 18 and '19, the lead 16 being inserted between the pliable conducting material andthe electrode, and being held in position-by the pressure of said elastic material.

It has also beenfound desirable to apply an insulating material, preferably in the form of a cement, around the element 16 and where ,it passes through the crystal surface and also on the associated surface of the crystal. A suitable cement has been found to be the Rochelle salt cement referred to above, it being applied to the crystal surface, when desired, in the manner described in my copending application Serial No. 655,800, filed August 6, 1923.

Fig. 5 shows a crystal 10 of the same character as the crystal 10 of Figs. 1 and 3 and having a girdle electrode 14 of the same general character as the girdle electrode 14 of crystal 10; the crystal 10, however has an internal electrode divided into .four parts, 30, 31, 32 and 33, according to the pyramidal poles or hour-glass structure of the crystal. These pyramidal poles are designated 34; and 35 in Fig. 2, and are indicated in the drawing by dotted lines 36 converging toward the seedling 37 from which the crystal is grown. To each of the electrode elements '30, 31, 32 and 33 is secured a lead 38, the method of securing said lead being one, such as described above.

Any number of these individual elements 30, 31, 32, n'iay'be connected in series or parallel to form a composite electrode to be joined to one terminal of a translating device, the other electrode being the girdle electrode 14:; or the girdle electrode may be dispensed with, by connecting elements 30 and 31 through their respective leads to form one composite electrode and connecting elements 32 and 33 through their respective leads to form the other electrode. The action of a crystal having twointernal electrodes instead of one internal and one external or girdle electrode will be more evident from a study of my article in the Proceedings of the American Institute of Electrical Engineers, November 1919, above referred to. From this article it will be seen that the electric poles of the crystal are orthogonal or that the pyramidal poles 34c and 35 are positive when-the remainder of the crystal is negative and vice versa. Series or parallel conductors in contact only with the pyramidal poles, therefore, may be em.- ployed scribed in relation to the structure of Figs.

1, 2 and 3 and sealed in a like manner. While specific examples of internal elecas one electrode \vhile series or paral lel conductors in contact only wlth the other portions of the crystal subsequently trode structures and compositions have been represented herein, it will be understood that the invention is not limited to these specific examples disclosed but it is susceptible of various adaptations and alternative forms in accordance with the appended claims.

That is claimed is:

1. A piezo-electric crystal having an electrode in its interior, said electrode being of a form designed to cover a large portion of the area of said crystal lying in a plane parallel to the plane defined by the b and 0 axes of said crystal.

Q. .A piezo-electric device, comprising a piezo-electric crystal having a pyramida pole, a girdle pole about said pyramidal pole, and a plate electrode in the interior of said crystal. v

3. A piezo-electric crystal having a plate electrode embeddedwithin and surrounded by said crystal.

4. A piezo-electric crystal having a pyramidal pole, and a plate electrode within said crystal and intersecting said pyramidal pole.

5. A piezo-ele'etric crystal having a plate electrode in its interior, said electrode lying in a plane parallel to the plane formed by the Z) and c axes of said crystal.

6. A piezo-electric crystal having a plate electrode therein, said electrode lyingin a plane in the middle'of said crystal along its (1 axis and parallel to the plane formed by its b and@ axes.

7. A piezo-electric crystal-having a plate electrode in its interior, said electrode being composed of metal foil.

8. A piezo-electric crystal having a plate electrode in its interior said electrode being coinposed'of metal foil and having a coating of adhesive material thereon.

9. A piezo-electric crystal having pyram-. idal poles. a plate electrode imbeddcd in said. crystal and intersecting said pyramidal poles, a cavity within said crystal, a mass of electrode inserted between said elements and means for cementing said elements to form an integral structure.

11. A piezo-elcctric crystal having pyramidal poles and being divided/into two elements along a plane perpendicular to the basal planes of said pyramidal poles, and an I electrode inserted between said elements, said electrode comprising metal foil sheets in contact with the ad aCent faces of said elements.

12. A piezo-electric crystal having pyramidal poles and being divided into two elements along a plane perpendicular to the I a f n adhesive material in said-cavity, and a con n basal planes of said pyramidal poles, ,and

i an electrode inserted between said elements,

said electrode comprising two adjacent integral metal foil sheets in contact with the central portions of the adjoining faces of i said elements and extending substantially to I the edges of said faces.

13. The method of producing a piezoelectric crystal device which comprises sawing a crystal in a plane perpendicular to the (1 axis of said crystal, inserting a plate con electric device which comprises sawing a crystal along a plane perpendicular to the (Z axis of said crystal to produce two elements, placing a plate electrode in contact with each of the adjacent faces of said elements, making a cavity in each of said faces, placing conductors in contact with said electrodes, and extending beyond the length of said crystal sealingsaid conductors to said crystal in said'cathodes and joining said elements to form a composite structure.

In Witness whereof, I hereunto subscribe my name this 4th day of February A. 1)., 1925.

ALEXANDER M. NICQLSON.

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