Title: Observation of impulse response for ultrasonic transducers by optical computed tomography
Abstract: The present study is aimed at developing accurate and simple techniques to observe the behavior of ultrasonic transducers and their holders. To know the impulse response of wideband type transducers driven in water, it is important to investigate the ultrasonic field pattern under actual performance. One solution would be given by the combination of the optical CT and the impulse response analysis by the M-sequence correlation method. The experimental arrangement of the Raman-Nath diffraction was used. The signal was given by a PIN-photodiode, which included the responses of all the components of the Fresnel diffraction. The optical measurement system using the M-sequence correlation method gives high stability and sensitivity over a wide frequency range. The ultrasonic signal in the megahertz region was processed by a low-cost slow A/D converter with 12-bit resolution. The experiment was conducted with a 13-mm concave transducer, and the instantaneous wave front was reconstructed every 50 ns. The effect of the electrodes could be clearly observed.