Recently,hybrid energy harvester has been considered as an attractive potential approach to response the worldwide energy crisis due to the combination of advantages from different harvesting mechanism.In this paper,a novel low-frequency wide-band hybrid energy harvester based on piezoelectric and triboelectric mechanism is presented and systematically studied including structural design,fabrication process,working principle simulation and measurement.With a vibrational excitation,the polyvinylidene fluoride(PVDF) cantilevers will vibrate and impact the polydimethylsiloxane(PDMS) film on the substrate,producing a piezoelectric output as well as a triboelectric output.The structural parameters of each cantilever are optimized using finite element simulation,and the well-designed PVDF cantilevers with controllable PDMS mass not only reduce the device working frequency but also enlarge the bandwidth.Under a sweep-frequency test,three voltage peaks induced by the piezoelectric part are observed at 15,32.5 and 47.5 Hz,with the value of 320,288 and 264 mV,respectively.With the combined triboelectric part,a 20 V peak-peak voltage is generated at 15 Hz.The electrical driving ability of this hybrid energy harvester also has been demonstrated by lighting up a commercial light emitting diode(LED).
HAN MengDiZHANG XiaoShengLIU WenSUN XuMingPENG XuHuaZHANG HaiXia
In this paper,a piezoelectric energy harvester based on spiral-shaped polyvinylidene fluoride(PVDF)cantilever is designed and fabricated for harvesting low frequency vibration energy in the environment.In this design,the spiral-shaped PVDF cantilever is major for lowering the resonant frequency by increasing the length of the cantilever;Copper and silicon proof masses on both sides are working on further decreasing the resonant frequency and widen its bandwidth.Due to the high flexibility of the PVDF cantilever,this device is extremely sensitive to vibration and can harvest weak vibration energy.Both simulation and experimental results have approved that this device can operate at very low frequency which is about 20 Hz and can effectively harvest energy from 15–50 Hz.The peak of the output voltage can reach 1.8 V with the acceleration of 0.2 g.This is a promising harvester for powering the wireless sensors in the future.
LIU WenHAN MengDiMENG BoSUN XuMingHUANG XianLiangZHANG HaiXia
Hardin's "The Tragedy of the Commons" prophesies the inescapable collapse of many human enterprises.The emergence and abundance of cooperation in animal and human societies is a challenging puzzle to evolutionary theory.In this work,we introduce a new decision-making criterion into a voluntary public goods game with incomplete information and choose successful strategies according to previous payoffs for a certain strategy as well as the risk-averse benefit.We find that the interest rate of the common pool and the magnitude of memory have crucial effects on the average welfare of the population.The appropriate sense of individuals' innovation also substantially influences the equilibrium strategies distribution in the long run.
This paper reports a controllable multi-functional black silicon surface with nanocone-forest structures fabricated by an optimized deep reactive ion etching(DRIE)technique using SF6/C4F8 in cyclic etching-passivation process,which is maskless,effective and controllable.The process conditions are investigated by systematically comparative experiments and core parameters have been figured out,including etching process parameters,pre-treatment,patterned silicon etching and inclined surface etching.Based on the experimental data,the formation mechanism of nanocone shape is developed,which provides a novel view for in-depth understanding of abnormal phenomena observed in the experiments under different process situations.After the optimization of the process parameters,the black silicon surfaces exhibit superhydrophobicity with tunable reflectance.Additionally,the quantitative relationship between nanocones aspect ratio and surface reflectance and static contact angle is obtained,which demonstrates that black silicon surfaces with unique functional properties(i.e.,cross-combination of reflectance and wettability)can be achieved by controlling the morphology of nanostructures.
A novel arc-shaped piezoelectric generator based on flexible PVDF thin film is presented and systemically studied.With a periodical external force,the generator can produce peak voltage of 45.6 V and peak power of 30.7μW.The maximum power density reaches 38.4μW/cm3with a 4 cm×2 cm×100μm device,at the optimum load resistance of 33.33 MOhm.The influence of frequency,size dimension and load resistance are investigated through experimental measurements.With this high output arc-shaped generator,capacitors can be effectively charged and three commercial LEDs have been directly lighted without any energy storage unit.
HAN MengDiLIU WenZHANG XiaoShengMENG BoZHANG HaiXia
