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Eddy-current (EC) testing is an effective electromagnetic non-destructive testing (NDT) technique.Planar eddy-current sensor arrays have several advantages such as good coherence, fast response speed, and high sensitivity, which can be used for micro-damage inspection of crucial parts in mechanical equipments and aerospace aviation.The main purpose of this research is to detect the defect in a metallic material surface and identify the length of a crack using planar eddy-current sensor arrays in different directions.The principle and characteristics of planar eddy-current sensor arrays are introduced, and a crack length quantification algorithm in different directions is investigated.A damage quantitative detection system is established based on a field programmable gate array and ARM processor.The system is utilized to inspect the micro defect in a metallic material, which is carved to micro crack with size of 7mm (length) ×0.1mm (width) ×1mm (depth).The experimental data show that the sensor arrays can be used for the length measurement repeatedly, and that the uncertainty of the length measurement is below±0.2mm.