Simultaneous Inversion of Thickness and Ultrasonic Longitudinal Velocity for Thin Layered Structure Based on Ultrasonic Reflection Coefficient Amplitude Spectrum Matching Analysis

For the overlapped signal and unknown longitudinal velocity leading to difficulty in measuring the thickness of thin layers, a method based on ultrasonic reflection coefficient amplitude spectrum (URCAS) matching analysis technique was proposed to characterize thickness and ultrasonic longitudinal velocity of thin layered structure simultaneously. An inverse algorithm based on the correlation coefficient method was introduced. The thickness and velocity were then determined by matching the theoretical and experimental URCAS within the effective frequency band of ultrasonic probe and inversing the ultrasonic testing parameters which corresponding to the maximum correlation coefficient. Experimental validation was conducted on the radar absorbing coatings (RAC) on the aluminum alloy substrates. The results show that this method can realize extraction of the ultrasonic parameters from the overlapped signal effectively, the relative errors between ultrasonic and micrometer measurement are in the range of 2.53%-3.