US2115145A

US2115145A - Piezoelectric crystal holder

Info

Publication number: US2115145A
Application number: US36467A
Authority: US
Inventors: Lawrence F Koerner
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1935-08-16
Filing date: 1935-08-16
Publication date: 1938-04-26
Anticipated expiration: 1955-04-26

Description

April 26, 1938. 1 F. KoERNr-:R

PIEZOELECTRIC CRYSTAL HOLDER Filed Aug. 16, 1935 3 Sheets-Sheet 1 INVENTOR By L .EKOERNER A TTORNEV April 26, 1938. F. KoERNER PIEZOELECTRIC CRYSTAL HOLDER Filed Aug. 16, 1935 3 Sheets-Sheet 2 wam, www

FIG. 7

' /NI/E'NTOR L F. KOERNER u). @uw

A TTORNEY April 26, 1938. L. F, KOERNER PIEZOELECTRIC CRYSTAL HOLDER Filed Aug. 16, 1935 5 Sheets-Sheet 3 F IG. /0

FIG. 9

/N VE N TOR L .F. KOERNER u) Umm ATTORNEY 206 20ami Patented Apr. 26, 1938 PIEZOELECTBJC CRYSTAL HOLDER Lawrence F. Xoerner, Summit, N. J.. anignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York l Application August 16, 1935, Serial No. 36,467

19 Claims.

yThis invention relates to piezoelectric apparatus and particularly to piezoelectric crystal holders.

One of the objects of this invention is t provide a piezoelectric crystal holder which may be small in height and compact ln size.

Another objectof this invention is to provide a piezoelectric crystal holder suitable for use on non-stationary radio equipment such as, for example, on aircraft.

Another object of this'invention is to reduce the capacity eiect in 'a piezoelectric crystal holder f holder suitable for use with various sizes and shapes of piezoelectric elements and the elec- 'trodes therefor.

Another object of this invention is to control pressure upon the surfaces of piezoelectric elements and upon the electrodes therefor.

Another object of this invention is to decrease the weight of electrodes for a piezoelectric element.

The particular forms of piezoelectric quartz crystal holders herein disclosed by way of example to illustrate the invention may be complete units ready for removable insertion in the oscillator circuit of a radio transmitter or receiver, for example, to control or maintain the frequency of oscillations at a desired value in accordance with the frequency characteristic of a suitable piezoelectric quartz crystal, for example.

The holder may consist of a molded Bakelite casing or container of cubical shape, for example, and a cover of the same material removably i'astened thereto by screws.

Terminals, including mechanically supporting pins or prongs, may be secured to the outside of the container and provide connections with a thermostatically-controlled heating element and a removable piezoelectric crystal and electrode assembly disposed inside thecontainer. A metal plate or partition disposed inside the container casing' may divide the container into two compartments. On one side of the partition plate, the thermostat and its corresponding heater may be mounted. 0n the opposite side of the partition plate, there may be provided an assembly consisting of a piezoelectric crystal, two electrodes, a removable insulating spacer surrounding at least a part of the periphery or edges of the electrodes and the crystal, and a plurality of resilient means including springs exerting suitable pressures on the spacer and also on the electrodes to hold the removable assembly in place within the container.

Ammer object of this inventionis to provide a (Cl. P11-427) A name-plate may be remo'vably secured to the cover of the enclosing case in such manner that the name-plate covers the screws securing the cover to the case thereby to render the contents ot the case accessible only upon removal of the name-plate as well as the cover.

Reduction in capacity losses may be obtained by utilizing dielectric materials as extensively as possible and by disposing metallic parts in such manner with respect to the electrodes as not to produce a short-circuiting capacitative connection therebetween. To reduce energy losses at high frequencies, the container casing and its cover may be formed of low-loss dielectric material.

In order to adapt the same holder to hold electrodes and crystals of various sizes and of various congurations, such as circular-shaped or squareshaped crystals and electrodes, for example, removable inserts or spacers of dielectric material having dimensions suitable for the electrodes, the crystals and the container compartment may be provided. Where the crystal and its electrodes are square-shaped, an L-shaped removable insert or spacer may be utilized to contact with two edges of each electrode.

Where unclamped operation of the crystal is desired, another insulating spacer partly or wholly surroundingthe peripheral edges of the crystal may have such slightly greater thickness with respect to the thickness of the crystal as to separate the two electrodes so that when this spacer is clamped between the two electrodes, the piezoelectric element itself is mechanically free to vibrate in unclamped position between the two electrodes and the spacer.

Resilient means in the form of a spring, for example, may be utilized to yieldably press one of the removable spacers, or the electrodes against the container or container cover. The spring may be in the form of a metallic spiral or coll spring, preferably of small diameter relative to the spacing of the electrodes, to avoid the introduction of an electrical capacity eiect with respect to the edges of the metal electrodes of the crystal.

Another spring of suitable tension value may be provided to resiliently press the electrodes and crystal together in clamped relation and also to press one of the electrodes in contact with the metallic heat-conducting partition which may be disposed in heat-conducting contact with the heating element. Such spring may be in the form of a V-shaped or bow-shaped leaf spring and may have a centrally disposed transverse corrugation or rib to permit the spring to be readily bent and adjusted by hand to the desired pressure to suit-the crystal which may be clamped between the electrodes.

