Ultrabroad Band Microwave Absorption of Carbonized Waxberry with Hierarchical Structure.

Developing microwave absorption materials with broadband and lightweight characters is of great significance. However, it is still a great challenge for carbonized biomass without loading magnetic particles to cover the broad microwave frequency. Herein, it is proposed to carbonize freeze-dried waxberry to make full use of its natural hierarchical gradient structure to target the ultrabroad band microwave absorption. The carbonized freeze-dried waxberry shows radial-gradient and hierarchical structure. The different components of hierarchical waxberry demonstrate gradient dielectric properties: the outer component shows anisotropic dielectric constants with smaller value, while the inner core shows higher dielectric constants. This gradient dielectric property is beneficial to the impedance matching and strong polarization. As a result, the bandwidth of carbonized waxberry exhibits an ultrabroad band microwave absorption, ranging from 1 to 40 GHz with the reflection loss value below -8 dB. Meanwhile, the bandwidth can cover from 8 to 40 GHz when the reflection loss is below -15 dB. The ultrabroad microwave absorption is attributed to the hierarchical radial-gradient structure of carbonized waxberry, which provides good impedance matching with air media. This achievement paves the way for the exploitation of natural hierarchical biomass as a superlight and broadband high-performance microwave absorption material.