Second Generation High Output Power Vibration Energy Harvester with High-Permeability Material

18.3.1 Prototype and Testing Platform

The schematic design of the high output power energy harvester is shown in Fig. 18.12. Two identical solenoids with high-permeability/insulator multilayer cores were placed on two sides of a vibrating hard magnet pair with antiparallel magnetization. The key components of this energy harvester are the two identical solenoids with a high-permeability (high-ц,) MuShield core inside, which are placed at two sides of the magnet pair and fixed on a vibrating stage. The magnets have antiparallel magnetization and are supported by a regular circular cross­section spring with its bottom fixed on the surface. When the magnet pair moves up and down with respect to the vibrating stage, the magnetic field inside each solenoid periodically changes its direction. The magnetostatic coupling between the solenoids and the time varying inhomogeneous bias magnetic field results in a nonlinear oscillation and a complete magnetic flux reversal in the solenoids. The presence of highly permeable cores dramatically increases the magnitude of magnetic flux inside the coils. Thus, a large induced voltage is generated on both

sides of the solenoid, and the output voltage can be doubled with serial connection of the two solenoids.

The entire device is powered by a vibrating stage, which is driven by an audio power amplifier. Voltage output of the harvester in time domain is mon­itored by a digital oscilloscope. The device picture is shown in Fig. 18.13. Each SmCo hard magnet has a dimension of 2.2 cm x 1.3 cm x 0.2 cm. Each solenoid core consists of 28-layers of high-permeability MuShield material, with a dimension of 2 cm x 2 cm x 0.002 in. Total volume of the energy harvester is 6.44 cm x 3.25 cm x 1.4 cm = 29.3 cm3, which includes the solenoids, the magnet pair, and air-gap. The coil resistance of each solenoid is 1.3 Й.