US2371613A - Piezoelectric crystal apparatus - Google Patents

Description

March 20, 1945.

l. E. FAIR PIEZOELECTRIC CRYSTAL APPARATUS Filed Dec. 51, 1942 3 Sheets-Sheet l INVENTOR l E. F4 IR A 7' TORNE V March 20, 1945. E M 2,371,613

PIEZQELECTRIC CRYSTAL APPARATUS Filed Dec. 31, 1942 I5 Sheets-Sheet 3 IN l/EN TOR E. FAIR By WM ATTORNEY Patented Mar. 20, 1945 2,371,813 PIEZOELEC'IBIO CRYSTAL APPARATUS Irvin E. Fair, Lynllhurst, N. 1., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application December 31, 1942, Serial No. 470,759

(Cl. 17l327) 16 Claims.

This invention relates to piezoelectric crystal apparatus, and particularly to wire support systems for piezoelectric crystal elements useful, for example, in oscillation generator systems, filter systems, and in electromechanical vibratory systems generally.

One of the objects of this invention is to prevent wire vibrations in wire-supported piezoelectric crystals from adversely affecting the desired crystal vibration.

Another object of this invention is to reduce the effects of vibrations in crystal supporting wires upon the crystal activity and frequency.

Another object of this invention is to improve theactivity and the frequency stability of wiresupported crystal elements.

In order that a piezoelectric crystal may vibrate freely, it is desirable that the means used to support the crystal and to maintain contact with its plated electrode surfaces have a low mechanical impedance and at the same time have suflicient rigidity that the complete crystal unit assembly when subjected to mechanical shock or other externally applied vibration may not change its characteristics as an oscillator. If a crystal supporting spring wire be fastened or otherwise held against the crystal at any point, the crystal when in an oscillating condition will tend to generate motion in the support wire in contact therewith, and the closer the support wire is placed to the nodal point of the crystal, the less will be the motion generated by the crystal in the support wire. Accordingly, the crystal supporting wires may be placed as close as possible to a nodal point of the crystal and also so constructed as to have a very low'mechanical impedance at or near the desired operating frequency or frequencies of the crystal. A type of support which meets this requirement is that of a thin spring wire or rod vibrating in flexure, one end thereof being in effect clamped at or near a wire node and the other end being free to vibrate in contact with the surface of the crystal. the length thereof being such that its frequency of antiresonance equals that of the crystal, or approximately so, so that very little energy from the crystal is required to drive the supporting wire. and any energy received by the supporting wire from the crystal is reflected from the clamped end of the supporting wire and thereby kept within the composite vibrating system.

In piezoelectric crystal devices of the spring wire supported type such as, for example, those disclosed in A. W. Ziegler Patent 2,275,122, dated into vibration as a result of the vibration of the crystal element which is suspended by such supporting wires, and the wire vibration may adversely affect the desired crystal vibrational frequency or render it sluggish in vibration or prevent its operation altogether in some cases. These adverse effects may be the more pronounced where the crystal element is relatively very small in size or where the supporting wires are not attached to the crystal element at or very near to a node thereof.

In accordance with this invention, a wire-supported crystal may be provided with massed weights or clamps placed on and suspended by the crystal supporting conductive lead wires, the massed weights being not only of sufficient mass but also of suitable location with respect to the nodes of the supporting wires as to prevent vibrations in the supporting wire system from adversely affecting the activity or the desired frequency vibration of the crystal element.

In accordance with a feature of this invention, a small solder globule or ball or other suitable mass may be placed or cast firmly on the flexible spring support g wire or wires at a selected location between t e crystal and the far or outermost end of the supporting wire system. More particularly, the small solder ball may be placed at or near a node of each supporting wire and away or remote from the loop of motion thereof, the eflective wire length between the crystal element and the solder ball being thereby made to have a natural frequency which is fundamentally or harmonically related to the desired crystal frequency, and the solder ball being made of a mass sufficient to prevent the crystal lead wire vibration from passing therethrough to the far or out- .ermost portion of the spring wire support remote from the crystal. Such small weights or loads of metal as lead-in solder balls placed on and suspended by the crystal supporting wires substantially at a node of motion thereof and made of adequate mass will function to reduce damping and improve the Q and operation of such wire mounted crystals.

