Design And Optimization For Induction Probe Of High Temperature Eddy Current Sensor

Aero-engines are prone to fatigue cracks and severe wear when working in an environment of high temperature,high pressure and severe vibration for a long time.Therefore,monitoring the parameters such as blade tip clearance and vibration amplitude is very important.Because the eddy current testing technology has the advantages of large measurement range,high resolution and sensitivity,and long-term work in harsh environments,it has broad application prospects in the field of non-destructive testing.However,the present eddy current sensor probe has the problems of large deformation,failure of electromagnetic characteristics,and low quality factor and sensitivity at high temperatures.In view of these problems,the main researches are as follows:(1)The principle of eddy current testing at high temperature was analyzed and an induction probe structure was designed.The equivalent circuit model was established by analyzing the basic working principle of the eddy current sensor.And the one-to-one mapping relationship between output impedance,temperature and displacement was deduced based on it.The reasons why general probes are not suitable for high-temperature environments were analyzed.According to the requirements of small size,high inductance and high quality factor,the induction probe was designed as a multi-layer planar spiral structure.The air core was used as the magnetic core of the induction probe,which solved the problem of the ferrite core failing in high temperature and low measurement accuracy.And according to the finite element simulation analysis,the shape and material of the probe coil were determined.(2)The influencing factors for the output impedance of the inductive probe were studied,and the structural parameters of the probe were optimized and made experimentally.First,through the coupling simulation of electromagnetic field in COMSOL,the influence of the excitation source frequency,the size and electromagnetic characteristics of the measured object on impedance characteristics of the probe was analyzed.Then Solid Works and COMSOL were used to establish a solution model for parametric analysis,and genetic algorithm was combined to establish a mathematical optimization model.These were all used to optimize the outer diameter,number of turns,line width and thickness of the coil with the goal of improving sensitivity and linearity.Finally,the LTCC process was studied and the parameters of key processes such as punching,screen printing and sintering were optimized according to the experimental measurement results,and the final sensing probe was obtained.The measurement results show the structure size of induction probe meets the design requirements,the coil wire diameter error is less than 5%,the relative position error is less than 10μm,and the overall electrical performance of the probe is excellent.(3)The experimental platform was built to test the impedance characteristics and displacement characteristics of the probe.It is mainly divided into three parts: signal acquisition and testing system,displacement control system and the measured target.The effect of frequency,measured object size and electromagnetic characteristics on the output impedance of the probe was measured.The results show that the probe exhibits inductive characteristics at low frequencies,with a self-resonant frequency of 1.8MHz,a quality factor of 17.65 at a working frequency of 1MHz,a measurement range of up to 5mm,and an impedance mode sensitivity of 16.8Ω/mm.The high-temperature experiment platform was built,and the structure and impedance parameters of the probe were measured after the probe was placed at 600°C for 4 hours to return to normal temperature.The comparison with the previous results shows that the structure and electrical properties of the probe don’t change significantly.The impedance characteristics of the probe were measured at high temperatures of 200°C,300°C,and 500°C.The results show that the change trend of the probe impedance at high temperatures is the same as that at room temperature,which verifies the feasibility of measuring displacement at high temperatures.