ANGULAR MEASUREMENT OF ACOUSTIC REFLECTION COEFFICIENT FOR SUBSTRATE MATERIALS AND LAYERED STRUCTURES BY V(Z) TECHNIQUE

An experimental method to evaluate the acoustic reflection coefficient as a function of the incident angle R(theta) for substrate materials or layered structures is presented. By measuring the acoustic material signature V(z) using a highly focused acoustic lens or transducer at normal incidence, the reflection coefficient R(theta)) can be reconstr ucted from the FFT of the complex V(z) signal (amplitude and phase of the echo). This technique has a great simplicity for the experimental procedure of R(theta) measurement. It overcomes the disadvantages of t he conventional method where the finite-aperture plane beam reduces th e angular precision and causes the unexpected non-specular reflection at critical incident angles. Results are given for different substrate materials, single plates and a three-layered bonded joint, and are co mpared to theoretical predictions. (C) 1997 Elsevier Science Ltd.