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Thermophotovoltaic (TPV) systems can be used to harvest thermal energy for thermoelectric conversion with much improved efficiency and power density compared with traditional photovoltaic systems. As the key component, selective emitters (SEs) can re-emit tailored thermal radiation for better matching with the absorption band of TPV cells. However, current designs of the SEs heavily rely on empirical design templates, particularly the metal-insulator-metal (MIM) structure, and lack of considering the overall performance of TPV systems and optimization efficiency. Here, we utilized a deep reinforcement learning (DRL) method to perform a comprehensive design of a 2D square-pattern metamaterial SE, with simultaneous optimization of material selections and structural parameters. In the DRL method, only the database of refractory materials with gradient refraction indexes needs to be prepared in advance, and the whole design roadmap will automatically output the SE with optimal Figure-of-Merit (FoM) efficiently. The optimal SE is composed of a novel material combination of TiO2, Si, and W substrate, with its thickness and structure precisely optimized. Its emissivity spectra match well with the external quantum efficiency curve of the GaSb cell. Consequently, the overall performance of TPV is significantly enhanced with an output power density of 5.78 W/cm2, an energy conversion efficiency of 38.26%, and a corresponding FoM of 2.21, surpassing most existing designs. The underlying physics of optimal SE is explained by the coupling effect of multiple resonance modes. This work advances the practical application potential of TPV systems and paves the way for addressing other multi-physics optimization problems and metamaterial designs. [ABSTRACT FROM AUTHOR]

Pandit[1] provides a review on the application of magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and related techniques, with which it is possible to access the motion of proteins, pigments, and lipids on sub-nanoseconds to millisecond timescales on very different length scales ranging from solubilized complexes to whole cells. Remarkably, the spectral density includes 50 high-frequency vibrational modes per pigment, besides a low-frequency part characterizing the pigment-protein coupling. Using this technique, excitation energy transfer between the bacteriochlorophyll a pigments of the LH2 complex of purple bacteria is studied. Two important points dealt with in the present Special Topic issue on "Photosynthetic Light-Harvesting and Energy Conversion" are the following: (i) Pigment-protein complexes undergo conformational transitions on many different timescales that include transitions between functionally relevant modes of light harvesting and photoprotection. [Extracted from the article]

An innovative electromagnetic energy harvester was developed using a compact four-ring single-resistor unit cell. To achieve efficient conversion of electromagnetic waves into electricity, we integrated the high-performance Bi2Te3 thermoelectric material onto the load resistor. Remarkably, this unit cell exhibits exceptional energy harvesting capabilities at a frequency of 5.8 GHz while maintaining polarization insensitivity. Through comprehensive analysis, we evaluated the energy harvesting efficiencies, power loss distribution, and current density distribution. Additionally, we investigated the impact of incident power on the unit cell's temperature and energy conversion efficiencies. To enhance energy concentration on the load, we ingeniously designed an "L-shaped" metal through-hole structure within the four-ring single-resistor unit cell. Our results demonstrate that the four-ring single-resistor unit cell achieves an impressive harvesting efficiency of 94.5% at 5.8 GHz, with a thermal conversion efficiency of 43.3 °C/W, an electrical conversion efficiency of 0.23 mV/°C, and an electrical response rate of 9.4 mV/W. Notably, when subjected to a power input of 7 W, the unit cell produces an output voltage of 65.9 mV, and its theoretical maximum output power reaches 180 mW. [ABSTRACT FROM AUTHOR]

In the energy harvesting field, it is critical to efficiently convert ambient vibrations into usable electrical energy, especially under conditions characterized by low amplitude and random excitations. This study introduces a novel hybrid bistable piezoelectric energy harvester (HBPEH) designed to optimize energy conversion in challenging environmental conditions. The HBPEH features a unique piezoelectric cantilever beam integrated with a dynamic amplifier at the fixed end, significantly enhancing both rotational and lateral displacements of the beam. This innovation lowers the threshold for snap-through events, crucial for maximizing energy transfer in bistable systems, and enables superior energy harvesting capabilities. Furthermore, the HBPEH demonstrates significantly higher power outputs when subjected to excitation intensities beyond critical levels, outperforming conventional energy harvesters. Extensive numerical and theoretical analyses confirm that the HBPEH offers a promising solution for applications hindered by suboptimal energy conversion rates. Its ability to operate effectively under diverse and unpredictable excitation conditions underscores the HBPEH's robustness and superiority in advanced energy harvesting scenarios. The design improvements introduced in this study highlight the potential of the HBPEH to transform energy harvesting approaches. By addressing the limitations of traditional harvesters, the HBPEH provides enhanced efficiency and reliability, making it suitable for a broader range of practical applications in variable environmental conditions. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) have been widely used to harness various forms of mechanical energy for conversion to electrical energy. However, the contentious challenge in characterising TENGs is the lack of standard protocols for assessing mechanical‐to‐electrical energy conversion processes. Herein, macroscopic signal analysis is used to identify three key charging events within triboelectric signals: charge induction (CI), contact electrification (CE), and electrostatic discharge (ESD). By considering two phases of motion during contact‐separation (approach and departure of the contact materials), CI arising from the motion of bound surface charge (varying electric field) between opposing contact materials is shown to dominate the measured displacement current signal, rather than the process of CE itself. Furthermore, the conventional signal (i. e. voltage, current, charge) interpretation of CE and CI during approach and departure phases is re‐assessed, to indicate that the sudden spike of current often observed immediately prior to contact (or after separation) arises from polarity inverting electrostatic discharge (ESD). This aspect of the measured triboelectric effect, which is often ignored, is crucial for the design of TENGs and hence, techniques to enhance the understanding and control over the stochastic occurrence of ESDs is explored. The methods proposed for the deconvolution of the macroscopic signal components of TENGs, and mitigation of ESD occurrences, will allow for precise quantification of the associated charging events. The applications of this study will template the design and development of future super‐TENGs with optimised energy conversion capabilities. [ABSTRACT FROM AUTHOR]

To alleviate resource shortage and environmental pollution, solar energy can be converted into thermal energy stored in phase change materials and in turn generate electrical energy. To enhance the solar energy utilization efficiency of solar‐thermal‐electrical conversion devices and prevent the heat loss to the environment at night, an intelligent solar‐responsive phase‐change system is innovatively designed consisting of a graphene aerogel film/paraffin wax stamen with an ultra‐high thermal conductivity of 46.7 W m−1 K−1, and thermally preserving aerogel film/liquid crystal elastomer bilayer petals that can bend solar‐responsively by the synergistic effect of solar‐thermal energy conversion and heat‐induced contraction. The solar‐responsive phase‐change system achieves daytime blooming for solar‐thermal conversion with simultaneous energy storage and nighttime closing for minimizing heat loss to the environment, exhibiting a high solar‐thermal conversion and energy storage efficiency of 89.4% and delaying its temperature drop by the thermal preservation effect of the petals. The assembled solar‐responsive solar‐thermal‐electric generator can reach an output voltage of 1033.8 mV at a light intensity of 500 mW cm−2 and continue to generate electrical energy during nighttime, holding tremendous promise in efficient solar energy conversion, storage, and utilization. [ABSTRACT FROM AUTHOR]

