Fig. 1. Schematic of basic structural unit of metamaterial absorber. (a) Top view of metallic circular rings in top and middle layers; (b) top view of metallic mesh in bottom layer; (c) side view; (d) three-dimensional view

Fig. 2. Simulated results of metamaterial absorber. (a) Reflectivity, transmissivity, and absorptivity; (b) equivalent spatial impedance

Fig. 3. Electric-field strength distributions in metamaterial absorber at different incident electromagnetic wave frequencies. (a) Metallic circular ring in top layer; (b) metallic circular ring in middle layer; (c) metallic mesh in bottom layer

Fig. 4. Surface current vector distributions in metamaterial absorber at different incident electromagnetic wave frequencies. (a) Metallic circular ring in top layer; (b) metallic circular ring in middle layer; (c) metallic mesh in bottom layer

Fig. 5. Simulated results of loss distributions in unit structure of metamaterial absorber at 9.98 GHz. (a) Ohmic loss in top metallic circular ring layer; (b) ohmic loss in middle metallic circular ring layer; (c) ohmic loss on surface of metallic mesh in bottom layer; (d) dielectric loss in upper dielectric layer; (e) dielectric loss in lower dielectric layer; (f) comparison of metallic ohmic loss and dielectric loss

Fig. 6. Simulated absorption curves of metamaterial absorbers with different metallic circular ring radii

Fig. 7. Simulated absorption curves of metamaterial absorber for incident electromagnetic waves with different spatial polarization angles

Fig. 8. Simulated absorption curves of metamaterial absorber for incident electromagnetic waves with different angles of inclination under (a) TE and (b) TM modes

Fig. 9. (a) Photo of metamaterial absorber sample (bottom side: enlarged view of 3×3 structural units); (b) diagram of experimental setup for transmissivity measurement; (c) diagram of experimental setup for reflectivity measurement

Fig. 10. Simulated and measured results of metamaterial absorber. (a) Absorptivity under normal incidence; (b) reflectivity under different incident angles