Scattering on mini underwater acoustic tank

Abstract

This paper presents measurements on a mini underwater test tank made of 12 mm thick of glass with dimension 2 m (length) ×1 m (width) ×1 m (height). The test tank inner walls had been fitted with perforated acoustical absorbent to avoid echoes. To prove that the test tank is free from scattering, we placed the sound source with 100° aperture in lower corner of the tank, then the hydrophone at calculated reflection angles by using ray-tracing technique at 30°, 40°, 50° and 60°, respectively. The sound frequencies were set both single frequency tone at 200 Hz, 600 Hz and 1000 Hz for narrowband setting and a composite of 500Hz-700Hz-900Hz-1100Hz-1300Hz for broadband settings. The hydrophone arrays were calculated at the sphere coordinate and then transformed into Cartesian to simultaneously record the intensity and frequency of direct and reflected sounds. The results showed that the farther the sensor to the sound intensity was amplified at certain locations. This suggests that the additive reflection occurs at places where they positively superposed. Furthermore, some results indicated that the sound intensity of narrowband signal was higher than those of the broadband at room temperature. We argue that the narrowband signal superposed with the same frequency tends to amplify the energy due to coherence compared to the broadband signal which may suffer more scattering.