The use of large ultrasonic transducers to improve transmission coefficient measurements on viscoelastic anisotropic plates

A study of the use of large transducers (80 mmx40 mm, 3.2 MHz center frequency) for the measurement of ultrasonic transmission coefficients is reported, Tests have been carried out on thick and thin glass plates and on a unidirectional carbon fiber composite plate. The material properties of the plates were obtained by comparing the transmission coefficient results at particular angles with the predictions of plane-wave theory for different material properties; the properties giving the best fit were then used to predict the transmission coefficients at other angles. The results of this preliminary study show that the use of large transducers makes it possible to obtain excellent agreement between measured transmission coefficients at all angles and those predicted using plane-wave theory. The large transducers give clearer definition of the transmission maxima than is obtained with smaller, conventional transducers, and also give good agreement with the predicted transmission coefficient amplitudes. This should improve the accuracy of inversion procedures for the determination of the real parts of the elastic constants from the frequencies of the transmission maxima, and the good amplitude agreement opens up the possibility of obtaining accurate estimates of the imaginary parts of the elastic constants. (C) 1997 Acoustical Society of America.