Defect depth estimation using magneto optical imaging with magnetophotonic crystal

Abstract

Non-destructive inspection (NDI) is used to detect defects for safety. The magneto optical (MO) imaging is an attractive method for NDI. The MO imaging can visualize defects as a light intensity of image, which depends on the polarization rotation angle of the MO film. The polarization rotation angle depends on the stray filed in the vertical direction. To accurately detect the stray field, it is necessary to enhance the Faraday rotation angle. Therefore, we focused on magnetophotonic crystal (MPC), which can enhance the MO effect with thin film, comprising the polycrystalline bismuth substituted yttrium iron garnet. We estimated the defect depth with the MPC located on the iron with a defect, which depth was varied from 1 mm to 10 mm. The results showed good agreement with the defect depth measured by the dial gauge.

Properties of Magnetic Garnet Films for Flexible Magneto-Optical Indicators Fabricated by Spin-Coating Method

“…Previously, the deposition process of the MO sensor required high-temperature thermal treatment [ 12 ] to crystallize the magnetic garnet because a sputtering method was used for the deposition of the magnetic garnet film [ 13 , 14 ]. Therefore, it was limited to a single crystalline substrate that was not able to deal with complicated shapes, such as a curved surface, which was contained in the test subject.…”