Simulation of Metasurface-Lined Circular Waveguides Demonstrating Below-Cutoff Propagation

It has been shown that the cutoff frequency of a PEC circular waveguide can be significantly reduced by inserting a relatively thin epsilon-negative and near-zero (ENNZ) metamaterial (MTM) liner inside the bore of a waveguide [1] , [2] . This reduction in cutoff frequency is caused by the introduction of a low-frequency backward-wave propagating mode. Reduction of the cutoff frequency allows for substantial miniaturization of the waveguide, opening the possibility for intriguing applications. The MTM-liner concept has been applied to the miniaturization of waveguide probes [3] and in traveling-wave MRI [4] with promising results.