Research On Thickness Measurement Of Metal Foils Based On Multi-Frequency Eddy Current Testing

Metal foil is widely used in coating manufacturing,semiconductor manufacturing,electronic component manufacturing and other fields.Thickness is one of the important parameters of metal foil,and accurate control of metal foil thickness is a very important link in actual production.In the high-precision metal foil rolling industrial production line,for the requirements of product quality monitoring,it is necessary to measure the thickness of metal foil on site,which challenges the real-time and accuracy of the thickness measurement method.Therefore,the thickness detection of metal foil products is a key problem in related industries,which has important research significance.Multi-frequency eddy current testing technology is an effective method to measure the thickness of metal foil due to its advantages of non-contact,real-time,low requirements for testing environment and high sensitivity for metal testing.Aiming at the problem of metal foil thickness measurement based on multi-frequency eddy current,this paper establishes the numerical model of eddy current testing,and carries out the research of metal foil thickness measurement technology based on model method and non-model method respectively.The main work and conclusions in this paper are as follows:Firstly,based on Maxwell's equations,the governing equations of eddy current field are derived,the FEM-BEM model of eddy current testing is established,and the eddy current signal simulation software is compiled.The simulation results are in good agreement with the experimental results,which verifies the correctness of the numerical model.Secondly,the equivalent transformer model of eddy current testing is applied to study the multi-frequency eddy current impedance signal.It is found that the imaginary part signal of inductance variation of multi-frequency eddy current probe will have a peak value.The influence of specimen thickness,conductivity,lift-off distance,coil geometric parameters and other factors on the peak frequency is explored.The results show that the peak frequency is inversely proportional to the specimen thickness and conductivity,and the product of the three It is a constant,but the value of the constant is related to the geometric parameters of the coil.On this basis,a new foil thickness measurement method based on peak frequency is proposed.The key influencing factors of performance parameters,such as precision,range and sensitivity,are simulated and studied.Experimental research is carried out to verify the effectiveness of the new method.Finally,it is proposed that the eddy current testing of foil thickness is a nonlinear programming problem when the conductivity is unknown.Based on MATLAB optimization tool function,the foil thickness inversion algorithm is proposed,and the excitation frequency optimization mechanism and method of multi-frequency eddy current testing technology are discussed.The results show that the excitation frequency is related to the sensitivity of the parameters to be measured,and the higher the sensitivity is,the higher the thickness measurement accuracy is.On this basis,a sensitivity based multi-frequency eddy current excitation frequency optimization method is proposed.The experimental results verify the effectiveness of the foil thickness inversion algorithm and the excitation frequency optimization method.The method of metal foil thickness measurement proposed in this paper has the advantages of simple calculation,high accuracy and fast calculation speed.This work can provide a theoretical basis for the research and development of new foil thickness detection instrument,and has good theoretical significance and engineering application value.There are 52 figures,15 forms and 83 references.