For a clearer understanding of the nature of this invention and the additional advantages, features and objects thereof, referenceis made to the following description taken in connection I with the accompanying drawings, in which like March 3, 1942, the wire support system may be set reference characters represent like or similar parts and in which:

Figs. 1 and 2 are enlarged front and side views respectively of a piezoelectric crystal mounting embodying this invention, Fig. 2 being a view taken on the line 2-2 of Fig. 1:

Fig. 3 is an enlarged detail view showing a support wire attached to the crystal by means of a solder cone soldered to a baked silver paste spot on the crystal element;

Fig. 4 is an enlarged'detail view showing a spherical solder ball Joining the ends of two wires forming a wire upport for a piezoelectric crystal device;

Fig. 5 is a greatly enlarged detail view of a crystal supporting wire fastened at one end to motion of the crystal plate I when in operation.

the crystal by means of a bell-shaped solder cone,

' and extending straight through a solder ball to an outer support;

Fig. 5;

Figs. 7,8 and 9 are enlarged view, showing,-

the use of a nodal soldered stirrup as a substitute for the nodal solder ball of Figs. 1, 2, 4, 5 and 6;

Fig. 10 is a perspective view of a modification of the crystal mounting shown in Figs. 1 and 2;

.Figs. -11 and 12 are respectively face and end views of a four-wire support system as applied particularly to a longitudinal mode typeof crystal element; and

Figs. 13 to 17 are views showing various modiilcations of the invention.

Referring to the drawings, Figs. 1 and 2 are enlarged front and side views. of a piezoelectric.

crystal device comprising a face-mode quartz crystal element I having opposite, conductive electrode coatings 2 and 8 formed integral therewith and thickened at the central regions of supv motion prevalent .in quartz crystals are the har- 7 1s Fig. 6 is an enlarged detail view showing a modification of the crystal supporting wire oiv the to it and, which may by their presence hinder The etching referred-to should notbe overdone inasmuch as with too much etching, the silver coatings 2 and! may have a tendency to flake .01! near the edges and corners of the crystal with a resulting absorption of energy from the crystal plate I and a decreased Q thereof. When the etching bath is agitated, the time of etching may be decreased andsome improvement in uniformity of resonant resistance .may be obtained. Also, the thickness of the crystal plate I may be.

adjusted to a suitable value relative to its major face dimensions in order to avoid nearby 01' coupled undesired frequencies or modes of.

motion therein, that mayinterfere with the desired resonance. Among theundesired modes of monic flexure modes vibrating along the thickness and propagated along the width'and length of the crystal plate I. Accordingly, the thicknessof the crystal plate I may-be adjusted relative to the major face dimensions in order to place undesired. modes in regions that do not conflict with the desired main resonant frequencyor with any desired secondary resonance thereof. f

The crystal coating land 3 may consist of I any suitable conductive coating such as, for example, a very thin coating of silver applied to the crystal surfaces by evaporation in vacuum port 4 where two horizontal or laterally extending supporting fine spring lead wires 6 and'l are soldered thereto by means oftwo small solder dots or cones 5. The outer ends of the two horizontal lead wires 8 and I are welded or soldered by a cast solder ball or other metallic mass ID to the top ends of two supporting upright semicircular spring wires 8 and 9 which may be a part thereof. The lower ends of the wires 8 and 9 are wound around and soldered to two pin ter minalsl2 of an enclosing container II, which may be hermetically sealed or evacuated and constructed of any suitable size, shape and material.

- be of the same or slightly larger diameter, as

may be required to support the crystal element I. It will be understood that the crystal element I may be of any type that it may be desired to mount, such as, for example, a quartz crystal element of the face shear mode type having its node or point of minimum motion at or near the center of the crystal element. Examples of such face shear mode crystals are, disclosed, for example, in G. W. Willard United States Paten 2,268,365, issued December 30, 1941.

To obtain stability in its resonant resistance,

the bare quartz plate I may be uniformly etched in hydrofluoric acid, for example, to remove any particles of quartz dust left in the small crevices 75 of the quartz plate I that are not tightly bonded or by other suitable process. At the points where the lead wires 6 and I are to be attached, a small spot 4 of baked silver paste maybe applied to the quartz and baked firmly thereon in a known manner. Y shaped bakedsilver paste spot 4 which has been baked onto the quartz crystal I at ornear a node thereof, a thin electrode fllm 2 or 3 of evaporated silver being applied thereover and a lead wire 6 being soldered to the baked silver paste spot I by means of a smallsolder dot or cone 5. The

leadwire 6 may. haveits end firmly embedded in the solder cone 5, as illustrated in Fig. 3..

