Fully Integrated Microsolenoid With Closed Magnetic Circuit for High Power Density MEMS Electromagnetic Vibration Energy Harvesters

This letter presents a highly efficient microsolenoid integrated with a closed magnetic circuit to enhance the power density of microelectromechanical systems (MEMS) electromagnetic energy harvesters. Compared with most MEMS electromagnetic energy harvesters adopting an air-cored planar coil, a high permeability closed magnetic circuit is specifically designed and integrated inside the microsolenoid with multiple wire turns for higher electromechanical coupling, which contributes to the effective increased power density of the MEMS energy harvester. Moreover, the wafer-level microsolenoid is compatible with nonlinear springs, which bring higher power output over a wideband frequency range. At an acceleration of 1
g
, the prototype shows a load power of 265.2 µW and normalized power density of 5.9 mW·cm
^-3
·g
^-2
with a load resistance of 40.1 Ω, accompanied with a half-power bandwidth of 30 Hz. The fully integrated solenoid is compatible with other soft magnetic-material and frequency-broadening mechanisms, providing adequate potential for comprehensive performance enhancement of MEMS electromagnetic energy harvesters.