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Balancing forces within weight-bearing joints such as the hip during joint replacement surgeries is essential for implant longevity. Minimising implant failure is vital to improve patient wellbeing and alleviate pressure on healthcare systems. With improvements in surgery, hip replacement patients are now often younger and more active than in previous generations, and their implants correspondingly need to survive higher stresses. However, force balancing currently depends entirely on surgical skill: no sensors can provide quantitative force feedback within the hip joint’s small, complex geometry. Here, we solve this unmet clinical need by presenting a thin and conformable microfluidic force sensor, which is compatible with the standard surgical process. We optimised the design using finite element modelling, then incorporated and calibrated our sensor in a model hip implant. Using a bespoke testing rig, we demonstrated high sensitivity at typical forces experienced during hip replacements. We anticipate that these sensors will aid implant positioning, increasing the lifetime of hip replacements, and represent a powerful new surgical tool for a range of orthopaedic procedures where force balancing is crucial.

The re-wiring of photosynthetic bio-machineries to electrodes is a forward-looking semi-artificial route for sustainable bio-electricity and fuel generation. Currently, it is unclear how the bio-material interface can be designed to meet the complex requirements for high bio-photoelectrochemical performance. Here, we developed an aerosol jet printing method for generating hierarchical electrode structures using indium tin oxide nanoparticles. We printed libraries of micropillar array electrodes varying in height and sub-micron surface features and studied the energy/electron transfer processes across the bio-electrode interfaces. When wired to the cyanobacterium Synechocysis sp. PCC 6803, micropillar array electrodes with micro-branches exhibited favourable biocatalyst loading, light utilisation and electron flux output, ultimately almost doubling the photocurrent of state-of-the-art porous structures of the same height. When the micropillars’ heights were increased from 50 to 600 µm, milestone mediated photocurrent densities of 245 µA cm–2 (the closest thus far to theoretical predictions) and external quantum efficiencies of up to 29% could be reached. This study demonstrates how bioenergy from photosynthesis could be more efficiently harnessed in the future and provide new tools for 3D electrode design.

The rewiring of photosynthetic biomachineries to electrodes is a forward-looking semi-artificial route for sustainable bio-electricity and fuel generation. Currently, it is unclear how the electrode and biomaterial interface can be designed to meet the complex requirements for high biophotoelectrochemical performance. Here we developed an aerosol jet printing method for generating hierarchical electrode structures using indium tin oxide nanoparticles. We printed libraries of micropillar array electrodes varying in height and submicrometre surface features, and studied the energy/electron transfer processes across the bio-electrode interfaces. When wired to the cyanobacterium Synechocystis sp. PCC 6803, micropillar array electrodes with microbranches exhibited favourable biocatalyst loading, light utilization and electron flux output, ultimately almost doubling the photocurrent of state-of-the-art porous structures of the same height. When the micropillars' heights were increased to 600 µm, milestone mediated photocurrent densities of 245 µA cm

Multi-functional up-conversion (UC) phosphors are highly desirable for many potentially technological applications. Here, Er3+- and Yb3+-doped SrBi4Ti4O15 (SBT:xEr3+/yYb3+) UC nanoparticles (NPs) have been successfully synthesized for the first time by a convenient EDTA-citrate approach. The structures and morphologies were characterized by powder X-ray diffraction, Fourier transform infrared reflectivity spectra, scanning electron microscopy, and transmission electron microscopy. Under 980 nm excitation, SBT:xEr3+/yYb3+ UCNPs exhibited bright green and weak red emissions. The UC emission properties were disclosed to be tightly dependent on the Yb3+ and Er3+ concentration and the involved UC mechanism was discussed. More importantly, the noncontact optical thermometric ability were assessed based on the thermo-responsive fluorescence intensity ratio (FIR) technique and the maximum sensitivity (Smax) of SBT:0.15Er3+/0.15Yb3+ UCNPs is about 0.0036 K–1. Excellent repeatability and stability were proven by the thermal-cycling measurements. Furthermore, prominent photo-thermal (PT) effect was obtained with the temperature coefficients (η) being 0.24 and 0.49 °C∙mm2/mW for SBT:0.15Er3+/0Yb3+ and SBT:0.15Er3+/0.15Yb3+ UCNPs, respectively, which showed that the incorporation of Yb3+ was a promising strategy to improve the PT capability. In addition, regularly dynamic response of the PT agent under periodic laser stimulation was also observed. These results imply that SBT:xEr3+/yYb3+ UCNPs could be potentially utilized in thermometers and PT agents.