For purposes of mechanical strength and electrical conductivity, a good joint is needed between the crystal I and the supporting lead wire land also between the lead wire 6 and the mount wire 8. The silver spot I may be burnished or' otherwise cleaned in order" to obtain'a clean surface for soldering the supporting wire 6 or I thereto. The proper shaping of the solder cone 5 results in a stronger joint between. the leadwire 6 or I and the silver spot 4. If the solder cone 5 is made too high and too narrow, it may under stress at the base thereof pull off from silver spot 4, and if the solder cone 5 is made too lowv in height, a straight-ended lead wired or I may under stress pull out from the solder-cone 5. Q I If desired, the end of the leadwire 6 or 1 may be bent at right angles, or bent in hook'form-v as illustrated in Fig. 3, in order to prevent it j from pulling out'fromthe solder cone :5. If desired, the soldering may be done by indirecth'eat ing such as by hot air blast or radiated heat, for example, in order to prevent possible damage to the tal by direct heating I Y The lead wires '5 and I may be soldered to the:

silver spot 4 on the crystalby using a small disc or pellet of solder placed therebetween and then fused to have the approximate cone or hell shape 7 ,as shown'in Fig. 3. The disc of solder referred to-may initially be of about .019-inch diameter d by .0l5-inchthickor'equivalent or other suitable volume, and may be composed of 40 per cent lead,

Fig-3 is a detail showing a circular stants of the crystal I.

I per cent tin with about 0.1 per cent silver added. The small quantity of silver is added to prevent the solder from absorbing the silver from the silver coatings I, I and I. A rosin alcohol flux in the proportion 01' 2 grams rosin to I ounces alcohol may be used for soldering. After solder- .ing, a camel's hair brush may be used to wash the soldered Joint with denatured alcohol.

Since the Q or ratio of mass reactance to resistance of ordinary soft solder itself-such as, for example, solder composed of 50 per cent tin and 50 per cent lead is rather low and decreases furth'er with an increase of temperature, and since the solder dot I occupies a moving area on the crystal surface and the same type of motion occurs in the solder I as that of the crystal in contact therewith, the effect of the solder dot I may be minimized by making it as small as possible and by placing it as near as possible to a crystal node thereby to minimize absorption of energy in the solder with resulting decrease of activity of the crystal I. The effect of the solder dot I on the activity of the crystal I may also be minimized by using a tin-antimony solder or other hard solder instead of the ordinary soft lead-tin solder since the former may have a better Q at the upper operating temperature limits due to its higher melting point. Accordingly, by using a hard solder such as, for example, a solder composed of 95 per cent tin and 5 per cent antimony, the effect of decreasing crystal activity at high temperatures maybe eliminated or reduced. This effect may also be reduced by limiting the amount of solder I, whether hard solder or soft solder is used. A lead-tin eutectic solder composed of 63 per cent tin and 37 per cent lead will permit less solder to be used at the crystal joint I and thereby reduce the amount of coupling to the supporting wire system. The effects produced by using different size solder dots I and different placement of the lead wires I and I on the crystal can be determined by their effects on the con- Typical constants for face shear mode CT crystals are: ratio of capacities-350 and Q-l5,000 to 30,000. The main effect of large solder dots I on the crystal is to reduce the Q since motion will be transmitted to it from the crystal I. The amount as well as the shape of the solder I at the crystal will affect the Q of the crystal I.

Fig. 4 is an enlarged detail showing the use of the spherical solder ball II for joining together the two ends of the lead wire I and the upright spring wire I embedded therein. While the supi porting spring wires I and I of Figs. 2 and 4 are therein shown in a particular position, namely, in planes at right angles with respect to the substantially coaxial lead wires I and I, it will be understood that they may extend from the solder balls II in any direction. As illustrated in Figs. 1 and 2, the upright spring wires 8 and 9 may have semicircular, circular or other bends therein to provide a resilient support for the crystal element I. As particularly illustrated in Figs. 1 and 2, the semicircular springs I and I may be in planes that are substantially parallel with respect to each other; or they may be inclined inwardly towards the crystal, or outwardly and away therefrom. The bent portions thereof may be elliptical or semicircular and may be of substantially. the same shape and size having their curved or bent portions extending from the same side of the horizontal coaxial lead wires I and l, as shown in Fig. 1, in order to prevent twisting of the horizontal lead wires I and 'I soldered thereto, whenever the crystal device is subjected to externally applied shock or jar, as may occur, for example, in mobile installations or during trade- 5 flirtation.

Fig. I is a greatly enlarged detail view of the crystal lead wire I or I arranged to extend straight through the solder ball II, and having a bell-shaped solder cone I for fastening the lead wireIorItothecrystalcoatingIorI. This bell-shaped type of solder cone I allows the lead wire I or I to be twisted in handling without much danger to breaking cone I and thereby forming a crater. For the purpose of analysis, the solder cone I is assumed to become part of the crystal I and to move with it, and the length of the lead wires I and I vibrating in iiexure is computed or determined from the top or apex of the solder cone I as described hereinafter. The amount of solder used in the cone I is kept at a minimum in order that the constants of the crystal equivalent circuit may not be modified too much by it. The effect of the solder in the cone I on the equivalent circuit is to raise the resistance in the equivalent circuit for the crystal and this resistance may increase with an increase in temperature. Accordingly. the amount of solder permissible in the cone I is determined by the maximum temperature at which the crystal unit is to be operated and the minimum Q allowable for the crystal unit.

