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This paper presents the development of a novel low power weigh-in-motion (WIM) system that uses cylindrical piezoelectric (PZT) elements for the dual purpose of sensing axle loads and harvesting mechanical energy for its operation. It provides details on the characterization the PZT sensing elements, the conditioning of their signals and describes the algorithms developed for determining speed, axle load and vehicle classification. These algorithms were coded in MATLAB® and converted to C in a format suitable for installing in a low power microcontroller unit (MCU). The system has the capabilities of monitoring vehicle speed, number of axles, axle spacing, axle loads and vehicle classification. It was tested in the laboratory by applying a range of loads and loading frequencies through a servo-hydraulic loading system. The results suggest sufficient accuracy and precision in measuring vehicle speeds, axle loads and determining vehicle class. Its low power requirements provide an inexpensive and sustainable method for obtaining roadway traffic data.

The unique characteristics of graphene have generated a lot of interest in the research community. A concept of utilizing graphene and its derivatives in the development of energy harvesters has just appeared in recent decades. This paper focuses on the application of reduced graphene oxide (rGO), a graphene derivative, in the development of wearable mechanical energy-harvesters to enable self-powered wearable sensing systems. Harvesting of energy has been a state-of-the-art phenomenon due to the ever-increasing requirement of power to run the sensing systems. Flexible systems that used rGO to gather energy with intensities ranging from a few microwatts to a few hundreds of microwatts have been used. Some examples are presented, focusing on the class of piezoelectric and triboelectric-based energy harvesters, with descriptions of their material composition, manufacturing methods, operating principle, and performance. Finally, the challenges and drawbacks of rGO-based energy harvesters are discussed, along with some of the potential solutions.

Rates of mass and heat transfer at the wall of a square agitated vessel fitted with semicylindrical turbulence promoters were measured using the electrochemical limiting diffusion current technique. Variables studied were promoter diameter, spacing between successive promoters, promoter orientation, impeller speed, and impeller geometry. The data were correlated by empirical dimensionless correlations. The promoters increased both the wall mass transfer coefficients and the volumetric mass transfer coefficients by factors ranging from 1.1 to 1.59 and 1.25 to 2.09, respectively depending on the operating conditions. Vertical turbulence promoters enhanced the rate of mass transfer by 3–29% more than the horizontal promoters. Confirming their economic worth, the turbulence promoters enhanced the mechanical energy utilization of the reactor up to 96%. Power consumption measurements revealed that the 45 ° impeller was more energy-efficient than the 90 ° impeller up to 54%. Besides the novelty of using turbulence promoters in agitated vessels rather than their common use in flow ducts, the present study used chemically active promoters as a catalyst support in conducting diffusion-controlled catalytic reactions at the wall. The novelty of using chemically active promoters qualified the present promoters to outperform the chemically inert promoters in enhancing the mass and heat transfer rates.

Quantitative percussion diagnostics (QPD) is a non-destructive evaluation method that has been used successfully in a number of applications. This technique involves a rod that is actuated to impact a specimen with a given amount of kinetic energy and the resulting mechanical response of the specimen as a function of time is measured using a piezoelectric force sensor. The mechanical energy returned to the rod is then analyzed. Because contact with the specimen is on the order of a few hundred microseconds, QPD can be used in situations and for specimen conditions (e.g. high temperature) that are not feasible for other nondestructive testing methods. The objective of the present study was to evaluate the use of QPD for characterization of defects in specimens fabricated using two additive manufacturing methods, i.e. cold spray deposition and laser powder directed energy deposition (LPDED). Cold spray specimens were produced using commercially pure nickel with varied process conditions including gas type (i.e. helium and nitrogen) and deposition rate. In addition, a Ti–6Al–4V specimen was manufactured using LPDED with varying porosity content. All specimens were characterized using both QPD and destructive methods (i.e. cross-sectional metallography) to compare results for observed defect characteristics. Cold spray specimens exhibited a lower energy return when they contained more porosity and/or surface roughness. Microscopic plastic deformation at highly porous surfaces was indicated during percussion testing that reached a saturation level after repeated percussion. Overall, the results showed that QPD can effectively evaluate cold spray and LPDED specimens for porosity and surface roughness.

The safe lander dynamics is an important part of the lunar landing mission. In this paper, a discrete element method (DEM) for lunar soil is set up, and the finite element method (FEM) for the lander is set up by shell elements and beam elements. The lander is regarded as a multibody system composed of a cabin, legs and footpads, and its motion characteristics are solved by multibody dynamics (MBD). A DEM-FEM-MBD coupling algorithm is developed to simulate the landing process of the lander considering landing mode and buffer mechanism, whose correctness is verified by comparison with a full-scale experiment involving lunar lander on earth. The effects of the mass, landing velocity and attitude of the lander on the safe landing are discussed. The buffering mechanism and influencing factors of lunar soil are analyzed. The results show that the impact force peak and impact depth gradually increase with the increase in the landing velocity and mass of the lander. Two kinds of inclined landing modes are defined and compared with vertical landing. It is found that the force on the landing leg that first contacts the lunar soil is significantly greater than that on the landing leg, that contacts later. The impact force peak on the lander under the two inclined landing modes is similar, but the impact depth of the 1-2-1 mode is significantly greater than that of the 2-2 mode. In the process of landing, lunar soil has the function of buffering dissipation. The energy dissipation rate is affected by the physical characteristics of lunar soil and the mechanical energy of the lander.

Abstract Harvesting abundant mechanical energy has been considered one of the promising technologies for developing autonomous self-powered active sensors, power units, and Internet-of-Things devices. Among various energy harvesting technologies, the triboelectric harvesters based on contact electrification have recently attracted much attention because of their advantages such as high performance, light weight, and simple design. Since the first triboelectric energy-harvesting device was reported, the continuous investigations for improving the output power have been carried out. This review article covers various methods proposed for the performance enhancement of triboelectric nanogenerators (TENGs), such as a triboelectric material selection, surface modification through the introduction of micro-/nano-patterns, and surface chemical functionalization, injecting charges, and their trapping. The main purpose of this work is to highlight and summarize recent advancements towards enhancing the TENG technology performance through implementing different approaches along with their potential applications. Graphic Abstract This paper presents a comprehensive review of the TENG technology and its factors affecting the output power as material selection, surface physical and chemical modification, charge injection, and trapping techniques.

