Achieving Super Broadband Electromagnetic Absorption by Optimizing Impedance Match of rGO Sponge Metamaterials

The reduced graphene oxide (rGO) sponges exhibit exciting electromagnetic absorption (MA) performance in high-frequency range. However, it is still a great challenge to realize desirable MA property at low frequency (2–4 GHz) due to the great difficulty in balancing the good interfacial impedance matching and strong dielectric loss. Herein, the MA metamaterials based on rGO sponge with different unit shapes are reported. The relationship between the unit shape and MA performance is explored by experiment and simulation. The results show that frustum pyramid metamaterial exhibits ultrabroad band MA; the qualified absorption (the reflection loss lower than −10 dB) of electromagnetic wave can be achieved at 2.4–40 GHz. The average absorption intensity is −22.9 dB in the band of 2–40 GHz. Moreover, the bandwidth for strong absorption with an absorption rate of 99% (−20 dB) is up to 32 GHz. It is significant that the reflection loss has ignorant change even though the incident angle is increased from 5° to 40°. These are contributed to the excellent impedance matching and strong dielectric loss. These lightweight frustum pyramid metamaterials are very promising in the application for broadband electromagnetic protection.