Derode A, Tourin A, Fink M
Laboratoire Ondes et Acoustique, Université Denis Diderot-Paris VII, ESPCI-CNRS (UMR 7587), 10 rue Vauquelin, 75005 Paris, France.
Phys Rev E Stat Nonlin Soft Matter Phys. 2001 Sep;64(3 Pt 2):036605. doi: 10.1103/PhysRevE.64.036605. Epub 2001 Aug 29.
This is the first article in a series of two dealing with the statistical moments of ultrasonic waves transmitted through a disordered medium with resonant multiple scattering. Only the first-order moment is considered here. An ultrasonic pulsed wave is transmitted from a point source to a 128-element receiving array through two-dimensional samples with various thicknesses. The samples consist of random collections of parallel steel rods immersed in water. Experimental results show that the ensemble-averaged transmitted wave forms ("coherent wave") exhibit a time-dependent frequency spectrum. Within the independent scattering approximation, this is well explained by individual resonances of the scatterers. The coherent wave only appears after ensemble averaging and has to be distinguished from the "ballistic wave," i.e., the first well-defined pulse that crosses the sample, which can be measured on every realization of disorder. A physical interpretation is given, which is based on the separation of the coherent wave between a rigid and a resonant contribution.
这是关于通过具有共振多重散射的无序介质传输的超声波统计矩的系列两篇文章中的第一篇。这里仅考虑一阶矩。一个超声脉冲波从点源通过具有不同厚度的二维样本传输到一个128元接收阵列。样本由浸没在水中的平行钢棒的随机集合组成。实验结果表明，系综平均传输波形（“相干波”）呈现出随时间变化的频谱。在独立散射近似下，这可以通过散射体的个别共振很好地解释。相干波仅在系综平均后出现，并且必须与“弹道波”区分开来，即穿过样本的第一个明确的脉冲，它可以在每次无序实现中测量到。基于相干波在刚性贡献和共振贡献之间的分离给出了一种物理解释。
