Energy Harvesting Research Articles

Broadband elastic energy harvesting based on achromatic meta-grating

Energy harvesting exploiting the inverse piezoelectric effect has been the subject of much attention and discussion in the field of elastic and structural dynamics. Recently, the ongoing development of elastic metamaterials and metasurfaces has opened up a new way to improve the quality of energy harvesting. Here, we proposed a new strategy for harvesting elastic energy in a plate, which is the use of the inverse piezoelectric effect to convert the elastic energy into electrical energy after the achromatic meta-grating has focused broadband flexural waves. A new theoretical method to design the achromatic meta-grating is proposed based on derived analytical expression of the phase shift of subunit. When a meta-grating, a thin plate and a piezoelectric patch are combined into an energy harvesting system, the elastic energy can be converted into electric energy by the system, and the output voltage can be amplified by twice that of the system without the meta-grating. A theoretical framework is built to analyze the performance of the energy harvesting system, and variational parametric analyses are carried out to obtain the optimal resistance, the optimal length, thickness and position of piezoelectric patch, which are 870Ω, 18mm, 0.2mm and 30mm, respectively. For the optimized system, the power harvested rate of the system is close to 4 in the frequency band of 6-8kHz. Finally, the design of the system based on the wave focusing principle is extended, and energy harvesters are designed for different frequency bands, which can all work under different excitation conditions (a local and a base excitations). Our work opens up a new route for elastic energy harvesting and may have broad application prospects in the development of self-powered sensors.

Fabrication and evaluation of a CMOS-based energy harvesting chip integrating photovoltaic and thermoelectric energy harvesters

This study explores the development of an energy harvesting chip (EHC) using a complementary metal oxide semiconductor (CMOS) process, addressing the need for efficient micro-scale energy harvesters in modern electronics. The EHC integrates a thermoelectric energy harvester (TEH) and a photovoltaic energy harvester (PEH) to maximize energy conversion efficiency. A key challenge in TEH design is enhancing power output, which is addressed by suspending the cold ends of 41 thermocouples within the TEH structure through post-processing. Experimental methods were employed to assess the performance of the TEH, revealing an output voltage of 21.4 mV and a maximum output power of 9.32 nW under a 3 K temperature difference. The TEH demonstrated a voltage factor of 8.9 mV/(mm2·K) and a power factor of 1.3 nW/(mm2·K2). The PEH was designed with novel patterned p-n junctions, integrating lightly doped n-type regions with interdigitated p-type doping to increase junction density, resulting in high conversion efficiency. The experimental results confirm the effectiveness of the EHC design, showcasing its potential in energy harvesting applications.

Energy harvesting by car-tire using piezoelectric polymer films blended with carbon-nanotubes

Energy harvesting through harnessing mobile cars is possible by combining mechanicals systems with advanced materials. Piezoelectric polymer blends with excellent mechanical properties facilitate energy harvesting using the car-tire as a source. Furthermore, by adding simplicity of preparation to the blends with multi-walled carbon nanotubes (MWCNT), an increase of energy conversion can lead to improved existing polyvinylidene fluoride/polymethylmethacrylate (PVDF/PMMA), films. This work focuses on investigating the best concentration of MWCNT to achieve car-tire energy harvesting as a sustainable and renewable energy option. The results show that 0.05 wt% of MWCNT is the best concentration among several values. A test set-up applying normal stress, simulating car-tire deformation indicated enhanced voltage generation. Compared to the energy consumption of combustion cars, the enriched films generate up to 4.3kWh. This energy is harvested over a car trip of 100 km. A higher nanotube concentration caused saturation of the blend film and poor output. The novel enriched polymer must be tested for resisting cyclic loads to encourage sustainable energy harvesting using car tires.

