Relevant Publications
This page contains a range of publications (journal articles, conference papers and book chapters) relevant to the field of energy harvesting.The EH Network resources have been contributed by members. If you are a member, please contribute.
Devices
Dr. Nina Roscoe, Dr Martin Judd, Leigh Fraser (National Grid), (2010) A Novel Inductive Electromagnetic Energy Harvester for Condition Monitoring Sensors. In: Proc. 3rd Int. Conf. on Condition Monitoring and Diagnosis (CMD2010), August 2010, Tokyo, Japan.Abstract: As the operation of electrical power networks becomes increasingly sophisticated, the role of condition monitoring is expanding. The burden of implementing additional condition monitoring will be eased if self-powered, fully autonomous sensors can be used to reduce installation and maintenance costs. Changing batteries is inconvenient and standard mains power is often not available where sensors are needed. Existing commercial inductive harvesters to power sensors must be fitted around high voltage transmission lines, which requires either a power outage or live line installation. In this paper, an alternative harvester is presented which can be installed at any location where there is sufficient magnetic field. Magnetic flux densities within a cable tunnel are considered, from which a suitable target is defined for the magnetic flux density range over which the harvester must provide power to the sensor. Optimisation of output power per unit volume limits cost and allows placement of sensors in locations with restricted space. Coil parameters to achieve high output power per unit volume are discussed and experimental results are presented that demonstrate effective energy harvesting. A coil design for a typical cable tunnel is proposed.
Meiling Zhu, Emma Worthington , Ashutosh Tiwari , (2010) Design Study of Piezoelectric Energy Harvesting Devices for Generation of a Higher Electrical Power Using a Coupled Piezoelectric-Circuit Finite Element Method. In: IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, vol. 57, no.2, 427-437.
Abstract: This paper presents a design study on the geometric parameters of a cantilever-based piezoelectric energy harvesting devices (EHD), which harvests energy from motion (vibration), for the purpose of scavenging more energy from ambient vibration energy sources. The design study is based on the coupled piezoelectric-circuit finite element method (CPC-FEM), previously presented by Dr. Zhu. This model is used in the paper to obtain the following simulation results for variations in geometric parameters such as the beam length, width and thickness, and the mass length, width and height: (1) the current flowing through and the voltage developed across the load resistor, (2) the power dissipated by the resistor and the corresponding vibrational displacement amplitude, and (3) resonant frequency. By studying these results, straightforward design strategies that enable the generation of more power are obtained for each geometric parameter, and a physical understanding of how each parameter affects the output power is given. It is suggested that, in designing with the aim of generating more power, the following strategies be used: (1) for the beam, a shorter length, larger width and lower ratio of piezoelectric layer thickness to total beam thickness are preferred in the case of a fixed mass. (2) for the mass, a shortened mass length and a higher mass height are preferred in the case of variation in the mass length and the mass height with mass width and mass value remain fixed, and a wider width and small mass height are preferred in the case of variation in mass width and height (mass length and value remain fixed, and (3) for the case of a fixed total length, a shorter beam length and longer mass length are preferred. With the design strategies, output powers from the device can reach above 1-2mW/cm3, much higher than the 200micro-W/cm3 currently achieved in the published literature. This is an encouraging prospect for enabling a wider range of applications of the EHDs.
Mike Friswell, Sondipon Adhikari, (2010) Sensor shape design for piezoelectric cantilever beams to harvest vibration energy. In: Journal of Applied Physics, 108[1], pp. 014901:1-6.
Abstract: Energy harvesting for the purpose of powering low power electronic sensor systems has received explosive attention in the last few years. A common device uses the piezoelectric effect for a cantilever beams at resonance to harvest ambient vibration energy. However most of these devices have a rectangular piezoelectric patch covering all or part of the beam. This paper considers the optimum design of such a device, and in particular investigates the effect that the size and shape of piezoelectric sensor has on the harvested energy. It is shown that significant increases in harvested energy may be obtained by optimising the sensor design
Ivo N Ayala-Garcia, Dibin Zhu, Steve Beeby, M J Tudor, (2010) Tunable kinetic energy harvester with dynamic over range protection. In: Smart Materials and Structures, vol 19, 115005.
Abstract: This paper describes the development and implementation of a self-powered control system that autonomously adapts the resonant frequency of an electromagnetic vibration-based energy harvester to ambient vibration frequency. The tuning mechanism adjusts the harvester's spring stiffness by varying the axial tensile force between two permanent magnets. The system adjusts the resonant frequency of the harvester from 64 to 78 Hz, increasing the operational bandwidth of the harvester from 0.26 to 14 Hz, using a single structure. The same tuning principle is also applied to protect the harvester from over range acceleration which could cause physical damage to its structure. The closed loop control uses the phase difference between the harvester output signal and ambient vibration, measured by an accelerometer attached to the vibration source, to adjust the tuning mechanism.
A Cammarano, Dr Steve Burrow, D Barton, A Carrella, L Clare, (2010) Tuning a resonant energy harvester using a generalized electrical load. In: Journal of smart materials and structures, vol. 19, 055003, March 2010, DOI: 10.1088/0964-1726/19/5/055003.