Electromagnetic generators are conventionally used to harvest energy from large water bodies, but they are ineffective for harvesting low hydro‐energy, such as raindrops or fogs, due to their bulky, heavy and immovable. Unfortunately, developing new strategies that are lightweight, small, and have high conversion efficiency to convert such low hydro‐energy into electricity remains a challenge. Herein, a flexible droplet‐based hybrid electricity generator (DHEG) consisting of a droplet‐based electricity generator (DEG) and an electromagnetic generator (EMG) is proposed to convert the dual energy of water droplets into electricity simultaneously. The DHEG is assembled by facilely merging DEG and EMG using conductive elastic multi‐walled carbon nanotubes/polydimethylsiloxane (MWCNTs/PDMS) film. The MWCNTs/PDMS film can not only serve as a bottom electrode for switching on the DEG, but also as an elastic component for the EMG to vibrate the coil when impacted by water droplets. Activated by a single 58.2 µL droplet falling from a height of 50 cm, the peak voltage, current and power generated by the DHEG are ≈84.6 V, ≈19.85 mA, and ≈595.8 µW, respectively. The energy conversion efficiency of the DHEG is up to ≈13.8%. This flexible hybrid generator may provide a promising strategy for effectively harvesting energy from raindrops. [ABSTRACT FROM AUTHOR]

This study introduces an innovative energy harvesting system designed for industrial applications such as fluid pipelines, air conditioning ducts, sewer systems, and subsea oil pipelines. The system integrates magneto-electric flow coupling and utilizes a dynamic vibration absorber (DVA) to mitigate the vibrations induced by fluid flow while simultaneously harvesting energy through magnetic dipole–dipole interactions in a vibration energy harvester (VEH). The theoretical models, based on Hamilton's Principle and the Biot–Savart Law, were validated through comprehensive experiments. The results indicate the superior performance of the small-magnet system over the large-magnet system in both damping and power generation. The study analyzed the frequency response and energy conversion efficiency across different parameters, including the DVA mass, spring constant, and placement location. The experimental findings demonstrated significant vibration reduction and increased voltage output, validating the theoretical model. This research offers new avenues for energy harvesting systems in pipeline infrastructures, potentially enhancing energy efficiency and structural integrity. [ABSTRACT FROM AUTHOR]

The study employed the water-based casting technique to prepare BST sheets, which were then combined with PDMS to BST composite sheets for wind energy harvesting. By adding 0.3–1.2 mol% Y 2 O 3 as an additive, the dielectric constant and the flexoelectric coefficient of the BST sheets were significantly enhanced. The Y 2 O 3 and BST powders were mixed to form a casting slurry with the appropriate viscosity, which was then cast into a sheet. After the sintering process, silver electrodes were coated on both surfaces of the sheet. To enhance the flexibility of the sheet, PDMS was applied to the silver-coated surfaces, creating a "sandwich structure" composite sheet. The flexoelectric properties of the composite sheets are characterized utilized the micro cantilever beam method. The energy harvesting experiments, conducted in a simulated wind tunnel environment, demonstrate that the composite sheets exhibit varying flexoelectric properties and energy conversion efficiencies, depending on their thickness. When the doping amount of Y 2 O 3 is 0.6mol%, the composite sheets with a BST layer thickness of 200 μm exhibit the highest flexoelectric coefficient of 1.1 μC/m; the composite sheets with a BST layer thickness of 100 μm exhibit the strongest current output capability of 4.2 nA. These findings indicate that the developed composite sheets could be promising for applications in renewable energy harvesting, particularly for capturing and converting wind energy into useable electrical power. [ABSTRACT FROM AUTHOR]

The primary goal of this study is to develop and test a small-scale horizontal-axis underwater Ocean Current Turbine (OCT) by creating a mathematical model for coupled dynamics aided by a Blade Element Momentum (BEM) simulation-integrated experimental approach. This research is motivated by the urgent need for sustainable energy sources and the vast potential of ocean currents. By integrating mathematical modeling with the experimental testing of scaled model OCTs, this study aims to evaluate performance accurately. The experimental setup involves encapsulating a 3D-printed turbine model within a watertight nacelle which is equipped with sensors for comprehensive data recording during towing tank tests. Through these experiments, we seek to establish correlations between the generated power, force, and rotational speed of the turbine's Permanent Magnet DC (PMDC) motor, which determines the turbine's capability to extract dynamic energy inflow. Moreover, this research aims to provide valuable insights into the accuracy and applicability of theoretical predictions in real-world scenarios by comparing the experimental results with BEM simulations. This combined approach not only advances our understanding of hydrokinetic energy conversion, but also contributes to the development of reliable and efficient renewable energy technologies that address global energy challenges while mitigating environmental impacts. [ABSTRACT FROM AUTHOR]

To enhance the piezoelectric properties of poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))-based composites and prepare a piezoelectric sensor with high sensitivity, two types of potassium sodium niobate (KNN) fillers, micro-particles (MPs) and micro-rods (MRs), were individually doped into a P(VDF-TrFE) matrix to form composites using a traditional solution-casting process. Identically, the two groups of P(VDF-TrFE)-based piezoelectric composites doped with KNN MPs and KNN MRs exhibited an enhanced β -phase and typical ferroelectricity with high residual polarization (P r), which resulted in good piezoelectric constant (d 33) and sensing electrical response. In contrast, the KNN MRs/P(VDF-TrFE) composite showed better piezoelectric output performance compared to the KNN MPs/P(VDF-TrFE) composite in all test scenarios, which is attributed to its depressed dielectric permittivity owing to the ameliorative conductivity dielectric loss. An output voltage (U) of 16 V, 4 V, and 6 V were recorded using 10 g zirconium ball impacting, finger tapping, and finger bending, respectively, in the KNN MRs/P(VDF-TrFE) sensors. This research demonstrates the impact of the filler shape on the electrical performance of P(VDF-TrFE)-based piezoelectric composites, which provides a reliable reference to enhance the energy harvesting and conversion performance of self-powered electronic devices. [ABSTRACT FROM AUTHOR]

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Sustainable energies from weather are the most ubiquitous and non-depleted resources. However, existing devices exploiting weather-dependent energies are sensitive to weather conditions and geographical locations, making their universal applicability challenging. Herein, we propose an all-weather sustainable glass surface integrating a triboelectric nanogenerator and radiative cooler, which serves as a sustainable device, harvesting energy from raindrops and saving energy on sunny days. By systematically designing transparent, high-performance triboelectric layers, functioning as thermal emitters simultaneously, particularly compatible with radiative cooling components optimized with an evolutionary algorithm, our proposed device achieves optimal performance for all-weather-dependent energies. We generate 248.28 Wm−2 from a single droplet with an energy conversion ratio of 2.5%. Moreover, the inner temperature is cooled down by a maximum of 24.1 °C compared to pristine glass. Notably, as the proposed device is realized to provide high transparency up to 80% in the visible range, we are confident that our proposed device can be applied to versatile applications. Weather-dependent energies are sensitive to weather and geographical conditions. Here, authors propose an all-weather sustainable device integrating a triboelectric nanogenerator and radiative cooler, enabling energy harvesting from rain and saving energy on a sunny day. [ABSTRACT FROM AUTHOR]

This paper provides a numerical simulation study of Magnetically Circular Layers of Triboelectric Nanogenerators (MCL-TENGs) for energy harvesting and self-powered sensing. The MCL-TENGs generate electrical energy by means of the conversion of mechanical energy into electrical energy through contact electrification and electrostatic induction. This paper concentrates on the numerical modeling of the copper/aluminum MCL-TENG and compares simulation results with experimental findings. The voltage comparison of copper MCL-TENGs (OC) between experimental and numerical simulations at 2000, 2500, and 3000 rpm showed Cu-EXP configuration voltages ranging from 4.1 to 4.4 V and Cu-FEM setup voltages ranging from 4 to 4.4 V. Meanwhile, aluminum MCL-TENGs showed Al-EXP configuration voltages ranging from 4.08 to 4.35 V and Al-FEM setup voltages ranging from 4 to 4.3 V across the third layer. The system can enhance the energy efficiency and sustainability of coastal bridge infrastructure by harvesting surplus energy from mechanical motion and converting it to electricity for self-powered sensing and monitoring systems. [ABSTRACT FROM AUTHOR]

