The measurement of small changes in ultrasonic velocity and attenuation

Abstract

Ultrasonic velocity and attenuation are defined by the solution

A = A_o, e^−az cos (kz-wt) (1)

for an ultrasonic wave propagating in the zdirection with a propagation constant k = 2π/λ = 2πf/v, a radian frequency w = 2πf, and an attenuation coefficient a. In these definitions, λ = wavelength, f = frequency, and v = phase velocity. In this traveling wave, the measurable quantities generally are v and a. If one creates a standing wave by superposing two oppositely directed traveling waves within a reflecting plenum, then the standing wave is described by a resonant frequency and a wavelength which give v, and by a decrement which yields a. In this paper only traveling wave methods for waves of infinitesimal amplitude will be treated. Methods for measuring small changes in v and a will be described.