A new rotational magnetomechanical transducer network model for a magnetostrictive unimorph is presented.
Often these laminated structures define an operating point about which the mechanical, magnetic and electrical
quantities show only small variations and the behavior can be decribed by a linear model. It is shown how
the magnetomechanical transduction coefficient in actuation direction, which is obtained via classical laminated
plate theory, holds also for the sensing relation. The magnetomechanical model is combined with electromagnetic
coil models. The electromagnetic and the magnetomechanical transducer are connected by a magnetic voltage
divider which takes demagnetization or the planar coil field distribution into account. The presented models can
be used for a fast analysis of existing systems and also for the optimization of new designs. The resulting circuit
description can be simplified, e.g. to a single impedance, by transforming network elements into other domains.
This work investigates the equivalence of thermodynamic potentials utilizing stress-induced anisotropy energy
and potentials using elastic, magnetoelastic, and mechanical work energies. The former is often used to model
changes in magnetization and strain due to magnetic field and stress in magnetostrictive materials. The enthalpy
of a ferromagnetic body with cubic symmetry is written with magnetization and strain as the internal
states and the equilibrium strains are calculated by minimizing the enthalpy. Evaluating the enthalpy using
the equilibrium strains, functions of the magnetization orientation, results in an enthalpy expression devoid
of strain. By inspecting this expression, the magnetoelastic, elastic, and mechanical work energies are identified to be equivalent to the stress-induced anisotropy plus magnetostriction-induced fourth order anisotropy.
It is shown that as long as the value of fourth order crystalline anisotropy constant K1 includes the value of
magnetostriction-induced fourth order anisotropy constant ΔK1, energy formulations involving magnetoelastic,
elastic, and mechanical work energies are equivalent to those involving stress-induced anisotropy energy. Further,
since the stress-induced anisotropy is only given for a uniaxial applied stress, an expression is developed for a
general 3D stress.
Energy density and coupling factor are widely used as figures of merit for comparing different active materials. These
parameters are usually evaluated as material constants assuming a linear behavior of the material over all operating
ranges. In this work it is shown that the operating conditions have an effect on the energy density and coupling factor
which cannot be ignored. A single crystal rod of Fe84Ga16 was characterized as a magnetostrictive actuator and sensor
under different quasi-static stress and magnetic field conditions. The material showed a saturation magnetostriction of
247 με and a maximum stress sensitivity of 45 T/GPa. A maximum energy density of 2.38 kJ/m3 and coupling factor
higher than 0.6 were calculated from experimental results. The experimental behavior was modeled using an energy
based non-linear approach which was further used to calculate the coupling factor and energy density as continuous
functions of stress and magnetic field in the material. Guidelines on optimal operating conditions for magnetostrictive
actuators and sensors using FeGa alloys have been suggested.
A model has been developed to predict the magnetic induction, elastic and magnetostrictive strain and mechanical stress
in a laminated structure with ferromagnetic and non-magnetic layers and subjected simultaneously to mechanical stress
and magnetic field. This model was obtained by coupling classical laminated plate theory to an energy-based statistical
magneto-mechanical model. The model can accommodate in-plane axial and shear forces as well as bending and
twisting moments and can predict both in-plane axial and shear strains and stresses. A stress-dependent Young's
modulus combined with an iterative algorithm was used to obtain non-linear magneto-mechanical response from a
unimorph actuator and sensor. The effect of tensile and compressive bias force on actuator performance and the effect of
DC magnetic bias field on sensor performance were studied. Possible applications areas for the model have been
Iron-Gallium alloys have demonstrated high compressive stress sensitivity (~ 30 T/GPa) along with considerable tensile strength (~ 515 MPa) and Young's modulus (~ 65 GPa) thus making them attractive materials for magnetostrictive sensors. In this work, four-point bending test was performed on single crystal Fe84Ga16 (Galfenol) under magnetic field to characterize its magneto-mechanical response in bending mode. The longitudinal and transverse strains (ε and ε) obtained under different mechanical loads (P) and DC magnetic bias fields (H) were used to estimate material properties like average Young's modulus (E) and Poisson's ratio (ν). The stress-dependent change in magnetic induction (B) at constant bias fields was obtained for different bending loads. The results of this study helps in understanding the behavior of and challenges related to Galfenol based magnetostrictive sensors which work in bending (flexural) mode.
There has been a growing need to develop non-contact sensors for use in real time structural health monitoring. Iron-Gallium alloys (Galfenol, Fe1-xGax, 0.13< x <0.21) appear to be a promising magnetostrictive material for such applications. This work discusses the concepts and methods used in developing a prototype Galfenol sensor for detecting bending induced strains and forces. The proof of concept experiment consists of two Galfenol patches attached on the top and bottom surfaces of an aluminum cantilevered beam. A solenoid applies a biasing magnetic field to the Galfenol patches. The change in Galfenol patch magnetic induction produced by compressive and tensile stresses during bending are continuously measured by a field sensor. The strains on the beam surface and Galfenol sensor surface are also measured using strain gages. The effect of biasing field at constant loading and the effect of loading at constant biasing field on the magnetic induction response have been investigated. A linear magneto-mechanical model for estimating the magnetic induction response for a given mechanical loading is presented.