GB1382542A - Alternating electric field coupling arrangements - Google Patents

Abstract

1382542 Surface wave devices SIEMENS AG 26 Jan 1973 [30 March 1972] 4007/73 Heading H3U Acoustic surface waves of the Bleustein type, i.e. in which the wave displacement is parallel to the propagation surface and transverse to the propagation direction are generated on a surface of a piezoelectric body, separated by a gap filled with glycerine, distilled water, a mixture of the two, or acetone from a second body, the liquid causing coupling to the piezo body by the electric field it supports. Transducer. Fig. 1.-Glass plate 2 supports vaporized-on interdigital transducer 5 on that surface adjacent the gap of liquid 3. Piezoceramic or bismuth germanium oxide piezo body 1 is polarized in a direction parallel to the transducer fingers, and the Bleustein wave is generated in the body 1 since the electric field from transducer 5 readily crosses the liquid 3 in view of its high dielectric constant. The bismuth germanium oxide body is cut in the (110) plane, with propagation in the (110) direction. The fingers of each comb of the transducer are spaced by an acoustic wavelength. Variable delay line, Fig. 2.-Piezoelectric body 11, polarized parallel to the fingers of vaporized-on transducer 5, is separated by liquid (3), Fig. 3 (not shown), from a second piezoelectric body 22 supporting output transducer 6. The liquid may be retained by spacer ledges 4, or, utilizing the capillarity of the liquid to ensure separation of the bodies, the ledges may be omitted. Delay time is varied by relative longitudinal displacement of bodies 11, 22, coupling between them being purely by electric fields passing via liquid (3), acting also as a lubricant. Dimensions, frequency, bandwidth, and delay times, are given. Travelling wave amplifier, Fig. 4.-Semiconductor body 222, in which a drift field is set up between metallized areas 7, is coupled via liquid 3 to piezoelectric body 111, causing amplification of the Bleustein wave passing from transducer 5 to transducer 6.