Effective Microwave Dielectric Properties of Ensembles of Spherical Metal Particles

Knowledge of dielectric and magnetic properties is crucially important in the numerical modeling of high-temperature microwave processing of materials. To enhance the accuracy of modeling for metal powders and metal-containing composites, adequate description is required for the interaction of the electromagnetic field with the electrically conductive particles. A theoretical model for the calculation of effective complex dielectric permittivity of an ensemble of spherical metal particles surrounded by thin insulating layers is presented. The model is based on the effective medium approximation. It accounts for the nonuniform distribution of the electromagnetic field that exists inside individual particles when the electromagnetic wavelength or penetration depth is smaller than the particle size. The effective dielectric losses predicted by the model can be highly significant compared with the magnetic losses that arise due to the eddy currents induced in metal particles by microwaves. Reasonable agreement with the experiment has been demonstrated for the millimeter-wave absorption in metal-ceramic composites with significant volume fraction of metal particles. The model can be utilized for assessing the feasibility of microwave heating of powder metals and metal-ceramic composites.