Eddy current testing of deep-lying defects in paramagnetic metals by flux-gate sensor
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摘要: 深层缺陷的涡流检测需要低频下灵敏度较高的磁传感器，基于磁通门磁强计灵敏度较高且无需低温冷却的优点，研制了深层涡流检测系统，通过对激励磁场平行分量置零后提高激励磁场幅度的方式，来提升检测深度和信噪比。在之前实现的6061铝合金14 mm检测深度的基础上，采用快速傅里叶变换的方法降低噪声、优化激励频率的方式提升检测深度，将铝合金的检测深度提高到16 mm，304不锈钢的检测深度达到20 mm。通过测量未知缺陷的最优激励频率，根据频率-深度曲线亦能大致估算其所处深度。Abstract: Eddy current testing of deep-lying defects needs highly sensitive magnetic sensors at low frequency, such as flux-gate sensors, GMR/GMI sensors, and SQUIDs. We built a flux-gate ECT system and measured the parallel component of the magnetic field of the eddy current. The measured parallel component could be set zero by adjusting the position of the induction coil. In our previous work, the detection depth of 6061 aluminum alloy was 14 mm. In this work, we measured the magnetic field amplitude-frequency curves to find out the optimized frequency. The data were processed by FFT method and the number of measured points was increased in order to reduce the noise. As a result, the detection depth of 304 stainless steel was 20mm, and that of 6061 aluminum alloy was increased to 16mm. The depths of unknown defects can also be estimated by measuring the optimized frequency.
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