Flexible Generation Research Articles

Flexible thermoelectric generator and energy management electronics powered by body heat

Uninterrupted, efficient power supplies have posed a significant hurdle to the ubiquitous adoption of wearable devices, despite their potential for revolutionizing human‒machine interactions. This challenge is further compounded by the requirement of these devices to supply dependable energy for data-intensive sensing and transmission. Traditional thermoelectric solutions fail to deliver satisfactory performance under conditions of extremely low voltages. Here, we present a novel solution of a wearable thermoelectric generator integrated with an energy management system, which is capable of powering sensors and Bluetooth by harnessing body heat. Distinct from previous works, our innovation lies in its ability to consistently operate even with a minimal temperature difference (i.e., 4 K) between the human skin and the ambient environment, ensuring reliable data transmission within a time as short as 1.6 s. Furthermore, our system can recharge utilizing body heat under ultralow voltage conditions (30 mV). Our developed system provides a novel pathway for the continuous, reliable monitoring of self-contained wearable devices without depending on batteries.

Flexible Generation and Manipulation of Microwave Bottle Beam Using a Reconfigurable Metamirror

Bottle beams have drawn considerable research interest due to their attractive features and applications in beam trapping. Herein, the flexible generation and modulation of bottle beams utilizing a reconfigurable metamirror over a non‐negligible frequency band ranging from 8.5 to 9.5 GHz is investigated. A varactor diode is embedded into each meta‐atom on the metamirror enabling the achievement of a nearly 2π phase coverage by varying the external bias voltage. Based on the caustic theory, several configurations of bottle beam with distinct radius a are realized as proof‐of‐concept validation. Besides, the flexible modulation of the operating frequency is analyzed by judiciously controlling the bias voltages applied to the metasurface. The experimental results are in good agreement with those obtained from numerical simulations. Such a flexible bottle beam generator shows good potential in the microwave regime for near‐field applications, such as imaging and power transmission.

A Fully Self-Powered Wearable Leg Movement Sensing System for Human Health Monitoring.

Energy-autonomous wearable human activity monitoring is imperative for daily healthcare, benefiting from long-term sustainable uses. Herein, a fully self-powered wearable system, enabling real-time monitoring and assessments of human multimodal health parameters including knee joint movement, metabolic energy, locomotion speed, and skin temperature, which are fully self-powered by highly-efficient flexible thermoelectric generators (f-TEGs) is proposed and developed. The wearable system is composed of f-TEGs, fabric strain sensors, ultra-low-power edge computing, and Bluetooth. The f-TEGs worn on the leg not only harvest energy from body heat and supply power sustainably for the whole monitoring system, but also serve as zero-power motion sensors to detect limb movement and skin temperature. The fabric strain sensor made by printing PEDOT: PSS on pre-stretched nylon fiber-wrapped rubber band enables high-fidelity and ultralow-power measurements on highly-dynamic knee movements. Edge computing is elaborately designed to estimate multimodal health parameters including time-varying metabolic energy in real-time, which are wirelessly transmitted via Bluetooth. The whole monitoring system is operated automatically and intelligently, works sustainably in both static and dynamic states, and is fully self-powered by the f-TEGs.

Flexible generation of high-performance superposed perfect vortex beams with metasurfaces

Vortex beams have been adopted as optical communications tools to improve the information capacity of free-space communication. Topological charge (TC) is a key parameter for analyzing vortex beams, specifically when defining wavelength division multiplexing and information coding capabilities. TC is typically proportional to the radial intensity profile and orbital angular momentum. The radial intensity profile of perfect vortex (PV) beams is TC-independent, thereby improving the efficiency of image processing and optical fiber transmission; however, PV beams generated in traditional ways are restricted in their degree of freedom for multiplexing and it can be difficult to distinguish PV beams with different TCs. Herein, we numerically simulate a single all-dielectric geometric metasurface to generate PV beams with intensity patterns corresponding to the TC. We increase the types of intensity modes by superposing specific polarization states of Laguerre–Gaussian beams, creating many options for optical communication transmission purposes.

Evolution of Thermoelectric Generators: From Application to Hybridization.

