Numerical and experimental evaluation of the magnetic interaction for frequency up-conversion in piezoelectric vibration energy harvesters

Theoretical and Applied Mechanics - AIMETA 2022

2023

Abstract. We propose a shielding technique for the magnetic field localization around permanent magnets (PMs) for sharpening the magnetic force-displacement curve in the frequency up-conversion (FuC) of piezoelectric vibration energy harvesters (PVEHs). We present a concept with theoretical formulation, computational analyses, and experimental validation that confirms the supposed principle. The numerical study on a PVEH shows that with the shielding, for varying actuation velocity, high values of peak power (50 mW – 150 mW) can be reached at low speeds (e.g. 0.5 m/s – 2.6 m/s). The unshielded device exhibits a good behavior for velocities over 3 m/s. This result makes the technique useful for the design of FuC mechanisms depending to its operating velocity.

Section: Experimental Validationmentioning

confidence: 70%

On the manipulation of the magnetic forces for improving the contactless plucking in piezoelectric vibration energy harvesters

Theoretical and Applied Mechanics - AIMETA 2022

2023

“…The first eigenfrequency of the cantilever is 659.2 Hz, 665.2 Hz, and 668.3 Hz for repulsive, no magnetic interaction and attractive cases, respectively. Through a MATLAB ® program, in which the modelling of the piezoelectric cantilever has been implemented [ 35 ], an eigenfrequency of 672.5 Hz is obtained without interactions. This value is 1% larger than the experimental one, because of the discretization approach.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, at parity of experimental conditions with comparable mechanical excitation employing the repulsive configuration, it is possible to further increase the electro-mechanical effectiveness of the piezoelectric converter compared to the attractive configuration. This is due to the bistable nature of the repulsive scheme that allows also inter-well oscillations [ 35 ].…”

Section: Resultsmentioning

confidence: 99%

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Piezoelectric Energy Harvesting from Low-Frequency Vibrations Based on Magnetic Plucking and Indirect Impacts

Nastro

Baù

et al. 2022

Sensors

Self Cite

This work proposes a mono-axial piezoelectric energy harvester based on the innovative combination of magnetic plucking and indirect impacts, e.g., impacts happening on the package of the harvester. The harvester exploits a permanent magnet placed on a non-magnetic mass, free to move within a predefined bounded region located in front of a piezoelectric bimorph cantilever equipped with a magnet as the tip mass. When the harvester is subjected to a low-frequency external acceleration, the moving mass induces an abrupt deflection and release of the cantilever by means of magnetic coupling, followed by impacts of the same mass against the harvester package. The combined effect of magnetic plucking and indirect impacts induces a frequency up-conversion. A prototype has been designed, fabricated, fastened to the wrist of a person by means of a wristband, and experimentally tested for different motion levels. By setting the magnets in a repulsive configuration, after 50 s of consecutive impacts induced by shaking, an energy of 253.41 μJ has been stored: this value is seven times higher compared to the case of harvester subjected to indirect impacts only, i.e., without magnetic coupling. This confirms that the combination of magnetic plucking and indirect impacts triggers the effective scavenging of electrical energy even from low-frequency non-periodical mechanical movements, such as human motion, while preserving the reliability of piezoelectric components.

“…Among different possibilities [7][8][9] a promising solution is the frequency upconversion (FuC) technique by means of permanent magnets. It exploits the magnetic force to create an impulsive phenomenon on a piezoelectric transducer [10] and it provides a contactless interaction, avoiding impact and potential damage of piezoelectric crystals.…”

Section: Introductionmentioning

confidence: 99%

Dynamical Behavior of Frequency up-Converted Piezoelectric Vibration Energy Harvesters at Different Velocities of Magnetic Interaction

2022 21st International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerME

Kohtanen

Corigliano

et al. 2022

Self Cite

This work proposes an experimental investigation on the dynamical behavior of a magnetically frequency upconverted piezoelectric energy harvester. The magnetic interaction arises between a tip magnet on a piezoelectric bimorph and a moving magnet. The latter is controlled through a low-frequency shaker at a fixed frequency of 3 Hz (typical of human motion). The analysis shows that the activation of the first mode of vibration is linked to the velocity of the magnetic interaction. Also, inherent material nonlinearities appear as a frequency shift of the first mode on the Fast Fourier Transforms of the output voltage near short circuit condition.