Research On Measuring Method Of Water Film Thickness On Inner Wall Of Microwave Resonance Sensor

The water film attached to the inner wall of the humidity sensor will affect the resonant frequency of the resonant cavity,thus affecting the accuracy of humidity measurement by the humidity sensor.,thus affecting the accuracy of measuring humidity.Accurate measurement of humidity is very important to ensure the safe operation and power generation efficiency of steam turbines,so it is very important to accurately measure the thickness of water film in the inner wall of the sensor.This article first introduces the basic theories such as the field equation and resonance frequency of the microwave resonator,and then explains the principle of water film thickness measurement—the basic concepts of the dielectric perturbation theory and the transverse resonance method.Based on the dielectric perturbation method and the transverse resonance method,the relationship between the thickness of the water film and the resonant frequency in the TE₁₀₁mode of the rectangular cavity is deduced,and a method for measuring the thickness of the water film in sections is proposed,and the range of the water film thickness is determined;Based on the dielectric perturbation method,the relationship between the water film thickness and the resonance frequency in the TE₁₁₁mode of the cylindrical cavity is derived.In order to allow wet steam to enter the resonant sensor freely and smoothly,a slotted rectangular resonant sensor and a slotted cylindrical resonant sensor were designed.By analyzing the current density distribution on the surface of the resonant cavity,the shape of the slit on the surface of the resonant cavity was designed,and the thickness of the isolator metal strip was determined according to the rectangular waveguide cutoff theory.Finally,the ANSOFT HFSS was used to simulate,and the simulation verified the feasibility and accuracy of measuring the thickness of the water film in the corresponding mode of the rectangular cavity and the cylindrical cavity;The piecewise method of measuring the thickness of water film in plane and the method of measuring the thickness of water film in circular surface based on the perturbation method are applied to the measurement of other medium films,such as the anti-corrosion coatings on metal surfaces,the oil film in steam turbines,etc.,Simulation experiments show that the method proposed in this paper is feasible and highly accurate.In addition,the rectangular water film thickness measurement cavity is improved to be applied to measure the internal humidity of the steam turbine in the TE₁₀₁mode.