Limitations on the Performance of Ultrasonic Delay Lines Using Vitreous Silica as the Delay Medium

Abstract

The information storage capabilities of ultrasonic delay lines using vitreous silica (a term used to denote both fused quartz made from powdered crystalline quartz and fused silica made by oxidation of SiCl4 in an oxygen-hydrogen flame) are limited at low frequencies by the variation in the shear wave phase velocity and at high frequencies by the attenuation-vs-frequency dependence of vitreous silica. Recent experimental data [D. B. Fraser, J. T. Krause, and A. H. Meitzler, Applied Physics Letters (In preparation)] on the shear attenuation coefficient versus frequency dependence and the constancy of shear wave phase velocity are presented and combined with analytical models to estimate the maximum digital signal storage capabilities of ultrasonic delay lines using vitreous silica. In addition, other factors influencing performance limits, such as the temperature dependence of loss, the temperature coefficient of delay time, and the magnitude of the acoustoelastic effect in vitreous silica, are discussed.