Design of vibration exciter by using permanent magnets for application to piezoelectric energy harvesting

We designed a piezoelectric energy harvesting system that can shift the resonant frequency to match the fixed external energy frequency. A permanent magnet (10 × 10 × 5 mm3) was attached to the free end of a cantilever beam, and a permanent magnet was attached to each of the four faces of a rotor at 90° angles. The effect of the size of the permanent magnets (40 × 20 × 10 mm3, 30 × 20 × 10 mm3, and 20 × 20 × 10 mm3) and the effect of the pole array distribution (NNNN, SSSS, NSNS, and NNSS) were experimentally investigated. The optimum conditions were determined by testing various distances between the magnets at different rpm's. The experiments showed that the maximum output power was generated for the minimum distance and largest magnet. The most effective approach to adjust the resonance frequency was to change the pole arrays of the magnets attached to the rotor. Furthermore, the optimum conditions were determined at each distance by changing the pole array and rpm. Software simulations support the experimental results.