Some Experimental Investigations of the Parametric Acoustic Array

The major disadvantage of the parametric acoustic array, preventing a more extensive practical exploitation of the number of advantageous qualities of the parametric array, is the low conversion efficiency due to the second order effects which form the basis of the parametric acoustic array. Procedures for a partial remedy of the major disadvantage are discussed. It is shown through experimental investigations, supported by numerical calculations, how valuable contributions to the increase of the difference-frequency pressure level and to a reduction of the difference-frequency beamwidth may be obtained by: (a) Increasing the virtual source level by an increase in the ratio of non-linearity and a decrease in the speed of sound and in the density of the fluid in the parametric acoustic array, (b) increasing the carrier wave amplitude, (c) using acoustic lens effects and (d) suitable amplitude modulating a carrier wave.