Where clamping of the piezoelectric element between the electrodes is utilized, the metal electrodes may have a suitable number of projections, as three or four clamping projections, adapted to nodally contact with the piezoelectric body and to provide a spacing of approximately 40.001 inch between the depressed portion of the the spring so coincide with the contact points.

between the electrode and the piezoelectric element, the electrodes may be of thin lightweight material since substantially no bending movements will be exerted on the electrodes.

The depressed portion of each crystal electrode may be formed by photo-etching to very accurately control the depth and uniformity of depth of the depression with respect to the projections and the spacing of the depression with respect to the crystal with which the projections may be in contact. The very uniform depth of electrode depression that may be obtained by etching results in such advantages as securing high frequency stability, avoiding arcing between .the crystal and the electrode, and avoiding damping of crystal vibrations due to lack of uniformity in spacing .between the electrode and crystal. The electrode having the etched depression permits the use of such desirable metals as stainless steel without grinding and subsequent heat treating thereof.

Where temperature control of the piezoelectric crystal element is desired as, for example, to stabilize the frequency of associated radio equipment, the holder unit may contain its own thermostat andl heater within the casing of the unit. The thermostat may be of the bimetallic dishshaped snap action type of relatively large current capacity and may be connected in series with and directly control the supply of energy to the heater from a circuit including the prongs or pins secured to the exterior of the casing and spaced to fit corresponding sockets associated 'with the radio equipment to be controlled.

Where the thermostat directly controls the supply of energy to the heater, an external heater relay may be dispensed with to thereby eliminate the expense of and servicing of such additional relay.

This type of thermostat may be conveniently used to maintain properly the frequency of the associated radio equipment where the piezoelectric element has a qzero or low temperature coeilicient of frequency in a. region above a certain critical temperature such as, for example +32 F. and where the ambient temperature remains within a range from about 40 F. to about +140 F.' for example. In this instance, the

thermostat may be adapted to connect .the vheater to the power supply at a temperature not less than a predetermined value such as, for example, about +41 F., and to disconnect the power at some temperature appreciably higher. 'I'his operating range is selected that the quartz crystal unit may always be maintained above the .temperature of +32 F. mentioned though the ambient temperature may drop to 40 F. for example. This method of operation is made pos-V sible by using a quartz crystal element of low temperature coefficient of frequency in a region above +32 F. for example, and is of considerable advantage since no power is consumed by the heater except during periods when the temperature drops below the +32 F. in the example mentioned.

The crystal holder herein disclosed may also be utilized as a non-temperature controlled unit where, for example, vthe ambient temperature will remain within the range suitable for the crystal element that is employed. In this case, the prong or pin connected with the heating element may be electricallyl disconnected from the source of power and the remaining prongs connected with the crystal element may be electrically connected, through sockets spaced to rit the prongs, with the electrodes of a suitable space discharge device.

For a clearer understanding of the nature of this invention and the additional features and objects thereof, reference is made to the following description taken in connection with the accompanying drawings in which like reference characters represent like or similar parts, and in which:

Fig. 1 is an enlarged view partly in section of a piezoelectric crystal holder taken on .the line I-I of Fig. 2;

Fig. 2 is another view, partly in section, of the piezoelectric crystal holder shown in Fig. 1;

Fig. 3 is a view of the piezoelectric crystal holder shown in Figs. 1 and 2 taken on the line 3--3 of Fig. 1;

Fig. 4 is an exploded view of the piezoelectric crystal holder shown in Figs. 1 to 3;

Fig. 5 is a view partly in section of a modification of the holder shown in Figs. 1 to 4;

Fig. 6 is a sectional view of the side terminal shown in Fig. 5 taken on the line 6 6 of Fig. 5;

Fig. 7 is a sectional view approximately to size of another modification of piezoelectric crystal holder;

Fig. 8 is another sectional view of the holder shown in Fig. 7;

Fig. 9 is a view of a modified form of removable insulating spacer;

Fig. 10 is another view of the spacer shown in Fig. 9;

Fig. 11 is a view of another modification of removable insulating spacer;

Fig. 12 is a view of another electrode assembly showing two removable insulating spacers;

Fig. 13 is a sectional view of the assembly shown in Fig. 12;

Figs. 14 and 15 are views of another modification of the invention;

Fig. 16 is a. sectional view of still another modification of crystal holder; and

Fig. 17 is another view of the U-shaped spacer and insulating support shown in Fig. 16.

The several piezoelectric crystal holders shown in these gures may be small in height, compact in size, suitable for use on non-stationary radio equipment such as, for example, on aircraft, and' suitable for use with various sizes and shapes of piezoelectric crystals and crystal electrodes. They are complete units ready for removable insertion in the oscillator circuit of a radio transmitter or receiver, for example, to control or maintain the frequency of oscillations at a desired value in accordance with the frequency characteristic of a suitable piezoelectric element such as a quartz crystal.

Referring to Figs. 1 to 4, the holder may con-- engaging two internally tapped brass inserts Il embedded in the cover I2. 'Ihe name-plate Il covers the screws Il securing the cover I2 to the case I l thereby to render the contents of the case Il accessible only upon removal 'of the nameplate I1 as well as the cover I2. To reduce energy losses at high frequencies, the container II and its cover I2 may be formed of a low energy loss type of Bakelite or phenol formaldehyde condensation product.

