RESONANT MICROWAVE-POWER ABSORPTION IN SLABS AND CYLINDERS

Resonant power absorption is an important phenomenon during microwave heating. The resonances that occur when plane electromagnetic waves ar e incident on infinitely long cylinders and slabs are investigated as a function of sample dimensions. For cylinders two kinds of incident w aves are studied: TM(z) when the electric field is oriented along the axis oi the cylinder and TE(z) when the magnetic field is oriented alo ng the axis. At a resonant condition the average power absorbed by the sample is a local maximum. Due to attenuation within the sample the r esonances decrease in intensity as the sample size increases. Using th e dielectric properties of water, resonances are found to be a functio n of the ratio of the sample dimension to the wavelength of radiation, )I,, in the sample. For slabs of thickness L and integer values of n, resonances occurred at L/lambda(s) = 0.5n; for cylinders of diameter D , resonances occurred at D/lambda(s) = 0.5n - 0.257. The generality of these relations to predict resonances in other food samples are shown using existing dielectric data. Resonances in cylinders for both pola rizations occurred at similar radii. However, the radius at which the first resonance occurred for the TM(z) case was absent in the TE(z) ca se.