Design and characterization of an

electromagnetic energy harvester for

vehicle suspensions

Lei Zuo, Brian Scully, Jurgen Shestani and Yu Zhou

Department

During the everyday usage of an automobile, only 10–16% of the fuel energy is used to drive

the car—to overcome the resistance from road friction and air drag. One important loss is the

dissipation of vibration energy by shock absorbers in the vehicle suspension under the

excitation of road irregularity and vehicle acceleration or deceleration. In this paper we design,

characterize and test a retrofit regenerative shock absorber which can efficiently recover the

vibration energy in a compact space. Rare-earth permanent magnets and high permeable

magnetic loops are used to configure a four-phase linear generator with increased efficiency and

reduced weight. The finite element method is used to analyze the magnetic field and guide the

design optimization. A theoretical model is created to analytically characterize the waveforms

and regenerated power of the harvester at various vibration amplitudes, frequencies, equilibrium

positions and design parameters. It was found that the waveform and RMS voltage of the

individual coils will depend on the equilibrium position but the total energy will not.

Experimental studies of a 1:2 scale prototype are conducted and the results agree very well with

the theoretical predictions. Such a regenerative shock absorber will be able to harvest 16–64 W

power at 0.25–0.5 m s−1 RMS suspension velocity.

The normalized waveforms of regenerated voltage of one

coil at 0◦ and 90◦ phases under peak-to-peak vibration amplitudes

2vmax/ω = 0.25H, 0.5H, 1H, 1.5H, where H = 11.35 mm.

In this paper we present the design, optimization, analysis and

experimental results of a retrofit regenerative shock absorber

for vibration energy harvesting from vehicle suspensions.

Theoretical predictions and experimental results agree very

well. A 1:2 scale prototype of a four-phase linear generator

was developed and characterized both experimentally and

analytically. The half-scale prototype was able to harvest 2–

8 W of energy at 0.25–0.5 m s−1 RMS suspension velocity. It

was also found that the frequency of the regenerated voltage

does not necessarily have the same frequency as the excitation.

Instead, the wave shapes of the regenerated voltage will depend

on excitation frequency, amplitude and equilibrium position.

The regenerated power will be the largest at a frequency around

the resonance of the vibration system. Though the voltage

waveform of the individual coil depends on the equilibrium

position, the total power of the four phases does not depend

on it.

Further research is underway to improve the energy

density and efficiency by taking the harvesting electrical circuit

and the harvester output resistance into accoun