This review provides a detailed overview of the energy harvesting technologies associated with piezoelectric materials along with the closely related sub-classes of pyroelectrics and ferroelectrics. These properties are, in many cases, present in the same material, providing the intriguing prospect of a material that can harvest energy from multiple sources including vibration, thermal fluctuations and light. Piezoelectric materials are initially discussed in the context of harvesting mechanical energy from vibrations using inertial energy harvesting, which relies on the resistance of a mass to acceleration, and kinematic energy harvesting which directly couples the energy harvester to the relative movement of different parts of a source. Issues related to mode of operation, loss mechanisms and using non-linearity to enhance the operating frequency range are described along with the potential materials that could be employed for harvesting vibrations at elevated temperatures. In addition to inorganic piezoelectric materials, compliant piezoelectric materials are also discussed. Piezoelectric energy harvesting devices are complex multi-physics systems requiring advanced methodologies to maximise their performance. The research effort to develop optimisation methods for complex piezoelectric energy harvesters is then reviewed. The use of ferroelectric or multi-ferroic materials to convert light into chemical or electrical energy is then described in applications where the internal electric field can prevent electron–hole recombination or enhance chemical reactions at the ferroelectric surface. Finally, pyroelectric harvesting generates power from temperature fluctuations and this review covers the modes of pyroelectric harvesting such as simple resistive loading and Olsen cycles. Nano-scale pyroelectric systems and novel micro-electro-mechanical-systems designed to increase the operating frequency are discussed.

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Piezoelectric and ferroelectric materials and structures for energy harvesting applications

High-Performance Piezoelectric Energy Harvesters and Their Applications

The piezoelectric generation of perovskite BaTiO3 thin films on a flexible substrate has been applied to convert mechanical energy to electrical energy for the first time. Ferroelectric BaTiO3 thin films were deposited by radio frequency magnetron sputtering on a Pt/Ti/SiO2/(100) Si substrate and poled under an electric field of 100 kV/cm. The metal-insulator (BaTiO3)-metal-structured ribbons were successfully transferred onto a flexible substrate and connected by interdigitated electrodes. When periodically deformed by a bending stage, a flexible BaTiO3 nanogenerator can generate an output voltage of up to 1.0 V. The fabricated nanogenerator produced an output current density of 0.19 μA/cm(2) and a power density of ∼7 mW/cm(3). The results show that a nanogenerator can be used to power flexible displays by means of mechanical agitations for future touchable display technologies.

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Piezoelectric BaTiO₃ thin film nanogenerator on plastic substrates.

The dramatic reduction in power consumption of current integrated circuits has evoked great research interests in harvesting ambient energy, such as vibrations, as a potential power supply for electronic devices to avoid battery replacement. Currently, most vibration-based energy harvesters are designed as linear resonators to achieve optimal performance by matching their resonance frequencies with the ambient excitation frequencies a priori. However, a slight shift of the excitation frequency will cause a dramatic reduction in performance. Unfortunately, in the vast majority of practical cases, the ambient vibrations are frequency-varying or totally random with energy distributed over a wide frequency spectrum. Hence, developing techniques to increase the bandwidth of vibration-based energy harvesters has become the next important problem in energy harvesting. This article reviews the advances made in the past few years on this issue. The broadband vibration-based energy harvesting solutions, covering re...

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Toward Broadband Vibration-based Energy Harvesting

This paper briefly overviews progress on the development of MEMS-based micropumps and their applications in drug delivery and other biomedical applications such as micrototal analysis systems (μTAS) or lab-on-a-chip and point of care testing systems (POCT). The focus of the review is to present key features of micropumps such as actuation methods, working principles, construction, fabrication methods, performance parameters and their medical applications. Micropumps have been categorized as mechanical or non-mechanical based on the method by which actuation energy is obtained to drive fluid flow. The survey attempts to provide a comprehensive reference for researchers working on design and development of MEMS-based micropumps and a source for those outside the field who wish to select the best available micropump for a specific drug delivery or biomedical application. Micropumps for transdermal insulin delivery, artificial sphincter prosthesis, antithrombogenic micropumps for blood transportation, micropump for injection of glucose for diabetes patients and administration of neurotransmitters to neurons and micropumps for chemical and biological sensing have been reported. Various performance parameters such as flow rate, pressure generated and size of the micropump have been compared to facilitate selection of appropriate micropump for a particular application. Electrowetting, electrochemical and ion conductive polymer film (ICPF) actuator micropumps appear to be the most promising ones which provide adequate flow rates at very low applied voltage. Electroosmotic micropumps consume high voltages but exhibit high pressures and are intended for applications where compactness in terms of small size is required along with high-pressure generation. Bimetallic and electrostatic micropumps are smaller in size but exhibit high self-pumping frequency and further research on their design could improve their performance. Micropumps based on piezoelectric actuation require relatively high-applied voltage but exhibit high flow rates and have grown to be the dominant type of micropumps in drug delivery systems and other biomedical applications. Although a lot of progress has been made in micropump research and performance of micropumps has been continuously increasing, there is still a need to incorporate various categories of micropumps in practical drug delivery and biomedical devices and this will continue to provide a substantial stimulus for micropump research and development in future.

