US1831829A - Piezo-electric translating device - Google Patents

Description

Nov. 17, 1931. A. A. THOMAS PIEZO ELECTRIC TRANSLATING DEVICE Original Filed March '24,. 1925 INVENTOR Patented Nov. 17, 1931 UNITED STATES PATENT OFFICE I ADOLPH A. THOMAS, OF NEW YORK, N. Y., ASSIGNOR 'IO WIRED RADIO, IlSTC OF NE YORK, N. Y., A CORPORATION OF DELAWARE I rmzo-nrno'rnrc TRANSLATING DEVICE Original application filed March 24, 1925, Serial No. 17,900. Divided and this application filed February 17, 1928. Serial No. 254,998.

My invention relates to means and methods for receiving and transmitting variable electric impulses by the use of so-called piezoelectric crystals. The piezo-electric devices and systems of my invention are particularly useful for translating feeble electric impulses into audible sound. For'this reason my invention finds special application in radio c1rcuits, although not limited to this field of utility.

It has been known for many years-s1nce about 1880-that certain crystals, when subjected to pressure in certain directions, become electrified; that is to say, they become a source of electric potential and produce a 'flow of current when properlyconnected in circuit. The reverse of this phenomenon has also been observed namely, when such a crystal is subjected to an electric strain, a change in the dimensions of the crystal takes place. In other words, it undergoes a slight expansion or contraction. Among substances exhibiting these peculiar properties, are or stals of turmaline, quartz, Rochelle salts, oracite, fluor-spar, and perhaps others. These crystals are known as piezo-electrlc crystals, and the electricity they produce is called piezo-electricity, which means electricity caused by pressure.

In the present invention, I make use of the foregoing properties of piezo-electric crystals to produce novel devices and systems for transmitting and receiving feeble electric currents or impulses of variable character and amplifying them sufiiciently' for acoustic reproduction. In carrying out my invention, I employ suitable piezo-electric crystals in the construction of telephone transmitters and receivers, radio loudspeakers, and generally in electric circuits in which a piezo-electric crystal is subjected to mechanical stresses to produce electric oscillations, or is subjected to electric stresses to control a working circuit of principles of my invention, so that those tion;

skilled in the art may fully understand the same. In these drawings 7 Fig. 1 is aside view, partly in section, of a telephone transmitter embodying my inven- Fig. 2 is a front view of Fig. 1, approximately on section line 22; a

Fig. 3 is a side view of a modified form of telephone transmitter or receiver having a piezo-electric crystal along an axis at right angles to the plane of the diaphragm;

Fig. 4 is a front view of Fig. 3,'with the diaphragm omitted, for clearness; and

' Fig, 5 shows diagrammatically a radioreceivmg circuit containing a piezo-electric crystal for operating a microphone or other resistance device in the output circuit.

Before proceeding with a detailed description of the various embodiments illustrated in the drawings, I want it understood that the figures are for the most part merely diagrammatic, and have been made as simple and clear as possible. This is particularly true as regards the representation of a piezo-electrio crystal, which I have shown in a conventional form to indicate any kind or form of piezo-electric crystal suitable for use in this inventon;

Referring to Figs. 1 and 2, a piezo-electric crystal K is firmly supported in any practical way, as between a pair of spring plates 1 mounted on a base 2. If desired, a bolt 3 or similar fastening member may be used to hold the crystal rigidly clamped between the plates. The member 3, if metal, should be insulated from the metal plates 1. The'crystal is so supported that at the back it rests or bears against an upstanding rigid wall 4 firmly mounted on the base 2 by screws 5 or otherwise. The wall or abutment 4 is preferably adjustable on the base by meansof elongated slots 6, through which the bolts 5 pass.

' On the wall 4 are mounted pins 7 which arry suitable conducting springs 8 in contact? with the opposite ends of the crystal. The pins 7 also act as binding posts for connecting wires 9, by which the crystal is connected in the desired circuit.

In front of crystal K is mounted n acoustic diaphragm 10 held in a frame diagrammatically indicated by 11. To the center of the diaphragm is secured a pressure plate or disk 12 arranged to bear against the adjacent face of the crystal.

The operation of the device shown in Figs.

land 2 will be clearly understood Without further description. It is only necessary to say that the vibrations of the diaphragm 10, due to sound waves impinging upon it, produce varying pressures in the crystal K and these pressures cause the crystal to generate electric currents, in accordance with the degree of pressure exerted at any particular moment. The ends of the crystal K, which are in contact with the springs 8, may be covered with tin foil or other conducting material, in order to secure a good electrical contact between the crystal and the springs. It will be understood that the rear abutment 4 is sufliciently strong and rigid to. remain .immovable (or practically so) under the pressures exerted on the crystal-by the disk'12 of the vibrating diaphragm. By making the abutment 4 adjustable toward and from the diaphragm 10, it is easy to secure the correct initial or normal contact pressure between the diaphragm and the crystal.

