Ultrabroad-band and low-frequency microwave absorption based on activated waxberry metamaterial

Low-frequency yet ultrabroad band microwave absorption still remains a great challenge due to contradiction between impedance match and electromagnetic loss. The natural biomass with hierarchical structure provides new solution to address this issue. The electromagnetic (EM) metamaterials show frequency-designable advantage while its absorption band width is often limited. Here we report an alternative EM metamaterial based on activated waxberry with gradient impedance profile. Strong microwave absorptions at low frequencies were experimentally realized with our fabricated metamaterial, achieving <-10 dB reflection loss at 1-4 GHz. Moreover, ultrabroad band feature is achieved with effective absorbing band (reflection loss < -10 dB) covering from 1 to 40 GHz. In addition, our meta-design exhibits nearly incident-angle independent property (from 5 to 40 degrees) on the microwave absorption. The excellent performance of our low-frequency meta-absorber is attributed to the excellent interface impedance match of meta-structure and the high dielectric loss due to chemical activation. The broad band absorption is due to the gradient radial microstructure of carbonized waxberry. Our new metamaterial is very promising in the electromagnetic shielding application especially at low frequency.