Quantitative exploration of the absorber behavior of metal-insulator-metal metamaterials within terahertz via an asymmetric peak model

Terahertz (THz) metamaterials have been developed for THz sensing, detection, imaging, and many other functions due to their unusual absorbers. However, the unusual absorption spectra change with different incident angles. Thus, we designed and fabricated a focal plane array with metal-insulator-metal (MIM) structure metamaterial absorbers for further research. The absorption spectrum with incident angles from 20 to 60 was measured using THz time-domain spectroscopy (THz-TDS), and the experimental results reveal that the absorption spectrum changes with incident angle variations. A basic analytical asymmetric peak model for extracting absorption-frequency characteristics was developed in this study to quantitatively explore this variation in the absorber behavior with incident angles. The best result was that the frequency corresponding to the highest absorption can be easily found using this peak model. The experimental data was coherent with the validation of the asymmetric peak model. Moreover, a second model to quantitatively relate parameters to the incident angle was discovered, allowing for the prediction of absorption spectrum shifts and changes. The absorption spectrum was predicted to have a valley-like absorption curve at particular incident angles based on the secondary models deduction. The proposed extraction method's essential feature is that it can be applied to any physics-based MIM metamaterial system. Such a model will guide the design and optimization of THz metamaterial absorbers, sensors, imagers, and many others.