16th International Conference
on Microwave and High Frequency Heating

18-21 September 2017, Delft, The Netherlands
09:45   Modeling of microwave and RF power applications (1)
Chair: Birgitta Raaholt
09:45
15 mins
MILD PASTEURISATION OF PACKAGED FOODS WITH WATER IMMERSED RADIO-FREQUENCY HEATING
Erik Esveld, Rian Timmermans, Ariette Matser
Abstract: Conventional pasteurisation of packed foods in an autoclaves requires a long time to reach a sufficient temperature in the centre. With RF pasteurisation, the time at high temperature (> 72°C) is significantly reduced with respect to conventional autoclave processing, while achieving the same microbial stability for the product. The result is that the colour, texture and taste of the vegetables in ready-to-heat meals is minimally affected and kept during prolonged chilled retail. The homogeneity of heating that must be achieved with immersed RF technology is crucial. This was achieved with the aid of a hot water surrounding during the radio-frequency heating and a careful balancing of the displacement currents. The non-conducting water surrounding does not absorb the RF energy, but instead increases the efficiency and robustness of the process. It ensures both a minimal thermal treatment everywhere and prevents over processing of the outside and corners. As the maximum internal temperatures stays well below the boiling point, the hermitically sealed packages can be pasteurised under ambient pressure conditions without the need of a vent.
10:00
15 mins
MODE STIRRER BASED ON MULTI-MATERIAL TURNTABLE FOR MICROWAVE HEATING
Jinghua Ye, Huacheng Zhu, Kama Huang
Abstract: Microwave non-uniform heating has been a main drawback of the microwave heating, many methods were proposal to solve the non-uniformity heating[1]. In this paper, a novel multi-material turntable structure is creatively proposed to improve the temperature uniformity in microwave ovens. Polyethylene (PE) and alumina are selected as the material composition of turntable. During the heating process, the processed material is placed on a fixed Teflon bracket which is over the constantly rotating turntable. By using COMSOL Multiphysics, we built the multi-physics models and simulated the heating process with a constantly rotating multi-material turntable. From Fig.1, we can clearly see that the electric field distribution in the microwave oven vary significantly with time, because of the rotation of the multi-material turntable. The position of a strong electric field at a certain moment is likely to shift largely at the very next moment. The coefficient of variation (COV), calculated as the ratio of the standard deviation to the mean, is adopted to quantify the non-uniformity of temperature in different heating process, as shown in Table 1. Table 1 shows that the multi-material turntable can improve the heating efficiency (up to 113%) and the heating uniformity (up to 51%) effectively.
10:15
15 mins
WAVEGUIDE MICROWAVE IMAGING: GEOMETRICAL PARAMETERS OF A SPHERICAL INHOMOGENEITY
Alexander Brovko, Ethan Murphy, Vadim Yakovlev, Taylor York
Abstract: Despite a widespread practical use of sophisticated imaging devices based on ultrasound, X-Ray, and MRI, the need of safe, accurate and cost-efficient imaging technologies is still acute [1]. This paper deals with the problem of development of reliable and robust computational techniques required for processing of data in microwave imaging performed inside closed metal cavities. We present a computational procedure for the use in microwave imaging of a spherical inhomogeneity in a dielectric sample. Expanding upon our earlier technique [2], we develop a procedure utilizing an artificial neural network performing numerical inversion and reconstructing geometrical parameters of a spherical inclusion. Instead of rotating the sample [2], we use a multiport microwave system, and data (complex S-parameters) for the network is produced by corresponding FDTD model. A series of computational experiments is presented for a standard four-port waveguide element (known as a Magic Tees Junction) containing a rectangular Teflon sample with a hidden dielectric or metal inclusion. The error in reconstruction of geometrical parameters (i.e., spatial coordinates and radius) of a dielectric (metal) sphere is shown to be around 2.5 (7.5)%. The study makes a theoretical background for the experimental program exploring the resources of multiport closed systems for practical microwave imaging applications.