Considerable thermal energy is emitted into the environment from human activities and equipment operation in the course of daily production. Accordingly, the use of thermoelectric generators (TEGs) can attract wide interest, and it shows high potential in reducing energy waste and increasing energy recovery rates. Notably, TEGs have aroused rising attention and been significantly boosted over the past few years, as the energy crisis has worsened. The reason for their progress is that thermoelectric generators can be easily attached to the surface of a heat source, converting heat energy directly into electricity in a stable and continuous manner. In this review, applications in wearable devices, and everyday life are reviewed according to the type of structure of TEGs. Meanwhile, the latest progress of TEGs' hybridization with triboelectric nanogenerator (TENG), piezoelectric nanogenerator (PENG), and photovoltaic effect is introduced. Moreover, prospects and suggestions for subsequent research work are proposed. This review suggests that hybridization of energy harvesting, and flexible high-temperature thermoelectric generators are the future trends.

Weavable yarn-shaped moisture-induced electric generator

Moisture-induced electric generation has emerged as a promising powering solution for next-generation wearable electronics since moisture is ubiquitous in the atmosphere. However, the practical applications of current film-shaped generators are limited by the challenge of wearable comfort and large-scale integration into wearables. Herein, we reported a strategy to prepare flexible and high-performance core-shell yarn-shaped moisture-induced electric generator (YMEG) via employing metal wire as the core electrode, polymer-salt solution-treated electrospun nanofiber mats as the active layer, and deposited sliver as the shell electrode. Through the moisture induced interaction between active layer and electrode, the obtained best performance of YMEG with length of 2 cm can produce a highly stable voltage of ∼0.8 V and a current density of 14.3 μA/cm2, reaching the state-of-the-art level among the reported one-dimensional fiber/yarn-shaped MEGs. Furthermore, benefiting from the weavability of YMEG, a dislocation ordered stacking strategy is created for effective integration of YMEG units into fabric, and realizing the simultaneous enhancement of output voltage and current. Such integrated fabric device can work normally under deformation and show successful practical use in power electronics and sensing system, demonstrating great potential to serve as an advanced energy accessory for wearable electronics.

Silicone Elastomer: Encapsulating Materials for Flexible Thermoelectric Generator

The flexibility of thermoelectric generators (TEG) is an encouraging factor to apprehend self-powered wearable applications as we move on in the demand of energy harvesting and compactness of electronic devices. Conventional rigid thermoelectric modules are not capable to cover irregular surfaces of the human body including unfavourable parameters like bulkiness, heaviness, fragile, and are expensive. In this study, we propose silicone elastomer as an obedient filling material for flexible thermoelectric generators matrix with conductive fabric as electrodes interconnect bismuth-telluride based thermoelectric legs which permit TEGs to adapt curved surfaces. This article presents the use of texture profile analysis (TPA) to mechanically characterize the hardness, adhesiveness, springiness, resilience, cohesion ratio, and chewiness of silicone elastomer. The ability to resist environmental effects such as water, moisture, heat, acid, alkali, corrosion, and weather aging are important for considering the filling material. In addition to these the statistically decreased adhesiveness and increased hardness, springiness, and chewiness identify silicone elastomer as a filling material for wearable thermoelectric devices. An output voltage of TEG for a temperature gradient of ~2°C shows it is highly sensitive to human body temperature.

A flexible piezoelectric generator based on KNN/PVDF composite films: Role of KNN concentration on the piezoelectric performance of generator

A flexible piezoelectric generator based on KNN/PVDF composite films: Role of KNN concentration on the piezoelectric performance of generator

Influences of the Runoff Partition Method on the Flexible Hybrid Runoff Generation Model for Flood Prediction

The partition of surface runoff and infiltration is crucial in hydrologic modeling. To improve the flood prediction, we designed four strategies to explore the influences of the runoff partition method on the flexible hybrid runoff generation model. The runoff partition strategies consist of a hydrological model without the runoff partition module, a two-source runoff partition method, an improved two-source runoff partition method considering the heterogeneity of the subsurface topography and land cover, and a three-source runoff partition method. The Xin’anjiang hydrological model was used as the modeling framework to simulate a six-hourly stream flow for the Xun River watershed in Shaanxi Province, China. And the saturation-excess runoff generation and infiltration-excess runoff generation mechanisms were combined to construct the flexible hybrid runoff generation model. The performances of the four strategies were compared and analyzed based on the continuous flow discharge as well as the flood events. The runoff components analysis method was used to test the model’s conformity with the reality of the watershed. The results showed that the three-source runoff partition method was not applicable to the flexible hybrid runoff generation model because it overestimated the surface runoff and almost ignored the subsurface stormflow runoff. The improved two-source runoff partition method outperformed the others as it considered the heterogeneity of the watershed.

