Tunable Magneto-Dielectric Polymer Nanocomposites for Microwave Applications

Magneto-dielectric polymer nanocomposites are investigated as a new class of functional materials well suited for RF and microwave device applications. Magnetite (Fe3O4) nanoparticles are homogeneously dispersed in a polymer matrix, which exhibits low losses at microwave frequencies. The monodispersion of the magnetic nanoparticles, with sub-10-nm diameters and tight size distribution, enhances the microwave properties of the engineered composite material by increasing the relative permeability and relative permittivity. Moreover, complex permeability and permittivity of the nanocomposite material can be tuned by an externally applied dc magnetic field with a strength that is achievable with commercial permanent magnets. Multilayered microstrip test fixtures and preexisting measurement techniques were conjointly implemented to extract the microwave properties of the nanocomposite material in the frequency range between 1-6 GHz. The measured data revealed tunability of 5.5% in the permittivity, 37% in the permeability, and more than100× reduction in the loss tangent at specific frequencies under externally applied magnetic fields.