LOW-FREQUENCY ACOUSTIC-WAVE GENERATION IN A RESONANT BUBBLE LAYER

The nonlinear response of a bubble layer subject to harmonic and bihar monic excitation at frequencies smaller than the individual bubble res onance frequency is considered. The nonlinear resonance properties of the layer and generation of difference-frequency signal sire studied a nalytically and numerically. It is found that, for bubble volume fract ions beta approximate to 10(-3) and pump amplitudes of the order of 10 (-1) atm, the power of the low-frequency signal (including waves radia ted in both directions) may reach 10% of the total power of the incide nt biharmonic wave. The efficiency is restricted by the rapid formatio n of shocks already at relatively low driving amplitudes, which may no t occur in a more complete model accounting for the inertia of the bub ble pulsations. (C) 1996 Acoustical Society of America.