Volume reverberation measurements of sediments in the laboratory

Abstract

The acoustic volume reverberation in sediments of different grain sizes was determined in the laboratory. Three sediments, fine sand, aquarium sand and aggregate, ranging in average grain size from 0.3 mm to 5.3 mm, were selected. An additional material, glass beads, with an average particle size of 1.7 mm, was also studied to investigate the influence of inhomogeneities in particle composition. In the experiment ten sets of 50 scattered pulses of pulse duration 88 µs and 180 kHz carrier frequency were averaged, and the envelope of the decaying tail was fitted with a logarithmic curve. The decay constants for the various sediments showed a variation with the grain size expressed by a = 10.3 - ƞ/0.0035 where a is the grain diameter in mm and ƞ the decay constant in Np/µs. The value of a can be estimated within ± 2.8 mm for a decay constant of 2.5 x 10ˉ² Np/µs. This relation is limited to the specific equipment used in the experiment and to the frequency of 180 kHz.­­