The last two decades have witnessed several advances in microfabrication technologies and electronics, leading to the development of small, low-power devices for wireless sensing, data transmission, actuation, and medical implants. Unfortunately, the actual implementation of such devices in their respective environment has been hindered by the lack of scalable energy sources that are necessary to power and maintain them. Batteries, which remain the most commonly used power sources, have not kept pace with the demands of these devices, especially in terms of energy density. In light of this challenge, the concept of vibratory energy harvesting has flourished in recent years as a possible alternative to provide a continuous power supply. While linear vibratory energy harvesters have received the majority of the literature’s attention, a significant body of the current research activity is focused on the concept of purposeful inclusion of nonlinearities for broadband transduction. When compared to their linear resonant counterparts, nonlinear energy harvesters have a wider steady-state frequency bandwidth, leading to a common belief that they can be utilized to improve performance in ambient environments. Through a review of the open literature, this paper highlights the role of nonlinearities in the transduction of energy harvesters under different types of excitations and investigates the conditions, in terms of excitation nature and potential shape, under which such nonlinearities can be beneficial for energy harvesting. [DOI: 10.1115/1.4026278]

On the Role of Nonlinearities in Vibratory Energy Harvesting: A Critical Review and Discussion

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 reviews possible strategies to increase the operational frequency range of vibration-based micro-generators. Most vibration-based micro-generators are spring-mass-damper systems which generate maximum power when the resonant frequency of the generator matches the frequency of the ambient vibration. Any difference between these two frequencies can result in a significant decrease in generated power. This is a fundamental limitation of resonant vibration generators which restricts their capability in real applications. Possible solutions include the periodic tuning of the resonant frequency of the generator so that it matches the frequency of the ambient vibration at all times or widening the bandwidth of the generator. Periodic tuning can be achieved using mechanical or electrical methods. Bandwidth widening can be achieved using a generator array, a mechanical stopper, non-linear (e.g. magnetic) springs or bi-stable structures. Tuning methods can be classified into intermittent tuning (power is consumed periodically to tune the device) and continuous tuning (the tuning mechanism is continuously powered). This paper presents a comprehensive review of the principles and operating strategies for increasing the operating frequency range of vibration-based micro-generators presented in the literature to date. The advantages and disadvantages of each strategy are evaluated and conclusions are drawn regarding the relevant merits of each approach.

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Strategies for increasing the operating frequency range of vibration energy harvesters: a review

The last decade has witnessed significant advances in energy harvesting technologies as a possible alternative to provide a continuous power supply for small, low-power devices in applications, such as wireless sensing, data transmission, actuation, and medical implants. Piezoelectric energy harvesting (PEH) has been a salient topic in the literature and has attracted widespread attention from researchers due to its advantages of simple architecture, high power density, and good scalability. This paper presents a comprehensive review on the state-of-the-art of piezoelectric energy harvesting. Various key aspects to improve the overall performance of a PEH device are discussed, including basic fundamentals and configurations, materials and fabrication, performance enhancement mechanisms, applications, and future outlooks.

A comprehensive review on piezoelectric energy harvesting technology: Materials, mechanisms, and applications

In an effort to eliminate the replacement of the batteries of electronic devices that are difficult or impractical to service once deployed, harvesting energy from mechanical vibrations or impacts using piezoelectric materials has been researched over the last several decades. However, a majority of these applications have very low input frequencies. This presents a challenge for the researchers to optimize the energy output of piezoelectric energy harvesters, due to the relatively high elastic moduli of piezoelectric materials used to date. This paper reviews the current state of research on piezoelectric energy harvesting devices for low frequency (0–100 Hz) applications and the methods that have been developed to improve the power outputs of the piezoelectric energy harvesters. Various key aspects that contribute to the overall performance of a piezoelectric energy harvester are discussed, including geometries of the piezoelectric element, types of piezoelectric material used, techniques employed to match the resonance frequency of the piezoelectric element to input frequency of the host structure, and electronic circuits specifically designed for energy harvesters.

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Energy harvesting from low frequency applications using piezoelectric materials

We propose a segmented piezoelectric energy harvester in the flexural mode for scavenging ambient vibration energy. 4 circuit connection patterns between segment piezoelectric bimorphs are presented. The resonant frequency of a segmented piezoelectric harvester is readily adjusted through changing either its geometrical configuration or circuit connection pattern, which can keep the harvester operating at the optimal state in environment with different ambient vibrations. The governing equations of a segmented piezoelectric harvester with alternate bimorphs are derived from the transfer-matrix technique. The numerical results show that the adaptability of a harvester to the operating environment can be improved greatly by designing the harvesting structure with adjustable resonant frequency.

Adjusting the resonant frequency of a segmented energy harvester through circuit connection patterns

This paper develops a novel multi-beam harvesting system with both electrical and mechanical coupling among piezoelectric beams. The harvesting system integrates multiple piezoelectric bimorphs (PBs) with different thicknesses into a system, bimorph beams are not only connected electrically in series or in parallel but also connected mechanically with springs at ends. Effect of spring stiffness for two connecting patterns among PBs, in series and in parallel, on improving energy harvesting performance is discussed in detail. Numerical results show that the end spring connection can effectively broaden the frequency-band of the harvesting structure and shift the operating frequency-band to match with the frequency of driving forcings.

A multi-beam piezoelectric harvesting system with both electrical and mechanical coupling among piezoelectric beams

This paper proposes a piezoelectric energy harvester experiment model, which composed of piezoelectric harvesting element, energy storage element, and a full bridge to connect them as an integrated system. A synchronized switch harvesting inductor (SSHI) is introduced in parallel with the harvesting structure to reverse voltage through the charge transfer between the output electrodes at the transition moments from closed- to open- circuit, i.e. the time when the harvesting structure deforms to the extreme position. The harvesting structure is driven to vibrate by vibration exciter which is acted by a voltage signal with a certain frequency. The method of capturing zero velocity is used to catch the moment when the harvesting structure deforms to the extreme position. SSHI closes synchronously, and delay a half period of the oscillator, composed by the inductor and effective capacitor of piezoelectric harvesting structure, then opens. This process is controlled by the technique of single chip microcomputer. Experimental results show SSHI processes have been achieved. An optimal rectified voltage can maximize the output power density of the piezoelectric energy harvester.

Experimental research on nonlinear coupling between two sides of rectification in piezoelectric energy harvester

We study electrically forced antiplane vibrations of a multilayered circular cylindrical piezoelectric shell of ceramics poled in the axial direction. The interfaces among the layers are modeled by the so-called shear-lag model. The linear theory of piezoelectricity is used. A theoretical analysis is performed. An exact solution is obtained. Electrical admittance, resonant frequencies, and distributions of the displacement and stress fields are calculated. It is found that the maximal admittance may appear at the first or higher resonances depending on the arrangement of the poling directions of the layers, and that the admittance and the electromechanical fields are sensitive to the interface bonding.

Huan Xue

Papers

Adjusting the resonant frequency of a segmented energy harvester through circuit connection patterns

A multi-beam piezoelectric harvesting system with both electrical and mechanical coupling among piezoelectric beams

Experimental research on nonlinear coupling between two sides of rectification in piezoelectric energy harvester

Electrically forced antiplane vibrations of a multilayered circular cylindrical piezoelectric shell of polarized ceramics with weak interfaces

Impact of solenoid effects on series impedance of three-core armoured cables