Abstract
We have designed a magnetic actuator based on giant magnetostrictive material Terfenol-D (Tb0.3 Dy0.7 Fe1.92). It is widely known that this material modifies its magneto-elastic properties as a function of the combination of both magnetization and prestress effects, however, other effects such as temperature may affect its optimal operation point. In order to simultaneously monitor these effects, we have implemented a system based on two FBGs connected in series, where one is physically attached to a structure which contains a cylindrical Terfenol-D rod and the other rests freely next to the first one with the aim of measuring and compensating the thermal offset and sensitivity drift. We have designed a strain amplification structure for get higher sensitivity in the strain measurement with the FBG sensor. This proposal allows to measure at long distance without adding additional components such as active elements or other sensors and also allowing to decouple the thermal offset and sensitivity drift. We have measured the Magnetostriction in the axial direction and in the perpendicular direction of the Terfenol-D rod with two perpendicular FBGs. In Figure 1(a) it is shown a schematic of the monitoring system with the strain amplification structure. It consists of a cylindrical structure made of brass containing the sample of Terfenol-D and surrounded by the coil needed to apply the axial magnetic field. In Figure 1(b) it is shown the amplified strain signal achieved by the strain amplification structure and the strain signal without amplification (directly attached to Terfenol) as a response to an applied a triangular magnetic field of 200kA/m amplitude and 0.002Hz frequency.
