US2278093A - Crystal holder - Google Patents

Description

INVENTORS HAROLD Q PETERSON 7NP L'l W/NANS h s 97\67%\ L/ M WN V H k 8 O m h 7 M V xx March 31 1942.

ATTORNEY.

' taincd with respect to Patented Man 31, 1942 2,278,093 CRYSTAL notosa Harold 0. Peterson and head, N. Y.,

Paul V. Winans, Riverassignors to Radio Corporation of America, a corporation of Delaware Application November 10, 1939,

8 Claims.

This invention relates to a crystal holder suitable for use in a piezo-electric quartz controlled oscillator of very high stability.

An object of this invention is to simplify and improve crystal holders generally.

Another object of this invention is to provide an improved crystal holder in which the physical position of the crystal is accurately mainthe crystal electrodes.

Still another object of this invention is to provide air gaps on both sides of the crystal to minimize its damping.

A feature of this invention is the arrangement of the simple component parts to provide ease of assembly and general electrical efficiency.

One of the difiiculties in obtaining extreme frequency stability in quartz crystal controlled oscillators is the change of frequency due to the mechanical or physical position of the crystal with respect to the electrodes. The novel crystal arrangement of this invention is such as will overcome these difficulties to a very large extent.

This invention will best be understood by referring to the accompanying drawing, in which:

Fig. l is a cross-sectional view of the improved crystal holder of this invention;

Fig. 2 is a plan view of Fig. 1 with the cover and upper electrode removed; and

Fig. 3 is a fragmentary sectional view taken on line 3+3 of Fig. 2.

Referring now in detail, to the drawing, the crystal holder comprises a circular metallic base electrode 3 and an upper electrode 2. Both electrodes are made of an alloy having a temperature coefficient of expansion very close to that of the piezoelectric crystal, such as for example Monel metal, which has been found satisfactory in a typical and practical application as its temperature coefficient is 13.7/ /C and quartz cut at right angles to, its axis=13.37/l0 /C and '7.9"I/l0 /C when out parallel to its.--axis. Another metal which might be used as electrodesis that of nickel steel whose temperature coeficient is from 0.9 to 12/10 /C. The'lower or base electrode has a depressed space or aperture 3 which is substantially equal in depth to the space between the upper electrode 2 and the crystal 5. The area of space 3 is equal to or substantially greater than the crystal surface but is of a different outline or shape, in order that a very small portion of the crystal will overlap Serial No. 303,720

in order that the crystal may slightly rest on the edge of electrode I. For example, as is shown in Fig. 2 of the drawing, a rectilinear retained in position crystal is arranged over a. circular aperture. The diameter of the aperture is greater than that of the width of the crystal but less than its diagonal, so that the extreme corners of the crystal are secured in a fixed location above aperture 3 by means of two small insulating blocks 1 which are fastened by any suitable means, such as for example by cement, .to the lower electrode I, and in turn connected to the crystal through a small quantity or drop of insulating cement. Block I is preferably made of hard rubber or Bakelite and the drop of cement 6 is preferably that of Glyptcl. The electrodes 1 and 2 are spaced by means of insulating pillars 8 which have a coefficient of expansion such as to maintain substantially constant oscillator frequency. These spacers are preferably that of lisolantite, fused quartz, or any other suitable material having similar characteristics, although Isolantite has been found satisfactory in certain typical ap plications. Spacing pillars B are retained in position by any suitable means, such as for ex ample pins 9, which are driven into electrode i. A'circular or ring-like insulating casing it forms the side walls of the holder to which is secured by means of screws ii! an insulating cover plate 2. The upper electrode 2 is held firmly against the spacer blocks 8 by coil springs iii which are by the centering pins it attached to electrode 2, and likewise a similar pin, if desired, may be inserted in the top cover plate 552. Electrical connections .to the electrodes may be made by means of a flexible lead i3 to'a terminal screw. it. The other electrical connection is made from the lower base electrode 6 by means of a screw (not shown) threaded into hole 01. The casing ring it is secured to base electrode l by means of three round head screws l8, which are tapped into the metallic base I.

Although Fig. 2 shows a circular space for retaining a rectilinear crystal, it is to be understood that other shapes, such as a three-sided crystal or a circular crystal and an oval space or vice versa, may also be used to minimize the damping by retaining the crystal on --the lower electrode at its extreme ends. Therefore, this invention should not be limited to the precise arrangement shown.

What is claimed is: I V

1. A piezo-electric crystal holder comprising an upper electrode,.a lower electrode spaced from said upper electrode, a rectilinear shaped piezoelectric crystal interposed between said electrodes, retaining means including a drop of cement located at two corners of said crystal, means for maintaining said crystal spaced with respect to both 01' said electrodes to obtain extreme frequency stability when the crystal is used in an oscillatory circuit.

2. A piezo-electric electrode. 4. A piezo-electric crystal holder'comprising an upper electrode, a lower electrode spaced from electrode, the area or which is such that at least two corners or the crystal rest above said aperture, two insulating is located near two 6. A piezo-electrlc crystal holder comprising an upper electrode, a rectilinear crystal, 0. lower electrode spaced from said upper electrode, said lower and upper electrodes being made 01 an face of said upper electrode, means including a circular depressed space in said lower electrode, the depth of said depressed space being substan- HAROLD o. PETERSON. PAUL v. WINANS.

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