Identification of layered material properties using wavelet transform of ultrasonic data

Presents a wavelet-based approach for extracting features from ultrasonic non-destructive evaluation (UNDE) data of a test specimen. These features are then used to obtain an estimate of the specimen's material properties. The materials of interest in the paper are composed of thin layers; this is the case, for example, in many state of the art hybrid materials. When these types of materials undergo UNDE, echoes from interior layers often overlap severely, causing information from individual layers to be obscured or lost completely. A complex-valued mother wavelet based on the impulse response of the test instrumentation system, is used to perform the wavelet transform and separate the overlapped echoes. The method was applied to acoustic data for a thin aluminum sheet. The extracted features displayed considerably enhanced fidelity as compared to the original wave form. Wave travel times and transmission coefficients obtained from the extracted features agree with expected values for the sample to within 7%. It is believed that the features extracted via the method outlined in the paper also provides considerable promise in the area of flaw detection and data compression.