Pressure dependence of the attenuation and sound speed in a bubbly medium: Theory and experiment

Abstract

Existence of bubbles in a medium changes the attenuation and sound speed (Cs) of the medium. The relationship between the nonlinear oscillations of the MBs and acoustical parameters of the medium is not fully understood. In this work, monodisperse solutions of lipid coated bubbles with mean diameter of 5.2 micron and peak concentration of (5000 microbubbles/ml) were sonicated with a broadband pulse with center frequency of 2.25 MHz. The attenuation and Cs, were measured over a pressure range of 10-100 kPa. Using our recent nonlinear model and by solving the Marmattont Model, the attenuation and Cs of the solution were numerically analyzed. Experimental results showed that as the pressure increased, the attenuation peak increased by ~7-8 dB while its frequency decreased from 2.05 to 1.55 MHz. The maximum Cs of the medium increased with pressure (1521 to 1529 m/s) and shifted towards lower frequencies (2.34 to 1.95 MHz). At a fixed frequency (e.g., 1.65 MHz) the Cs increased by ~14%. The Cs of the bubbly medium remained the same as the Cs in the absence of bubbles at the frequency of the attenuation peaks. Numerical simulations were in good agreement with experimental observations and confirm the experimentally observed phenomenon.