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 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.

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Many industrial applications incorporate rotating shafts with fluctuating speeds around a required mean value. This often harmonic component of the shaft speed is generally detrimental, since it can excite components of the system, leading to large oscillations (and potentially durability issues), as well as to excessive noise generation. On the other hand, the addition of sensors on rotating shafts for system monitoring or control poses challenges due to the need to constantly supply power to the sensor and extract data from the system. In order to tackle the requirement of powering sensors for structure health monitoring or control applications, this work proposes a nonlinear vibration energy harvester design intended for use on rotating shafts with harmonic speed fluctuations. The essential nonlinearity of the harvester allows for increased operating bandwidth, potentially across the whole range of the shaft's operating conditions.

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Many industrial applications incorporate rotating shafts with fluctuating speeds around a desired mean value. This often harmonic component of the shaft speed is generally undesirable, since it can excite parts of the system and can lead to large oscillations (potentially durability issues), as well as to excessive noise generation. On the other hand, the addition of sensors on rotating shafts for system monitoring or control poses challenges due to the need to supply power to the sensor and extract data from the rotating application. In order to tackle the requirement of powering sensors for structure health monitoring or control applications, this work proposes a nonlinear vibration energy harvester design intended for use on rotating shafts with harmonic speed fluctuations. The essential nonlinearity of the harvester allows for increased operating bandwidth, potentially across the whole range of shaft’s operating conditions.

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.

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