A design method for low-frequency rotational piezoelectric energy harvesting in micro applications

A rotational piezoelectric energy harvester is an electromechanical device that converts ambient mechanical rotation into electric power. The gravity-based method of using the gravity to excite the cantilever beam to deform in the vertical plane has received great attention. The harvester operates effectively at a narrow frequency band, which must be matched with the excitation frequency. For micro applications, low-frequency harvesters are often very difficult to design due to the specific limitations of the size and weight and the thickness of the piezoelectric material. Moreover, low-frequency harvesters require high precision in production and assembly, and small errors can cause large frequency error deviations. In response to this problem, this paper proposes a scheme for designing low-frequency rotational piezoelectric energy harvester, wherein the tuning is accomplished by changing the distance between the mass and the center of rotation. Furthermore, the paper establishes a theoretical model and presents a relationship for frequency adjustment. The experimental results achieved with a piezoelectric fiber composite fit the theoretical results well. The simulation and experimental results show that the resonance frequency of the harvester could be decreased by 63% when the distance between the mass and the center is five times the length of the harvester.

     

Model-based design and test of vibration energy harvester for aircraft application

This paper deals with a development process of a vibration energy harvesting device in aircraft applications. The vibration energy harvester uses ambient energy of mechanical vibration and it provides an autonomous source of energy for wireless sensors or autonomous applications. This application presents a complex engineering problem and the vibration energy harvester consists of precise mechanical part, electro-mechanical converter, electronics and a powered application. It can be perceive as a mechatronic system and a mechatronic approach was used for development of our vibration energy harvester. An essential step of development process is simulation modeling which is based on mechatronic approach. Presented model-based design of vibration energy harvester is very useful during development process and the whole development process of the autonomous energy source is presented in this paper. The main aim of the paper is an introduction of our development methodology and our approach is presented on a sample of the vibration energy harvester for aircraft applications under project ESPOSA.     

Artificial intelligence based optimization for vibration energy harvesting applications

This paper deals with optimization studies based on artificial intelligence methods. These modern optimization methods can be very useful for design improving of an electromagnetic vibration energy harvester. The vibration energy harvester is a complex mechatronic device which harvests electrical energy from ambient mechanical vibrations. The harvester design consists of a precise mechanical resonator, electromagnetic converter and electronics. The optimization study of such complex mechatronic device is complicated however artificial intelligence methods can be used for set up of optimal harvester parameters. Used optimization strategies are applied to optimize the design of the electro-magnetic vibration energy harvester according to multi-objective fitness functions. Optimization results of the harvester are summarized in this paper. Presented optimization algorithms can be used for a design of new energy harvesting systems or for improving on existing energy harvesting systems.     

Comparative study of conventional and magnetically coupled piezoelectric energy harvester to optimize output voltage and bandwidth

Energy harvesting has experienced significant attention from researchers globally. This is due to the quest to power remote sensors and portable devices with power requirements of tens to hundreds of μW. Hence, ambient vibration energy has the potential to provide such power demands. Thus, cantilever beams with piezoelectric materials have been utilized to transduce mechanical energy in vibrating bodies to electrical energy. However, the challenge is to develop energy harvesters that can harvest sufficient amount of energy needed to power wireless sensor nodes at wide frequency bandwidth. In this article, piezoelectric energy harvester (PEH) beams with coupled magnets are proposed to address this issue. With macro fiber composite as the piezoelectric transducer, mathematical models of different system configurations having magnetic couplings are derived based on the continuum based model. Simulations of the system dynamics are done using numerical integration technique in MATLAB software to study the influence of magnetic interactions in generating power and frequency bandwidth due to base excitations at low frequency range. Experimental results comparing conventional system and the proposed piezoelectric beam configurations with coupled magnets are also presented. Finally, the optimal beam separation distance between the magnetic oscillator and PEH is presented in this work.

     

A level set approach for optimal design of smart energy harvesters

The proliferation of Micro-Electro-Mechanical Systems (MEMS), portable electronics and wireless sensing networks has raised the need for a new class of devices with self-powering capabilities. Vibration-based piezoelectric energy harvesters provide a very promising solution, as a result of their capability of converting mechanical energy into electrical energy through the direct piezoelectric effect. However, the identification of fast, accurate methods and rational criteria for the design of piezoelectric energy harvesting devices still poses a challenge. In this work, a level set-based topology optimization approach is proposed to synthesize mechanical energy harvesting devices for self-powered micro systems. The energy harvester design problem is reformulated as a variational problem based on the concept of topology optimization, where the optimal geometry is sought by maximizing the energy conversion efficiency of the device. To ensure computational efficiency, the shape gradient of the energy conversion efficiency is analytically derived using the material time derivative approach and the adjoint variable method. A design velocity field is then constructed using the steepest descent method, which is further integrated into level set methods. The reconciled level set (RLS) method is employed to solve multi-material shape and topology optimization problems, using the Merriman–Bence–Osher (MBO) operator. Designs with both single and multiple materials are presented, which constitute improvements with respect to existing energy harvesting designs.     

