Development of Piezoelectric Harvesters with Integrated Trimming Devices

Abstract

Featured Application: Trimming devices integrated with the structural layer of the harvester are proposed for improving energy harvesting at low frequency and in the presence of periodic excitation with multiple harmonics. Abstract: Piezoelectric cantilever harvesters have a large power output at their natural frequency, but in some applications the frequency of ambient vibrations is different from the harvester's frequency and/or ambient vibrations are periodic with some harmonic components. To cope with these operating conditions harvesters with integrated trimming devices (ITDs) are proposed. Some prototypes are developed with the aid of an analytical model and tested with an impulsive method. Results show that a small trimming device can lower the main resonance frequency of a piezoelectric harvester of the same extent as a larger tip mass and, moreover, it generates at high frequency a second resonance peak. A multi-physics numerical finite element (FE) model is developed for predicting the generated power and for performing a stress-strain analysis of harvesters with ITDs. The numerical model is validated on the basis of the experimental results. Several configurations of ITDs are conceived and studied. Numerical results show that the harvesters with ITDs are able to generate relevant power at two frequencies, owing to the particular shape of the modes of vibration. The stress in the harvesters with ITDs is smaller than the stress in the harvester with a tip mass trimmed to the same frequency.

Development of a Novel Piezoelectric Harvester Excited by Raindrops

“…The damping ratio was 0.021 (mean value) with a standard deviation of 0.001, this value is larger than the one measured in open-circuit (0.015), since the load resistance contributes to damping [19]. Finally, the generated voltage decreases with respect to the open-circuit voltage, the mean peak-to-peak value was 2.48 V with a standard deviation of 0.24 V. This result agrees with the ones found for harvesters excited by base vibrations [33,38]. Starting from Equation (19), the collected energy was calculated and a mean value of 1.58 μJ was obtained (with a standard deviation of 0.23 μJ).…”

“…Usually cantilever harvesters excited by raindrops are simulated, taking into account only the first mode of vibration of the system [31,32]. Multi-mode dynamic models of cantilever harvesters have already been presented in the scientific literature, but they refer to the case of a harvester excited by base vibrations [33,34,35]. In that case, the cantilever is loaded by the distributed inertia force caused by the distributed mass of piezoelectric and structural materials and by the lumped inertia force caused by the tip mass.…”

Analysis and Control of Vibrations of a Cartesian Cutting Machine Using an Equivalent Robotic Model

“…First, guess values of these variables are found considering that two close resonance peaks are obtained when a main vibrating system with natural frequency Ω = 2π f n is coupled with an ancillary oscillator (AO) tuned to the same frequency. Analytical and experimental results show that the original resonance peak at Ω is substituted by two new resonance peaks, the former at lower frequency, the latter at higher frequency [9,10]. The frequency interval between the two peaks depends on the ratio between the masses of the AO and of the main system (mass ratio).…”

Bidirectional Piezoelectric Energy Harvester

“…Also, it must be mentioned that cantilever L 2 can operate as a dynamic vibration damper (DVA) for cantilever L 1 . Numerous reports of DVA applications in piezoelectric energy harvesters can be found [20,21,22]. Operation of cantilever L 2 as DVA is avoidable for the proposed energy harvester, therefore, it was controlled that proper geometrical parameters of cantilevers would not be selected during the numerical investigation.…”

“…Based on numerical and experimental investigations it can be assumed that proposed energy harvester can be used to harvest bidirectional vibrations by torsional and bending modes. However, the authors do not mention an intention to investigate bidirectional operation principle [20].…”