Patent GB-454595-A (GB)
Title: Improvements in or relating to piezo electric devices and methods of making the same
IPC: H01L41/317
Filed: 1935-04-05
Abstract: 454,595. Piezo - electric crystals. STEVENS, A. H., 5, Quality Court, Chancery Lane, London.-(Brush Development Co. ; 3715, Euclid Avenue, Cleveland, Ohio, U.S.A.) April 5, 1935, No. 10619. [Class 40 (v)] A method of making piezoelectric devices comprising bodies formed of watersoluble crystalline material of high specific inductive capacity and having electrodes on one or more surfaces thereof consists in applying directly to the body surface to be electroded a thin coating of conducting material in a wet state and sufficiently finely divided to be adapted when dry to adhere to the piezo-electric material in intimate contact therewith, causing the wet coated surface to dry and thereafter applying additional conductive material to the coating to increase its conductivity. As shown in Fig. 1, platelike elements 3 of piezo-electric material, such as Rochelle salt, are clamped between masks 1, 2 and colloidal graphite, such as that known under the Registered Trade Mark " Aquadag " is applied by means of the atomizer 5. The spraying is preferably carried out intermittently in order to give an opportunity for excess water to evaporate. The Aquada,g paste or cream may be thinned with alcohol or distilled water or alternatively the paste may be applied to the crystal surface with a brush. Further, instead of Aquadag, finely ground commercial graphite powder or mixtures of the colloidal graphite and such commercial graphite powder suspended in a solution of alcohol, benzol, water &c., or finely divided metal, such as a suspension of colloidal gold, may be sprayed on the crystal surface. After the electrode material has been applied an electrode lead extension in the form of a strip of metal foil may be cemented thereto and this lead covered by additional finely divided electrode material or by a sheet of metal foil adapted to cover wholly or in part the electrode material. Figs. 8, 9 and 11 show the invention applied to a piezoelectric unit of the multiple-plate flexing type, such as described in Specification 318,934, [Class 40 (v)]. This unit comprises two plates 10, 11 each of which carries on its two faces colloidal graphite electrode coatings 12. The plates are cemented together by cement 16 with a thin sheet metal electrode extension 13 clamped between them. The inner end of the extension 13 is crimped to form teeth 13<a>, which penetrate the cement 16 to make electrical contact with the inner coatings 12. The two arms 14<a>, 14b of a partially split further electrode extension 14 are cemented as shown to the outer coatings 12, metal foil elements 15 being cemented over the parts 14<a>, 14b. In a modification of this arrangement, Figs. 12-14, (not shown), the central extension 13 is omitted and electrical connection between the inner coatings 12 is obtained by distributing powdered or finely granulated conducting material, such as silver, over one of the coatings before the plates are cemented together or by mixing such granular material in the cement 16. Separate electrode extensions covered by strips 15 are then cemented to the outer coatings. Specification 366,252 also is referred to.