Near-perfect transmission through thick apertures by inserting connected ring resonators

We report the largely enhanced transmission of electromagnetic waves through periodic subwavelength thick apertures in an opaque plate by inserting connected ring resonators through the apertures at selected microwave frequencies. In principle, nearly 100% of zero-order transmission could always be achieved theoretically without considering the loss and disorder for arbitrary thickness of the metallic plate. And this phenomenon is not highly sensitive to the geometrical parameters, which allows rather large fabrication errors. As a proof-of-concept study, two typical types of realistic samples composed of connected ring resonators are proposed and can achieve 0.8 or even higher transmittance both in simulations and experiments. In addition, one of them can also be made into a polarization converter with arbitrary rotation angles and high efficiency simultaneously. The frequency of low-order resonance-induced transmission is found to be determined mainly by the wire configuration and its geometric scale, but weakly dependent on the periodicity and diameters of holes and wires. The agreement between experimental results and numerical simulations also exhibits its great practicability in telecommunications.