High-contrast and ultra-narrowband terahertz metamaterial absorber based on two-dimensional trenched metal meta-grating

Metamaterial absorbers (MAs) made of metallic materials are capable of confining incident energy on the structural surface, which offers an ideal platform for sensitive detection and integrated devices. However, realizing a high-contrast, ultra-narrow band resonance in metamaterials remains an intractable issue. In this work, we numerically exhibit a simple MA design based on a two-dimensional trenched metal meta-grating, which features a single ultra-narrow band resonance within a clean background spectrum ranging from 0 to 2 THz. The absorption resonance characteristics a linewidth of 0.4 GHz and a Q factor of 2407, thanking to interference effect between the low-order surface plasmon polariton and Wood’s anomaly as well as further assistance from introducing the air trench. The evolutions of the absorption resonance with the key geometric parameters are numerically discussed and elucidated by the Smith curve of the reflective s-parameters. The sensing performance of the MA is also evaluated. Benefited from the exposed and widely spread resonance electromagnetic field fully interacting with the analyte, the saturated thickness, maximum sensitivity and maximum sensing figure of merit for the all-metal MA sensor can be respectively as high as about 300 μm, 800 GHz/RIU and 2000, verifying the superior performance of the MA sensor. Such narrow band MAs with exposed resonant fields offer possible options for other application such as spectroscopically and nonlinear enhancing devices.