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

Energy harvesting technologies have been explored by researchers for more than two decades as an alternative to conventional power sources (e.g. batteries) for small-sized and low-power electronic devices. The limited life-time and necessity for periodic recharging or replacement of batteries has been a consistent issue in portable, remote, and implantable devices. Ambient energy can usually be found in the form of solar energy, thermal energy, and vibration energy. Amongst these energy sources, vibration energy presents a persistent presence in nature and manmade structures. Various materials and transduction mechanisms have the ability to convert vibratory energy to useful electrical energy, such as piezoelectric, electromagnetic, and electrostatic generators. Piezoelectric transducers, with their inherent electromechanical coupling and high power density compared to electromagnetic and electrostatic transducers, have been widely explored to generate power from vibration energy sources. A topical review of piezoelectric energy harvesting methods was carried out and published in this journal by the authors in 2007. Since 2007, countless researchers have introduced novel materials, transduction mechanisms, electrical circuits, and analytical models to improve various aspects of piezoelectric energy harvesting devices. Additionally, many researchers have also reported novel applications of piezoelectric energy harvesting technology in the past decade. While the body of literature in the field of piezoelectric energy harvesting has grown significantly since 2007, this paper presents an update to the authors' previous review paper by summarizing the notable developments in the field of piezoelectric energy harvesting through the past decade.

https://iopscience.iop.org/article/10.1088/1361-665X/ab36e4/pdf

A review of energy harvesting using piezoelectric materials: state-of-the-art a decade later (2008–2018)

Mobility (transport of people and goods) is a socio-economic reality and need for which is bound to grow in the coming years. Modes of transport should be safe, economic and reasonably environmental friendly. Hydrogen could be ideal as a synthetic energy carrier for transport sector as its gravimetric energy density is very high, abundantly available in combined form on the earth and its oxidation product (water) does not contribute to greenhouse gas emissions. However, its sustainable production from renewable resources economically, on-board storage to provide desirable driving range, usage in durable energy conversion devices and development of infrastructure for its delivery remain significant challenges. In this article, recent developments in the field of production, storage, transport and delivery of hydrogen along with environmental and safety aspects of its use as an energy carrier are presented. Almost any energy source can be used to produce hydrogen. Presently, non-renewable sources dominate hydrogen production processes but the need of the hour is to develop and promote the share of renewable sources for hydrogen production to make it completely sustainable. Hydrogen may be used as fuel for almost any application, where fossil fuels are used presently and would offer immediate benefits over the conventional fuels, if produced from renewable sources. For achieving a successful "hydrogen economy" in the near future, the technical and economic challenges associated with hydrogen must be addressed quickly. Finding feasible solutions to different challenges may take some time but technological breakthrough by way of on-going efforts do promise hydrogen as the ultimate solution for meeting our future energy needs for the transport sector.

Hydrogen: A sustainable fuel for future of the transport sector

A comprehensive review on vibration based micro power generators using electromagnetic and piezoelectric transducer mechanisms

Ambient vibration energy harvesters: A review on nonlinear techniques for performance enhancement

We illustrate electroelastic modeling, analysis and simulation solutions, and experimental validation of hybrid piezoelectric (PE) and electromagnetic (EM) energy harvesting from broadband random vibration. For a more practically available ambient source, the more compact expressions of mean power and spectral density (SD) involving dimensionless parameters are derived when the harvester is subjected to random excitation. In the study, it is assumed that the base excitation is white noise. Then, the effect of acceleration SD, load resistance, coupling strength on harvester performances are analyzed by numerical calculation and simulation, and the results are validated by the experimental measurements. It is founded that, only if the load resistance of PE and EM element meet the impedance matching can the hybrid energy harvester output the maximal mean power and spectral density at the resonant frequency, which increases with PE load resistance increasing, but hardly affected by load resistance of EM element; the variation extent of mean power with SD of acceleration increasing varies with the load resistance, and it is up to the maximum under the condition of optimal load; moreover, the stronger the coupling strength is, the wider the frequency band becomes, and the greater the mean power and power spectral density are, while the increasing extent decreases with the coupling strength increasing. Besides, the coupling strength can affect the internal resistance of harvester. Furthermore, with coupling strength increasing, the decreasing degree of mean power falls when the load resistance is greater than the optimal load.