Terminals, including three mechanically supporting hollow tubular metal pins or prongs 2l, 2i and 22 each having rounded tips 22 may be secured to the outside of the container I0 and provide connections, by

wires

24, 2l and 20 disposed centrally within and soldered to the tips 23 of studs 2t, 2i and 22 respectively, with a thermostatically controlled heating element Il and a piezoelectric crystal assembly including a piemelectrlc crystal and electrodes Il and I2 all disposed inside the container Il.

Where temperature control of the piezoelectric crystal element 40 is desired as. for example, to

stabilize the frequency of associated radio equipment (not shown), the heat source metallic casing 30 may be provided and may include therein any suitable heating resistance element 20a having one terminal soldered to the casing Il and the other soldered to a contact 2l, which, when the thermostat 31 is operated, is connected by the switch 34 to a contact l5, which is joined to a terminal 2|, the latter being connected by the wire 2l to the pin 20. 'Ihe side of the resistance element 30d connected to the frame I0 of the heat source is also connected to the plate 80 by means of the metal mounting screws Il and $5. The plate I is connected to the pin 22 by the wire 20 which may be soldered to the plate t0 or to the terminal 80.

'I'he bimetallic dish-shaped snap action disc l1 is supported by the heater casing III and, in response to selected temperature values, controls the switch 34. 'Ihe switch 34 and its cooperating contacts u and l5 may be of relatively large current capacity and in closed position are connected in series with and directly control the supply of heating energy to the heater 30a from a circuit including the connection pins 2l and 22 secured tothe exterior of the casing III. Since the

thermostat

34, 21 directly controls the supply of energy to the heater 20', an external heater relay may be dispensed with to thereby eliminate the expense and servicing of such relay. This type of thermostat shown in Figs. 1 to 4 may be conveniently used, for example, to maintain properly the frequency of the associated radio ,equipment (not shown) where the piezoelectric element 40 has a relatively small temperature coefficient of frequency above a critical temperature as about +32 F. for example, and the ambient temperature remains within a range from about 40 F. to about +140 l". for example. The thermostat 3l, 21 may be adapted to connect the heater 30a to the power supply at a temperature of about +41 F. for example, and

preciably higher. 'Ihis operating range is sej 3v todisconnectthepoweratsometemperatureap-llectedrthat the quarta element 4l may always'be maintained above' about +32 l". for example. though the ambient temperaturey may drop to about -40 P. for example. This m'ethod of operation -is made possible by using aquartz element 4l having a aero or low temperature coefilcient of'frequency above +32' l". and is of considerabie advantage since no power is consumed by the heater Il except during periods when `the temperature drops below a predetermined value. It will be understood that the crystal holders herein disclosed may also be utilized as a nontemperature controlled unit where, for example, the ambient temperature will remain within any range suitable for the crystal element Il, which may be. for example, a crystal adapted to function at temperatures below +32 F.

Each of the metal electrodes l0 and 52 for the crystal l. has four nat-surfaced corner projecting portions I4 which are adapted to contact the four corners of the crystal element I0 and a. central depressed portion I0 the surface of which is adapted to be uniformly spaced about 0.001 Inch or less from the surface of the crystal element Il. The depressed central portion 56 of the electrodes 5I and l2 may be formed by photo-etching, for example, to very accurately control the depth and uniformity of the depression l0 with respect to the projections 54 and the spacing of the depresion it with respect to the crystal Il with which the projections 54 are in contact. The purpose of the uniform depth of depression formed by the depressed portions 5I of the electrodes 5I and 52 is to secure frequency stability, to avoid arcing between the crystal element 4I and the

electrodes

50 and 52 and to avoid damping of vibrations of the crystal element 40 due to lack of uniformity in spacing between the depressed portions 5I of the

electrodes

50 and 52 and the crystal 40 which is clamped between the four projections 54 of the electrodes il and 52. The electrodes 50 and I2 may be formed of stainless steel, for example.

A metal plate or partition 60 slidable in oppositely disposed grooves tI and 62 in the interior walls of the container I0 mechanically divides the container Il into two compartments. On one side of the brass partition plate 60 in heat conducting relation therewith the thermostatcontrolled heater casing 3l may be mounted by the two screws N and 05 engaging two tapped openings .l and 61 in the brass mounting plate t0. The screws 64 and 05 extend only part way into the plate il topermit the electrode 50 to have a flat surfa contact relation with the plate 60. On the opposite side of the partition plate 60 there may be provided an assembly consisting oi' the metal electrode 50 disposed in heat conductive and in electrical conductive relation with the plate Il, the piezoelectric crystal III, the metal yelectrode 52, a phosphor bronze leaf spring 10, a brass connector plate 80 `disposed in contact with an interior wall of the Bakelite casing lli, an L-shaped removable insulating spacer 0I disposed' in slidably fitting relation between the metal plates il and il and surrounding a part of the periphery or edges of the electrodes 50 and l2, a phenol fibre strip l2, and a coil spring I" disposed in a pocket |02 in the bottom of the container I0 and exerting suitable pressure on the insulating strip l2, the insulating spacer 9| and also on the edges of the electrodes I0 and 52 to hold the assembly in place against the cover |2 of the container l0.

