LINEAR DISPLACEMENT SENSOR-BASED ON THE MAGNETOOPTICAL FARADAY-EFFECT

We report in this work the theoretical analysis of a linear displaceme nt sensor based on the magneto-optical Faraday effect. The sensor cons ists of a rod of a magneto-optically active material that can be dislo cated along the axis of a magnetic configuration formed by two equal h ollow cylindrical permanent magnets, uniformly magnetized, arranged wi th opposite polarities. The performance of the sensor is discussed in terms of the inner and outer diameters of the two magnets, the sample and magnet lengths, the residual magnetic-field strength of the perman ent magnets, the Verdet constant of the magneto-optically active mater ial and the wavelength of the light source employed. We show that it i s possible to have a practical sensor system that is almost linear ove r a distance equivalent to 90% of the total sample length, with a depa rture from linearity smaller than 1% and capable of detecting displace ments as small as 1 mu m when a rod of HOYA FR-5 paramagnetic glass is used as the magneto-optically active medium and a He-Ne laser at 543 nm as light source. (C) 1998 Elsevier Science S.A. All rights reserved .