Multiple cell configuration electromagnetic vibration energy harvester

Abstract

This paper reports the design of an electromagnetic vibration energy harvester that doubles the magnitude of output power generated by the prior four-bar magnet configuration. This enhancement was achieved with minor increase in volume by 23% and mass by 30%. The new ‘double cell’ design utilizes an additional pair of magnets to create a secondary air gap, or cell, for a second coil to vibrate within. To further reduce the dimensions of the device, two coils were attached to one common cantilever beam. These unique features lead to improvements of 66% in output power per unit volume (power density) and 27% increase in output power per unit volume and mass (specific power density), from 0.1 to 0.17 mW cm−3 and 0.41 to 0.51 mW cm−3 kg−1 respectively. Using the ANSYS multiphysics analysis, it was determined that for the double cell harvester, adding one additional pair of magnets created a small magnetic gradient between air gaps of 0.001 T which is insignificant in terms of electromagnetic damping. An analytical model was developed to optimize the magnitude of transformation factor and magnetic field gradient within the gap.

Piezoelectric MEMS for energy harvesting

“…To obtain an approximation of the critical size where piezoelectricity becomes more useful, Figure 1 plots harvester volume versus normalized output power (normalized by acceleration and multiplied by frequency) for various piezoelectric and electromagnetic prototypes reported in the literature. 5 From Figure 1 , it can be determined that the critical size is in the vicinity of ∼ 0.5 cm 3 . At a smaller device volume than this critical size, the electromagnetic transformation factor (similar to electromechanical coupling in piezoelectrics)…”

“…Marin et al have studied the scaling of output power as a function of effective material volume ( v ) for different mechanisms. 5 By taking into account constitutive equations for the respective conversion mechanisms, the output power of the electromagnetic mechanism is proportional to v 2 , while that of the piezoelectric mechanism is proportional to v ¾ . Thus, at smaller scales, the piezoelectric mechanism becomes more attractive as compared to electromagnetics.…”

MEMS Technologies for Energy Harvesting

“…Piezoelectric transduction is an advantageous mechanism to convert vibrationto-electric energy for small scales as stated by Marin et al [61] and Cook et al [62]. Marin studied the relationship between the effective material volume (ν) and the output power for different mechanisms.…”

“…The output power for the piezoelectric mechanism is proportional to v 3/4 , while that for the electromagnetic mechanism is proportional to v 2 . At volumes smaller than 0.5 cm 3 the electromagnetic transformation factor is reduced abruptly [61]. The piezoelectric mechanism has the highest energy conversion efficiency [63,64] and is the most appropriate technology for the scale of MEMS devices [65,66].…”

High Power Density Levitation-Induced Vibration Energy Harvester

“…Thus, most currently reported cantilevers operate at frequencies higher than 50 Hz (Marin, Bressers, and Priya 2011). Furthermore, cantilever-based devices are generally devoid of broadband behavior at their resonance frequencies, therefore limiting their capability outside the resonance region (Mann and Sims 2009).…”