. The container Il may interchangeably hold electrodes and crystals of various siaes and of various shapes such as, for example, the circular-shaped crystal and electrodes of Fig. 11 or the square-shaped crystals and electrodes shown in the remaining figures. For this purpose. removable inserts or spacers of dielectric material having external dimensions suited to the dimensions of the compartment between the parallel spaced plates 50 and50 and having internal conilgurations suitable for the edges of the electrodes may be provided. Where the crystal and its electrodes are square-shaped, an L-shaped removable insert or spacer 50 as shown in Figs. 1 to 4 may be utilized.

The coil spring yieldably presses the L- shaped spacer 00 against the lower edges 5| and 53 of the

electrodes

50 and 52 and also presses the lopposite edges of the same electrodes against the container cover |2. Sufficient pressure is applied by the spring |00 to the edges of the

electrodes

50 and 52 to prevent vibration thereof when in service.- The'spring |00 is in the form of a metallic spiral or coil spring and may be of small diameter relative to the spacing of the

electrodes

50 and 52 to reduce to a minimum its electrical capacity effect with respect to the two edges and 5I of the

metallic electrodes

50 and 52.

'I'he spring 10 resiliently presses together in clamped relation the

electrodes

50 and 52 and the crystal 40 and also presses electrode 50 in contact with the metallic heat conducting plate 50 which is disposed in contact with the heat source casing 50. The spring 'I0 is in the form of a V-shaped leaf spring and may have a centrally disposed integral transverse corrugation or rib 12 extending across its entirel width to permit the spring to be readily bent at the corrugated portion 12 and adjusted by hand to the desired and somewhat critical pressure to suit the crystal 40 which may be clamped between the

electrodes

50 and 52. In a particular instance.'

the pressure exerted by the spring 'l0 was of the order of about five pounds.

The spring has approximately the same projected area as the area of the major surfaces of the

electrodes

50 and 52. 'I'he upper and lower ends 14 and 'I5 respectively, of the spring 10 register with the four flat pads or projections 54 of the

electrodes

50 and 52. Where the pressure points I4 and 'l5 of the spring I0 so coincide with the contact points 54 between the electrodes 5I and 52 and the piezoelectric element 40, the electrodes 55 and 52 may be of relatively thin lightweight material since substantially no bending movements will be then exerted on the

electrodes

50 and 52.

Electrical connections for the crystal holder shown in Figs. l to 4 are as follows: The connection pin 2| is connected with the high voltage side of the piezoelectric crystal element 40 by a circuit which includes the wire soldered to the tip 23 of the hollow tubular pin 2|, the brass connector plate 80 disposed along the internal walls of the insulating container I0 and soldered at 5| to the wire 25, the corrugated portion 'l2 of the spring 10, and the crystal electrode 52. 'I'he connection pin 22 may be connected with the electrode 50 by a direct or indirect circuit which includes the wire 25 soldered to the tip 23 of the hollow pin 22. The insulated terminal 3| of the heater is connected lwith the connection pin 25 by the insulated wire 24 which is soldered to the tip 2l of thevpin 2l. The two lower corners of the partition plate 50 are removed at 55 as shown in Fig. 4 to permit the insulated wire 25, for example. the pass from one side of the plate 55 lto the other side thereof. A portion of the upper half of the brass plate 50 may be removed as shown at 50 in Fig. 4 to permit a connector plate 05a as shown in Fig. 6 to pass from one side of the plate 50 to the other side thereof and without contact therewith when a connection to theelectrode 52 is made from a side terminal ||0 as shown in Figs. 5 and 6 instead of from a pin terminal 2| as shown in Figs. 1 to 4.

Through sockets corresponding to the spacing and dimensions of the pins 20, 2| and 22, the pin 2| may be connected to a control grid, for example, of a space discharge device, the pin 22 may be connected with a grounded cathode of lthe space discharge device and also with one terminal of a suitable source of energy for the heater 30, the pin 20 being connected with the other terminal of such heat energy source.

Figs. 5 and 6 show a modification of the crystal holder illustrated in Figs. 1 to 4. In Figs. 5 and 6, a brass side terminal ||0 having an opening is secured to the container l0 and is spun over and soldered at 2 to a brass connector plate 50a which is disposed on two internal walls ||4 and ||5 of the container I0 and which makes contact with the corrugation 12 of the spring 10 in the same manner as the connector plate 50 shown and described in connection with Figs. 1 to 4. In the modification shown in Figs. 5 and 6,

there is no electrical connection with the pin 2|,

the connection with the side terminal ||0 by means of the connector plate 60a being substituted. Otherwise, the device shown in Figs. 5 and 6 is of the same construction as that shown in Figs. l1 to 4.

In Figs. 7 and 8, a metallic leaf spring |20 of substantially thersame area as the area of the

electrodes

50 and 52 may have end portions |22 and |24 located so as to register with the projections 54 of the

electrodes

50 and 52 between which the piezoelectric crystal element is clamped with a spacing of approximately 0.001 inch or less between the central depressed portion of each electrode and 52 and the quartz element 40. The

electrodes

50 and 52 may be constructed from a sheet of stainless steel or iron suitably plated with chromium, for example. Where the pressure points |22 and |24 for example, of the spring |20 coincide with the contact points 54 between the

electrodes

50 and 52 and the quartz element 40, the electrodes may be made of relatively light material since substantially no bending movements will be exerted. An adjusting screw |25 engaging a support |20 is adapted to adjust the pressure of the spring |20 to a value suitable for the

electrodes

50 and 52, and the piezoelectric element 40. The spring |20 exerting a maximum pressure of about five pounds may be utilized, for example, when the

electrodes

50 and 52 have a thickness of about onefsixteenth of an inch and the width and length dimensions of the piezoelectric element 40 are of the order of about 28 and 38 millimeters, respectively. When a quartz element 40 of smaller dimensions is used, the pressure exerted by the spring |20 may be reduced. It will be understood that inrall cases, the pressure of the spring |20 will be adjusted to suit the particular crystal and electrode assembly that may be interchangeably used with the' crystal holder I0 by reason of the 75 aus,

removable assembly including the removable L- shaped insulating spacer disposed between the metallic plates 00 and 00a and contacting the lower edges of the electrodes 00 and y52.

