Design and Analysis of Slot Based Transparent Magnet-Less Non-Reciprocal Metasurfaces

The goal of this research is to design and analysis of transparent magnet-less non-reciprocal gyrotropic metasurfaces (MNMs). Non-reciprocal response requires breaking of the timereversal symmetry and could be realized with quantities that are odd vector under time reversal such as magnetic field, current, momentum and orbital angular momentum. Current biasing is used to break the time-reversal symmetry and to achieve transparent non-reciprocal gyrotropic response. A 2D periodic array of annular slotted ring structure terminated with big slot patches and loaded with semiconductor-based unidirectional components is suggested to realize a transparent magnet-less non-reciprocal gyrotropy. It is shown that the big slot termination is required for matching of the annular slotted transmission line and the unidirectional component. Thus, a slot MNM is designed to achieve a travelling wave resonance, i.e. the rotating magnetic dipole response as magnetized ferrite molecules. Reflection and transmission coefficients of the designed structure are numerically computed to prove the ferrite-like non-reciprocal gyrotropic response of the structure. Moreover, asymmetrical response of the structure under x- and y-polarized plane wave incidence is highlighted and a rotated design is suggested to have a symmetrical non-reciprocal response in the expense of destroying the ferrite-like non-reciprocal gyrotropy. A physical explanation of the non-reciprocal gyrotropy, achieved by prohibiting one of the counter-propagating eigenstates of the slot MNM, is provided by utilizing the Sturm- Liouville theory. In order to understand the electromagnetic response of a metasurface, bianisotropic surface parameters of the metasurface is analytically derived in terms of reflection and transmission dyadics from discontinuity of the electromagnetic fields. Bianisotropic surface parameters of the slot MNM is extracted from the numerical simulation results. Magnetic dipole moment response of the slot MNM is evident from its large surface impedance parameters. Since surface impedance parameters of the structure is very large compared to other bianisotropic surface parameters, a simple transmission-line model is suggested to model the single-layer slot MNMs. Although ferrite-like transparent non-reciprocal behaviour could be achieved with slot MNMs, there is a non-negligible reflection from the structure due to its subwavelength nature. In order to circumvent the reflection issue of slot MNMs, reflection cancellation methods are discussed and a tentative analysis is employed. First, the duality theorem is exploited to cancel the reflection of slot MNMs since the designed structure could be characterized with a magnetic dipole moment.