Genack Azriel Z, Huang Yiming, Maor Asher, Shi Zhou
Department of Physics, Queens College of the City University of New York, Flushing, NY, 11367, USA.
Physics Program, The Graduate Center of the City University of New York, New York, NY, 10016, USA.
Nat Commun. 2024 Mar 23;15(1):2606. doi: 10.1038/s41467-024-46748-0.
The diffusion model is used to calculate both the time-averaged flow of particles in stochastic media and the propagation of waves averaged over ensembles of disordered static configurations. For classical waves exciting static disordered samples, such as a layer of paint or a tissue sample, the flux transmitted through the sample may be dramatically enhanced or suppressed relative to predictions of diffusion theory when the sample is excited by a waveform corresponding to a transmission eigenchannel. Even so, it is widely assumed that the velocity of waves is irretrievably randomized in scattering media. Here we demonstrate in microwave measurements and numerical simulations that the statistics of velocity of different transmission eigenchannels are distinct and remains so on all length scales and are identical on the incident and output surfaces. The interplay between eigenchannel velocities and transmission eigenvalues determines the energy density within the medium, the diffusion coefficient, and the dynamics of propagation. The diffusion coefficient and all scattering parameters, including the scattering mean free path, oscillate with the width of the sample as the number and shape of the propagating channels in the medium change.
扩散模型用于计算随机介质中粒子的时间平均流以及无序静态构型系综平均下波的传播。对于激发静态无序样本（如一层油漆或一个组织样本）的经典波，当样本由对应于传输本征通道的波形激发时，相对于扩散理论的预测，透过样本的通量可能会显著增强或抑制。即便如此，人们普遍认为波的速度在散射介质中会不可挽回地随机化。在此，我们通过微波测量和数值模拟证明，不同传输本征通道的速度统计是不同的，并且在所有长度尺度上都保持如此，在入射面和出射面上是相同的。本征通道速度与传输本征值之间的相互作用决定了介质内的能量密度、扩散系数以及传播动力学。随着介质中传播通道的数量和形状变化，扩散系数以及所有散射参数（包括散射平均自由程）会随着样本宽度而振荡。
