Pattern recognition in the ultrasonic imaging of reverberant multilayered structures

Abstract

Often the existence of reverberations in the ultrasonic pulse-echo imaging of multilayered structure prevents the direct characterization of each layer. The reverberating pattern is governed by the integrity of the layers, and deterioration of these layers can generate complex and unpredictable patterns. Analytical models for the classification of reverberant patterns using both normal and unique angle scanning schemes are presented. The theoretical model has been utilized in the experimental studies of a particular multilayered reverberant environment that exists in the detection of corrosion and/or volatile changes in stem generator tubing used in nuclear power plants. Various reverberant patterns can be recognized that are in close agreement with theoretical predictions.

Identifying the Signal of Interest for Partially Overlapping Ultrasonic Echoes

“…The position and amplitude of echo signals from such systems may be of interest for thickness estimation or defect detection [1]- [11]. In many cases, ultrasonic interrogation of multilayer systems results in overlapping echo signals that originate at different interfaces.…”

Ultrasonic Flaw Detection and Imaging through Reverberant Layers via Subspace Analysis and Projection

“…The reverberation clutter, r(t), is of quasiperiodic nature damped over time, where the periodicity and the degree of damping depend on the thickness and density of the layer. Under ideal measurement conditions (e.g., the layer is immersed in water in the far field of the transducer), the reverberation signal from the layer can be modeled as the superposition of the time-shifted and amplitude-scaled replicas of the transducer pulse echo wavelet, s e (t), as [1] r(t) = ρs e (t) + σ 12 σ 21…”

“…Therefore, such reverberation signals (which are also referred to hereafter as reverberation clutter, or simply clutter) must be suppressed or sufficiently mitigated in order to reveal the target echoes. The majority of the existing approaches dealing with reverberation are based on the ideal acoustic wave propagation model in the layered media [1,[3][4][5][6]. For example, Saniie and Nagle have developed analytical models of reverberation patterns measured from multilayered media [1].…”

“…The majority of the existing approaches dealing with reverberation are based on the ideal acoustic wave propagation model in the layered media [1,[3][4][5][6]. For example, Saniie and Nagle have developed analytical models of reverberation patterns measured from multilayered media [1]. These models are used for the classification of echoes associated with each layer.…”

“…In particular, industrial materials are often manufactured in the forms of multiple layers, which present strong reflections at layer interfaces when exposed to ultrasound testing. These reflections usually repeat themselves in the course of an ultrasonic measurement, giving rise to strong and repeating reverberation patterns [1]. In medical ultrasound, direct access to the tissue of interest is not always possible, and hence ultrasonic measurements are often performed through another tissue or anatomic structure [2].…”