Self-biased magnetic photonic crystals for unidirectional antennas

We propose a new magneto-dielectric metamaterial exhibiting unidirectional (non-reciprocal) wave propagation properties without using an external magnetic bias field. Previous demonstration of the unique properties of such magnetic photonic crystals (MPCs) was carried out under a large external DC magnetic field (~0.7 T). This magnetic bias is required to induce Faraday rotation within the ferrimagnetic layers of the MPC. Obviously, the high field requirement is of concern for practical antenna applications. In the new design, we imbedded the magnetic bias into the MPC structure in the form of permanently magnetized M-type hexaferrite layers. We show that with proper material parameters and layer thicknesses, it is possible to obtain a dispersion diagram that exhibits spectral non-reciprocity (i.e. ω(K) ≠ ω(-K)) and a stationary inflection point (ω\´=ω"=ω\´\´\´=0). The latter is responsible for the so-called “frozen mode” and a corresponding increase in group delay.