Storing Energy in the Mechanical Domain
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Storing Energy in the Mechanical Domain O.G. Súchil1, G. Abadal1, F. Torres1 1
Dept. Enginyeria Electrònica, Universitat Autònoma de Barcelona, Bellaterra, 08193, SPAIN.
ABSTRACT Self-powered microsystems as an alternative to standard systems powered by electrochemical batteries are taking a growing interest. In this work, we propose a different method to store the energy harvested from the ambient which is performed in the mechanical domain. Our mechanical storage concept is based on a spring which is loaded by the force associated to the energy source to be harvested [1]. The approach is based on pressing an array of fine wires (fws) grown vertically on a substrate surface. For the fine wires based battery, we have chosen ZnO fine wires due the fact that they could be grown using a simple and cheap process named hydrothermal method [2]. We have reported previous experiments changing temperature and initial pH of the solution in order to determine the best growth [3]. From new experiments done varying the compounds concentration the best results of fine wires were obtained. To characterize these fine wires we have considered that the maximum load we can apply to the system is limited by the linear buckling of the fine wires. From the best results we obtained a critical strain of εc = 3.72 % and a strain energy density of U = 11.26 MJ/m3, for a pinned-fixed configuration [4]. INTRODUCTION Other approaches have been made to store energy in a mechanical domain. Different models study the potential for storing energy in the elastic deformation of springs made, for instance, with carbon nanotubes (CNTs). The main limitation of this storage is the strength of the material besides an electrochemical reaction, which for some cases is easier to control than an electrochemical battery [1]. Recently the study of materials as the ZnO has been increased due to its versatile and wide range of properties such as range of conductivity, high transparency and piezoelectricity inter alia. Furthermore different structures can be obtained depending on the fabrication method, and due to its wide range of morphologies it can be used in different applications [5]. As a piezoelectric material previous studies have been made, using the principle of applying a stress to a ZnO nanowire array to obtain an output potential. This approach has been used to create high output nano generators (HONG) reported by Wang Z.L. et al. [6]. Another aspect of interest is its low fabrication cost by using a simple aqueous growth known as the hydrothermal method, reported by Vayssieres et al. [7]. This method produces good results in morphology and density over the substrate and it can be controlled by varying the solution conditions. For our particular case of study, the purpose is to fabricate a well-aligned array of ZnO nanowires grown in a Si/Au substrate that later will be compressed all at once, in order to store the energy caused by the strain of each nanowire. To achieve this goal the study has to be divided in two main branches. The first is the op
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