Abstract: A fundamental drawback of vibration-based energy harvesters is that they
typically feature a resonant mass/spring mechanical system to amplify the
small source vibrations; the limited bandwidth of the mechanical amplifier
restricts the effectiveness of the energy harvester considerably. By
extending the range of input frequencies over which a vibration energy
harvester can generate useful power, e.g.\ through adaptive tuning, it is
not only possible to open up a wider range of applications, such as those
where the source frequency changes over time, but it is also possible to
relax the requirements for precision manufacture or the need for
mechanical adjustment in~situ. In this paper, a vibration-based energy
harvester connected to a generalised electrical load (containing both real
and reactive impedance) is presented. It is demonstrated that the reactive
component of the electrical load can be used to tune the
harvester system to significantly increase the output power away from the
resonant peak of the device. An analytical model of the system is
developed, which includes non-ideal components arising from the physical
implementation, and the results are confirmed by experiment. The -3dB
(half-power) bandwidth of the prototype energy harvester is shown to be
over three times greater when presented with an optimised load
impedance compared to the same harvester presented with an optimised
resistive-only load.
typically feature a resonant mass/spring mechanical system to amplify the
small source vibrations; the limited bandwidth of the mechanical amplifier
restricts the effectiveness of the energy harvester considerably. By
extending the range of input frequencies over which a vibration energy
harvester can generate useful power, e.g.\ through adaptive tuning, it is
not only possible to open up a wider range of applications, such as those
where the source frequency changes over time, but it is also possible to
relax the requirements for precision manufacture or the need for
mechanical adjustment in~situ. In this paper, a vibration-based energy
harvester connected to a generalised electrical load (containing both real
and reactive impedance) is presented. It is demonstrated that the reactive
component of the electrical load can be used to tune the
harvester system to significantly increase the output power away from the
resonant peak of the device. An analytical model of the system is
developed, which includes non-ideal components arising from the physical
implementation, and the results are confirmed by experiment. The -3dB
(half-power) bandwidth of the prototype energy harvester is shown to be
over three times greater when presented with an optimised load
impedance compared to the same harvester presented with an optimised
resistive-only load.
D Barton, Dr Steve Burrow, L Clare, (2010) Energy harvesting from vibrations with a nonlinear oscillator. In: Journal of Vibrations and Acoustics, 132, 021009, 2010, DOI:10.1115/1.4000809.
Abstract: In this paper we present a nonlinear electromagnetic energy
harvesting device that has a broadly resonant response. The
nonlinearity is generated by a particular arrangement of magnets
in conjunction with an iron-cored stator. We show the resonant
response of the system to both pure-tone excitation and
narrow-band random excitation. In addition to the primary resonance,
the super-harmonic resonances of the harvester are also
investigated and we show that the corresponding mechanical upconversion
of the excitation frequency may be useful for energy
harvesting. The harvester is modeled using a Duffing-type equation
and the results compared to the experimental data.
harvesting device that has a broadly resonant response. The
nonlinearity is generated by a particular arrangement of magnets
in conjunction with an iron-cored stator. We show the resonant
response of the system to both pure-tone excitation and
narrow-band random excitation. In addition to the primary resonance,
the super-harmonic resonances of the harvester are also
investigated and we show that the corresponding mechanical upconversion
of the excitation frequency may be useful for energy
harvesting. The harvester is modeled using a Duffing-type equation
and the results compared to the experimental data.
Dibin Zhu, Steve Roberts, Michael John Tudor, Steve Beeby, (2010) Design and experimental characterization of a tunable vibration-based electromagnetic micro-generator. In: Sensors and Actuators A: Physical, 158 (2). pp. 284-293.
Abstract: Vibration-based micro-generators, as an alternative source of energy, have become increasingly significant in the last decade. This paper presents a new tunable electromagnetic vibration-based micro-generator. Frequency tuning is realized by applying an axial tensile force to the micro-generator. The dimensions of the generator, especially the dimensions of the coil and the air gap between magnets, have been optimized to maximize the output voltage and power of the micro-generator. The resonant frequency has been successfully tuned from 67.6 to 98 Hz when various axial tensile forces were applied to the structure. The generator produced a power of 61.6-156.6uW over the tuning range when excited at vibrations of 0.59ms^2. The tuning mechanism has little effect on the total damping. When the tuning force applied on the generator becomes larger than the generator's inertial force, the total damping increases resulting in reduced output power. The resonant frequency increases less than indicated from simulation and approaches that of a straight tensioned cable when the force associated with the tension in the beam becomes much greater than the beam stiffness. The test results agree with the theoretical analysis presented.
Dibin Zhu , Michael John Tudor, Steve Beeby, (2010) Strategies for increasing the operating frequency range of vibration energy harvesters: a review. In: Measurement Science and Technology, Vol. 21 022001.
Abstract: This review presents 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, nonlinear (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 review 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.
Dr. Nina Roscoe, Dr Martin Judd, John Fitch (National Grid), (2009) Development of magnetic induction energy harvesting for condition monitoring. In: Proc. 44th Int. Universities Power Engineering Conference (UPEC 2009), Glasgow, UK, September 2009.
Abstract: Condition monitoring can play an important supporting role in the supply of electrical power. Autonomous wireless condition monitoring sensors have the potential to ensure reliability, at lower cost, as the power supply system complexity increases. This paper explores the practical issues surrounding the use of magnetic induction to power sensors, from which design drivers are developed. The relationship between available output power and energy harvester volume is analysed and verified by experiment. The impact of core shape and core material choice is demonstrated by the results, and a design approach is presented to benchmark and optimise volume efficiency. These results are used to show how the harvester could be scaled to suit different combinations of conductor current and output power.
Meiling Zhu, Emma Worthington , (2009) Design and Testing of Piezoelectric Energy Harvesting Devices for Generation of Higher Electric Power for Wireless Sensor Networks. In: Proceeding IEEE Sensors 2009, Chrischurch, New Zealand, 25-28 Oct., 2009, pp.699-702.
Abstract: This paper reports our design and testing results on the electric output performance of a vibration-based piezoelectric energy harvesting device (PEHD). The PEHD is a cantilever with a sandwich structure and seismic mass attached to the tip. The geometric parameters of the device are based on optimization design with a volume of around 1cm3 and at a targeted resonant frequency of 80-100 Hz. A maximum output power of 370�¼W at 15.5 volts into a 325k�© resistive load is generated at the resonant frequency of 87Hz and under an acceleration of 0.23g. Quite remarkably, this power is a very encouraging power figure that gives the prospect of being able to power a wider range of applications than is currently possible in wireless sensor network.
Dr. Kok Swee Leong (Stephen), Neil White, Nick Harris, (2009) Fabrication and characterisation of free-standing thick-film piezoelectric cantilevers for energy harvesting.. In: Measurement Science and Technology, Volume 20, Number 12 .
