Energy harvesting from torsional vibrations using a nonlinear oscillator

Harvesting ambient energy in a variety of systems and applications is a relatively recent trend, often referred to as Energy Harvesting. This can be typically achieved by harvesting energy (that would otherwise get wasted) through a physical process aiming to convert energy amounts to useful electrical energy. The harvested energy can be thermal, solar, wind, wave or kinetic energy, with the last class mainly referring to harvesting energy from vibrating components or structures. More often these oscillations are error states from the systems’ ideal function and through harvesting this potentially wasted energy could be reclaimed and become useful. Regardless of the generally low power output of the devices designed to harvest energy from vibrations, their use remains an attractive concept, which is mostly attributed to the growing use of modern electronic devices that exploit the low power requirements of semi-conductors. Energy Harvesting applications are often met in situations where a network of essential electronic devices, such as sensors in Structural Health Monitoring or bio-implantable devices, becomes hardly accessible. Harvesting ambient vibrations to power up these devices offers the option to utilize wireless sensors rendering these systems autonomous. Typical cases of systems, where ambient vibrations are ubiquitous are met in automotive and aerospace applications. Besides their potentially adverse impact, the energy carried by vibrating parts could be harvested, such that wireless sensors are powered. In this paper, a concept for harvesting torsional vibrations is proposed, based on a concept that employs magnetic levitation to establish a nonlinear Energy Harvester. Experience has shown that linear harvesters require resonant response to operate, often leading to low performance of the device when the excitation frequency deviates from resonance conditions. This is why harvesters with essential nonlinearity are preferred, since they are able to demonstrate high response levels over wider frequency regions. Herein, the conducted study aims to demonstrate the functionality of this concept for torsional systems. A mathematical model of the coupled nonlinear electromechanical system is established, seeking preliminary estimates of the harvested power. The compelling attribute of this system lies in the dependency of its linear natural frequency on the excitation frequency, which is found to cause multiple response peaks in the corresponding frequency spectra. Moreover, the selection of the static equilibrium of the levitating magnet is found to greatly influence the system’s response.