Ultra-low frequency energy harvesting using bi-stability and rotary-translational motion in a magnet-tethered oscillator
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ORIGINAL PAPER
Ultra-low frequency energy harvesting using bi-stability and rotary-translational motion in a magnet-tethered oscillator Hailing Fu · Stephanos Theodossiades · Ben Gunn · Imad Abdallah · Eleni Chatzi
Received: 27 May 2020 / Accepted: 6 August 2020 © The Author(s) 2020
Abstract Harvesting ultra-low frequency random vibration, such as human motion or turbine tower oscillations, has always been a challenge, but could enable many potential self-powered sensing applications. In this paper, a methodology to effectively harness this type of energy is proposed using rotary-translational motion and bi-stability. A sphere rolling magnet is designed to oscillate in a tube with two tethering magnets underneath the rolling path, providing two stable positions for the oscillating magnet. The generated magnetic restoring forces are of periodic form with regard to the sphere magnet location, providing unique nonlinear dynamics and allowing the harvester to operate effectively at ultra-low frequencies (< 1 Hz). Two sets of coils are mounted above the rolling path, and the change of magnetic flux within the coils accomplishes the energy conversion. A theoretical model, including the magnetic forces, the electromagnetic conversion and the occurring bi-stability, is established to understand the electromechanical dynamics and guide the harvester design. End linear springs are designed to maintain the periodic double-well oscillation when the H. Fu (B) · S. Theodossiades · B. Gunn Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough LE11 3TU, UK e-mail: [email protected] I. Abdallah · E. Chatzi Department of Civil, Environmental and Geomatic Engineering, ETH Zurich, Zurich, Switzerland e-mail: [email protected]
excitation magnitude is high. Parametric studies considering different design factors and operation conditions are conducted to analyze the nonlinear electromechanical dynamics. The harvester illustrates its capabilities in effectively harnessing ultra-low frequency motions over a wide range of low excitation magnitudes. Keywords Bi-stability · Energy harvesting · Rotarytranslational motion · Nonlinear dynamics
1 Introduction Condition-based monitoring is widely employed for predicting potential system failures and reducing maintenance costs in mechanical structures and critical infrastructure [1–3]. Wireless sensors are one of the key enablers to condition-based monitoring, but they generally require regular battery recharging or replacement, introducing human intervention and maintenance costs. Converting the available passive energy sources in the location where sensors are mounted into electricity provides a self-contained power supply solution [4,5], but it faces challenges in meeting the energy demands of sensing functions in many cases [5,6]. This is especially difficult when energy sources have low-frequency content and random bursts. Different mechanisms have been adopted in the literature to harness low-frequency and random motions, adopt
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