We have designed a temperature and strain monitoring system for a magnetic actuator based on the giant magnetostrictive material Terfenol-D (Tb 0.3 Dy 0.7 Fe 1.92) with Fiber Bragg grating (FBG) sensors. Magneto-elastic properties of Terfenol-D depend on magnetization, stress prehistory , and temperature. In order to simultaneously monitor these effects, we have implemented a system based on a cylindrical Terfenol-D rod monitored with four FBGs that allows making the appropriate compensations on the strain measurement due to temperature drift. We have measured the magnetostriction in the axial and the transverse directions for the Terfenol-D rod with two perpendicular FBGs, and calculated the Poisson ratio. An additional mechanical system for strain amplification has been designed in order to increase sensitivity, by a factor of 4, in the strain measurement with the FBG sensor.

IntroductionSensors based on optical fibers are becoming increasingly important for the measurements at long distance and also because of the possibility of multiplexing several sensors connected in series without the requirement of additional circuitry or power elements in the area except the optical sensing device. Magnetostrictive materials have been used for the construction of magnetic sensors and actuators, tunable optical filters, etc. The fiber Bragg gratings (FBG) have the great advantage of being immune to electromagnetic interference while maintaining the simplicity of the measurement system and reducing the number of elements involved in this process. FBG is based on a periodic modulation of the refractive index of the core in the optical fiber, the period of the modulation determines the wavelength of the reflected light called Bragg wavelength [1] and is given by; 2 Λ, where is the reflected Bragg wavelength, is the effective refractive index is effective refractive index of the core and Λ is the period of the perturbation. The Bragg wavelength can be expressed as the sum of the effects of two contributions mainly strain and