Vortex-induced vibration and energy harvesting of cylinder system with nonlinear springs

Vortex-induced vibration is a common fluid–structure coupling phenomenon in ocean engineering. As a nonlinear stiffness structure caused by anisotropic deformation and support gap, nonlinear spring is of great significance in the field of vortex-induced vibration. Based on the structural dynamics equations and the wake oscillator model, the vibration model of the 2-Degree of Freedom cylinder system with the nonlinear stiffness spring is established. The stiffness ratio, mass ratio, and damping ratio of the cylinder system are changed, and the amplitude and frequency response are analyzed to obtain the effect of nonlinear spring on vortex-induced vibration. The results show that the cylinder system with a nonlinear stiffness spring can maintain a high vibration amplitude in a large Reynolds number range, and the smaller the mass ratio, the more significant the effect is. When m*=1.5, the amplitude of the cylinder system in a cross flow is greater than 0.6 at Re = 180 000–480 000. The energy harvesting in the vortex-induced vibration of cylinder systems with nonlinear stiffness springs is also studied. The efficiency depends on the damping ratio and Reynolds number. When the damping ratio is constant, the energy harvesting efficiency increases first and then decreases with the Reynolds number increases. When m*=1.5, the energy harvesting efficiency of the cylinder system is 19.27% with Re= 35 000 and damping ratio ξ=0.155. As a kind of renewable energy, energy harvesting in vortex-induced vibration is a potential development direction in the future energy field.

Self-powered human movement measurement with a unidirectional ratchet driven wearable energy harvester

A large amount of energy is generated during human movement which is mostly not effectively utilized. To collect human movement energy and utilize it rationally, a wearable piezoelectric-electromagnetic energy harvester (WPEEH) driven by a unidirectional ratchet is proposed, which adopts the principle of up-conversion to convert mechanical energy into electrical energy. The electromagnetic power generator unit is used to obtain energy to power the sensing circuit, while piezoelectric generator unit can be used for both energy generation and self-powered sensing. A spring push rod and a ratchet structure are used to convert the swinging of the human limb into the unidirectional rotation of the device to enhance its energy harvesting efficiency. The theoretical model of the WPEEH is established, and the experimental test platform is built. The results show that the WPEEH is able to generate a maximum power of 17.2 mW at an oscillation frequency of 1.5 Hz. In the actual wearable test, the proposed energy harvester is able to supply the harvested energy to the low-power electronic devices through capacitors, and it enables to light up 42 LEDs as well as to drive the digital thermo-hygrometer to work continuously and stably. Apart from having excellent properties of a high output power and low drive frequency, the proposed energy harvester also exhibits a high energy density (7.1 × 10–5 W/cm3). What’s more, the speed of human movement can be predicted and calculated for different individuals by testing the results of the swing frequency with a maximum error of 2.71 %. The investigation proves that the proposed WPEEH can measure human movement and has great potential in the field of power supply for low-power electronic devices.

Energy Harvesting Deadline Monotonic Approach for Real-time Energy Autonomous Systems

This paper presents an innovative scheduling algorithm designed specifically for real-time energy harvesting systems, with a primary focus on minimizing energy consumption and extending the battery's lifespan. The algorithm employs a fixed priority assignment which is the deadline monotonic policy, we have chosen it for its optimality and superior performance compared to other fixed priority scheduling methods. To achieve a balance between energy efficiency and system performance, we incorporated a DVFS (Dynamic Voltage and Frequency Scaling) technique into the algorithm. This adaptive approach enables precise control over the processor's operating frequency, effectively managing energy consumption while ensuring satisfactory system functionality. The core objective of our scheduling algorithm centers on optimizing energy utilization in real-time energy harvesting systems, specifically tailored to extend the battery's operational life. Rigorous evaluations, including comprehensive comparisons against established fixed priority scheduling algorithms, validate the algorithm's efficacy in significantly reducing energy consumption while preserving the system's overall functionality. By combining the deadline monotonic policy and DVFS technique, our proposed algorithm emerges as a promising solution for energy-autonomous systems, contributing to the advancement of sustainable energy practices in real-time applications. As energy harvesting technologies continue to progress, our algorithm holds valuable potential to provide critical insights for enhancing the efficiency and reliability of future energy harvesting systems.

