Magnetodielectric emulsion as a tunable microwave-absorbing material

Abstract

Controlled liquid absorbers of microwave radiation are a promising area of fundamental and applied research. This study focuses on the microwave properties of magnetodielectric emulsions within the 8.2–12 GHz frequency range. A magnetodielectric emulsion consists of water microdroplets suspended in a hydrocarbon-based ferrofluid. When subjected to a magnetic field, the water droplets form an anisotropic chain structure that strongly absorbs microwave radiation. The absorption properties of the emulsion depend on the magnitude of the external biasing magnetic field, droplet concentration, and radiation frequency. Notably, the absorption coefficient can increase with field strength and emulsion concentration. A range of dispersed phase concentrations exist at which the magnetic field exerts its greatest influence. Numerical modelling has shown that the pivotal factor influencing electromagnetic energy dissipation in an emulsion is the mutual location of the water microdroplets. Several fundamentally different mathematical models have been employed to quantitatively interpret experimental data and describe the structural state of magnetodielectric emulsions: the effective medium model, the linear chains imitation, and the direct dynamic modelling of the structure. It has been shown that the effective medium model is inapplicable to the determination of the absorption coefficient of structured samples in the microwave range. Full interpretation of the experimental data is possible through numerical modelling of the wave field, taking into account the chain-like structures. Direct dynamic modelling is used to determine the microgeometry of the structures. The results of the studies indicate that magnetodielectric emulsions have prospects of application as electromagnetic radiation absorbers.