A delay-and-Boolean-ADD imaging algorithm for damage detection with a small number of piezoceramic transducers

The delay-and-sum (DAS) imaging algorithm usually sends an excitation signal at each piezoceramic transducer and obtains a defect image by using transmitter–sensor pair signals to draw ellipses or hyperbolas. A delay-and-Boolean-ADD (DABA) imaging algorithm is developed for defect detection of plate-like structures with a small number of piezoceramic transducers. This new method requires sending only one excitation signal for each detection, and obtains a better defect image by employing Boolean ADD operation instead of addition or multiplication operation in the DAS algorithm. A reflection coefficient is introduced in the new algorithm to attenuate the signals reflected from the boundary. The widely used envelop-detection method based on Hilbert-transformation is replaced by a new envelop-detection technique based on a local maximum value to increase the accuracy of locating. An additional time shift due to the excitation signal itself is also considered to decrease the location error. The results of the experiments conducted on an aluminum plate indicate that the proposed DABA imaging algorithm combining with the new techniques can detect a bonded mass defect accurately and efficiently. (paper)