Magnetostrictive materials are a class of smart materials that have the capability to convert mechanical energy to magnetic energy and vice versa. This transfer of energy makes these materials good candidates for both sensing and actuation applications. A device constructed of one of these materials could perform the same function as current parts that utilize several components which would increase the durability, and lead to smaller components. The potential uses of these materials cover a broad range of applications, including self-sensing actuators due to the fact that smart materials are bidirectionally-coupled. An additional benefit in relation to sensors is that magnetostrictive materials can operate in a non-contact fashion. Measuring the magnetic response to a stress input can be done using different non-contact techniques which would reduce the complexity from current force sensors. Galfenol, an alloy of iron and gallium, is a promising material for both actuation and sensing due to the moderately large strain it exhibits under a magnetic field combined with the material's mechanical robustness. Galfenol has properties similar to steel which allow for machining, extruding, and other load bearing applications. These mechanical properties make Galfenol unique relative to other smart materials, which generally are brittle.
This research looks to further the study of Galfenol by documenting the behavior of Fe81.6Ga18.4 under various loading conditions in relation to the development of a force sensor. The characterization of these alloys involves applying a stress to the sample and measuring the corresponding change in magnetization. Both major and minor loop responses were observed over a range of stresses and fields. These were compared for sensitivity and used to determine model parameters. Additional minor loop testing was conducted at high frequencies to determine the material's dynamic behavior as a sensor. The sensitivity was observed to decrease with increasing frequency. Using a modulation technique allowed for a means of relating the input stress to the output voltage while being independent of frequency when that frequency was in a range well below the frequency of the carrier frequency. The relationship between the input stress and output magnetization was also compared with constitutive models for Galfenol to further validate the models to be used towards the development of a force sensor. The relationship between the input stress and the output magnetization is non-linear and exhibits hysteresis, so the characterization of these responses will be beneficial in the creation of sensors utilizing Galfenol.