Showing papers on "Energy harvesting published in 2017"
TL;DR: A soft skin-like triboelectric nanogenerator that enables both biomechanical energy harvesting and tactile sensing by hybridizing elastomer and ionic hydrogel as the electrification layer and electrode, respectively is reported, providing new opportunities for multifunctional power sources and potential applications in soft/wearable electronics.
Abstract: Rapid advancements in stretchable and multifunctional electronics impose the challenge on corresponding power devices that they should have comparable stretchability and functionality We report a soft skin-like triboelectric nanogenerator (STENG) that enables both biomechanical energy harvesting and tactile sensing by hybridizing elastomer and ionic hydrogel as the electrification layer and electrode, respectively For the first time, ultrahigh stretchability (uniaxial strain, 1160%) and transparency (average transmittance, 962% for visible light) are achieved simultaneously for an energy-harvesting device The soft TENG is capable of outputting alternative electricity with an instantaneous peak power density of 35 mW m −2 and driving wearable electronics (for example, an electronic watch) with energy converted from human motions, whereas the STENG is pressure-sensitive, enabling its application as artificial electronic skin for touch/pressure perception Our work provides new opportunities for multifunctional power sources and potential applications in soft/wearable electronics
852 citations
TL;DR: In this article, both TENG-enabled vibration energy harvesting and self-powered active sensing are comprehensively reviewed and problems pressing for solutions and onward research directions are also posed to deliver a coherent picture.
666 citations
Abstract: This paper presents a state-of-the-art review on a hot topic in the literature, i.e., vibration based energy harvesting techniques, including theory, modelling methods and the realizations of the piezoelectric, electromagnetic and electrostatic approaches. To minimize the requirement of external power source and maintenance for electric devices such as wireless sensor networks, the energy harvesting technique based on vibrations has been a dynamic field of studying interest over past years. One important limitation of existing energy harvesting techniques is that the power output performance is seriously subject to the resonant frequencies of ambient vibrations, which are often random and broadband. To solve this problem, researchers have concentrated on developing efficient energy harvesters by adopting new materials and optimising the harvesting devices. Particularly, among these approaches, different types of energy harvesters have been designed with consideration of nonlinear characteristics so that the frequency bandwidth for effective energy harvesting of energy harvesters can be broadened. This paper reviews three main and important vibration-to-electricity conversion mechanisms, their design theory or methods and potential applications in the literature. As one of important factors to estimate the power output performance, the energy conversion efficiency of different conversion mechanisms is also summarised. Finally, the challenging issues based on the existing methods and future requirement of energy harvesting are discussed.
628 citations
TL;DR: In this paper, a review focusing on flexible energy harvesting system based on polyvinylidene fluoride based polymers, with an emphasis on manipulating and optimising the properties and performance of the polymeric materials and related nanocomposites through structuring the material at multiple scales.
Abstract: Energy harvesting exploits ambient sources of energy such as mechanical loads, vibrations, human motion, waste heat, light or chemical sources and converts them into useful electrical energy. The applications for energy harvesting include low power electronics or wireless sensing at relatively lower power levels (nW to mW) with an aim to reduce a reliance on batteries or electrical power via cables and realise fully autonomous and self-powered systems. This review focuses on flexible energy harvesting system based on polyvinylidene fluoride based polymers, with an emphasis on manipulating and optimising the properties and performance of the polymeric materials and related nanocomposites through structuring the material at multiple scales. Ferroelectric properties are described and the potential of using the polarisation of the materials for vibration and thermal harvesting using piezo- and pyro-electric effects are explained. Approaches to tailor the ferroelectric, piezoelectric and pyroelectric properties of polymer materials are explored in detail; these include the influence of polymer processing conditions, heat treatment, nanoconfinement, blending, forming nanocomposites and electrospinning. Finally, examples of flexible harvesting devices that utilise the optimised ferroelectric polymer or nanocomposite systems are described and potential applications and future directions of research explored.
366 citations
TL;DR: In this article, a review of the development of fiber-based energy harvesting and storage devices is presented, focusing on dye-sensitized solar cells, lithium-ion batteries, supercapacitors and their integrated devices.
