Uniform temperature distribution in microwave heating achieved via rotating electric field.

Microwave heating (MWH) is widely used in various industrial and research applications due to its advantages such as rapid heating rates, energy efficiency, and low overall processing temperatures. However, a critical challenge in conventional MWH systems is temperature non-uniformity, which arises from the formation of nodes and antinodes due to standing wave patterns inside the cavity. In this study, we propose an improved MWH system that enhances temperature uniformity through cavity system optimization. To achieve a uniform electric field distribution, we implemented a rotating electric field by employing a multi-waveguide system combined with a phase-shifting technique. Furthermore, we increased the wavelength within the cavity by adjusting the waveguide height, resulting in further uniformity enhancement. Simulation and experimental results confirmed that the proposed system achieves uniform heating over a 150 mm area, with the electric field distribution showing less than 5% variation. The temperature coefficient of variation (COV) was successfully reduced to below 5%, clearly demonstrating the system's capability to significantly improve uniformity in microwave heating. These results validate the effectiveness of the proposed system in achieving stable and uniform thermal processing, even for large-area samples.