Abstract: Research into energy harvesting from ambient vibration sources has attracted great interest over the last few years, largely as a result of advances in the areas of wireless technology and low-power electronics. One of the mechanisms for converting mechanical vibration to electrical energy is the use of piezoelectric materials, typically operating as a cantilever in a bending mode, which generate a voltage across the electrodes when they are stressed. Typically, the piezoelectric materials are deposited on a non-electro-active substrate and are physically clamped at one end to a rigid base. The presence of the substrate does not contribute directly to the electrical output, but merely serves as a mechanical supporting platform, which can pose difficulties for integration with other microelectronic devices. The aim of this paper is to describe a novel thick-film free-standing cantilever structure that does not use a supporting platform and has the advantage of minimizing the movement constraints on the piezoelectric material, thereby maximizing the electrical output power. Two configurations of the composite cantilever structure were investigated: unimorph and multimorph. A unimorph consists of a pair of silver/palladium (Ag/Pd) electrodes sandwiching a laminar layer of lead zirconate titanate (PZT). A mulitmorph is an extended version of the unimorph with two pairs of Ag/Pd electrodes and three laminar sections of PZT.
Shaofan Qi, Roger Shuttleworth, S. Olutunde Oyadiji, (2009) Multiple Resonances Piezoelectric Energy Harvesting Generator. In: ASME 2009 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2009) , September 21-23, 2009 , Oxnard, California, USA.
Abstract: Energy harvesting is the process of converting low level ambient energy into usable electrical energy, so that remote electronic instruments can be powered without the need for batteries or other supplies. Piezoelectric material has the ability to convert mechanical energy into electrical energy, and cantilever type harvesters using this material are being intensely investigated. The typical single cantilever energy harvester design has a limited bandwidth, and is restricted in ability for converting environmental vibration occurring over a wide range of frequencies. A multiple cantilever piezoelectric generator that works over a range of frequencies, yet has only one Piezo element, is being investigated. The design and testing of this novel harvester is described.
Zijing Wong, Jize Yan, Kenichi Soga, Ashwin A. Seshia, (2009) A multi-degree-of-freedom electrostatic MEMS power harvester. In: the 9th international workshop on micro and nanotechnology for power generation and energy conversion applications (Power MEMS 2009), Dec 1-4, 2009, Washington DC, USA, pp. 300-303.
Abstract: This paper reports the design, modeling and experimental characterization of a multi-degree-of-freedom electrostatic vibration energy harvester. The potential of harvesting vibrational energy at multiple input frequencies and achieving displacement amplification in the response is investigated. To better understand the device performance at a system level, a numerical model which incorporates mechanical and electrical analysis in a charge constrained conversion circuit is developed. Experimental results on a microfabricated prototype demonstrate a maximum measured output power of 0.076 �¼W at 1.4 kHz for an external load of 5.1 M�©. We also experimentally demonstrate that the output power varies with the square of input acceleration and DC bias voltage.
Dr Steve Burrow, L clare, (2009) Open-loop power conditioning for vibration energy harvesting. In: Electronics Letters, Vol.45, Issue 19, pp999-1000. September 2009.
Abstract: Energy harvesters feature a high impedance output that complicates subsequent power conditioning because operation in the peak power region violates the stability criterion for converters with voltage regulation. By using a flyback converter in open-loop discontinuous mode and a shunt voltage regulator it is demonstrated that a harvester can be operated in an optimal manner whilst ensuring stability. A circuit is described that draws unity power factor from the harvester, provides output voltage regulation and consumes 180μW of quiescent power.
Alex Weddell, Dr Neil Grabham, Nick Harris, Neil White, (2009) Modular Plug-and-Play Power Resources for Energy-Aware Wireless Sensor Nodes. In: Sixth Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks - SECON 2009, 22-26 June 2009, Rome, Italy.
Abstract: Wireless sensors are normally powered by non-rechargeable batteries, but these must be replaced when depleted. Recent developments in energy harvesting technology allow sensors to be powered by environmental energy where it is present, but the wide range of situations where sensors are deployed means that it is desirable for the energy components of a sensor node (i.e. batteries, supercapacitors, and power generation devices) to be selected and configured at the time of node deployment. Previous energy harvesting-powered systems have been designed for specific energy hardware and been difficult to adapt for different resources. Energy-awareness is useful for state-of-the-art network algorithms, but present systems do not provide a standardized or straightforward way for nodes to monitor and manage their energy hardware.
The developments reported in this paper deliver a reconfigurable energy subsystem for wireless autonomous sensors. The new system permits energy modules to be selected and fitted to the sensor node in-situ, in a plug-and-play manner, without the need for reprogramming or the modification of hardware. The node can monitor and intelligently manage its energy resources and assess its overall energy status by analyzing its level of stored energy and rate of power generation. These activities are facilitated by a proposed common hardware interface (which allows multiple energy modules to be connected) and an electronic datasheet structure for the energy modules. The system has been verified through the development and testing of a prototype wireless sensor node which operates from a mix of energy sources.
The developments reported in this paper deliver a reconfigurable energy subsystem for wireless autonomous sensors. The new system permits energy modules to be selected and fitted to the sensor node in-situ, in a plug-and-play manner, without the need for reprogramming or the modification of hardware. The node can monitor and intelligently manage its energy resources and assess its overall energy status by analyzing its level of stored energy and rate of power generation. These activities are facilitated by a proposed common hardware interface (which allows multiple energy modules to be connected) and an electronic datasheet structure for the energy modules. The system has been verified through the development and testing of a prototype wireless sensor node which operates from a mix of energy sources.
Dr. Kok Swee Leong (Stephen), Neil White, Nick Harris, (2008) Free-standing thick-film piezoelectric device. In: Electronics Letters , Volume 44, Issue 4 .
