Correlation length facilitates Voigt wave propagation
  Under certain circumstances, Voigt waves can propagate in a biaxial composite medium even though the component material phases individually do not support Voigt wave propagation. This phenomenon is considered within the context of the strong--permittivity--fluctuation theory. A generalized implementation of the theory is developed in order to explore the propagation of Voigt waves in any direction. It is shown that the correlation length--a parameter characterizing the distributional statistics of the component material phases--plays a crucial role in facilitating the propagation of Voigt waves in the homogenized composite medium. 
Tom G. Mackay (University of Edinburgh) and Akhlesh Lakhtakia   (Pennsylvania State University)