Modeling and analysis of hybrid piezoelectric and electromagnetic energy harvesting from random vibrations

This paper investigates the influence of the electromechanical coupling effect on the performances of a hybrid piezoelectric and electromagnetic energy harvester. For a common hybrid energy harvester, we derive an accurate analytical solution and get expressions for the resonant frequency shift, output power, amplitude and conversion efficiency. Then, based on various degrees of coupling effect, the performance of the harvester is studied with different load and excitation frequency, and compared with piezoelectric-only and electromagnetic-only energy harvesters. The results show that the bigger the coupling coefficient, the greater the resonant frequency shift, output power and conversion efficiency. In the weak coupling and medium coupling, the performances of the hybrid energy harvester are better than those of the two separate energy harvesting techniques; however, the hybrid energy harvester does not increase the power and conversion efficiency in contrast with the piezoelectric-only and electromagnetic-only energy harvester in strong coupling. In addition, the optimal load resistance of the hybrid energy harvester is related to the strength of the coupling effect; moreover, the optimal load resistance of the electromagnetic harvesting element for the hybrid harvester is bigger than that of the electromagnetic-only harvester in the medium and strong coupling. Through analysis of the results, ways of boosting the performances of the hybrid energy harvester are found.

http://iopscience.iop.org/article/10.1088/0964-1726/23/6/065016/pdf

An analysis of the coupling effect for a hybrid piezoelectric and electromagnetic energy harvester

A nonlinear hybrid piezoelectric (PE) and electromagnetic (EM) energy harvester is proposed, and its working model is established. Then the vibration response, output power, voltage and current of nonlinear hybrid energy harvester subjected to harmonic excitation are derived by the method of harmonic balance, and their normalized forms are obtained by the defined dimensionless parameters. Through numerical simulation and experimental test, the effects of nonlinear factor, load resistance, excitation frequency and the excitation acceleration on amplitude and electrical performances of hybrid energy harvester are studied, which shows that the numerical results are in agreement with that of experimental tests. Furthermore, it can be concluded that the bigger nonlinear factor, the lower resonant frequency; moreover, there is an optimal nonlinear factor that make the harvester output the maximum power. In addition, the output power of nonlinear hybrid energy harvester reaches the maximum at the optimal loads of PE and EM elements, which can be altered by the excitation acceleration. Meanwhile, the resonant frequency corresponding to the maximum power rises firstly and then falls with PE load enhancing, while it rises with EM load decreasing; furthermore, the frequency lowers with the acceleration increasing. Besides, the larger acceleration is, the bigger power output and the wider 3 dB bandwidth are. Compared with performances of linear hybrid energy harvester, the designed nonlinear energy harvester not only can reduce the resonant frequency and enlarger the bandwidth but also improve the output power.

Theoretical analysis and experimental study for nonlinear hybrid piezoelectric and electromagnetic energy harvester

MEMS piezoelectric energy harvester is optimally designed and fabricated, and its vibration characteristics, output voltage, power, power spectral density (SD) and frequency response function under harmonic and random excitation is studied by theory analysis, simulation and experimental test. For the designed MEMS piezoelectric energy harvester, the accurate solutions and expressions of amplitude, voltage, power and power spectral density are derived. Then, vibration characteristic, voltage, power and power SD with different load resistance, sinusoidal acceleration and random acceleration SD are simulated and tested; moreover, frequency response function of MEMS piezoelectric energy harvester is obtained by experimental test, and the results are consistent with theoretical model. When sinusoidal acceleration is 0.6 g, the maximal amplitude of mass is 116 µm and the power density is 0.1 mW/cm 3 . By testing results, output voltage of piezoelectric energy harvester is proportional to the amplitude, and the amplitude at optimal load is smaller than of at open circuit because of the feedback effect of load resistance. In addition, output power SD linearly increases with acceleration SD increasing. When acceleration SD is 5 × 10 −4 (m/s 2 ) 2 /Hz, power SD is 1.24 µW 2 /Hz.

Design, fabrication and performances of MEMS piezoelectric energy harvester

Through establishing the electroelastic model of hybrid piezoelectric(PE) and electromagnetic(EM) energy harvesting from random vibrations, normalized expressions of mean amplitude, voltage, current, power and their spectral density (SD) are derived, and effects of electromechanical coupling strength on harvester’s performances are studied by numerical calculation and experimental test. It is found that the stronger coupling effect, the smaller amplitude and working space required, and the bigger mean voltage, current and power output until up to their maximums. Furthermore, variation extent of mean voltage, current and power with the PE and EM load increasing varies with the coupling strength. Besides, coupling strength changes the SD distributing in frequency domain. In the weak coupling, maximal SD of voltage, current and power are at the natural frequency of harvester. However, with the coupling effect strengthening, the frequency corresponding to peak spectral density is bigger than the natural frequency, and the 3dB bandwidth of harvester is much larger accordingly; moreover, the bandwidth decreases with EM load increasing while it rises firstly and fall later with PE load increasing, which reaches the maximum at the optimal load. The analysis results can provide certain criteria for hybrid piezoelectric-electromagnetic energy harvester design.

Huatong Cai

Papers

Modeling and analysis of hybrid piezoelectric and electromagnetic energy harvesting from random vibrations

An analysis of the coupling effect for a hybrid piezoelectric and electromagnetic energy harvester

Theoretical analysis and experimental study for nonlinear hybrid piezoelectric and electromagnetic energy harvester

Design, fabrication and performances of MEMS piezoelectric energy harvester

Coupling effect analysis for hybrid piezoelectric and electromagnetic energy harvesting from random vibrations