Abstract: A free-standing thick-film cantilever sensor structure is presented. Such
devices find use in applications such as vibration detection or energy
harvesting. The structure was fabricated by screen printing layers of
lead zirconate titanate between silver/palladium electrodes and cofiring
the layers together with a carbon sacrificial layer (deposited
underneath) in an air environment at a temperature of 850 C. The
free-standing structure, of dimensions 18 mm long by 9 mm wide
and thickness of 50 mm, was found to produce electrical powers of
up to 95 nW at an acceleration level of 9.81 m/s2 (1 g), when driving
a 60 kOhm load resistance.
devices find use in applications such as vibration detection or energy
harvesting. The structure was fabricated by screen printing layers of
lead zirconate titanate between silver/palladium electrodes and cofiring
the layers together with a carbon sacrificial layer (deposited
underneath) in an air environment at a temperature of 850 C. The
free-standing structure, of dimensions 18 mm long by 9 mm wide
and thickness of 50 mm, was found to produce electrical powers of
up to 95 nW at an acceleration level of 9.81 m/s2 (1 g), when driving
a 60 kOhm load resistance.
M. T. Penella-López, Manel Gasulla, (2007) A review of commercial energy harvesters for autonomous sensors. In: Proceedings IMTC 2007, Warsaw, Poland, May 1-3, 2007.
Abstract: Current commercial autonomous sensors are mainly powered by primary batteries. Batteries need to be replaced and hence can become the largest and most expensive part of the system. On the other hand, our environment is full of waste and unused energy such as that coming from the sun or mechanical vibrations. As a result, commercial energy harvesters are increasingly available to power autonomous sensors. This work presents and analyses commercial energy harvesters currently available. First, environmental energy sources are classified and described. Then, energy harvesting principles are described and some guidelines are given to calculate the maximum power consumption allowed and the energy storage capacity required for the autonomous sensor. Finally, commercial energy harvesters are evaluated to determine their capability to power a commercial autonomous sensor in some given circumstances.
Applications
Alex Weddell, Geoff Merrett, Bashir Al-Hashimi, (2011) Photovoltaic Sample-and-Hold Circuit Enabling MPPT Indoors for Low-Power Systems. In: IEEE Transactions on Circuits and Systems I: Regular Papers, (in press).Abstract: Photovoltaic (PV) energy harvesting is commonly used to power autonomous devices, and maximum power point tracking (MPPT) is often used to optimize its efficiency. This paper describes an ultra low-power MPPT circuit with a novel sample-and-hold and cold-start arrangement, enabling MPPT across the range of light intensities found indoors, which has not been reported before. The circuit has been validated in practice and found to cold-start and operate from 100 lux (typical of dim indoor lighting) up to 5000 lux with a 55cm2 amorphous silicon PV module. It is more efficient than non-MPPT circuits, which are the state-of-the-art for indoor PV systems. The proposed circuit maximizes the active time of the PV module by carrying out samples only once per minute. The MPPT control arrangement draws a quiescent current draw of only 8uA, and does not require an additional light sensor as has been required by previously-reported low-power MPPT circuits.
Dr Carol Featherston, Karen Holford, Greg Waring (Cardiff University), (2009) Thermoelectric Energy Harvesting for Wireless Sensor Systems in Aircraft. In: Key Engineering Materials, 413-414, 487-494 .
Abstract: The use of structural health monitoring in the aerospace industry has many benefits including improved safety, reduced maintenance and extended aircraft lifecycles. A major focus of current research in this area is the development of wireless sensor 'nodes' which rely on batteries as a power source, severely limiting the product lifespan. This paper presents the results of work carried out to examine the feasibility of replacing or supplementing existing battery power supplies using thermoelectric energy conversion from ambient temperature differences in aircraft. An average power demand of 1mW over a typical sensor duty cycle is identified for current wireless sensor hardware. Temperature differentials between the wing fuel tanks and external air are determined and a theoretical model for thermoelectric energy harvesting potential is developed. Results indicate that average power outputs sufficient for the intended application of 6.6-22mW could be achieved during flight, based on a commercially available thermoelectric module of 30x30x4.1mm. An experimental investigation of the performance of this module when subjected to appropriate temperature conditions, using a Ranque-Hilshe vortex tube to generate easily controlled temperatures to -25C is described. Excellent consistency is demonstrated between theoretical predictions and experimental results, confirming the accuracy of the theoretical model.
M. T. Penella-López, J. Albesa, Manel Gasulla, (2009) Powering wireless sensor nodes: primary batteries versus energy harvesting. In: Proceedings IMTC 2009, Singapore, 5-7 May 2009, pp. 1625-1630.
Abstract: Wireless sensor networks (WSNs) are increasingly used in many fields. Still, power supply of the nodes remains a challenge. Primary batteries are mainly used but energy harvesting offers an alternative, although not free of problems. This paper compares the use of primary batteries against solar cells. Basic principles are first enunciated, then generic design examples are presented and finally actual deployed nodes of a WSN are illustrated.
Alex Weddell, Geoff Merrett, Nick Harris, Bashir Al-Hashimi, (2008) Energy Harvesting and Management for Wireless Autonomous Sensors. In: Measurement + Control, 41 (4). pp. 104-108. ISSN 0020-2940.
Abstract: Wireless autonomous sensors that harvest ambient energy are attractive solutions, due to their convenience and economic benefits. A number of wireless autonomous sensor platforms which consume less than 100uW under duty-cycled operation are available. Energy harvesting technology (including photovoltaics, vibration harvesters, and thermoelectrics) can be used to power autonomous sensors. A developed system is presented that uses a photovoltaic module to efficiently charge a supercapacitor, which in turn provides energy to a microcontroller-based autonomous sensing platform. The embedded software on the node is structured around a framework in which equal precedent is given to each aspect of the sensor node through the inclusion of distinct software stacks for energy management and sensor processing. This promotes structured and modular design, allowing for efficient code reuse and encourages the standardisation of interchangeable protocols.
