On the Ohmic Heating of Particulates

Abstract

Summary form only given. In high power microwave systems, heating of the contaminants on metallic surfaces and dielectric surfaces is known to cause localized damage. Recently, there has been experimental evidence which shows that the heating via the RF magnetic field in a microwave resonant cavity may be dominant, even when the particulates or the medium appear to be non-magnetic in nature. This paper provides the most general theory, to date, on the degree of absorption of the RF electric field energy and of the RF magnetic field energy in particulates. The particulate may possess an arbitrary electrical conductivity, and both the medium and the particulate may assume general values of permittivity and permeability. Under the assumption that the wavelength of the electromagnetic field in the medium is large compared with the particulate size, we provide an accurate account of the degree of ohmic heating by the radio frequency (RF) electric field and by the RF magnetic field of the electromagnetic field. It is found that, in general, heating by the RF magnetic field is dominant whenever delta<a, where delta is the resistive skin depth and a is the radius of the particulate. Analytic scaling laws in the various regimes are derived, from the static case to very high frequency, and for ratios of delta/a ranging from zero to infinity. The calculation is extended to a transient electromagnetic pulse. Also constructed is the loss tangent of the medium, resulting from a distribution of particulates. The analysis may form a theoretical basis in the heating phenomenology of particulates.