Achieving wideband, ENZ-independent electromagnetic tunneling in coaxial waveguides

Efficient electromagnetic (EM) wave transmission through subwavelength channels is crucial for developing compact photonic and terahertz (THz) devices. Current approaches, typically based on structural resonances or epsilon-near-zero (ENZ) materials, are effective but fundamentally limited by resonant phenomena, restricting their operational bandwidth. This work introduces a novel, to the best of our knowledge, ENZ-independent electromagnetic tunneling mechanism that facilitates ultra-wideband operation. We demonstrate that by leveraging geometric design and impedance engineering, a simple coaxial waveguide can achieve highly efficient subwavelength power transmission without relying on specific material resonances. This approach is remarkably scalable and robust against dimensional variations, maintaining exceptional transmission efficiency across a broad frequency spectrum. Our ENZ-independent strategy opens new avenues for designing versatile, broadband systems for subwavelength energy manipulation, with significant implications for microwave/THz engineering and nanophotonics.