PDP Electrodes Defect Test Based On Eddy Current Testing

PDP, plasma display panel, is a kind of display technology that the electrode ionizes gas to discharge. The state of PDP electrodes will directly affect the image display of PDP. With the development of PDP display technology, PDP electrodes'width and pitch become smaller, the probability of defects increases. So it is important to detect defects in the PDP electrodes. Eddy current testing is based on electromagnetic induction, one of the five conventional detection methods in the nondestructive testing field. In conventional eddy current testing methods impedance plane diagrams are required, and defects are artificially recognized with the equivalent comparison method, which requires inspectors with high quality and is likely to cause misjudgments. Also, this results in low automation level. Therefore, it is necessary to study a new kind of eddy current testing device to overcome shortcomings of artificial detection and apply to the automatic detection of PDP electrode defects.On the basis of eddy current testing basic principles and the basic theories in the electromagnetic field, this thesis takes the finite element analysis(FEA) software ANSYS as the basic analysis tool and the PDP electrode as research object, simulates the distribution of electromagnetic field around PDP electrodes and analyzes electromagnetic field around the GMR sensor. This thesis has done a lot of theoretical analyses and simulations, some main conclusions are as follows:(1)The rail of the exciting coil, perpendicular to PDP electrodes, has great interferences with detection date, so the GMR sensor should be far away from the rail. Also there should be a long exciting coil on both sides of the sensor to create a stable magnetic field environment, which is good for the following data processing and defect judgments.(2)The intensity of eddy current in PDP electrodes increases with the increase of exciting current and exciting frequency, so is the intensity of magnetic field caused by eddy current.(3)The intensity of eddy current in PDP electrodes decreases with the increase of lift-off distance, so is the intensity of magnetic field caused by eddy current.(4)Defects in PDP electrodes change the flow of eddy current, which results in changes of magnetic field. The size of defects in X, Y, Z direction is respectively called width, thickness and length in this paper. The length of defects determines the position of peak value in Bz distribution curve and affects the peak value. The width and depth of defects both affect peak value but not its position.(5)Electrodes on both sides of the detected electrode have little effect on detection data and don't affect defect judgments.