Abstract: Power systems and electronic devices that are bulky and rigid are not practical for use in wearable applications that require flexibility and breathability. To address this, a range of 1D energy harvesting and storage devices have been fabricated that show promise for such applications compared with their 2D and 3D counterparts. These 1D devices are based on fibres that are flexible and can accommodate deformation, for example, by twisting and stretching. The fibres can be woven into textiles and fabrics that breathe freely or can be integrated into different materials that fit the curved surface of the human body. In this Review, the development of fibre-based energy harvesting and storage devices is presented, focusing on dye-sensitized solar cells, lithium-ion batteries, supercapacitors and their integrated devices. An emphasis is placed on the interface between the active materials and the electrodes or electrolyte in the 1D devices. The differing properties of these interfaces compared with those in 2D and 3D devices are derived from the curved surface and long charge transport path in 1D electrodes. Wearable electronic devices need to be flexible and breathable, as well as show high performance. In this Review, 1D energy harvesting and storage devices — in the form of fibre-based systems — are outlined, focusing on the interfaces in typical 1D configurations.
353 citations
TL;DR: Flexible piezoelectric nanogenerator can be applied as self-powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.
Abstract: Piezoelectric nanogenerators with large output, high sensitivity, and good flexibility have attracted extensive interest in wearable electronics and personal healthcare. In this paper, the authors propose a high-performance flexible piezoelectric nanogenerator based on piezoelectrically enhanced nanocomposite micropillar array of polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE))/barium titanate (BaTiO3 ) for energy harvesting and highly sensitive self-powered sensing. By a reliable and scalable nanoimprinting process, the piezoelectrically enhanced vertically aligned P(VDF-TrFE)/BaTiO3 nanocomposite micropillar arrays are fabricated. The piezoelectric device exhibits enhanced voltage of 13.2 V and a current density of 0.33 µA cm-2 , which an enhancement by a factor of 7.3 relatives to the pristine P(VDF-TrFE) bulk film. The mechanisms of high performance are mainly attributed to the enhanced piezoelectricity of the P(VDF-TrFE)/BaTiO3 nanocomposite materials and the improved mechanical flexibility of the micropillar array. Under mechanical impact, stable electricity is stably generated from the nanogenerator and used to drive various electronic devices to work continuously, implying its significance in the field of consumer electronic devices. Furthermore, it can be applied as self-powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.
312 citations
TL;DR: A high-power-output textile triboelectric nanogenerator (TENG) with 3D orthogonal woven structure is developed for effective biomechanical energy harvesting and active motion signal tracking and a smart dancing blanket is designed to simultaneously convert biomechanicals energy and perceive body movement.
Abstract: The development of wearable and large-area energy-harvesting textiles has received intensive attention due to their promising applications in next-generation wearable functional electronics. However, the limited power outputs of conventional textiles have largely hindered their development. Here, in combination with the stainless steel/polyester fiber blended yarn, the polydimethylsiloxane-coated energy-harvesting yarn, and nonconductive binding yarn, a high-power-output textile triboelectric nanogenerator (TENG) with 3D orthogonal woven structure is developed for effective biomechanical energy harvesting and active motion signal tracking. Based on the advanced 3D structural design, the maximum peak power density of 3D textile can reach 263.36 mW m−2 under the tapping frequency of 3 Hz, which is several times more than that of conventional 2D textile TENGs. Besides, its collected power is capable of lighting up a warning indicator, sustainably charging a commercial capacitor, and powering a smart watch. The 3D textile TENG can also be used as a self-powered active motion sensor to constantly monitor the movement signals of human body. Furthermore, a smart dancing blanket is designed to simultaneously convert biomechanical energy and perceive body movement. This work provides a new direction for multifunctional self-powered textiles with potential applications in wearable electronics, home security, and personalized healthcare.
288 citations
TL;DR: In this paper, a soft, stretchable electronic-skin-based biofuel cell (E-BFC) is presented, which exhibits an open circuit voltage of 0.5 V and a power density of nearly 1.2 mW cm−2 at 0.2 V.
