COMPLETE FDTD ANALYSIS OF MICROWAVE-HEATING PROCESSES IN FREQUENCY-DEPENDENT AND TEMPERATURE-DEPENDENT MEDIA

It is well known that the temperature rise in a material modifies its physical properties and, particularly, its dielectric permittivity, Th e dissipated electromagnetic power involved in microwave heating proce sses depending on epsilon(omega), the electrical characteristics of th e heated media must vary with the temperature to achieve realistic sim ulations, In this paper, we present a fast and accurate algorithm allo wing, through a combined electromagnetic and thermal procedure, to tak e into account the influence of the temperature on the electrical prop erties of materials, First, the temperature dependence of the complex permittivity ruled by a Debye relaxation equation is investigated, and a realistic model is proposed and validated. Then, a frequency-depend ent finite-differences time-domain ((FD)(TD)-T-2) method is used to as sess the instantaneous electromagnetic power lost by dielectric hyster esis. Within the same iteration, a time-scaled form of the heat transf er equation allows one to calculate the temperature distribution in th e heated medium and then to correct the dielectric properties of the m aterial using the proposed model. These new characteristics will be ta ken into account by the EM solver at the nest iteration, This combined algorithm allows a significant reduction of computation time, An appl ication to a microwave oven is proposed.