Clairvoyance and online scheduling in real-time energy harvesting systems

Real-time energy harvesting systems are designed using a microprocessor, a rechargeable energy storage unit and an energy harvester. The theoretical analysis shows that an optimal solution to the underlying online scheduling problem requires time lookahead which can be incompatible with the common stochastic nature of ambient energy.     

Opportunistic routing in wireless sensor networks powered by ambient energy harvesting

Energy consumption is an important issue in the design of wireless sensor networks (WSNs) which typically rely on portable energy sources like batteries for power. Recent advances in ambient energy harvesting technologies have made it possible for sensor nodes to be powered by ambient energy entirely without the use of batteries. However, since the energy harvesting process is stochastic, exact sleep-and-wakeup schedules cannot be determined in WSNs Powered solely using Ambient Energy Harvesters (WSN–HEAP). Therefore, many existing WSN routing protocols cannot be used in WSN–HEAP. In this paper, we design an opportunistic routing protocol (EHOR) for multi-hop WSN–HEAP. Unlike traditional opportunistic routing protocols like ExOR or MORE, EHOR takes into account energy constraints because nodes have to shut down to recharge once their energy are depleted. Furthermore, since the rate of charging is dependent on environmental factors, the exact identities of nodes that are awake cannot be determined in advance. Therefore, choosing an optimal forwarder is another challenge in EHOR. We use a regioning approach to achieve this goal. Using extensive simulations incorporating experimental results from the characterization of different types of energy harvesters, we evaluate EHOR and the results show that EHOR increases goodput and efficiency compared to traditional opportunistic routing protocols and other non-opportunistic routing protocols suited for WSN–HEAP.     

Power sensitivity of vibration energy harvester

This paper deals with a power sensitivity improvement of an electromagnetic vibration energy harvester which generates electrical energy from ambient vibrations. The harvester provides an autonomous source of energy for wireless applications, with an expected power consumption of several mW, placed in environment excited by ambient mechanical vibrations. An appropriately tuned up design of the harvester with adequate sensitivity provides sufficient generating of electrical energy for some wireless applications and maximal harvested power depends on a harvester mass, frequency and level of the vibration and sensitivity of the energy harvester. The design of our harvester is based on electromagnetic converter and it contains a unique spring-less resonance mechanism where stiffness is provided by repelled magnetic forces. The greater sensitivity of the harvester provides more generated power or decrease of the harvester size and weight.     

Surface integrity and size dependent modeling and performance of non-uniform flexoelectric energy harvesters

Piezoelectric energy harvesters have recently been the focus of several researchers over several years due to their effectiveness at submicron scales by including the flexoelectric effect. Though the size-dependency of the flexoelectric effect had been examined at nanoscales, the size dependent effects of the material structure had been neglected; these nanoscale models do not accurately represent models at the nanoscale. A robust reduced-order model is introduced in this study that incorporates material structure size-dependency through the couple stress theory, the effects of the surface profile by examining the average roughness and slope of roughness and the impacts of the surface stress through the Gurtin–Murdoch surface elasticity theory on a non-uniform cantilever beam energy harvester. Couple stress considerations greatly impact all examined systems, harden the system, and increase the power bandwidth whereas surface roughness influences the expected harvestable power and optimal loading of the system, by reducing expected power output. This analysis shows the importance of considering the size dependent effects on the performance of flexoelectric energy harvesters in nanoscale.

     

High efficiency,wide load bandwidth piezoelectric energy scavenging by a hybrid nonlinear approach

Energy harvesting from ambient energy sources and particularly vibrations have been of significant interest over the last decades for powering consumer electronics. However, vibration energy harvesters that use the piezoelectric effect feature limited output power and load dependency. The purpose of this paper is to present a hybrid technique that consists of combining two nonlinear techniques for enhancing the conversion abilities while providing a relative load independency. Although the proposed scheme relies on the use of two existing approaches, it will be shown that the operation of the overall system is different from the behavior of the two techniques taken separately, allowing four energy extraction cycles per vibration period. Theoretical analysis validated through experimental results indicates that the proposed scheme allows harvesting up to 6 times more energy while having a relative independency from the load connected to the harvester.     

Wideband auto-tunable vibration energy harvester using change in centre of gravity

Microsystem Technologies - Energy harvesters are preferred for enhancing the life of IoT nodes. In this paper, a vibration energy harvester with wideband auto-tunable resonant frequency for...     

带质量块的微型压电式风能采集器研究

基于风致振动机理的微型风能采集器可以将风能转换为电能,在无线传感等领域具有广阔应用前景.漩涡脱落频率与风速成正比,当漩涡脱落频率与微型风能采集器固有频率接近时,采集器有较高输出功率,因此为了在低风速环境应用风能采集器,需要降低其固有频率.引入质量块可以降低微型压电式风能采集器的固有频率,使其在较低风速下产生较高输出功率...     