Nanofluidic channels inspired by electric eels open a new era of efficient harvesting of clean blue osmotic energy from salinity gradients. Limited by less charge and weak ion selectivity of the raw material itself, energy conversion through nanofluidic channels is still facing considerable challenges. Here, a facile and efficient strategy to enhance osmotic energy harvesting based on drastically increasing surface charge density of MXenes subnanochannels via oxygen plasma is proposed. This plasma could break Ti–C bonds in the MXenes subnanochannels and effectively facilitate the formation of more Ti–O, C═O, O–OH, and rutile with a stronger negative charge and work function, which leads the surface potential of MXenes membrane to increase from 205 to 430 mV. This significant rise of surface charge endows the MXenes membrane with high cation selectivity, which could make the output power density of the MXenes membrane increase by 248.2%, reaching a high value of 5.92 W m−2 in the artificial sea‐river water system. Furthermore, with the assistance of low‐quality heat at 50°C, the osmotic power is enhanced to an ultrahigh value of 9.68 W m−2, which outperforms those of the state‐of‐the‐art two‐dimensional (2D) nanochannel membranes. This exciting breakthrough demonstrates the enormous potential of the facile plasma‐treated 2D membranes for osmotic energy harvesting. [ABSTRACT FROM AUTHOR]

This study primarily investigates the adaptability and performance of hydraulic–electric regenerative dampers for high-speed trains by substituting conventional primary dampers with hydraulic–electric regenerative dampers. The primary objectives are to develop a detailed model of primary suspension regenerative damper (PSRD) energy conversion that incorporates factors such as oil pressure loss, motor efficiency, and overall system efficiency, and to perform a comprehensive comparative analysis of vibration responses, wheel wear, comfort indices, and power generation using an integrated MATLAB and SIMPACK co-simulation platform. The results reveal that at an operational speed of 350 km/h, the dynamic responses of the carbody, bogie, wheelset, and dampers equipped with the proposed PSRD systems closely align with those of conventional primary vertical damper systems. The detailed PSRDs' hydraulic–mechanical–electrical model effectively captures the subtleties of oil pressure fluctuations and their impacts. The wear distribution and magnitude across the vehicle remain consistent during acceleration, constant, and deceleration speeds, ensuring uniform wear characteristics. Under real-world railway operational conditions, the ride comfort metrics of vehicles fitted with regenerative dampers are comparable to those with conventional primary vertical dampers. Furthermore, each regenerative damper can generate up to 21.72 W of electrical power, achieving a generation efficiency of 45.28%. Finally, a test rig was designed and fabricated to validate the primary suspension regenerative damper (PSRD) model, showing good agreement between predicted and actual damping force and power regeneration, with results indicating a peak damping force of 12.5 kN and approximately 230 W of regenerated power. This research provides a theoretical foundation and experimental validation for implementing power regeneration mechanisms in railway transportation, demonstrating that the hydraulic–mechanical–electrical PSRD model can fulfil the performance criteria of conventional dampers while offering substantial energy harvesting capabilities. This advancement not only enhances energy efficiency but also contributes to the sustainable development of high-speed rail systems. [ABSTRACT FROM AUTHOR]

This paper presents a complete electromechanical (EM) model of piezoelectric transducers (PTs) independent of high or low coupling assumptions, vibration conditions, and geometry. The PT's spring stiffness is modeled as part of the domain coupling transformer, and the piezoelectric EM coupling coefficient is modeled explicitly as a split inductor transformer. This separates the coupling coefficient from the coefficient used for conversion between mechanical and electrical domains, providing a more insightful understanding of the energy transfers occurring within a PT and allowing for analysis not previously possible. This also illustrates the role the PT's spring plays in EM energy conversion. The model is analyzed and discussed from a circuits and energy harvesting perspective. Coupling between domains and how loading affects coupled energy are examined. Moreover, simple methods for experimentally extracting model parameters, including the coupling coefficient, are provided to empower engineers to quickly and easily integrate PTs in SPICE simulations for the rapid and improved development of PT interface circuits. The model and parameter extractions are validated by comparing them to the measured response of a physical cantilever-style PT excited by regular and irregular vibrations. In most cases, less than a 5–10% error between measured and simulated responses is observed. [ABSTRACT FROM AUTHOR]

[Display omitted] Carbon nanostructures derived from human hair biowaste are incorporated into polyvinylidene fluoride (PVDF) polymer to enhance the energy conversion performance of a triboelectric nanogenerator (TENG). The PVDF filled with activated carbon nanomaterial from human hair (AC-HH) exhibits improved surface charge density and photoinduced charge generation. These remarkable properties are attributed to the presence of graphene-like nanostructures in AC-HH, contributing to the augmented performance of PVDF@AC-HH TENG. The correlation of surface morphologies, surface charge potential, charge capacitance properties, and TENG electrical output of the PVDF composites at various AC-HH loading is studied and discussed. Applications of the PVDF@AC-HH TENG as a power source for micro/nanoelectronics and a movement sensor for detecting finger gestures are also demonstrated. The photoresponse property of the fabricated TENG is demonstrated and analyzed in-depth. The analysis indicates that the photoinduced charge carriers originate from the conductive reduced graphene oxide (rGO), contributing to the enhanced surface charge density of the PVDF composite film. This research introduces a novel approach to enhancing TENG performance through the utilization of carbon nanostructures derived from human biowaste. The findings of this work are crucial for the development of innovative energy-harvesting technology with multifunctionality, including power generation, motion detection, and photoresponse capabilities. [ABSTRACT FROM AUTHOR]

A thermodynamic model of a skin-wearable annular thermoelectric generator (WATEG) system for harvesting human body heat is developed. The human skin is recognized as a three-layer structure, consisting of the subcutis layer, the dermis, and the epidermis. The heat exchange caused by blood perfusion and metabolic heat generation within skin tissue are taken into account using dual-phase-lag (DPL) bioheat conduction theory. Based on the maximum power density, the matched external load resistance, optimal fill factor, and optimal configuration dimensions of thermoelectric semiconductors and fin heat sink are provided through the numerical results. Additionally, the dynamic thermal responses of the WATEGs under various convective heat dissipation conditions at heat sink which occur during physical activities of the human body such as walking, jogging, and sprinting are also studied. The influence of metabolic heat generation within skin tissue is found to be relatively small and can be disregarded. However, neglecting blood perfusion results in a significant underestimation by approximately 30% in the steady-state energy conversion performance of the WATEG. The optimal fin height for achieving the maximum power density per unit mass of the aluminum-based heat sink is identified, and it is established at 10 mm, aligning with a heat convection coefficient of 10 W/m2 K. The analytical model developed in this paper proves to be highly beneficial in the design and fabrication of actual WATEGs used for self-powered wearable microelectronic devices. [ABSTRACT FROM AUTHOR]