Flexible piezoelectric energy harvesters (PEHs) have attracted extensive interest because of their ability to transform mechanical energy into electric power. Here, PEHs were fabricated using P(VDF-TrFE)-based piezoelectric composite films containing lead zirconate titanate (PZT) powder and –OH-functionalized graphene (HOG) nanosheets (HOG-P/P). Among all composites, a high open-circuit voltage (Voc) of approximately 50 Vp-p and a maximum power density of 1.4 μW/cm2 were obtained from a HOG-P/P PEH with 0.10 wt% HOG nanosheets and 15 wt% PZT under bending–releasing mode. Moreover, the PEH exhibited a stable voltage output after 3000 bending–releasing cycles. In addition, the PEH harvested mechanical energy from human body movements and generated an output voltage and current of 60 V and 8 μA during the finger bending–releasing process, lighting up 30 commercial white LEDs. The enhanced piezoelectric performance can be attributed to the introduction of HOG nanosheets and PZT powder. This work provides an effective strategy for improving the output performance of P(VDF-TrFE)-based PEHs.

Self-powered implantable devices have the potential to extend device operation time inside the body and reduce the necessity for high-risk repeated surgery. Without the technological innovation of in vivo energy harvesters driven by biomechanical energy, energy harvesters are insufficient and inconvenient to power titanium-packaged implantable medical devices. Here, we report on a commercial coin battery-sized high-performance inertia-driven triboelectric nanogenerator (I-TENG) based on body motion and gravity. We demonstrate that the enclosed five-stacked I-TENG converts mechanical energy into electricity at 4.9 μW/cm3 (root-mean-square output). In a preclinical test, we show that the device successfully harvests energy using real-time output voltage data monitored via Bluetooth and demonstrate the ability to charge a lithium-ion battery. Furthermore, we successfully integrate a cardiac pacemaker with the I-TENG, and confirm the ventricle pacing and sensing operation mode of the self-rechargeable cardiac pacemaker system. This proof-of-concept device may lead to the development of new self-rechargeable implantable medical devices., Self-powered implantable devices have the potential to extend device operation, though current energy harvesters are both insufficient and inconvenient. Here the authors report on a commercial coin battery-sized high-performance inertia-driven triboelectric nanogenerator based on body motion and gravity that can be used to charge a lithium-ion battery and integrated into a cardiac pacemaker.

Soft low-Reynolds-number robotics hold the potential to significantly impact numerous fields including drug delivery, sensing, and diagnostics. Realizing this potential is predicated upon the ability to design soft robots tailored to their intended function. In this work, we identify the effect of different geometric and symmetry parameters on the motion of soft, autonomous robots that operate in the low-Reynolds-number regime and use organic fuel. The ability to power low-Reynolds-number soft robots using an organic fuel would provide a new avenue for their potential use in biomedical applications, as is the use of a polymeric biocompatible material as is done here. We introduce a simple and cost-effective 3D-printer-assisted method to fabricate robots of different shapes that is scalable and widely applicable for a variety of materials. The efficiency of chemical energy to mechanical energy conversion is measured in soft low-Reynolds-number robots for the first time, and their mechanism of motion is assessed. Motion is a result of a periodic and oscillatory change in the charge state of the gel. This work lays the groundwork for the structure-function design of soft, chemically operated, and autonomous low-Reynolds-number robots.

Interfaces between a liquid and a solid (L-S) are the most important surface science in chemistry, catalysis, energy, and even biology. Formation of an electric double layer (EDL) at the L-S interface has been attributed due to the adsorption of a layer of ions at the solid surface, which causes the ions in the liquid to redistribute. Although the existence of a layer of charges on a solid surface is always assumed, the origin of the charges is not extensively explored. Recent studies of contact electrification (CE) between a liquid and a solid suggest that electron transfer plays a dominant role at the initial stage for forming the charge layer at the L-S interface. Here, we review the recent works about electron transfer in liquid-solid CE, including scenerios such as liquid-insulator, liquid-semiconductor, and liquid-metal. Formation of the EDL is revisited considering the existence of electron transfer at the L-S interface. Furthermore, the triboelectric nanogenerator (TENG) technique based on the liquid-solid CE is introduced, which can be used not only for harvesting mechanical energy from a liquid but also as a probe for probing the charge transfer at liquid-solid interfaces.

Ferromagnetic liquids undergo reversible magnetization changes upon varying external magnetic field levels. The movement of ferromagnetic liquid droplets across a coil under an external magnetic field holds promise as an energy transducer from mechanical force to electricity; however, it suffers from an adhesive issue between the ferromagnetic liquid and the solid pedestal. We introduce a superhydrophobic support that uses antiwetting surfaces to remarkably reduce adhesion during the movement of ferromagnetic liquid droplets. Maxwell numerical simulation was utilized to analyze the working mechanism and improve further electrical outputs. By controlling the droplet size, the strength of the magnetic bottom and the tilting speed of the test condition, we generated a ferromagnetic liquid droplet-based superhydrophobic magnetoelectric energy transducer (FLD-SMET) that can convert vibrational energy to electricity. When a 100 μL ferromagnetic liquid droplet was used for FLD-SMET under a 13 mT magnetic field, an electrical voltage response of 280 μV and electrical current response of ∼7.5 μA were generated using a shaking machine with a tilting speed of 9.5°/s. We thus show that such a device can serve as a self-powered light buoy floating on a water surface. Our study presents an applied concept for the design of droplet-based energy harvesters to convert surrounding vibrational energy to electricity.

Electric energy generation from falling droplets has seen a hundred-fold rise in efficiency over the past few years. However, even these newest devices can only extract a small portion of the droplet energy. In this paper, we theoretically investigate the contributions of hydrodynamic and electric losses in limiting the efficiency of droplet electricity generators (DEG). We restrict our analysis to cases where the droplet contacts the electrode at maximum spread, which was observed to maximize the DEG efficiency. Herein, the electro-mechanical energy conversion occurs during the recoil that immediately follows droplet impact. We then identify three limits on existing droplet electric generators: (i) the impingement velocity is limited in order to maintain the droplet integrity; (ii) much of droplet mechanical energy is squandered in overcoming viscous shear force with the substrate; (iii) insufficient electrical charge of the substrate. Of all these effects, we found that up to 83% of the total energy available was lost by viscous dissipation during spreading. Minimizing this loss by using cascaded DEG devices to reduce the droplet kinetic energy may increase future devices efficiency beyond 10%.

