Case studies of microwave applicators for industrial heating processes

The topic of this dissertation is to develop a complete process of designing industrial applicators by means of computer-aided design methods. The work consists of case studies of single higher order mode circular cylindrical applicators for industrial heating processes. Uniform heating is an important issue to be addressed first in most industrial microwave heating applications. The methodology used in our project is to find means to excite the exact design mode, which is the required condition before one can successfully apply the knowledge of the predicted power density distribution to obtain a uniform heating profile. First, normal modes inside applicators are found by an iterative method, which is used to find resonant frequencies and electric and magnetic field patterns by solving modal solutions constrained by boundary conditions for multi-layered vi coaxial circular cylindrical structures. Information gained from the normal modes includes suitable geometries of the applicator and possible coupling schemes. Next, optimal dimensions are found for the coupling aperture, which is used for high Q and high power applicators. Complex and realistic models can be built based on information and experiences from simplified models, which need less computation time in running numerical simulations and have simpler analytic solutions. Single higher order mode applicators with high processing volumes and moderate high dielectric losses within them need elaborate adjustments of their configurations in order to operate significantly on their single design modes. A periodic-structured geometry is suggested. Finally, if the dielectric losses become very high, the coaxial probe, instead of the coupling aperture is utilized to couple microwave power in the periodicstructured applicator. Complete analyses for two types of applicators, including plots of reflection coefficient and electric fields, heating profiles, etc., are performed. In summary, this project encompasses a wide range of problems that together address the feasibility of operating industrial applicators in a single higher order design mode, and, in the meanwhile, realizing the goal of uniform heating by exact excitation of the design mode.