Ultralight and Low-cost Structural Absorbers with Enhanced Microwave Absorption Performance Based on Sustainable Waste Biomass

As a practical microwave absorber, besides satisfying the basic broadband absorption performance, the density, cost, and process complexity are considerable factors in radar stealth and electromagnetic protection field as well. Here, a simple and economical structural absorber (SA) is proposed to remarkably broaden the absorption bandwidth of biochar from banana peel. By optimizing the size parameters of the unit cell, the optimal SA shows more than 90% absorption in the frequency range from 3.4 to 18 GHz by employing a lightweight porous carbon derived from sustainable biomass. The lightweight porous biochar endows SA low-density properties with surface density of only 0.574 g cm-2. In such SA, the greatly enhanced absorption performance is mainly originated from the synergistic effect of microscopic and macroscopic scales. By optimizing the pattern design of SA, the effective impedance is matched with free-space in a wide frequency, thus dissipating more electromagnetic waves through multiple resonances and edge scattering effects. Additionally, whether transverse electric or transverse magnetic polarizations, stable broadband absorption can be maintained in a wide incidence angle. Thus, this work provides a new prospect for waste utilization of banana peel and a facile low-cost route to greatly extend the microwave absorption bandwidth.