GB582232A - Improvements in electromechanical delay devices - Google Patents

Abstract

582,232. Electromechanical delay lines. WESTERN ELECTRIC CO., Inc. June 30, 1944, No. 12546. Convention date, July 8, 1943. [Classes 40 (iii) and 40 (v)] A wide-band high-frequency delay line comprises an aperiodic liquid or solid medium for transmitting mechanical vibrations and is terminated by L-cut crystals which, Fig. 1 (not shown), have their faces equally inclined to the three crystallographic arcs in Rochelle salt and vibrate longitudinally, i.e. parallel to the applied electric field, with broad resonance. The transmission band is widened by using, at each end of the line, two or more such crystals having overlapping characteristics. A common transmission path may comprise a tube 16, Fig. 4, of metal, glass, plastic or the like containing a liquid such as xylene hexafluoride, in which vibrations travel with low velocity, in lieu of castor oil. At each end is a header 17 mounting two or more transducer units corresponding to different bands of frequency, each of which contains a crystal 21 supported on a plate 22 and backed by a steel resonator 23. In order to prevent reflection and interaction between adjacent units, each unit is provided with an attenuator comprising fine-mesh screens 20 and a damping liquid enclosed by a soft rubber diaphragm 19. The capacitance of the crystals is tuned out by inductances 24. A separate tube 16 may be provided for each frequency range, the attenuators being omitted. Instead of a liquid, the transmission medium may comprise a solid such as cellulose acetate butyrate or some of the polyesters, loaded with heavy particles of a metal such as permalloy or tungsten to reduce the velocity, Fig. 5 (not shown). High attenuation is secured at the terminal transducer units in this case by interposing a length of a plastic such as cellulose acetate between each transducer unit and the transmission medium.