A Study of the Characteristics of Scattering Attenuation by Physical Modelling


Scattering attenuation (1/Qs) depends not only on wave frequency but also on scatterer size. Using void holes as scatterers in a thin duralumin plate, and with the ka value (k is the wave number, a the scatterer radius) being changed systematically from 0.05 to 5, the fluctuation of direct waves between a homogeneous and a scattering medium are observed in order to calculate the scattering attenuation by 2-D physical model experiments. The experimental results show that 1/Qs has a peak around ka = 0.5. At high frequency, 1/Qs is proportional to (ka)^-1, whereas at low frequency the decay of 1/Qs relative to (ka)^4 is steeper than predicted by Rayleigh scattering. The medium can be considered to be q quasi-homogeneous one, and the scattering effect can be neglected when ka < 0.05. The velocity fluctuation has a sharp change at ka= 0.5. The velocity of the scattering medium doesn¡¦t change when 0.5 < ka, is less that in a homogeneous medium and exhibits a constant fluctuation when ka < 0.5. Whether the wave length is smaller or greater than the scatter size, the P- and S- waves have the same scattering attenuation coefficients if they have the same ka value.

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