精细表面下细小缺陷的磁光涡流成像实时探测

Real-Time Testing for Fine Defects beneath Precision Surface Using Magnetic-Optic Imaging Technique

磁光涡流成像检测装置可实现精细表面下细小缺陷探测。在该装置中,通过物体表面上方的交流激励线圈实现传统的涡流感应,涡流所感应的磁场由法拉第效应来检测。为了实现表面下缺陷的检测目标,激光穿过安放在激励线圈中的特殊的磁光晶体,激光偏振方向在晶体中的旋转大小取决于检测区域磁场的大小,缺陷将使检测区域磁场分量发生变化并使偏振光的旋转角发生相应变化,通过一光学装置转化成“明”或“暗”图像,该光学装置由传统的显微镜、照明系统、偏振器和CCD图像传感器组成。给出了初步的实验探测结果。

A new, laser supported, magneto-optic/eddy current imaging technique is introduced for fine defects testing beneath precision surface. In the experimental setup, the induction of eddy currents is conventionally performed by an alternating current excitation coil above the object surface. The magnetic field induced by the eddy currents is detected by using Faraday effect. For this target, a laser beam is passed through a special magneto-optic crystal integrated in the excitation coil. The polarization direction of laser beam is rotated in the crystal depending on the local magnetic field. The area distribution of rotation angle caused by the defects is transformed into 'light' or 'dark' picture using an optical setup, which comprises a conventional microscope, a lighting, a polarimeter, and a CCD sensor.