3B-1 Flaw Detection in Layered Media Based on Parametric Modeling of Overlapping Ultrasonic Echoes

In materials consisting of several thin layers, multiple reflections within the structure give rise to received ultrasonic signals composed of overlapping echoes. In this paper we present a parametric model that can be used to decompose such signals into the individual reflections. We derive a maximum likelihood estimator for the the model parameters, which are then used in a generalized likelihood ratio test (GLRT) to detect flaws in multi-layered structures. We show with simulations how the presence of a thin bonding layer in a three-layer structure can be detected. The probability of detection is shown to be ap96%, for a signal-to-noise ratio (SNR) of 15 dB and a probability of false alarm of 5 %