Investigation of electrical properties for cantilever-based piezoelectric energy harvester

In the present era, the renewable sources of energy, e.g., piezoelectric materials are in great demand. They play a vital role in the field of micro-electromechanical systems, e.g., sensors and actuators. The cantilever-based piezoelectric energy harvesters are very popular because of their high performance and utilization. In this research-work, an energy harvester model based on a cantilever beam with bimorph PZT-5A, having a substrate layer of structural steel, was presented. The proposed energy scavenging system, designed in COMSOL Multiphysics, was applied to analyze the electrical output as a function of excitation frequencies, load resistances and accelerations. Analytical modeling was employed to measure the output voltage and power under pre-defined conditions of acceleration and load resistance. Experimentation was also performed to determine the relationship between independent and output parameters. Energy harvester is capable of producing the maximum power of 1.16 mW at a resonant frequency of 71 Hz under 1g acceleration, having load resistance of 12 k Omega. It was observed that acceleration and output power are directly proportional to each other. Moreover, the investigation conveys that the experimental results are in good agreement with the numerical results. The maximum error obtained between the experimental and numerical investigation was found to equal 4.3%

DEVELOPMENT OF PIEZOELECTRIC ENERGY HARVESTING SYSTEM FOR LOW-FREQUENCY VIBRATIONS

Harvesting energy from vibration sources has attracted the interest of researchers for the past three decades. Researchers have been working on the potential of achieving self-powered MEMS scale devices. Piezoelectric cantilever harvesters have caught the attention in this field because of the excellent combination of high-power density and compact structure. The main objective of this thesis is to develop a novel and optimum piezoelectric harvester system using lumped parameter model (LPM) for given vibration sources. The finite element model (FEM) is used in this work as an original approach to be utilized for optimal design optimization. Three types of validations are accomplished to solidify the use of FEM in mimicking the distributed parameter model (DPM) for linearly tapered piezoelectric cantilevers. The first two validations are accomplished using beam deflection and relative transmissibility functions. Comparisons between the FEM and the DPM developed by the literature are performed. The third validation is carried for an electromechanical piezoelectric cantilever in FEM. Results confirmed the effectiveness of the developed FEM. A number of significant contributions are achieved while fulfilling the aim of this work. First, a dimensionless parameter, Power Factor (PF), is derived and used to understand the impact of the geometry on the piezoelectric harvester performance. The PF showed an optimum performance at a taper ratio of 0, taking the full length of the cantilever and thickness ratio of 0.7. Second, the accuracy of the LPM for linearly tapered piezoelectric harvesters and optimal design are investigated. Results indicated that the percentage of the deflection error between the LPM and the FEM reaches 9% when the taper ratio is zero. However, when tip-mass to cantilever ratios are larger than 2, the error decreases to less than 0.5% leading to more accurate results in the vibrational response of the beam. Further studies on the accuracy are accomplished using the relative transmissibility function. Results showed that as the taper ratio decreases towards zero, the percentage error of using the LPM to predict the vibration response increases significantly to 55%. These results lay the foundation for the third contribution of developing correction factors for tapered and optimal piezoelectric cantilever harvesters using FEM. Comparisons of the corrected LPM and FEM for different configurations are examined. Results indicated that as the taper ratio decreases, the surface power density increases. However, the developed optimal design exhibits the highest surface power density of 1.40×104 [(mW/g2)/ m2] which is 16.4% more than the best following shape of a taper ratio 0.2 and 58% more than the taper ratio 1. Furthermore, a parametric study of the optimal design is performed to scrutinize the effect of various parameters on the harvester performance. Finally, detailed criteria for designing the optimal piezoelectric harvester for different conditions are structured

Gembinių pjezoelektrinių energijos surinkimo sistemų su netaisyklingais skerspjūviais tyrimas

A dissertation analyses the problems of increasing an output power of piezoelectric energy harvesters based on single cantilever and cantilever arrays. The main aim of dissertation is to propose a method to increase an output energy density and power density of piezoelectric layer of cantilever type energy harvester by introducing irregular cross section of the cantilever and rigidly composed cantilevers in cantilever arrays. The dissertation covers a review of the most relevant scientific literature, numerical and experimental investigations of piezoelectric energy harvesters based on cantilevers with different irregular cross-sections and cantilever arrays based on rigidly composed cantilevers. The dissertation consist of introduction, three chapters, general conclusions, references, list of scientific publications published by the author of the topic of dissertation and three appendixes. The introduction covers problem relevance, formulation of the goals and objectives, introduces novelty of the dissertation and overviews the dissertation structure. The first chapter describes background and motivation of mechanical vibrations energy harvesting, an overviews the main mechanical vibrations energy harvesting technologies and their operation principles. The second chapter is related to numerical and experimental investigations of piezoelectric energy harvesters based on rectangular and trapezoidal cantilevers with irregular cross-sections. The cross-sections of cantilevers were modified by rectangular, cylindrical and trapezoidal gaps. Electrical and mechanical characteristics of the piezoelectric cantilevers were analysed while different shape gaps were used. The third chapter presents numerical and experimental investigations of polygon type piezoelectric energy harvesters. Three different designs of the cantilever arrays introduced and investigated i. e. rectangular, saw-tooth and polygon type. The investigation reveals influence of rigidly composed cantilevers and irregular cross-sections to electrical and mechanical characteristics of the energy harvesting systems. Seven scientific articles, related to the topic of the dissertation were published: 4 papers were published in journals with citation index and included to Clarivate Analytics Web of Science database, 1 paper was published in conference material book indexed in Clarivate Analytics Web of Science “Conference Proceedings” database, 2 papers were published in the journals included in other databases. The results of the dissertation were presented at 5 international conferences

