The Villari effect of magnetostrictive materials, a change in magnetization due to an external stress, is used for sensing
applications. For a dynamically loaded sensor, one measures the time-varying magnetization on the material. The
question is, from these measurements, could information be extracted about all the applied stresses (the three axial and
the three shear) on the material? In a previously developed rate-equation model [P. Weetman and G. Akhras, SPIE
Proceedings Vol. 7644, 76440R], essentially the inverse of this problem was discussed where the input was a set of
known stresses and the output was the calculated resulting magnetizations.
A preliminary conceptual design of a Galfenol based 3D dynamical sensor is presented. In the proposed prototype
sensing device, one can measure the time-varying magnetization and its derivative in all three directions. Incorporating
the previously developed 3D rate equation model, a new model is developed pertaining to this sensor. It will be shown
that, under certain conditions, all stresses can be found from the magnetization measurements. The required calculations
are presented and then performed on a sample set of magnetization data for validation. From this model, the implications
to future sensing devices are discussed as well as suggestions on improvements to the model and the prototype.
One and three-dimensional computational models for the dynamical sensing response of Galfenol based magnetostrictive
devices are developed. The sensing model calculates the fraction of magnetic moments oriented along each of the
energetically preferred directions of the crystal as a function of time, which can then be used to determine the time
evolution of the total magnetization. Results from the sensing model are compared to quasi-static loading experiments
for validation and extraction of phenomenological parameters. As a sample application, the sensing model is
incorporated into an AC energy harvesting circuit to predict the magnetization and energy harvested under dynamical
This paper explores a unified energy-based approach to model the non-linear behavior of both
magnetostrictive and piezoelectric materials. While the energy-approach developed by Armstrong has been
shown to capture the magnetostrictive behavior of materials such as Terfenol-D<sup>1</sup> and Iron-Gallium<sup>2</sup> along
different crystallographic directions, extending this approach to piezoelectric materials presents a
considerable challenge. Some piezo-electric materials such as PMN-PT and BaTiO<sub>3</sub> may undergo phase
changes under applied electric fields and stress in addition to polarization switching. A modeling approach
is developed in this paper to capture these effects. Finally, it is shown that the constitutive behavior for the
piezo-electric/magnetostrictive layers, coupled by a simple blocked-force approach, is likely to model the
behavior of magneto-electric composites.
Dielectric elastomers are known to produce large transverse strains in response to electrically induced Maxwell stresses and thus provide a useful form of electromechanical actuation. The transverse strain response of silicone (Dow Corning HS III RTV) based Maxwell stress actuators have been measured earlier as a function of driving electric field, frequency and pre-load. Experimental results show that a pre-load initially causes an increase in the strain. However, this increase appears to be a function of the relative geometries of the electroded area and of the specimen itself. The transverse strains in these materials decrease when larger values of pre-load are applied. Models of hyperelasticity that are capable of describing the large deformation of polymer materials have been used to interpret our results. Numerical finite element simulations of the material’s behavior using a hyperelastic model provides good agreement with most of our observations on the electric field and pre-strain dependencies of the transverse strain.