High-Efficiency Continuous-Flow Microwave Heating System Based on Asymmetric Propagation Waveguide

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Continuous-flow microwave heating is widely used in chemical engineering and other fields. However, during microwave heating, the load’s electrical permittivity change will affect microwave heating efficiency. In this article, a WR430 asymmetric propagation waveguide is proposed based on gradient-index metasurfaces (GIMs), which can achieve high-efficiency continuous-flow heating with a large range of permittivity. First, asymmetric microwave propagation is realized in a WR430 3-D waveguide model, and the influence of metasurfaces index, thickness, and discrete element size is analyzed. Second, the asymmetric propagation waveguide is realized by fluted medium based on the permittivity equivalent method. The results show that the microwave inside the waveguide can only propagate along one direction at 2.4–2.6 GHz. Finally, the proposed waveguide is applied to a continuous-flow heating system. Compared with the single-mode cavity, multimode cavity, and waveguide water load, the proposed method can improve heating robustness and efficiency with different loads. Experiments show that the microwave absorption efficiency is stable and greater than 90% in the proposed system when the permittivity of the load changes drastically. The proposed system has a simple structure and strong applicability, which can replace the three-stub tuner and get rid of the circulator and water load for continuous-flow heating.