• Energy Research

Recycling ambient energies with electric generators instead of employing batteries with limited lifespans has motivated a large scientist community over two decades. Sea waves exhibit a large energy density. The amount of energy that could be extracted from the sea waves is very high. This work describes a technique of sea wave energy extraction based on a piezoelectric conversion and an analogy with thermodynamic Ericsson loops. By synchronizing external electric field to the maximum and the minimum of the sea wave mechanical stress excitations, the piezoelectric material dielectric hysteresis loop area is increased corresponding to the maximum of the energy available. In this article, technical solutions are proposed for the in site deployment of the proposed technique (maximum and minimum detection, external electric field source synchronization). Experimental measuring benches have been developed to monitor the sea wave mechanical excitation and to determine precisely the energy-harvesting potential. Adequate dielectric hysteresis model is proposed to numerically determine the best configuration (frequency, amplitude) of electric field to impose. Even if the Ericsson technique requires external electronic devices, the weak consumption of such components allows a large enhancement of the amount of energy extracted compared to a basic piezo element conversion.

In the framework of electromechanical energy conversion devices for vibrational energy harvesting, magnetostrictive materials are an attractive alternative solution to the brittleness of piezoelectric materials. Electromagnetic systems have low voltage output at a low frequency while magnetostrictive materials are suitable for a larger frequency bandwidth. In this work, a special experimental emphasis is placed on Fe80Si9B11 (also known as Metglas 2605SA1) alloy. The ultimate energy conversion abilities are investigated by performing experimental Ericsson cycles as well as through theoretical predictions using a dedicated model for the magnetic curves at the material scale. Typical output magnetic energy densities ranged between 0.1 and 1 mJ/cm3/cycle under moderate stress (<100 MPa) and magnetic excitation (up to 4 kA/m). Apart from its energy conversion abilities, Metglas 2605SA1 also features attractive characteristics for realistic applications in microgenerators, such as a low price, which is an important advantage for the mass production and cost-effectiveness of the harvester. Furthermore, its soft magnetic property reduces the need for high magnetic fields and yields a well-adapted solution from a system point of view. It is therefore shown that this material is a suitable conversion material according to the available stress and magnetic excitation magnitudes, in addition to economic considerations.

Abstract The elastocaloric effect denotes the ability of a material to release or absorb heat when the material is stretched and released respectively. This effect may be used to design an alternative cooling device. This work focuses on the development of a cooling device using natural rubber (NR) as the elastocaloric material. It consists of a solid–solid heat exchange between a cyclically stretched elastocaloric material and two exchangers, respectively put in contact with the elastocaloric material when it is stretched or released. An experimental device was designed and tested in order to assess the temperature span and cooling power (PC) achievable by NR based single stage device. The effect of the thickness of the NR is also discussed. It is shown that it was possible to transfer nearly 60% of the heat absorption potential of the NR from the cold heat exchanger. From the measurements, the highest PC was found to be 390 mW (430 W kg−1) for a 600 µm thick sample, and 305 mW (540 W kg−1) for a 400 µm thick sample. The temperature span was found to be similar for both materials, ranging 1.5 °C–1.9 °C.

Magneto-rheological (MR) elastomers contain micro-/nano-sized ferromagnetic particles dispersed in a soft elastomer matrix, and their rheological properties (storage and loss moduli) exhibit a significant dependence on the application of a magnetic field (namely MR effect). Conversely, it is reported in this work that this multiphysics coupling is associated with an inverse effect (i.e. the dependence of the magnetic properties on mechanical strain), denoted as the pseudo-Villari effect. MR elastomers based on soft and hard silicone rubber matrices and carbonyl iron particles were fabricated and characterized. The pseudo-Villari effect was experimentally quantified: a shear strain of 50 % induces magnetic induction field variations up to 10 mT on anisotropic MR elastomer samples, when placed in a 0.2 T applied field, which might theoretically lead to potential energy conversion density in the mJ cm-3 order of magnitude. In case of anisotropic MR elastomers, the absolute variation of stiffness as a function of applied magnetic field is rather independent of matrix properties. Similarly, the pseudo-Villari effect is found to be independent to the stiffness, thus broadening the adaptability of the materials to sensing and energy harvesting target applications. The potential of the pseudo-Villari effect for energy harvesting applications is finally briefly discussed.

Controlling the polarization state of ferroelectric materials, and more particularly piezoelectric polymers, is critical to ensure good operation of actuators or sensors using such energy conversion mechanisms. More specifically, the modeling and prediction of the hysteretic behavior of such materials is a critical aspect for the fabrication of robust and accurate devices. The purpose of this article is to present a model based on mathematical functions describing hysteretic behavior as a sum of elementary polarizations arising from combined avalanche and saturation physical effects. Predicted responses show good agreement with experimental measurements, and extension of the model for taking into account electric field-induced crystallization during operations is presented. Finally, the proposed model is simple to implement and does no require heavy computational and memory requirements, as it relies on pure mathematical functions and only requires unidimensional distribution of elementary polarizations. © 2015 Wiley Periodicals, Inc.

Abstract A model of structured Magneto-rheological Elastomer made of a soft matrix filled by magnetic particles was studied for energy harvesting, in pure shear condition. The particles were supposed to be aligned in a chain along which the magnetic field is applied and considering a shear strain applied in a plane perpendicularly to the chain. As the strain is applied and assuming the deformation is homogeneous and the particles remain aligned, both of the axis of their alignment and inter-distance between particles change, affecting their magnetic state. The aim of this work is to evaluate how far the magnetic induction variation induced by mechanical solicitation can be converted into electric signal. We firstly analyzed the magnetic susceptibility of a particle in the chain, and then derived an analytical expression for the composite permeability as a function of shear strain. FEM simulations taking into account the particle magnetic saturation was also performed to estimate the optimal conditions (magnetic field values, shear amplitude, etc.) maximizing the energy conversion potentials.

Energy harvesting has been studied with great interest in recent years. Ambient vibration is a potential energy resource for low-power devices or electronic devices in extreme/remote area. Methods on enhance the energy conversion amount has been long been a main subject in energy harvesting field. The present study developed a precise model working under hybrid of electrical and mechanical excitations in an Ericsson loop cycles which highly increases the converted energy. Consideration of the dynamic behavior of the nonlinearity of the piezoceramic under high amplitude excitation, the model gives precise prediction of energy conversion amount. This technique can be applied in both energy harvesting and monitoring area. Experiments have been done for different kinds of samples. Comparisons between energy conversion with or without the new coupling technique have been reported and it allows validating this new configuration. © 2014 IEEE.