in ultrasonic delay lines with thickness-driven piezoelectric transducers, it is necessary to have electrode and, possibly, bonding layers in the sound transmission path. If these layers have characteristic impedances that are substantially different from those of the piezoelectric transducer and the delay medium, they act as mismatched transmission line sections between the transducer and its load, and transform the normally real load impedance into a complex one. The resulting shifted and deformed response curves are computed for a large number of layer parameters by means of Mason's equivalent circuit. From these plots, information as to permissible layer thickness, etc., may be obtained and used in the design procedure of ultrasonic delay lines. In digital delay lines, where linear phase response is a design requirement, any intermediate layers should be as thin as possible or be closely matched to the delay medium in order to avoid fast ripples in the frequency response, which would give rise to side lobes far away from the main signal in the time domain. Copyright © 1969 by The Institute of Electrical and Electronics Engineers, Inc.
