US1925577A

US1925577A - Oscillating crystal

Info

Publication number: US1925577A
Application number: US489474A
Authority: US
Inventors: Edgar D Tillyer
Original assignee: American Optical Corp
Current assignee: American Optical Corp
Priority date: 1930-10-17
Filing date: 1930-10-17
Publication date: 1933-09-05
Anticipated expiration: 1950-09-05

Description

Sept. 5, 1933. D, 'n 1,925,577

OSCILLATING CRYSTAL Filed Oct. 17, 1930 1.0 8 Q5 31 6 w p 8 w wENroR c 15 DZ. dgar D. Jill er.

A; BY

Patented Sept. 5, 1933 UNiTE STATES PATENT OFFICE OSCILLATIN G CRYSTAL setts Application October 17, 1930. Serial No. 489,474

11 Claims.

This invention relates to oscillating crystals and has particular reference to a crystal to be used in an oscillating circuit or a resonator circuit and to improved means of producing same. The principal object of the invention is to provide a very low frequency oscillating crystal, improved means of producing same and for increasing the electrostatic stress on said crystal.

Another object of the invention is to provide an improved process of producing piezo electric crystals wherein the frequency oscillations of crystals of the same length may be lowered.

Another object of the invention is to provide m ans wherein a crystal bar which has been accidentally out too short, causing it to be of a higher frequency than desired, may be corrected or made to oscillate at a lower frequency or at the frequency desired.

Another object of the invention is to provide simple, inexpensive and efficient means for producing low frequency crystals or crystals of desired frequency oscillations, reducing the cost of manufacture of same, assuring high efficiency and particularly reducing wastage by eliminating the production of non-usable crystals, as has hitherto occurred.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawing and it will be understood that many changes be made in the exact details of construction and steps of the process Without departing from the spirit of the invention as expressed in the accompanying claims. I, therefore, do not wish to be limited to the exact details and arrangements of parts and steps of the process shown as the preferred forms only have been shown by way of illustration.

Referring to the drawing:

Fig. I is a perspective view of a portion of a quartz crystal illustrating diagrammatically in dotted lines how the oscillating crystals are cut from said quartz crystal.

Fig. II is a perspective view illustrating a step in the process of manufacture of the oscillating crystal.

Fig. III is a perspective view of the finished crystal embodying the invention.

Fig. IV is a sectional View of the crystal taken on line Iii-JV of Fig. III.

Fig. V is a plan view showing the finished crystal in its holder.

Fig. V1 is a perspective view of a modified form of theinvention.

To form crystal oscillators having the proper tension and compression for long wave purposes it has been necessary in the past to first cut the mother crystal normal to its longitudinal axis and then out it perpendicular to one of its natural faces. The member thus formed was then cut to a given length to produce the frequency oscillations desired. The factor controlling the oscillations being the length of the finished crystal bar. If the bar was relatively short its frequency oscillations were high, it was long its frequency oscillations were low. With the above method in the past much difficulty has been encountered in obtaining the desired range in frequency oscillations, particularly the low frequencies, many of which especially the exceptionally low frequencies could not be obtained. This was due mostly to the fact that the mother crystals in their natural form were not large enough to permit an oscillating crystal of the required length to be formed.

Another serious drawback in the past has been the large percentage of wastage in the manufacture of crystals of the above character due mostly to the accidental cutting of the crystals too short and also to the limitations in usable crystals obtainable from the mother crystal, that is, crystals which are of suificient length to produce the frequency oscillations desired.

The prime object therefore of my invention is to provide means whereby the frequency oscillations of crystals that have been accidentally out too short and thereby spoiled may be rectified or reclaimed by lowering its oscillations to the original requirements. This improved means of lowering the frequency oscillations of crystals also facilitates the making of low frequency oscillators which have hitherto been impossible to obtain.

Referring to the drawing wherein like characters of reference designate like parts throughout the several views, the crystal 1 embodying the invention is formed similar to the prior art crystal by first cutting the mother crystal 2 normal to its longitudinal axis A-A which is its optical axis as indicated by the dotted line 3 in Fig. I, thence cutting the section perpendicular to one of the natural faces 4 of the mother crystal as indicated by the dotted lines 5 and thence concaving the sides of the bar which lie in a plane parallel with the longitudinal axis of the mother crystal as shown at 6. The purpose of cutting the bar from the mother crystal as described above is to produce the proper tension and compression for long wave purposes.

The length of the bar and the concaving of the sides thereof are in this instance the controlling factors governing the frequency oscillations of the crystal. By concaving the sides of the crystal as shown at 6 the frequency oscillations of the crystal are lowered, causing the crystal to oscillate ata much lower frequency than prior art crystals of the same length. In this manner a much lower frequency oscillator may be formed than has hitherto been possible to obtain. It is apparent that by concaving the sides of crystals which have been accidentally out too short to produce the frequency oscillation desired, that the frequency oscillations of said crystals may be rectified or made to accurate requirements.