As illustrated in Fig. 5, the lead wire I or I extends straight through the solder ball II which is suspended thereby and is attached to the support wire I or I by any suitable means such as a solder Joint II. Alternatively, instead of soldering, the lead wires I and I may be spot welded at II, to the supporting spring wires I and I without softening the phosphor bronze lead wires I and I to any appreciable extent. A very tight bond at II is obtained by such spot welding. Also, a solder pellet may be placed on the Joint II and spot welded at the same time in order to add weight at the joint II. if it is found necessary to add additional weight at this joint in order to keep standing waves off the mounting spring wires I and I.

Fig. 6 is a greatly enlarged view illustrating another type of crystal wire support utilizing a headed wire at Ia, in place of a solder cone I of Fig. 5, for attaching the lead wire I or I to the crystal I. The headed wire end Ia may be similar to that of an ordinary nail head and may be connected to the crystal coating I by sweating the wire head Ia to the crystal coating I. The wire head In may be a machined part and may be made of constant or uniform dimensions for many or all types of mountings. The amount of solder necessary to sweat the wire head Iain the silver spot I of the crystal I is considerably less than that used in a solder cone I, and hence the headed wire form of mounting Ia as illustrated in Fig. 6 will have less dissipation of energy at the higher temperatures. Moreover, the coupling between the vibrating system of the wires I and 1 and the vibrating system of the crystal I is reduced by the use of the headed wire In shown in Fig. 6. This results in reducing what may be termed a double system of standing waves on the wires I and I, one resulting from reflections from the solder ball II or clamped end of the wire, and the other resulting from reilections between the two or more resonant wires I and I coupled through the crystal I. These away the top or apex of the.

effects may be reduced by a reduction of the coupling between the crystal I and the wire vibrating systems 6 and I. It is difllcult if not impractical to try to balance the solder cones sufliciently to prevent the crystal motion from being transmitted to the lead wires 8, I, 8, 9. In most cases, the considerable amount of crystal motion transmitted to the lead wires 6, I, 8, 9 may be suflicient to set up standing waves therein.

Instead of using the integral form of headed wire 5a, the nail head form of Fig. 6 may consist of a metal washer having a small central opening of about the same size as the outer boundary of the wire 6 or I, the washer opening being placed'on the extreme end of the wire 6 or I and soldered both to the wire 6 or 1 and crystal coating 4 at the same time. By proportioning the thickness and the diameter of the washer, the joints between the wire and washer and between the washer and crystal plating may be made to have the same strength. If desired, the-washer may be stamped cone-shape, the larger diameter of the cone being placed at the jointbetween the washer and the crystal plating 4.

' As stated hereinbefore, the ends of the support wires 6 and I attached to the crystal I move with the crystal motion at the region of attachment, whether a shear, longitudinal, flexure or other type of face-mode or thickness-mode vibration is employed in the crystal I.

The effect of the wire support system on the crystal frequency may be reduced by increasing the size of the crystal element I, thus increasing the ratio of mass of the crystal I with respect to the mass of the wire supports. In the case of face-mode crystals the frequency of which is determined mainly by the major face dimensions, the thickness dimension may be conveniently increased in order to increase'the crystal mass relative to the supporting wire system. Since in practice the lead wires 6 and I are not ordinarily attached to the crystal exactly at a nodal point thereof, some of the motion of the crystal I is imparted to the lead wires 6 and 1 which support the crystal I, and the lead wires, therefore, become a part of the mechanically vibrating system. If the lead wires 6 or I' should be terminated at or too near a loop or point or maximum motion thereof, such as multiple half wavelengths of the desired'crystal frequency, a high mechanical impedance would be presented at the point of contact 5 between the crystal I and the lead wires 6 and I, which would tend to prevent motion of the crystal I and absorb energy from it with resulting increased resistance at resonance, and where there are several supporting lead wires on the crystal I, considerable energy may be absorbed from the crystal I.

It is possible to damp or dissipate the motion in the wires 6, I, 8, 9 by placing thereon along the entire lengths thereof some clamping or dissipative medium such as, for example, rubber cement, cotton sleeving, gold or other soft metal plating or other viscous material. Such dissipative media on the supporting lead. wires may be used to improve the activity. of the crystal I, but at the same time they tend to reduce the springiness of the lead wires 6, I. Alternatively,

instead of using such dissipative media, the crys-.

