Fig. 1. (a) Applications of metamaterials [16], [17], [18]. (b) Ⅰ Early structure of MMA [19]. Ⅱ Metamaterials are bonded to magnetic metals [20]. Ⅲ bionic moth-eye array design [21]. Ⅳ new artificial design [22]. Ⅴ 3D printing for preparation of MMA [23].

Fig. 2. Some common ordinary absorbing materials. Carbon-based materials [33], [34], [35], [36]. Metal-based absorbing materials [37], [38], [39] and composite absorbing materials [40], [41], [42].

Fig. 3. (a) Narrow frequency MMA [6]. (b) Dual-frequency terahertz MMA [79]. (c) The unit cell of MMA with polarization insensitivity [81]. (d) MMA with wide-Angle incident absorption characteristics [82]. (e) Schematic drawing of tunable MMA under external loading [86]. (f) Bionic simulation of MMA anti-reflection silicon column array [89].

Fig. 4. (a) The sketch-map of ferrite-wire MMA unit cell. Front view, side view, and structure parameters [96]. (b) Unit cell of the ferrite based tunable MMA, side views and schematic representation of measurements [97]. (c) Schematic diagram of the magnetically tunable Mie resonance-based dielectric metamaterial, and four sets of phases representing the dynamic changes of the magnetic field distribution in the unit cell [99]. (d) Schematic view of unit cells of the tunable MMA, and simulate the absorption of this MMA in different external magnetic fields [100].

Fig. 5. (a) The microstructures of moth eye. (b) FCIP distribution in absorber, in which the mass ratio of FCIP to PU was 2.5: 1. (c) Experiment and simulation diagram of RL of MMA [21]. (d) Pachliopta aristolochiae biomimetic MMA and corresponding current vortex [115]. (e) The frustules and the design of diatom frustule-inspired nanoparticle arrays [116].

Fig. 6. (a) Schematic representation of a unit cell of the three-layer TiN MMA. (b) SEM image of the fabricated TiN absorber. (c) Simulated and measured absorption spectra for the TiN MMA. (d) The absorption spectra for the Au and Ag MMA [127]. (e) Schematic 3D view of a unit cell of the periodic pattern. (f) Simulated and measured RL of the patterned magnetic absorber. (g) The picture of the patterned absorber [130]. (h) RL for the flat absorbers consisting of the CIFs-based composite at different thicknesses. (i) 3D structure of the as-designed MMA. (j) The experiment simulation absorption spectra [131].

Fig. 7. (a) The split ring resonator unit-cell and the four basic units with different rotation angles are composed of the super unit [141]. (b) The perspective and front view of a pyramidal MMA, and comparison of absorbing performance between pyramidal absorber and other absorbers [142]. (c) Unit cell geometry of the broadband absorber and simulated reflection coefficient for polarization angles under normal incidence [143]. (d) 3D preparation of honeycomb MMA [144].

Fig. 8. (a) 3D printing of multiple layers of MMA. (b) RL of four waves with different incident angles [145]. (c) Four honeycomb 3D models with different parameters. (d) A cross section of a honeycomb structure [149]. (e) Carbon sphere synthesis process and electromagnetic simulation diagram [150]. (f) Dual-principles strategy for the preparation of dielectric absorbers [151].