Design optimization in geometry of seismic mass for MEMS based cantilever type piezoelectric energy harvester for motor vibrations

Piezoelectric energy harvesters are suitable for vibration energy harvesting due to simple design, operation and fabrication in MEMS technology. Cantilever structures fixed from one end and seismic mass at the other must tune to different resonance frequency to ensure wideband frequency operation. Adequate width to length ratio of cantilever is required to avoid curling of cantilevers (bending). Effect of increase in width of the cantilever structure on resonance frequency has been investigated and also compared analytically in this paper. An optimized design has been proposed which compensates for the increase in resonance frequency due to increase in width by changing the geometry of the seismic mass. With the change in geometry of seismic mass a shift in center of mass has been achieved towards the free end of the cantilever which reduces the resonance frequency which is desirable. The design optimization of seismic mass reported in this paper reduces the resonance frequency by 4.27 % which is appreciated as it is required to harvest ambient vibrations having low frequency

Towards an on-chip power supply: Integration of micro energy harvesting and storage techniques for wireless sensor networks

The lifetime of a power supply in a sensor node of a wireless sensor network is the decisive factor in the longevity of the system. Traditional Li-ion batteries cannot fulfill the demands of sensor networks that require a long operational duration. Thus, we require a solution that produces its own electricity from its surrounding and stores it for future utility. Moreover, as the sensor node architecture is developed on complimentary metal-oxide-semiconductor technology (CMOS), the manufacture of the power supply must be compatible with it. In this thesis, we shall describe the components of an on-chip lifetime power supply that can harvest the vibrational mechanical energy through piezoelectric microcantilevers and store it in a reduced graphene oxide (rGO) based microsupercapacitor, and that is fabricated through CMOS compatible techniques. Our piezoelectric microcantilevers confirm the feasibility of fabricating micro electro- mechanical-systems (MEMS) size two-degree-of-freedom systems which can solve the major issue of small bandwidth of piezoelectric micro-energy harvesters. These devices use a cut-out trapezoidal cantilever beam to enhance the stress on the cantilever’s free end while reducing the gap remarkably between its first two eigenfrequencies in 400 - 500 Hz and 1 - 2 kHz range. The energy from the M-shaped harvesters will be stored in rGO based microsupercapacitors. These microsupercapacitors are manufactured through a fully CMOS compatible, reproducible, and reliable micromachining processes. Furthermore, we have also demonstrated an improvement in their electrochemical performance and yield of fabrication through surface roughening from iron nanoparticles. We have also examined the possibility of integrating these devices into a power management unit to fully realize a lifetime power supply for wireless sensor networks

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

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

CMOS-MEMS PIEZOELECTRIC ENERGY HARVESTING SYSTEM

This paper reports a low-cost, high-sensitivity CMOS-MEMS piezoelectric energy harvester with large proof mass. Piezoelectric has known to be the best in harvesting ambient vibration energy. Its simple theory to produce voltage with stress and vibration has come to many optimization researches to produce the best structure with low natural frequency and high yield strength. Four common materials have been compared to see the performance of generating the voltage output. Zinc Oxide, ZnO thin film was utilized as the best piezoelectric material and device was designed using the infamous cantilevered-beam structure which known as the best structure to produce high sensitivity of vibration and has the highest stress effect at the beam tip attached to the stator comb or fixed end. This structure is indeed compatible with CMOS-MEMS fabrication. The structure has been designed and simulated. The device has a sensitivity of I 13.4 J!VIg and the structure has been carefully optimized to avoid structured damage due to undesired mode by incorporating the parallel beam to the cantilever-based structure

Simulation of spiral-shaped mems human energy harvester using piezoelectric transduction

Energy harvesters are one of the focus areas in the field of research. The complex smart devices and miniaturized electronic design limit the use of traditional wired power source. The need for an efficient human energy harvester for such devices is growing exponentially every year due to an increase in the demand of energy sources and power requirement for the electronics. In the recent years, the trend of research is leading us to come up with a better solution of replacing the use of non-renewable energy with the renewable sources. Human energy harvesting technique has evolved as an efficient substitute to these. But there are few challenges in designing such energy harvesters. Firstly, obtaining higher efficiency. Moreover, since the efficiency is lower it is difficult to obtain enough energy considered to size. The goal is to model and simulate small scale energy harvester which harvests the ambient energy efficiently. There are several advantages of human energy harvester which make it beneficial, cost-effective and has grabbed the attention of researchers since past several years. In this thesis report, a human energy harvester has been designed in a 2-loop spiral design and simulated to obtain an efficient design using piezoelectric materials.Includes bibliographical reference