Development of piezoelectric harvesters with integrated trimming devices

Piezoelectric cantilever harvesters have a large power output at their natural frequency, but in some applications the frequency of ambient vibrations is different fromthe harvester\u2019s frequency and/or ambient vibrations are periodicwith some harmonic components. To copewith 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

A tunable triboelectric wideband energy harvester

The ability to efficiently convert mechanical energy into electrical energy has become an important topic of discussion and research in the last decade. Triboelectric generators have recently been popular for vibration energy harvesting, but despite plenty of research on its material aspect, research on combining mechanical characteristics and voltage generation output has been sparse. Many energy harvesters suffer from low operating bandwidths and are usually restricted to operating at a specific frequency. We propose a tunable triboelectric energy harvester that has a large response over a wide frequency bandwidth at low frequencies. The tunability is implemented by axially pre-loading a beam that reduces the system stiffness. This stiffness reduction strengthens the collisions that naturally occur in the triboelectric generators, resulting in larger voltage outputs. As the system stiffness decreases, the impacts occur over a broader frequency range, widening the frequency bandwidth. To describe the dynamic and voltage responses, a continuous electromechanical model is derived. The presented mathematical model sheds light on the coupled characteristics of mechanical vibration and triboelectric voltage generation, and can be used as a design tool for high-efficiency energy harvesters to operate wireless sensor networks

USE OF A TRIBOELECTRIC GENERATOR FOR A TUNABLE WIDEBAND ENERGY HARVESTER AND A THRESHOLD SHOCK SENSOR

The prevalence of triboelectricity as a transduction mechanism has increased rapidly in recent years. We will discuss two uses for triboelectric generators. One design is a tunable wideband energy harvester. An axial force and amplitude limiter work together to create an energy harvester that can accommodate various frequency sources and have a large operating bandwidth. The addition of the compressive axial force also softens the system, which allows for higher voltage outputs. A proof of concept of a threshold shock sensor is proposed that incorporates bi-stability along with the triboelectric effect. A clamped-clamped buckled beam will switch stable states when a threshold shock amplitude is experienced and a voltage peak will occur during this switching of states. Levels of input acceleration can be related to voltage output, which increases the value of the concept. Thorough continuous electro-mechanical models will be produced for each design and the validity of these models will be tested

Magnetoelastic Beam with Extended Polymer For Low Frequency Vibration Energy Harvesting

Ambient energy in the form of mechanical kinetic energy is mostly considered waste energy. The process of scavenging and storing such energy is known as energy harvesting. Energy harvesting from mechanical vibration is performed using resonant energy harvesters (EH) with two major goals: enhancing the power scavenged at low frequency sources of vibrations, and increasing the efficiency of scavenging energy by increasing the bandwidth near the resonant frequency. Toward such goals, we propose a piezoelectric EH of a composite cantilever beam with a tip magnet facing another magnet at a distance. The composite cantilever consists of a piezoelectric bimorph with an extended polymer material. With the effect of the nonlinearity of the magnetic force, higher amplitude can be achieved because of the generated bi-stability oscillations of the cantilever beam under harmonic excitation. The contribution of the this paper is to demonstrate lowering the achieved resonant frequency down to 17 Hz compared to 100 Hz for the piezoelectric bimorph beam without the extended polymer. Depending on the magnetic distance, the beam responses are divided to mono and bi-stable regions, for which we investigate static and dynamic behaviors. The dynamics of the system and the frequency and voltage responses of the beam are obtained using the shooting metho

Electrode coverage optimization for piezoelectric energy harvesting from tip excitation

Piezoelectric energy harvesting using cantilever-type structures has been extensively investigated due to its potential application in providing power supplies for wireless sensor networks, but the low output power has been a bottleneck for its further commercialization. To improve the power conversion capability, a piezoelectric beam with different electrode coverage ratios is studied theoretically and experimentally in this paper. A distributed-parameter theoretical model is established for a bimorph piezoelectric beam with the consideration of the electrode coverage area. The impact of the electrode coverage on the capacitance, the output power and the optimal load resistance are analyzed, showing that the piezoelectric beam has the best performance with an electrode coverage of 66.1%. An experimental study was then carried out to validate the theoretical results using a piezoelectric beam fabricated with segmented electrodes. The experimental results fit well with the theoretical model. A 12% improvement on the Root-Mean-Square (RMS) output power was achieved with the optimized electrode converge ratio (66.1%). This work provides a simple approach to utilizing piezoelectric beams in a more efficient way