Modelling and Simulating
A. Abdelkefi, Fehmi NAJAR, A. H. Nayfeh, S Ben Ayed, (2011) An energy harvester using piezoelectric cantilever beams undergoing coupled bending-torsion vibrations. In: Smart Materials and Structures, vol. 20, p. 115007.Abstract: Recently, piezoelectric cantilevered beams have received considerable attention for vibration-to-electric energy conversion. Generally, researchers have investigated a classical piezoelectric cantilever beam with or without a tip mass. In this paper, we propose the use of a unimorph cantilever beam undergoing bending-torsion vibrations as a new piezoelectric energy harvester. The proposed design consists of a single piezoelectric layer and a couple of asymmetric tip masses; the latter convert part of the base excitation force into a torsion moment. This structure can be tuned to be a broader band energy harvester by adjusting the first two global natural frequencies to be relatively close to each other. We develop a distributed-parameter model of the harvester by using the Euler-beam theory and Hamilton's principle, thereby obtaining the governing equations of motion and associated boundary conditions. Then, we calculate the exact eigenvalues and associated mode shapes and validate them with a finite element (FE) model. We use these mode shapes in a Galerkin procedure to develop a reduced-order model of the harvester, which we use in turn to obtain closed-form expressions for the displacement, twisting angle, voltage output, and harvested electrical power. These expressions are used to conduct a parametric study for the dynamics of the system to determine the appropriate set of geometric properties that maximizes the harvested electrical power. The results show that, as the asymmetry is increased, the harvester's performance improves. We found a 30% increase in the harvested power with this design compared to the case of beams undergoing bending only. We also show that the locations of the two masses can be chosen to bring the lowest two global natural frequencies closer to each other, thereby allowing the harvesting of electrical power from multi-frequency excitations.
Alex Weddell, Geoff Merrett, Tom Kazmierski, Bashir Al-Hashimi, (2011) Accurate Supercapacitor Modeling for Energy-Harvesting Wireless Sensor Nodes. In: IEEE Transactions on Circuits and Systems II: Express Briefs, (in press).
Abstract: Supercapacitors are often used in energy-harvesting wireless sensor nodes (EH-WSNs) to store harvested energy. Until now, research into the use of supercapacitors in EH-WSNs has considered them to be ideal or over-simplified, with non-ideal behavior attributed to substantial leakage currents. In this brief, we show that observations previously attributed to leakage are predominantly due to redistribution of charge inside the supercapacitor. We confirm this hypothesis through the development of a circuit-based model which accurately represents non-ideal behavior. The model correlates well with practical validations representing the operation of an EH-WSN, and allows behavior to be simulated over long periods.
Maria Gorlatova, Aya Wallwater, Gil Zussman, (2011) Networking Low Power Energy Harvesting Devices: Measurements and Algorithms. In: IEEE INFOCOM'11, Shanghai, China, April 2011.
Abstract: Recent advances in energy harvesting materials and ultra-low-power communications will soon enable the realization of networks composed of energy harvesting devices. These devices will operate using very low ambient energy, such as indoor light energy. We focus on characterizing the energy availability in indoor environments and on developing energy allocation algorithms for energy harvesting devices. First, we present results of our long-term indoor radiant energy measurements, which provide important inputs required for algorithm and system design (e.g., determining the required battery sizes). Then, we focus on algorithm development, which requires nontraditional approaches, since energy harvesting shifts the nature of energy-aware protocols from minimizing energy expenditure to optimizing it. Moreover, in many cases, different energy storage types (rechargeable battery and a capacitor) require different algorithms. We develop algorithms for determining time fair energy allocation in systems with predictable energy inputs, as well as in systems where energy inputs are stochastic.
Michele Pozzi, Meiling Zhu, (2011) Plucked piezoelectric bimorphs for knee-joint energy harvesting: modelling and experimental validation. In: Smart Mater. Struct., (20) 055007.
Abstract: The modern drive towards mobility and wireless devices is motivating intensive research in energy harvesting technologies. To reduce the battery burden on people, we propose the adoption of a frequency up-conversion strategy for a new piezoelectric wearable energy harvester. Frequency up-conversion increases efficiency because the piezoelectric devices are permitted to vibrate at resonance even if the input excitation occurs at much lower frequency. Mechanical plucking-based frequency up-conversion is obtained by deflecting the piezoelectric bimorph via a plectrum, then rapidly releasing it so that it can vibrate unhindered; during the following oscillatory cycles, part of the mechanical energy is converted into electrical energy. In order to guide the design of such a harvester, we have modelled with finite element methods the response and power generation of a piezoelectric bimorph while it is plucked. The model permits the analysis of the effects of the speed of deflection as well as the prediction of the energy produced and its dependence on the electrical load. An experimental rig has been set up to observe the response of the bimorph in the harvester. A PZT-5H bimorph was used for the experiments. Measurements of tip velocity, voltage output and energy dissipated across a resistor are reported. Comparisons of the experimental results with the model predictions are very successful and prove the validity of the model.
G. Litak, Mike Friswell, Sondipon Adhikari, (2010) Magnetopiezoelastic energy harvesting driven by random excitations. In: Applied Physics Letters, 96[5], pp. 214103:1-3.
Abstract: This letter considers a nonlinear piezomagnetoelastic energy harvester driven by stationary Gaussian white noise. The increase in the energy generated by this device has been demonstrated for harmonic excitation with slowly varying frequency in simulation and validated by experiment. This paper considers the simulated response of this validated model to random base excitation and shows that the system exhibits a stochastic resonance. If the variance of the excitation were known then the device may be optimized to maximize the power harvested, even under random excitation
Shaikh Faruque Ali, Sondipon Adhikari, Mike Friswell, (2010) Piezoelectric energy harvesting with parametric uncertainty. In: Smart Materials & Structure, IOP, 19 (2010) 105010 (9pp) .