Abstract: This article describes the fabrication, characterization, and real-life application of a soft, stretchable electronic-skin-based biofuel cell (E-BFC) that exhibits an open circuit voltage of 0.5 V and a power density of nearly 1.2 mW cm−2 at 0.2 V, representing the highest power density recorded by a wearable biofuel cell to date. High power density is achieved via a unique combination of lithographically-patterned stretchable electronic framework together with screen-printed, densely-packed three-dimensional carbon-nanotube-based bioanode and cathode array arranged in a stretchable “island-bridge” configuration. The E-BFC maintains its performance even under repeated strains of 50%, and is stable for two days. When applied directly to the skin of human subjects, the E-BFC generates ∼1 mW during exercise. The E-BFC is able to power conventional electronic devices, such as a light emitting diode and a Bluetooth Low Energy (BLE) radio. This is the first example of powering a BLE radio by a wearable biofuel cell. Successful generation of high power density under practical conditions and powering of conventional energy-intense electronic devices represents a major step forward in the field of soft, stretchable, wearable energy harvesting devices.
286 citations
TL;DR: The proposed system with solar energy harvesting demonstrates that long-term continuous medical monitoring based on WBAN is possible provided that the subject stays outside for a short period of time in a day.
Abstract: Internet of Things (IoT) is a new technological paradigm that can connect things from various fields through the Internet. For the IoT connected healthcare applications, the wireless body area network (WBAN) is gaining popularity as wearable devices spring into the market. This paper proposes a wearable sensor node with solar energy harvesting and Bluetooth low energy transmission that enables the implementation of an autonomous WBAN. Multiple sensor nodes can be deployed on different positions of the body to measure the subject’s body temperature distribution, heartbeat, and detect falls. A web-based smartphone application is also developed for displaying the sensor data and fall notification. To extend the lifetime of the wearable sensor node, a flexible solar energy harvester with an output-based maximum power point tracking technique is used to power the sensor node. Experimental results show that the wearable sensor node works well when powered by the solar energy harvester. The autonomous 24 h operation is achieved with the experimental results. The proposed system with solar energy harvesting demonstrates that long-term continuous medical monitoring based on WBAN is possible provided that the subject stays outside for a short period of time in a day.
272 citations
22 Nov 2017
TL;DR: For optimizing performances of TENG, the structural designs, material selections, and hybrid energy cells are presented and the progress in TENG made as flexible power sources by integrating flexible materials and stretching structures is reviewed.
Abstract: The triboelectric nanogenerator (TENG) as a new power-generation technology was reported by Wang and co-workers in 2012 Because of its great potential for scavenging mechanical energy from living environment and sustainably driving portable devices, many researchers have developed various methods to improve output performances of TENG In this paper, we review the progress in TENG made as flexible power sources by integrating flexible materials and stretching structures, especially for the applications of flexible electronics For optimizing performances of TENG, the structural designs, material selections, and hybrid energy cells are presented The reported TENG as flexible power sources has the potential applications in lighting up light emitting diodes (LEDs), powering sensors, and monitoring biomechanical motions
263 citations
TL;DR: In this paper, two different freestanding, multifunctional TENGs are successfully developed that can be used to harvest three types of energies including water waves, air flowing, and water flowing.
Abstract: Triboelectric nanogenerator (TENG) has been considered to be a more effective technology to harvest various types of mechanic vibration energies such as wind energy, water energy in the blue energy, and so on. Considering the vast energy from the blue oceans, harvesting of the water energy has attracted huge attention. There are two major types of “mechanical” water energy, water wave energy in random direction and water flow kinetic energy. However, although the most reported TENG can be used to efficiently harvest one type of water energy, to simultaneously collect two or more types of such energy still remains challenging. In this work, two different freestanding, multifunctional TENGs are successfully developed that can be used to harvest three types of energies including water waves, air flowing, and water flowing. These two new TENGs designed in accordance with the same freestanding model yield the output voltages of 490 and ≈100 V with short circuit currents of 24 and 2.7 µA, respectively, when operated at a rotation frequency of 200 rpm and the movement frequency of 3 Hz. Moreover, the developed multifunctional TENG can also be explored as a self-powered speed sensor of wind by correlating the short-circuit current with the wind speed.
TL;DR: An entirely new approach is presented and the results suggest that this novel approach can finally produce flexible TEGs that have the potential to challenge the rigid T EGs and provide a pathway for the realization of self-powered wearable electronics.
