Sergey Soldatov

Microwave cavity perturbation technique for high-temperature dielectric measurements

The present work is motivated by the use of microwaves for the catalytic conversion of carbon dioxide to carbon monoxide. Chemical reactions like this are running at catalyst temperatures of more than 800 °C. The appropriate design of the microwave assisted reactor requires the exact knowledge of the dielectric properties of the catalyst and catalyst support materials up to those high temperatures. For this purpose a measurements system based on the cavity perturbation method was built. The system is using a rectangular TE104 cavity with a resonance frequency at 2.45 GHz and a quality factor Q ≈ 12000. A novel synthetic calibration method based on numerical full-wave modeling has been developed as an alternative to traditional calibration methods. The results of high temperature dielectric measurements for polyether ether ketone (PEEK), MACOR glass ceramics and zirconia are presented.

System for in-situ dielectric and calorimetric measurements during microwave curing of resins

The use of new materials is of great interest for science, research and industry. Fiber composite materials such as carbon fiber or glass fiber composites find due to their lightweight potential, as well as their mechanical and physical features increasing application in aerospace engineering, the automotive industry and the general engineering. The main obstacle to these materials is the difficulty of manufacturing with long cycle times and high energy consumption. Therefore, it is of great interest to find new approaches, which accelerate the production of fiber composites, while making it more energy-efficient. Here, the microwave curing is a promising technology for the preparation of fiber-reinforced composites, as it is faster and more cost-effective, because it is based on the volumetric heating of the material. This motivated the development of various microwave systems and processes. Nevertheless, for a successful system and process design the detailed knowledge of the dielectric properties of materials is mandatory. Therefore, a system for in-situ monitoring of curing processes of thermoset resins under microwave heating was developed. The main function of the measurements instrument is the dielectric characterization of resins based on the cavity perturbation technique. Here, the electromagnetic source used for dielectric characterization of the material under test is used for dielectric heating at the same time. The cavity operates at 2.45 GHz in the TE111 mode. It has an unloaded quality factor of 11500. In addition, a calorimetric analysis of the exothermal curing process is envisaged.

A microwave applicator for high homogeneous high temperature heating of catalysts

Using microwave heating allows for a fast and efficient volumetric heating. For chemical reactors microwaves permit to generate the heat inside the catalyst bed directly at the location where the reaction takes place. However, compared to conventional heating it is difficult to achieve a homogeneous temperature profile. At least for large scale applicators, which are not small in all dimensions compared to the wavelength, one has standing wave patterns resulting from interference of different reflected and scattered parts of the microwave. Hence, the electromagnetic field shows a pattern consisting of field minima and maxima which result in thermal “cold” and “hot” spots. This paper describes a new scalable approach for an applicator at 2.45 GHz that achieves a homogeneous field and hence a homogeneous heating throughout the applicator.

Microwave system for in-situ dielectric and calorimetric measurements in a wide temperature range using a TE 111 -mode cavity

The various developments in microwave material processing have shown that the microwave curing of fiber reinforced plastics can be much more energy efficient compared to conventional heating methods. This motivated the development of different microwave systems and processes. Nevertheless, the accurate knowledge of the dielectric properties of materials at the carrier frequency is one of the keys for successful design of microwave applicators and processes. Therefore, a system for accurate in-situ monitoring of the dielectric and the calorimetric properties during microwave heating has been developed. The dielectric characterization bases on the cavity perturbation technique. The microwave source operating at 2.45 GHz is utilized for both, the cavity resonance properties measurements and the dielectric heating of the material at the same time. A TE111-mode cylindrical cavity having an unloaded quality factor of 11.500 is used as microwave applicator.