Currently, a significant number of automobiles are equipped with internal combustion engines. In urban areas, a significant number of transportation methods have detrimental environmental effects through the release of pollutants resulting from the combustion of fossil fuels. In addition to the emission of toxic pollutants, internal combustion engines experience significant energy losses through exhaust emissions. Advanced technological applications have the potential to recover of a portion of the waste heat from exhaust ducts. Evaluations conducted by scholars across several disciplines highlight diverse perspectives on the recycling of thermal energy from exhaust gases as a means of mitigating pollution sources. However, this review focuses on the utilization of thermoelectric generators for harvesting a fraction of the aforementioned dissipated energy. The energy harvesting system is comprised of three components: the heat exchanger, which serves as the heat source; the cooler, which functions as the heat sink; and the thermoelectric generators, which act as the heat engine sandwiched between the heat exchanger and the cooler. This review examines the diverse exterior designs of heat exchangers and coolers and categorizes them accordingly. Additionally, it identifies the optimal installation locations for harvesting systems and explores the impact of design variations, choice of metals for manufacturing, and internal topography on the generation of electrical power. The primary findings of this review emphasize the significance of prioritizing the design of heat exchangers over coolers. This is because the uniformity of the temperature distribution within the heat exchanger plays a crucial role in governing the overall performance. Moreover, the installation of the system on petrol engines was seen as more cost-effective in comparison to its installation on diesel engines, primarily due to the higher magnitude of energy emitted from the exhaust gases of the former as opposed to the latter. To the best of the author's knowledge, this review classification has never been performed before. This can be considered a brief path map and a starting point for future work by researchers and investigators in designing heat exchangers and coolers and choosing the locations of TEG system installations. Then profitable investment from the data that has been prepared and summarized. [ABSTRACT FROM AUTHOR]

Flexoelectricity is often studied at the macroscopic scale for energy conversion and harvesting. The fact that microstructural heterogeneities can have a profound impact on a material's flexoelectric response has been under-appreciated and largely unexplored. To capture the effects of microstructure on both the macroscopic flexoelectric behavior and the development of microscopic electric field that drives such microscale processes, we develop a computational framework that enables the quantification of how the microstructure can influence the flexoelectric behavior of heterogeneous materials. The specific material evaluated is a porous composite of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride polymer and aluminum (Al) particles. The models explicitly resolve the Al particles and voids within the microstructure. The focus of the analysis is on assessing the physical mechanisms that enhance the macroscopic flexoelectric output and determining the effective flexoelectric coefficient of the inhomogeneous material. The approach also allows the contributions of individual strain gradient components to the effective flexoelectric coefficient to be delineated and offers a method of determining the flexoelectric coefficients associated with individual strain gradient components using measurements of the macroscopic flexoelectric responses of microstructures with different concentrations of Al particles and voids. It is concluded that the enhancement of local strain gradients near the Al particles and voids and the activation of contributions from multiple strain gradient components are the primary mechanisms for the increase in the macroscopic flexoelectric output of the composites. The macroscopic flexoelectric coefficient under cantilever beam bending is found to rise linearly with the Al content, consistent with the experimental measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two kinds of natural and renewable materials are combined to fabricate novel 2D membranes for osmotic energy conversion. • The heterogeneous membranes help to the balance of the trade-off between ion selectivity and ion flux. • A record power density of ∼16.57 W/m2 is achieved with the synergism of space and surface charge. • The ion transport mechanism is theoretically investigated by numerical simulations based on Poisson and Nernst–Planck models. As promising prospects for renewable power harvesting, two-dimensional (2D) nanochannels for osmotic energy capture in a reverse electrodialysis arrangement have garnered significant attention. However, existing 2D nanochannel membranes have shown limited power generation capabilities due to challenges in balancing ion flux and selectivity. Here, we construct montmorillonite (MMT)/TEMPO-mediated oxidation cellulose nanofibers (TOCNFs) nanocomposite membranes for enhanced ion transmembrane transport. The intercalation of TOCNFs not only enlarges the interlayer distance, but also provides abundant space charge inside the nanochannels. Benefiting from the strong ion selectivity and high ion flux, the composite membrane achieves a remarkable power output of ∼16.57 W/m2 in the gradient of artificial seawater and river water, exceeding that of the state-of-the-art heterogeneous membrane-based osmotic energy conversion systems. Both experimental and theoretical findings confirm that the synergism of space and surface charge plays a crucial role in promoting osmotic energy conversion. This research contributes valuable insights into the optimization of 2D membranes for efficient clean energy harvesting purposes. [ABSTRACT FROM AUTHOR]

Ocean wave energy is an inexhaustible clean new energy resource, and wave direct-drive linear generator is an energy converter receiving wide attention, but it suffers from the deficiencies of difficult energy harvesting, slow movement speed, large size, and small power generation, etc., so there is an urgent requirement to develop high-efficiency small-scale energy conversion devices. In this paper, a Pneumatic Drive Linear Generator (PDLG) is provided as a high efficient compact wave energy converter (WEC). The structure design and automatic reciprocating control system for the PDLG are implemented. The field distribution characteristics and parameters effects are analyzed using the finite-element method based on scalar magnetic potential. Finally, a prototype was fabricated to verify the performance of the PDLG. The experimental results are in good agreement with that of the theoretical prediction. The results of the study show that the provided PDLG can meet the requirements of high efficient wave energy harvesting, compact structure, and larger power generation. [ABSTRACT FROM AUTHOR]

Thermal emission is typically associated with a blackbody at a temperature above absolute zero, which exchanges energy with its environment in the form of radiation. Blackbody thermal emission is largely incoherent both spatially and temporally. Using principles in nanophotonics, thermal emission with characteristics that differ considerably from those of a blackbody has been demonstrated. In particular, by leveraging intrinsic properties of emerging materials or via nanostructuring at the wavelength or sub-wavelength scale, one can gain control over the directionality, temporal coherence, and other more exotic properties of thermal radiation. Typically, however, these are fixed at the time of fabrication. Gaining dynamic control of thermal emission requires exploiting external mechanisms that actively modulate radiative properties. Numerous applications can benefit from such thermal emission control, for example, in solar energy harvesting, thermo-photovoltaic energy conversion, radiative cooling, sensing, spectroscopy, imaging, and thermal camouflage. In this Tutorial, we introduce thermal emission in two domains: the far-field and the near-field, and we outline experimental approaches for probing thermal radiation in both ranges. We discuss ways for tailoring the spatial and temporal coherence of thermal emission and present available mechanisms to actively tune these characteristics. [ABSTRACT FROM AUTHOR]

Mechanical energy harvesting performances of poly(vinylidene fluoride) (PVDF) based composites are most often correlated with their polar phase and the individual piezoelectricity of the used filler materials. Here we show that the significant enhancement of space charge polarization of the said composites can play the key dominant role in determining their mechanical energy harvesting performance regardless of their polar phase and individual piezoelectricity of the used fillers. For this purpose, ionic liquid has been incorporated into PVDF/0.5(Ba0.7Ca0.3)TiO3–0.5Ba(Ti0.8Zr0.2)O3 (BCZT) composites which led to a huge enhancement in space charge polarization. The gradual addition of ionic liquid into 10 wt% BCZT loaded PVDF (PBCZT) has helped in extraordinarily enhancing the conductivity gradually which has confirmed the huge enhancement of space charge polarization. However, after a certain limit of ionic liquid addition, the polar phase of the composite films is decreased. Despite this, the output voltages from the piezoelectric and piezo-tribo hybrid nanogenerators (PENGs and HNGs, respectively) fabricated by using the developed films have been found to be increased gradually with the increase in the ionic liquid amount in PBCZT composite. As the amount of BCZT filler was kept fixed for all the films, this result has confirmed the key role of space charge polarization of PVDF-based composites in determining their mechanical energy harvesting performances compared to the effect of polar phase and individual piezoelectricity of filler. The optimized PENG and HNG devices have shown the output voltage as high as 52 and 167 V, respectively, with power densities ∼85 and 152 μ W cm−2 which predicted their excellent usability in real life energy conversion devices. This work also shows that the effect of extraordinarily enhanced space charge polarization is effective in improving the performance of all types of mechanical energy harvesting devices regardless of their mechanisms (piezoelectric or hybrid). [ABSTRACT FROM AUTHOR]

