Design and Optimization of a Tubular Linear Electromagnetic Vibration Energy Harvester

This paper presents the design and optimization of tubular linear electromagnetic transducers (LETs) for the applications of large-scale vibration energy harvesting from vehicle suspensions, tall buildings, or long-span bridges. The LETs are composed of magnet and coil assemblies, which convert the vibration energy into electricity when moving relatively with each other. The parameters of the LETs, such as the thickness of the magnets in the axial direction and the thickness of the coils in the radial direction, are optimized using finite-element method to achieve high power density and damping density. Four LETs with different configurations namely, single-layer axial magnets and steel spacers, double-layer axial magnets and steel spacers, single-layer axial and radial magnets, double-layer axial and radial magnets are investigated for further improvement. It is found that the parameter optimization can increase the power density [W/m
$^{3}$
] of LETs to 3.8 times compared with the initial design by Zuo and coworkers, and the double-layer configuration with both radial and axial magnets can improve the power density up to 5.6 times, approaching to the energy dissipation rate of traditional oil dampers. A prototype using off-shelf axial NdFeB magnet is built and tested on a vibration shaker. The experiment results show that the prototype of 63.5 mm (
$2.5^{\prime\prime}$
) outer diameter and 305 mm (12 in) compressed length can harvest 2.8 W power at 0.11 m/s relative velocity and provide a damping coefficient of 940 N·s/m. It is estimated that average 26–33 W electrical power and 1680–2142 N·s/m damping coefficient can be achieved at 0.25 m/s root-mean-square velocity for different LETs of
$3^{\prime\prime}$
outer diameter and
$12^{\prime\prime}$
compressed length.