Recently, flutter-driven triboelectric nanogenerator (TENG) has shown huge potential in wind energy harvesting from ambient environments. However, almost all the reported devices are based on parallel structure which suffers from a critical problem of insufficient contact between triboelectric surfaces. In this work, we propose an angle-shaped TENG (AS-TENG) with the above issue resolved. The device is based on two Al layers stacked to form an angle shape and a FEP film positioned in between by sharing a common side. Thanks to this design, the FEP film can contact fully and intimately with the Al layers to facilitate the effect of contact electrification and electrostatic induction. Compared with the existing parallel-structured TENG, the AS-TENG shows an overwhelming output performance because of the enhanced contact area. Furthermore, the AS-TENG is introduced a wedge-shaped wind guide channel which can provide a driving force for the flutter and hence lower the start-up wind speed largely. To further enhance the electric output, the AS-TENGs can be facilely integrated into a 360° radial array, showing an enlarged windward area and a high level of integration. The AS-TENG array can be applied to harvest outdoor weak wind and act as a direct power source to charge a capacitor or drive electronic devices. This work provides a design strategy for natural weak wind scavenging which may push forward the practical applications of TENG for wind power.

Summary Force sensors that are thin, low-cost, flexible, and compatible with commercial microelectronic chips are of great interest for use in biomedical sensing, precision surgery, and robotics. By leveraging a combination of microfluidics and capacitive sensing, we develop a thin, flexible force sensor that is conformable and robust. The sensor consists of a partially filled microfluidic channel made from a deformable material, with the channel overlaying a series of interdigitated electrodes coated with a thin, insulating polymer layer. When a force is applied to the microfluidic channel reservoir, the fluid is displaced along the channel over the electrodes, thus inducing a capacitance change proportional to the applied force. The microfluidic molds themselves are made of low-cost sacrificial materials deposited via aerosol-jet printing, which is also used to print the electrode layer. We envisage a large range of industrial and biomedical applications for this force sensor., Graphical abstract, Highlights Highly flexible, capacitive force sensors based on microfluidics Linear capacitance response to applied force Rapid prototyping of low-cost and robust force sensors via aerosol-jet printing Tunable design for various sensitivities and force measurement ranges, Jing et al. report a thin, conformable force sensor based on a combination of microfluidics and capacitive sensing. The low-cost sensor is fabricated via aerosol-jet printing and shows a highly linear response with adjustable design parameters for tunable sensitivities and force ranges.

Coronavirus disease 2019 (COVID-19) as a severe acute respiratory syndrome infection has spread rapidly across the world since its emergence in 2019 and drastically altered our way of life. Patients who have recovered from COVID-19 may still face persisting respiratory damage from the virus, necessitating long-term supervision after discharge to closely assess pulmonary function during rehabilitation. Therefore, developing portable spirometers for pulmonary function tests is of great significance for convenient home-based monitoring during recovery. Here, we propose a wireless, portable pulmonary function monitor for rehabilitation care after COVID-19. It is composed of a breath-to-electrical (BTE) sensor, a signal processing circuit, and a Bluetooth communication unit. The BTE sensor, with a compact size and light weight of 2.5cm3 and 1.8g respectively, is capable of converting respiratory biomechanical motions into considerable electrical signals. The output signal stability is greater than 93% under 35%-81% humidity, which allows for ideal expiration airflow sensing. Through a wireless communication circuit system, the signals can be received by a mobile terminal and processed into important physiological parameters, such as forced expiratory volume in 1s (FEV1) and forced vital capacity (FVC). The FEV1/FVC ratio is then calculated to further evaluate pulmonary function of testers. Through these measurement methods, the acquired pulmonary function parameters are shown to exhibit high accuracy (>97%) in comparison to a commercial spirometer. The practical design of the self-powered flow spirometer presents a low-cost and convenient method for pulmonary function monitoring during rehabilitation from COVID-19.

