US1848630A

US1848630A - Piezo electric crystal

Info

Publication number: US1848630A
Authority: US
Inventors: Edward O Hulburt
Original assignee: Individual
Current assignee: Individual
Priority date: 1925-12-23
Filing date: 1925-12-23
Publication date: 1932-03-08
Anticipated expiration: 1949-03-08

Description

M mhs, 1932. EjQQHULBURT I 1,848,630

PIEzo ELECTRIC-CRYSTAL Original Filed Dec, 23, 1925 Edward 0. `llulburt.

Petenced Mer.`a,f1f932f UNITED STATES PATENT OFFICE Y EDWARD o. numwn'rfor wasnme'ron, ms'rnrc'r or comnmm f :erano-morale CRYSTAL appneatieamea recenter as, -raars, serial No. 77,404. aenewea August s, rsa1.

My invention relates broadly to piezo-electric crystals more particular-lyto thev mounting of crystals and the provision of terminals and loadedlilmsthe'reon for establishing connectionewith the surface of the crystals and determining the frequency o f operation thereof in "vacuum tube circuits.-

The object of my invention is to provide an arrangement of terminals for piezo-electric crystals. V

Another object of my invention is to provide a conductive coating foropposite faces of the piezo electric crystal in such a form and mass that the frequency of-oscillation of piezo-electric crystals maybe fixed within certain limits.

A further object of myvinve'ntion is to provide a coating of metal on a. crystal toy produce a. ,crystal unit havinga zero coetlicient of frequency change per degree change of temperature.

Oscillator systems utilizing. a crystal to control'the frequency provide a means for holding the crystal between flat plates. Ex-

perience has indicated that films of oil, dust, etc. -destroy the oscillating pro erties of the` crystaland theexperience hasl edA tothe inference that metallic filihsor adhering coatings would have' the salnleinhibitplfyaction. I have -ei'ed,howeve,that me tallic films wheudepositedby cathode sputter' bychemi'cal methods,or alike process, o not'havea deleterious A*effect on the crystal but on thevc'o'ntrary the coatings seemto share to a gx-e'ater'or less extent t-hevvibra-l tions of thecrystal-making it possible for the crystal so coated to be used advantageously as a. generator of sustained oscillations.

I have also discovered that the 4frequency of oscillation vof a coated crystal may be selectively 'fixed by varying the thickness of the films or by secu i to the films other materials by any suita soldering. v.

I have further discovered that by selectle process vsuch as ing suitable metals to be used as the coating,- the temperature coeicient of frequency change ma be made tobe aero, an important factor in t e operation of crystal'controlled circuits where the 'temperature of the apparatus may var from time to time which.,v

ordinarily in t e .casev of electrodes merely restin in contact with the surfaces of the crysta would tend to cause a frequency shift. l The preferred location of the films is upon the opposite sides of the crystal but I do not limit myself to such locatlons for the films ma cover the crystal entirely or only in part or y adding metal, such as solder, on a part of the coatings.

The single figure of drawing shows a crystal having coated surfaces according to my invention.

My invention has been illustrated in the attached diagram wherein the electron tube V is shown with its electrodes connected in circuit with the piezo electric crystal frequency determining system and with the oscillator circuit O.y The frequency determinin circuit includes the piezo electric crysta Q having the films T deposited on opposite faces thereof in intimato contact ywith the crystal surface throughout the area .vide af la er'of metal impregnated in the surfaceo the crystal. These films increase the elliciency ofv operation of the crystal as shown by the increased output of the circuits using crystals coated in the manner herein disclosed. This increase in efficiency may be due to several causes, such as the elimination of brush discharge, leakage, `or perhaps thc concentration of the components of the stray oscillations within the crystal into oscillations along the desired axis.

Furthermore, the selection of the metal used, and the selection of the thickness of the metal film in relation to the dimensions of the crystal are important factors in the determination of the constants of the resultant crystal unit. By the variation in the constants of the metal film, a crystal may be controlled to operate the same or differently under the varying conditions of operation, which varying conditions, for example, may be a bread range of temperatures. Under the ordinary conditions of operation it is most desirable to have a crystal that will insure a constant frequency irrespective of the varying temperature conditions under which it is operating.

With my system of coating crystals the wires that connect the crystal into the circuits in which it may be used, may be secured to the films by solder or other like methods, thus assuring a lower Contact resistance than has heretofore been known.

Having thus described my invention what I claim as new is:

1. A. piezo electric crystal, metallic films deposited on the surfaces of said crystal, said films each adherin intimately to said crystal and having a thic ness proportioned to the natural frequency of the unloaded crystal and the desired frequency of the loaded crystal for selectively fixing the frequency of operation of said crystal.

2. A piezo-electric crystal having a cathodical y deposited coating of metal upon each of its electrode surfaces, the thickness of at least one of the coatings determined by the fundamental frequency of 'the piezoelectric crystal and by the desired resonant frequency of the coated crystal.

3. A piezo-electric crystal having a cathodically deposited coating of metal upon each of its electrode surfaces, the thickness of each of the coatings determined by the fundamental frequency of the piezo-electric crystal and by the desired resonant frequency of the coated crystal.

4. The method of adjusting the free vibration period of a piezo electric element which comprises grinding said element to a thickness slightly less than that corresponding to the free vibration period desired for said element, and applying a conductive coating to a lateral surface of said element for changing its free vibration period to the desired value.

5. The method of adjusting the free vibration period of a piezo electric element which comprises grinding said element to a thickness slightly less than that corresponding to the free vibration period desired for said element, applying a metallic coating to a lateral surface of said element, and adjusting the average thickness of said coating and element to a value corres onding to the deaired free vibration eriod EDW `RD O. HULBURT.