Temperature-dependent complex permittivity of several electromagnetic susceptors at 2.45 GHz

Electromagnetic susceptors, understood as trans-ductors of energy, from radiative to thermal, are of high interest when combined with materials that are non-efficient by themselves in a heating process using microwave technology. Susceptors can be either embedded into the material (as filaments, powders, etc.) or attached to them as a supplementary layer added on their interfaces. The loss factor modelled as the imaginary part of the complex permittivity of a material can predict the result of the pyroelectric effects that underlies during its microwave heating process. Such mechanisms have a dependence on temperature, hence the heating process rate may evolve with time as the temperature varies. Furthermore, the heat transfer coefficient can also vary with the temperature. Both, the loss factor and the heat transfer coefficient are involved in the heat transfer equation, and their dependence with the temperature can largely justify the thermal runaway effects. Such effects are noticeable when the heat generation and transfer rates overcome the period of time required by any artifacts introduced inside a microwave exposure chamber for leveling the volumetric heating uniformity. This study focuses on determining the complex permittivity of several susceptors at the 2.45-GHz frequency, in the temperature range 30-70 °C.This research has been developed under the project Ref. HAR2016-77203-P “Alternativas al descere en la fundición de cascarilla cerámica (ceramic shell casting): técnica por microondas (II)”, granted by the Ministerio de Economía y Competitividad of Spai