TL;DR: The recent progress and advantages of wearable self-powered electronic sensing systems for mobile or personal attachable health monitoring applications, and an overview of various types of wearable electronic sensors, including flexible tactile sensors, wearable image sensor array, biological and chemical sensor, temperature sensors, and multifunctional integrated sensing systems are presented.
Abstract: Wearable/flexible electronic sensing systems are considered to be one of the key technologies in the next generation of smart personal electronics. To realize personal portable devices with mobile electronics application, i.e., wearable electronic sensors that can work sustainably and continuously without an external power supply are highly desired. The recent progress and advantages of wearable self-powered electronic sensing systems for mobile or personal attachable health monitoring applications are presented. An overview of various types of wearable electronic sensors, including flexible tactile sensors, wearable image sensor array, biological and chemical sensor, temperature sensors, and multifunctional integrated sensing systems is provided. Self-powered sensing systems with integrated energy units are then discussed, separated as energy harvesting self-powered sensing systems, energy storage integrated sensing systems, and all-in-on integrated sensing systems. Finally, the future perspectives of self-powered sensing systems for wearable electronics are discussed.
TL;DR: The proposed rectenna is general and simple in structure without the need for a matching network, suitable for high-efficiency wireless power transfer or energy harvesting applications and of great significance for many applications.
Abstract: Impedance matching networks for nonlinear devices such as amplifiers and rectifiers are normally very challenging to design, particularly for broadband and multiband devices. A novel design concept for a broadband high-efficiency rectenna without using matching networks is presented in this paper for the first time. An off-center-fed dipole antenna with relatively high input impedance over a wide frequency band is proposed. The antenna impedance can be tuned to the desired value and directly provides a complex conjugate match to the impedance of a rectifier. The received RF power by the antenna can be delivered to the rectifier efficiently without using impedance matching networks; thus, the proposed rectenna is of a simple structure, low cost, and compact size. In addition, the rectenna can work well under different operating conditions and using different types of rectifying diodes. A rectenna has been designed and made based on this concept. The measured results show that the rectenna is of high power conversion efficiency (more than 60%) in two wide bands, which are 0.9–1.1 and 1.8–2.5 GHz, for mobile, Wi-Fi, and ISM bands. Moreover, by using different diodes, the rectenna can maintain its wide bandwidth and high efficiency over a wide range of input power levels (from 0 to 23 dBm) and load values (from 200 to 2000 Ω). It is, therefore, suitable for high-efficiency wireless power transfer or energy harvesting applications. The proposed rectenna is general and simple in structure without the need for a matching network hence is of great significance for many applications.
TL;DR: This review provides a summ ary of radio frequency (RF) power harvesting technologies in order to serve as a guide for the design of RF energy harvesting units.
Abstract: Wireless power transmission was conceptualized nearly a century ago. Certain achievements made to date have made power harvesting a reality, capable of providing alternative sources of energy. This review provides a summ ary of radio frequency (RF) power harvesting technologies in order to serve as a guide for the design of RF energy harvesting units. Since energy harvesting circuits are designed to operate with relatively small voltages and currents, they rely on state-of-the-art electrical technology for obtaining high efficiency. Thus, comprehensive analysis and discussions of various designs and their tradeoffs are included. Finally, recent applications of RF power harvesting are outlined.
TL;DR: In this paper, a flexible hybrid device that can be conformally attached on soft surface like human skin to harvest diversity touch energies based on electrospun nanofiber mat was presented.
TL;DR: In this paper, the authors investigated scavenging of human body heat and the optimization of the power conversion efficiency from body core to the application, and compared two approaches: (1) a high output voltage, low thermal resistance, low electric resistance mTEG in combination with a low-input voltage coupled inductors based DC-DC converter.
TL;DR: In this article, the authors proposed a resource-allocation solution for the HCRSN to achieve the sustainability of spectrum sensors and conserve the energy of data sensors, which is achieved by two algorithms that operate in tandem: a spectrum sensor scheduling (SSS) algorithm and a data sensor resource allocation (DSRA).
