Acoustic scattering measurements by an ultra-broadband transducer using multilayer piezoelectric elements

Abstract

A Langevin-type broadband transducer has been built using multilayer piezoelectric elements. The resonance frequency of this element was 138 kHz, but the quality factor was very low and the transducer had broadband sensitivities due to Langevin structure. The useful frequency band was 20-150 kHz and the beam widths at 38 and 120 kHz were 21.2 and 6.6 degrees, respectively. An echo-sounding system has been constructed using commercially available equipments and the system calibration and acoustic scattering measurements have been conducted using a 2-ms linear-frequency-modulated signal. The system response has been successfully determined using a 20.6-mm-diameter tungsten carbide sphere as a standard target. Furthermore, the target strength (TS) spectrum of a 38.1-mm-diameter tungsten carbide sphere has been measured and the measured TS spectrum was in good agreement with the predicted TS spectrum based on the exact modal series solution. [Work supported by Grant-in-Aid for Scientific Research and TUMSAT.]