Magnetic-polymer flexible composites for electromagnetic interference shielding applications

Abstract

NiCuZnCo ferrites are ideal for electromagnetic interference (EMI) shielding applications due to their high permeability and low loss. These ferrites have an operating frequency of around 1 GHz due to the Snoek’s limit. To further enhance the operating frequency range of these materials, the present work reports the development of magnetic-polymer composites by embedding NiCuZnCo ferrite into a poly-dimethyl-siloxane (PDMS) polymer matrix. These composites blend the properties of ferrite and polymer, offering distinct features. The thermal stability of the PDMS-magnetic composite is observed at ~400 °C. The surface morphology of ferrite and its integration with the PDMS matrix are investigated using a field emission-scanning electron microscope (FE-SEM). The morphology of the ferrite in the composite material is nearly spherical. While the magnetic-PDMS composites exhibit lower saturation magnetization than the pure ferrite, the magnetization steadily increases with rising ferrite content in the PDMS matrix. Notably, the DC electrical resistivity of the ferrite-PDMS samples is of the order of 10¹² Ω.cm at room temperature. The samples’ electromagnetic properties, such as complex permittivity, complex permeability, and shielding effectiveness, are investigated in the frequency range of 1.0 MHz to 3.6 GHz. Interestingly, the composites showcase ferromagnetic resonance between the 1.8 and 2.6 GHz range, suggesting potential applicability in EMI shielding applications. Because of the higher ferrite concentration, the composite with 45% ferrite-loaded PDMS has a high SE_A of approximately 56 dB at a frequency of 1.7 GHz.