Array Type Eddy Current Phase Sensor And Its Imaging Method Research

Eddy current testing is widely used in electric power,petrochemical,aerospace,manufacturing and other industries due to its fast detection speed,high precision of results and no need for contact among the many non-destructive testing technologies.The traditional eddy current testing method mainly obtains the near surface defect information of the specimen by detecting the impedance variation of the coil,and the detection effect on the internal and subsurface defects is poor,the detection result is not intuitive,and the coil impedance is susceptible to interference from lift-off noise,so it is difficult to accurately identify and classify different types of defects.In view of the above problems,this thesis conducts a series of research on array phase sensor and imaging method.Firstly,the eddy current phase gradient is selected as the characteristic quantity of the detection signal.The double air-cored coil is used as the phase sensor,and its geometric parameters and excitation frequency are analyzed by finite element.Based on the analysis results,the detection model for measuring the eddy current phase gradient is established,and its detection effect is subjected to finite element analysis.The swept-frequency eddy current testing experimental system is designed.The system uses sinusoidal current excitation to scan the specimen.The digital phase sensitive demodulation technology is used to extract the phase gradient of the detected signal in real time and obtain the visual detection result.The eddy current testing experiment was carried out on the aluminum plate by the system.Change the lift-off and the types of defects to analyze and summarize the detection effect of the phase gradient measurement method.The research results show that the phase gradient is used as the characteristic quantity of the detection signal,and the method of swept-frequency eddy current detection of the conductive material by the dual air-cored coil sensor can effectively suppress the lift-off noise,accurately identify and classify different types of defects,and obtain better visual inspection results.