Combining integrated solar combined cycle with wind-PV plants to provide stable power: Operation strategy and dynamic performance study

Building a multi-energy complementary power generation system is a viable way to encourage the use of renewable energy and decarbonize power generation. However, the intermittent nature of renewable power generation, such as photovoltaic and wind power, has prompted concerns regarding power grid stability. To balance such fluctuations, energy storage systems or other flexible power generation technologies should be integrated. In this paper, the peak regulation ability of integrated solar combined-cycle has been enhanced via employing a gas/oil exchanger between the top and bottom cycle. When integrating high penetration intermittent renewable energy, an appropriate operational strategy towards high-quality steady power output regulation is proposed. Dynamic performance analysis of the system, coupled characteristic of heat and mass transfer between subsystems have been highlighted. The case study demonstrates that fluctuations of the multi-energy complementary system power output can be controlled below 0.3 MW without renewable energy curtailment, even though wind-PV power generation fluctuates from 0.3 MW to 26.1 MW with variations per second reaching −2.8/3.7 MW. Furthermore, the system's levelized cost of electricity is down to 0.0512 $/kWh, which is cost-competitive with conventional power generation technologies.

Staggered-layer-boosted flexible Bi2Te3 films with high thermoelectric performance.

Room-temperature bismuth telluride (Bi2Te3) thermoelectrics are promising candidates for low-grade heat harvesting. However, the brittleness and inflexibility of Bi2Te3 are far reaching and bring about lifelong drawbacks. Here we demonstrate good pliability over 1,000 bending cycles and high power factors of 4.2 (p type) and 4.6 (n type) mW m-1 K-2 in Bi2Te3-based films that were exfoliated from corresponding single crystals. This unprecedented bendability was ascribed to the in situ observed staggered-layer structure that was spontaneously formed during the fabrication to promote stress propagation whilst maintaining good electrical conductivity. Unexpectedly, the donor-like staggered layer rarely affected the carrier transport of the films, thus maintaining its superior thermoelectric performance. Our flexible generator showed a high normalized power density of 321 W m-2 with a temperature difference of 60 K. These high performances in supple thermoelectric films not only offer useful paradigms for wearable electronics, but also provide key insights into structure-property manipulation in inorganic semiconductors.

Nanoengineering Approach toward High Power Factor Ag2Se/Se Composite Films for Flexible Thermoelectric Generators.

Herein, a flexible Ag2Se/Se composite film with a high power factor has been fabricated on a nylon membrane. The film has a high density and contains well-crystallized Ag2Se grains and embedded Se nanoinclusions, which exhibits not only excellent flexibility but also a comparably large room-temperature power factor and Seebeck coefficient of up to 2023 μW m-1 K-2 and -155 μV K-1, respectively. The high Seebeck coefficient is ascribed to the energy-filtering effect as caused by the Se/Ag2Se heterointerface. The assembled flexible thermoelectric generator (4-leg) exhibits a maximum output power of 1135 nW and a power density of up to 16.4 W m-2 when the applied temperature difference is 30 K. This work offers a feasible method to design high-performance and low-cost flexible thermoelectric generators used for wearable electronics.

