Propagation constant and the velocity of the coherent wave in a dense strongly scattering medium

Frequency- and time-domain experiments are conducted to study the effective propagation constant of the coherent wave in a dense strongly scattering medium. A wide-band microwave signal (10-40 GHz) is propagated through randomly distributed glass spheres with a 5.73 mm average diameter and separated into incoherent and coherent fields. The real and imaginary parts of the propagation constant are obtained from the coherent field. The narrow size distribution of the particles enables the authors to study scattering from the Rayleigh region through the Mie resonance scattering region. The results of the experiments are compared to independent scattering, effective-field approximation (Foldy´s), and the higher order quasi-crystalline approximation (QCA) using Mie scattering coefficients and the Percus-Yevick approximation for the pair-distribution function. The phase and group velocities of the coherent wave are obtained from the effective propagation constant and compared with theory. In addition, the velocity of the coherent wave in random media is measured using the time-domain technique. It is shown that the velocity of the coherent wave in random media is neither phase nor group velocity