Composable life under the extensive global warming of the Earth encourages the progress of renewable energy devices and the adoption of new technologies, such as artificial intelligence. Regarding enormous potential of wave energy and its consistency, wave energy converter (WEC) plays vital role in uniform energy harvesting field. In this paper, the significant environmental changes in the ocean prompt us to propose an intelligent feedback control system to mitigate the impact of disturbances and variable wind effects on the efficacy of WECs. Deep reinforcement learning (DRL), as a powerful machine intelligence technique, is capable of identifying WECs as black-box models. Therefore, based on the DRL model, the disturbance and unmeasured state variables are simultaneously estimated in the extended state observer section. Leakage in identification data and real-time application requirements of limited number of layers in the deep neural networks are compensated by implementation of immersion and invariance-based extended state observer which improves coping with the unwanted exogenous noises as well. In the overall intelligent control system, the estimated parameters are inputted into the DRL as the actor-critic networks. The initial actor network is responsible for predicting the control action, while the subsequent critic network determines the decision criterion for evaluating the accuracy of the actor's estimated amount. Next, the output value of the critic stage is backpropagated through the layers to update the network weights. The simulation test results in MATLAB indicate the convergence of unmeasured parameters/states to the corresponding true values and the significance of newly designed intelligent DRL method. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) is one of the forefront technologies in energy harvesting, which can convert mechanical energy into electricity. Polydimethylsiloxane (PDMS) has been widely used as a friction layer for TENGs due to its high electron affinity and flexibility. In this work, a novel and green approach to fabricating a high-performance PDMS TENG is proposed by using yeast cells. Porous-structured PDMS produced by the formation of CO2 products of a fermentation reaction of baker's yeast is found to significantly improve the TENG performance. The effects of yeast cell concentration in PDMS on morphologies, chemical composition, and TENG performance of the porous PDMS films are investigated. It is found that the average pore size formed in PDMS film depends on yeast cell concentration, which affects the electrical outputs of TENG. The modified PDMS TENG showed improved TENG performance with the highest power density at 5.14 w/m2. The application of the fabricated porous PDMS to harness mechanical energy from body movement is demonstrated. Our work has presented a novel and effective technique using a biological approach to modify PDMS into a porous structure using yeast cells, which has the potential for flexible and wearable TENG to harvest mechanical energy from body movement. [ABSTRACT FROM AUTHOR]

Natural organisms have developed various biological ion channels/transporters to maintain normal life activities to adapt to changing environments. Significantly, ion transporters with active ion transport property show much more controllability on these activities due to a variety of external stimuli, giving guidance to construct artificial counterparts for overcoming the issues in simple nanofluidic systems restricted by self‐diffusive ion transport. Herein, a 2D nanofluidic system based on a Janus membrane (i.e., JM) is constructed, which can achieve light‐driven active ion transport and do favor for ionic power harvesting in electrolyte systems with equal concentrations. The JM is obtained through sequentially assembled montmorillonite (MMT) decorated with photoelectric molecules (i.e., PMMT) and MXene nanosheets. Due to the formed intramembrane electric field and temperature gradient caused by the efficient charge separation and localized thermal excitation under light illumination, a photovoltaic‐driven force and thermo‐osmotic are generated for preferential ion transport. In addition, the unidirectional active transport is employed to harvest ionic power, showing an output power density of 2.0 mW m−2 and a high‐performance energy conversion efficiency of 8.3 × 10−4%. The effects of the light intensity, electrolyte concentration and species on energy conversion performance are investigated, showing the university for ionic power harvesting. [ABSTRACT FROM AUTHOR]

Osmotic energy harvesting was a promising way to alleviate energy crisis with reverse electrodialysis (RED) membrane-based technology. Charged hydrogel combined with other materials was an effective strategy to overcome problems, including restricted functional groups and complicated fabrication, but the effect of the respective charges of the two materials combined on the membrane properties has rarely been studied in depth. Herein, a new method was proposed that charged hydrogel was equipped with charged filter paper to form dual network fiber-hydrogel membrane for osmotic energy harvesting, which had excellent ion selectivity (beyond 0.9 under high concentration gradient), high ion transference number and energy conversion efficiency (beyond 32.5% under wide range concentration gradient), good property of osmotic energy conversion (~4.84 W/m2 under 50-fold KCl and ~6.75 W/m2 under simulated sea water and river water). Moreover, the power density was attributed to the surface-space charge synergistic effect from large amounts overlapping of electric double layer (EDL), so that the transmembrane ion transport was enhanced. It might be a valid mode to extensively develop the osmotic energy harvesting. [ABSTRACT FROM AUTHOR]

Modern energy systems are large distributed systems and, as a rule, contain energy storage systems and, in particular, hydrogen batteries and hydrogen production systems. The use of hydrogen for energy transportation has recently been actively studied in a number of scientific projects. To ensure continuous operation of instrumentation and control equipment on long hydrogen pipelines (gas and cryogenic), it is important to ensure constant autonomous power supply to these systems. This can be solved using micromechanical energy microgeneration systems for the uninterrupted operation of various sensors, which are installed in large numbers on almost all elements of the structure and infrastructure. In addition, an important area of scientific research is the revision of the concepts and appearance of traditional devices of modern renewable energy: windmills, solar cells, turbines, etc. Fundamentally new energy devices are on the agenda, capable of recovering mechanical energy of any power and supplying it to the consumer in the form of a given specific energy flow. Collection of chaotically distributed natural energy of the environment (mechanical energy in the form of: vibrations, acoustic vibrations, wave energy, gusts of wind, tornadoes, precipitation, vibrations of the earth's crust, etc.), as well as collection of dissipated energy from artificial sources (iron and automobile highways, airstrips, spaceports, production facilities, etc.) with the help of mechanical microgenerators will allow the recovery and conversion of mechanical energy of various powers, including low power, into a universal energy carrier - hydrogen. Mechanical vibrations of artificial origin are of particular interest due to their widespread use for domestic and industrial purposes in a wide range of vibrations. The energy of mechanical vibrations can be collected and converted into electrical energy using piezoelectric, electromagnetic, triboelectric or electrostatic (capacitive) energy converters. Electrostatic microelectromechanical energy converters are considered the most promising among other energy converters, since their manufacturing processes are based on standard technology for the production of integrated circuits and microelectromechanical systems. Energy conversion by an electrostatic converter is carried out due to an external mechanical force that does work against the force of attraction of the charged electrodes of a variable capacitor. To transfer the received electrical energy to the load of the consuming device, the electrostatic converter is connected to the corresponding electrical circuits (conditioning circuits). Such a system as a whole is a kind of microgenerator or energy collector. Microenergy flow recovery systems integrated into large energy systems will ensure the collection and recovery of significant amounts of energy for remote energy consumers. At the same time, the concept of a distributed mechanical energy recovery system is quite simple: a mechanical energy receiver - a converter into electrical energy - a preliminary electrical storage device - an energy distributor - an electric energy accumulator - an electrolyser - a hydrogen accumulator - a fuel cell. To optimize the operation of the working circuit, including preliminary electrical systems for energy storage and conversion: capacitors and electric energy accumulators, electrolyzers; To ensure their durability and reliability, flexible automatic control of electrical power distribution is necessary. The real work was done to solve that problem. In addition, for extended and large power facilities it is important to ensure widespread sensory control of system parameters. At the same time, if all sensors receive power from an autonomous energy-generating device, then the costs of creating extended communications for instrumentation will be sharply reduced. In addition, the reliability of the control system will significantly increase. The results of studying operation features of a kinetic microgenerator with reduced output voltage are presented. The performance of a multi-stage modified Bennet doubler is compared to a system including a two-stage modified Bennet doubler and a diode-capacitor voltage divider. It is shown that with an increase of the number of stages in the modified Bennet doubler, the conversion of mechanical energy into electrical energy becomes less and less efficient. At the same time, for achieving the maximum energy accumulation rate (power), a two-stage power amplifier based on the Bennet doubler is preferable. It is established that when analyzing the operation of a diode-capacitor voltage divider, it is necessary to take into account the intrinsic (reverse) capacitances of the discharging diodes affecting the divider operation significantly. The divider behavior features while changing the load resistance and the intrinsic capacitances of the discharge diodes are found and analyzed. Analytical expressions linking the main characteristics of the microgenerator as a whole with the parameters of the electronic components used are derived. It is shown that for expanding the range of the "correct" division of the divider, it is necessary to use discharge diodes with minimal intrinsic capacitances, and also that connecting a load to the Bennet doubler as a voltage divider changes the permissible capacitance modulation depth of the variable capacitor. This paper examines the concepts of creating large energy-generating flows based on arrays of micromechanical energy converters placed on optimal energy-efficient receiving surfaces and analyzes the issues of cryogenic production, storage, consumption and transportation of hydrogen. Stationary and mobile cryogenic storage systems for hydrogen are considered. Much attention is paid to the safety of large cryogenic and gas hydrogen systems. [ABSTRACT FROM AUTHOR]

