Fabrication, Modeling and Characterization of Magnetostrictive Short Fiber Composites

Magnetostrictive materials have a wide variety of applications due to their great capability as sensors and energy-harvesting devices. However, their brittleness inhibits their applications as magnetostrictive devices. Recently, we developed a continuous magnetostrictive Fe-Co-fiber-embedded epoxy matrix composite to increase the flexibility of the material. In this study, we fabricated random magnetostrictive Fe-Co short fiber/epoxy composite sheets. It was found that the discontinuous Fe-Co fiber composite sheet has the magnetostrictive properties along the orientation parallel to the length of the sheet. Finite element computations were also carried out using a coupled magneto-mechanical model, for the representative volume element (RVE) of unidirectional aligned magnetostrictive short fiber composites. A simple model of two-dimensional, randomly oriented, magnetostrictive short fiber composites was then proposed and the effective piezomagnetic coefficient was determined. It was shown that the present model is very accurate yet relatively simple to predict the piezomagnetic coefficient of magnetostrictive short fiber composites. This magnetostrictive composite sheet is expected to be used as a flexible smart material.

Non-linear dynamics of the Villari effect in the presence of a non-homogeneous magnetic field

Investigations of systems with an active magnetostrictive element generally assume the presence of an external homogeneous bias magnetic field. This article, however, presents the results of a study investigating a bimorph magnetostrictive-aluminium beam vibrating in a non-homogeneous bias field. By comparing results obtained under different operating conditions of the system, the combined effect of the non-linear beam stress and the non-homogeneous external magnetic field on the dynamics of the Villari phenomenon is determined. The preliminary results prove that the application of non-linear magnetic fields to the magnetostrictive devices ensures the extension of energy harvesting bandwidth of these devices and can be used to improve their control possibilities. A study of time series and hysteresis loops provides more detailed information about the non-linear magnetization and dynamics of the system.

Design and Simulation of a Magnetic Shape Memory (MSM) Alloy Energy Harvester

We present the simulation and development of a vibration energy harvester based on an active element made of Ni-Mn-Ga Magnetic Shape Memory (MSM) alloy. As the MSM element is subjected to mechanical stress within an external magnetic field, its magnetization changes in proportion to its length, facilitating energy generation in a pick-up coil. Whereas conventional piezo and magnetostrictive devices operate with small (sub-millimeter) stroke at high frequencies (kHz range), the MSM harvester is best suited to longer (millimeter range) stroke at a low frequency (100 Hz or below). Power output of 20 mW has been demonstrated with the prototype device operating at 45 Hz.

Effect of Stress and Magnetic Field on Young’s Modulus of Tb0.3Dy0.7Fe2 Oriented Alloy

The <110> grain oriented alloy was grown by zone melting directional solidification technique. The strain-stress curves of Tb0.3Dy0.7Fe2 <110> oriented alloy in different magnetic fields have been measured and the magnetic field dependence of Young’s modulus under different compressive stress has been confirmed. It is found that Young’s modulus gradually decreases with increasing the magnetic fields when the compressive stress is in the range of 15-25 MPa and changes a little in the range of 40-50 MPa. The experimental result indicates that the magnetic field has a marked effect on the Young’s modulus of the Tb0.3Dy0.7Fe2 <110> oriented alloy at a low compressive stress and its change should be considered during the design of magnetostrictive devices.

Power Harvesting Through Magnetostrictive Devices: A Linear Model

Energy harvesting, sometimes referred to as “power scavenging” or “energy extraction”, can be defined as “converting ambient energies such as vibration, temperature, light, RF energy, etc. to usable electrical energy by using energy conversion materials or structures, and subsequent storage of the electrical energy for powering electric devices”. There has been a significant increase in the research on vibration-based energy harvesting in recent years. In this contest magnetostrictive devices are considered a promising technology. The Villari effect, also known as the inverse magnetomechanical effect, is the change in magnetization that a magnetostrictive material undergoes when subjected to an applied uniaxial stress. This effect pertains to the transduction of energy from the elastic to the magnetic state and is inverse of Joule magnetostriction. Furthermore, the Villari effect exhibits many of the attributes of the direct magnetostrictive effect since its physical origin lies in magnetoelastic coupling. Transducers utilizing the Villari effect consist of a coil wound on a core of magnetostrictive material. In this paper, a linear magnetomechanical coupling model is developed to analytically calculate the potential electrical power such transducers can generate when subjected to applied harmonic mechanical vibration. Theoretical results are confirmed by experimental tests on two different magnetostrictive devices.