Analysis And Optimum Design Of Thin-layer Condu Ctivity Eddy Current Sensor Coil

At present,four-probe method is a common method to measure the conductivity of ITO thin films,but it has irreversible destructive effect on the thin films.Non-contact eddy current conductivity detection method is a better choice,and the design of high sensitive eddy current detection coil is very important.In this paper,Maxwell finite element software is used to simulate and optimize the design of probe coil of eddy current sensor by constructing coil model with magnetic tank with different parameters and analyzing the real voltage response curve of probe coil.The main research work and conclusions are as follows:(1)The analysis and optimization design of coil structure parameters are completed.Based on the simulation and analysis of the influence of coil structure,measured object size,detection distance and frequency on coil magnetic field distribution,response curve and quality factor,the optimization design of coil is completed.The results show that when the coil excitation frequency is 300 kHz,the linear degree of the voltage response curve is the best when the plane coil turns are 20 turns and the line diameter is 0.3 mm,and the detection distance is 1 mm,which improves the quality factor of the coil by 5%compared with that before optimization.The linear degree of the voltage response curve is the best when the coil layer is 3,each layer is 8 turns,the diameter of the coil is 0.2 mm,and the detection distance is 1.5 mm.Compared with the coil quality factor before optimization,the linear degree of the voltage response curve is 85%.(2)The influence of the size,conductivity and permeability of the magnetic tank on the coil impedance and response sensitivity was studied.The simulation results show that when the excitation frequency of the coil is 300 kHz,increasing the width of the magnetic circuit and reducing the length of the magnetic circuit can increase the resistance and inductance of the coil,and increasing the width and length of the magnetic circuit is conducive to improving the sensitivity of the coil.When the conductivity is less than 100S/m,the coil sensitivity almost remains unchanged,while when the conductivity is greater than 100S/m,the coil sensitivity deteriorates.When the permeability is less than 1500H/m,the greater the permeability is,the higher the sensitivity of the coil is.When the permeability is greater than 1500H/m,the sensitivity of the coil is almost unchanged.(3)The experimental demonstration of the above simulation results has been completed.The impedance and quality factor of six spiral coils with different turns and wire diameters are measured,and the results are in good agreement with the simulation results.The winding coils are applied to the sensors respectively.The test results show that the output voltage of the sensor made of 3-layer,8-turn and 0.21 mm diameter coils is 236 mV,which is 188 mV higher than that made of 1-layer,5-turn and 0.44 mm diameter coils.The conductance of ITO is measured by the sensor made of optimized coil,and the error is less than 5%.