Dual-Band Terahertz Metamaterial Absorber and Its Refractive-Index-Sensing Application for Material Films

Metamaterial absorbers are an emerging and rapidly growing technology with potential applications in optoelectronics, such as refractive index sensing and energy harvesting. Herein, a dual-band terahertz metamaterial absorber is investigated by exploiting a patch of circular loops and cross-shaped structures. The designed absorber composes of a periodic metallic metasurface and a continuous reflector layer, which are separated by a benzocyclobutene dielectric film. The perfect absorptivity properties of the absorber, revealed at frequencies of 0.6 and 1.2 THz, can be flexibly designed by manipulating the geometrical dimensions. A sample of the designed absorber prototype is manufactured under a microfabrication process and measured through a terahertz time-domain spectrometer in free space. In addition, the potential application of the proposed terahertz absorber in refractive index sensing is analyzed and experimentally verified, which has an excellent unit sensitivity of 0.13 THz/RIU at 0.6 THz and 0.27 THz/RIU at 1.2 THz, respectively. The practicability in sensing applications is verified by coating polyimide and poly(dimethylsiloxane) dielectric films on the surface of the absorber, and the absorption frequency shifts at 1.2 THz are practically coincident with the simulated ones. This proposed prototype is an effective manner for terahertz metamaterial absorbers with potential applications in the sensor field.