Power flow and energy distribution of magnetostatic bulk and surface waves in dielectric layered structure

A theoretical study of power flow and energy distribution of guided magnetostatic surface and bulk waves in a dielectric layered structure consisting of a ferrimagnetic layer sandwiched between free space and grounded dielectric has been presented. Starting from generalized Poynting theorem for dispersive media, the expressions for power flow per unit area and energy density have been derived under the magnetostatic approximation. The velocity of energy flow has been shown to be equal to group velocity, which implies the consistency of the magnetostatic approximation with general principle of wave propagation. The analysis reveals that the power flow in air or dielectric regions occurs in a direction opposite to that of phase propagation, while, inside ferrimagnetic region, the magnetostatic wave power usually flows along or opposite to that of phase propagation depending on whether the wave in question is a forward or backward wave. The region of non-dispersive delay, obtained exclusively for forward waves, is identified with the sharp decrease in the magnitude of power in ferrimagnetic and dielectric regions, immediately after the peaks have been obtained. No such behaviour is obtained for backward waves.