Figs. 3 and 4 illustrate, more or less diagrammatically, an arrangement in which the crystal is mounted in a position at right angles to that shown in Figs. 1 and 2. The crystal K of.Figs. 3 and 4 is firmly clamped between a pair of spring plates 13 mounted on a base 14. The supporting plates 13 are preferably ofi'set'at 15 to provide shoulders jor receiving the bottom face of the crystal. The rear end of crystal K rests against an upstanding wall 16 mounted on the base 14 by screws 17 or'in any other practical way. The wall' 16 forms an immovable abutment for the crystal. The forward end of crystal K is in contact with the center of an acoustic di hragm 18, which is properly mounted in a ame diagrammatically indicated at 19.

The crystal K is included in circuit by means of conductors 20-, which are attached to the conducting plates 13 in any convenient way. The abutment 16, like the abutment 4 of Figs. 1 and 2, may be adjustable with respect to the diaphragm 18, so as to secure the correct normal position of the crystal K with respect to the diaphragm 18 and the abutment 16.

As the operation of the device asshown in Figs. 3 and 4 is similar to that of Figs. 1 and 2, nothing further need be said on this point. The device of Figs. 3 and 4 may be used as a receiver or as a transmitter.

In Fig. 5 I have diagrammatically shown a crystal K rigidly mounted at one end in a suitable support 21, which is held rigid. The opposite end of crystal K is in contact with the movable disk or diaphragm 22 of a microphone M, which may be of any approved orm or structure. It will be understood that the microphone M is illustrated in a purely diagrammatic way and is intended to represent any suitable resistance device adapted to be varied by varying pressures of the crystal K against the movable diaphragm 22. The microphone M is connected in a circuit 23, which has a battery B and a primary coil 24. The secondary coil 25 is intended to represent a part of whatever mechanism is operated or controlled by variable currents in circuit 23. This will be understood by those skilled in the art without further description. The crystal K is included in a circuit 26. For this purpose I may use a pair of conducting plates 27 held in intimate electric contact with opposite faces of the crystal, as diagrammatically indicated in Fig. 5. The circuit wires are attached to the conducting plates 27 in any practical way. The circuit 26 is inductively or otherwise connected with a detectorcircuit 28, which receives electric oscillations from an antenna 29.

As the operation of radio-receiving cir cuits is generally well understood b radio engineers, I need only say, in spea ing of the operation of Fig. 5, that the variable voltages induced in circuit 26 by the receiving oscillations in circuit 28 subject crystal K to variable electric strains or pressures, and consequently the crystal undergoes slight expansion and contraction in the direction of its longitudinal axis. That is to say, the crystal moves toward and from the diaphragm 22 of the microphone in a vibratory manner, according to the electric oscillations of the circuit 26. These mechanical move ments of the crystal 22 vary the resistance of the microphone M and thereby produce current variations in the circuit 23, which is normally supplied with substantiall constant potential from the battery B. T e current variations in coil 24 induce corresponding variations in the secondary coil 25, which may operate a loudspeaker or any other electrical device. The vibrations of crystal K produce variations in the resistanceof the microphone M in such a way that the electrical effect of the crystal movements is amplified in the circuit 23, and therefore in the coil 25.

When I speak of a piezo-electric crystal, both in the description and in the claims, I do not necessarily mean a complete crystal, but I include any part or section of a crystal that ma be found to be operative. For instance, a p ate, rod or bar may be out from a crystal and used in constructing my invention. The dimensions of such a crystal section will depend upon the kind and size of crystal used. Furthermore, the direction of the most effective mechanical and electrical strain in the crystal will vary with different kinds of crystals, so that the best way of mounting the crystal is often a matter of ex erimentation, which may readily be carrie out by those skilled in the art. When I, therefore, in certain claims refer to opposite ends of the crystal being in contact with movable members, I mean any two contact faces or points of the crystal between which physical movements of the crystal will take place.

Although I have explained my invention by means of certain constructions and ar rangements, I wish to be understood that I have done so merely by way of illustration, and not as a restriction or limitation of my invention. It is obvious that the various novel features of my invention may be mechanically embodied in other ways and by other means than herein set forth.

This application is a division of my copending case filed March 24, 1925, Serial Number 17,900, and is filed because of an ofiicial requirement of division which made it 2 impossible for the applicant to present the following claims in his original case.

I claim as my invention:

1. The combination of a base, a air of spaced members supported on said ass, a

piezo-elec-tric element arranged between said members, and a third member supported transversely between said pair of members and passing, through said element.

2. The combination of a base, a pair of spaced spring plates supported on said base, a piezo-electric element arranged between said plates, and a bolt supported crosswise by said plates and passing through said element.

as ADOLPI-I A. THOMAS.

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