On the Measurement of Ultrasonic Velocity in Solids

A new method has been developed for the accurate measurement of the velocity of compressional waves in solid specimens. This is based on the cancellation of a traveling wave train, which has undergone reflection at the ends of the specimen, by a second wave train launched from the same transducer. A description is given of the experimental system employed. A correction must be made for the phase shift which occurs when the ultrasonic signal is reflected at the interface between specimen and transducer. A theoretical study of the effects of the transducer and coupling film shows that the correction is a function of the resonant frequency of the transducer and of the ratio of acoustic impedance of the transducer to that of the specimen. The application of the correction enables the velocity of propagation to be determined to within 1 in 104.