tal activity and stability may be improved by using a properly placed single massed weight III on each of the lead wires 6 and I in order to reflect, rather than to dissipate, the wave motion therein. By the use of such weights I0, harmful vibrations in the crystal supporting leads 6,

amount of motion in the lead wires 6 and I, and

I. 8, 9 connecting the crystal I with the mounting posts I2 may be eliminated by compelling the lead wires 6 and I adjacent the crystal plating I to vibrate in eflect as a clamped-free bar between the weights III on the lead wires and the crystal l. The weights III may consist of any suitable massed weight fastened to the lead wires 8 and'lat a proper point thereon. The proper point is at or near the wire nodal point or that at which the portion of the lead wires 6 and I between the solder dot 5 on the crystal I and the weight I0 acts as a clamped-free bar in resonance to the motion transmitted to the wires 6 and I by the crystal I. tions of the lead wires between the weight Ill and its far ends I2 may be bent or mounted inany' manner without affecting the activity or fredamping is introduced into the crystal I when the weight In is placed at or near one of the wire nodal points. The weights I0 may be placed oil the wire nodal points up to about a quarter of the distance between the nodes providing the motion transmitted to the wire 6 or I is not so great as to effect too much damping of the crystal I. The allowablevariation in any case depends upon the the size of the crystal I relative to its supporting wire system.

When the solder mass III is substantially nod-- ally located on the support wires 6 and I and is of sufiicient mass relative to the support wires, the support wires 6 and I between the mass Ill and the crystal element I become a composite vibrator at the crystal frequency and the support wires 8 and 9 between the solder mass I0 and the fixed base I2 do not afiect the crystal vibration adversely. Loads I0 so placed on the mount. wire system of the crystal I preserve high crystal activity or high Q," and low activity of the crystal I resulting from coupling between the vibrating wire supports and the crystal I may be avoided. The procedure of placing the weights III at the nodal regions on the wire supports controls, the mechanical coupling between the crystal and the crystal supporting wire system. The mass I0 is added at a specified distance along the lead wires 6 and I on both sides of the crystal I to cause reflection of the flexure vibrations produced on the lead wires 6 and l by the crystal I when it is operated. The distance is selected to cause maximum output in the crystal oscillator unit. The solder balls ID are placed on the lead wires 6 and I at or near a node thereof corresponding to the frequency of the crystal. Since in most cases the solder ball I0 need not be exactly at a node of the lead wires, the wire length between the solder ball l0 and the crystal element I may be a fixed value representing a. compromise suitable for use with crystals of diilerent frequencies but which are not too widely diiferent in frequencies.-

The small balls of solder III are placed ,41, 4,

'54, etc. of a wavelength of the waves produced on f the lead wires 6 and I from the top or apex of the solder cone 5. Depending upon the particular design, the solder balls Ill may be about .060 inch in diameter or of other suitable value-to give a mass sufllcient to prevent motion on the outer support wires 8 and 9 from adversely affecting the crystal vibration. When such solder weights The remaining porilareusedonandsuspendedbythewirest and I, theends of-the lead wires 8 and I beyondths weights Il may be soldered to the supp t at any point without aifecting the crystal resonant frequency or activity. The size of' the solder ball weight II is determined just sumcient to prevent vibration from the crystal I from being transmitted past the weight It. This allows the support to be fastened at any point on the wire support on the side of the weight II away from the crystal I.v The weight for one particular case was about 1.5 milligramsv of solder. Only a small amount of mass II is n and where the mam II is adamped material suchas a lead-tin solder, there will be little or no motion of the wires outside the load points Ill. Any suitable means may be employed to space and place the nodal solder ball II at a given distance from the crystal surface.

Accordingly, with the lead wires 6 and I soldered onto the crystal platinss 4, each soldered Junction itself mova and generates a transverse wave in the lead wires 6 and I, the motion being roughly indicatedby the dotted line in Fig. 5. -When the leadwire i or I is soldered by the solder ball II at a point corresponding to a nodal point on the lead wires t and I, there is no adverse reaction on the crystal. But ii' the lead wire 6 or I should be soldered at a point B, which is a loop or point of maximum motion in the lead wire I or I, the effect is to offer a high mechanical impedance at the point of contact I with the crystal I which would be reflected as a lowering of the activity of the crystal I. The nodes and loops on the lead wires 6 and I may be determined by trial, as by using a fixed clamp support on the lead wires 6 and I at various distances from the crystill I. When the clamp occurs at a loop of motion in the lead wire 6 or I, the oscillator activity may decrease to zero. The effects of clamping the lead wires 6 and I over wide ranges around the wire nodes thereof is to give a change in crystal frequency, the amount of which will be determined by the coupling between the lead wires 6 and I and the crystal I. A clamp or weight III placed at or near a node of motion on the lead wires 6 and I gives good activity for the crystal unit and stabilims the frequency.

The motion in the lead wires 8 and I is roughly that of a round rod vibrating in clamp-free fiexure. However, this is not strictly a case of pure clamp-free eflfect, since the point of contact 5 with the crystal I, which is the assumed free end, is restricted to a small slope, and the other end at the solder ball II is more of a yielding type supportthanafixedtypeof clamp.

