MEASUREMENT OF THE ACOUSTIC NONLINEARITY PARAMETER IN LIQUID-MEDIA USING FOCUSED ULTRASOUND

The principle and the experimental results for a finite amplitude method to measure the acoustic nonlinearity parameter B/A of liquid media using focused ultrasound are presented. The present method takes both absorption and diffraction into account. A liquidlike sample is inserted in the focal region of the acoustic field formed by a spherically focusing Gaussian source. The response of the amplitudes and phases of the fundamental and second harmonic components of the transmitted wave is observed at the post focal region to obtain the experimental value of a quantity named R(F), which incorporates the nonlinearity parameter of the sample. The measurement of linear acoustic properties is also carried out using the same focusing source. The value of B/A is determined through comparison between experimental and theoretical values of R(F). The experimental results for 4.5-ml volume samples at the fundamental frequency of 1.9 MHz validate the present method. This suggests the possibility of obtaining the B/A imaging from an acoustic mic