Efficiency enhancement of a cantilever-based vibration energy harvester

Extracting energy from ambient vibration to power wireless sensor nodes has been an attractive area of research, particularly in the automotive monitoring field. This article reports the design, analysis and testing of a vibration energy harvesting device based on a miniature asymmetric air-spaced cantilever. The developed design offers high power density, and delivers electric power that is sufficient to support most wireless sensor nodes for structural health monitoring (SHM) applications. The optimized design underwent three evolutionary steps, starting from a simple cantilever design, going through an air-spaced cantilever, and ending up with an optimized air-spaced geometry with boosted power density level. Finite Element Analysis (FEA) was used as an initial tool to compare the three geometries’ stiffness (K), output open-circuit voltage (Vave), and average normal strain in the piezoelectric transducer (εave) that directly affect its output voltage. Experimental tests were also carried out in order to examine the energy harvesting level in each of the three designs. The experimental results show how to boost the power output level in a thin air-spaced cantilever beam for energy within the same space envelope. The developed thin air-spaced cantilever (8.37 cm3), has a maximum power output of 2.05 mW (H = 29.29 μJ/cycle)

Performance Enhancement of Cantilever Beam Piezoelectric Energy Harvesters

During the last decade, driven by the need, energy harvesting has drawn considerable attention due to the cost-effectiveness and simplicity of the structure. The most important feature or advantage of energy harvesters is their energy sources which are coming from the energy that would be wasted otherwise to the ambient surroundings. Among the three types of energy conversion methodologies, piezoelectric energy harvesters (PEHs) have been highlighted as a self-power source of energy for small wireless sensors with low required power input due to their simple converting structure. While conventional piezoelectric materials possess ideal sensing properties, the microfabrication of these structures typically requires access to the sophisticated equipment and cleanroom facilities. Moreover, the fabrication process is time-consuming and expensive, researchers found it interesting to resort to micro-electromechanical system (MEMS) designs with inexpensive, simple and green-based materials and simple fabrication techniques such as paper. Generally, the paper-based devices have offered significant benefits but their recorded performance is significantly below that of the ones of the commercial smart structures. Their development is still in the early stage of growth and they need to be properly designed to satisfy the general requirements of the commercial products. Geometry optimization, sizing and functionalizing are among the strategies which can be adopted to boost the performance of all types of piezoelectric energy harvesters including the paper-based piezoelectric energy harvesters (PPEH). Therefore, the major contributions of this work are improvement of the performance of piezoelectric energy harvesters using the geometry modification, sizing analysis and functionalizing. In this work, the governing equations of piezoelectric cantilevers based on both Euler-Bernoulli and Timoshenko beam theories are developed and solved using one type of element with a great rate of convergence called superconvergent element (SCE). The theoretical analysis was validated against results published in the open literature and the results indicate that the proposed method yields higher accurate results. Further, the effect of non-uniformity on the electrical output and efficiency of Piezoelectric Energy Harvesters (PEH) are studied. Then, the influence of sizing and application of a series of piezoelectric cantilever energy harvesters on the performance of structure are studied. The effect of the shape of the piezoelectric elements is also investigated below. Eventually, development of functionally graded piezoelectric materials (FGPMs) for non-uniform beams are presented to evaluate the effect of functionalizing

On the Efficiency Enhancement of an Actively Tunable MEMS Energy Harvesting Device

In this paper, we propose an active control method to adjust the resonance frequency of a capacitive energy harvester. To this end, the resonance frequency of the harvester is tuned using an electrostatic force, which is actively controlled by a voltage source. The spring softening effect of the electrostatic force is used to accommodate the dominant frequency of the ambient mechanical vibration within the bandwidth of the resonance region. A single degree of freedom is considered, and the nonlinear equation of motion is numerically integrated over time. Using a conventional proportional–integral–derivative (PID) control mechanism, the results demonstrated that our controller could shift the resonance frequency leftward on the frequency domain and, as a result, improve the efficiency of the energy harvester, provided that the excitation frequency is lower than the resonance frequency of the energy harvester. Application of the PID controller in the resonance zone resulted in pull-in instability, adversely affecting the harvester’s performance. To tackle this problem, we embedded a saturation mechanism in the path of the control signal to prevent a sudden change in motion amplitude. Outside the pull-in band, the saturation of the control signal resulted in the reduction of harvested power compared to the non-saturated signal; this is a promising improvement in the design and analysis of energy harvesting devices

Enhancement of energy harvesting performance for a piezoelectric cantilever using a spring mass suspension