The frequency f of a spring phosphor bronze clamp-free long rod or wire vibrating in flexure is given by the equation:

where v=transmission velocity of longitudinal waves in centimeters per second d=diameter of rod in centimeters or the direction of particle motion l=length of rod in centimeters or direction of Propagation m=l.875 for the first fiexure mode; and

=(n%)r for the second, third, etc. fiexure mode where n is the numerical order of the mode of vibration as 2.3, etc.

From Equation 1, the length of a given rod or wire at a given frequency may be computed.

As an example, assuming a' loo-kilocycle per second crystal I using a spring phosphor bronze wire rod of I millimeter in diameter, the length l of such clamp-free wire rod for the first mode will be and for the second mode will be l=.567 centimeter. 4

As another illustrative example for a phosphor bronze lead wire I or I of .0063 inch diameter acting as a clamp-free support, the length 1 thereof to have a frequency of 164 kilocycles per second is for the first mode l=.02'I'I inch.

These illustrative values from Equation 1 indicate approximate nodal points on the lead wires 6 and l where the wire 8 or I may be clamped so thatthe mechanical impedance of the wires 6 or I at the crystal I will be so low that its restriction to the motion of the crystal I will be negligible. The Q of the crystal I will decrease as the lead wire anti-nodes or loops are approached, which occur half-way between the values given by Equation 1, and the decrease in Q will be proportional to the degree of coupling between the two mechanical systems constituting the wire system and the crystal I.

Also, as indicated by Equation 1, the proper length of the lead wire 6 or I varies inversely as the square root of the frequency, and, accordingly, where the same lead wires 8 and I are used to support a crystal I having more than one effective resonnance frequency, the distance to the lead wire solder ball It must be a compromise in order to isolate the supporting system at both the lower and the higher resonances.

The simple fiexure formulas (1) apply in the case of a long thin rod or wire. When the length ".225 centimeter 40 l approaches or becomes equal to or less than the wire diameter, the resonating wire support member may be designed according to the particular mode of its vibration which may be, for example, a shear mode of motion especially in the case of the higher frequencies, such as 5 megacycles per second, for example. In the case of a wire support soldered to the crystal coating, the theory of resonating supports is similar to that heretofore discussed but takes into account also the actual solder cone connection 5 that fastens the wires 6 and l to the crystal I, and the special coupling between the crystal I and the wire vibrating system.

It will be understood that the solder ball III acts as a clamp for the wires 8 and I and may be placed at any point along the wires 6 and I corresponding to a wire node. The size or diameter of the solder ball III need only be sufiicient to act as a clamp, and, in general, the size will be in proportion to the wire diameter. The spacing between the solder ball Ill and the head or top of the cone 5 may be roughly computed from Equation 1, or may be determined by experiment. In practice, the optimum spacing as determined by test may be found to be slightly greater than that given by the Formula 1, due to the fact that the crystal or free end of the wires 6 and I is restricted to a small slope. The diameter of the solder ball III that acts as a clamp may also be determined experimentally by increasing its size or mass until there are no standing waves on the wires at the side of the solder ball I ll remote from the crystal I.

wire supports illustrating the use of a nodal massed weight I in the form of'a soldered wire stirrup II instead of asolder ball III-as illustrated II are as hereinbefore described securely atin Figs. 1, 2, 4, -and 6. Except for the substitution of the soldered stirrups Illa, I I in place of the solder ball III, Fig. l is similar to Fig. 4 and Fig. 8

is similar to Fig. 5 or 6. Fig. 9 shows the hairpin type stirrup ,II placed at a node on the lead wire 6 or 1 prior to soldering it thereto by means of the solder mass Ilia ofFigs. 7 and 8. As illustrated inFig. 9, th U-shaped copper wire stirrup II may besqueezed or clamped on or over the lead In Flfls. 13 to 16, the massed nodal weights Ilb wires .6 and I at or near a node thereof and then, as illustrated in Fig. 7 or 8, soldered thereto on the siderat IIla'away from the crystal I, in' order to remove the eifects of standing waves in the supportingwires 8 and 8; The crystal I may then be" ground tothe'desiredfrequency andsoldered into the spring mount wires I ands with little or no changes in the crystal activity or-frequency.

The U-shaped copper wire stirrup I I may be used to -properly locate and space the. solder mass Illa ata given distance from the crystal surface so that the resulting soldered stirrup" Illa, II is at or 'hereinbefore I *tached to the wires 6 and I and substantially centered thereon, the line of adhesion to the wires-8 and 'I being clear cut and definite. particularly on'the side thereof that is facing toward the crystal I. I

Figs. 13 to 17 are schematic views illustrating various modifications of wire supported crystals.

secured upon the crystal support wires 8 and I are illustrated as being of cubical form although and I. In Figs. 14 and 15, for example, the nodal weights IOb are shown at points on those parts of the wires 8 and I that are remote from the crystal l and removed from the L-bends in the vwires 8 and 1. It will be understood that the weights Iflb are located on the support wires in such positions and for the same purposes as herenear a node on thelead wires '8 and, I.- "The U-shaped stirrup II itself may be composed of soft tempered and having an over all length when bent into U shape of about V inch, for example. Alternatively, the massed weight Ilia, II may consist of a small copper or other disc'threaded ,on and soldered to the lead wires'i'and- I at or near a node thereof.

