Daniele Davino

Experimental tests of a magnetostrictive energy harvesting device toward its modeling

This paper deals with a recently proposed device for energy harvesting from environmental vibrations, employing a magnetostrictive material. Even if most of the modeling efforts were focused on a linear approach, more complex and nontrivial phenomena are experimentally observed. A sample of such nontrivial behaviors, suggesting the definition of potentially more effective models, is described and discussed in this paper.

Capacitive Load Effects on a Magnetostrictive Fully Coupled Energy Harvesting Device

Vibration energy harvesting is a promising method to feed ultra-low power devices as wireless sensors, mems, etc. The accuracy of the design of the harvesting device, and then the harvested power, strongly depends on the modeling quality of the magnetostrictive relationships and on the device modeling in general. A further important issue is the optimization of the converted power with respect to the frequency of the vibration source, which is critical for low frequencies. The use of a capacitor in the electric circuit allows more harvested power at low frequencies and open the possibility of power optimizing stages. This analysis could be reliably carried out only in connection to a sufficiently realistic modeling of the employed material. Aim of the paper is therefore to study, by the definition of a simple nonlinear model, the effects of the capacitive load and of the mechanical source on the power conversion performances of the device. Several numerical examples are presented and discussed.

A Two-Port Nonlinear Model for Magnetoelastic Energy-Harvesting Devices

The aim of this paper is to present a two-port equivalent circuit that is able to describe the main features of an energy-harvesting device based on magnetoelastic materials. The magnetomechanical model behind the equivalent circuit is nonlinear and fully coupled. Therefore, the most part of the typical real-device behavior, without the limits of linear magnetomechanical modeling, is described. A preliminary validation of the model, by exploiting experimental data, is provided. Moreover, simulation tests and comparisons to the linear model are also carried out to underline the basic features of the proposed nonlinear approach. To this end, numerical results of the harvested power and peak voltage for the two devices in different working conditions are presented and discussed.

Fully coupled modeling of magneto-mechanical hysteresis through ‘thermodynamic’ compatibility

The paper proposes a phenomenological model for magneto-elastic interactions in materials with hysteresis, where both mechanical and magnetic variables are fully coupled. The approach allows one to provide a tool for the description of the energy conversion mechanism in the presence of losses, for example, in harvesting devices. The present approach takes into account exchange between mechanical and magnetic energies, as well as dissipation due to hysteresis phenomena. Using the concept of hysteresis potentials, it is shown that the model is consistent with classical nonequilibrium thermodynamics. The effectiveness of the approach is demonstrated by comparison with experimental data.

Design and Test of a Stress-Dependent Compensator for Magnetostrictive Actuators

Magnetostrictive transducers are employed for several purposes where, often, the applied mechanical stress strongly affects the device hysteretic behavior. This issue complicates the design of controllers where such variable has to be considered as an additional input. Nevertheless, a compensation scheme with two input variables can be defined and fruitfully utilized in a suitable invertibility region. Aim of this paper is to present a novel compensation algorithm able to take into account the applied mechanical stress. Numerical results compared with experimental data, over a magnetostrictive actuator, show that the proposed approach leads to lower compensation errors with respect to stress-independent, classical, compensators.

Experimental properties of an efficient stress-dependent magnetostriction model

In this paper a generalization of a stress-dependent magnetostriction phenomenological model is presented. The model makes use of a classical Preisach operator and of a memoryless bivariate function and includes a pure elastic contribution. It is shown that, even if the structure of the model is simple, the operator state is still influenced by the applied stress. This property is important because the model is able to catch real magnetostrictive behavior in the presence of complex time evolutions of both the variables, current and stress. Experimental and numerical results confirm the effectiveness of the proposed approach.

Analysis of a magnetostrictive power harvesting device with hysteretic characteristics

A model for the description of the energy harvesting in magnetostriction devices is discussed. In particular, the effects of hysteresis, normally observed in these materials, are highlighted and compared to the predictions of the linear modeling. The coupling of the model to the circuit equations leads to a differential equation with hysteresis, which could provide an effective macroscopic description of the energy conversion mechanism taking place in these devices. Numerical tests are performed in order to show the effect of a magnetic field bias on the generated electric power.

Fast Inverse Preisach Models in Algorithms for Static and Quasistatic Magnetic-Field Computations

This paper proposes the analysis and application of the Preisach inverse, which is implemented in a very simple fashion, and allows applying them easily into electromagnetic codes formulated in terms of a vector potential. Such an algorithm has been proposed in real-time control of hysteretic systems but never in the numerical analysis of devices employing ferromagnetic materials. Such a model has also been compared to other Preisach-based models. Their properties are briefly discussed and accurate analyses of their performances are reported, both in terms of accuracy and computational efficiency.

Energy Harvesting Tests With Galfenol at Variable Magneto-Mechanical Conditions

This paper deals with the experimental characterization of Galfenol (iron-gallium alloy) and its energy harvesting capabilities. Two rods are considered, one with a stress annealing treatment. The impact on the harvesting performance of magnetic bias, mechanical prestress and termination resistor are considered. Moreover, the performed measurements allow to verify an important feature of the energy conversion of this magneto-mechanical material: the energy harvested loops, in the B-H plane, are confined within the magnetic characteristics at the extrema of the applied stress. This suggests the significance of the static characteristics in the energy conversion process.

Experimental analysis of vibrations damping due to magnetostrictive based energy harvesting

The paper deals with the mechanical vibrations damping effect induced by a magnetostrictive energy harvesting device properly working. The proposed experimental setup allows us to investigate, through time-domain measurements, the dependence of the mechanical damping from parameters like magnetic bias and external load, affecting the global harvested power. This result would underline the promising possibility to reduce mechanical vibrations and obtain power harvesting at the same time.