<p>Ultrasonic tomography using linear wave velocity has been applied in detecting defects in solids. The resolution depends on the ultrasonic frequency and the number of transmitters and receivers. Nonlinear ultrasonics using higher harmonics generation has the capability in detecting sub-wavelength defects. In this study, a new measurement approach is developed to reconstruct the tomographic images in solids using linear and nonlinear ultrasonics with single measurement. The number of transmitter and receiver array in relation to varying inclusion size and density is identified using numerical simulation. It is demonstrated that the resolution of tomography image and the detectability of flaws are significantly influenced by the number of transducers and their arrangement. In terms of nonlinear ultrasonic, the higher harmonic generation approach is applied to measure the nonlinearity coefficient and tomographic image is developed using nonlinearity coefficient under straight ray-based assumption. In the measurement approach, the receivers are selected at the frequency of the second harmonics of the transmitters. The received ultrasonic signal is decomposed into harmonics such that the time of flight of the first harmonics is used to construct the velocity map whereas the nonlinearity coefficient obtained by the first and second harmonic amplitudes is used to construct the nonlinearity coefficient-based map. It is demonstrated that the number of transmitter and receiver array for detecting similar size of defects using acoustic nonlinearity coefficient-based tomography is lower than linear velocity-based tomography method.&nbsp;</p>

A Systematic Approach to Develop Linear and Nonlinear Tomography With Single Measurement

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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