Abstract
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.
Highlights
Microwave heating is based on the transformation of alternating electromagnetic field energy into thermal energy by affecting the molecular polarity of a material
We have proposed a new kind of method to improve the impedance matching and achieve high heating efficiency in microwave heating
Choosing water as heating sample, an impedance matching layer made of triplelayered dielectric slabs is designed and applied to a single mode heating cavity
Summary
Microwave heating is based on the transformation of alternating electromagnetic field energy into thermal energy by affecting the molecular polarity of a material. Aiming at practical microwave heating applications, in this work, a novel approach to achieve impedance matching and improve heating efficiency in microwave heating process is proposed. It is realized by placing an impedance matching structure between the air and the heating sample to minimize the power reflections on the air-heating sample interface. The effectiveness of the proposed impedance matching technology is investigated numerically and experimentally by comparing the reflection coefficients and heating efficiency with and without impedance matching structure. THE PRINCIPLES AND REALIZATION OF THE PROPOSED IMPEDANCE MATCHING BASED TECHNOLOGY
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