Multilayer Structures of a Zn_0.5Ni_0.5Fe₂O₄-Reduced Graphene Oxide/PVDF Nanocomposite for Tunable and Highly Efficient Microwave Absorbers

Attenuating electromagnetic waves with an absorption-dominant mechanism is still an arduous challenge, despite the recent progress in fabricating advanced electromagnetic interference (EMI) shields. In this study, EMI shielding materials with an outstanding absorption performance were developed. As such, in the first step, we report a practical method for synthesizing magnetic Zn0.5Ni0.5Fe2O4 (ZnNiFe) nanoparticles. The magnetic hysteresis loop reveals that the synthesized magnetic nanoparticles are superparamagnetic with a saturation magnetization of 75.8 emu/g. Thereafter, we propose an EMI absorber using a multilayer assembly of polyvinylidene fluoride sheets containing low concentrations of reduced graphene oxide (rGO) and ZnNiFe. It is shown that the EMI shielding effectiveness increases from 23.93 to 29.05 dB, and the shielding by reflection decreases from 6.5 to 0.5 dB. This happens as the number of layers increases from two to nine at a fixed total thickness of 1.8 mm and filler loadings of 1 wt % rGO and 5 wt % ZnNiFe. More importantly, the nine-layer sample shows an absorption coefficient of A = 0.91, which translated into absorption of more than 91% of the incident wave. To the best of our knowledge, this is the highest ever reported absorbance for a polymer-based EMI shield. It is hypothesized that the superior absorbance of the nine-layer structure originates from (1) multiple internal reflections inside the shield due to the presence of numerous conductive layers and (2) supermagnetic properties of ZnNiFe nanoparticles, leading to enhanced magnetic loss.