US1869160A - Piezo-electric resonator - Google Patents

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y 932. w. A. MARRISON PIEZO ELECTRIC RESNATOR Filed May ll, 1928 Fle. 2.

/NVENTOR By %ARRL-WWA! v a Chemical solvent, for example, hydrofluoric' Patented July 26, 1932 UNITED STATES PATENT OFFICE WABREN A. IARBISON, OF OBANGE, NEW JERSEY, ASSIGNOR TO BELL 'TELEPEONE LABORATOBIES, INCOBPOBATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK PIEZO-ELECTRIC RESONATOR Application med-Ka 1928. Serial No. 27 7317.

This invention relates to piezo-electric crystal resonators and more particularlyto.

a method of adjusting them to operate at a desired frequency.

An object of the inventionis to secure a very hi 'hdegree of precision in the' adjustment o? piezo-electric crystals, so thatthey will oscillate at a desired frequency.

Another object is to produce crystals having uniform contact surfaces, thcreby avoiding irregularities in their activity and in the frequency at which they will oscillate.

A further object of the inventionis to provide means for facilitating the selection of ood resonators.

t present, piezo-electric resonators such as quartz resonators, for example, are adjusted for frequency by lapping, e., by slowly grinding one surface of the resonator with a fine-abrasive. In the use of this method abrupt variations, in the surface of the crystal frequently occur. These variations atfect its activity and the frequency at which it oscillates.

In accordance with the present invention acid, is used to dissolve material from the surface of a Crystal to produce an etched surface which is free from irregularities. Commercal hydrofiuoric acid may be used and the length of exposure depends on the change in the Crystal necessary to render it resonant to the desired frequency. The change in frequency, obtaned for a given shape of resonator and given temperature and concentration of the solvent is believed to be approximately directly proportional to the length of exposure.

In the drawing: v

Fig. l is a piezo-electric resonator which has been cut' from a natural crystal to such dimensions as to have approximately the desired resonance frequency.

Fig. 2 illustrates the process disclosed herein and shows the resonator 1 immersed in hydrofiuoric acid 2 contained in a suitable container or .beaker 3, as of lead.

Fig. 3 is a View of the resonator after being adjusted to the desired frequency by exposure to the acid.

Advantages of chenical treatment of crystals are that material is removed from 'the entire surface of the crystal to render it uniform, and the Crystal may be very precisely adjusted`to oscillatc at a selected frequency.

As in the past, the resonating element is cut from the natural Crystal, its dimensions being. slightly greater than those necessary to its vibrat-ion at the desired frequency. In cutting from the natural crystal, irregularities are likely to occur in the surfaces. The Chemical solvent to which the element is exposed, serves to dissolve the irregularities and if necessary toits reduction to'the proper dinensions, a nitnrm layer is dissolved from the surfacesof the element. The dimensions of the element are precisely adjusted to a value such that it will' vibrate at the desired frequency.

In order to deternine whether a crystal was free from' twinning when prepared by the method heretofore practiced, it has been necessary to cut the 'esonator to the size desired for use, polish the resonator, and to examine it with special optical apparatus.

With the present method the crude Crystal is cut into slabs of large dimensions from which a number of resonators may be'cut. The slab is then exposed to the action of a Chemical solvent toproduce an etched surface, whereby defects, notably twinning, are rendered visible to the unaided sight. A sec-- tion of the slab 'is then selected which is freethen exposed to the action of the Chemical solvent until it is reduced to such dimensions they have been brought to the finished state.

WVhat is claimed is: 1. The method of producing a quartz crys- Consequently' it pro- Vides a method for selecting crystals before' 'tal element which omprises cutting the crystal element to the approXimate-size and dissolving a portion of said Crystal element with hydrofiuoric acid.

2. The method of'adjusting a quartz crystal element to a desired size which comprises treating said Crystal element with hydrofluoric acid.

3. A quartz crystal resonator having a substantially uniform chemically etched surface.

tal element having uniform contact surfaces,

which comprises treating a quartz Crystal element with a substance which is a Chemical solvent for the Crystal.

' 5. The method of producing a piczo-electrically active quartz element which comprises cutting a slab from a natural quartz Crystal having piezo-electric properties, exposing the slab to the action of a Chemical solvent whereby defects in the slab are readily 'dctectable and cutting a resonator' from a section which is free from defects.

6. The method of producing a piezo-electrically active quartz element which comprises cutting a slab from a natural quartz Crystal having piezo-electric properties and. cxposing said slab to the action of hydrofiuoric acid. r

In witness whereof, I hereunto subscribe my name this 10th day of May, 1928.

WARREN A. MARRISON.

4. The method of producing a quarrtz crys-'

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