Nonlinear Sound Generation of Subharmonic and Ultraharmonics in Water-Saturated Sandy Sediments

Abstract

Nonlinear acoustic characteristics of sediments are very important to understand nonlinear phenomena of marine gassy sediments. Acoustic characteristics of thesubharmonic and the ultraharmonic sound waves generated in water-saturated sandy sediments were investigated. When a harmonic sound wave with highamplitude was incident on the water-saturated sandy sediments, the subharmonic and the ultraharmonic components of incident wave were generated due to the nonlinearity of water-saturated sandy sediments. The pressure levels of these nonlinear sound waves were 15 dB to 30 dB higher than the background noise level at the fundamental frequency with maximum incident acoustic pressure. The subharmonic and the ultraharmonic pressure levels also decreased for the increase of the grain size of sandy sediments. The fundamental and the harmonic frequency components of the incident wave affected on the subharmonic and the ultraharmonic pressure levels.