Phase transformation enabled textile triboelectric nanogenerators for wearable energy harvesting and personal thermoregulation

The practical applications of environmentally friendly wearable textile triboelectric nanogenerators (t-TENGs) are constrained by inadequate heat dissipation, moisture permeability, and outdoor durability, particularly in humid and high-temperature environments. This study introduces a novel passive cooling strategy by integrating super-hydrophilic titanium dioxide solvent-free TiO2 nanofluids (TiO2 nfs) into cellulose acetate (CA) fibrous membranes (TiO2 nfs@CA) to achieve human comfort and efficient energy harvesting. Interestingly, the phase transformation of TiO2 nfs around boy temperature range (32-38 °C) effectively regulates the surface temperature of TiO2 nfs@CA fibrous membranes. In comparison with pristine CA fabric, TiO2 nfs@CA textile demonstrates exceptional solar reflectance (93.43%), high infrared emissivity (85%), excellent water vapor transport rate (12.6gm-2 h-1), and a significant cooling effect of 4-8 ℃ for both human skin and indoor environments. TiO2 nfs significantly enhances their ultraviolet resistance as well as mechanical properties and dielectric properties while improving triboelectric output performance with output voltage (66V), current (2.7 μA), and power density (82mWm-2). And TiO2 nfs@CA t-TENGs exhibit superior multifunctionality in terms of energy harvesting capabilities along with pressure sensing abilities for real-time movement monitoring including foot movements assessment as well as recovery evaluation for human body health maintenance purposes. Overall, TiO2 nfs@CA t-TENGs with the skin-friendly, dyeable, and recyclable properties provides a novel approach towards comfortable self-powered wearable devices that enable practical foot movement prediction alongside health monitoring.

Structural multistability for multi-speed wind energy harvesting from vortex-induced vibrations

Abstract Piezoelectric energy harvesters utilizing vortex-induced vibrations (VIV) have been extensively studied for converting wind energy into usable power for microelectronics. In this work, we explore the use of structural bistability to increase the range of flow speeds over which energy can be harvested without the need for complicated assemblies. We propose a harvester system featuring a piezoelectric transducer bonded to a cantilevered bistable composite laminate, which has two distinct equilibrium shapes at room temperature. To enhance the VIV, we attach a cylindrical bluff body to the free edge of the harvester. The structure’s inherent bistability allows for high power generation at two different flow speeds, contrasting with the single synchronization region typical of linear piezoelectric harvesters. We develop a reduced-order model to predict power output across varying flow speeds and validate these predictions through wind tunnel experiments, showing good agreement. Furthermore, we conduct a parametric study to optimize the model parameters for maximum power output. Our results demonstrate that the bistable harvester can generate up to 4.5 mW of power over a wind speed range of 9.3 m s−1–11.7 m s−1, outperforming the limited speed range of traditional linear VIV-based harvesters. This work underscores the potential to design VIV-based energy harvesters capable of operating efficiently across multiple flow speed ranges using a single structure with its dual stable configurations.

On the use of fractal geometry to boost galloping-based wind energy harvesting

In this study, we introduce fractal bluff bodies to galloping energy harvesters (GEH) to improve the performance of wind energy harvesting. Three basic sectional shapes are proposed for GEH, from which four fractal bluff bodies are developed. An aero-electro-mechanical model with distributed parameters is established to elucidate the underlying mechanism. Then numerical simulations and wind tunnel tests are conducted based on a fabricated prototype. Compared with the conventional galloping energy harvester with a cuboid bluff body (GEH-CB), the GEH with a fractal bluff body (GEH-FB) owns a lower cut-in wind speed and can generate higher voltages. The galloping critical wind speed for GEH-FB is reduced by 0.4 m/s. Furthermore, the output voltage can increase by 51.97% at the wind speed of 5 m/s. Especially, compared to the GEH-CB, the GEH-FB demonstrates a great advantage in terms of power density, being approximately 164.1% higher. Three-dimensional computational fluid dynamics (3D-CFD) shows that the wake vortex area and the space between the adjacent vortices both increase, which explains the aerodynamic mechanism of a large aerodynamic force and a performance enhancement in wind galloping energy harvesting. Finally, some practical application tests exhibit the effectiveness of the proposed fractal galloping harvesters.

