A ``Sampled-Continuous Wave'' Ultrasonic Technique and Spectrometer

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Abstract
A continuous wave ultrasonic measurement technique, which is particularly well suited to the study of inherently single‐ended acoustic systems, is presented. In this method the cw signal which establishes acoustic resonance is interrupted for the period during which sampling of particle motion amplitude is accomplished. The ``sampled‐cw'' technique incorporates the freedom from crosstalk associated with pulse—echo methods while retaining the monochromaticity of cw schemes. Analyses of the relative sensitivities of pulse—echo, ``sampled‐cw,'' and cw ultrasonic techniques are presented. A detailed description is given of a sampled‐cw spectrometer which includes a frequency locking scheme.