Ultrasonic Delay Lines for Digital Data Storage

This paper describes the design features and performance characteristics of a delay line design which is specifically intended for digital data applications. The design consists basically of a delay medium in the form of a long, thin strip with piezoelectric ceramic, thickness‐shear mode transducers bonded to the end faces. The strip acts as an elastic waveguide in which the energy contained in an input elastic pulse is propagated by a number of modes with varying amounts of dispersion. By the proper use of absorbing material along the edges of the strip, it is possible to suppress selectively the more dispersive modes and thereby reduce the width of the output pulse to the extent that megacycle bit rates may by used even in lines with delays of the order of 10 msec. Since the medium acts as a waveguide, long delays may be obtained at relatively low loss. In a typical design, to be described in detail, the line has a delay of 4.3 msec, an insertion loss of 34 db, and a maximum bit rate (on a nonreturn‐to‐...