Coupled Thermo-Electric-Elastic Piezoelectric Vibration Energy Harvester With Axial Movement: Modeling, Verification, and Analysis

Abstract In the field of rail transport and aerospace field, vibration energy harvesting is inevitably subjected to coupled excitations, including train wheel–track interaction induced friction heat and forced vibration, periodic thermal radiation, and vibration excitation. This paper investigates a coupled thermo-electric-elastic piezoelectric vibration energy harvester with axial movement under external heat flux and mechanical force load. The coupled forced vibration equation, coupled electric equation, and coupled thermoelastic heat conduction equation are derived and solved by Green's function theory. To analyze the effect of excitations on the response characteristics, the decoupled method is utilized to solve the coupled multi-field equations and obtain the displacement, electric, and temperature distribution closed-form solutions. The displacement coupling effect induced temperature distribution and the thermo-electric coupling effect triggered displacement are respectively decoupled and analyzed. The obtained closed-form temperature distribution and displacement solutions are verified by the finite element method. To further verify the obtained solutions, a numerical method is conducted by decoupling the coupled multi-field equations and comparing them with prior solutions. Additionally, the different height-to-length ratios, axially moving speeds, and external force load are analyzed in detail. The results indicate that the displacement, temperature distribution, and output voltage vary with external conditions due to the coupled multi-field effect. Overall, this work investigates the thermo-electric-elastic coupling effect on the axially moving piezoelectric energy harvesting, which is beneficial to promote theoretical investigations of the coupled multi-field energy harvesting system and accelerate the practical applications in the aerospace field.

Wet-adaptive Strain Sensor Based on Hierarchical Core-sheath Yarns for Underwater Motion Monitoring and Energy Harvesting

Bifunctional flexible electronics with motion monitoring and energy harvesting have broad application prospects in day-to-day activities of human society. Nevertheless, conventional electronics are difficult to adapt to the wear comfortability and anti-sensing interference properties in wet environments. Herein, a wet-adaptive spandex/graphene@cotton/polyurethane yarn (SGCPY) sensor is fabricated with excellent sensing and triboelectric performance, which comprises core layer of spandex fibers, middle layer of graphene@cotton sensing fibers and outer layer of spindle-knotted polyurethane nanofibers. Benefiting from its unique structure, as-prepared SGCPY sensor exhibits high mechanical properties (~80%), superhydrophobic performance (>130°), good strain sensitivity (1.82) and fatigue resistance (12000 cycles) even under water condition. The usage of the SGCPY sensor is demonstrated for the stable monitoring of human body motions and human-machine interaction in both air and water environments. When SGCPY sensor weave as plain fabric, the textile also can convert various mechanical energy into electric power for driving electronic device, showing a maximum voltage of ~3.9V and ~0.7V with solid-solid and liquid-solid contact. This work fosters the in-depth study of textile-based electronics for underwater applications and highlights the promising prospects of multi-functional flexible electronics based on textiles.

Efficient multichannel energy harvesting with dedicated energy transmitters in CR-IoT networks

Radio Frequency (RF) energy harvesting is strongly believed to be a sustainable solution to the power depletion problem in battery powered IoT devices. In addition to harvesting energy from ambient RF signals, the use of dedicated energy transmitters (ETs) that transmit energy to nearby IoT devices via RF signals has recently been proposed. In this paper, we study the problem of designing an energy harvesting policy for a group of cognitive radio-enabled IoT (CR-IoT) devices served by a number of ETs to maximize the minimum of their charging rates. With the help of cognitive radios, a CR-IoT node is capable of changing its frequency channel of operation allowing for multi-channel energy harvesting. Frequency channels are assumed to be opportunistically accessible depending on the activity of wireless users that are licensed to use those channels. The problem entails the design of the ET’s transmission policy (to what CR-IoT device, and over what channel) and the design of an ambient harvesting policy for every CR-IoT device (when it is not served by ETs). The problem is formulated as a mixed integer linear program (MILP). The objective is to maximize a lower bound on the total harvested energy in a given time frame per CR-IoT node. This optimization is subject to scheduling, total energy budget, and maximum transmit power constraints. Given the intractability of MILP formulations, a sub-optimal algorithm is proposed. Extensive experimentation is carried out to assess the effectiveness of the proposed sub-optimal algorithm by comparing it to the MILP’s solution obtained using IBM CPLEX solver with a limit on the execution time. We also combine our sub-optimal algorithm withe the CPLEX solver to produce a new two-stages algorithm that improves the original one by around 47%. Finally, we investigate the effect of multiple parameters including number of ETs, number of channels, and channel availability probability on the minimum charging rate.

