Radio Frequency and Microwave Power Absorption in Spherical Shaped Objects

Abstract

Microwave and radio frequency heating has great promise in many engineering and biomedical applications because of its non-contact, volumetric selective heating. However, the heating patterns and temperature distributions are non-uniform due to non-uniform electromagnetic power absorptions. In this study, we present a closed-form analytic expression of electromagnetic field distribution and power absorption in a spherical shaped object. A simplified Maxwell’s equation that represents plane wave is solved in spherical coordinates using vector potentials and separation of variables. The electromagnetic power absorption is obtained from the electromagnetic field distribution within the object using Poynting theorem. The analytical expressions of the electric field and power generation are evaluated for meat balls of 1.0, 2.0, 3.0 and 5.0 cm radii and two different electromagnetic frequencies. Results show that the strength of the absorbed electromagnetic wave and power absorption is highly dependent on the radius of the dielectric sphere. The presence of local maxima of electric and magnetic field strength due to the constructive interference of the reflection and transmission of electromagnetic wave in the target object are found in all sizes. However numbers of peaks or valleys are more in larger meat balls. The spatial distribution of microwave power absorption follows the trend of electromagnetic field distribution. The positions of local maxima and minima of power absorption and electromagnetic field distributions vary with the radius of the sphere and applied frequencies. It indicates that the uniform and effective electromagnetic power absorption can be facilitated by the proper design of the object of interest and selection of an appropriate frequency.