Abstract
In this paper, the phase gradient is taken as the characteristic quantity of defect testing signal by using the phase spectrum analysis method of spatial domain, and the phase gradient of testing signal is extracted by using the digital phase- sensitive demodulation technology to detect and classify different types of defects in the plate metal sample. Dual air core coil eddy current sensor and 1-10kHz multi-frequency excitation signal are used to identify surface defects, lower surface defects and internal defects of the sample. The experimental results show that this experimental system can effectively detect defects, and visual detection results can be obtained through phase spectrum analysis of spatial domain. The phase gradient is used as the characteristic quantity to effectively suppress the influence of lift-off effect, making the detection results more accurate.
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