针对谐振腔传感器内壁水膜和盐垢会降低湿度测量精度的问题, 文章提出一种用于测量圆柱腔内壁介质薄膜厚度的方法。此方法基于介质微扰法的原理, 使用双曲余弦开缝形谐振腔作为传感器, 工作于TE111模式来测量介质薄膜厚度。以水膜为例, 理论推导了谐振腔水膜厚度与谐振频率的关系, 并通过仿真分析了TE111模式准确测量水膜的可行性; 采用矢量场方程的方法建立了TE111模式下谐振腔端面电流密度分布线的数学模型, 并设计了双曲余弦开缝形谐振腔传感器。仿真结果表明: 该谐振腔的电磁特性、辐射特性和流动特性均良好, 电磁泄露率基本为0, 取样误差为-1.25%, 符合设计要求; 可准确测量水膜、盐垢、油膜和污垢等介质薄膜的厚度, 且它们的膜厚均与谐振频率偏移量呈线性关系, 与理论相符。

In order to solve the problem that the water film and salt scale on the inner wall of the resonant cavity sensor could reduce the accuracy measurement of the wetness, a method for measuring the dielectric film thickness on the inner wall of cylindrical cavity is proposed in this paper. Based on the principle of dielectric perturbation method, this method uses the hyperbolic cosine-shaped slot resonator as a sensor, working at the TE111 mode to measure the dielectric film thickness. Taking the water film as an example, the relationship between the water film thickness and the resonant frequency is deduced theoretically, and the feasibility of measuring the water film by TE111 mode is analyzed through simulation. We establish the mathematical model of the current density distribution line of the cavity end face for the TE111 mode by the method of vector field equation, and design the hyperbolic cosine-shaped slot resonator sensor. The simulation results show that the performances of the electromagnetic characteristics, radiation characteristics and flow characteristics of the resonator are all relatively well. The electromagnetic leakage rate is basically 0, and the sampling error is -1.25%, which meet the design requirements. The water film thickness, salt scale, oil film, fouling and other dielectric films can be measured accurately. It is also shown that the film thickness is linearly related to the resonance frequency offset, which are consistent with the theory.