Critical coupling-assisted extraordinary electromagnetic transmission unrestricted by aperture size

Extraordinary electromagnetic transmission is a captivating physical phenomenon that exhibits enhanced transmission efficiencies through metal films with subwavelength apertures. Although various mechanisms exist to achieve this effect, attaining ultrahigh extraordinary transmission through very small apertures in a metal film remains a challenge. Here, based on the principle of critical coupling, we demonstrate near-unity extraordinary electromagnetic transmission using a wire-through-hole metasurface. The extraordinary transmission effect is not constrained by the size of the metal aperture, which, in principle, can be arbitrarily small. The maximum transmission at the critical coupling condition can reach 100% in numerical simulations and 93.7% in experiments. The polarization of the transmitted wave can be rotated with an arbitrary angle without sacrificing the transmission efficiency by simply bending the metal wires. Our work introduces a mechanism for extraordinary electromagnetic transmission and lays the foundation for the development of advanced devices, such as high-efficiency sensors, filters, and communication systems.