Energetic Criterion for the Radiation of Floquet Waves in Infinite Anisotropic Periodically Multilayered Media

The aim of this paper is to express in a correct manner the radiation conditions in terms of Floquet waves in an infinite anisotropic periodically multilayered medium. These waves are linear combinations of the classical plane waves propagating in each layer of the medium and are defined by the eigen vectors of the transfer matrix of the unit cell of the medium, termed "period". As the propagation reference of each Floquet wave is only known at each interface separating two successive periods (stroboscopic effect), the corresponding pseudo Floquet wave number which thus can be defined just gives an apparent propagation direction and not the effective propagation direction of a propagative Floquet wave. The propagation direction for each propagative Floquet wave is given by the sign of its normal power flux, involving its corresponding eigen vector. The problem is first analysed in isotropic periodically multilayered media with normal incidence and then extended to anisotropic periodically multilayered media.