Micro-displacement Measurement Based On Magneto-optical Effect

Magneto-optical effect comes from the interaction between light and magnetic material. Up to now, many kinds of magneto-optical effects have been obtained, such as, Faraday effect, Zeeman effect, Kerr effect, Cotton-montton effect, magnetic dichroism, magnetic laser light scattering, and so on. Magneto-optical effect has broad application prospects in scientific research and industrial production, so it has been paid continuous attention to the study of physics and materials.Magneto-optical material researched in this paper is the laminated composite of Terfenol-D and polycarbonate which have ferromagnetic property and elasticity respectively. Terbium dysprosium iron has excellent magnetostrictive effect, and polycarbonate shows stress birefringence effect under the condition of room temperature. When elastic coupled, they can produce the magnetostrictive induced stress birefringence. This phenomenon is called magneto-induced birefrigent effect.In this paper, polycarbonate stress birefringence effect is characterized. According to Saint-Venant principle, it could be explained that a stress gradient exists in PC when TDF is under the influence of external bias magnetic field. Not only the laminated composite material's interfacial stress induced under the action of magnetic field and the resulting photoelastic phase relationship between stress and strain are analyzed, but also the theoretical model of derive the output light intensity variation with the spot displacement is obtained.On account of the theoretical prediction, a detector system is designed in order to measure micrometric displacement. In this system, the change of light intensity under different external bias magnetic field is recorded through illuminometer. It is found that the light intensity of light point projected on PC decreases with the increase of the distance of composite interface and also the distance between the light point and the center line of sample.Besides, the linear relation between the light intensity through PC and the thickness of PC is also analyzed from theory and experiment, the precision of which could reach micron dimension. Furthermore, this detector system measuring micro-displacement has simplified design and intuitionistic principle. The preparation for measuring samples is simple and tandetny. Last but not the least, this technic has strong practical application in two-dimensional micro-displacement measurement.