After an extensive review of previous research, it was evident that the heat exchanger design governs the harvesting of electricity from the I.C. engine exhaust gases, which is then included, and not the cooler, which is then excluded. This was determined by the range of temperature differences between the inlet and outlet of the heat exchangers, which were significant larger than those of the coolers. Therefore, the cold-side temperature of the thermoelectric generator was considered to be constant. However, this limitation reduces the CPU time and costs. In this study, the authors developed and solved differential equations that describe turbulent flow within heat exchangers. A modified k-ɛ turbulent model with a finite volume method was used along with an automatic adaptive mesh generation technique to achieve a precise numerical simulation and convergent criterion. Additionally, the authors proposed five interior designs for the heat exchangers, including empty, hybrid girders, zigzag girders, punched zigzag girders, and waffles, while preserving the same number of thermoelectric generators (60 units) in each design and keeping the external dimensions of the heat exchanger unchanged at 400 × 305 × 25 mm3. The boundary conditions were kept the same for all five designs for suitable comparison. An acceptable level of convergence was achieved when the results were confirmed in the existing literature. The comparison among the five distinct designs was based on the results obtained regarding the conversion of energy to electrical power (i.e., energy harvesting) and the pressure drop caused by the interior design of the heat exchanger. The findings indicated that the heat exchanger with the highest surface temperature uniformity and a reasonable pressure drop could produce an acceptable output power. Therefore, the hybrid girder heat exchanger was the most efficient, generating approximately 731.2 W of energy, which was excellent when compared to a recent study [48] where the amount of energy produced was approximately doubled three and a half times. In addition, it achieved the best balance between the accepted harvested energy and a reasonable pressure drop of 170.7 mm H2O. This was followed by the zigzag girders at 537 W. Conversely, the empty design was found to be the least effective, generating only 210.5 W. [ABSTRACT FROM AUTHOR]

Nanofluidic membranes have demonstrated great potential in harvesting osmotic energy. However, the output power densities are usually hampered by insufficient membrane permselectivity. Herein, we design a polyoxometalates (POMs)-based nanofluidic plasmonic electron sponge membrane (PESM) for highly efficient osmotic energy conversion. Under light irradiation, hot electrons are generated on Au NPs surface and then transferred and stored in POMs electron sponges, while hot holes are consumed by water. The stored hot electrons in POMs increase the charge density and hydrophilicity of PESM, resulting in significantly improved permselectivity for high-performance osmotic energy conversion. In addition, the unique ionic current rectification (ICR) property of the prepared nanofluidic PESM inhibits ion concentration polarization effectively, which could further improve its permselectivity. Under light with 500-fold NaCl gradient, the maximum output power density of the prepared PESM reaches 70.4 W m−2, which is further enhanced even to 102.1 W m−2 by changing the ligand to P5W30. This work highlights the crucial roles of plasmonic electron sponge for tailoring the surface charge, modulating ion transport dynamics, and improving the performance of nanofluidic osmotic energy conversion. Nanofluidic membranes have great potential in harvesting osmotic energy, but performance is hampered by insufficient permselectivity. Here, the authors solve this problem with a polyoxometalate-based nanofluidic plasmonic electron sponge membrane. [ABSTRACT FROM AUTHOR]

In recent years, renewable and sustainable triboelectric nanogenerators have attracted attention due to their high energy conversion rate, and enhancing their functionality further contributes to their applicability across various fields. A pH-sensitive triboelectric nanogenerator (pH-TENG) has been prepared by electrostatic spinning technology, with anthocyanin as the pH indicator and environmentally friendly polyvinyl alcohol (PVA) as the substrate. Among many friction-negative materials, the pH-TENG exhibits the best combination with fluorinated ethylene propylene (FEP) and yields an open-circuit voltage of 62 V, a short-circuit current of 370 nA, and a transferred charge of 21.8 nC. At a frequency of 3 Hz, it can charge a 4.7 μF capacitor to 2 V within 45 s, effectively powering a thermometer. Furthermore, the presence of anthocyanin does not affect the pH-TENG's power generation performance and enables the monitoring of a wide range of environmental pH changes, with an ΔE change of 28.8 ± 7.6. Therefore, pH-TENG prepared with environmentally friendly materials can bring new available materials to the biological and medical fields. [ABSTRACT FROM AUTHOR]

Simultaneous wireless information and power transmission (SWIPT) allows the use of RF signals for both information detection and energy harvesting. Integration of cooperation, NOMA and SWIPT can provide energy-efficient, reliable, and spectral-efficient networks. Therefore, this study aims to design energy harvesting-enabled cooperative NOMA (C-NOMA) networks. This work investigates relay selection for multiple relay downlink C-NOMA networks with SWIPT in the presence of interference. The analytical closed-form outage probability expressions for the proposed relay selection are derived. Subsequently, the impact of various parameters, including the number of available relay nodes, energy harvesting parameters, and energy conversion efficiency, is analyzed on the performance of proposed networks. The finding showed that system performance improves with the number of intermediate relaying nodes, transmit power, and energy conversion efficiency. Comparative analysis of NOMA and time division multiple access TDMA proved the superiority of NOMA over traditional OMA schemes. [ABSTRACT FROM AUTHOR]

In the field of new environmental energy harvesting technology, wind energy and piezoelectric energy harvesting have become research hotspots. By utilizing wind energy into vibration energy, i.e., wind-induced vibration effect is a research hotspot in the field of environmental energy harvesting. This article comprehensively analyzes the research status and development trend of piezoelectric energy harvesters based on wind-induced vibration effects at home and abroad. It was found that the conversion process of wind energy to vibration energy is mainly based on flutter, galloping, and acoustic resonance. The conversion of vibration energy into electrical energy is mainly piezoelectric power generation, supplemented by magnetic induction power generation and friction power generation. For high power density and small volume application scenarios, resonant cavity type wind vibration energy collection is the main development trend. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP) doped with 4-N,N-dimethylamino-4-N-methyl-stilbazolium tosylate (DAST) composites with various concentrations of DAST dye is prepared using the casting method. The crystal structure and optical properties of the pure and P(VDF-HFP)/DAST composites with various contents of DAST dye are investigated using various techniques such as UV–Vis spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and polarized optical microscopy (POM). The analysis of XRD data and FTIR spectra revealed that the β-fraction has been improved in the composite samples with increasing the content of DAST dye. Analysis of UV spectra displayed that the optical band gap of P(VDF-HFP) pure copolymer is 5.41 eV and has been reduced to be 3.75 eV for P(VDF-HFP)/10 wt% DAST that will be suitable for efficient systems of energy conversion and multijunction-based layer solar cells. Also, it is found that the nonlinear and linear optical parameters of the composite samples are DAST dye-dependent. Thermally stimulated depolarization current (TSDC) technique has been applied to investigate the dipolar and space charge relaxations of the composites. Moreover, it is observed that the pyroelectricity and piezoelectricity are enhanced with increasing the content of DAST dye. The highest content of the DAST dye showed maximum values of the pyroelectric and the piezoelectric coefficients of ~ 4 × 10–5 C/m2 K and ~ 34 pC/N at stress of 6.27 × 105 Pa, respectively. Our results of the polymer/dye composites give an opportunity of a promising material for flexible piezoelectricity devices used in many potential applications and energy harvesting systems. [ABSTRACT FROM AUTHOR]

