Magnetic Optic Imaging For The Visualization Of Subsurface Testing

With the rapid development of the laser and optoelectronic technology in communication and military affairs in recent years, the difficult problem of detecting minute defect under fine surface emerged. On one hand, people are paying more and more attention on the surface quality because that high energy laser and the photodetection equipment of high sensitivity cannot be separated from ultra-fine reflecting surface; on the other hand, the micro-electronic mechanism combined with integrated circuit technology and precision machinery has introduced a series of new technology, such as micro-aerocraft, micro-satellite, and micro-robot. So the complete quality measurement is needed in order to use these technologies in mass production.Non-destructive test (NDT) is one of the efficient paths for measuring sub surface defect. Along with the progression of optoelectronics, semiconductor, computer and image processing technology, optoelectronic NDT is increasingly applied in measuring field. It rectifies the shortage of contact measurement in accuracy and speed, and improves the automation and the real time. Traditional NDT, such as X-ray, Y -ray and ultrasonic detection, has low resolving power. At one time, researchers at home and abroad had enthused about laser impact, ultrasonicmicroscope and the like. But it didn't come to maturity because the system is complicated, the cost is too high, and the performance is not ideal. This paper introduces a new-style magneto-optic / eddy micro-imaging technology. The new equipment is based on Faraday Magneto-Optical Effect, and transforms the distribution of magnetic field into laser polarization figure. Magneto-optic imaging technology is a new method of eddying measurement, which not only preserves the merit of conventional eddy current inspection, but also realizes the visual NDT of sub surface's minute defect by replacing measuring coil by laser.In this paper, the general situation of NDT and the technical specifications of the project are firstly introduced. On the basis of comparing several kinds of measuring methods at home and abroad, the author put forward the measurement of using magneto-optic element as photoelectric sensor.In chapter 2 and 3, the fundamental principle and the design of new type sensor are introduced respectively, including the whole structure design scheme and the chief component of the equipment, and the detailed design of optical system and circuit is described at length.The image processing methods and steps suitable to this project are presented in chapter 3, comprising the expression of image and some operating principles of image processing, such as filtration and binarization.Finally, some of the experiments are introduced, and the comparison between this system and conventional eddy current sensor has been done.In conclusion, this photoelectric detection system is a mixture of magneto-optic imaging technology, image data acquisition and processing, and image display, which has realized the NDT of sub surface. The theoretical method of this measuring system enriches the theories and methods of non-destructive test field, and offers use for reference in practical measuring problems. For example, it can be use for measuring whether there is fatigue crack and corrosion crack on the surface and sub surface of plane. Magneto-optic / eddy micro-imaging technology has the characteristics as follows: (1) The results are visible and pellucid, and can be easilypreserved, which reduces the measuring difficulty and shorten the people's training time; (2) The clearance of surface cladding, such as paint, is not needed before measuring, because the quality of the image is not influenced on the whole, and the only thing that must be insured is the better reflecting property of the measured surface; (3) It can make real-time imaging measurement on sub surface and surface defect. The measuring depth depends on the depth of penetration of the eddy, and the distance between the defect and the surface affects the imaging definition. The deeper the defect is, the d...