- Fig. 10 is a perspective view of a crystal mount ing, similar to that of Figs. 1 and 2, having the laterally extending lead wires 6 and I terminated in the solder masses III or 10a which form the l soldered joints between'the lateral lead wires 1 and I and upright spring wires 8- and 8. The

upright spring wires 8 and 8 in this instance, as

, shown in Fig. 10, comprisefull elliptical or circu lar-shaped springs, the two'semicircular springs 8 together forming a plane that is substan-- tiallyiparallel to the plane of the two semicircular springs 9. If desired, additional bent springs (not shown) may extend laterally between the hou's-' ing I4 and either or both of the springs 8 or 8' for the purpose of laterally bracing or stabilizing and. damping lateral oscillations in the springs 8 and ill As anvexample, the lateral stabilizing springs for the'spring crystal mounting may consist of extensions; of'the spring wires 8 and 'I of Figs. 1, 2 and 10, the, spring wire extensions extending outwardly from the solder balls I0 and' then being sprung in bent quarter-circular form .against the opposite inner side walls of the enclosing cover'or container I4. Such lateral "stabilizing-springs are useful as snubbers' for protection against shoclr or jar and also for dampening the effects of acoustical resonance waves' upon the crystalduring operation. Figs;11and'12 illustrate, respectively, face and end views of a four-wire support system as applied particularly to a longitudinal mode type of i crystali having longitudinally'divi'ded platings orcoatings 2a, 2b, 3a, 3b. The four L-bent spring lead wires 6 and I provide the nodal supports for the crystal Iand also the individual electrical connections for the crystal I, andin" addition are provided with the massed solder weights III or Illa as hereinbefore described, suit- ;ably spaced from the crystal I for the purposes as hereinbefore described. The balls I0 may becomposed of soft solder or of other metal or material and eachmay ordinarily weigh from, 12 to 20 milligrams ormore, for example. The balls inbefore described in connection with the solder balls I0 and the soldered stirrups IOa. Fig. 17 25, .016 inch diameter tinned phosphor bronze wire,

- reference to particular wire support mountings for particular crystals, it maybe applied generally to wire supported crystal units, examples of which are given in United States Patent 2,275,122, issued March 3, 1942, to A. W. Ziegler. Although this invention has been described and illustrated in relation to specific arrange- -ments, itis to be understood that it is capable of application in other organizations and is, therefore, not to be limited to the particular embodiments disclosed, but only by the scope of the appended claims and the state of theprior art.

What is claimed is: 1. A piezoelectric crystal mounting comprisin a flexible spring lead wire support attached to andsuspending said crystal, a solder ball fastened on said wire support substantially at a node thereof and away from a loop of motion therein, the wire length between said ball and said crys-' tal being substantially equal to an odd order multiple of a quarter wave-length of said crystal frequency whereby the natural frequency of said wire length is related to said frequency of said i a spring wire for supporting said solder ball.

2.: Piezoelectric crystal apparatus comprisings piezoelectric crystal, asupporting spring wire sei'requencyof said crystal, and means including I cured to said crystal and flexibly suspending said crystal, and a massed weight suspended on said wire substantially at a node thereof andintermediate the ends thereof, the wire length between said massed weight and said crystal having a natural frequency substantially equal to the frequency of said crystal and means including a bent flexible spring wire fastened to said first-mentioned wire. on the side of said weight that is away from said crystal for supporting said weight.

' 3. A mounting for a piezoelectric crystal cornprising crystal supporting flexible spring lead wires fastened to the crystal and carried by supports, and a clamp supported by and placed on each of said crystal supporting lead wires, said clamps each consisting of a massed weight fastened onto each of said lead wires substantially at a nodal point thereof, the length dimension of that portion of each of said lead wires between said weights and the crystal being made of a value to render each of said portions of said lead wires substantially a vibrating clamped-free .bar in resonance to the motion transmitted tosaid portions by the crystal, said weights being means for reflecting said motion and comprised of suf iicient mass to substantially eliminate said motion from the crystal from being transmitted through said weights to said supports through the remaining portions of said supporting wires, whereby the activity and frequency of the crystal are not appreciably affected by said supporting wires.

4. A crystal mounting in accordance with claim 3 wherein said resonant lead wire portions are substantially coaxial with respect to each other, substantially perpendicular to the major surfaces of the crystal, and fastened to the crystal substantially at points of minimum motion thereof.

