High-efficiency microwave heating method based on impedance matching technology

In a microwave heating process, part of microwave power may be reflected on the air-heating sample interface due to the impedance mismatching, caused by the relative dielectric permittivity difference between the air and the heating sample. To overcome this problem, a novel impedance matching based technology is proposed. It designs and inserts an impedance matching structure between the air and the heating sample, which mitigates the drastic permittivity difference on both sides. This realizes good impedance matching and obtains the minimized reflection on the interface, hence highly efficient microwave heating is achieved. In this work, the mechanism of the proposed technology and the synthesis of such an impedance matching structure is illustrated, and then verified by an experiment using 500W 2.45GHz microwave power to heat a box of water. An impedance matching structure consisting of three homogeneous dielectric slabs is designed, and the heating cases with and without the impedance matching structure are compared. Both simulation and measurement results show that the impedance matching structure decreases the reflection coefficient of the microwave power from -1.8 dB to -25.6 dB, and correspondingly improves the heating efficiency from 34% to above 86.15%. A further analysis estimates the technology’s robustness and effectiveness for various heating sampling, showing that the heating efficiency maintains above 80% even when the heating sample’s relative permittivity ranges from 27 to 75.