lor in the form of a small -leaf spring, for ex-l ample, suitably fastened to the cover |2 and having at its free end or part, an insulating member 'in contact with the upper edges of the

electrodes

50 and 52 to prevent short-circuiting of the elec trodes.

The remaining parts' of the device shown in Figs. 'l and 8 are of the same construction and arrangement as those shown of like reference numerals in Figs. l to 6. 'It will be noted that V the terminal ||0 is connected to the high voltage. side of the crystal element 40 by a circuit including the connector plate 00a connected withy the side terminal ||0, the adjusting screw u|20, the spring |20 and the electrode I2. 'Ihe pin 22 is connected with the low voltage side of the crystal 40 through the metal partition plate 00 and the electrode 50. 'Ihe metal plate 00 supports the thermostat-controlled heater 00, forms a heat conducting path between the. heater 00 and the electrode 50, and forms part of the electrical connection between the electrode 50 and the pin 22.

electrodes

50 and 52 instead of only two adjacent edges of each

electrode

50 and 52 as shown in Figs. 1 to 8. The coil spring |00 holds the removable spacer |40 in position against the cover |2 of the container |0. The leaf spring 10 holds the crystal 40 and the

electrodes

50 and 52 in position. Electrical connections with the

electrodes

50 and 52 are made as hereinbefore described through the spring and metal plate 00 and through the metal partition plate 00.

Fig. 11 shows a. removable Bakelite spacer |42 like the spacer 40 of Figs. 9 and l0 but having an opening |44 therein of circular form adapted to-hold a crystal |45 of circular shape and a pair of equal diameter electrodes |40 and |41 of the same configuration. The spacer |42 being of the same external dimensions as the spacer 40 may be substituted for the spacer |40 and removably arranged in the crystal holder |0 as shown in Fig. 10. It will beunderstood that a suitable spring similar to the spring 10 of Fig. 10 may be utilized to hold the circular-shaped equal diameter crystal |45 and electrodes |40 and |41 of Fig. `l'l in clamped position against the metal partition 80 of Fig. 10.

Referring to Figs. 12 to 17, where unclamped operation of the piezoelectric crystal 40 is desired, an additional insulating spacer of Bakelite, such as the spacer |00 of Figs. l2 and 13 wholly surrounding the edges of the crystal 40 or the U- shaped spacers |10 of Figs. 14 and l5 and |00 of Figs. 16 and 17 partly surrounding the peripheral edges of the crystal 40 may have such slightly greater thickness with respect to the thickness of the crystal 40 as to separate the two flat-surfaced piezoelectric crystal 40, lthe spacer |00 and the electrodes |00 and |02 all disposed within the rectangular opening |4I of the spacer |40 and held in position and electrically connected by the spring 10 and the plate 00 in the manner shown in Fig. 10.

In Figs- 14 and 15, the U-shaped spacer |10 surrounds three edges of the quarts element 40 and has a thickness suiiiciently greater than the thickness of the piezoelectric element 40 to allow free movement of the element 40 between the electrodes |00 and |02 which are held in posi- -tion by the leaf spring |20, the L-shaped spacer made to the electrode |02 through the connector plate 00a and the side terminal ||0 but it will be understood that they may also be madeif desired from the pin 2| through the metal plate 00 as shown in Figs. 1 to 4.

In Figs. 16 and l'l, a casing 20| in which the piezoelectric apparatus is enclosed, may be composed, for example, of aluminum or of molded resin consisting of phenol formaldehyde condensation product. A suitable quartz piezoelectric element 40 vwhich may have a zero or low temperature coeiiicient of frequency is supported in unclamped position between the two atsurfaced metal electrodes |00 and |02 and the insulating U-shaped spacer |00. The electrodes |00 and |02 are held in position by an aluminum frame 205, a fixed insulating support 200 composed, for example, of phenol bre and attached to the frame 205 by a screw 200, a resilient insulated support 201 and a metal pin 200. 'Ihe electrodes |00 and |02 have flat surfaces adjacent the piezoelectric element 40. 'I'he U-shaped spacer |00 surrounds three edges of the crystal 40 and is spaced therefrom a suitable distance such as, for example, about one millimeter to allow iree unclamped vibration of the crystal 40. The thickness of the U-shaped spacer |00 is slightly greater than the thickness of the piezoelectric quartz crystal `40 to allow unclamped vibration of the crystal 40. The electrodes i 00 and |02 and the spacer |00 fit into a groove in the fixed support 200. A small metal leaf spring 200 preferably of narrow width relative to the spacing of the electrodes |00 and |02 is attached at its center to the support 201. Two screws 2|0 passing through two holes in the ends of the metal leaf spring 200, secure the vspring 200 to the frame 205. 'I'he spring 200 resiliently presses the insulating support 201 against the upper edges of the electrodes |00 and |02 to hold the assembly in position.