Battery-and wire-less tire pressure measurement systems (TPMS) sensor

This paper focuses on the design and development of a tire pressure measurement systems (TPMS) sensor powered by on-the-go piezoelectric energy harvesting. The prime research motivation was to achieve replacement of a limited capacity power source such as a battery with an on-the-go power generation method in order to enhance TPMS lifespan and simplify the design, with the former having greater priority. Very low cost and highly flexible piezoceramic (PZT) bender elements are used to generate power inside the automobile wheel assembly thereby replacing the battery and eliminating the need for a motion sensing mechanism and/or circuitry since PZT harvesters only produce power during wheel rotation. A fully operational sensor configuration which proves the feasibility of PZT based energy harvesting as a substitute for a permanent power source is discussed in detail.     

Fabrication of aluminium doped zinc oxide piezoelectric thin film on a silicon substrate for piezoelectric MEMS energy harvesters

Thin film piezoelectric materials play an essential role in micro electro mechanical system (MEMS) energy harvesting due to its low power requirement and high available energy densities. Non-ferroelectric piezoelectric materials such as ZnO and AlN are highly silicon compatible making it suitable for MEMS energy harvesters in self-powered microsystems. This work primarily describe the design, simulation and fabrication of aluminium doped zinc oxide (AZO) cantilever beam deposited on <100> silicon substrate. AZO was chosen due its high piezoelectric coupling coefficient, ease of deposition and excellent bonding with silicon substrate. Doping of ZnO with Al has improved the electrical properties, conductivity and thermal stability. The proposed design operates in transversal mode (d ₃₁ mode) which was structured as a parallel plated capacitor using Si/Al/AZO/Al layers. The highlight of this work is the successful design and fabrication of Al/AZO/Al on <100> silicon as the substrate to make the device CMOS compatible for electronic functionality integration. Design and finite element modeling was conducted using COMSOL? software to estimate the resonance frequency. RF Magnetron sputtering was chosen as the deposition method for aluminium and AZO. Material characterization was performed using X-ray diffraction and field emission scanning electron microscopy to evaluate the piezoelectric qualities, surface morphology and the cross section. The fabricated energy harvester generated 1.61?V open circuit output voltage at 7.77?MHz resonance frequency. The experimental results agreed with the simulation results. The measured output voltage is sufficient for low power wireless sensor nodes as an alternative power sources to traditional chemical batteries.     

RF energy harvesting systems: An overview and design issues

One of the main challenges in implementing sensor devices for internet of things (IoTs), is the means for the operating power supply. RF energy harvesting (RFEH) presents a promising solution as RF power is a suitable choice particularly for cases where solar harvesting is not feasible. However, in spite of RF communication system design being a well‐established, there are several challenges poised for the implementation of the RFEH systems especially for harvesting the ambient RF signals. The challenges can be widely categorized as the overall conversion efficiency, bandwidth, and form factor. In this article, an exhaustive survey on the different RFEH system that is reported is carried out and discussed. Important design issues are identified with insights drawn. First, we have presented the challenges in designing antennas for RFEH systems. This is followed by rectifier circuits and matching networks, and eventually a general frame work for designing of ambient RFEH systems is deduced.     

Micro harvester using isotropic charging of electrets deposited on vertical sidewalls for conversion of 3D vibrational energy

The design and fabrication process of an integrated micro energy harvester capable of harvesting electrical energy from low amplitude mechanical vibrations is presented. A specific feature of the presented energy harvester design is its capability to harvest vibrational energy from different directions (3D). This is done through an innovative approach of electrets placed on vertical sidewalls, allowing miniaturization of 3D capacitive energy harvester fabrication on monolithic CMOS substrates. A new simple electret charging method using ionic hair-dryers is used. The charging performance of SiO₂ and CYTOP electrets are characterized for electrets in horizontal arrangement and electrets deposited on vertical sidewalls.     

Simulation of maximum power in the wearable thermoelectric generator with a small thermopile

Miniature thermopiles that could be fabricated by using modern thin- and thick-film technologies are discussed as a power supply to wearable devices. The maximum power that can be produced by a thermopile of a medium-to-small size was simulated in case of typical thermal properties of humans and their living environment. The local thermal resistances of human being required for the simulation were obtained experimentally. The designs of wearable thermoelectric generators are discussed. The general design optimization of wearable thermoelectric energy harvester with a miniature thermopile was performed in case of near-maximum power generated per unit volume of thermoelectric generator. The obtained performance characteristics allow prediction of the application area for wearable energy harvesters of human body heat and the perspectives of their market success.     

Modeling the performance of a micromachined piezoelectric energy harvester

Piezoelectric energy microgenerators are devices that generate continuously electricity when they are subjected to varying mechanical strain due to e.g. ambient vibrations. This paper presents the mathematical analysis, modelling and validation of a miniaturized piezoelectric energy harvester based on ambient random vibrations. Aluminium nitride as piezoelectric material is arranged between two electrodes. The device design includes a silicon cantilever on which AlN film is deposited and which features a seismic mass at the end of the cantilever. Euler–Bernoulli energy approach and Hamilton’s principle are applied for device modeling and analysis of the operation of the device at various acceleration values. The model shows good agreement with the experimental findings, thus giving confidence into model. Both mechanical and electrical characteristics are considered and compared with the experimental data, and good agreement is obtained. The developed analytical model can be applied for the design of piezoelectric microgenerators with enhanced performance.