https://www.nectec.or.th/mems/download/MEMS-based%20Micropumps%20in%20Drug.pdf

MEMS-based micropumps in drug delivery and biomedical applications

This paper deals with the analysis of different beam shapes for piezoelectric energy harvesters. The theory is based on the well-established Rayleigh–Ritz method for piezoelectric compound structures. It is validated by experiments with triangular-shaped and rectangular-shaped beams. It turns out that triangular-shaped beams are more effective than rectangular-shaped ones in terms of curvature homogeneity independent of the proof mass. This effect is opposed by the adverse mass distribution and the increased stiffness of triangular-shaped beams. Therefore, the overall efficiency is only weakly influenced by the beam shape. Nevertheless triangular-shaped beams drastically outperform rectangular ones in terms of tolerable excitation amplitude and maximum output power.

https://iopscience.iop.org/article/10.1088/0960-1317/18/10/104013/pdf

Characterization of different beam shapes for piezoelectric energy harvesting

A piezoelectric energy converter is presented, whose resonance frequency can be tuned by applying mechanical stress to its structure. The converter consists of a piezo-polymer cantilever beam with two additional thin arms, which are used to apply an axial preload to the tip of the beam. The compressive or tensile prestress applied through the arms leads to a shift of the beam's resonance frequency. Experiments with this structure indicate a high potential: the resonance frequency of a harvester to which a compressive preload was applied could be altered from 380 Hz to 292 Hz. In another experiment, a harvester with stiffened arms was tuned from 440 Hz to 460 Hz by applying a tensile preload. In combination with automatic control of the applied force, this type of structure could be used to enhance the performance of energy harvesters in vibrating environments with occasional shifts of the vibrational frequency.

https://iopscience.iop.org/article/10.1088/0960-1317/19/9/094006/pdf

Bidirectional frequency tuning of a piezoelectric energy converter based on a cantilever beam

This paper presents an electromagnetic vibration scavenger that exhibits a tunable eigenfrequency. By applying a static electrical field the eigenfrequency can be shifted. This feature is originated from exploiting the elastostriction of the utilized piezoelectric bimorph suspension. It is demonstrated that in the tuning operation mode more than 50 µW are scavenged continuously across the feasible frequency range of 20 Hz.

https://iopscience.iop.org/article/10.1088/0960-1317/20/3/035025/pdf

Electromagnetic vibration harvester with piezoelectrically tunable resonance frequency

We present the design, fabrication and testing of a novel medical implant based on a high performance silicon micropump. An analytical model was exploited for further optimization of our micropump design. The experimental data obtained are in a good accordance to theory. The limits of the analytical model are discussed and numerical studies are performed to examine the pressure loss over the valves of the micropump in detail. The presented micropump shows a flow rate of 1.8 ml/min and can build up and maintain backpressures up to 60 kPa. The overall size of the micropump is 30 mm × 11 mm × 1 mm. The driver electronics for the piezoelectric actuators is explained and the energy consumption is estimated. Two sphincter prosthesises of different sizes were developed and tested. The general medical capability as a prosthesis has been proven.

A high performance bidirectional micropump for a novel artificial sphincter system

https://iopscience.iop.org/article/10.1088/1468-6996/16/1/015003/pdf

Frank Goldschmidtboeing

Papers

Characterization of different beam shapes for piezoelectric energy harvesting

Bidirectional frequency tuning of a piezoelectric energy converter based on a cantilever beam

Electromagnetic vibration harvester with piezoelectrically tunable resonance frequency

A high performance bidirectional micropump for a novel artificial sphincter system

Highly elastic conductive polymeric MEMS