US2150328A - Mounting arrangement for piezoelectric crystals - Google Patents

Description

Mamh 14, 1939. Q E, KEALL ET AL 2,150,328

MOUNTING ARRANGEMENT FOR PIEZOELECTRIC CRYSTALS Filed June 16, 1937 INVENTORS OSWOZD EBB AM KEAZZ ERIC OWE/V SM/7H Patented Mar. 14, 1939 UNITED STATES FATENT OFFICE MOUNTING ARRANGEMENT FOR PIEZO- ELECTRIC CRYSTALS poration of Delaware Application June 16, 1937, Serial No. 148,462 In Great Britain June 25, 1936 11 Claims.

This invention relates to mounting arrangements for quartz and other piezo-electric crystals. Known methods of mounting piezo-electric crystals-especially those methods in common use for crystals for radio receiving apparatusoffer various difficulties. Where the crystal is mounted loosely between plates there is the difiiculty that mechanical shock must be guarded against otherwise variations in performance will result; where the crystal is held lightly in place between plates its electric selectivity is impaired; and where light spring contacts bearing on metal films on the crystal are used means must be provided for positioning the crystal without applying to it such mechanical pressure as will appreciably impair its electrical efiiciency while at the same time there must be protection against mechanical shock. These difiiculties with known crystal mounts can be overcome in the laboratory but the object of the present invention is to provide mounts which can be simply manufactured in quantity and will nevertheless result in uniformity of performance, freedom from mechanical shock and electrical stability and sensitivity of a high order.

According to this invention, a piezo-electric crystal is supported between conductive members of metal wool which make electrical contact with opposite faces of said crystal.

Preferably, the crystal is positioned between the metal wool members by means of an insulating bridge piece from a pair of metal supports fused through the footstep of an evacuated glass envelope and contact is made to the opposite faces of the crystal by means of pads of steel wool which are also carried by said supports which act as the connection means for the crystal.

The invention is illustrated in the accompanying drawing, in which:

Fig. 1 shows in elevation and Fig. 2 in plan, one embodiment of the invention;

Figs. 3 and 4 being views, respectively, similar to Figs. 1 and 2 and showing another embodiment.

Referring to Figs. 1 and 2, there is employed an evacuated glass envelope I with the usual reentrant footstep 2 through which are fused two support and connector rods or wires 3, l. A quartz crystal 5 is mounted in a mica bridge piece 6 which is held between the two supports 3, 4 in any convenient way, for example by means of collars 1 attached to the bridge piece and fixed on the supports. The crystal 5, shown as rectangular, is a loose fit in a hole in the bridge piece.

Also carried from the supports are metal cups 8, 9 or the like, in each of which is positioned a brush or pad it, ll of fairly fine steel wool. One pad ll) of steel wool contacts lightly with one operative face (the top) of the crystal and the other H contacts lightly with the other (the bottom).

In order to facilitate the obtaining of good contact, the operative faces of the crystal (with which the steel wool pads 19, H contact) are provided with thin metal or other suitable conducting coatings, e. g. graphite; e. g. metal coat ings may be sputtered on or they may be obtained by depositing suitable metallic solutions or suspensions and then firing. Known commercially available metallic solutions or suspensions may be transformed into metal coatings by firing at a temperature of about 400 C.a temperature well below the critical temperature of quartz. In the firing process it is advisable to raise the temperature and allow the crystal to cool off fairly slowly in order to minimize risk of splitting the crystal. Where mass produced crystal units are in question, the fired solution method of obtaining the metal coatings would appear to be preferable to the spluttering method.

The steel wool employed should be of a grade slightly coarser than ordinary cotton cool; if finer grade steel wool is employed, there is a slight risk that individual hairs of the woo-l-which in a very fine wool are difficult to see-may be left in such positions as to give short circuits from pad to pad.

The mica bridge 6 may conveniently be about 3 mils thick and the hole or slot therein (in which the crystal is a loose fit) is preferably such as to clear the crystal by about 0.5 mm. all round.

The pressure between. the pads l8, H and the crystal 5 may be adjusted in air before performing the operation of sealing the unit (consisting of the crystal, bridge, pads and supports) in position. After scaling in, the envelope is partially or highly evacuated, one result of evacuation being to reduce the effective resistance of the crystal and thus increase its electrical selectivity.

