Abstract:

A method for the measurement of intrinsic scattering object properties is presented. This procedure is based on the measurement of the scattered acoustic field as a function of scattering angle and frequency. Measurements are normalized using analytically determined expressions for emitter and detector beams resulting from a combination of unfocused linear elements arranged in a circular configuration. The spatial effects of finite emitter pulse length and detector gate length are represented by a convolution formula valid for narrow-band signals and long receiver gates. The method includes correction for target absorption as well as measurement of the directly transmitted acoustic power in the free field, yielding the average differential scattering cross section per unit volume. Measured results for two phantoms consisting of glass microspheres embedded in agar show good relative agreement with theory for varying angle, frequency, and phantom properties. For the phantoms employed, scattering effects, rather than increased absorption, are shown to account for most of the difference in transmission loss between pure agar and agar with glass spheres.