US2133647A - Electromechanical vibrator - Google Patents

Description

Oct. 18, 1938. G w MERGE 2,133,647

ELECTROMECHANICAL VIBRATOR Filed June 25, 1931 WW/WM/Z INVENTOR 69 9 2 i7 3 '7 15 gf 'y ATTORNEY Patented Oct. 18, 1938 UNITED STATES PATENT OFFICE 19 Claims.

The present invention relates to electromechanical vibrators, and more particularly to piezo-electric crystals, and to supports and holders therefor. The present application is a continuation in part of applications Serial Nos. 695,- 094, filed February 25, 1924, and 98,220, filed March 29, 1926.

Piezo-electric crystals, while vibrating, have a tendency to move bodily from side to side between their electrodes. This is undesirable, because tending to cause erratic changes in frequency. Attempts to center the crystal by engagement with its periphery are not wholly satisfactory, because the'dimensions of the periphery change periodically with the vibratory expansions and contractions of the crystal (in the case of a'crystal plate vibrating in the thickness mode, the thickness of which is small compared with its other dimensions). Attempts to clamp the crystal against movement, on the other hand, might interfere with its free vibration.

An object of the invention is to provide a new and improved holding device that, while positively preventing the vibrator from moving bodily, permits it to vibrate freely.

Even if the crystal were to be held against bodily movement, the friction of its bodily con- 'tact with an adjacent surface of relatively large area also tends to introduce frequency changes, and a further object of the invention, therefore,

"is to obviatesuch friction, particularly at the vibrating portions of the crystal.

Other and further objects will be explained hereinafter and will be particularly pointed out in the appended claims.

With the above ends in view, a feature of the invention resides in holding the vibrator nodally and, in particular, at points substantially along the electric axis or substantially along the optic axis of the piezo-electric crystal. The vibrator may thus be held at the said points entirely out of contact with any other points or surfaces. The

holding members may be adiustable. The crystal electrodes may be adjustable independently of the holding members.

The invention will now be explained in connection with the accompanying drawing, in which Fig. lis a vertical, longitudinal sec'tionptaken upon the line l-l of Fig. 2, looking in the direction 'of the arrows, of a preferred embodiment of the invention; Fig. 2 is a similar section'taken upon the line 2-2 of Fig. l, lookinglnthedirection of the arrows; Figs. 3, 4 and 5 are "views of modifications; Fig. 6 is a vertical, longitudinal section taken upon the line 6-4 of Fig. 5, looking in the direction of the arrows; Hg. 7 is a diagrammatic view illustrating the various axes of a piezo-electric crystal; and Fig. 8 is a view similar to Fig. 1 of a modification.

A flat rectangular quartz plate 2 is illustrated in Fig. 7, having three axes, as follows: the optic axis, indicated by the arrow 0, parallel to the lengthwise natural edges of the original quartz crystal; the electric axis E, parallel to two opposite, natural faces of the original crystal; and the third axis B, perpendicular to the optic and electric axes O and E. In Fig. 1, for example, the optic axis is shown longitudinally disposed, and longer than either of the other axes.

A quartz slab 2 of this character, when inserted between conducting electrodes I and I2, suitably connected in an electric circuit, as by means of binding posts it and it, will exhibit its piezoelectric properties. In Fig. 4, the binding post It is extended outwardly from within the housing, through the insulating cover ll, hereinafter mentioned, disposed opposite to the electrode 8 to which the binding post it is electrically connected. The electric circuit may be any of the vacuum-tube circuits disclosed in the said applications, including a frequency multiplier or harmonic producer, so as to multiply the frequency of the oscillations by a predetermined integer. The harmonic producer or frequency multiplier may combine any desired number of vacuum tubes. In the said circuits, the disturbing eifects,-such as those produced by changes of temperature, changes of mounting supports, changes of electrical constants, and the like,--on the frequency of oscillations usually amount to less than one one-hundredth of one per cent of the frequency. These small effects are nevertheless well under control, in the present invention, and are themselves utilized to introduce useful minute variations of frequency, when desired. If the crystal 2 rests freely between the electrodes l and 12, however, it has a tendency to slide from side to side during its vibrations; and

fixed. It is, however, held so as to vibrate freely,

according to the desired mode of vibration, without restriction, without interfering with its vibraquency. This may be effected by applying the clamping pressure over or at small medial areas, corresponding to the nodes of movement of the tions, and without introducing variations in frevibrating crystal, where there is no vibratory movement of the crystal, either substantially along an optic axis or substantially along a medial electric axis E. The crystal being otherwise free to vibrate, it vibrates freely, either according to its longitudinal or transverse mode of vibration, as the case may be.

