Ultrasonic nondestructive evaluation of a three-layered medium

An ultrasonic technique for a simultaneous measurement of the acoustical properties of a three-layered medium (adhered/interphase layer/adhered) has been developed. Normally incident longitudinal waves are considered. It is assumed that the wavelength may be large compared to all three thicknesses, allowing the use of low-frequency transducers. Only the amplitude spectrum of the transfer function in through-transmission is used. The inverse problem has been solved for the following two 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 three wavespeeds.