Wide bandwidth 2-DoF electromagnetic MEMS energy harvester for low g applications

This paper presents the design of a 2-DoF electromagnetic MEMS energy harvester, optimized to be realized using commercially available microfabrication processes. The proposed 2-DoF system consists of two inter-connected vibrating masses to achieve dynamically amplified displacement amplitude, at low-frequency and low-g vibrations with wide operational bandwidth. The vibrating microstructure, with sputtered NdFeB magnets, is designed considering microfabrication constraints of MetalMUMPs process. The stationary planar microcoils are designed using 0.35 μm CMOS MIMOS process. The vibrating microstructure and stationary planar microcoils are bonded together using photoresist with thickness of 30 μm. The magnets are arranged in a Halbach array configuration to concentrate the magnetic field on the stationary microcoils side while cancelling the field nearly zero on the other side. The input acceleration value with respect to overall damping is optimized, for a structurally limited gap of 160 μm between the inner and outer mass of the 2-DoF vibrating system, using design of experiments (DOE) based response surface models. For the proposed design, two resonant frequencies of 40.7 and 89.6 Hz are obtained with an operational bandwidth of 49 Hz. With an input acceleration value of 0.442g, an induced voltage of 18 mV and output power of 0.82 nW is btained at the first resonant frequency while an induced voltage of 14 mV and output power of 0.54 nW is obtained at the second resonant frequency. The normalized power density of the proposed energy harvester design is 7.94 × 10⁻⁷ (W/cm³/g²) at 40.7 Hz, with an overall device volume of 0.0058 cm³.