## 1 Introduction  
In recent several years, metamaterial perfect absorbers [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22] as an important and special branch of the metamaterials have received extensive attention because of their excellent and controllable resonance characteristics that frequently used in the application fields of selective thermal emitters, materials detection, sensing, imaging, and so on. The first metamaterial perfect absorber composed of three function layers (electric ring resonator-insulation dielectric layer-metal strip) was demonstrated at the microwave regime in the year of 2008 [1]. In this three-layer resonance structure, the bottom metal strip can effectively block the transmission of the incident waves, and the proper thickness of dielectric spacer layer can make the impedance of the metamaterial structure matched to that of the air. As a result, a resonance absorption peak with near-perfect absorbance can be obtained [1; 2; 3; 4; 5; 6; 7; 8]. In fact, in addition to the perfect absorption of incident electromagnetic waves, there are many technologies to achieve the regulation of electromagnetic waves, such as nano-particles [23], near-zero-index materials [24], metasurfaces [25], graphene [26], metamaterials [27]. Some novel and interesting phenomena (including electric/equivalent magnetic currents [28], displacement currents [29], surface waves [30] etc.) have also been explored and studied in the process of light regulation. Although there are many technologies and ways to achieve the regulation of electromagnetic waves, they are difficult or encounter obstacles in achieving the perfect absorption of light. Not to mention that these technologies can regulate the absorption resonance performance of the suggested devices. Generally, the resonance frequency of the metamaterial absorber can be effectively tuned or changed from optical to microwave regimes by scaling the structure size of the metallic patterns [18; 19; 20; 21; 22; 23; 31; 32; 33]. For example, total visible band metasurface perfect absorber based on coupled Mie resonance was demonstrated in [18]. Near-perfect absorption at 0.70 THz was presented by using a side length (or width) of 39 \(\upmu\)m of an electric split-ring-resonator [32]. Microwave metamaterialabsorber operated at 8.96 GHz was designed by expanding the size of the pattern, such as an array of 1.8 mm dielectric cube material [33]. The absorption bandwidth of these light absorbers is very narrow (typically less than 20% of the resonance frequency), which makes these absorbers has promising in sensing related fields, such as detection of changes in the surrounding environment, determination of refractive index of analytes. Based on the fact that the multiple-band metamaterial absorbers have the great application prospects in terms of the materials detection and analysis, thermal imaging, and sensing, very recently, the research interest of metamaterial absorbers has been transferred to the multiple-band light absorption. In general, the superposition effect of multiple single-band resonance absorption peaks can obtain the multiple-band metamaterial absorbers. Stacking and super-unit coplanar structures are the two most frequently used construction methods to realize the multiple-band metamaterial absorbers. For instance, triple-band metamaterial absorber can be obtained by cascading three metallic layers [34; 35; 36]. The combination of three (or three groups of) different sizes of metallic patterns in a super-unit coplanar structure was designed to achieve the triple-band near-perfect absorption response [37; 38; 39; 40; 41; 42]. Nowadays, the device design is mainly focused on the trends of simplicity, miniaturization and compact. However, the methods mentioned above are obviously not meeting the trends.