Rectangular cavity-based perfect dual-band absorber with wide incidence angle in terahertz region

In this paper, a dual-band perfect metamaterial absorber(MA) based on rectangular cavity with wide incidence angle is proposed in the terahertz region. The unit of the absorber is composed of three different size rectangular cavities which are placed vertically on a metal plate. The numerical results show that the MA has two distinctive absorption bandwidths from 3.7586 to 4.0977THz and 5.7635 to 6.0746THz, respectively, with both absorption rates larger than 90%. Besides, the resonant frequency can be calculated based on rectangular cavity theory, which provides a design guideline for MA of such type. The theoretical predictions of the resonance frequencies have excellent agreements with the simulation ones. What's more, the physical mechanism of the perfect absorption can be explained based on the distribution of E-field in the absorber and the standing wave theory. Our results provide a new way on realizing perfect absorption based on rectangular cavity.