A novel double-arch piezoelectric energy harvester for capturing railway track vibration energy

This study introduces a novel piezoelectric stack energy harvester with a double-arched frame structure. This design effectively cushions impacts from track vibrations, thereby protecting the fragile piezoelectric stack made of brittle materials. The energy harvesting characteristics of the device are studied in detail through experiments and theoretical simulations. The harvester's output voltage depends on the external resistance and increases with higher resistance. The optimal resistance for the single X-direction piezoelectric stack is 340kΩ, which can output 0.519mW of power under a 3Hz frequency and an 8kN sinusoidal load. The Y-direction piezoelectric stack outputs 0.012mW, resulting in a total output of 1.050mW for the entire harvester. The output power of the harvester is positively correlated with the load vibration frequency, increasing rapidly for frequencies below 9Hz. The impact of load magnitude on the harvester's output shows a generally linear increase. In impact experiments, the single X-direction piezoelectric stack successfully lit 54 LEDs under a 5J energy impact, demonstrating the harvester's high power density and potential for practical applications.

Facile hydrothermal synthesis of Bi2Fe4O9/rGO composite for catalytic reduction of 4- nitrophenol

Reduced graphene oxide (rGO) based composites have shown encouraging results in the application field of environmental protection, biology, energy harvesting and energy storage. This article presents a detailed study on the structural, microstructural, optical, and magnetic properties of hydrothermally prepared bismuth ferrite (Bi2Fe4O9)/rGO composite. The catalytic reduction of the toxic 4-nitrophenol into useful 4-aminophenol using the synthesized composite was illustrated. The Bi2Fe4O9/rGO composite sample demonstrated superior catalytic activity compared to pure Bi2Fe4O9, with a reaction rate constant of 0.26398 min–1. The stability and reusability tests forecasted the use of the composites as a low-cost catalyst for wastewater treatment applications.

Temperature-induced phase transition of liquid metal for shape-adaptive triboelectric nanogenerator

Flexible wearable electronics are expected to fit different parts of the human body. However, existing energy harvester and sensor still face the difficulties of adhering to complex surfaces and spontaneously fixing to the human body. In this work, a shape-adaptive triboelectric nanogenerator (SA-TENG) based on the phase transition of liquid metal (Cd-In-Sn-Pb-Bi eutectic alloy, LM) has been constructed to achieve efficient wearable energy collection and sensitivity-tunable pressure sensing. The shape-adaptive energy harvester (SA-EH) prepared by constructing hole arrays on the electrode could be directly fixed on different parts of the human body to harvest mechanical energy for driving wearable electronics. It can generate a transferred charge density of 90.5 μC/m2 and an average power density of 45.1 mW/m2. The natural oxide layer of LM suppresses the loss of liquid electrode and increases the output by 18 % with charge trapping-blocking effect. Furthermore, a sensitivity-tunable pressure sensor (ST-PS) fabricated with microstructures on the surface of SA-TENG can realize the sensitivity of over 2.48 kPa−1 as well as the ultra-wide pressure detection range from 0.42 kPa to 113.17 kPa, and the LM-based shielding layer can weaken external interference. This novel electrode design has greatly expanded the applications of TENGs in wearable electronics.

Multiple-arc cylinder under flow: Vortex-induced vibration and energy harvesting

The shape of a cylindrical cross-section affects the vibrational performance. The vortex-induced vibration (VIV) phenomena of multiple-arc cylinders were numerically investigated to assess their impact on hydrodynamic energy harvesting and potential vibration suppression across a flow velocity range of 0.2 m/s to 1.4 m/s (1.767×104<Re<1.237×105). The study involves five types of multiple-arc cylinders: 4-arc, 8-arc, 16-arc, 24-arc, and circular cylinders. The accuracy of the numerical method was validated through comparison with experimental data. Specifically, increasing the number of arcs generally enhances overall energy conversion efficiency. Then, the VIV response and energy conversion results of the 24-arc cylinder are similar to those of the circular cylinder with maximum efficiency. Notably, the 4-arc cylinder achieves a global maximum amplitude of 0.074 m (A*=0.83) and a power output of 4.4 W with the new P+T mode, making it the most effective configuration for flow velocities between 0.7 and 0.9 m/s. For vibration suppression of multiple-arc cylinders, the appropriate arc structure effectively reduces amplitudes. The small vortices generated by the arc structures disrupt the separation of normal vortices from the boundary layer, leading to approximately a 50% reduction in amplitude responses for 8-arc and 16-arc cylinders.

