Theoretical excitation of 2-D (1, 1) cavity mode with asymmetric sword-shaped notched square resonators for metamaterial perfect multiband absorbers in infrared range.

1-D cavity modes in 1-D resonators, such as strips, have been used to design multiband metamaterial perfect absorbers. As for 2-D resonators, such as squares and crosses, most studies still focus on exciting the 1-D cavity modes. In this paper, a symmetry-breaking idea is proposed for 2-D cavity mode excitation. An asymmetric sword-shaped notched square resonator is proposed to excite a new 2-D (1, 1) cavity mode, in addition to the 1-D (1, 0) and (3, 0) cavity modes. Thus, a triple-band MPA was successfully produced with average absorptivity of 98.8% in the infrared range. The 2-D cavity mode provides better performance as a biosensor than the 1-D cavity modes do. To obtain more absorption bands, a six-band metamaterial perfect absorber with average absorptivity of 97.2% was successfully produced by combining two sword-shaped notched square resonators with different sizes. A nine-band metamaterial perfect absorber was successfully produced with average absorptivity of 94.5% by combining three sword-shaped notched square resonators with different sizes.