Measurement of Acoustic Absorption Coefficient in Inhomogeneous Media and Biological Tissues with Phase Conjugated Ultrasonic Waves

A comparative study of two methods of measuring the acoustic absorption coefficient is performed - a standard one based on registering the amplitude of wave transmitted through a test sample and of its modification with application of phase conjugate ultrasonic waves. The insert-substitution technique was used as an example of the standard method. It is shown that wave front distortions of probing beam due to structure heterogeneities and scattering objects in test samples provoke significant errors in measurements by the standard method. At the same time, usage of phase conjugate waves permits to almost completely eliminate the errors for the measurements in the presence of phase heterogeneities of test samples. This is also the case for low concentrations of scatterers with sizes comparable to the acoustic wavelength. In the other cases, including measurements in biological tissues, the phase conjugation method permits to obtain more reliable estimations of dissipative losses than the standard one.