Electromagnetic Wind Energy Harvester With Dual-Branch Reed And Resonant Cavity

With the development of new technology and environmental protection and the depletion of the Earth’s fossil energy, to develop new clean energy technologies by harvesting energy from the environment is increasingly becoming a necessity. Harvesting energy from the environment to power the portable devices or sensor network nodes can effectively solve a series of problems caused by the current battery-powers. Wind energy is a clean and renewable energy source, to harvest it by electromagnetic or piezoelectric ways to provide energy for wireless sensor networks has a great value.This thesis reviews the current status of wind energy harvesting and has a detailed analysis and research for the properties of wind fluid and principles of wind energy, then we proposed a new electromagnetic system based on dual-branch and forked-like reed and resonant cavity structure to harvest wind energy, the research details are as follows:First, a theoretical analysis and experimental research in-depth for the resonant cavity and dual-branch reed was conducted. Experiments show that the dual-branch reed not only increases the vibration amplitude of the piezoelectric reed but also exhibits a wide wind speed range. After the experiments and simulation analyses, a new mathematical model was established for a further research on this structure. We took the vibration of the reed in the resonant cavity as the damping forced vibration of a triangular pulse excitation. This model well explained why the dual-branch reed can vibrate much stronger than the no-branch reed. The experiment proved that the proposed structure and model are feasible and efficacious.Then a new electromagnetic resonant cavity wind energy harvester combined with dual-branch reed and turning fork-like vibrator was demonstrated to harvest wind energy for wireless sensor nodes. Compared with electromagnetic structures in the past, the proposed magnetic circuit has a better linearity and a magnetic loop that more effectively increases the rate of the change of magnetic flux. Moreover, the motion of the free magnet is directed vertically to the direction of the magnetic pole for a zero resistance startup mode and a compact construction. We also designed a tuning fork-like reed structure to reduce system losses. To achieve maximum output power, we defined a virtual resistance to deal with the decrease of the electromotive in the circuit caused by the Lorentz force between the magnet and the induced magnetic field of the coils when the circuit is turned on.Finally, experiments show that when the wind inlet size is60mmx60mm, the maximum output power and conversion efficiency can reach56mW at wind speed of20.3m/s and2.3%at wind speed of4m/s, respectively, with wind speed from3.2m/s to21.2m/s. The experiments show that this electromagnetic wind energy harvester has high output power and wide wind speed range.