Influence of reducing agent concentration on properties of flexible microwave absorbing coating containing silver coated FeSiAl powders

In this study, silver coated FeSiAl powders (Ag@FeSiAl) with various reducing agent concentrations were synthesized. Then the powders were incorporated with polyurethane (PU) to prepare a flexible microwave absorbing coating with frequency-selective surface (FSS) structure. TEM analysis revealed that silver nanoparticles were uniformly distributed within the FeSiAl matrix with high crystallinity. SEM demonstrated that as the reducing agent concentration increased, the amount of silver particles on the powders surface grew, then agglomeration and free silver emerged at higher concentrations. XPS spectra confirmed the metallic state of silver and carbon functionalization, linking elemental composition to structural characteristics. Particle size distribution initially widened and then narrowed with increasing concentrations, leading to an initial increase and subsequent decrease in average particle size. Coating thickness and reducing agent concentration were shown to affect absorption properties significantly. At 8 g/L, the coating achieved a maximum reflection loss of −40.90 dB, while the effective absorption bandwidth reached 2.91 GHz at 10 g/L. Excessively high concentrations caused poor impedance matching as well as reducing performance. FSS design helps to enhance the absorption performance, achieving a 3.69 GHz bandwidth with a absorbing bandwidth of 8.71–12.4 GHz. Electric and magnetic field distributions provided insight into the interplay of FSS structural parameters, illustrating their impact on absorption behavior.