Referring, first, to the piezo-electric-crystal holder shown in Figs. 1 and 2, the crystal plate 2 is held at diametrically oppositely disposed nodal points I and 3, at opposite sides or edges or faces of the crystal, substantially along an optic axis 0, substantially at the mid-points of said edges. The nodes are seldom exactly along an optic axis, but they are usually substantially so. Preferably, the vibrator 2 is recessed or slotted or notched at these points I and 3, at oppositely disposed edges of the vibrator 2, to receive the oppositely disposed ends of a pair of oppositely disposed retainer members or screws 5 and I extending transversely of the hereinafter-mentioned mounting plates into the slots or notches or recesses formed in the opposite sides or edges of the crystal. As an illustration relative to dimensions, the recesses I and 3 may be inch in diameter. The free ends of the screws 5 and 'I constitute pins extending toward each other and filling said notches and the vibrator is thus held against lateral displacement or other bodily movement out of its position between the pin ends of the screws 5 and I. The screws 5 and I may be adjusted in lugs 9 and I5 carried or otherwise supported by a fiat rectangular mounting base plate I! to hold or support the crystal centered with re- I spect to and from said mounting plate with any desired degree of tightness, thus to adjust the degree of nodal pressure, but without introducing substantial energy loss from the vibrating crystal to its supports. Damping of the vibrating crystal is thus reduced to the minimum.

The electrodes 8 and I2 are shown spaced slightly apart from the opposite faces of the crystal, with the crystal as horizontally disposed over the plate II, with its upper flat surface adjacent to the smooth lower fiat surface of the elec-- trode I2, and its lower fiat surface disposed adjacent to the upper fiat surface of the electrode 8. Electrical connection with the upper surface of the crystal 2 may be established through the electrode I2, and with the lower surface of the crystal 2 through the electrode 8, into any electricv circuit, such as a high-frequency generator.

resonant mode of vibration may be in the direc- The - clamping members 58 and GI,- of relatively small area compared to the dimensions'of the vibrator 2, are integrally connected with the electrodes 8 and I2, and are positioned so as to clamp the vibrator at its nodes. In Fig. 4, the same result is attained by making the vibrator 2 lenticular in shape, the convex sides 4 and 5 thus engaging the fiat electrodes 8 and I2 at relatively small nodal areas, where a node of motion is produced in the crystal body during its vibration. The electrode 8, in the modification of this Fig. 4, constitutes the bottom metal wall or base plate of a metal container, box or housing having vertical side walls I I integral with the bottom wall 8, upon which bottom wall 8 the vibrator 2 is centrally located, as shown. The electrode I2, in the modification of Fig. 4, is disposed adjustably in the housing, between the crystal 2 and an insulating cover I8, which cover may be constituted of hard rubber. The side walls II are shown spaced from at least two sides of the crystal. In Figs. 5 and 6, illustrating a crystal 2 designed more particularly for vibration in the direction of its length, the electrode I2 is provided with an intermediately disposed projection or bridge or spacing piece I22 and the electrode 8 with two projections or bridges or spacing pieces I20, disposed one on each side of the middle point. The vibrator 2, supported solelyby and between the electrodes 8 and I2, is gripped or clamped'by the projections I28 and I22 along small medial areas corresponding to nodal zones of movement. The projections I28 and I22, as shown, are disposed between the electrodes 8 and I 2 and the faces of the crystal near the middle of the length of the crystal or other nodal zones. As in the case of the other modifications, the crystal is thus substantially horizontally supported between and adjacent to the lower substantialy horizontally disposed substantially fiat surface of the upper electrode I2 and the upper substantially horizontally disposed substantially fiat surface of the lower electrode 8, withits oppositely disposed substantially fiat upper and lower faces substantially horizontally disposed respectively adjacent and substantially parallel to the respective substantially fiat surfaces oiv the electrodes. In this case, too, the pressure of the projections against the crystal may be adjusted; and here, too, the projections are so narrow in width that the frequency of vibration of the crystal is substantially unaffected by a change in such pressure. The electrodes 8 and I2, with the crystal disposed between them are clamped together as a unit between two insulating members I I8 by bolts I24. As explained in the said application, Serial No. 98,220, the devices illustrated in the various views may be mounted in a sealed vessel (not shown) of metal or glass that is evacuated to remove air or other gases and that is kept in a constant-temperature bath.

