Imaging algorithms for locating damage via in situ ultrasonic sensors

Permanently mounted ultrasonic sensors arranged as a spatially distributed array are being considered for in situ monitoring of the integrity of structural components. Here we consider two imaging algorithms for locating damage based upon changes in received signals. All transducer pairs in the array are considered, with each transducer acting in turn as a transmitter and the remaining transducers as receivers. The first imaging algorithm is based upon spatially distributing the differenced signals between each transducer pair as per expected arrival times for discrete scatterers. The resulting images, which consist of concentric ellipses, are summed over all pairs to form the final image. The second algorithm is based upon the cross correlation between waveforms originating from the same transmitter and received by two different transducers. The cross correlation waveforms, which capture the time difference of arrival between two pairs, are similarly distributed and summed to form the final image via a hyperbolic rather than an elliptical relationship. Results are shown for artificial damage in an aluminum plate.