Design of multimode-circular microwave cavity for agri-food processing

Abstract

This article presents a design for multimode-circular microwave cavity at 2.45 GHz as a section of vertical-typed microwave oven for agri-food processing. Microwave cavity with a diameter of 100 cm and a height of 25 cm was modeled using CST2006® commercial software. Finite integral method was performed to solve the model for design criteria including waveguide arrangement to obtain low coupling and uniform distribution, and choke design to minimize microwave leakage. Simulation results show that perpendicular arrangement of two waveguides with 30° angle apart from each other yielded the minimal mutual coupling. With this waveguide arrangement, microwave power density was linearly loss into the grape model in radial direction from wall toward the center of cavity. Simulated electric field (E-field) distribution agreed with experimental E'-field distribution on fresh grape as it was converted into heat captured by thermal imaging camera. The cavity design with three square choke of 31×31 mm2 (λ/4) placing with space of 20 mm (λ/6) exponentially attenuated the E-field. Attenuation trend of simulation agreed with experimental that of measurement which was below safely limit of 5 mW/cm2. Findings from this work are useful for the scale-up of multisection/multi-mode microwave oven suitable for agri-food drying process.