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Time Resolution Improvement of Linear Chirp Excitation Ultrasonic Testing Based on Frequency-Phase-Amplitude Modulation Excitation

The goal of this study is to improve the time resolution of linear chirp ultrasonic testing by employing frequency-phase-amplitude modulation excitation, combined with pulse compression. The proposed coded signal is a blackman-windowed linear chirp signal with 13-bit barker code, in which a blackman-windowed chirp signal is applied on every subpulse of barker code. Compared with linear chirp excitation, pulse compression output of the proposed excitation suppresses the side lobe better and decreases the main lobe width. As a result, time resolution is improved. The proposed coded signal performance of improving the time resolution is studied via numerical and experimental investigations. The simulation is implemented using a proprietary computing K-wave toolbox. The effects of chirp bandwidth and duration on the proposed coded signal excitation are then analyzed based on the simulation mode. The simulation results show that chirp bandwidth has less impact on proposed coded signal excitation than chirp excitation. The proposed coded signal is more suited to an ultrasonic exciting signal. In order to investigate the actual performance of chirp-B13-BW excitation in weld ultrasonic testing, experiments are conducted to test discontinuities in carbon steel weld samples. The obtained results show that the time resolution increases significantly by the employment of chirp-B13-BW excitation, compared with conventional brief pulse excitation and chirp excitation.

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