Nonlinear acoustic crack detection in thermoelectric wafers

We present an acoustic technique for noninvasive crack detection in small (approximately 30.0 ×18.0 × 0.5 mm) thermoelectric wafers. The technique is based on exciting the wafers with a low-frequency signal that drives the crack to open and close periodically, and a high-frequency signal that is permitted to propagate through the closed crack and prohibited from propagating through the open crack. Interaction between the low- and high-frequency signals and the crack leads to generation of acoustic nonlinearities in the wafer. In contrast to existing acoustic crack detection techniques we utilize standing waves within the wafers to facilitate simultaneous crack detection throughout the wafer, we do not require uniform dimensions and material properties between wafers, and we do not affix the transducer to the wafers to avoid damaging the wafers. We present a mathematical model of the acoustic nonlinearity generation process and develop a procedure for identifying cracked wafers. We implement this technique experimentally and correctly identify cracked and crack-free wafers with total error in low single digits. This acoustic crack detection technique finds application in manufacturing of thermoelectric wafer and other wafers, where identifying cracks early in the manufacturing process results in significant time and cost savings. We present an acoustic technique for noninvasive crack detection in small (approximately 30.0 ×18.0 × 0.5 mm) thermoelectric wafers. The technique is based on exciting the wafers with a low-frequency signal that drives the crack to open and close periodically, and a high-frequency signal that is permitted to propagate through the closed crack and prohibited from propagating through the open crack. Interaction between the low- and high-frequency signals and the crack leads to generation of acoustic nonlinearities in the wafer. In contrast to existing acoustic crack detection techniques we utilize standing waves within the wafers to facilitate simultaneous crack detection throughout the wafer, we do not require uniform dimensions and material properties between wafers, and we do not affix the transducer to the wafers to avoid damaging the wafers. We present a mathematical model of the acoustic nonlinearity generation process and develop a procedure for identifying cracked wafers. We implement this technique...