A spring-mass suspension is proposed in this paper for enhancing vibration energy harvesting performances of piezoelectric cantilevers. The suspension is inserted between the piezoelectric cantilever and the vibration base. Two key criteria are proposed for designing the present structure towards simultaneous broadband and intensive energy harvesting. On the one hand, the natural frequency of the spring-mass suspension is tuned close to that of the piezoelectric beam. On the other hand, the inertial mass of the suspension is chosen much greater than the cantilever mass. The amplification of the dynamic response over a broader frequency band of the proposed configuration is validated via vibration analyses. A prototype device in accordance with the proposed design is subsequently developed for experimental evaluations. The present structure widens the effective bandwidth from 7.6 Hz to 22.2 Hz, while increasing the maximum harvested power from 0.01436 mW/g to 0.4406 mW/g compared to the conventional cantilevered energy harvester

Toward Small-Scale Wind Energy Harvesting: Design, Enhancement, Performance Comparison, and Applicability

© 2017 Liya Zhao and Yaowen Yang. The concept of harvesting ambient energy as an alternative power supply for electronic systems like remote sensors to avoid replacement of depleted batteries has been enthusiastically investigated over the past few years. Wind energy is a potential power source which is ubiquitous in both indoor and outdoor environments. The increasing research interests have resulted in numerous techniques on small-scale wind energy harvesting, and a rigorous and quantitative comparison is necessary to provide the academic community a guideline. This paper reviews the recent advances on various wind power harvesting techniques ranging between cm-scaled wind turbines and windmills, harvesters based on aeroelasticities, and those based on turbulence and other types of working principles, mainly from a quantitative perspective. The merits, weaknesses, and applicability of different prototypes are discussed in detail. Also, efficiency enhancing methods are summarized from two aspects, that is, structural modification aspect and interface circuit improvement aspect. Studies on integrating wind energy harvesters with wireless sensors for potential practical uses are also reviewed. The purpose of this paper is to provide useful guidance to researchers from various disciplines interested in small-scale wind energy harvesting and help them build a quantitative understanding of this technique

Gapped cantilever for the enhancement of strain sensitivity and energy efficiency

Cantilever structures have been widely used in a large variety of transducer applications. For cantilever based transducers, piezoresistive/piezoelectric mechanisms has always been a popular choice due to the advantages of being low cost, simple structure and portability. However, low sensitivity is recognized as a major disadvantage of these transducers compared with optical based measurement. In this research, a gapped cantilever structure is proposed to potentially increase the sensitivity by orders of magnitude. In order to guide the design, an advanced analytical model is developed, and the increased strain sensitivity is theoretically demonstrated. In addition, optimizations with this model interestingly reveal that the gapped cantilever is much more efficient than conventional cantilever from energy perspective as well. Applications of gapped cantilever structure including piezoresistive accelerometer, vibration energy harvester and resonant mass sensor are carefully investigated in this work. Multiple prototypes of these applications both in meso-scale and micro-scale are designed, manufactured and characterized. The testing results show good agreement with theoretical expectation, and demonstrate a good potential of gapped cantilever structure for the enhancement of strain sensitivity and energy efficiency

Piezoelectric Energy Harvesting System Via Impact And Vibration – A Review

Recently, the vibrational energy harvesting devices have been studied and developed significantly. Although battery is the main power source for electronic devices, it still has some limitations, particularly its life time. Piezoelectric transducer is one of the devices that can be used for the vibration energy harvesting system. It has higher power density compared to the others. A comprehensive review on piezoelectric energy harvesting system is discussed and presented in this paper. The techniques of the piezoelectric energy harvester such as impact and vibration modes are reviewed. The power generator developed for the impact-based piezoelectric energy harvester is addressed in this paper. It can be concluded that the piezoelectric energy harvesting system can generate output power in the range of 34.6nW to 1.34W

Bifurcation analysis and nonlinear dynamics of a capacitive energy harvester in the vicinity of the primary and secondary resonances

The objective of the present study is to examine the effect of nonlinearity on the efficiency enhancement of a capacitive energy harvester. The model consists of a cantilever microbeam underneath which there is an electret layer with a surface voltage, which is responsible for the driving energy. The packaged device is exposed to unwanted harmonic mechanical excitation. The microbeam undergoes mechanical vibration, and accordingly, the energy is harvested throughout the output electric circuit. The dynamic formulation accounts for nonlinear curvature, inertia, and nonlinear electrostatic force. The efficiency of the device in the vicinity of the primary and super-harmonic resonances is examined, and accordingly, the output power is evaluated. Bifurcation analysis is carried out on the dynamics of the system by detecting the bifurcations in the frequency domain and diagnosing their respective types. One of the challenging issues in the design and analysis of energy-harvesting devices is to broaden the bandwidth so that more frequencies are potentially accomodated within the amplification region. In this study, the effect of the nonlinearity on the bandwidth broadening, as well as efficiency improvement of the device, are examined. It is seen that as the base excitation amplitude increases, the vibration amplitude does also increase and accordingly the nonlinearity dominates. The super-harmonic resonance regions emerge and get bigger as the vibration amplitude increases, and pull-in gaps appear in the frequency response curves