This article presents a novel 2.45 GHz compact double comb-shaped slotted rectenna system designed to capture RF energy from the environment. The proposed rectenna integrates two comb-like structures into a square patch antenna, and a voltage doubler rectifier circuit with a small footprint, measuring 48x31x1.5mm3. The design features semi-circular slots at the patch center to improve bandwidth and impedance matching, while the double comb structures enhance antenna return loss characteristics and radiation performance. The rectenna prototype was constructed on a 1.5 mm thick, cost-effective FR-4 substrate. Both modeling tools and measurements were used to analyze the rectenna harvesting capacity. The analysis results show a return loss (S11) of -10 dB across a fractional bandwidth of 17.14% between 2.3 GHz and 2.48 GHz. The rectifier circuit achieves a maximum energy conversion efficiency of 83% at 2.45 GHz and an output voltage of 2.2V with a 2 kO load resistance. The analysis of experimental data demonstrates that the proposed rectenna efficiently harvests RF energy from the surrounding environment. [ABSTRACT FROM AUTHOR]

The choice of mechanical and electrical topologies can affect piezoelectric energy harvesting efficiency, but the problem of achieving high-efficiency energy conversion in energy harvesters stacked as cantilevers has not been perfectly solved. This study focuses on the topology of piezoelectric elements in a stacked vehicle suspension vibration energy harvesting device. Through theoretical analysis, the stress expressions of the excited and driven elements are derived. The stress of the piezoelectric elements is affected by the positions of the connection and excitation points. A stress model was established for a four-piece piezoelectric element connected by a thin light rod in ANASYS. The simulation results show that the average stress in the piezoelectric bending element model is maximum when the excitation and connection points are located at both ends of the free end. Compared with the middle position of the free end of the piezoelectric element, the average stress of the model is increased by 92.904%. Considering the difference in voltage generated by piezoelectric elements, four kinds of electrical topology are designed and analyzed experimentally. When the driven elements are connected in parallel and then connected in series with the excited element, the output power varied the least with the change of load resistance. The system produces a high power and offers a wide selection of load resistors. When the load is 26 kΩ, a single set of four piezoelectric elements produces 86.407 mW of output power. [ABSTRACT FROM AUTHOR]

Tribovoltaic effect is a phenomenon of the generation of direct voltage and current by the mechanical friction on semiconductor interface, which exhibits a brand‐new energy conversion mechanism by the coupling of semiconductor and triboelectrification. Here, the origin, interfaces, characteristics, mechanism, coupling effect and application of the tribovoltaic effect is summarized and reviewed. The tribovoltaic effect is first proposed in 2019, which has developed in various forms tribovoltaic nanogenerator (TVNG) including metal‐semiconductor, metal‐insulator‐semiconductor, semiconductor‐semiconductor, liquid‐solid and flexible interfaces. Compared with triboelectric nanogenerator, the TVNG has the characteristics of direct‐current, high current density (mA‐A cm−2) and low impedance (Ω‐kΩ). The two mainstream views on the tribovoltaic generation mechanism, one dominated by built‐in electric fields and the other dominated by interface electric fields, have been elaborated and summarized in detail. The tribo‐photovoltaic effect and tribo‐thermoelectric effect are also discovered and introduced because they can easily interact with other multi‐physical field effects. The TVNGs are suitable for making energy harvesting and self‐powered sensing devices for micro‐nano energy applications. This paper not only revisit the development of the tribovoltaic effect, but also makes prospects for mechanism research, device fabrication and integrated application, which can accelerate the evolution of smart wearable electronics and intelligent industrial components. [ABSTRACT FROM AUTHOR]

Under the threat of energy crisis and environmental pollution, the technology for sustainable and clean energy extraction has received considerable attention. Owing to the intensive exploration of energy conversion strategies, expanded energy sources are successfully converted into electric energy, including mechanical energy from human motion, kinetic energy of falling raindrops, and thermal energy in the ambient. Among these energy conversion processes, charge transfer at different interfaces, such as solid–solid, solid–liquid, liquid–liquid, and gas‐contained interfaces, dominates the power‐generating efficiency. In this review, the mechanisms and applications of interfacial energy generators (IEGs) with different interface types are systematically summarized. Challenges and prospects are also highlighted. Due to the abundant interfacial interactions in nature, the development of IEGs offers a promising avenue of inexhaustible and environmental‐friendly power generation to solve the energy crisis. [ABSTRACT FROM AUTHOR]

Due to the development of wireless communications, there has been a growth in the use of IoT devices and sensor nodes. A potential power source for powering equipment in remote or inaccessible locations is necessary. This research investigates the feasibility of employing digital television (DTV) signals as an energy harvesting system, with a focus on RF-DC conversion using a voltage multiplier circuit. Commercial 5 and 9 element yagi-uda antennas are used as receiver for ambient DTV signal. The device's performance is initially evaluated within the laboratory setting, it has been shown that when the RF signal generator is at 660 MHz, the proposed energy harvesting device can generate a maximum DC voltage of 781.3 mV and 1056.4 mV for 5 and 9 element antenna, respectively. This is based on measurement of voltage output when using the input signal from DTV base stations in Thailand. It was found that the voltage output levels decreased gradually with increasing distance ranging from 153.4 V at 0.1 km to 4.5 mV at 10 km for 5 element yagi-uda antenna. In contrast, the 9-element yagi-uda antenna consistently exhibited higher voltage levels, ranging from 354.7 mV at 0.1 km to 12.6 mV at 10 km. [ABSTRACT FROM AUTHOR]

The search for novel materials with enhanced characteristics for the advancement of flexible electronic devices and energy harvesting devices is currently a significant concern. Multiferroics are a prominent example of energy conversion materials. The magnetoelectric conversion in a flexible composite based on a piezopolymer layer and a magnetic elastomer layer was investigated. The study focused on investigating the dynamic magnetoelectric effect in various configurations of external alternating and constant homogeneous magnetic fields (L-T and T-T configurations). The T-T geometry exhibited a two orders of magnitude higher coefficient of the magnetoelectric effect compared to the L-T geometry. Mechanisms of structure bending in both geometries were proposed and discussed. A theory was put forward to explain the change in the resonance frequency in a uniform external field. A giant value of frequency tuning in a magnetic field of up to 362% was demonstrated; one of the highest values of the magnetoelectric effect yet recorded in polymer multiferroics was observed, reaching up to 134.3 V/(Oe∙cm). [ABSTRACT FROM AUTHOR]

