Uniform Microwave Heating via Electromagnetic Coupling Using Zeroth-Order Resonators

Abstract

We propose microwave heating via electromagnetic coupling using zeroth-order resonators (ZORs) to extend the uniform heating area. ZORs can generate resonant modes with a wavenumber of 0, which corresponds to an infinite guide wavelength. Under this condition, uniform heating is expected because the resulting standing waves would not have nodes or antinodes. In the design proposed in this paper, two ZORs fabricated on dielectric substrates are arranged to face each other for electromagnetic coupling, and a sample placed between the resonators is heated. A single ZOR was investigated using a 3D electromagnetic simulator, and the resonant frequency and electric field distribution of the simulated ZOR were confirmed to be in good agreement with those of the fabricated ZOR. Simulations of two ZORs facing each other were then conducted to evaluate the performance of the proposed system as a heating apparatus. It was found that a resonator spacing of 25 mm was suitable for uniform heating. Heating simulations of SiC and Al₂O₃ sheets were performed with the obtained structure. The heating uniformity was evaluated by the width L_50% over which the power loss distribution exceeds half the maximum value. This evaluation index was equal to 0.397λ₀ for SiC and 0.409λ₀ for Al₂O₃, both of which exceed λ₀/4, the distance between a neighboring node and antinode of a standing wave, where λ₀ is the free-space wavelength. Therefore, the proposed heating apparatus is effective for uniform microwave heating. Because of the different electrical parameters of the heated materials, SiC can be easily heated, whereas Al₂O₃ heats little. Finally, heating experiments were performed on each of these materials. Good uniformity in temperature was obtained for both SiC and Al₂O₃ sheets.