Analysis of Magnetic Plucking Configurations for Frequency Up-Converting Harvesters

Abstract

Low-temperature effects on up-conversion emission of Er3+/Yb3+-co-doped Y2O3 V Lojpur, M G Nikoli, M D Dramianin et al. Abstract. Magnetic plucking applies the strategy of frequency up-conversion in inertial energy harvesting when the energy source, such as human motion, only provides excitations with very low and irregular frequencies. This paper presents an analysis of three different magnet configurations to achieve magnetic plucking based on a three-dimensional analytical cube permanent magnet model: direct repulsive configuration, orthogonal configuration and indirect repulsive configuration. Simulation and experimental results indicate that the indirect repulsive configuration generates the largest tip displacement given the pratical constraints in designing a wearable energy harvester. We have implemented this configuration in a wrist-worn rotational energy harvester to pluck multiple piezoelectric beams. Other configurations, however, can potentially be advantageous in applications with alternative constraints. IntroductionEnergy harvesting for wearable wellness sensors could provide the potential for continuous health monitoring by eliminating the need to replace or recharge batteries manually. The inherent limitation of utilizing human motion as the source for inertia energy harvesting is that it only provides excitations with very low and irregular frequencies. Frequency up-conversion is a commonly used strategy to tackle this issue by transforming the low-frequency input motion into high-frequency resonance of the transducer. Plucking is one technique which applies such a strategy. Eccentric rotorbased wearable energy harvesters have been demonstrated in previous endeavors either using magnets [1][2] or pins [3][4] to pluck piezoelectric beams. Magnetic coupling provides better reliability since it can be designed contact-free. Usually magnets are arranged to pluck the beam in the direction of magnet motion with either a direct repelling or an attractive configuration [5], i.e. in-plane plucking. While the in-plane plucking introduces a stronger jump phenomenon in the cantilever beam, the outof-plane deflection configuration provides the capability of fabricating multiple beams in the harvester on a single substrate. Furthermore, mechanical design complexity is reduced and space utilization is increased which ultimately improves power output. However, if the magnets are simply aligned, as in the direct repulsive configuration in Figure 1, the overall thickness of the harvester will grow. Additionally, in this configuration the opposing magnets can get stuck in a side by side orientation, i.e. there is a pull-in effect. Thus exploring alternative magnet configurations with the ability to trigger out-of-plane plucking as well is worthwhile.Among all the possible combination of orientations, we present two alternative magnet configurations: the orthogonal and the indirect repulsive configuration, which not only have demonstrated the capability of triggering plucking but also are free of the pull-in effe...

On magnetic plucking configurations for frequency up-converting mechanical energy harvesters

“…This work expands upon a previous analysis on magnetic plucking configurations based on static magnetic force profiles [15] (i.e. interaction between one fixed magnet and one moving magnet).…”

“…(b)(c)(d), the beam deflection direction is perpendicular to the plane of magnet motion in the out-of-plane plucking configurations. This arrangement enables the possibility of fabricating multiple beams on a single substrate [15] which reduces assembly complexity when multiple beams are embedded in the device to achieve higher power output. In addition, it has better MEMS process compatibility when the device is scaled down.…”

Recent Advances in Human Motion Excited Energy Harvesting Systems for Wearables

“…[ 101 ] Another strategy of improving the system response is a plucking mechanism, which allows the transducer to oscillate at a natural frequency regardless of low‐frequency excitation. [ 102 ] In such device, the cantilever beam is plucked by the proof mass, and then oscillates at its natural frequency after being released. [ 103,104 ] Lockhart et al used multiple pins fixed on the proof mass to pluck the piezoelectric cantilever beams, achieving an average power of 11 μW.…”

Wearable inertial energy harvester with sputtered bimorph lead zirconate titanate (PZT) thin-film beams

“…A comparison among different magnet configurations to achieve magnetic plucking [26] suggests that the primary advantage of out-of-plane plucking configurations in implementing a multi-beam harvester lies in the manufacturability and associated difficulty in assembly especially when the device is miniaturized. For instance, a prototype utilizing a star-shape piezoelectric element with out-of-plane plucking in [21] demonstrated the feasibility of fabricating multiple bimorph PZT beams on a single substrate. Out-of-plane plucking configurations usually lead to light electromechanical coupling with high dependency on the speed of moving magnet.…”

“…This strategy essentially enables a resonant oscillator to operate in a non-resonant fashion. Typically the frequency upconversion strategy is implemented in piezoelectric energy harvesters including impact-based operation [12][13][14], mechanical plucking via pins [15,16] and magnetic coupling [17][18][19][20][21]. Methods involving mechanical contact for the excitation usually suffer from reliability problems.…”