The pin or plunger 200 exerts a suitable pressure on the electrode |02 by means of a coil spring 2| I, the convolutions of which surround the plunger 200. This pressure insures constant 3 anales contact between the electrodes and` |02 and the U-shaped spacer |00. Both thev plunger 200 and the spring 2|| are contained wlthina screw member 2|2. The screw member 2|2 isinserted 5 in a metallic bushing 2|0. The bushing 2|0 is .secured to an insulating support 2M, which may be composed of phenol libre. The phenol nbre support 2H is, in turn, iixedly attached to the frame 20,5.

"When temperature control oi the piezoelectric -crystal 40 is desired, a thermostat-controlled heater 80 as shown in Figs. 1 to 4, ior example, may be mounted in the space 2|0 and secured by screws 8l' and 85 (Fig. 1) to the i'rame 200 at 2|1. As shown in Figs. 1 to 4, the thermostat may comprise a bimetallic cupped disc 01 having a contact switch 00 nxedly attached -thereto which, when the cup-shaped disc 01 assumes a convex conguration in response to a predeter mined temperature. engages two suitable metal-l lic contacts to supply energy to the heater 00. 'I'he bimetallic cupped disc 01 may be. for example, of the type disclosed in U. S. Patent 1,448,240 granted to J. A. Spencer. The heating unitl 90 may comprise any suitable heating coil wound on a mica card, for example.

The frame 205 may be suitably attached as by bolts (not shown) to a base composed, for example, of laminated

phenol ilbre sections

224 and 225. The base 220 ilts into the casing 20| and may be secured thereto by suitable screws (not shown). Three spaced prongs 221, 220 and 229, corresponding to prongs 20, 2| and 22 of Figs. 1 to 4, provide connections to the piemelectric crystal 40 and to the heating unit if utilized. 'I'he prong 220 is connected to the bushing 2|3 by a wire 200. 'I'he prong 220 may be connected by a wire (not shown) to the thermostat. The prong 221 may be connected 40 l to the frame 205. Since the metal electrode'l00 Ris disposed in contact with the metal frame 205, current may pass from the prong 220 to theprong 221 by a circuit including the wire 230, metallic bushing 2|0, screw member 2|2,

plunger 208, electrode |92, quartz element 00,

electrode |90, and frame 205. The heating circuit, if utilized, may be completed from the prong 229 through the switch of the thermostat, the heating coil and the frame 205 to prong 221. 'Ihe three prongs 221, 220 and 229 are insertable in suitably spaced sockets (not shown). Heating current may be applied to the prongs 221 and 229, while the leads from the oscillator or other apparatus to be associated with the piezoelectric element 40 may be connected to the prongs 221 and 228.

If the replacement of one piezoelectric element 40 by another is desired, the casing 20| may be disengaged from the frame 220 and the screw member '2|2 rotated in such manner that the plunger 208 is separated from the electrode |92 with which the plunger 200 is normally in contact as shown in Fig. 16. Bypressing the resilient support 201 in an upward direction, the electrodes |90 and i 92, the spacer |00 and the quartz crystal 40 are easily removed from` the frame 205. To place the electrode assembly in the frame 205, the resilient support 201 is pressed in an upward direction and the electrodes |90 and |92, the quartz crystal I0 and the spacer |80 placed in normal position in the apparatus. The screw member 2|2 is then rotated until suflicient pressure is exerted by the plunger 208 on the electrode |92 to hold the aS- sembly in place.

vspacer upon removal of the cover |2 without dissame manner that the Vpiezoelectric element 40 is Asa modiiled arrangement, the two electrodes 00 and 02 each having the four clamvinl Projections 04 for clamping the marginal corners of the piezoelectric quartz crystal 40 as illustrated in connection with lllgs.A 1 to l1|), may be replaced by 5 two electrodes ot suitable dimensions-each having two ilatmaior surfaces without projections 04 such as the electrodes |00 and |02 of Figs. 13, 14, and 16 and an insulating spacer, such as the U- shaped spacer |100! Fig. 14 or |00 of Fig. 18, 10 clamped therebetween for permitting unclamped vibration ot a piezoelectric,crystal such as the crystal 40..A The U-shaped spacer such as the spacer |10 o! Figs. 14 and 15 may be arranged in any of the holders oi' Figs. 1 to 10 in the position 15 as shown in Figs. 14 and -15 or may be inverted from such position shown in Figs. 14 and 15 so that the opening between the sides thereof will be at the top of the holder adjacent the cover end |201 the holders of Figs. 1 to 15 thereby to 20 allow removal and replacement ot the crystal plate 40 through such opening in the U-shaped assembling the electrodes such as the pair oi electrodes |00 and |92 and the springs 10 or |20 25 of Figs. l to 15. With such inverted arrangement oi the U-shaped spacer, the same arrangement ot the L-shaped spacer 90 and the springs |00 or |00 may be med as illustrated in the crystal holders shown in Figs. 1 to 4 and in Figs. 14 and 80 15 for example.

