Seminar: Backscattering-Protected Waveguide by Using Duality

#Waveguide #metasurface #antenna

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Abstract

Topological edge modes have garnered significant attention for their ability to support robust, backscattering-immune wave propagation. While traditionally associated with non-reciprocal systems, recent advances have extended these concepts to reciprocal media through the implementation of parity-time-duality (PTD) symmetry. A waveguide exhibiting PTD symmetry features a cross-section where geometric inversion along a specific axis results in dual (complementary) boundary conditions. This symmetry ensures immunity to backscattering caused by discontinuities or sharp corners, provided these perturbations also respect the PTD condition. Several structural implementations, though not always explicitly labelled under PTD symmetry, have demonstrated these principles. A central component in these designs is the use of metasurfaces to engineer the necessary boundary conditions. Early configurations employed complementary reactance surfaces to sustain a so-called line wave at their interface. An alternative architecture was introduced, consisting of a parallel-plate waveguide (PPW) where each side employs dual boundary conditions—typically realized using perfect electric conductor (PEC) and perfect magnetic conductor (PMC) surfaces. This configuration enforces PTD symmetry and supports only the desired edge mode, thus achieving propagation protected by backscattering. The implementation of PMC boundaries was enabled by metasurfaces, particularly high-impedance mushroom-type electromagnetic bandgap (EBG) structures, providing an effective PMC response. Experimental demonstrations confirmed the viability and robustness of this approach. In the presentation, several practical devices based on PTD-symmetric principles are showcased, highlighting the versatility of the concept. These include compact and reconfigurable components such as directional couplers, mode converters, and waveguide bends, all benefiting from the inherent robustness and low-loss characteristics offered by PTD-symmetric waveguides.

• Date: 26 May 2025
• Time: 03:00 AM UTC to 04:00 AM UTC
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• Hong Kong, Hong Kong
• Hong Kong

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