Voigt waves in homogenized particulate composites based on isotropic dielectriccomponents

Abstract

Homogenized composite materials (HCMs) can support a singular form of opticalpropagation, known as Voigt wave propagation, while their component materials do not. Inessence, Voigt waves represent coalescent degenerate eigenmodes of the correspondingpropagation matrix. Crucially, the existence of Voigt waves stems from the non-Hermitiannature of this propagation matrix, which in turn is a manifestation of the dissipative natureof the HCM. This phenomenon was investigated for biaxial HCMs arising fromnondissipative isotropic dielectric component materials. The biaxiality of these HCMsstems from the oriented spheroidal shapes of the particles which make up the componentmaterials. An extended version of the Bruggeman homogenization formalism wasused to investigate the influence of component particle orientations, shapes andsizes, as well as volume fractions of the component materials, upon Voigt wavepropagation. Our numerical studies revealed that the directions in which Voigtwaves propagate are highly sensitive to the orientations of the component particlesand to the volume fractions of the component materials, but less sensitive tothe shapes of the component particles and less sensitive still to the sizes of thecomponent particles. Furthermore, whether or not an HCM supports Voigt wavepropagation at all is critically dependent upon the sizes of the component particlesand, in certain cases, upon the volume fractions of the component materials.