Design And Fabrication Of Eddy Current Micro-Sensor

Surface cracks on metal work piece, due to fatigue, brittleness, thermal stress and other factors, can easily lead to incidents, and the cracks are too small to find at the beginning. In this paper, the array micro-sensor based on eddy current technology is designed and fabricated with MEMS (Micro-Electro-Mechanical Systems) for metal surface tiny cracks detection as early as possible.The paper first introduces the principle of eddy current nondestructive testing and makes some theoretical calculation about the sensor design. Besides, the impact of main parameters on eddy current sensor, such as the lift-off height, excitation frequency, the turns and size of inductance coils, the work-piece conductivity and permeability are analyzed by means of Mat-lab platform. Then, taking the subject requirements and laboratory EDM(Electrical Discharge Machining) conditions into account, the artificial surface cracks with width of50μm to200μm on2mm thick304steel are manufactured. Finally, the sensor is designed to be composed of a single excitation coil layer and two serial detection coil layers on the silicon substrate. There are square and round planar spiral structures with10turns for detection coils and single turn for excitation coils respectively in order to compare with each other. And the cross-section of detection Cu coils are10μm×10μm,20μm×15μm,30μm×15μm. The Eddy Current Micro-Sensor on Si subtract is fabricated by UV-LIGA:sputtering, lithography and electroforming.The result shows that the design and fabrication of micro-eddy current sensor have achieved the desired purpose.