Guiding and focusing of spoof surface plasmon polaritons on conical metal wire with periodically helical grooves

In this work, we propose a smooth transition structure from a coaxial waveguide to a helically plasmonic waveguide, which can achieve high-efficiency guiding and focusing of spoof surface plasmon polaritons on the conical metal wire decorated with periodically helical grooves. Numerical simulations of the proposed structure show that the amplitude of surface electric field at the conical endpoint is nearly 30 times higher than that of the feed from 20GHz to 35GHz. The strong energy concentration and superfocusing on the tip of the proposed conical plasmonic waveguide can find important applications in near-field imaging, and sensing in the microwave and terahertz frequencies.