A piezoelectric based energy harvester with dynamic magnification: modelling, design and experimental assessment

This work presents a simple and innovative piezoelectric energy harvester, inspired by fractal geometry and intrinsically including dynamic magnification. Energy harvesting from ambient vibrations exploiting piezoelectric materials is an efficient solution for the development of self-sustainable electronic nodes. After an initial design step, the present work investigates the eigenfrequencies of the proposed harvester, both through a simple free vibration analysis model and through a computational modal analysis. The experimental validation performed on a prototype, confirms the accurate frequency response predicted by these models with five eigenfrequencies below 100 Hz. Despite the harvester has piezoelectric transducers only on a symmetric half of the top surface of the lamina, the rate of energy conversion is significant for all the investigated eigenfrequencies. Moreover, by adding a small ballast mass on the structure, it is possible to excite specific eigenfrequencies and thus improving the energy conversion

Design and development of a parametrically excited nonlinear energy harvester

An energy harvester has been designed, fabricated and tested based on the nonlinear dynamical response of a parametrically excited clamped-clamped beam with a central point-mass; magnets have been used as the central point-mass which pass through a coil when parametrically excited. Experiments have been conducted for the energy harvester when the system is excited (i) harmonically near the primary resonance; (ii) harmonically near the principal parametric resonance; (iii) by means of a non-smooth periodic excitation. An electrodynamic shaker was used to parametrically excite the system and the corresponding displacement of the magnet and output voltages of the coil were measured. It has been shown that the system displays linear behaviour at the primary resonance; however, at the principal parametric resonance, the motion characteristic of the magnet substantially changed displaying a strong softening-type nonlinearity. Theoretical simulations have also been conducted in order to verify the experimental results; the comparison between theory and experiment were within very good agreement of each other. The energy harvester developed in this paper is capable of harvesting energy close to the primary resonance as well as the principal parametric resonance; the frequency-band has been broadened significantly mainly due to the nonlinear effects as well as the parametric excitation

Piezoelectric based energy harvesting on low frequency vibrations of civil infrastructures

Piezoelectric-based energy harvesting is an efficient way to convert ambient vibration energy into usable electric energy. The piezoelectric harvester can work as a sustainable and green power source for different electric devices such as sensors and implanted medical devices. However, its application on civil infrastructures has not been fully studied yet. This dissertation aimed to study and improve the piezoelectric-based energy harvesting on civil infrastructures, especially on bridge structures. To reach the objective, a more accurate model for piezoelectric composite beams was built first, which can be adopted for the modeling of different kinds of energy harvesters. The model includes both direct and inverse piezoelectric effects and can provide a better prediction for the dynamic response and energy output of a harvester. Secondly, to examine the piezoelectric-based energy harvesting on civil infrastructures, four concrete slab-on-girder bridges that represent the majority of bridges in the United States were modeled and used as the platforms for the energy harvesting. Piezoelectric cantilever–based harvesters were adopted for the energy harvesting performance simulation considering their wide usage. Different parameters of the bridges and the harvester were studied regarding to the harvesting performance. Two major problems for energy harvesting on civil infrastructures were identified, namely their low frequency vibrations and wide frequency ranges. Then, a multi-impact energy harvester was proposed to improve the harvesting performance under the vibration of low frequencies. The multi-impact was first introduced and theoretically proven. Theoretical and experimental studies for the multi-impact energy harvester were conducted. Both the results show an increased energy output power than the one from the conventional cantilever-based energy harvester. A parametric study was also presented which can serve as a guideline for the design and manufacture for the proposed harvester. Finally, a nonlinear energy harvester was proposed utilizing the magnet levitation. A larger band width was expected due to the stiffness non-linearity of the system. A theoretical model was built for the harvester and its energy output was simulated under the excitation of sinusoidal vibrations and bridge vibrations. The simulation results show a promising way to apply energy harvesting in the field of civil engineering