Patent GB-626365-A (GB)
Title: Improvements in or relating to piezoelectric crystal apparatus
IPC: H03H9/05
Filed: 1946-12-23
Abstract: 626,365. Piezo-electric crystal mountings. WESTERN ELECTRIC CO., Inc. Dec. 23, 1946, No. 37771. Convention date, Dec. 28, 1945. [Classes 40 (v) and 40 (vi)] A piezo-electric crystal element is held between two insulating plates, the faces of the plates facing the crystal having electrode coatings thereon and also raised areas of metallic coating which are in contact with the crystal to space the electrodes therefrom. Fig. 4 shows a ceramic plate 2 having its central area 31 metallized to form an electrode and thicker coatings 30 around the periphery. An area on the reverse face of the plate is also metallized and is connected to the electrode by the silvered or gilded surface of two holes 32 through the plate. The electrode may be divided in two along a diameter. In one alternative arrangement the thicker coatings are applied in small circular areas around the periphery of the plate (Figs. 7 to 9, not shown), and in another the electrode plating is thickened around the edge, for example by making the plating concave (Figs. 11-13, not shown). Fig. 1 shows a thickness mode crystal element (e.g. of AT or BT cut quartz) supported between. two ceramic plates 2, 3 of the Fig. 4 type which are clamped between silver plated pins 9 and 11 by means of a tinned brass plate 7 and a plated spring 34. The pins are supported in a metal casing 15, 17, 19 by glass seals 13. Fig. 15 shows a crystal element 1 supported between insulating plates 2, 3 having horizontally bisected coatings 31A and 31B, the plates being urged together by V-shaped springs 60. A screening disc 56 has two further discs 58 fastened by eyelets 57 to its surfaces and these protrude into metallized grooves 40 in the plates to resiliently support the crystal. Disc 56 is sealed between two annular flanges 54 whichcarry the enclosing glass envelope 52. Plated wires 50 are soldered to the metallized holes in the plates which connect to the electrodes. Locating pins 41 are soldered to one plate and slide into grooves in the edge of the other. Fig. 17 shows an oscillator in which a crystal Q is excited in a mechanical-harmonic mode by means of a circuit T1 tuned to the harmonic and connected in the cathode grid and screen grid circuit in the Hartley fashion. A tuned circuit T2 in the anode lead mav be tuned to select a yet higher harmonic. Capacitor C1 neutralizes the static self-capacitance of the crystal. The Specification as open to inspection under Sect. 91 also shows modifications of the circuit of Fig. 17 in which tuned circuit T2 replaces resistor R3 and in which the positions of condenser C1 and crystal Q are interchanged (Figs. 18 and 19, Cancelled, not shown). In an alternative arrangement (Fig. 20, Cancelled), the balanced crystal circuit is connected between anode and grid. A further arrangement (Fig. 21, Cancelled) uses a crystal having separate pairs of input and output electrodes, while in Fig. 22 (Cancelled) a similar crystal is used in a push-pull circuit. With these arrangements output frequencies of up to 170 Mc/s., representing the 33rd harmonic, may be obtained.