Flywheel energy storage systems (FESS) are devices that are used in short duration grid-scale energy storage applications such as frequency regulation and fault protection. The energy storage component of the FESS is a flywheel rotor, which can store mechanical energy as the inertia of a rotating disk. This article explores the interdependence of key rotor design parameters, i.e., shape, operating speed, rotor radius, standby losses, and choice of material, and their influence on the energy storage characteristics of the FESS. Two commercially manufactured metal flywheels with distinct energy storage characteristics are used as case studies to examine the potential benefit of using shape optimization in combination with operating speed, size, and material selection for rotor design. A sequential hybrid optimization strategy that combines a global genetic algorithm with a gradient-based local method is used to solve the rotor shape optimization problem. The choice of an optimal combination of operating speed and rotor radius, together with shape optimization, is demonstrated to provide 21–46% improvements in the energy capacity of two existing commercial FESS designs. Results show that self discharge losses in the rotor can be reduced by designing optimally shaped rotors with large radii operating at low speeds. It is advantageous, on an “energy-per-cost of material” basis, to use steel as the rotor material for optimally shaped flywheels with large radii operated at low speeds. Conversely, aluminium is a better choice of material for flywheels with smaller radii operated at high speeds.

Light-fueled actuators are promising in many fields due to their contactless, easily controllable, and eco-efficiency features. However, their application in liquid environments is complicated by the existing challenges of rapid deformation in liquids, light absorption of the liquid media, and environmental contamination. Here, we design a photothermal pneumatic floating robot (PPFR) using a boat-paddle structure. Light energy is converted into thermal energy of air by an isolated photothermal composite, which is then converted into mechanical energy of liquid to drive the movement of PPFRs. By understanding and controlling the photothermal actuation, the PPFR can achieve an average velocity of 13.1 mm s-1 in water and can be modified for remote on-demand differential steering and self-sustained oscillation. The PPFR may be modified to provide a lifting mechanism, capable of moving 4 times the PPFR mass. Various shapes and materials are suitable for the PPFR, providing a platform for liquid surface transporting, water sampling, pollutant collecting, underwater photography, and photocontrol robots in shallow water.

The development of triboelectric nanogenerator (TENG) technology which can directly convert ambient mechanical energy into electric energy may affect areas from green energy harvesting to emerging wearing electronics. And, the material of triboelectric layer is critical to the mechanical robustness and electrical output characteristics of the TENGs. Herein, a MXene enhanced electret polytetrafluoroethylene (PTFE) film with a high mechanical property and surface charge density is developed. The MXene/PTFE composite film was synthesized by spraying and annealing treatment. With the doping of MXene, the crystallinity of composite film could be tuned, leading to an enhancement in the tensile property of 450% and reducing the wear volume about 80% in the friction test. Furthermore, the as-fabricated TENG with this composite film outputs 397 V of open-circuit voltage, 21 µA of short-circuit current, and 232 nC of transfer charge quantity, which are 4, 6, and 6 times higher than that of the TENG made by pure PTFE film, respectively. Therefore, this work provides a creative strategy to simultaneously improve the mechanical property and electrical performance of the TENGs, which have great potential in improving device stability under a complex mechanical environment.

The development of wireless monitoring is currently restricted by the short lifetime of batteries, requiring frequent replacement. Utilization of abundant mechanical energy from the surrounding environment has attracted increasing attention in real-time monitoring. Herein, a coil-levitated hybrid generator was developed for the efficient harvesting of mechanical energy from mechanical motion. The novel coil-levitated structure adapted to the metal and magnetic environment. The output currents were systematically analyzed at different operation modes based on the unique combination of triboelectrification, electromagnetic induction, and piezoelectric effect. Under the excitation of vibration frequency and amplitude of 8 Hz and 5 mm respectively, the as-constructed triboelectric nanogenerator delivered a peak power density of 11.40 W/m3 at 10 MΩ. Meanwhile, the middle electromagnetic part and bottom piezoelectric generator provided peak power densities of 6.97 and 79.93 W/m2 at 10000 Ω, respectively. More importantly, the battery charging experiment was verified, in which a 30 mA h Li-ion battery can be charged from 2.57 to 3.27 V in about 90 min. In sum, a self-powered temperature and vibration monitoring system was successfully developed based on hybrid generator, promising for realizing wireless monitoring of mechanical equipment without any external power supply.

Conventional teaching about the law of conservation of mechanical energy (LCME) often results with students trying to solve problems by remembering similar problems they already covered in classes. Consequently, many students fail to transfer their knowledge to simplest real-life problems. Therefore, a pre-test – post-test quasi-experiment was conducted to evaluate the effects of an alternative, system-based approach to teaching about LCME. The study included 70 upper-secondary students from the First Bosniak Gymnasium Sarajevo, Bosnia and Herzegovina. Firstly, all students learned about energy in a conventional way. Then they wrote a test on LCME and had three additional hours of teaching about this topic, where one group of students learned in line with the forces-variant of the system approach (e.g., discussing conservative and non-conservative forces) and the other group with the process-variant of the same approach (e.g., discussing system’s states and processes like in thermodynamics). For both variants, only three hours of system-based teaching proved to substantially improve the students’ level of LCME understanding compared to the level of understanding they had after conventional teaching. It follows that the system approach may work well at the upper-secondary level, if it is introduced through the scaffolding-and-fading technique. Keywords: quasi-experiment, mechanical energy, teaching materials, teaching strategies

The triboelectric nanogenerator (TENG) is a new mechanical energy harvesting technology in which the typical viscoelastic material polydimethylsiloxane (PDMS) is widely used. Micro-/nano-textures are often fabricated on the PDMS surface to enhance the electrical performance of TENG. As the contact region decreases to micro/nano scale, the adhesive forces become dominant. However, there is still a lack of contact mechanics model considering both material viscoelasticity and the adhesive forces to guide the surface texture design. In this paper, the explicit data-fitting formulas based on the fractional derivative Zener model are firstly derived to identify the viscoelastic constitutive parameters, which can not only avoid the influence of the initial contact point, but also ensure the accurate conversion between the creep compliance and the relaxation modulus function. Then a viscoelastic-adhesive contact model based on the fitted constitutive parameters is established, and the numerical algorithms such as bi-conjugate stabilized (Bi-CGSTAB) method and fast Fourier transform (FFT) technique are employed to analyze the effects of material viscoelasticity and texture sizes on the contact and electrical performance. It is shown that, compared with results from the elastic-adhesive contact model, the contact area ratio based on the viscoelastic-adhesive contact model is significantly larger, which is much closer to the experimental results. Among the selected sizes of pyramid texture, the higher electrical performance can be obtained from the textures with a smaller pitch and a larger width under the heavier applied load. This study can provide a theoretical reference for the design of viscoelastic surface texture of TENG.

