Study And Application Of GMR Sensor In Nondestruction Test

As one of the most significant inspection methods,nondestructive test(NDT)plays a vitally important role in inspecting defects of key components,eliminating potential security issues and guaranteeing devices normal operation ranging from aerospace industry to naval and automotive manufacture.However,how to improve detection accuracy is a complex and urgent problem to tackle.Based on the principle of low-frequency Eddy Current Testing,a novel experimental scanning system using Giant Magneto-Resistance(GMR)sensors is studied.Firstly,the configuration of probe is studied.The sensitivity of conventional pick-up coil reduces with decreasing frequency.And the eddy current probe based on GMR with only one exciting coil has lower detection accuracy when inspecting defects due to turbulence of exciting field.For that matter,what the configuration of the GMR probe developed is to add one extra cancellation coil aimed to minimize the applied magnetic field at the sensor position.In this thesis,a non-destructive test model is created and simulated through software ANSOFT MAXWELL.The results show that the magnetic field at the sensor position varies greatly while it is small around the sensor.Then the novel probe is made in-kind according to the simulation model.Secondly,a experimental scanning system which mainly consists of hardware circuit and software design is created especially for the novel probe.The hardware part includes signal generation circuit,power amplifier circuit and signal condition one.And the signal generation circuit is used for generating a sine wave to excite the coil,the signal condition one mainly contains lock-in amplifier and low-pass filter circuit for initially conditioning experimental data before further processing.The software part focuses on Micro Controller Unit(MCU)program for controlling DDS chip and LABVIEW program in order to achieve real-time processing and observation of data.After debugging,the whole module is under normal operation.Finally,an nondestructive test is conducted.And the experimental results indicate that the novel GMR probe with higher detection accuracy can detect the flaws seated in the specimen.