Generation of subharmonic and difference frequency acoustic waves in a water-saturated sandy sediment

Abstract

Generation of subharmonic and difference frequency acoustic waves in a water-saturated sandy sediment was investigated. Subharmonic frequency acoustic wave was observed to be generated due to the nonlinearity of water-saturated sandy sediment when the fundamental frequency acoustic wave exceeded a certain threshold pressure amplitude. Pressure spectrum level of the subharmonic frequency acoustic wave linearly increased as the driving acoustic pressure amplitude increased. The pressure level was 10 dB higher than the background noise level. Generation of the difference frequency acoustic wave was also observed by the collinear acoustic waves with two different fundamental frequencies. The pressure level of the difference frequency acoustic wave was 5 dB higher than the background noise level. It seems very useful to evaluate the nonlinear parameter of water-saturated sandy sediment without disturbing the sediment. Such nonlinear acoustic responses of water-saturated sandy sediment can be utilized for the diagnosis of marine gassy sandy sediment.