Spoof surface whispering-gallery mode supported by two concentrically coupled textured ring resonators

The Whispering-Gallery Mode (WGM) is very useful for sensing applications due to the exposure of an evanescent field. In a previous work we have shown that a surface WGM can be excited at the exterior of a negative-permittivity or -permeability material layer attached to a dielectric microresonator, which can amplify the evanescent field and then further advance the sensitivity. In this paper a wheel-shaped resonator which consists of two concentrically coupled textured rings is designed to generate the surface WGM and a sensor prototype is fabricated. The results show that the coupling gap between the two textured rings has provided a new freedom to manipulate the resonant characteristic and field confinement effect. Since most energies are concentrated in the vicinity of the gap, this region is quite sensitive to a slight change in the sample substance. Experimental results at the microwave frequencies are consistent with simulation and verify the performances of the sensor