Two perspectives on equipartition in diffuse elastic fields in three dimensions.
Two perspectives on equipartition in diffuse elastic fields in three dimensions.
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三维弥散弹性场均分的两种观点。
DOI：
10.1121/1.3177262
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
Richard L. Weaver
中科院分区：
文献类型：
--
作者：
M. Perton;F. Sánchez;A. Rodríguez;Michel Campillo;Richard L. Weaver
弹性动力学格林函数可以从漫射场运动的相互关系中得到。为了提取准确的格林函数，需要光照场的完美漫射。然而，场的扩散依赖于能量的均分，通常用波强度在方向和偏振上的分布来描述。在完整的三维弹性空间中，横波和纵波具有固定比例的能量密度。另一方面，也有另一种观点，认为相等的能量与独立的振动模态有关。这两种方法是等价的，并且描述了至少两种均分发生的方式。作者收集了三维全空间扩散弹性场的理论结果，并将其推广到半空间问题。在这种情况下，能量在大约一个瑞利波长内作为深度的函数发生明显的波动。作者从这两种方法推导出扩散能量密度，发现它们是相等的。这里的结果是基准，其中完美的漫射光场是假设。对格林函数检索相关归一化的一些实际含义出现，它们对介质成像有一些影响。
The elastodynamic Green function can be retrieved from the cross correlations of the motions of a diffuse field. To extract the exact Green function, perfect diffuseness of the illuminating field is required. However, the diffuseness of a field relies on the equipartition of energy, which is usually described in terms of the distribution of wave intensity in direction and polarization. In a full three dimensional (3D) elastic space, the transverse and longitudinal waves have energy densities in fixed proportions. On the other hand, there is an alternative point of view that associates equal energies with the independent modes of vibration. These two approaches are equivalent and describe at least two ways in which equipartition occurs. The authors gather theoretical results for diffuse elastic fields in a 3D full-space and extend them to the half-space problem. In that case, the energies undergo conspicuous fluctuations as a function of depth within about one Rayleigh wavelength. The authors derive diffuse energy densities from both approaches and find they are equal. The results derived here are benchmarks, where perfect diffuseness of the illuminating field was assumed. Some practical implications for the normalization of correlations for Green function retrieval arise and they have some bearing for medium imaging.