As another modified arrangement, where it is desired to have a single holder contain two piezoelectric elements o! the same or diiIerent frequencies instead of only one element as illustrated 85 in the several gures herein, the additional piemelectric element may be disposed in the space designated ior the thermostat and heater in the disposed as shown in the drawings. The addi- 40 tional piezoelectric element may be connected between the ground prong and the prong that is normally connected with the heater terminal where a heater is used or that is normally disconnected when no heater is used. For example, in 45 the modication shown in Fig. 1, the additional piezoelectric element may'be symmetrically assembled and connected in the space at the lett of the partition plate in exactly the same manner as the crystal 40 isassembled and connected in the 50 space at the right o1' the partition plate 00, the high voltage side of the additional crystal being connected with the prong 20 in the same manner that the high voltage side oi the crystal 40 is con. nected with the prong 2|, and the low voltage side 05 of both crystals being connected by the partition plate 00 and the flexible wire 26 with the common or ground prong 22.

. Although this invention has been described and illustrated in relation to speciilc arrangements, 0o it is to be understood that it is capable of application in other organizations and is, therefore, not to be limited tithe particular embodiments disclosed but only by the scope of the appended claims and the state of the prior art.' 05 What is claimed is: 1. Piezoelectric apparatus comprising a piezoelectric crystal, a plurality of metallic electrodes for said crystal, a thermostat-controlled heat source, an insulating container enclosing said 70 crystal, electrodes and heat source, said container having a removable insulating cover, a plurality of metallic connection terminals including a plurality of spaced pins or prongs secured externally t0 said container, a removable metallic heat con- 15 said connector plate ducting partition disposed within said container in contact with said heat source and in contact with one of said electrodes, a metallicconnector plate disposed in contact with an internal wall '.of said container, means connecting said partition with one of said terminals, means connecting th another of said terminals, a removable i.- haped insulating spacer disposed between said partition and said connector plate and disposedin contact with the edges of said plurality of electrodes, means including a removable spring resiliently exerting pressure on said spacer and on said edges of said electrodes to prevent shifting of saidspacer and said electrodes, and means comprising a removable leaf spring disposed in contact with said connector plate and in contact with`\a surface of 'one of said electrodes for resiliently exerting pressure on said electrodes and on said crystal.

2'. Piezoelectric apparatus comprising a piezoelectric crystal, a plurality of removable electrodes for said crystal, a thermostat-controlled heating element, an insulating container enclosing said crystal, electrodes and heating element.

a plurality of metallic terminals including a plurality of pins or prongs secured externally to said container, a removable metallic heat conducting partition disposed within said container in contact with said heating element and in contact with one of said electrodes, a metallic connector pla-te disposed in contact with an internal wall of said container, means connecting said partition with one of said terminals, means connecting said connector plate with another of said terminals, a removable insulating spacer disposed between said l partition and said connector plate and disposed in contact with the `edges of said plurality of electrodes, means resiliently exerting pressure on said spacer, and means resiliently exerting pressure on said electrodes.

3. Piezoelectric apparatus comprising a piezoelectric crystal, a plurality of removable electrodes for said crystal, a thermostat-controlled heating element, an insulating container enclosing said crystal, electrodes and heating element, said container having a removable insulating cover, a plurality of metallic terminalsi including a plurality of pins or prongs secured externally to said container, a removable metallic heat conducting partition disposed within said container in contact with said heating element and in contact with one of said electrodes, a metallic connector plate disposed in contact with an internal wall of said container, means connecting said partition with one of said terminals, means connecting said connector plate with another of said terminals, and means including a removable insulating spacer and a plurality of resilient devices positioning and interconnecting said electrodes and crystal between said partition and said connector plate.

4. Piezoelectric apparatus comprising a piezoelectric crystal, a plurality of removable electrodes for said crystal, an insulating container enclosingsaid crystal and said electrodes, a plurality of metallic terminals including a plurality of prongs secured externally to said container, a plurality of metallic connector plates disposed in spaced parallel relation within said container, means connecting one of said plates with one of said terminals, means connecting another of said plates with another of said terminals, a removable L-shaped insulating spacer disposed in contact with the edges of said plurality of electrodes, means including a spring resiliently exerting pressure on said spacer and on said edges of said plurality of electrodes. and means including a leaf spring connected with one of said plates and resiliently exerting pressure on a surface oi' one of said electrodes and pressing another of said electrodes against another of said plates.

5. Piezoelectric apparatus comprising a piezoelectric crystal, Ya plurality ofremovable electrodes for said crystal, an insulating container enclosing said crystal and electrodes, a plurality of metallic terminals including a plurality of prongs secured externally to said container, a plurality of metallic connector plates disposed in 'spaced parallel relation within said container,

means connecting one of said plates with one of said terminals, means connecting another oi'` said plates with another of said terminals, a removable insulating spacer disposed in contact with the edges of said plurality of electrodes, means resiliently exerting pressure on said spacer and on said edges of said plurality of electrodes, and means connected with one of said plates and resiliently exerting pressure on a surface of one of said electrodes and pressing another of said electrodes against another of said plates.

6. Piezoelectric apparatus comprising a piezoelectric crystal, a plurality of electrodes for said crystal, an insulating container enclosing said crystal and electrodes, a plurality of metallic connector plates disposed in spaced parallel relation within said container, a removable L-shaped insulating spacer disposed in contact with the edges of said plurality of electrodes, means including a spring resiliently exerting pressure on said spacer and on said edges of said plurality of electrodes, and means incuding a leaf spring connected with one of said plates and resiliently exerting pressure on a surface of one of said electrodes and pressing another of said electrodes against another of said plates.

