Trapping EM Power by Hollow Cylinders

Thin tubes can trap the electromagnetic (EM) energy, emitted wirelessly from a near-field source. The optimal dimensions of these hollow cylinders are determined for an extensive range of complex permittivities characterizing their material and the reported power enhancement is found practically independent of the antenna location. The spatial distribution of the signal reveals the reshaping in the paths of incoming rays and unveils the nature of the developed resonances in the vicinity of the photonic tubes, for both wave polarizations. The concept is experimentally demonstrated at the UHF band with the use of dense dielectric claddings; enhancement up to two orders of magnitude is recorded. The presented results constitute limits in terms of the EM energy accumulation for a simple configuration and, thus, can be utilized in various wireless power transfer (WPT) applications.