Direct measurement of ultrasonic dispersion using a broadband transmission technique

A broadband, through-transmission technique is described that measures directly the change in phase velocity with frequency without first measuring the absolute phase velocity at different frequencies. The method only requires the measurement of the specimen's thickness and recording of two pulses: one without and one with the specimen inserted between the transmitting and receiving transducers. From the two pulses, the dispersion as well as the attenuation can be determined using Fourier analysis without phase unwrapping. Experimental results of two specimens show an excellent agreement between the measured dispersion and the dispersion determined from the measured attenuation using a time causal model. This agreement verifies the model as well as demonstrates the accuracy and precision of the proposed method. (C) 1999 Elsevier Science B.V. All rights reserved.