7. Piezoelectric apparatus comprising a piezoelectric crystal, a plurality of electrodes for said crystal, an insulating container enclosing said crystal and electrodes, a plurality of metallic conductor plates disposed in spaced parallel relation within said container, a removable insulating spacer disposed in contact with the edges of said plurality of electrodes, means resiliently exerting pressure on said spacer and on said edges of said plurality of electrodes, and means connected with one of said plates and resiliently exerting pressure on a surface of one of said electrodes and pressing another of said electrodes against another of said plates.

8. Piezoelectric apparatus including a piezoelectric element, a plurality of electrodes for said element, an enclosing container for said element and said electrodes, and means for removably and resiliently positioning said electrodes within said container including a rigid insulating retaining member disposed in contact with a plurality of the edge faces of each of said plurality of electrodes and a spring exerting compression on said insulating member and on the edges of said plurality of electrodes.

9. Piezoelectric apparatus including a piezoelectric element, a plurality of electrodes for said element, an enclosing container for said element and said electrodes, and means for removably and resiliently positioning said electrodes within said container, said positioning means including a rigid insulating body disposed in contact with adjacent edges of said plurality of electrodes, and a spring exerting compression on said insulating body.

10. Piezoelectric crystal apparatus including a piezoelectric crystal, a plurality of electrodes for said crystal, a housing for said crystal and said electrodes, and means locating said electrodes within said housing including removable retaining means contacting the adjacent outer edges of said plurality of electrodes and a spring exerting compression on said retaining means.

11. Piezoelectric crystal apparatus including a piezoelectric crystal, a plurality of electrodes for said crystal, a housing for said crystal and said electrodes, and means locating said electrodes withinsaid housing including removable L-shaped retaining means contacting two of the outer edges of each of said plurality of electrodes.

12. In a piezoelectric crystal holder, a container, a piezoelectric crystal, electrodes for said crystal, and means resiliently positioning said electrodes and said crystal within said container including removable spacing means contacting at least a part of the outer edges of said electrodes and having a thickness greater than the thickness of said crystal.. v

13. Piezoelectric apparatus including a plurality of electrodes, a piezoelectric crystal disposed between said electrodes, means detachably dis- 'posed between said electrodes .for spacing said electrodes a distance greater than the thickness of said crystal, means-.detachably disposed in contact with at least a part of the outer edges of said `electrodes for positioning said electrodes, and` means resiliently holding said spacing means and said electrodes. f

i4. Piezoelectric apparatusfsincluding a plurality of electrodes, a piezoelectric crystal disposed between said electrodes, "an insulating spacer detachably disposed betWeen'said electrodes and having a thickness greater than the thickness of said crystaland surrounding at least a part of the whole peripheral edge of said crystal, and means resiliently holding said spacer and said electrodes comprising a rigid insulating body disposed in contact with the edge faces of said plurality of electrodes, 4a. spring exerting compression on said body, and. a spring exerting pressure on a major surface of one of said electrodes.

15. Piezoelectric apparatus including a plurality of electrodes, a piezoelectric crystal disposed between said electrodes, a spacer disposed between said electrodes and having a thickness greater than the thickness of said crystal and surrounding at least a part of the whole peripheral edge of said crystal. a spacer having a thickness greater than the thickness of said first mentioned spacer and surrounding at least a part o`f the peripheral edges of said electrodes, and means positioning said spacer and said electrodes.

16. Piezoelectric apparatus including a pair of spaced parallel metal plates, a piezoelectric ele'- ment, a pair of electrodes each having -a fiat surface, a U-shaped insulating spacer surrounding three edges of said element and having a thickness greater than the thickness of said element, means including a spring for clamping said U-shaped spacer between said fiat surfaces of said pair of electrodes and for holding said electrodes and connecting said electrodes with said plates, an L-shaped insulating spacer surrounding two edges of each of said electrodes and having a thickness substantially equal to the spacing between said pair of plates, and means including a resilient device for exerting pressure on said L-shaped spacer.

17. Piezoelectric apparatus including a piezoelectric crystal, a plurality of electrodes for said crystal, an enclosing container for said crystal and said electrodes, a removable insulating spacer disposed in contact with the edge faces of said plurality of electrodes, means supported by said containerv and resiliently exerting pressure on said spacer and on said edge faces of said electrodes, and means supported by said container and resiliently exerting pressure on a major surface of at least one of said electrodes.

18. Piezoelectric apparatus including a piezoelectric crystal, a plurality of electrodes for said crystal, an insulating spacer disposed in contact with the edge faces of said plurality of electrodes, means including a resilient device for exerting pressure on said spacer in a direction substantially parallel to the major surfaces of said electrodes, and means including another resilient device for exerting pressure on said electrodes in a direction substantially perpendicular to the I'najor surfaces of said electrodes.

19. Piezoelectric crystal apparatus including a plurality of crystal electrodes, means including a resilient device for exerting clamping pressure on the major surface of said electrodes, and means disposed in contact with adjacent edge surfaces of said plurality Aof electrodes and including another resilient device for exerting clamping pressure on said edge surfaces.

LAWRENCE F. KOERNER.