Miniaturized or microscale generators that can effectively convert weak and random mechanical energy into electricity have significant potential to provide solutions for the power supply problem of distributed devices. However, owing to the common occurrence of friction and wear, all such generators developed so far have failed to simultaneously achieve sufficiently high current density and sufficiently long lifetime, which are crucial for real-world applications. To address this issue, we invent a microscale Schottky superlubric generator (S-SLG), such that the sliding contact between microsized graphite flakes and n-type silicon is in a structural superlubric state (an ultra-low friction and wearless state). The S-SLG not only generates high current (~210 Am−2) and power (~7 Wm−2) densities, but also achieves a long lifetime of at least 5,000 cycles, while maintaining stable high electrical current density (~119 Am−2). No current decay and wear are observed during the experiment, indicating that the actual persistence of the S-SLG is enduring or virtually unlimited. By excluding the mechanism of friction-induced excitation in the S-SLG, we further demonstrate an electronic drift process during relative sliding using a quasi-static semiconductor finite element simulation. Our work may guide and accelerate the future use of S-SLGs in real-world applications., It is difficult to achieve high current density and long lifetime for micro generators owing to the common friction and wear. Here the authors invent a microscale Schottky superlubric generator to tackle this issue, reporting not only high current and power densities but also long lifetime of at least 5,000 cycles.

In the past decades, many mechanical metamaterials with uncommon static properties have been reported. On the other hand, mechanical metamaterials possessing extraordinary dynamic performance, also referred to as acoustic/elastic metamaterials, have gained more and more attractions. Examples include acoustic cloaking metamaterials that can generate an invisible region for acoustic waves, zero-stiffness metamaterials that can isolate vibrating mechanical energy, origami-based metamaterials that can realize the directional transmission of elastic waves and so on. To better understand the mechanisms adopted in dynamic mechanical metamaterials and present a general view about the existing works, we have reviewed some representative works and categorized them based on the ways of how these mechanical metamaterials manipulate the interactions between matters and mechanical energy. To distinguish the different categories of the dynamic mechanical metamaterials, we use a pair of binary numbers to measure the changing states of the magnitude and direction of the energy flow, respectively. A summary of some research works with associated reference numbers is presented in this paper with emphasis on the operating frequency, working bandwidth, and characteristic size of the element.

Owing to their good flexibility, biocompatibility, and capability to convert mechanical energy to electrical energy, electrospun poly(vinylidene fluoride) nanofibers (PVDFNFs) have attracted considerable attention for energy harvesting as well as wearable and self-powered electronics. However, inadequate mechanical strength and low piezoelectric output are major concerns for their practical application. Herein, we report an effective method for fabricating mechanically robust PVDFNFs with enhanced piezoresponse by incorporating phenyl-isocyanate functionalized graphene oxide (IGO) as an efficient nanofiller. The presence of IGO endowed PVDFNFs with a rough surface morphology, enhanced crystallinity, and electroactive β phase. Excitingly, enhancements of 303% and 332% in the ultimate tensile strength and modulus, respectively, were achieved for the IGO-incorporated PVDFNFs. Furthermore, the acoustic sensitivity of the composites was 63.09% higher than that of the pristine PVDFNFs. The composites had a minimum sensing force of 0.012 N, which was 20% less than the minimum sensing force of the pristine PVDFNFs. The incorporation of IGO enhanced the power generation capability of the composites by 55.23% compared with that of the pristine PVDFNFs. Thus, the as-prepared composites hold great promise for the fabrication of mechanically robust, high-performance piezoelectric composites for mechanical energy conversion applications.

In this work, a systematic approach of waste (thermal/mechanical) energy harvesting and storage potential is studied in Ba0.85Zr0.15TiO3 (BZT) ceramics. The effect of stress on energy storage density (harvesting/storage) and electrocaloric performance is also studied. For this purpose, polarization–electric field hysteresis loops were recorded at various temperatures and uniaxial compressive stress. The Olsen cycle and electro-mechanical cycle are used for direct waste heat or mechanical energy to electrical energy conversion. A thermal energy-harvesting density of 42 kJ/m3 per cycle was obtained when the Olsen cycle was operated between 296–343 K and 0.25–1.5 MV/m. The electro-mechanical cycle-based energy harvesting is estimated as 78 kJ/m3 under the applied stress of 5–160 MPa and the electric field of 0.25–1.5 MV/m. The energy storage density is found as 39 kJ/m3 at zero stress field and 343 K, which increases to 53 kJ/m3 under the biased stress of 80 MPa in a wide operating temperature range of 296–328 K. It is observed that the high energy storage is a result of the reduction of the hysteresis loss. The electrocaloric temperature is found as 0.16 K and 0.18 K under the 0 and 80 MPa stress fields, respectively. Overall, the reported findings will enrich our understanding of the stress effect on BZT materials, which offers high performance for energy harvesting and storage-based applications. Moreover, this work can be also helpful in improving the energy storage density and electrocaloric effect via stress confinement.

