ULTRASONIC NONDESTRUCTIVE EVALUATION OF A 3-LAYERED MEDIUM

An ultrasonic technique for a simultaneous measurement of the acoustic al properties of a three-layered medium (adherend/interphase layer/adh erend) has been developed. Normally incident longitudinal waves are co nsidered. It is assumed that the wavelength may be large compared to a ll three thicknesses, allowing the use of low-frequency transducers. O nly the amplitude spectrum of the transfer function in through-transmi ssion is used. The inverse problem has been solved for the following t wo cases: (1) simultaneous determination of thickness h and wavespeed c of any one of the three layers, given h and c of the remaining two; and (2) simultaneous measurement of the three thicknesses, given the t hree wavespeeds.