It is possible to adjust the electrode I2 toward and from the vibrator, in Fig. 1, by means of bolts 63 and nuts 85. The bolts 63 extend through openings in the insulating base I1 and an insulating top mounting plate 61, to which the electrodes 8-- and I2 are respectively secured by screws 69, and the electrode I2 is maintained separated from the vibrator 2 by springs 69 mounted over the rods 63 between the insulating members I1 and 61. The degree of nodal pressure may similarly be adjusted in Fig. 3. Similar pressure adjustment may be eilected with the device of Fig. 4 by screwing up or down, through the insulating cover I8, of the said housing, the threaded binding post I8 that is integral with the electrode I2, though the electrode I2 may be adjusted so as to be wholly free of the upper surface 8 of the crystal so as to leave an air gap between the electrode I2 and the said upper surface 6 of the crystal 2.

If desired, as illustrated-in Fig. 8, the base H of Figs. 1 and 2 may be metallic, with integral lugs 9 and I5, in which event a separate electrode 8 would not be required, as the base I! may then itself act as such electrode.

In the modifications of Figs. 3 to 6, the vibrator rests on the electrode 8. In Fig. 4, the lower side 4 of the crystal is shown contacting with the base plate I, and the crystal 2 is secured in the casing or housing between the electrodes I and I! without being in any way restricted, so that it is free to vibrate mechanically between the opposed electrodes'8 and I2, according to any of its modes or periods of natural vibration or any of its overtones of such modes of vibration. Among these are the longitudinal and transverse modes of vibration. In the device of Figs. 1 and 2, on the other hand, the crystd is entirely free of the electrodes, being spaced from, and between, them. No frequency changes due to friction can possibly be introduced, therefore, in the device of Figs. 1 and 2; and as for Figs. 3 to 6, the same result is attained by clamping fixedly at the relatively small nodal areas before mentioned. In all cases, the constancy of the frequency is unaffected from error sources of this nature.

As is also explained in the said applications. I have also found that very minute variations of frequency of the order of one three-hundredth of one per cent may be introduced by bringing the electrodes more or less near to the piezo-electrlc vibrator. This is of importance in the final adjustment of such a vibrator, where extreme precision of frequency is required.

By means of this variable-capacity coupling between the crystal and the tuned circuit, the oscillator is thus capable of generating any wave within the limits of a predetermined band, and the period of the crystal may be increased or decreased by any desired amount so that the oscillator may sustain oscillations of any selected frequency within the predetermined band. By gradually varying the air gap between the electrode l2 and the surface 8 of the crystal 2 to vary the frequency of the piezo-electric device 2, corresponding changes will be effected in the beforementioned multiplied or harmonic frequency within predetermined limits.

It will, of course, be understood that the invention is not restricted to the exact embodi-v ments thereof that are illustrated and described herein, as modifications may be made by persons skilled in the art, and all-such are considered to fall within the spirit and scope of the invention, as defined in the appended claims.

What is claimed is:

1. An electromechanical vibrator comprising a piezo-electric-crystal body, electrodes, and means for holding the body between the electrodes at points substantially along the optic axis of the body to prevent bodily movement of the body out of a predetermined position.

2. An electromechanical vibrator comprising a 'piezo-electric-crystal body, electrodes, means for holding the body between the electrodes'at points substantially along the optic axis of the body to prevent bodily movement oftl'ie body out of a predetermined position, and means for adjusting the electrodes.

3. An electromechanical vibrator comprising a piezo-electric-crystal body, electrodes, and two oppositely disposed holding members having portions of relatively small area engaging the body at two opposite points substantially along the optic axis of the body to prevent bodily movement of the body out of a predetermined position.

4. An electromechanical vibrator comprising a piezo-electric-crystal body, electrodes, two oppositely disposed holding members having portions of relatively small area engaging the body at two opposite points substantially along the optic axis of the body to prevent bodily movement of the body out of a predetermined position, and means for adjusting the members.

5. An electromechanical vibrator comprising a piezo-electric-crystal body, electrodes, means for adjusting the electrodes, and means independent 6 of the electrodes for holding the body spaced from and between the electrodes against bodily movement out of a predetermined position.

8. Piezo-electric-crystal apparatus comprising a rectangular mounting plate, a piezo-electric 10 crystal supported from said mounting plate, said piezo-electric crystal being slotted at opposite sides thereof, a pair of retainer members supported by said mounting plate and extending into the slots formed in said piezo-electric-crystal elel5 ment for centering said piezo-electric-crystal element with respect to said mounting plate.

7. In a piezo-electric-crystal apparatus, a mounting plate, a piezo-electric-crystal element.

a pair of retainer members carried transverse]! to of said mounting plate, pins extending from each of said retainer members, said pieao-electriccrystal element being slotted at opposite edges thereof for receiving said pins for centering said piezo-electric-crystal element with respect to said 25 I mounting plate, and means for establishing electrical connection with the upper surface of said piezo-electric-crystal element.