With the increasing demand for smart wearable clothing, the textile piezoelectric pressure sensor (T-PEPS) that can harvest mechanical energy directly has attracted significant attention. However, the current challenge of T-PEPS lies in remaining the outstanding output performance without compromising its wearing comfort. Here, a novel structural hierarchy T-PEPS based on the single-crystalline ZnO nanorods are designed. The T-PEPS is constructed with three layers mode consisting of a polyvinylidene fluoride (PVDF) membrane, the top and bottom layers of conductive rGO polyester (PET) fabrics with self-orientation ZnO nanorods. As a result, the as-fabricated T-PEPS shows low detection limit up to 8.71 Pa, high output voltage to 11.47 V and superior mechanical stability. The sensitivity of the sensor is 0.62 V·kPa−1 in the pressure range of 0–2.25 kPa. Meanwhile, the T-PEPS is employed to detect human movements such as bending/relaxation motion of the wrist, bending/stretching motion of each finger. It is demonstrated that the T-PEPS can be up-scaled to promote the application of wearable sensor platforms and self-powered devices.

In this work, the discharging process of the binary mixture composed of sphere and sphere-paired particles in a two-dimensional silo was studied. High-speed camera and self-developed particle tracking velocimetry (PTV) program were used to capture the flow behaviors of all particles. The key parameters of mixed flow, including coordination number, horizontal displacement and mechanical energy loss in the discharge process, were highlighted. It was found that the increase of sphere-paired particles can decrease the average coordination number of particles during the discharging process. The analysis about the loss of mechanical energy and the horizontal displacement of particles indicated that sphere-paired particles preferentially squeezed out sphere particles from fast flow field above the outlet. Moreover, an empirical formula was proposed to assess the influence of the proportion of sphere-paired particles on the discharge flow rate. Sphere-paired particles tended to hinder the discharging process, which was caused by the rotation around their centroids and the angular deflection close to angle of the hopper.

With the excellent structural design, rotary triboelectric nanogenerator (R-TENG) is suitable for harvesting mechanical energy such as wind energy and water energy to build a self-powered electrochemical system for environmental science. The electrochemical performance has been greatly improved by using the pulsed direct-current (PDC) output of a TENG; however, a full-wave PDC (FW-PDC) is hardly realized in R-TENG devices due to existence of phase superposition. Here, a R-TENG with FW-PDC output is reported to perform a self-powered electro-Fenton system for enhancing the removal efficiency of levofloxacin (OFL). By adjusting the rotation center angle ratio between each rotator and stator unit, the phase superposition of R-TENG caused by multiple parallel electrodes can be effectively eliminated, thus achieving the desired FW-PDC output. Because of the reduced electrode passivation effect, the removal efficiency of OFL is improved by 30% under equal electric charges through using the designed R-TENG with FW-PDC output compared to traditional R-TENG. This study provides a promising methodology to improve the performance of self-powered electrochemical process for treating environment pollutions.

For harvesting, mechanical energy converts to electrical energy using piezoelectric devices. In this study, piezoelectric flexible (PF) was synthesized form composite materials of polyvinylidene di...

The triboelectric effect has recently demonstrated its great potential in environmental remediation and even new energy applications for triggering a number of catalytic reactions by utilizing trivial mechanical energy. In this study, Ba4Nd2Fe2Nb8O30 (BNFN) submicron powders were used to degrade organic dyes via the tribocatalytic effect. Under the frictional excitation of three PTFE stirring rods in a 5 mg/L RhB dye solution, BNFN demonstrates a high tribocatalytic degradation efficiency of 97% in 2 h. Hydroxyl radicals (•OH) and superoxide radicals (•O2－) were also detected during the catalysis process, which proves that triboelectric energy stimulates BNFN to generate electron-hole pairs. The tribocatalysis of tungsten bronze BNFN submicron powders provides a novel and efficient method for the degradation of wastewater dye by utilizing trivial mechanical energy.

Recently, a novel mechanical energy harvesting method named triboelectric nanogenerator (TENG) is reported, and it has aroused great repercussions in the academic fields. But, the complex preparation process still limits its wide application. In this paper, the cotton film was used as the triboelectric material to fabricate a novel wearable TENG (W-TENG). The polytetrafluoroethylene (PTFE) film and cotton film play the role of triboelectric pair. The W-TENG can be used to harvest low-frequency mechanical energy in our environment, especially for human body mechanical energy, and then convert them to electrical energy. In addition, the cotton coated with conductive ink plays the role of conductive material for TENG. The Voc and Isc of W-TENG can reach 556 V and 26 μA, respectively. As for the maximum power density of W-TENG, it can arrive at 0.66 mW/cm2. Also, a combined W-TENG was proposed to improve the electrical output. Moreover, the W-TENG can play the role of human motion sensor for human walking posture monitoring. This will open up a new path for the preparation of high output TENG at low cost, and promote the TENG devices in the field of sports monitoring.

Constructing hybrid nanogenerators (NGs) based on triboelectric effect and piezoelectric effect can combine the merits of the individual type of NG thus have drawn great attention in flexible wearable electronics. Herein, we prepared flexible BiFeO3 (BFO) film in a simple and cost-effective way, which was used to fabricate a wearable hybrid piezoelectric-triboelectric nanogenerator (H–P/TENG) with silk fiber. By optimizing the experimental conditions, the highest open-circuit voltage of 110 V and short-circuit current density of 3.67 μA/cm2 were achieved under 1 Hz contact-separation movement. The device also showed the best output power density of 151.42 μW/cm2 with load resistance of 250 MΩ. Stimulating by moving body, the fabricated H–P/TENG successively realized the harvest and conversion of mechanical energy into electric energy, demonstrating great potential to monitor posture and establish a self-powered system. Moreover, the proposed H–P/TENG exhibited great stable output after 1800 contact-separation cycles, indicating the outstanding structure stability and fatigue resistance. This work will provide not only a facile and viable way to realize the application of ferroelectric materials in H–P/TENG but also new opportunities for developing monitor posture and self-powered systems.

Summary An efficient energy-management strategy is critical for the energy utilization of triboelectric nanogenerators (TENGs), of which the switch and convertor are two key parts. However, common switches only withstand limited voltage (∼102 V), while the convertors for electrostatic energy are diversely designed without standard principles. Here, we report a simple, tunable auto-spark switch to achieve energy accumulation and fast release and develop a standard design procedure of matched transformer for electrostatic energy conversion. We establish an ultrahigh voltage (over 7.5 kV) energy-management system for TENG. Ultrahigh output charge of 660 μ C per cycle, pulsed power density of 11.13 kW m−2, and constant power density of 291 mW m−2 at 3 Hz are all achieved. With this energy-management unit, TENGs can continuously power a wireless sensors network at 1 Hz. This energy-management approach enables TENGs to present a breakthrough in practical applications.

