PHYSICAL INTERPRETATION OF FLOQUET WAVES PROPAGATING IN AN ANISOTROPIC PERIODICALLY MULTILAYERED MEDIUM

The aim of this paper is to better understand the correspondence betwe en the classical plane waves propagating in each layer of an anisotrop ic periodically multilayered medium and the Floquet waves. The last ar e linear combinations of the classical plane waves. Their wave number is obtained from the eigenvalues of the transfer matrix of one cell of the medium. We have defined a Floquet polarisation which varies with its position in the periodically multilayered medium. This allows us t o define a Floquet waves displacement by analogy with the one of the c lassical plan waves, and to verify the equality of the two displacemen ts at any interface separating two layers. The periodically multilayer ed medium is then equivalent to a dummy material, and one can draw dis persion curves. In low frequencies range, when the relation between th e Floquet wave numbers and the frequency is linear, the multilayered m edium can be homogenised ; the Floquet polarisation at different inter faces tends to a limit which is the polarisation of the classical plan e wave in the homogenised medium.