In Fig. V there is shown a diagrammatic illustration of the crystal mounted in its support 7. The support '7 in this instance is formed with curved electrodes 8 shaped to conform substantially to the shape of the crystal, and positioned one at each side of the crystal and as close together as possible. The elec-- trodes are connected through the electrical leads 9 to an oscillating circuit or a resonator circuit. Although applicant has shown only one type of support it is to be understood that any suitable crystal support may be used in connection with this type of crystal oscillator providing the electrodes are positioned adjacent the cut away faces of the crystal. The purpose of this arrangement is to increase the electrostatic stress on the crystal by decreasing the space between the electrodes. The more closely related the electrodes are the greater the electrostatic stress on the crystal will be.

It is apparent that by properly concaving the sides of a crystal which has been acciden tally out too short that the original frequency oscillations desired may be obtained. The more concave the sides of the crystal are the lower its frequency oscillations will be. It is quite apparent that by first selecting a crystal bar which is relatively long and thence greatly concaving its sides that the finished crystal will oscillate at a frequency much lower than any prior art crystal obtainable. In this manner a complete range in frequency oscillators may be obtained.

In Fig. VI there is shown a slight modification in which instead of concaving the sides 6 of the crystal 1 it is shown with its central portion reduced to two parallel faces 10. The function of the crystal is the same as when it is concaved. Attention is called to the fact that the crystals 1 may be reduced or concaved on any or all of their sides.

From the foregoing description it will be seen that I have provided simple, efiicient and economical means for producing low frequency crystal oscillators and for increasing the electrostatic stress on said crystals and also means whereby non-usable crystals of the past may be rectified and made use of.

Having described my invention I claim:

1. A piezo electric element comprising a relatively long crystal bar having a pair of its opposed longitudinal faces concaved, said faces lying in a plane parallel with the longitudinal axis of the mother crystal.

2. A piezo electric element having substantially the shape of a rectangular parallelepiped and having its longitudinal axis normal to the longitudinal axis of the mother crystal and having a reduced portion intermediate its ends and on the sides of the crystal. which lie in a plane parallel with an axis of the mother crystal.

3. A piezo electric element having substantially the shape of a rectangular parallelepiped and having its longitudinal axis normal to the longitudinal axis of the mother crystal and having a pair of its opposed longitudinal faces reduced in thickness intermediate their ends and on the sides of the crystal which lie in a plane parallel with a longitudinal axis of the mother crystal.

4. In a device of the character described, a piece electric crystal element having a portion intermediate its ends cut away to reduce its thickness, said cut away portion lying in a plane parallel with the longitudinal axis of the mother crystal, and a pair of spaced electrodes positioned one adjacent each side of the reduced portion and lying substantially parallel with the cut away part of said portion, the space between said electrodes being at a point adjacent said intermediate cut away portion less than the thickest portion of the crystal.

5. In a device of the character described, a relatively long piezo electric crystal bar having a face cut away to reduce the thickness of the bar intermediate its end, said face lying in a plane parallel with the longitudinal axis of the mother crystal and a pair of electrodes posiied one adjacent the cut away face and the adjacent the opposite face and in spaced "ton so that the distance between said electro at a point adjacent said intermediate cut away portion is less than the thickest portion of the crystal.

6. In a device of the character described, a relatively lon piezo electric crystal bar having a pair of opposed longitudinal faces cut away intermediate its ends, said faces lying in a plane p llel with the longitudinal axis of the mother crystal and a pair of spaced electrodes positioned one adjacent each cut away face of the crystal. bar and shaped to conform substantially to the shape of said face, the space between said electrodes being at a point adjacent said intermediate cut away portion less than the thickest portion of the crystal.

'7. A piezo electric element and holder comprising a crystal bar having its longitudinal axis lying in a plane normal to the longitudinal axis of the mother crystal and extending perpendicular to a face of said mother crystal and having pair of its opposed longitudinal faces which lie in a plane parallel with the axis of the mother crystal cut away intermediate their ends to lower the frequency of oscillation of said crystal and a pair of spaced electrodes positioned one adjacent each cut away face of the crystal bar and shaped to conform substantially to the shape of said face, the space between said electrodes being at a point adjacent said intermediate cut away portion less than the thickest portion of the crystal.

8. The method of changing the vibration frequency of a piezo electric oscillator comprising forming a crystal bar member having its longitudinal axis lying normal to the longitudinal of the mother crystal and extending perpendicular to a natural face of said crystal and reducing the thickness of said bar member intermediate its ends in a plane parallel with the longitudinal axis of the mother crystal to change the frequency of oscillation of said crystal.

9. A piezo electric element comprising a relatively long crystal bar having a pair of its opits intermediate its ends cut away to reduce its thickness, and a pair of spaced electrodes positioned one adjacent each side of the cut away portion and lying substantially parallel with the cut away part of said portion, the space between said electrodes being less than the thickest portion of the crystal at a point adjacent said intermediate cut away portion.

EDGAR D. TILLYER.