The exploration of renewable energy technology is increasingly important owing to depletion of fossil fuels and the environmental pollution caused by the use of fossil fuels. Converting mechanical energy to electrical energy is one approach to developing renewable energy. However, the harvesting of ultralow-frequency mechanical energy is a challenge that limits the development of energy harvesting technology. To address this difficult problem, this paper proposes a nonlinear hybrid energy harvester in which an electromagnetic generator (EMG) and a triboelectric generator (TEG) are coupled to harvest the mechanical energy from ambient vibrations at ultralow frequencies. The energy harvester is combined with a quasi-zero-stiffness (QZS) mechanism composed of four QZS springs and a linear spring to produce a large-amplitude response and improve the energy harvesting performance. The effect of the mechanical condition (linear, quasi-zero-stiffness and bistable) on the efficiency of energy harvesting is analysed analytically and verified by theoretical and numerical analyses. The dynamics responses of the nonlinear energy harvester influenced by systematic parameters are also dissected. This work provides a guideline for improving the ultralow frequency ambient vibration energy harvesting performance of a TEG through nonlinearity.

With the rapid development of the Internet of Things (IoT), the number of sensors utilized for the IoT is expected to exceed 200 billion by 2025. Thus, sustainable energy supplies without the recharging and replacement of the charge storage device have become increasingly important. Among various energy harvesters, the triboelectric nanogenerator (TENG) has attracted considerable attention due to its high instantaneous output power, broad selection of available materials, eco-friendly and inexpensive fabrication process, and various working modes customized for target applications. The TENG harvests electrical energy from wasted mechanical energy in the ambient environment. Three types of operational modes based on contact-separation, sliding, and freestanding are reviewed for two different configurations with a double-electrode and a single-electrode structure in the TENGs. Various charge transfer mechanisms to explain the operational principles of TENGs during triboelectrification are also reviewed for electron, ion, and material transfers. Thereafter, diverse methodologies to enhance the output power considering the energy harvesting efficiency and energy transferring efficiency are surveyed. Moreover, approaches involving not only energy harvesting by a TENG but also energy storage by a charge storage device are also reviewed. Finally, a variety of applications with TENGs are introduced. This review can help to advance TENGs for use in self-powered sensors, energy harvesters, and other systems. It can also contribute to assisting with more comprehensive and rational designs of TENGs for various applications.

With the development of information technology, data acquisition based on Internet of things (IoT) distributed sensor network becomes more and more important. Therefore, a novel triboelectric nanogenerator (SC-TENG) based on the sock cloth to harvest mechanical energy. The sock cloth and PTFE film constitute the triboelectric materials of SC-TENG, and the copper foil is used as the conductive electrode. The SC-TENG can not only be used to harvest mechanical energy, but also can be used as the self-powered sensor in the field of intelligent sports. The maximum Voc and Isc of SC-TENG can achieve 267 V and 3.4 µA, respectively. And the maximum output power can arrive at 225.6 µW. As the lightweight, flexible and wearable TENG device, this design can promote the development of TENG devices in the intelligent sports.

Today, rapid depletion of energy sources forces us to discover alternative sustainable electrical energy sources quickly. The aim of this work was to develop a ternary composite of PU resin/carbon black/PZT to be an efficient mechanical energy harvester. Specifically, this present work attempted to find the optimum weight ratio of a PU resin/carbon black/PZT composite that could provide the highest mechanical-to-electrical conversion efficiency. The PU resin was the main matrix. Carbon black (CB) was added to improve conductivity while still maintaining good casting property. Then, PZT was added to generate electricity. Testing several weight ratios of this composite, it was found that the samples ratio of 60:20:20 was optimum and able to generate an average voltage of 0.357 V/in2. This ternary composite material has a candidate to into a practical and efficient electrical energy harvester source

The energy crisis has been global havoc due to increasing demand in energy sectors which further have a serious impact on declining fossil fuels. There is a quest to develop green alternative sources of energy such as biomass, geothermal, photovoltaics. The piezoelectric nanogenerator has also been a fascinating technology to harvest small level mechanical energy to an electrical output. The vibration energy from walking, rail/air vehicles, tires, sound waves are converted efficiently to usable energy. This report shows the fabrication of PVDF thin film using the solvent casting route. The various properties like structural, morphology, dielectric, piezoelectric, and ferroelectric are analyzed. Further, a piezoelectric nanogenerator was fabricated and results of poled and unpoled films have been investigated. The device output was utilized to light up a LED and charge a commercial capacitor.

In vehicles, problems happen while driving on bumps on road & improper road conditions. The objective of this research is to optimize the performance of the helical coil spring used in the suspension of cars of hatchback segment by varying different parameters of the spring to make it more efficient than the existing coil springs used in current hatchbacks. The helical compression spring utilized in mechanical system or shock may be a machine designed to free or damp shock impulse and dissipate mechanical energy. A helical compression coil spring which is used in four-wheel cars which are belonging in the hatchback category of the Indian automotive market. It is observed that the vehicle drifts towards one side due to the high weight of the suspension system and loads. This problem can be solved by redesigning and optimizing the suspension spring. This project consists of analytical methods and Finite Element Analysis completed from modeling, meshing, and post-processing of front suspension springs to validate calculations. By using Finite Element Analysis (FEA), the structural strength of the coil spring is also evaluated in present work. Based on theoretical and software result comparison is made for the optimum result which meets all requirements which were suggested.

This research paper is an attempt to present an insight into the use of micro electromechanical systems (MEMS) technology harvesting of green energy. One of the common examples of MEMS technology is by utilizing bimorph cantilever beams. Subsequently, it has also been discussed that Bimorph cantilever beam based sensors with high sensing ability could be used for harvesting energy from the physical environment. In this paper, we concentrate on the comparative analysis of the MEMS and piezoelectric materials which are used to design bimorph cantilever beams and convert mechanical energy into electrical energy. Detailed performance analysis of bimorph cantilever beams made of different materials has been carried out through various simulation models. Design and the simulation of bimorph cantilever beam is performed using Comsol multiphysics 5.2. state of art software. Comparative analysis of Lead zirconate (PZT-4D) and Lead zirconate (PZT-7A) has been done in this research to find more suitable material for fabrication of bimorph cantilever beams. PZT-7A is found to provide better electrical output for various analysis performed.

