On the analysis of microwave power and heating characteristics for food processing: Asymptotes and resonances

This paper presents a comprehensive analysis on microwave power absorption and associated heating characteristics for various food materials. The analysis is based on a closed form solution, which is derived from the first principle. It has been shown that both absorbed power distributions and average absorbed power exhibit three distinct behaviors as sample length (2L) is varied from 2L ≪ λm/2π to 2L ≫ Dp, where λm and Dp are wavelength and penetration depth within the material, respectively. These three regimes are termed as thin (2L ≪ λm/2π), resonating (λm/2π  2L  Dp) and thick (2L ≫ Dp) samples. A complete characterization of absorbed power has been established in all the three regimes. This work also provides a correlation for the prediction of resonating sample lengths, which for the first time takes into account the effect of dielectric properties (λm and Dp) of the material and free space and also the influence of various distributions of microwave incidence. It has been shown that the closed form analysis on absorbed power presented in this work can be used to forecast the heating characteristics and various distributions of microwave incidence may be used to suitably alter the heating characteristics. Overall, the analysis presented in this work can be used as a guideline to predict optimal heating strategy for microwave assisted food processing.