Wave-Mode Configurable Ultrasonic Non-Destructive Evaluation System Using Optoacoustic Prism

We demonstrate a multi-mode ultrasonic non-destructive evaluation (NDE) system based on a hybrid transducer including an optoacoustic (OA) prism. In this system, the OA prism with a flexible curved transmitter is capable of not only generating acoustic signals with high OA conversion efficiency but also covering a wide angular range to initiate various acoustic wave modes into a specimen whose interface is in contact with the OA prism. The latter angular manipulation provides great flexibility for NDE, which is uniquely enabled by developing and employing the curved OA transmitter coated on the prism. Using finite-element-based simulation, we validate acoustic signal generation and propagation inside an aluminum specimen. Then, excitation, propagation, and acquisition of shear and Rayleigh wave modes are confirmed experimentally. As feasibility demonstration, our hybrid transducer system, consisting of the OA prism and a piezoelectric receiver, is utilized for NDE of an aluminum specimen which includes air void discontinuity of 5-mm diameter. This is realized by multi-mode acoustic excitation from the OA prism with incident angles of 33°, 42°, 47°, and 60°. This exhibits detection accuracy error less than 2% as confirmed by comparing calculated and measured time-of-flight values. Such OA prism-based realization of all range of angular wave modes allows our system to be potentially useful for NDE over broad metallic materials as long as their sound speed is faster than that of the OA prism, without causing additional reverberation noise commonly observed in conventional piezoelectric counterparts.