A new class of lightweight smart materials based on a polymeric matrix with embedded magnetic micro-particles was developed. The application of a magnetic field (MF) during the foaming of samples ...induced, along the MF lines, the alignment of magnetic particles dispersed in the polymer thus forming chain-like reinforcing structures. The aligned micro-particles induced an anisotropic mechanical behaviour, strongly improving the mechanical stiffness and strength along the MF direction compared to unfilled systems. Most notably, the chain-like structures imparted a magneto-sensitive behaviour to the lightweight materials. In fact, foams showed a direct relationship between the foams elastic response and the intensity as well as the shape of the time dependent MF applied during their magneto-elastic characterisation. This magneto-elastic behaviour has been obtained at low MF strength (below 200 kA m−1).
Magnetostrictive and all multifunctional materials have experienced in the last decades a growing technological interest. Several contributions, in the literature, propose the above-mentioned ...materials in innovative sensors and actuators both for bulk and MEMS devices. More recently, magnetostrictive materials have been proposed for energy harvesting applications by exploiting the so-called Villari effect. In this case, the behavior and the amplitude of the piezo-magnetic coefficients are an important element to evaluate the conversion efficiency. Aim of this paper is to study the experimental behavior of the piezo-magnetic coefficients of a commercial Terfenol-D rod under controlled conditions.
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.
•A magnetic field sensor based on Fe-Ga alloy and Fiber Bragg Grating is developed.•The demagnetizing field is investigated and exploited to widen the detection range.•Full quadrant field detection ...is achieved by a permanent magnet bias system.•A prototype has been realized by a 3D printing technology.•The approach is suitable for field sensing based on other multifunctional materials.
A magnetic field sensor prototype is developed and tested in this work. The device exploits a Galfenol rod, i.e. a giant magnetostrictive Iron-Gallium alloy, integrated with a Fiber Bragg Grating. In particular, the full-scale range of the sensor can be modulated through the exploitation of the geometrically dependent effect of the demagnetizing field. Indeed, it pushes toward higher fields the magnetic saturation by producing a sort of magnetic shield in the material. As a consequence, the geometrical viewpoint is included into the frame of the entire design process, with the aim of investigate how it influences the detectability range and the performance of the sensor. Furthermore, a permanent magnet system providing a DC bias magnetic field has been designed and exploited to allow the device to be able to measure both negative and positive magnetic fields.
The paper aims to provide a more accurate analysis of a magnetostrictive energy harvesting device by proposing a FEM model which, assuming a realistic nonlinear characteristic of the material, is ...able to describe the harvesting phenomena in presence of the eddy currents induced by the Villari effect. The study is focused on the investigation of the influence of those parameters, such as pre-stress and bias, on the field dynamics and, consequently, on the eddy currents loss phenomena which cannot be disregarded if a reliable prediction of the global performances of these devices is required. The numerical results are computed by considering a compressive stress-driven vibration source and show spatial profiles of the fields, losses, and recovered powers in different operating conditions. Comparisons with the linear model are also provided.
Superconductivity and ferroelectricity are typically thought of as incompatible because the former needs free carriers, but the latter is usually suppressed by free carriers. This is unless the ...carrier concentration is sufficiently low to allow for polar distortions and mobile electrons to cooperate. In the case of strontium titanate with low carrier concentration, superconductivity and ferroelectricity have been shown to be correlated via various tuning methods, such as strain. Here, we report theoretically and experimentally evaluated Grüneisen parameters whose divergent giant values under tensile stress indicate that the dominant phonon mode which enhances the superconducting order is the ferroelectric transverse soft phonon mode. This finding puts strong constraints on other phonon modes as the main contributors to the enhanced superconductivity in strained strontium titanate. The methodology shown here can be applied to strain tune and probe properties of other materials with polar distortions including topologically nontrivial ones.
The paper proposes a novel magnetic field sensor where a technique for hysteresis compensation is employed. The sensor integrates a magnetostrictive material with a Fiber Bragg Grating (FBG) strain ...sensor. Because of hysteresis and non-linear phenomena taking place in such materials, the sensor’s performances may be sensibly reduced. To this aim, magneto-elastic material is accurately modelled in order to
compensate hysteresis. In particular, the proposed approach allows to
embed the compensation algorithm in the developed device, yielding to a more linear response of the sensor and to a reliable reconstruction of magnetic field. Results are shown and discussed.
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.
The paper tackles the analysis of the magnetostrictive energy harvesting phenomena by formulating a model where the hysteretic static characteristic of the material and eddy currents induced by ...Villari effect are taken into account. The study aims to analyze the main loss mechanisms involved in this kind of devices, highlighting the impact of the hysteretic material behavior with respect to the linear and non-linear memoryless approaches.
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