8. A piezo-eiectric-crystai holder comprising, in combination, a member having a fiat surface, a flat rectangular plate of material possessing piezoelectric properties disposed over the flat surface of said member, said plate having a longer longitudinal axis than its transverse axis, said plate having slots formed on each edge at diametrically opposite points along one of said axes and pins disposed over said flat surface, said pins being disposed in the slots of said plate for preventing lateral displacement thereof.

9. A piezo-electric-crystal holder comprising in so combination, a member having a fiat surface, a flat piezo-electric plate, said plate having notches cut into its sides said notches being disposed at nodal points along said sides, and means positioned upon said member for engaging said 45 notches and preventing lateral movement of said plate upon said member.

10. A piezo-electric-crystal holder comprising. in combination, a member having a smooth fiat surface, a piezo-electric-plate adapted for frego quency control of the oscillations of a high-frequency generator positioned over the fiat surface of said member, said piezo-electric-plate having notches cut into the sides thereof at points corresponding to the nodal points of these sides, and as means associated with saidmember for engaging in the notches of said plate for preventing lateral movement of said plate with respect to said' member.

11. In piezo-electric-crystal apparatus, a meso tallic mounting plate, a piezo electric-crystal element having its lower surface positioned over said mounting plate and being notched on each of two edges thereof substantially at the midpoints of said edges, a pair of retainer members 05 attached to said mounting plate, pins extending from each of said retainer members toward each other and so positioned and of such size as to engage and substantially fill said notches in said piezo-electric-crystal element, and means for es- 70 tablishing electrical connection'with the upper surface of said piezo-electric-crys'tal element.

12. An electromechanical vibrator comprisin a substantially freely vibratory piezo-electriccrystal body, electrodes, and two rods having ends 16 disposed opposite to each other and contacting the crystal body at two oppositely disposed regions of relatively small area for securely supporting the crystal body between the electrodes.

13. An electromechanical vibrator comprising a substantially freely vibratory .piezo-electriccrystal body having recesses, electrodes, and

means in the recesses contacting the crystal body at two points for securely supporting the crystal body between the electrodes.

14. An electromechanical vibrator comprising a substantially freely vibratory piezo-electriccrystal body having a recess, electrodes, holding means, and means in the recess and cooperating with the holding means to contact the crystal body at two regions of relatively small area for securely supporting the crystal body between the electrodes against bodily movement out of a predetermined position, the holding means and the recess being disposed along one of the axes of the crystal.

15. An electromechanical vibrator comprising a piezo-electric-crystal body in the form of a bar the length of which is large compared with its other dimensions and that is freely vibratory according to a natural mode of vibration in the direction of its length, two oppositely disposed supports provided with clamping rods having oppositely disposed ends of relatively small area the dimensions of which are small compared with the length and the width of the bar, and means for causing the .clamping rods to clamp oppositely disposed small nodal portions of the body between the two portions of relatively small area to hold the body nodally clamped and solely supportedbetween the said two portions of relatively small area. I

16. An electromechanical vibrator comprising a piezo-electric-crystal body having electrodes at opposite faces thereof substantially at right angles to the electric axis of the body, the body being in the form of a bar the length of which is large compared with its other dimensions and having a centrally disposed nodal region with respect to which it is freely vibratory according to a natural mode of vibration in the direction of its length, two oppositely disposed supports provided with clamping rods having oppositely disposed ends of relatively small 'area the dimensions of which are small compared with the length and width of the bar, and means for adjusting one of the clamping rods to cause the clamping rods to clamp between the two portions of relatively small area oppositely disposed small nodal portions of the body at opposite sides of the nodal region to hold the body nodallyclamped and solely supported between the said two-portions or relatively small area.

17. An electromechanical vibrator comprising a substantially freely vibratory piezo-electriccrystal body having recesses in oppositely disposed faces, electrodes, and screw-threaded members contacting the crystal body in the recesses at two substantially point-like regions for securely supporting the crystal body between the electrodes.

18. Anelectrome'chanical vibrator comprising a substantially freely vibratory piezo-electriccrystal body having recesses disposed along one of the axes of the crystal, electrodes, and means in the recesses contacting the crystal body at two regions of relatively small area for securely supporting the crystal body between the electrodes.

19. An electromechanical vibrator comprising a substantially freely vibratory piezo-electric-' crystal body, electrodes, and means contacting the crystal body at two regions of relatively small area at the edged the crystal body along an axis of the crystal for securely supporting the crystal body between the electrodes.

GEORGE W. PIERCE.

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