Generalisation and evaluation of macroscopic models for microwave susceptors in contact with heated foods

[EN] Introducing a thin conductive layer into a finite-mesh (as inherent in e.g. finite difference time domain (FDTD) and finite element (FEM) methods) typically requires a dedicated equivalent macroscopic model allowing for computationally effective and accurate electromagnetic (EM) and thermal simulations. Thin conductive layers, such as microwave susceptors, characterised by their surface resistance (Rs), are adequately represented with a dielectric surrogate layer of higher thickness and proportionally scaled conductivity, maintaining the value of Rs. Systematic evaluation of macroscopic models of microwave susceptors used for enhancing the heating efficiency of microwavable food packages has been reported in [1]. Our studies therein focus on validity, accuracy and practical application limits of the proposed macroscopic models of thin metallic layers, in terms of power dissipated in susceptor placed in free space and irradiated by EM wave, at all angles of incidence. In this work we extend our studies to real-life simulation scenarios, in which microwave susceptor is in contact with food. We first consider a four-layer model as in Fig. 1(left) and conduct both analytical and numerical conformal FDTD calculations. The accuracy and application limit of the macroscopic model are investigated for all incidence angles and both, TE and TM polarisations of the impinging EM wave, for different foods. We aim to determine a range of optimum, in terms of power dissipated in the susceptor, values of the susceptor’s surface resistance in all those cases. The results of our canonical calculations with the four-layer model of Fig.1(left) are validated in the 3D FDTD modelling scenario of Fig.1(right), representative of a real-life domestic oven. While for normal incidence our results are in overall agreement with some of the previously published observations [2], they are formalised and generalised to constitute reliable guidelines for microwave oven and food packaging designers and manufacturers. We also show cases where some of the earlier rule-of-the-thumb guidelines fail.Celuch, M.; Wilczynski, K.; Olszewska-Placha, M. (2019). Generalisation and evaluation of macroscopic models for microwave susceptors in contact with heated foods. En AMPERE 2019. 17th International Conference on Microwave and High Frequency Heating. Editorial Universitat Politècnica de València. 245-252. https://doi.org/10.4995/AMPERE2019.2019.9847OCS24525

Application of dielectric resonators to surface impedance measurements of microwave susceptors

[EN] This paper describes the application of dielectric resonators (DR) to the measurements of surface impedance of microwave susceptors. We demonstrate that the single-post (SiPDR) configuration is applicable to plain susceptors before use, while the split-post (SPDR) configuration - to crazed susceptors after use. Attention is given to the full characterisation of active packaging, that is, the influence of paper support on the overall electric losses is also investigated. The measurements can be preformed with various form-factor VNAs, including benchtop VNAs and hand-held FieldFox, though the most economical setup is constructed with a dedicated computer-controlled microwave signal oscillator system available under the name of Q-Meter. Finally, an extension of dielectric resonator measurements to surface imaging is presented, achieved by incorporating the resonator in a 2D automatic scanner.This project has received funding from the European Union’s Horizon 2020 research and innovation programme (H2020-NMBP-07-2017) under grant agreement MMAMA No. 761036.Celuch, M.; Rudnicki, J.; Krupka, J.; Gwarek, W. (2019). Application of dielectric resonators to surface impedance measurements of microwave susceptors. En AMPERE 2019. 17th International Conference on Microwave and High Frequency Heating. Editorial Universitat Politècnica de València. 500-505. https://doi.org/10.4995/AMPERE2019.2019.9953OCS50050

Time-domain analysis of dispersive transmission lines

We present and compare three time domain algorithms for calculating the dispersion characteristics of transmission lines of arbitrary cross-section : the 2-DV FD-TD, the Complex SCN TLM and the 2-DV SCN TLM proposed in this work. All the algorithms prove efficient, as a result of reducing the numerical analysis to two space dimensions. Their accuracy is demonstrated by means of comparison with the results obtained by other methods, for a range of practical examples of microwave guiding structures. We also introduce a new type of excitation which further improves the efficiency and reliability of the time-domain approach

Advanced Modelling Techniques for Resonator Based Dielectric and Semiconductor Materials Characterization

This article reports recent developments in modelling based on Finite Difference Time Domain (FDTD) and Finite Element Method (FEM) for dielectric resonator material measurement setups. In contrast to the methods of the dielectric resonator design, where analytical expansion into Bessel functions is used to solve the Maxwell equations, here the analytical information is used only to ensure the fixed angular variation of the fields, while in the longitudinal and radial direction space discretization is applied, that reduced the problem to 2D. Moreover, when the discretization is performed in time domain, full-wave electromagnetic solvers can be directly coupled to semiconductor drift-diffusion solvers to better understand and predict the behavior of the resonator with semiconductor-based samples. Herein, FDTD and frequency domain FEM approaches are applied to the modelling of dielectric samples and validated against the measurements within the 0.3% margin dictated by the IEC norm. Then a coupled in-house developed multiphysics time-domain FEM solver is employed in order to take the local conductivity changes under electromagnetic illumination into account. New methodologies are thereby demonstrated that open the way to new applications of the dielectric resonator measurements

Advanced modelling techniques for resonator based dielectric and semiconductor materials characterization

This article reports recent developments in modelling based on Finite Difference Time Domain (FDTD) and Finite Element Method (FEM) for dielectric resonator material measurement setups. In contrast to the methods of the dielectric resonator design, where analytical expansion into Bessel functions is used to solve the Maxwell equations, here the analytical information is used only to ensure the fixed angular variation of the fields, while in the longitudinal and radial direction space discretization is applied, that reduced the problem to 2D. Moreover, when the discretization is performed in time domain, full-wave electromagnetic solvers can be directly coupled to semiconductor drift-diffusion solvers to better understand and predict the behavior of the resonator with semiconductor-based samples. Herein, FDTD and frequency domain FEM approaches are applied to the modelling of dielectric samples and validated against the measurements within the 0.3% margin dictated by the IEC norm. Then a coupled in-house developed multiphysics time-domain FEM solver is employed in order to take the local conductivity changes under electromagnetic illumination into account. New methodologies are thereby demonstrated that open the way to new applications of the dielectric resonator measurements.ISSN:2076-341

Electromagnetic and Semiconductor Modeling of Scanning Microwave Microscopy Setups

This article presents finite difference time domain (FDTD) and finite element method (FEM) based electromagnetic modeling and simulation of an industrial scanning microwave microscopy (SMM) material measurement setup. These two methods have been employed to cross verify each other for classical electromagnetic simulations of the homogeneous conductive materials under SMM. For the SMM simulations involving semiconductor materials, however, a coupled multiphysics solver is required in addition to the pure electromagnetic analysis. As a solution to this problem, an FEM-based semiconductor Poisson-Drif-Diffusion (PDD) solver and its coupling to transient electromagnetic solver is presented in this article. The considered SMM setup consists of a conductive fine tip suspended at a certain height above the sample. For the validation purposes of electromagnetic solvers, the numerical modeling was based on both the time domain FEM (TD-FEM) and FDTD. Both numerical methods extract the scattering parameters from the computed field of the conductive or dielectric samples. At the second stage of the analysis, the TD-FEM solver is coupled with the time domain PDD semiconductor solver in order to simulate charge transport and explain behavior of the charges in semiconducting domains under electromagnetic illumination similar to SMM setups.ISSN:2379-879

Open platform GUI for comparative FDTD and FEM computation of material microwave measurement scenarios

We report the developments of an open platform graphical user interface (GUI) for the modelling of microwave setups popularly used in material measurements. The GUI is based on FreeCAD libraries and designed to launch EM solvers in FEM and FDTD, full 3D and BOR formulations