The arrangement of Figs. 1 and 2 is satisfactory for crystals of relatively short length but where long crystals are in question there is a tendency for the crystal to rock about an axis passing through the pads It, I I so that it may fall out of the holder. To avoid this defect, it is preferred to employ the modification shown in Figs. 3 and t for a long crystal. In Figs. 3 and 4, there are employed two U-shaped pieces l2, 13 of wire which may be supported as shown from the sup- 5 ports 3, 4 or if preferred, may be supported by additional wires fused into the footsteps 2 but not employed as electrical connectors. The ends of these pieces of wire extend across near the ends of the crystal but are spaced from its operative faces, the wire ends in one case (wire i2) passing over the crystal and in the other case (Wire [3) passing underneath. The wire ends are near enough to the crystal to prevent its falling out of the holder as a result of mechanical shock, e. g. during transport.

Although in the figures glass pinches of ordinary form are illustrated, ring seals may be employed or the form of construction now usual in socalled all-metal valves may be employed, with an outer cylinder acting as a screening case. Again the envelope may be fitted with a suitable base (not shown) fitted with contacts for insertion into a co-operating holder, e. g. an ordinary valve holder.

What is claimed is:

1. A mounting arrangement for a piezo-clectric crystal characterized in that the crystal is supported between conductive members of metal wool which malte electrical contact with opposite faces of said crystal.

2. A piezo-electric crystal mounting arrangement comprising a piezo-electric crystal positioned between metal wool contact members by means of an insulating bridge piece carried between metal supports which also support the said metal wool contact members and also act as electrical connectors leading thereto.

3. An arrangement as claimed in claim 2 wherein the crystal, bridge piece and contact members are mounted in a hermetically sealed glass envelope through which the support memhere are fused.

4. A piezo-electric crystal holder comprising a crystal supported between metal wool contact members and guided by an insulating plate, said contact members and said insulating plate being carried by metal supports, said metal supports being mounted in a hermetically sealed partially evacuated envelope, and connection leads passing through said envelope for making electrical connection to said contact members.

5. A piezo-electric crystal holder comprising a crystal supported between metal wool contact members and guided by an insulating plate, said contact members and said insulating plate being carried by metal supports, said metal supports be ing mounted in a hermetically sealed highly evacuated envelope, and connection leads passing through said envelope for making electrical connection to said contact members.

6. A piezo-electric crystal holder comprising a crystal having its faces coated with a thin metallic layer supported between metal wool contact members and guided by an insulating plate, said contact members and said insulating plate being carried by metal supports, said metal supports being mounted in a hermetically sealed envelope, and connection leads passing through said envelope for making electrical connection to said contact members.

7. A mounting arrangement for a piezo electric crystal characterized in that the crystal is supported between conductive members of metallic steel wool which make electrical contact with opposite faces of said crystal.

8. A piezo-electric crystal mounting arrangement comprising a piezo-electric crystal positioned between metal wool contact members by means of an insulating bridge piece having an aperture therein wherein said crystal is loosely guided, said bridge piece being carried between metal supports which also support the said metal wool contact members and also act as electrical connectors leading thereto.

9. A piezo-electric crystal holder as claimed in claim 8 wherein means are provided for preventing the crystal irom being shaken out of the aperture in said bridge piece.

10. A piezo-electric crystal mounting arrangement comprising a piezo-electric crystal positioned between metal wool contact members by means of an insulating bridge piece having an aperture therein wherein said crystal is loosely guided, said bridge piece being carried between metal supports which also support the said metal wool contact members and also act as electrical connectors leading thereto, and means comprising two guide members oppositely disposed to prevent the crystal from being shaken out of the aperture in said bridge piece.

11. A piezo-electric crystal mounting arrangement comprising a piezo-electric crystal positioned between metal wool contact members by means of an insulating bridge piece having an aperture therein wherein said crystal is loosely guided, said bridge piece being carried between metal supports which also support said metal wool contact members and also act as electrical connectors leading thereto, and means comprising two U-shaped guide members oppositely disposed to prevent the crystal from being shaken out of the aperture in said bridge piece.

OSWOLD EDWARD KEALL. ERIC OWEN SMITH.

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