Simultaneous lightwave information and power transfer for NLOS ultraviolet communications under different weather conditions

In this work, a power allocation scheme for ultraviolet communication (UVC) with simultaneous lightwave information and power transfer (SLIPT) is proposed. Based on the non-line-of-sight (NLOS) single scattering channel model, the path loss and bit error rate (BER) performance of the UVC system with different geometrical parameters are analyzed. The effects of three types of weather, light rain, fine weather and severe fog conditions are considered. It is proved that the path loss is minimized on foggy days with minimum BER, followed by sunny days. The proposed SLIPT approach that the receiving energy is in turn divided into two parts, one for energy harvesting (EH) and the other for information decoding (ID). The system is designed to optimize energy harvesting for autonomous power supply, while ensuring a specified BER threshold and maintaining spectral efficiency. The effects of three types of weather on the SLIPT system are further investigated. It is demonstrated that under shorter communication distance(r), smaller elevation angle of receiving terminal (βR), larger field of view (FoV) and lower spectral efficiency(η) conditions, a higher percentage of energy is allocated for EH, with foggy days being the most favorable. The extreme geometric parameters of rainy condition can lead to the inability of communication, which needs to be limited to r ≤ 10 m, elevation angle of Rx ≤ 6°, FOV ≥100°, spectral efficiency ≤3, under the preset parameters in this paper.

TFE Terpolymers: Once Promising - Are There Still Perspectives in the 21st Century? Part II: Processing, Properties, Applications.

Tetrafluoroethylene (TFE) terpolymers have emerged as advantageous substitutes for polytetrafluoroethylene (PTFE). Therefore, they are being considered as alternatives to PTFE in many application areas. The advantages of TFE terpolymers include their facile processability at elevated temperatures, their solubility in some polar organic solvents, their inertness against aqueous acids, aqueous bases and a large number of mostly nonpolar organic solvents, their low dielectric constant, their low refractive index as well as useful electro- and thermochemical properties. This review on TFE terpolymers focuses on their processing including shaping and surface modification as well as on selected properties including wettability, dielectric properties, mechanical response behavior, chemical stability, and degradability. Applications including their use as elastomeric sealing material, liner and cladding layer as well as their use as material for membranes, microfluidic devices, photonics, photovoltaics, energy storage, energy harvesting, sensors, and nanothermitic composites will be discussed. The review concludes with a discussion of the future potential of TFE terpolymers and scientific challenges to be addressed by future research on TFE terpolymers.

Energy harvesting and movement tracking by polypyrrole functionalized textile for wearable IoT applications

Textiles for health and sporting activity monitoring are on the rise with the advent of smart portable wearables. The intention of this work is to design wireless monitoring wearables, based on widely available textiles and low environmental impact production technologies. Herein we have developed a polymeric ink which is able to functionalize different types of textile fibers (including silver conducting fibers, cotton, and commercial textile) with polypyrrole. These fibers were weaved together with a thinner silver conducting fiber and carbon fiber to form a touch-sensitive energy harvesting system that would generate an electric output when mechanical pressure is applied to it. Different prototypes were manufactured with loom weaving accessories to simulate real textile cloths. By simple touch, the prototypes produced a maximum voltage of 244 V and a maximum power density of 2.29 W m−2. The current generated is then transformed into a digital signal, which is further utilized for human motion or gesture monitorization. The system comprises a wireless block for the Internet of Things (IoT) applicability that will be eventually extended to future remote health and sports monitoring systems.

A passive self-excited oscillation AC low-voltage energy harvesting circuit without a bridge

Most current electromagnetic energy harvesters use capacitor voltage multipliers or boost circuits controlled by external signals to step up and store energy. However, for most low-voltage output electromagnetic energy harvesters, generating switching control signals and rectification results in significant energy loss. To reduce these losses, this paper proposes an AC boost circuit without additional power supply or rectifier bridge, designed for low-voltage electromagnetic energy harvesting. Both theoretical analysis and experimental results confirm the effectiveness of the proposed interface. The results show that the circuit can start self-excited boosting at an initial voltage of 0.48V and achieve an AC-DC conversion efficiency of 71.3 % within an input voltage range of 0–2.9V.