When microdroplets with quasi‐spherical contact angles coalesce together on a low‐adhesion substrate, the capillary‐inertial expansion of the liquid bridge induces a dramatic out‐of‐plane jumping event due to symmetry breaking. From the onset of merging, droplet jumping initiates after a capillary‐inertial time scale of tci∼1–100 ${t}_{\text{ci}}\sim 1\mbox{--}\,100$ μs with characteristic jumping speeds of order vj∼0.1 ${v}_{{\rm{j}}}\sim 0.1$ m/s. This coalescence‐induced jumping‐droplet effect is most commonly observed among a population of growing dew droplets on a superhydrophobic condenser, but can also occur by colliding deposited droplets together or during droplet sliding on fog harvesters. In this review, we cover the historical development of capillary‐inertial jumping droplets, summarize the decade‐long effort to rationalize the ultra‐low energy conversion efficiency and critical droplet size of the phenomenon, and then present 15 variations on a theme of jumping. Capillary‐inertial jumping droplets are not only a visceral illustration of the surprising power of surface tension at the microscale but they also have the potential to enhance phase‐change heat transfer, enable self‐cleaning surfaces, combat frost formation, harvest energy, and govern the rate of disease spread for wheat crops. [ABSTRACT FROM AUTHOR]

Rainbow trapping is a phenomenon that enables vibration confinement due to the gradual variation of the wave velocity in space, which is typically achieved by means of locally resonant unit cells. In the context of electromechanical metastructures for energy harvesting, this strategy is employed to improve mechanical-to-electrical energy conversion and thereby to maximize the harvested power. In contrast to structures endowed with either mechanical or electromechanical resonators, we investigate a hybrid configuration that leverages the synergistic interplay between them. We compare numerical results for different grading laws in comparison to prior efforts on the topic, demonstrating enhanced energy harvesting and wideband vibration attenuation capabilities of the hybrid metastructure. We also discuss the formation of grading-induced localized modes and we shed light on the role of the motion of individual resonators on the overall power output increase. [ABSTRACT FROM AUTHOR]

The development of high-performance lead-free K0.5Na0.5NbO3-based piezoceramics for replacing commercial lead-containing counterparts is crucial for achieving environmentally sustainable society. Although the proposed new phase boundaries (NPB) can effectively improve the piezoelectricity of KNN-based ceramics, the difficulty of achieving saturated poling and the underlying multiscale structures resolution of their complex microstructures are urgent issues. Here, we employ a medium entropy strategy to design NPB and utilize texture engineering to induce crystal orientation. The developed K0.5Na0.5NbO3-based ceramics enjoys both prominent piezoelectric performance and satisfactory Curie temperature, thus exhibiting an ultrahigh energy harvesting performance as well as excellent transducer performance, which is highly competitive in both lead-free and lead-based piezoceramics. Comprehensive structural analysis have ascertained that the field-induced efficient multiscale polarization configurations irreversible transitions greatly encourages high saturated poling. This study demonstrates a strategy for designing high-performance piezoceramics and establishes a close correlation between the piezoelectricty and the underlying multiscale structures. There are difficulty of achieving saturated poling and understanding of multi-scale structures in (K, Na)NbO3 ceramics. Here, the authors find atomic-scale polymorphic distortion and micrometer-scale high-density thin striped domains, which is key for high saturated poling. [ABSTRACT FROM AUTHOR]

Harnessing and effectively utilizing abundant and sustainable solar energy is regarded as a promising solution to the global energy crisis. Forests, being nature's largest light energy capturing units, bestow oxygen and shelter upon all living beings, making them an invaluable gift to humanity. Apart from serving as natural air ionizers, load-bearing structures, and traditional building materials, wood and its derivatives can also be employed in cutting-edge sustainable applications. Their manifold advantages encompass a naturally porous and hierarchical structure for efficient water and nutrient transport, low thermal conductivity, mechanical stability, as well as versatile chemistry achieved through structural engineering and chemical or thermal modifications. This review provides an overview of the synergistic optical and thermal applications of wood for seawater desalination, wastewater treatment, and light management in energy-efficient buildings. The emphasis lies on elucidating the structure and application properties of wood with respect to establishing a symbiotic relationship between solar energy and wood towards sustainability. [ABSTRACT FROM AUTHOR]

Energy transformation requires replacing power plants based on fossil raw materials with renewable energy. Energy harvesting plays an important, although not fully appreciated, role here. Distributed, local power supply systems for small receivers, based on various sources which previously dissipated energy, may contribute to changing the current energy paradigm. This article presents an overview of energy harvesting technologies and various energy sources used in this process. Particular attention was paid to sources of a less conventional nature. The aim of this article is to encourage and direct scientists with the potential to explore this topic to look for new, previously unexploited energy sources and innovative and effective methods of obtaining useful energy in the harvesting process. [ABSTRACT FROM AUTHOR]

Conventional wearable bio-integrated electronics predominantly utilize materials such as silicon, which possess rigid and flat characteristics, in contrast to the flexible and curved nature of the human skin. This mismatch poses challenges in developing wearable devices specifically engineered to monitor electrophysiological signals, deliver therapeutic stimulations, convert biomechanical energy, and, most importantly, establish high-quality interfaces between biological tissues and devices. An effective strategy includes incorporating innovative materials that possess mechanical properties like skin with high biocompatibility. Through material processing with design and engineering strategies, the fabrication of ultrathin and stretchable devices that can completely attach to the contour of the skin is possible. This review highlights the importance of materials that possess both mechanical compatibility with the skin and established biocompatibility. Furthermore, the design strategy and engineering of the materials allow devices to encompass stretchability and form conformal contact with the skin. Then, we explore a range of devices, including sensors, stimulators, and energy harvesters, specifically designed for optimal integration with the skin. Lastly, the conclusion offers insights into potential prospects. [ABSTRACT FROM AUTHOR]

Magnetostrictive alloys hold great promise for Energy Harvesting applications due to their inherent durability. However, their implementation often results in usable voltage ranges that fall significantly below common electronic standards like 1.6, 3.3, and 5 volts. Consequently, the utilization of electronic circuits becomes essential to amplify the voltage and enhance energy conversion efficiency. Over the past few decades, numerous conversion techniques have been devised for other intelligent materials, such as piezoelectrics, some of which have even made their way into commercial products. Surprisingly, there is a dearth of specialized techniques, if not a complete absence, tailored to magnetostrictive devices. Among potential solutions, a suitable AC–DC Boost converter stands out as a highly promising candidate for addressing this challenge, but this solution has never been fully characterized. Then, this paper presents thorough experimental validations of such a converter, driven by a real-time Arduino board equipped to measure source time periods and operate under various conditions. We present several cases demonstrating the circuit's substantial potential for enhancing energy harvesting from magnetostrictive materials. [ABSTRACT FROM AUTHOR]

A temperature-doubler circuit is the functional equivalent of a voltage-doubler in the thermal domain. Effective temperature-doubler circuits could benefit energy scavenging from fluctuating thermal resources, e.g. the diurnal cycle. However, the current paradigm relies on static photonic designs of the selective solar absorber or blackbody emitter, which aims at maximizing energy harvesting from either the sun or outer space, but not from both. Furthermore, photonic and thermal optimizations have not yet been coupled to maximize the power output. Here we develop a general framework to optimize the energy acquisition and conversion simultaneously to maximize a temperature-doubler's power output under a realistic solar-thermal boundary condition. With an ideal self-adaptive absorber/emitter to fully exploit the thermodynamic potential of both the sun and outer space, the theoretical limit of the temperature-doubler circuit's average output power in a diurnal cycle is found to be 168 W m−2, a 12-fold enhancement as compared to the blackbody emitter. We provide a numerical design of such a self-adaptive absorber/emitter, which, combined with a thermoelectric generator, generate 2.3 times more power than the blackbody emitter in a synthetic "experiment". The model further reveals that, as compared to traditional thermal circuits, the key merit of the temperature-doubler is not to enhance the total power generation, but to convert the fluctuating thermodynamic input to a continuous and stable power output in a 24 h day-night cycle. [ABSTRACT FROM AUTHOR]