Electromagnetic resonant cavity wind energy harvester with optimized reed design and effective magnetic loop

We demonstrate a new electromagnetic resonant cavity wind energy harvester combined with dual-branch reed and turning fork vibrator 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. The dimensions of the wind inlet were 60 mm × 60 mm. The maximum output power and conversion efficiency can reach 56 mW at wind speed of 20.3 m/s and 2.3% at wind speed of 4 m/s, respectively, with wind speed from 3.2 m/s to 21.2 m/s. The experiments show that this electromagnetic wind energy harvester has high output power and wide wind speed range.