Microwave properties of composites based on glass microsphers coated with ferromagnetic compounds

In this study, glass microspheres (GMs) of varying sizes, both pure and decorated with nano-sized bimetallic Ni(80)Fe(20) particles, were incorporated into epoxy-based composites filled with 3 wt% graphite nanoparticles (GNPs) to create 2D and 3D structures. The electromagnetic interference (EMI) shielding properties were analyzed in the Ka-band (25–36 GHz). The addition of GMs altered the frequency dependence of shielding efficiency (SE T ) and shifted the balance between shielding by reflection (SE R ) and absorption (SE A ). In GNPs-only composites, SE A was much smaller than SE R , whereas in all GMs-containing materials, SE A significantly exceeded SE R . At higher frequencies, the absorption-to-reflection loss ratio increased, reaching 4 at 36 GHz. For 2D GM structures with a thickness of 0.6–0.8 mm, absorption exhibited a sharp frequency dependence at lower frequencies. In contrast, 3D GM structures with a thickness greater than 2.5 mm maintained a frequency-independent absorption with a value of 0.95. These results highlight that incorporating GMs into epoxy/3%GNP composites enhances absorption mechanisms in their interaction with electromagnetic waves.