Theoretical guidance for the rational design of FeCo foams toward efficient electromagnetic wave absorption in 2.0-8.0 GHz range

Effective electromagnetic (EM) wave absorption with minimal coating thickness in the low-to mid-frequency range (2.0-8.0 GHz) remains a significant challenge. Herein, the EM parameters required for low-to mid-frequency EM wave absorption are systematically investigated, and CST Microwave Studio is employed to model and simulate how these target parameters can be realized through microstructural design. The results demonstrate that increasing the real parts of the relative permittivity (ε_r′) and permeability (μ_r′) is benificial for achieving low-to mid-frequency EM wave absorption with reduced coating thickness. Moreover, CST simulations reveal that, for the same material system and identical volume filling fraction, increasing the specific surface area of the absorber contributes to an enhancement of ε_r′. Guided by these principles, FeCo cubes, FeCo particles, and FeCo foams with controlled specific surface areas and high permeability were synthesized. Experimental results confirm that an increased specific surface area effectively enhances ε_r′, thereby promoting low-to mid-frequency absorption. As a result, the FeCo foam achieves an effective absorption bandwidth (EAB) of 3.2 GHz (4.8-8.0 GHz) in the C-band with a coating thickness of 2.0 mm, and 1.5 GHz (2.1-3.6 GHz) in the S-band with a coating thickness of 4.0 mm. This work provides valuable insights into the rational design of advanced low-to mid-frequency EM absorbing materials.