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

Abstract

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.

Optimization of an Impact-Based Frequency Up-Converted Piezoelectric Vibration Energy Harvester for Wearable Devices

“…Such a fact could be the main disadvantage of an impact-based energy harvester. Another interesting aspect could be to implement the concept in a real wearable device and test it for human motion activities, as conducted in [ 29 ]. It would also be interesting to extend the study to the case of indirect impacts, e.g., the impacts on the substrate on which the piezoelectric transducer is installed.…”

“…To overcome this issue, different studies in the literature propose the adoption of frequency up-conversion [ 17 ], which can be achieved via the non-linear behaviour of structural elements [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ], buckling [ 21 , 22 , 23 , 24 ], and magnetic interaction [ 25 , 26 , 27 , 28 ]. In other cases, with the purpose of increasing the scavenged energy, arrays of resonant converters are proposed [ 29 , 30 , 31 , 32 ], and the adoption of special metamaterials is introduced [ 33 , 34 , 35 ]. On the other hand, for ultra-low ambient frequency, dry reciprocating friction is exploited [ 36 ].…”

A method to enhance the nonlinear magnetic plucking for vibration energy harvesters

“…However, since the mass is supposed to be driven externally at a constant velocity, its dynamics does not appear in the system (2). To perform numerical simulations, the same data of the beam used in [28] are assumed. All physical and geometrical characteristics are summarized in Table 1.…”

A Review of Nonlinear Mechanisms for Frequency Up-Conversion in Energy Harvesting

“…However, the environment in which EHs operate predominantly holds energy distributed over frequencies within 100 Hz ( [4,[29][30][31]). When considering powering wearable electronics, human motion frequencies typically range between 1 and 5 Hz ( [32][33][34]). As explained earlier, EHs must be minimally invasive and as small as possible, resulting in high natural frequencies (hundreds or thousands of hertz).…”

“…Other researchers designed systems where impacts occur at the seismic or tip mass of the harvester [89,90]. Rosso et al [32] proposed enhancing a cantilever piezoelectric energy harvester through indirect impacts on a moving mass and nonlinear magnetic interaction, demonstrating that magnetic interaction efficacy depends on motion energy levels. Additionally, techniques involving mixed transduction mechanisms have been explored.…”