Abstract: The design and analysis of energy harvesting devices is becoming increasing important in recent years. Most of the literature has focused on the deterministic analysis of these systems and problem of uncertain parameters has received less attention. Energy harvesting devices exhibit parametric uncertainty due to errors in measurement, errors in modeling and variability in the parameters during manufacture. This paper investigates the effect of parametric uncertainty in the mechanical system on the harvested power, and derives approximate explicit formulae for the optimal electrical parameters that maximise the mean harvested power. The maximum of the mean harvested power decreases with increasing uncertainty, and the optimal frequency at which the maximum mean power occurs shifts. The effect of the parameter variance on the optimal electrical time constant and optimal coupling coefficient are reported. Monte-Carlo based simulation results are used to further analyse the system under parametric uncertainty.
Zhi Ang Eu, Hwee-Pink Tan, Winston K. G. Seah, (2010) Design and Performance Analysis of MAC schemes for Wireless Sensor Networks Powered by Ambient Energy Harvesting. In: Elsevier Journal of Ad Hoc Networks, Accepted 23 July 2010.
Abstract: Energy consumption is a perennial issue in the design of wireless sensor networks (WSNs) which typically rely on portable sources like batteries for power. Recent advances in ambient energy harvesting technology have made it a potential and promising alternative source of energy for powering WSNs. By using energy harvesters with supercapacitors, WSNs are able to operate perpetually until hardware failure and in places where batteries are hard or impossible to replace. In this paper, we study the performance of different medium access control (MAC) schemes based on CSMA and polling techniques for WSNs which are solely powered by ambient energy harvesting using energy harvesters. We base the study on (i) network throughput (S), which is the rate of sensor data received by the sink, (ii) fairness index (F), which determines whether the bandwidth is allocated to each sensor node equally and (iii) inter-arrival time which measures the average time difference between two packets from a source node. For CSMA, we compare both the slotted and unslotted variants. For polling, we first consider identity polling. Then we design a probabilistic polling protocol that takes into account the unpredictability of the energy harvesting process to achieve good performance. Finally, we present an optimal polling MAC protocol to determine the theoretical maximum performance. We validate the analytical models using extensive simulations incorporating experimental results from the characterization of different types of energy harvesters. The performance results show that probabilistic polling achieves high throughput and fairness as well as low inter-arrival times.
Zhi Ang Eu, Hwee-Pink Tan, Winston K. G. Seah, (2010) Opportunistic Routing in Wireless Sensor Networks Powered by Ambient Energy Harvesting. In: Elsevier Journal of Computer Networks, Accepted 15 May 2010.
Abstract: 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 is 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.
Minan Zhu, Dr Martin Judd, P. J. Moore, (2009) Energy Harvesting in Substations for Powering Autonomous Sensors. In: Proc. 3rd Int. Conf. on Sensor Technologies and Applications (SENSORCOMM '09), Athens, Greece, June 2009, pp. 246-249.
Abstract: The benefits of enhanced condition monitoring in the asset management of the electricity transmission infrastructure are increasingly being exploited by the grid operators. Adding more sensors helps to track the plant health more accurately. However, the installation or operating costs of any additional sensors could outweigh the benefits they bring due to the requirement for new cabling or battery maintenance. Energy harvesting devices are therefore being proposed to power a new generation of wireless sensors. The harvesting devices could enable the sensors to be maintenance free over their lifetime and substantially reduce the cost of installing and operating a condition monitoring system.
Meiling Zhu, Emma Worthington, James Njuguna, (2009) Analyses of Power Output of Piezoelectric Energy Harvesting Devices Directly Connected to a Load Resistor Using a Coupled Piezoelectric-Circuit . In: IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, July 2009, vol.56, no.7, 1309-1318.
Abstract: This paper presents, for the first time, a coupled piezoelectric-circuit finite element model (CPC-FEM) to analyse the power output of a vibration-based piezoelectric energy harvesting device (EHD) when it is connected to a load resistor. Special focus is given to the effect of the load resistor value on the vibrational amplitude of the piezoelectric EHD, and thus on the current, voltage, and power generated by the device, which are normally assumed to be independent of the load resistor value in order to reduce the complexity of modelling and simulation. The presented CPC-FEM uses a cantilever with a sandwich structure and a seismic mass attached to the tip to study the following characteristics of the EHD as a result of changing the load resistor value: (1) the electric outputs: the current through and voltage across the load resistor, (2) the power dissipated by the load resistor, (3) the displacement amplitude of the tip of the cantilever, and (4) the shift in the resonant frequency of the device. It is found that these characteristics of the EHD have a significant dependence on the load resistor value, rather than being independent of it as is assumed in most literature. The CPC-FEM is capable of predicting the generated output power of the EHD with different load resistor values while simultaneously calculating the effect of the load resistor value on the displacement amplitude of the tip of the cantilever. This makes the CPC-FEM invaluable for validating the performance of a designed EHD before it is fabricated and tested, thereby reducing the recurring costs associated with repeat fabrication and trials. In addition, the proposed CPC-FEM can also be used for producing an optimised design for maximum power output.
Guoliang Ye, Jize Yan, Zijing Wong, Kenichi Soga, Ashwin A. Seshia, (2009) Optimisation of a Piezoelectric System for Energy Harvesting from Traffic Vibrations. In: Proceedings of the IEEE International Ultrasonics Symposium, (IEEE IUS2009), Sept. 20-23, 2009, Roma, Italy.
Abstract: Piezoelectric systems are viewed as a promising
approach to energy harvesting from environmental vibrations.
The energy harvested from real vibration sources is usually
difficult to estimate analytically. Therefore, it is hard to optimise
the associated energy harvesting system. This work investigates
the optimisation of a piezoelectric cantilever system using a
genetic algorithm based approach with numerical simulations.
The genetic algorithm globally considers the effects of each
parameter to produce an optimal frequency response to scavenge
more energy from the real vibrations while the conventional
sinusoidal based method can only optimise the resistive load for
a given resonant frequency. Experimental acceleration data from
the vibrations of a vehicle-excited manhole cover demonstrates
that the optimised harvester automatically selects the right
frequency and also synchronously optimises the damper and the
resistive load. This method shows great potential for optimizing
the energy harvesting systems with real vibration data.
approach to energy harvesting from environmental vibrations.