Polymer materials with mechanical energy-to-electricity conversion capability at high temperatures are highly desirable to develop energy harvesters, sensors, and other flexible devices for applications under harsh high-temperature conditions but remain an enormous challenge to develop. Herein, we report a polymer membrane that can convert mechanical energy into electricity at both room and high temperatures. The membranes were prepared by heat stabilization treatment of electrospun polyacrylonitrile (PAN) fibrous membranes to make PAN have a cyclized structure. The devices made of the treated PAN membranes can work at a temperature as high as 550 °C, which has never been reported on other polymer-based energy harvesting devices so far. A 2.5 × 2.5 cm2 device at 450 °C can generate a 9.7 V voltage (up to 62 V, 4 μA current) with a maximum power density of 26.4 mW cm−2. We further show that the oxidation cyclization of PAN due to stabilization treatment plays an essential role in achieving the high-temperature energy conversion. The energy conversion is mainly originated from a piezoelectric effect. We used the energy generated under high-temperature conditions to power commercial LEDs and charged capacitors to demonstrate the application. The electrical energy generated from a single device is sufficient to run a commercial LEDs. After rectification, it can also be stored in capacitors for further use. The PAN membranes are flexible and air permeable. They may form a novel polymer transducer candidate to develop flexible energy devices for various applications in high-temperature environments.

Generating electricity from the available mechanical energy (from a turbine) through an unconventional method involving piezoelectric material can reduce the complications involved in generation & transmission of the energy. Here we have developed an “Energy Harvesting Pulley” which converts the available mechanical energy into electrical energy with the help of piezoelectrics. This pulley is further covered with a layer of abrasive material. With most of the conventional sources of energy running out, the world is slowly moving towards unconventional ones like, solar energy, tidal energy, wind energy etc. Piezoelectric energy harvesting techniques are one such unconventional method of energy generation. The existing AC generators are designed to produce voltages as high as 120 or above & hence need a higher level of insulation. This also makes them overheat. On the other hand, our “Energy Harvesting Pulley” was found to produce AC voltages ranging from 20 V to 60 V by transmitting 1HP power through the pulley. The abrasive layer proved to be a sufficient insulator and it also gives us an additional advantage of reducing slippage. In essence this “Energy Harvesting Pulley” of ours is less costly, easier to insulate, & much safer to handle. Hence it can be used to generate voltages, as low as 20 V and as high as we want them to generate. The voltage generated can be increased even above 120 V by increasing the power transmitted through them.

Conventional vehicles depend on crude energy extracted from the fossil fuels such as diesel and petrol, which undergoes internal combustion to liberate the chemical energy stored inside the fuel. This energy is then converted into mechanical energy inside the engine to produce the necessary work for propelling the vehicle accompanied with release of incomplete combustion products such as CO and CO2. Now days a lot of research is concentrated on developing more efficient and eco-friendly ways of generating the energy for propulsion so as to reduce the amount of carbon footprint in the atmosphere. The present work is an effort in the direction of generation of energy for propelling the vehicles in an environmental friendly way by utilising compressed air. During the process of compression, work is being done on the air, which causes an increment in the total pressure of the air. This increment of the total pressure is stored as the energy inside the compressed air, which will be utilised for the running the vane of the motor to generate the necessary work for propulsion. The present work utilises the compressed air at 3 atm to run the motor. The work output of the motor for different vane angles was measured for various casing diameters of 50 mm, 100 mm, 150 mm respectively and the results were plotted. The average time of running of the motor was found out to be 7 h.

In this study, we developed an approach to additive manufacturing of three-dimensional (3D)-architected CoCrFeNiMn high-entropy alloys by direct ink writing combined with thermal sintering. The 3D-architected CoCrFeNiMn lattices exhibit the outstanding energy absorption capacity that expands the envelope of existing architected materials. Such a high-energy absorption ability originates from the bend-dominated deformation mode of the 3D-architecture as well as the fully-annealed homogeneous microstructure of equiaxed grains, which collectively lead to remarkable strain hardening upon deformation. Our study provides a new avenue for 3D-printing advanced architected materials with extreme mechanical energy absorption for a myriad of structural applications.

With the advent of electronic circuits, automation and hand held devices have become quite common in the life of mankind. Also, to reduce consumption of fossil fuels policy decisions are made wherein electric vehicles ply on the road by 2030. This increasing demand of energy has led to the development of sustainable and even low energy producing sources. In this paper, use of piezoelectric crystals for generation of electricity from pavement systems is discussed. Movement of vehicles on roads impart mechanical energy and piezoelectric crystals have been used to convert this mechanical energy to electrical energy. Using PZT rods, an energy harvesting unit has been developed and the effectiveness of this module has been investigated for pavement system comprising of sand and aggregate layers. Parametric studies have been carried out for different magnitudes of load and frequency of loading. The manuscript also compares the displacements of sand-aggregate system having PZT module at its interface with a system without the module. Experimental studies revealed that the voltage generated is dependent upon the stiffness of the PZT module and the voltage increases with magnitude and frequency of loading.

The timely biochemical detection of environmental pollutants or infectious disease is a predominant challenge for global health and people living in remote areas. However, the energy supply is still difficult for both the pretreatment and test steps, especially for diagnostics in resource-limited environments or outdoor point-of-care testing. Herein, we demonstrate a hand-powered triboelectric nanogenerator (TENG) system, which can simultaneously accomplish centrifugal pretreatment and analysis without an additional power supply. The complete separation of plasma from red blood cells can be achieved within 1.5 min at an operation frequency of 1 Hz. Besides, according to the impressive high rotational speed of 7500 rpm, the rotating mechanical energy can be efficiently recycled by the TENG to power different electronic devices, such as an electronic watch or thermometer. As a demonstration, the pretreatment of lake water and the detection of hydrogen peroxide contained in it has been realized. The combination of the system with different types of sensors will further promote its applications in multifarious biochemical detections. Moreover, this TENG system is effective, field-portable and ultra-low cost, and is promising for battery-free point-of-care diagnostic systems for outdoor or harsh environments.