High-performance g-C3N4 coated single-walled carbon nanotube composite films for flexible thermoelectric generators

Thermoelectric (TE) devices consisting of p-type and n-type single-walled carbon nanotubes (SWCNTs) based films, which can gather waste heat and turn it into electrical power, show potential application in supplying power for wearable electronic devices. In this study, graphitic carbon nitride (g-C3N4) has been prepared by high temperature pyrolysis of melamine and confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction pattern (XRD), respectively. Then the prepared g-C3N4 is composited with SWCNTs via mechanical mixing and vacuum-filtering method to obtain free-standing flexible g-C3N4/SWCNT thermoelectric composite films. The results demonstrate that g-C3N4 is efficiently covered on the surface of SWCNTs via interfacial π-π interaction, and g-C3N4 layer with several nanometers coated on SWCNTs simultaneously improves the electrical conductivity (σ) and the Seebeck coefficient (S) of g-C3N4/SWCNT. At a mass ratio of 2.5 % for g-C3N4/SWCNT, an optimal power factor value of 163.0 ± 1.0 μW m−1 K−2 is obtained for g-C3N4/SWCNT with the σ of 702.6 ± 1.6 S cm−1 and the S of 48.2 ± 0.2 μV K−1 at room temperature. Finally, a self-powering TE device composed of three pairs of p-n junctions is manufactured, and the actual output power is about 1.13 μW at the temperature difference of 50 K. As a result, this study offers a straightforward way to enhance the thermoelectric performance of single-walled carbon nanotubes, which can be utilized in flexible power generators.

Tellurium-nanowire-doped thermoelectric hydrogel with high stretchability and seebeck coefficient for low-grade heat energy harvesting

To harvest low-grade heat energy from human body, flexible thermoelectric generators (TEGs) are highly necessitated and have attracted significant interests. However, developing novel thermoelectric materials with high stretchability and seebeck coefficient is still challenging. Here we report a tellurium-nanowire-doped (Te-NW-doped) PEDOT:PSS/polyvinyl alcohol (TPP) hydrogel with excellent mechanical and thermoelectric characteristics. The effect of Te-NWs doping on the thermoelectric characteristics has been systematically investigated and the optimized TPP hydrogel exhibits a large seebeck coefficient value of 787 μV K−1, a low thermal conductivity of 0.468 W m−1 K−1, and a high tensile strain value of ⁓ 400%. Furthermore, a wearable thermoelectric module with a staggered Z-shaped structure is developed to achieve a voltage output of 138 mV when it is applied on the human arm. After being integrated with a power management unit, the TPP TEG module enables the operation of electronic devices like a commercial calculator and a white LED, which exhibits great potential for applications in human heat energy harvesting and wearable electronics.

Utilization of existing hydrocarbon wells for geothermal system development: A review

This review focuses on repurposing abandoned hydrocarbon (oil and gas) wells for the geothermal system development. There are approximately three million abandoned wells in the United States alone, and these wells emit alarming amounts of greenhouse gases and pose serious health hazards. These issues can be addressed by repurposing abandoned wells for the utilization of geothermal energy systems, leading to an increase in the number of geothermal systems deployments. Despite this potential, there are only a few numbers of installations of a geothermal system converted from hydrocarbon wells. Therefore, this study presents a comprehensive review on the current status of abandoned wells, potential risks to environment and human health they pose, and available feasibility and pilot studies on repurposing oil and gas wells for geothermal system development. The challenges, opportunities, and pathways to improve the current understanding of repurposing wells are presented in detail. Utilization of existing wells for an advanced geothermal energy storage system development for flexible energy generation is proposed.

Optimization of high-performance flexible thermoelectric generator from material synthesis to simulation and device application

Recently, flexible thermoelectric (f-TEG) power generators have attracted great attention due to their ability to capture waste heat from curved heat sources and convert it into useful electrical power. This study presents the material synthesis, theoretical optimization, module fabrication, and device application of a high-performance f-TEG. Firstly, n-type Bi2Te2.7Se0.3 and p-type Sb1.5Bi0.5Te3 TE materials were synthesized via a low-cost and fast fabrication process of mechanical alloying, cold pressed followed by a sintering process. The n-type and p-type materials exhibit maximum ZT values of 0.7 and 1.1, respectively. Then, the transport properties were used to optimize the geometry of the f-TEG in COMSOL Multiphysics. Based on the optimized parameters, a flexible module was developed which consists of 70 thermocouples each has a leg dimension of 1 × 1.5 × 2 mm3. The fabricated f-TEG measured on the arm generates an open circuit voltage, and power output of 93 mV, and 556 µW, respectively, at a temperature difference of 10 °C. The device was tested with a custom-made two-wire wireless ECG (electrocardiogram) and TEG harvester. Charge and discharge times of the supercapacitor and the efficiency of the TEG harvester were determined for the temperature difference of 10 °C. The test results show that the f-TEG can generate enough power to supply energy to the wireless ECG, but the efficiency of the boost converter is as low as 20%.

