Low-Frequency Electromagnetic Energy Harvesting from Highway Bridge Vibrations

Abstract

This paper focuses on energy harvesting from low-frequency vibrations in bridges via an electromagnetic device. Two pre-stressed concrete highway bridges are considered as case studies. In situ vibration measurements are reported and analyzed. An electromagnetic vibration energy harvester (VEH) with a low resonant frequency (tunable around 4 Hz) has been designed. The VEH is of the cantilever type, with 12 magnets mounted on a beam and acting as an inertial mass. By electromagnetic induction, the moving magnets produce an electric current in a surrounding conductive coil. A single-degree-of-freedom model of the VEH is presented with the main purpose of estimating the electrical power generated under various operating conditions. A procedure for identifying the model parameters from simple measurements is described. Optimizing the coil geometry so as to maximize the electromechanical coupling is crucial to maximize the output power. That issue does not seem to have been addressed in the literature and is discussed in detail in this paper. The coil that has been fabricated approximates that optimal geometry. For harmonic excitation with normalized amplitude, the designed VEH achieves the best power density to date among experimentally validated low-frequency electromagnetic VEHs. During a field test on a highway bridge, the harvester produced an average power of 112 μW through a load resistance of 3.3 kΩ. We present a simple formula for estimating the output power of electromagnetic VEHs in terms of traffic intensity. That formula could be useful in future studies related to vibration energy harvesting in bridges.