| With the widely application of wireless and portable electronics in wireless sensor networks and micro-electromechanical systems(MEMS), power supply is increasingly become a major bottleneck hindering their development. Traditional batteries and electric wires have the characteristics of short life cycle, complex wiring and some other defects, which make them unable to meet the power requirements of these electronics. At the same time, the rapidly developing technology of large-scale integrated and ultra low-power circuit has made the power consumption of many electronic products reduce to the level of mW and even uW. Thus, the technology of converting ambient energy into electrical energy to make electronic devices self-powered is proposed and has been widespread concerned.The alternative energy sources in our environment include wind, thermal, acoustic, solar, electromagnetic, vibration energy, and so on. Among them, wind is abundant in nature, clean and renewable. Furthermore, wind is one type of the earliest exploited energy by human, and is also an important direction of autonomous powered technology research both at home and abroad. Compared with small-size turbine wind energy generators, flow-induced vibration energy collectors have the advantages of simple processing and easy to miniaturization, and are the main developing direction of wind energy harvester. Most of the reported wind-induced vibration energy harvesters can only operate efficiently in a narrow wind speed range and a mismatch of the range may result in these harvesters’ incapacity or a significant decrease in their performance. On the other hand, most devices are designed to harvest wind energy in a single direction. However, in fact, the wind speed and direction in natural environment are generally unstable or time-varying, rendering the above-mentioned harvesters have low collection efficiency and lead to a waste of wind energy.In order to address the limitations of the existing approaches including narrow working wind speed range and single-directional operation, an innovatively designed piezoelectric harvester for harvesting the energy from wind with a wide speed range and multiple directions is demonstrated. In the harvester, an arc-shaped elastic beam, instead of conventional thin cantilever beams was adopted to extract wind energy, which is capable of responding to multi-directional wind excitations without any extra accessory and exhibiting different oscillating patterns under wind excitations with different speeds as well as coming from different directions, and this will finally realize multi-directional and a wide speed range of wind energy harvesting. The operating modes and the selection criteria of the piezoelectric material were investigated. The flow-induced vibration feature of the harvester was analyzed combined with vortex-induced vibration and flutter theories including their mechanical models. The motion behavior of the harvester was simulated by the software of COMSOL Multiphysics, and then the harvester’s electrical output characteristic was studied. A prototype was fabricated and the collecting performances of the harvester when wind coming from front(Mode I), back(Mode II), side(Mode III) and top(Mode IV) were tested. The results show that the harvester works efficiently with wind exciting from the four directions in a speed range of 2~17 m/s and products the maximum open-circuit voltages of 25.0 V, 34.2 V, 14.2 V and 26.0 V in Mode I, Mode II, Mode III and Mode IV, respectively. In addition, the electrical output characteristics of the harvesters with four different radians were tested. The impedance matching experiment indicates that the harvester can achieve the peak powers of 0.84 m W at 17 m/s, 1.73 mW at 17 m/s, 0.33 mW at 17 m/s and 0.27 mW at 11 m/s in Mode I, Mode II, Mode III and Mode IV, respectively. To prove the practical value of the harvester, an application was demonstrated and 18 serial-connected Light-emitting diodes(LEDs) were lit up simultaneously at the wind speed of 10.5 m/s. |
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