Abstract-A microwave cavity and heating system for microwave processing and in situ dynamic measurements of the complex permittivity of dielectric materials at high temperatures ( 1000 C) 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 1000 C. 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.

No abstract

No abstract

Penaranda-Foix, FL.; Janezic, MD.; Catalá Civera, JM.; Canós Marín, AJ. (2012). Full-wave analysis of dielectric-loaded cylindrical waveguides and cavities using a new four-port ring network. IEEE Transactions on Microwave Theory and Techniques. 60(9):2730-2740. doi:10.1109/TMTT.2012.2206048. > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract-In this paper, a full-wave method for the electromagnetic analysis of dielectric-loaded cylindrical and coaxial waveguides and cavities is developed. For this purpose, a new 4-port ring network is proposed, and the mode-matching method is applied to calculate the Generalized Admittance Matrix (GAM) of this new structure. A number of analyses on dielectric-loaded waveguide structures and cavities have been conducted in order to validate and to assess the accuracy of the new approach. The results have been compared with theoretical values, numerical modeling from the literature, and data from commercial electromagnetic simulators. The method has been also applied to the accurate determination of dielectric properties, and we provide an example of these measurements as another way to validate this new method.

This paper reports the development of a stand-alone and portable instrument designed to measure the complex permittivity of dielectric materials at microwave frequencies. The equipment consists of an in-house singleport vectorial reflectometer and a resonant coaxial bi-reentrant microwave cavity where the material under test is placed inside a Pyrex vial, making the device appropriate for measuring liquids, semi-solids, powders and granular materials. The relation between the dielectric properties of the involved materials and the cavity resonance has been solved by numerical methods based on mode-matching and circuit analysis. In order to increase the measurement range, so that low to high loss materials can be characterized in the same cavity, the effect of the coupling network is de-embedded from the resonance measurements. The performance of the newly devised instrument is evaluated by error/uncertainty analysis and comparative studies with other wellestablished instruments and methods. Errors lower than 2% in the dielectric constant, and 5% in the loss factor, are found. This simple, portable, affordable and robust device could help non-specialized personnel to accurately measure dielectric properties of materials used in a wide range of microwave applications.