---

Microwave absorbing materials (MAMs) are vital for mitigating electromagnetic interference, a growing concern with the proliferation of electronic devices and 5G technology. Biomass char, a carbon material derived from organic sources, holds promise for MAMs due to its cost-effectiveness and porous nature. However, achieving a balance between conduction loss and interface polarization loss remains challenging with conventional heating methods.

A recent study introduces an innovative hybrid heating technology using microwave-confined plasma. This method significantly enhances the properties of cellulose char by improving both conduction and polarization losses. Compared to traditional heating, the new approach almost doubles the char’s conductivity and increases the content of C-O bonds, which possess longer bond lengths and higher dielectric susceptibility than C=O bonds. Additionally, the process embeds more condensed carbon nanoparticles in the char, boosting heterointerface polarization loss.

In practical terms, the improved biochar shows a significant enhancement in microwave absorption. For example, a sample prepared with the new method (MW900-40%) demonstrated a tangent loss range of 0.69 to 0.97 over 2.0 to 18.0 GHz, outperforming the conventionally heated sample (CH900-40%), which ranged from 0.34 to 0.64.

To maximize absorption efficiency, researchers designed a double-layer absorber with different MW900 loadings based on multilayer impedance gradient principles. This design achieved a minimum reflection loss of -59.0 dB at 15.9 GHz and an effective absorption bandwidth of 10.0 GHz at a thickness of 4.0 mm. Simulations confirmed the effectiveness of this structure in optimizing impedance matching and microwave dissipation distribution, marking a significant advancement in the development of high-performance MAMs.