Dynamic Measurement of Dielectric Properties of Materials at High Temperature During Microwave Heating in a Dual Mode Cylindrical Cavity

A microwave cavity and heating system for microwave processing and in situ dynamic measurements of the complex permittivity of dielectric materials at high temperatures (~1000ºC) has been developed. The method is based on a dual-mode cylindrical cavity where heating and testing are performed by two different swept frequency microwave sources. A cross-coupling filter isolates the signals coming from both sources. By adjusting the frequency bandwidth of the heating source and the level of coupling to the cavity, an automatic procedure allows for the establishment of a desirable level of heating rate to the dielectric sample to reach high temperatures in short cycles. Dielectric properties of materials as a function of temperature are calculated by an improved cavity perturbation method during heating. Accuracy of complex permittivity results has been evaluated and an error lower than 5% with respect to a rigorous analysis of the cavity has been achieved. The functionality of the microwave dielectric measurement system has been demonstrated by heating and measuring glass and ceramic samples up to 1000ºC. The correlation of the complex permittivity with the heating rate, temperature, absorbed power, and other processing parameters can help to better understand the interactions that take place during microwave heating of materials at high temperatures compared to conventional heating.Manuscript received February 17, 2015; revised May 08, 2015 and June 22, 2015; accepted June 27, 2015. Date of publication July 20, 2015; date of current version September 01, 2015. This work was supported by the Ministerio de Economia y Competitividad (MINECO) under Project TEC2012-37532-C02-01 and by the European Regional Development Funds (ERDF).Catalá Civera, JM.; Canós Marín, AJ.; Plaza González, PJ.; Gutiérrez Cano, JD.; García Baños, B.; Penaranda-Foix, FL. (2015). Dynamic Measurement of Dielectric Properties of Materials at High Temperature During Microwave Heating in a Dual Mode Cylindrical Cavity. IEEE Transactions on Microwave Theory and Techniques. 63(9):2905-2914. https://doi.org/10.1109/TMTT.2015.24532632905291463