Abstract
A new method for obtaining depth distribution of the nonlinearity parameter B/A and the frequency-dependent attenuation coefficient is outlined. In this method, the higher frequency probe pulse wave, superposed coaxially on the lower frequency pump pulse wave, is modulated nonlinearly due to their propagation, and is received as an echo signal. The relationship between these acoustic parameters and the modulation characteristics of the probe pulse wave is derived by the division of the spectra of modulated echo signals with each other. The possibility of canceling out of error factors, such as the frequency-dependent acoustic reflection coefficient of random scattering medium, in the above division process is discussed. A preliminary evaluation of this method is made by using an experimental system. B/A values are obtained for various kinds of sponge test targets immersed in water, n-propyl alcohol, isopropyl alcohol, ethylene glycol, or diethylene glycol; and for agar graphite phantom.
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