5. A crystal mounting in accordance with claim 3 wherein said crystal supporting wires have substantially coaxial portions and said weights are placed thereon intermediate the ends of said substantially coaxial portions.

6. A crystal mounting in accordance with claim 3 wherein said resonant wire portions are substantially coaxial with respect to each other, said remaining wire portions are angularly disposed with respect to said resonant wire portions, and said weights are placed at the junctions between said resonant wires and said angularly disposed wires.

7. A crystal mounting in accordance with claim 3 wherein said weights are carried by bent spring wires.

8. A crystal mounting in accordance with claim 3 wherein said weights comprise a mass of solder on said crystal supporting wires.

9. A crystal mounting in accordance with claim 3 wherein said weights each comprise a spherical solder ball surrounding a portion of said lead wires.

10. A crystal mounting comprising a face shear mode piezoelectric crystal element having a nodal point substantially at the center of the crystal element, metallic coatings formed integral with the major faces of said crystal element, crystal supporting conductive lead wires soldered to said crystal coatings substantially at the centers of said major faces of said crystal element, spring mounts including bent spring wires carrying said lead wires, and a solder mass placed on each of said lead wires substantially at a node thereof, said mass of solder being of adequate mass to substantially prevent energy from being transmitted therethrough to said spring mounts.

11. A crystal mounting comprising a face shear mode piezoelectric crystal element having a nodal point substantially at the center of the crystal element, metallic coatings formed integral with the major faces of said crystal element, crystal supporting conductive spring lead wires soldered to said crystal coatings substantially at the centers of said major faces of said crystal element, spring mounts including bent spring wires carrying said lead wires, and a solder mass placed on each of said lead wires substantially at a node thereof, said mass of solder being of adequate mass to substantially prevent energy from being transmitted therethrough to said spring mounts, said lead wires being soldered to said spring mounts substantially at said nodes of said lead wires.

12. A crystal mounting comprising a face shear mode piezoelectric crystal element having a nodal point substantially at the center of the crystal element, metallic coatings formed integral with the major faces of said crystal'element, crystal supporting conductive lead wires soldered to said crystal coatings substantially at the centers of said major faces of said crystal element, spring mounts including bent spring wires carrying said lead wires, and a solder mass placed on each of said lead wires substantially at a node thereof and being of adequate mass to substantially prevent energy from being transmitted therethrough to said spring mounts, said solder mass comprising a ball of soft lead-tin solder.

13. A crystal mounting comprising a face shear mode piezoelectric crystal element having a nodal point substantially at the center of the crystal element, metallic coatings formed integral with the major faces of said crystal element, crystal supporting conductive spring lead wires soldered to said crystal coatings substantially at the centers of said major faces of said crystal element, spring mounts including bent spring wires carrying said lead wires, and a massed weight placed on each of said lead wires substantially at a node thereof and being of adequate mass to substantially prevent energy from being transmitted therethrough to said spring mounts, said massed weight comprising a U- shaped copper wire clamped over said lead wires at said node and soldered thereto on the side away from said crystal element.

- 14. A mounting for a piezoelectric crystal having metallic platings on its opposite major faces, mounting spring wires soldered to said crystal platings, a solder ball weightplaced on each of said wires substantially at a nodal point of said wires, the wire distance between said weights and said crystal platings being a value to allow said wires to vibrate substantially as a clamped-free bar. at the crystal frequency, the size of said solder ball weights being suflicient to prevent vibration from the crystal from being transmitted past said weights, and support wires fastened at points on said first-mentioned wires on the sides of said weights that are away from said crystal.

l5. Piezoelectric crystal apparatus comprising a face mode piezoelectric quartz crystal element having conductive electrode coatings formed integral therewith, a plurality of conductive resilient wire supports for said crystal element, each of said wire supports being soldered at one end thereof to one of said crystal coatings adjacent the nodal region of said crystal element and at its opposite end being carried by a base, each of said wire supports having a mass of solder comprising a cast solder ball or globule disposed thereon intermediate said ends of said wire support, the portions of said wire supports between said solder masses and said base having bends therein comprising springs, said mass being spaced on said wire substantially at a node thereof, the length of said wire between said mass and said crystal element being a value to provide flexure mode vibrations therein of a natural frequency for said length of said wire equal to the frequency of said crystal element, and said mass being of a magnitude suflicient to terminate said vibrations.

16. Piezoelectric crystal apparatus comprising a piezoelectric crystal, supporting spring wires for said crystal, a sinille massed weight suspended by each of said wires intermediate the ends thereof, the portions of said wires between said weights and said crystal being tuned to vibrate at a harmonic mode of vibration with a irequency substantially equal to the frequency IRVIN E. FAIR.

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