The energy harvested from real vibration sources is usually
difficult to estimate analytically. Therefore, it is hard to optimise
the associated energy harvesting system. This work investigates
the optimisation of a piezoelectric cantilever system using a
genetic algorithm based approach with numerical simulations.
The genetic algorithm globally considers the effects of each
parameter to produce an optimal frequency response to scavenge
more energy from the real vibrations while the conventional
sinusoidal based method can only optimise the resistive load for
a given resonant frequency. Experimental acceleration data from
the vibrations of a vehicle-excited manhole cover demonstrates
that the optimised harvester automatically selects the right
frequency and also synchronously optimises the damper and the
resistive load. This method shows great potential for optimizing
the energy harvesting systems with real vibration data.
Yang Yaowen, Tang Lihua, Li Hongyun, (2009) Vibration Energy Harvesting Using Macro-Fiber Composites. In: Smart Materials and Structures, Vol.18, No.11, 115025.
Abstract: The decreasing energy consumption of today's portable electronics has invoked the possibility of energy harvesting from the ambient environment for self-power supply. One common and simple method for vibration energy harvesting is to utilize the direct piezoelectric effect. Compared to traditional piezoelectric materials such as lead zirconate titanate (PZT), macro-fiber composites (MFC) are characterized by their flexibility on large deformation. However, the energy generated by MFC is still far smaller than that required by electronics at present. In this paper, a vibration energy harvesting system prototype with MFC patches bonded to a cantilever beam is fabricated and tested. A finite element analysis (FEA) model is established to estimate the output voltage of the MFC harvester. The energy accumulation procedure in the capacitor is simulated by using the electronic design automation (EDA) software. The simulation results are validated by the experimental ones. Finally, to optimize the efficiency of energy harvesting, the effects of the electrical properties of MFC as well as the geometric configurations of the cantilever beam and MFC are parametrically studied by combining the FEA and EDA simulations.
Yang Yaowen, Tang Lihua, (2009) Equivalent Circuit Modeling of Piezoelectric Energy Harvesters. In: Journal of Intelligent Material Systems and Structures, Vol. 20, No.18, 2223-2235.
Abstract: Last decade has seen growing research interest in vibration energy harvesting using piezoelectric materials. When developing piezoelectric energy harvesting systems, it is advantageous to establish certain analytical or numerical model to predict the system performance. In the last few years, researchers from mechanical engineering established distributed models for energy harvester but simplified the energy harvesting circuit in the analytical derivation. While, researchers from electrical engineering concerned the modeling of practical energy harvesting circuit but tended to simplify the structural and mechanical conditions. The challenges for accurate modeling of such electromechanical coupling systems remain when complicated mechanical conditions and practical energy harvesting circuit are considered in system design. In this article, the aforementioned problem is addressed by employing an equivalent circuit model, which bridges structural modeling and electrical simulation. First, the parameters in the equivalent circuit model are identified from theoretical analysis and finite element analysis for simple and complex structures, respectively. Subsequently, the equivalent circuit model considering multiple modes of the system is established and simulated in the SPICE software. Two validation examples are given to verify the accuracy of the proposed method, and one further example illustrates its capability of dealing with complicated structures and non-linear circuits.
Sondipon Adhikari, Mike Friswell, Daniel J. Inman, (18) Piezoelectric energy harvesting from broadband random vibrations. In: Smart Materials & Structures, 18[11], pp. 115005:1-7.
Abstract: Energy harvesting for the purpose of powering low power electronic sensor systems has received explosive attention in the last few years. Most works using deterministic approaches focusing on using the piezoelectric effect to harvest ambient vibration energy have concentrated on cantilever beams at resonance using harmonic excitation. Here, using a stochastic approach, we focus on using a stack configuration and harvesting broadband vibration energy, a more practically available ambient source. It is assumed that the ambient base excitation is stationary Gaussian white noise, which has a constant power-spectral density across the frequency range considered. The mean power acquired from a piezoelectric vibration-based energy harvester subjected to random base excitation is derived using the theory of random vibrations. Two cases, namely the harvesting circuit with and without an inductor, have been considered. Exact closed-form expressions involving non-dimensional parameters of the electromechanical system have been given and illustrated using numerical examples.
Other
M. T. Penella-López, Manel Gasulla, (2010) Runtime extension of low-power wireless sensor nodes using hybrid-storage units. In: IEEE transactions on instrumentation and measurement, March 2010, vol. 59, n. 4, p. 857-865..Abstract: The sensor nodes of wireless sensor networks remain inactive most of the time to achieve longer runtimes. Power is mainly provided by batteries, which are either primary or secondary. Because of its internal impedance, a significant voltage drop can appear across the battery terminals at the activation time of the node, thus preventing the extraction of all the energy from the battery. Additionally, internal losses can also be significant. Consequently, the runtime is reduced. The addition of a supercapacitor in parallel with the battery, thus forming a hybrid-storage device, has been proposed under pulsed loads to increase the power capabilities and reduce both the voltage drop and the internal losses at the battery. However, this strategy has not yet thoroughly been analyzed and tested in low-power wireless sensor nodes. This paper presents a comprehensive theoretical analysis that extends previous works found in the literature and provides design guidelines for choosing the appropriate supercapacitor. The analysis is supported by extensive experimental results. Two low-capacity (< 200 mAh) batteries were tested together with their hybrid-storage unit counterparts when using an electronic load as a pulsed current sink. The hybrid-storage units always achieved a higher runtime. One of the batteries was also tested using a sensor node. The runtime extension was 16% and 33% when connecting the hybrid-storage unit directly and through a dc-dc switching regulator to the sensor node, respectively.
O. López-Lapeña, M.T. Penella-López, Manel Gasulla, (2010) A new MPPT method for low-power solar energy harvesting. In: IEEE transactions on industrial electronics, September 2010, vol. 57, no. 9, pp. 3129-3138.
