Ultrasonic Solid Delay Lines

The development of an ultrasonic delay line for the storage of pulses 1 microsecond long for periods up to 2000 microseconds is discussed. Theoretical considerations of the piezoelectric transducer involving the quartz crystals and acoustical constants of the medium developed by Emslie, Huntington, and Benfield, are applied to determine the band width and power loss of the delay line. Problems, peculiar to the use of solids because of the presence of more than one mode of propagation and the distribution of energy between the different modes on reflection from an air surface, are evaluated for a wide range of Poisson ratios. Measurements of velocity and attenuation in some polycrystalline metals, single crystals, and glasses are given. Fused quartz was found to be the most promising material. Delay lines constructed using a light source and photo-elastic pick-up were not completely developed, but several types using crystal pick-up as well as transmitter were satisfactory. For delay times longer than 300 microseconds, multiple reflection paths in two and three dimensions were used and their preparation from fused quartz discussed.