Magnetic-free, fully integrated, compact microwave circulator using angular-momentum biasing

Conventional non-reciprocal devices use ferromagnetic materials and an impressed external magnetic bias to break time-reversal symmetry. This solution typically leads to impractically large devices, losses and it is incompatible with integrated circuit technology. We discuss here a different approach to realize non-reciprocal microwave components and materials, based on biasing meta-molecules with the angular-momentum vector. We show that this solution can provide as large non-reciprocity and isolation as magnetically-biased ferrite components, but without their drawbacks. In particular, we present the design and realization of an integrated, magnetic-free, compact microwave circulator realized with conventional circuit components on a dielectric substrate, fully compatible with integrated circuit technology. By using appropriate spatiotemporal modulation of a magnetic-free distributed-element resonating ring, we report over 47 dB isolation and a deeply subwavelength size. We also envision the realization of non-reciprocal metasurfaces and metamaterials based on the same principle.