IEEE TAP Paper Published (03-Feb-2022)

Our paper on metagrating-inspired solutions for suppressing reflections in waveguide bends, written by Liran Biniashvili and Ariel Epstein, has been published in the IEEE Transactions on Antennas and Propagation. The paper derives a semianlaytical methodology to devise locations for subwavelength scatterers that would eliminate spurious scattering in rectangular waveguide discontinuities by producing secondary fields that destructively interfere with the unwanted reflections in the input port. The analytical model requires modal expansions in the straight waveguide sections (rectangular waveguide modes) as well as in the junction (treated as a radial waveguide section), allowing efficient and accurate retrieval of scattering coefficients without requiring numerical solvers. Including a small scatterer in the junction is performed by incorporating the suitable Green’s function, allowing for calculation of the potential spots as well as the required induced current for mitigation of back reflections while retaining passivity – similar to what has been achieved for metagratings for free space beam manipulation. The examination of these perfect transmission locations reveal fundamental insights regarding the scattering processes within the junction, manifested in the formation of symmetric and antisymmetric solution branches. The work is completed by deriving approximated analytical formulas for the radius of a metallic cylindrical post that can implement the subwavelength scatterer in practice, showing good performance also in terms of bandwidth and sensitivity to fabrication inaccuracies. The work introduces a simple, effective, and semianalytically designed solution for seamless waveguide bends, while demonstrating the versatility of the metagrating concept, beyond beam manipulation.

PRB Paper Published (14-Dec-2021)

Our paper on sinusoidally-modulated metasurfaces with normal polarizability, written by Ph. D. student Amit Shaham and Ariel Epstein, was published in the Physical Review B. The paper analyzes rigorously this fundamental case study for the first time, revealing that due to the non-local nature of the normal polarizability distribution, unconventional difference equations governing the relation between the metasurface properties and the scattering coefficients are formed. These feature unique instability conditions, which cannot be addressed by simply relying on the Meixner-Schafke theorem. Our work shows that introduction of infinitesimal losses (unavoidable in practice) mitigates this issue, leading to a stable solution to the scattering coefficients. Based on the developed analytical formalism, it is shown that such surfaces exhibit reflection properties corresponding to Wood’s anomaly, with a resonant notch in the angular response. These observations, verified experimentally via a suitable prototype, highlight the exceptional properties of metasurfaces with normal susceptibility components, laying the grounds for further explorations of spatially-varying versions of such formations.