Biomedical subjects
Publications and source records attributed to A C Metaxas.
The use of parallel computing in the finite element analysis of microwave heating applicators is discussed. Numerical results for a multiple feed cavity at 896 MHz and a cavity with a mode stirrer at 2.45 GHz are presented, and it is shown that for the two structures parallelism is most effectively introduced at different levels in the analysis.
The use of the resistive sheet for characterizing thin metallic films is presented in a microwave heating context. A finite edge element formulation is used to include the resistive sheet surface integral in both the frequency and time domains. The properties of the resistive sheet are compared with analytical expressions for the reflection, transmission and absorption coefficients and a correction factor is suggested to improve the accuracy of the numerical implementation. Results are presented for single and multimode systems.
AMPERE (Association for Microwave Power in Europe for Research and Education) is a "European" non-profit association devoted to the promotion of microwave and radio frequency heating techniques for research and industrial applications. Despite the fact that AMPERE is a European association, it has a world-wide membership which comprises industrialists, academics, researchers and consultants. This brief paper focuses on the trends in the subject matter and activities in the biennial AMPERE conferences held in Europe since 1986.
This paper gives a brief resume of the numerical work carried out over the past decade at the Electricity Utilisation Group usingfinite elements for the characterization of RF and microwave heating systems. Maxwell's equations are solved in 3D while for coronas the Poisson's and particle continuity equations are solved in 2D. In addition work on modeling thin films and the use of parallel computing describes the latest work to emanate from the group.
In this paper the resonant modes of a radio frequency industrial heating applicator system are determined numerically. This is carried out using a finite element eigenvalue calculation of the electric field of the system. Both the complex linear and nonlinear forms of the generalized large sparse eigenproblem are solved, the latter being obligatory when material properties are frequency-dependent. The basis is the Implicity Restarted Arnoldi/Lanczos Methods which can be used to calculate the multiple resonant modes occurring in the operating frequency range of interest. Once the resonant modes of a specific system have been obtained, an electric equivalent circuit model can be derived. The numerical results presented are compared to experimental measurements carried out on a prototype experimental system showing good agreement.
The precursor of arcs in radio frequency heating systems, namely corona discharges, are examined numerically in this paper, using the finite element-flux corrected transport technique. A point-plane configuration is used as a first approximation for a radio frequency applicator and the effects of the operating frequency and pressure on the current output, charge densities, corona onset voltage and light output are investigated. It was found that an increase in the operating frequency around the radio frequency part of the spectrum, resulted in an increase in the corona onset voltage, which accounts for the less arc-prone behavior of microwave systems. Also, a decrease in the pressure resulted in a reduction of the corona onset voltage, and thus the increased possibility of arc formation in radio frequency systems operating under vacuum conditions.
A study is made into the numerical modeling of wall losses for a microwave heating application. It makes use of a surface integral term for both a frequency and time domain finite edge element formulation in order to model the wall impedance of the enclosed microwave cavity. The paper describes how the surface element matrix of the complex wall impedance is combined with the matrix formulation. The results are checked against analytical expressions for a single mode resonant cavity. An analysis on the effect of lossy walls is provided using four low-loss material insertions over a range of surface conductivities.
This paper describes a new self-resonating switch-mode power-supply for driving CW magnetrons, based on the Boucherot effect. A detailed circuit analysis is given and its performance is evaluated for an 800 W/2450 MHz magnetron, whilst work at high power driving a magnetron up to 40 kW is reported. A comparison of the supply with the conventional power-supply used in microwave ovens is made and the principal features of the new design are found to be: low energy dissipation under short-circuit conditions, low ripple current and voltage waveforms that result in more precise control in the range 20-100% of rated power, high efficiencies and small size and weight.