Abstract: The incorporation of cognitive radio (CR) and energy harvesting (EH) capabilities in wireless sensor networks enables spectrum and energy-efficient heterogeneous CR sensor networks (HCRSNs). The new networking paradigm of HCRSNs consists of EH-enabled spectrum sensors and battery-powered data sensors. Spectrum sensors can cooperatively scan the licensed spectrum for available channels, whereas data sensors monitor an area of interest and transmit sensed data to the sink over those channels. In this paper, we propose a resource-allocation solution for the HCRSN to achieve the sustainability of spectrum sensors and conserve the energy of data sensors. The proposed solution is achieved by two algorithms that operate in tandem: a spectrum sensor scheduling (SSS) algorithm and a data sensor resource allocation (DSRA) algorithm. The SSS algorithm allocates channels to spectrum sensors such that the average detected available time for the channels is maximized, while the EH dynamics are considered and primary user (PU) transmissions are protected. The DSRA algorithm allocates the transmission time, power, and channels such that the energy consumption of the data sensors is minimized. Extensive simulation results demonstrate that the energy consumption of the data sensors can be significantly reduced, while maintaining the sustainability of the spectrum sensors.
TL;DR: In this paper, an ultrathin flexible single electrode triboelectric nanogenerator (S-TENG) was demonstrated, which not only could harvest mechanical energy from human movements and ambient sources, but also could sense instantaneous force without extra energy.
Abstract: The trends in miniaturization of electronic devices give rise to the attention of energy harvesting technologies that gathers tiny wattages of power. Here this study demonstrates an ultrathin flexible single electrode triboelectric nanogenerator (S-TENG) which not only could harvest mechanical energy from human movements and ambient sources, but also could sense instantaneous force without extra energy. The S-TENG, which features an extremely simple structure, has an average output current of 78 μA, lightening up at least 70 LEDs (light-emitting diode). Even tapped by bare finger, it exhibits an output current of 1 μA. The detection sensitivity for instantaneous force sensing is about 0.947 μA MPa−1. Performances of the device are also systematically investigated under various motion types, press force, and triboelectric materials. The S-TENG has great application prospects in sustainable wearable devices, sustainable medical devices, and smart wireless sensor networks owning to its thinness, light weight, energy harvesting, and sensing capacities.
TL;DR: In this article, a spring-assisted TENG was designed and investigated for harvesting low-frequency water wave energy, and four optimized basic units were connected in parallel and packaged into a sealed box.
TL;DR: In this article, a piezoelectric energy harvester module based on polyvinylidene fluoride (PVDF) polymer for roadway applications was presented, which exhibited stable performance and durability over the repeated number of bending cycles.
TL;DR: In this paper, the authors proposed a power management (PM) strategy by extracting maximum energy from TENG and transferring the energy to storage unit employing optimized Inductor-Capacitor (LC) oscillating.
TL;DR: In this article, an integrated triboelectric nanogenerator array device based on air-driven membrane structures is demonstrated, which can drive a series of integrated TENG units effectively and simultaneously.
TL;DR: A combined energy- aware interface with an energy-aware program to deal with the mismatch through managing the energy flow from the energy storage capacitor to the WSNs is introduced.
Abstract: Intensive research on energy harvesting powered wireless sensor nodes (WSNs) has been driven by the needs of reducing the power consumption by the WSNs and increasing the power generated by energy harvesters. The mismatch between the energy generated by the harvesters and the energy demanded by the WSNs is always a bottleneck as the ambient environmental energy is limited and time varying. This paper introduces a combined energy-aware interface with an energy-aware program to deal with the mismatch through managing the energy flow from the energy storage capacitor to the WSNs. These two energy-aware approaches were implemented in a custom developed vibration energy harvesting powered WSN. The experimental results show that, with the 3.2-mW power generated by a piezoelectric energy harvester under an emulated aircraft wing strain loading of $600~\mu \varepsilon $ at 10 Hz, the combined energy-aware approaches enable the WSN to have a significantly reduced sleep current from $28.3~\mu \text{A}$ of a commercial WSN to $0.95~\mu \text{A}$ and enable the WSN operations for a long active time of about 1.15 s in every 7.79 s to sample and transmit a large number of data (388 B), rather than a few ten milliseconds and a few bytes, as demanded by vibration measurement. When the approach was not used, the same amount of energy harvested was not able to power the WSN to start, not mentioning to enabling the WSN operation, which highlighted the importance and the value of the energy-aware approaches in enabling energy harvesting powered WSN operation successfully.