Abstract: This paper describes a new maximum-power-pointtracking (MPPT) method focused on low-power (< 1 W) photovoltaic (PV) panels. The static and dynamic performance is theoretically analyzed, and design criteria are provided. A prototype was implemented with a 500-mW PV panel, a commercial boost converter, and low-power components for the MPPT controller. Laboratory measurements were performed to assess the effectiveness of the proposed method. Tracking efficiency was higher than 99.6%. The overall efficiency was higher than 92% for a PV panel power higher than 100 mW. This is, in part, feasible due to the low power consumption of the MPPT controller, which was kept lower than 350 ���¼W. The time response of the tracking circuit was tested to be around 1 s. Field measurements showed energy gains higher than 10.3% with respect to a direct-coupled solution for an ambient temperature of 26 ���ºC. Higher gains are expected for lower temperatures.
A. Cuadras, Manel Gasulla, Vittorio Ferrari, (2010) Thermal energy harvesting through pyroelectricity. In: Sensors and actuators A. Physical, March 2010, vol. 158, no. 1, pp. 132-139..
Abstract: Pyroelectric cells based on fabricated screen-printed PZT and commercial PVDF films are proposed as thermal energy harvesting sources in order to supply low-power autonomous sensors. The cells are electrically modelled as a current source in parallel with output impedance. Heating and cooling temperature fluctuations generated by air currents were applied to the pyroelectric converters. The generated currents and charges were respectively in the order of 10�7 A and 10�5 C for temperature fluctuations from 300K to 360K in a time period of the order of 100 s, which agrees with the theoretical model. Parallel association of cells increased the generated current. The dependence of the generated current on relevant technological parameters has been also characterized. Finally, current from cyclic temperature fluctuations was rectified and stored in a 1 F load capacitor. Energies up to 0.5 mJ have been achieved, enough to power typical autonomous sensor nodes during a measurement and transmission cycle.
Maria Gorlatova, Peter Kinget, Ioannis Kymissis, Dan Rubenstein, Xiaodong Wang, Gil Zussman, (2010) Energy Harvesting Active Networked Tags (EnHANTs) for Ubiquitous Object Networking. In: IEEE Wireless Communications, Vol. 17, No. 6, pp. 18-25, Dec. 2010.
Abstract: This article presents the design challenges posed by a new class of ultra-low-power devices referred to as Energy-Harvesting Active Networked Tags (EnHANTs). EnHANTs are small, flexible, and self-reliant (in terms of energy) devices that can be attached to objects that are traditionally not networked (e.g., books, furniture, walls, doors, toys, keys, produce, and clothing). EnHANTs will enable the Internet of Things by providing the infrastructure for various novel tracking applications. Examples of these applications include locating misplaced items, continuous monitoring of objects, and determining locations of disaster survivors. Recent advances in ultra-low-power circuit design, ultra-wideband (UWB) wireless communications, and organic energy harvesting techniques will enable the realization of EnHANTs in the near future. The harvesting components and the ultra-low-power physical layer have special characteristics whose implications on the higher layers have yet to be studied (e.g., when using UWB communications, the energy required to receive a bit is significantly higher than the energy required to transmit a bit). In this paper, we describe paradigm shifts associated with technologies that enable EnHANTs and demonstrate their implications on higher-layer protocols. Moreover, we describe some of the components we have designed for EnHANTs. Finally, we briefly discuss our indoor light measurements and their implications on the design of higher-layer protocols.
Minan Zhu, Peter Baker, Dr. Nina Roscoe, Dr Martin Judd, John Fitch (National Grid), (2009) Alternative Power Sources for Autonomous Sensors in High Voltage Plant. In: Proc. Electrical Insulation Conference (EIC 2009), Montreal, Canada, pp. 36-39, June 2009.
Abstract: Enhanced condition monitoring of the electric grid infrastructure could be achieved by adding more sensors to track the plant health more accurately. However, the installation or operating costs of any additional sensors could outweigh the benefits they bring due to the requirements for new cabling or battery maintenance. High voltage plant, such as substation, contains several potential energy sources. Harvesting the energy from ambient sources to power sensors could support a move towards autonomous wireless condition monitoring sensors while reduced the overall cost of owning and operating an enhanced condition monitoring system. This paper reviews the potential sources of power that may be used to supply autonomous sensor nodes.
Maria Gorlatova , Peter Kinget, Ioannis Kymissis, Dan Rubenstein, Xiaodong Wang, Gil Zussman, (2009) Challenge: Ultra-Low-Power Energy-Harvesting Active Networked Tags (EnHANTs). In: Proc. ACM MobiCom'09 , September 20-25, 2009, Beijing, China.
Abstract: This paper presents the design challenges posed by a new class of ultra-low-power devices referred to as Energy-Harvesting Active Networked Tags (EnHANTs). EnHANTs are small, flexible, and self-reliant (in terms of energy) devices that can be attached to objects that are traditionally not networked (e.g., books, clothing, and produce), thereby providing the infrastructure for various novel tracking applications. Examples of these applications include locating misplaced items, continuous monitoring of objects (items in a store, boxes in transit), and determining locations of disaster survivors. Recent advances in ultra low-power wireless communications, ultra-wideband (UWB) circuit design, and organic electronic harvesting techniques will enable the realization of EnHANTs in the near future. In order for EnHANTs to rely on harvested energy, they have to spend significantly less energy than Bluetooth, Zigbee, and IEEE 802.15.4a devices. Moreover, the harvesting components and the ultra-low-power physical layer have special characteristics whose implications on the higher layers have yet to be studied (e.g., when using ultra-low-power circuits, the energy required to receive a bit is an order of magnitude higher than the energy required to transmit a bit). These special characteristics pose several new cross-layer research problems. In this paper, we describe the design challenges at the layers above the physical layer, point out relevant research directions, and outline possible starting points for solutions.
