Research And Design Of Eddy Current Flaw Detection System For Metallic Materials Based On Giant Magneto Resistance Sensor

Eddy current nondestructive testing(NDT)is a kind of electromagnetic nondestructive testing technology based on Faraday's law of electromagnetic induction.It is a technique to determine the presence of defects in the magnetic material by the eddy current induced in the detection of electrically metallic material.The detection technology has the advantages of no coupling agent,non-contact measurement,high detection sensitivity,high speed,simple operation,low cost and applicable to all conductive materials,etc.Based on the research of eddy current testing technology and GMR sensor,the paper designs an eddy current testing system of metal material based on GMR sensor combined with FPGA technology.The main research work of the paper is as follows:(1)The basic principle of eddy current testing is studied in depth.The traditional eddy current testing technology and the solving model are analyzed,and the limitation of traditional eddy current testing technology is understood.The design of a new eddy current testing system based on GMR sensor is proposed.The GMR effect and the principle and application of GMR sensor are further studied.The GMR sensor model suitable for the system is selected.(2)The hardware design of GMR eddy current testing system can be divided into two aspects: first,the excitation signal circuit based on the FPGA-based DDS technology,the circuit is mainly used for high precision sine signal of different frequency,so as to meet the need of eddy current testing system of different depth of defect detection.Second,the detection signal processing circuit based on the FPGA-based SOPC technology.The main function of the circuit is to amplify,filter,collect,analyze and display the output signals of GMR sensors.It is proved by experiments that the modules of the system work well and have high signal to noise ratio.(3)The VHDL language is used to write various modules of the FPGA on the Quartus II software platform;SOPC Builder is used to create SOPC systems to meet system's requirements.The C++ language is used to complete the programming of the system software so as to achieve the normal operation of the system.(4)The eddy current edge detection experiment of metal material is designed to test the performance of GMR eddy current flaw detection system.The crack detection experiment for metallic materials is designed to verify the defect detection ability of the system.The experimental results show that the system is stable,reliable and has strong defect detection ability.