Study of the permittivity of composite materials filled with non-spherical inclusions of diverse structure

Abstract The shape of inclusions significantly affects the permittivity of composites comprising these inclusions. The paper studies composites filled with flake-like inclusions. Three different values of the permittivity were compared. First, the permittivity value was calculated following the Maxwell mixing rule for diluted mixtures. Then, the size and shape of particles were statistically studied to retrieve the spectral geometrical function. This function was applied to the Bergman–Milton spectral theory to evaluate the effective permittivity of the composite. Also, microwave measurements were made to derive the permittivity of the composites. It was shown that using the spectral geometrical function reconstructs the permittivity value that is close to the measured value. It was also demonstrated that the increase in particle elongation enhances the permittivity. Insulating shell made of SiO 2 reduces the effective permittivity, which is especially pronounced for elongated particles. Optimization of the shape of inclusions based on the analysis of spectral geometrical function gives a new tool to synthesize electromagnetic composites with the desired permittivity values that are appropriate for many technical applications.