The absorption coefficient measurement of the underwater material in water tube with the wide-band pulse method

The traditional underwater absorption coefficient measurement is limited in low frequency due to the limitation of the pulse tube length. A wide-band pulse tube method based on the "post-processing" inverse is proposed. The first procedure is to measure the response of the entire system for signal processing. Then, excite the transducer with wide-band, short-duration signals. Finally, process the received signals with the tested system transfer function and recover the "blurred" reflective signals of standard reflector and testing sample respectively. Simulation work was implemented to verify the advantage of "post-processing" inverse filter over "pre-processing" inverse filter in terms of low frequency measurement. To verify the proposed method, two different wide-band pulses of separate frequency range are adopted to measure the same rubber material. Experimental results indicate that wide-band pulse method and CW pulse method have good agreement in both low frequency range and high frequency range. Wide-band pulse method is of high efficiency, and the low frequency reaches 350 Hz. It can widen the low frequency range.