Angle-Insensitive Toroidal Metasurface for High-Efficiency Sensing

This article presents a novel toroidal metasurface that is able to support a toroidal response at almost all incident angles for a transverse magnetic (TM) wave at the microwave range. A flat band is observed from the calculated band structure where the radiation power of the toroidal response is highest around 7.51 GHz. A high transmission at a resonant frequency is observed from the simulated and measured transmission coefficients with different incident angles, whereas the transmission is lower at the rest frequency range. The resonance frequency at a high sensitivity of 0.78 GHz/refraction index unit (RIU) is experimentally demonstrated, which is very sensitive to the thickness and the refraction index of the surrounding materials such that the proposed toroidal metasurface could be used for a tunable highly efficient filters.