We consider a small device for converting the medium’s flow energy, which is designed based on the use of a crank mechanism. A blade interacting with the flow is fixed on the connecting rod of the mechanism and the crank shaft is connected to the electric generator’s rotor. The system has a control input that allows us to control how much of the energy taken from the flow is converted into electricity. It is assumed that such control is carried out by changing the total external resistance in the local circuit of the electric generator of the device. The dependence of the average mechanical power in the steady-state operating modes on the gain of the control action is described. The effect of the flow rate, the dry friction coefficient in the mechanism slider, and other model parameters on this dependence is investigated. To construct the corresponding bifurcation diagrams, we use a numerical-analytical iterative method for generating periodic motions with the specified properties, which develops the Andronov–Pontryagin approach.

Automotive components are excited dynamically by interior (engine, gear system) and exterior effects (rough street surfaces, aerodynamics). This leads to dynamically induced vibrations which can end in fatigue cracking of components and/or undesirable acoustic emissions. With recent trends in optimizing/minimizing mass of vehicles, vibration problems are becoming an even more pronounced problem. In this research, a way has been investigated to reduce structural vibrations for a simple aluminium cantilever beam object, which is deduced from a cantilever beam of an automotive engine-transmission system. For this academic example the vibration has been reduced by attaching friction strips. The goal is to minimize the overall mass of the structure (cantilever beam plus friction strips) and simultaneously control the vibration amplitude. The energy lost due to the friction between the friction strips and the body of the vibrating beam will reduce the overall mechanical energy of the vibrating system and hence the vibrations will be controlled.

Inspired by microorganisms in nature, a new type of waste-energy-driven catalytic film was explored for the first time using magnetically actuated artificial cilia. Due to its singular characteristic ciliary movement, the inner-motile catalytic film is capable of capturing waste mechanical energy from flows, which can unexpectedly drive electrochemical reactions in solutions. Based on this, the piezoelectric deposition of Ag nanoparticles was achieved for the first time, which makes Ag nanoparticles distribute more evenly on the body of ZnO nanowires, enhancing the catalytic performance dramatically. Moreover, the influence of Ag nanoparticles on the piezoelectric catalysis was also detected, which can boost the deeper understanding of the piezo-catalytic mechanism. In summary, the inner-motile strategy facilitates the realization of waste-energy-driven catalytic technology, providing a new working prototype for driving the piezo-chemical reaction.

Hysteretic damping of a material or structure loaded within its elastic region is the dissipation of mechanical energy at a rate independent of the frequency of vibration while at the same time directly proportional to the square of the displacement. Generally, reproducing this frequency-independent damping can be computationally complex and requires prior knowledge of the system’s natural frequencies or the full time history of the system’s response. In this paper, a new model and numerical procedure are proposed whereby hysteretic material damping is achieved in the time domain. The proposed procedure is developed based on modifying the viscous model through a correction factor calculated exclusively using the local response. The superiority of the proposed approach lies in its ability to capture material hysteresis without any knowledge of the eigen- or modal frequencies of the system and without knowledge of the past time history of the system’s response or the characteristics of any excitation forces. A numerical procedure is also presented for implementing the proposed model in vibration analysis. The simplicity of the approach enables its generalisation to continuous systems and to systems of multi-degrees of freedom as demonstrated herein. The proposed model is presented as a correction to the viscous damping model which makes it attractive to implement into commercial finite element package using user-defined element subroutines as demonstrated in this study.

To realize the high-efficiency acquisition of environmental mechanical energy, traditional triboelectric nanogenerators (TENGs) based on contact-separation consist of two separate triboelectric layers. Their large contact-separation gap increases the overall volume of the device, making it difficult to realize miniaturization and flexibility. This work, therefore, presents a fully enclosed all-in-one-shaped flexible TENG (FEAST) with an air cavity using rubber mixing and high-temperature vulcanization. The air pressure inside the enclosed air cavity facilitates effective contact-separation of the FEAST. The homogeneous integration between the triboelectric layer and the electrode layer enhances structural firmness without using extra spacer materials. The developed FEAST presents excellent mechanical durability even after 10000 cycles. By increasing the active contact area between the triboelectric materials, a maximum peak-peak output voltage, current, and power density of 130 V, 1.1 µA, and 277 mW/m2, respectively, were obtained with an effective stress area of 1 cm2. Moreover, the fully enclosed structure ensures that the output performance is not affected by the external environment. The FEAST was fixed onto the sole of a shoe to demonstrate its applicability in harvesting mechanical energy from human motions. Overall, the developed method provides a simple approach for optimizing the structure of TENGs and is compatible with large-scale manufacturing.

The electrokinetic effect to convert the mechanical energy from ambient has gained sustained research attention because it is free of moving parts and easy to be miniaturized for microscale applications. The practical application is constrained by the limited electrokinetic energy conversion performance. Herein, we report vertically oriented MXene membranes (VMMs) with ultrafast permeation as well as high ion selectivity, in which the permeation is several thousand higher than the largely researched horizontally stacked MXene membranes (HMMs). The VMMs can achieve a high streaming current of 8.17 A m-2 driven by the hydraulic pressure, largely outperforming all existing materials. The theoretical analysis and numerical calculation reveal the underlying mechanism of the ultrafast transport in VMMs originates from the evident short migration paths, the low energy loss during the ionic migration, and the large effective inlet area on the membrane surface. The orientation of the 2D lamella in membranes, the long-overlooked element in the existing literatures, is identified to be an essential determinant in the performance of 2D porous membranes. These understandings can largely promote the development of electrokinetic energy conversion devices and bring advanced design strategy for high-performance 2D materials.

Wind energy caused the transverse vibration of the beam, and the mechanical energy of vibration is transferred to electrical charge by piezoelectric transducer. In the current study, the active and passive control of energy release from a galloping bluff body is found. The system consists of a bluff body in front of wind which is mounted on a cantilever beam and supported by piezoelectric sheets. The nonlinear motion of the Euler–Bernoulli beam and conservation of electrical energy is modeled by lumped ordinary differential equations. The wind force on bluff body is modeled by moving mesh techniques in OpenFoam software where the fluid and solid corresponding dynamics are connected in timescales. The position of piezoelectric actuator and the location of bump are the two parameters considered for optimization analysis of galloping device. Genetic algorithms are used to find the optimal arrangements. Numerous models are offered for a clamped−clamped supported beam.