Magnetostrictive whisker sensor application of carbon fiber-alfenol composites

Long strips of material cut from magnetostrictive Fe-Al (alfenol) and Fe-Ga (galfenol) rolled sheets with a preferred orientation are flexible yet have a high elastic modulus. They resemble animal whiskers and are effective as flow sensors, responding with local changes in magnetization due to bending stresses induced from the drag force during fluid flow. Both tensile and compressive stresses are simultaneously applied on opposite sides of the whisker neutral axis when the whisker bent, and thus the magnetostrictive whisker sensor must be able to withstand the range of tensile and compressive stress loadings caused as the whisker bends. In this study, we investigate application-related properties of alfenol and galfenol thin sheets and carbon fiber composite-coated sheets for use in whisker flow sensors. Being able to reduce sensor thickness is important for improving flexibility as the sensors deflect. The net voltage changes in the Hall sensor were proportional to the applied tip force. Magnetostriction is strongly dependent on texture development, and this was explored for several sample thicknesses in the two alloys. Goss, (011) [100], single grain was well developed in the both of 0.32- and 0.45 mm thick sheets, while the 0.20 mm thick sample shows {113} grain growth in galfenol. For alfenol, the Goss grain was globally grown in the whole sample with the overall thicknesses. For utilization of these sensors for real situations, carbon fiber was added to the alfenol whiskers as a protective layer. Bending experiments were performed on a carbon fiber-alfenol composite with a Hall sensor to see if magnetomechanical transduction was impaired. We observed that the Hall sensor output signal from the composite was improved by about 75% from that of a bare alfenol strip. Finite element modelling showed that the composite induced more internal stresses on the alfenol strip with the same degree of bending.