Математическая модель волновой зубчатой передачи с генератором волн внешнего деформирования

The paper considers a spatial mathematical model of a wave gear with the annular generator of the external deformation waves. Calculation method was based on determination of the elastic interaction between flexible wheel, rigid wheel and wave generator. Numerical studies confirmed the adequacy of the proposed mathematical model. Theoretical studies of the influence of preload in the gearing and initial clearance between the flexible wheel and the deforming washers on the forces acting on the wave generator bearings were conducted. It is shown that a decrease in the specified clearance leads to an increase in loads on the bearings. By calculation, torsional rigidity characteristics of the wave gear with an external deformation generator were obtained for various interference values in the gearing and the clearance.

A self-powered electro-coagulation system afforded by flexible electromagnetic flag wind generators for efficient removal of arsenic from water

In the past few years, human activities, such as mining and metallurgical industries, have made the arsenic concentration in natural waters elevate. To provide clean and safe water to people worldwide, tremendous endeavors have been made to accomplish low-cost and effective treatment of arsenic-containing water. Among the methods employed, electro-coagulation has been the one that stands out attributable to its high efficiency and low cost. However, its high energy consumption has become an obstacle to further applications, particularly in the regions where electricity is limited. Here, an innovative self-powered electro-coagulation system (SPECS) driven by flexible electromagnetic flag wind generators (FEFWGs) is developed to realize the power-free removal of dissolved arsenic in water. The FEFWGs exhibit an excellent output performance under a moderate wind speed (6.3 m s−1), with a peak open-circuit voltage of 3.7 V and a peak short-circuit current of 13.6 mA. Using the SPECS to purify polluted water, a large volume of wastewater containing 5 ppm of arsenic can be purified with our SPECS in 20 min, which is more efficient than that of existing reports.

A Software-Defined Radar for Low-Altitude Slow-Moving Small Targets Detection Using Transmit Beam Control

Low-altitude slow-moving small (LSS) targets are defined as flying at altitudes less than 1000 m with speeds less than 55 m/s and a radar crossing-section (RCS) less than 2 m2. The detection performance of ground-based radar using the LSS target detection technique can be significantly deteriorated by the diversity of LSS targets, background clutter, and the occurrence of false alarms caused by multipath interference. To address the LSS target detection problem, we have devised a novel two-dimensional electronic scanning active phased array radar system that is implemented in the software-defined radar architecture and propose a transmit beam control algorithm based on the low peak-to-average ratio (PAPR). Meanwhile, we devised a flexible arbitrary radar waveform generator to adapt to complex environmental situations. Field experiment results effectively demonstrate that our radar can be used to detect LSS targets. Moreover, an ablation experiment was conducted to verify the role played by transmit beam control and adaptive waveform optimization and generation in improving the system performance.

Optimizing Output Performances in Stationery Papers–Based Hybrid Inorganic–Organic Flexible Thermoelectric Generators

Flexible and foldable paper‐based thermoelectric generators (PTEGs) have drawn industrial attention due to the wide applications in heat energy harvesting and sensing. Herein, optimization of the output performances of flexible and hybrid inorganic–organic PTEGs fabricated on stationery paper substrates from poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and graphite as p‐type and n‐type materials, respectively, is presented. By choosing simplistic processes such as polyethyleneimine (PEI)‐treated graphite pencil traces and brush‐painted PEDOT:PSS films, robust and sustainable PTEG devices are fabricated. It is first time shown that different qualities of stationery papers can have significant impact on the output performance of PTEGs, attributed to their variance in substrate roughness. Thus, output powers of ≈1.93 and ≈0.68 nW for ΔT = 70 K are obtained for TE generators prepared from emery and office paper legs (four‐pair assembled on Kapton), respectively, suggesting emery paper to have significant better performance. Transient flexibility and fatigue of each device type are also tested where emery paper–based PTEG appears to be more robust. A detail comparison of the device performances on the different types of paper substrates are exclusively presented experimentally and thereafter computationally validated by COMSOL modeling to predictably control and enhance the output performance of reported PTEGs.