Embedded-Ultrasonics Structural Radar for Nondestructive Evaluation of Thin-Wall Structures

Embedded-Ultrasonics Structural Radar (EUSR) is a new concept and methodology for in-situ nondestructive evaluation (NDE) of thin-wall structures. EUSR utilizes (a) a Piezo Wafer Active Sensors (PWAS) array embedded onto the structure; and (b) electronic modules for signal transmission/reception, processing, and interpretation. The EUSR methodology is developed as an extension of our previous work on the Lamb wave propagation NDE. Based on the study of the Lamb wave characteristic, the excitation signal is optimized to obtain good signal to noise ratio. Lamb wave speed-frequency curve is plotted to obtain the wave speed of the excitation signal. This wave speed is then used to map the EUSR data from time domain to distance domain, thus the locations of the reflectors can be visually displayed. The EUSR algorithm is adopted from the beamforming process currently used in phased-array radar applications. Each element in the PWAS array plays the role of both transmitter and receiver. A circuit is designed to change the role of the PWAS in a round robin fashion. The responses of the structure to all the excitation signals are collected. By applying the EUSR algorithm, an appropriate delay is applied to each signal in the data set to make them all focus on a direction denoted by angle φ. When this angle φ is changed from 0 to 180 degrees, a virtual scanning beam is formed and a large area of the structure can be interrogated. The EUSR algorithm is explained in this paper. Experimental results from a proof-of-concept EUSR system are also presented.