Research On Microwave Displacement Sensor Based On Resonant Cavity Perturbation Theory And Re-entrant Resonant Cavity

Modern manufacturing industry is developing in the direction of automation,integration and intelligence.As a key component in the closed-loop control system to provide feedback of moving distance and position,displacement sensor plays a crucial role in the accuracy and reliability of the whole automatic control system,the development of displacement sensors is an important driving force for the advancement of the machinery industry.At present,there are numerous sensors for displacement measurement,with different principles and methods,and their performance also varies greatly.Microwave measurement and detection technology is also used to design displacement sensors due to its advantages of fast response time,miniaturization and easy circuit integration.However,existing microwave displacement measurement solutions are gradually becoming difficult to meet the demand for displacement sensor measurement range and sensitivity in the mechanical industry due to the limitations of sensor size and structure.And in the operation of large machinery and equipment and actual industrial production,line displacement and angular displacement are two common displacement measurement indicators.In this context,based on the conventional substrate integrated waveguide re-entrant cavity resonator and guided by the resonant cavity perturbation theory,this paper designs two new double re-entrant cavity sensors for measuring linear and angular displacements,respectively,with the following main work results.(1)Design of double re-entrant resonant cavity line displacement sensor with loaded ring gapsA microwave cavity sensor with high measurement range and high sensitivity is designed for precise line displacement measurement based on a pair of back-to-back stacked double re-entrant cavity structures loaded with ring gaps.The design takes the electric field distribution characteristics inside the resonant cavity as the starting point,and investigates the structural advantages of the double-entry resonant cavity compared with the traditional re-entrant resonant cavity;the ring gap is loaded inside the resonant cavity structure,the copper layer from the ring gap to the capacitance post increases the measurement range,and the ring gap suppresses the edge capacitance,so that the sensitivity of the sensor is improved.Then,based on the resonant cavity and transmission line theory,an equivalent LC circuit model derived from the sensor structure parameters is established,and the equivalent resistance and ideal variation ratio in the LC equivalent circuit are derived from the interrelationship between the quality factors of the resonant cavity.After deriving the equivalent circuit model,the mechanism of the effect of the line displacement of the copper sheet introduced into the resonant cavity on the gap capacitance inside the resonant cavity is analyzed,and a physically derived line displacement measurement model based on this basis is constructed.After constructing the displacement model,a prototype sensor device is fabricated using printed circuit board technology,and a line displacement measurement platform is built to discuss the effect of copper thickness on sensitivity and linearity by actually measuring the correspondence between the line displacement of different thicknesses of copper sheets and the transmission curve of the sensor,and the displacement model is calibrated to verify the reliability of the displacement model.Finally,by analyzing the measurement results,the sensor achieves a measurement range of 0-27 mm and a sensitivity of 0.058GHz/mm.(2)Design of a double semicircular re-entrant resonant cavity angular displacement sensorBased on the conventional re-entrant resonant cavity,a microwave angular displacement sensor with high measurement range and high linearity is designed by improving the position and number of capacitor posts in the resonant cavity.Firstly,the design concentrates the induced electric field around the metal wall by changing the position of the metal capacitor post,then determines the shape of the resonant cavity and the position of the feed line through simulation analysis.The shape of the capacitance post was chosen to be a semicircle in order to achieve angular displacement measurements,while a double capacitance post is used to enhance the sensitivity of the sensor.After the structure of the sensor is determined,the electric field distribution after the feed is used to verify whether the design goal is achieved.After describing the sensor structure,how the mixed dielectric constants in the induced electric field region change when an angular displacement occurs is analyzed,and the sensing measurement mechanism is explained using resonant cavity perturbation theory.Then,by constructing the equivalent circuit model of the sensor,the resonant cavity parameters that affect the gap capacitance size are obtained,and the correlation between the structural parameters and the sensitivity is obtained according to the electromagnetic simulation technique,the structural parameters of the resonant cavity are optimized.Finally,a prototype sensor is fabricated and its ability to measure angular displacement is experimentally investigated.It is verified that the sensor is in good agreement with the simulation results and can measure the angular displacement in the range of 0°-140° with a sensitivity of 1.7MHz/° while maintaining high linearity.