TL;DR: In this paper, the authors developed a lightweight, flexible and sustainable power source by fabricating a nanofibrous membrane constructed wearable triboelectric nanogenerator (NM-TENG), which is capable of converting human biomechanical energy into electricity for next-generation wearables.
TL;DR: In this paper, a rotational energy harvesting method based on piezoelectric transduction and frequency up-conversion has been proposed to collect low-speed rotational energies from ambient hosts.
TL;DR: In this paper, a single-crystalline (1 − x)Pb(Mg1/3Nb2/3)O3−(x)pb(Zr,Ti)O 3 (PMN-PZT) energy harvester was successfully driven with in- vivo energy harvesting enabled by high-performance single crystalstalline PZT.
Abstract: Additional surgeries for implantable biomedical devices are inevitable to replace discharged batteries, but repeated surgeries can be a risk to patients, causing bleeding, inflammation, and infection. Therefore, developing self-powered implantable devices is essential to reduce the patient's physical/psychological pain and financial burden. Although wireless communication plays a critical role in implantable biomedical devices that contain the function of data transmitting, it has never been integrated with in vivo piezoelectric self-powered system due to its high-level power consumption (microwatt-scale). Here, wireless communication, which is essential for a ubiquitous healthcare system, is successfully driven with in vivo energy harvesting enabled by high-performance single-crystalline (1 − x)Pb(Mg1/3Nb2/3)O3−(x)Pb(Zr,Ti)O3 (PMN-PZT). The PMN-PZT energy harvester generates an open-circuit voltage of 17.8 V and a short-circuit current of 1.74 µA from porcine heartbeats, which are greater by a factor of 4.45 and 17.5 than those of previously reported in vivo piezoelectric energy harvesting. The energy harvester exhibits excellent biocompatibility, which implies the possibility for applying the device to biomedical applications.
TL;DR: In this paper, the authors have developed nanogenerators based on piezoelectric and triboelectrics effects for mechanical energy harvesting, and those based on pyroelectric and thermoclectric effects for thermal energy harvesting.
Abstract: Nanoenergy is a field of studying the small-scale, highly efficient energy harvesting, storage, and applications by using nanomaterials and nanodevices. Nanogenerators are developed to harvest these small-scale energies in the ambient environment, which were first invented in our group in 2006. In the past decade, we have developed nanogenerators based on piezoelectric and triboelectric effects for mechanical energy harvesting, and those based on pyroelectric and thermoelectric effects for thermal energy harvesting. We also explored other novel nanogenerators such as that based on ion streams. The proposed nanogenerators will facilitate the development of self-powered systems, which enables efficient energy utilization and sustainable operations of mobile devices for “smart” wearable technology, health monitoring, biomedical sensing, environmental protection, and even security.
TL;DR: The achievable rate region of wirelessly powered two-way communication with a fixed relay is derived and the gain is precisely quantified, and it is possible to quantify the relative advantage of spending energy on moving versus on transmission in wirelesslypowered two- way communication.
Abstract: While two-way communication can improve the spectral efficiency of wireless networks, distances from the relay to the two users are usually asymmetric, leading to excessive wireless energy at the nearby user. To exploit the excessive energy, energy harvesting at user terminals is a viable option. Unfortunately, the exact gain brought by wireless power transfer (WPT) in two-way communication is currently unknown. To fill this gap, in this paper, the achievable rate region of wirelessly powered two-way communication with a fixed relay is derived. Not only this newly established result is shown to enclose the existing achievable rate region of two-way relay channel without energy harvesting but also the gain is precisely quantified. On the other hand, it is well-known that a major obstacle to WPT is the path-loss. By endowing the relay with mobility, the distances between the relay and users can be varied, thus providing a potential solution to combat pathloss at the expense of energy for transmission. To characterize the consequence brought by such a scheme, a pair of inner and outer bounds to the achievable rate region of wirelessly powered two-way communication under a mobile relay is further derived. By comparing the exact achievable rate region for the fixed relay case and the achievable rate bounds for the mobile relay case, it is possible to quantify the relative advantage of spending energy on moving versus on transmission in wirelessly powered two-way communication.
TL;DR: In this paper, a nonlinear multi-stable system, composed of a non-linear restoring mechanism and a linear damper-like generator, was proposed to enhance the absorption efficiency of a heaving wave energy converter.