Research On Eddy Current Testing Based On Magnetoelectric Sensors

With the rapid development of industry,metal materials are spreading in all walks of life in recent years.However,metals are easily oxidized and corroded in the air and cause cracks or defects,there will be certain safety hazards.Eddy current testing has the advantages of fastness,convenience,and no need for couplant,which is widely used in testing metal conductive materials.Identifying metal defects in time can effectively prevent accidents.But for small cracks,the sensitivity of traditional detection coils is not enough to identify them.The magnetoelectric sensor has the advantages of high sensitivity,low noise,simple structure and low cost,which has great application prospects in eddy current testing.In order to solve the problems of low sensitivity and high noise of the traditional detection coil,a magnetoelectric sensor is proposed to replace the traditional detection coil as a detection probe.In this paper,the principle of the magnetoelectric sensor is studied through the equivalent circuit method,and the magnetoelectric coefficient under different frequencies is modeled and calculated.The influence of sensor’s size and DC magnetic field H_biason the magnetoelectric effect is further studied.On this basis,magnetoelectric sensors were fabricated and a magnetoelectric test system was built.The magnetoelectric coefficient of the full frequency domain magnetoelectric sensor was tested,and the high sensitivity of the magnetoelectric sensor was verified at the resonance frequency.Then the static characteristics of the magnetic sensor such as linearity,hysteresis,repeatability and so on of the magnetoelectric sensor are studied.The finite element simulation software COMSOL was used to establish the eddy current testing model,and the influence of excitation frequency,lift-off value and the conductivity of the tested body on the eddy current effect was analyzed.Then we designed a magnetoelectric eddy current probe suitable for eddy current testing.Aiming at the problem that the self-noise of the magnetoelectric sensor will affect the detection accuracy,a strategy of using a differential magnetoelectric sensor to eliminate noise is proposed.From the perspective of the common mode rejection ratio,the sensitivity of the differential magnetoelectric sensor is theoretically analyzed better than that of a single magnetoelectric sensor.Specific experiments on metal defects through the eddy current detection platform have verified that the ability of the magnetoelectric sensor to identify defects is far superior to that of traditional detection coils.And we compared the detection accuracy of a differential magnetoelectric sensor and a single magnetoelectric sensor.The experimental results are consistent with the theoretical analysis.Finally,the L-M optimization algorithm is used to realize the quantitative evaluation of defect length and depth in data processing.