| Eddy current testing(ECT)technology is a non-destructive testing method which is widely used to detect metal plate with defects based on the principle of electromagnetic induction.However,traditional eddy current sensors cannot be adapted meet the detection needs for large and complex structures.Therefore,flexible eddy current testing(FECT)technology has been developed.Because the flexible eddy current sensor can be bent and folded arbitrarily,and it is easier to design flexible eddy current array sensors to improve the detection efficiency,it is very suitable for defect detection and health status monitor of surface of complex metal structures.The advantages of flexible eddy current sensors for detecting metal components with complex structural surfaces are self-evident,but how to reduce false detection rates,increase sensitivity,improve detection efficiency,and optimize sensor performance are important and difficult issues in the process of eddy current detection.In this thesis,A series of optimization studies are carried out on the performance of flexible eddy current sensors based on the flexible printed circuit board technology.A novel flexible flower shaped eddy current sensor is proposed to reduce the lift-off effect in the detection process of the eddy current sensor,it consists of a detection coil and a plurality of symmetrical excitation coils.According to the number of excitation coils,the types of flexible flower-shaped eddy current sensors are divided into four coils,six coils,eight coil and ten-coil flexible flower-shaped eddy current sensor,respectively.The flexible differential internal butterfly-shaped eddy current array sensor and the flexible differential external butterfly-shaped eddy current array sensor are proposed for petroleum drill pipes defect detection.They are both composed of a butterfly excitation coil and four sets of differential detection coils,by designing the sensor into butterfly-shaped,which has a certain folding angle to match the curvature of the threaded surface of the petroleum drill pipe.The proposed flexible flower-shaped eddy current sensor is theoretically analyzed based on the Biot-Savart law,the results indicate that the total induced magnetic field by detection coil can be equivalent to 0,so the proposed sensor can suppress the lift-off effect in the process of eddy current testing.In addition,compared with the single-coil eddy current sensor,the designed flexible flowershaped eddy current sensor has higher sensitivity and better signal-to-noise ratio during the detection process.In the theoretical analysis of the flexible differential butterfly-shaped eddy current array sensor,the performance of the flexible differential butterfly-shaped eddy current array sensor is analyzed from the perspective of the excitation coil and the detection coil,respectively,and provide the theoretical basis for optimization of its sensitivity and signal-tonoise ratio.The two proposed flexible eddy current sensors are simulated based on COMSOL Multiphysics software to verify the correctness of the theoretical analysis and provide a basis for the fabrication of the flexible eddy current sensor.The simulation results show that the flexible flower-shaped eddy current sensors with different coils can suppress lift-off,and the flexible differential butterfly-shaped array eddy current sensor not only has high sensitivity and low false detection rate when detecting different types of defects,but also can locate the defects on the thread surface according to the signal of the different testing coils.The flexible flower-shaped eddy current sensor and the flexible differential butterfly-shaped eddy current array sensor are manufactured based on flexible circuit board printing technology,respectively,and their experimental platforms are also set up.In the design of the flexible eddy current sensor,in order to ensure the high sensitivity and high signal-to-noise ratio of the sensor,the line width of the detection coil and the line distance should be the same.For the verification of the flexible flower-shaped eddy current sensor,the impedance analyzer is used to acquits the experimental data.For the verification of the flexible differential butterfly-shaped eddy current array sensor,a portable multi-channel flexible eddy current testing based on single chip microcomputer is designed,it includes the LCD screen which can display the measurement results in real time,the 4G and WIFI modules can connect the mobile data display terminal.On the basis of the two built platforms,the flexible flowershaped eddy current sensor and the flexible differential butterfly-shaped eddy current array sensor are both experimentally verified,and the experimental results are consistent with the simulation results. |