Biosensors are powerful analytical tools for biology and biomedicine, with applications ranging from drug discovery to medical diagnostics, food safety, and agricultural and environmental monitoring. Typically, biological recognition receptors, such as enzymes, antibodies, and nucleic acids, are immobilized on a surface, and used to interact with one or more specific analytes to produce a physical or chemical change, which can be captured and converted to an optical or electrical signal by a transducer. However, many existing biosensing methods rely on chemical, electrochemical and optical methods of identification and detection of specific targets, and are often: complex, expensive, time consuming, suffer from a lack of portability, or may require centralised testing by qualified personnel. Given the general dependence of most optical and electrochemical techniques on labelling molecules, this review will instead focus on mechanical and electrical detection techniques that can provide information on a broad range of species without the requirement of labelling. These techniques are often able to provide data in real time, with good temporal sensitivity. This review will cover the advances in the development of mechanical and electrical biosensors, highlighting the challenges and opportunities therein.

Advances in nanoscience and nanotechnology-related have revolutionized technologies related to sensors and portable electronic appliances, thus opening up a whole new dimension to modern-day life. However, with the explosive growth witnessed in sensor and wearable technologies, new challenges have surfaced, including how to power these without relying solely on traditional power sources such as batteries. Although battery technology itself has taken great strides in terms of environment-friendly materials and portability, their energy density still remains insufficient to power these electronic gadgets without making them ungainly and bulky. In this chapter, we discuss energy harvesting from mechanical and thermal sources in the environment, particularly in the context of small-power applications. Functional nanomaterials possessing good piezoelectric/triboelectric and thermoelectric, respectively, properties need to be integrated into new device platforms for ease of integration into different areas of application, including clothing or onto skin, and to enable greater flexibility and/or stretchability of the device itself for greater versatility. In this context, manufacturing routes including microscale additive manufacturing processes such as printing and electrospinning, as well as fiber/fabric coating, are presented as a route toward developing flexible and smart energy harvesting and sensing for next-generation autonomous devices.

Force sensors that are thin, low cost, flexible and compatible with commercial microelectronic chips are of great interest for use in biomedical sensing, precision surgery, robotics and in various “smart control” technologies. By leveraging a novel combination of microfluidics and capacitive sensing we have developed a thin, flexible force sensor that is conformable and robust. The sensor consists of a partially filled microfluidic channel made from a deformable material, with the channel overlaying a series of interdigitated electrodes that are coated with a thin polymer layer for insulation. When a force is applied to a fluid reservoir at the base of the channel, the fluid is displaced along the channel, passing over the electrodes and thus inducing a capacitance change, which is proportional to the amount of force applied. The microfluidic molds themselves are made of low-cost sacrificial material inks deposited via aerosol-jet printing, which is also used to print the electrode layer. The sensors exhibit a nearly linear change in capacitance in response to external load, with a sensitivity of up to 3.8 pF/N and a force range of up to 9 N achieved with the present design. We quantify the effects of changing the electrode morphology, liquid permittivity, sensor thickness and geometry, as well as the thickness of the insulation layer over the electrodes, on sensor range and sensitivity, using a combination of experiments and finite element analysis simulations. We further demonstrate how the sensor can be used to remotely control a robotic clamp. The conformable force sensors developed here are thin, flexible and facilitate easy signal processing. The fabrication processes are low-cost, amenable to fast prototyping and mass manufacturing. We envisage a large range of industrial and biomedical applications for this novel force sensor.

The requirements for modern electronic devices, particularly those intended for wearable or human health monitoring applications, have rapidly evolved to being both flexible and stretchable. Hence devices, as well as interconnects, need to be capable of retaining functionality even when being mechanically deformed. Most approaches towards achieving this rely on printing or transferring structures onto elastomeric substrates that can withstand stretching. However, the processing involved can often be cumbersome, and the structures themselves tend to suffer from poor fatigue and/or are limited by the mechanical properties of the underlying substrate. Here, we introduce an aerosol-jet printing technique by which fully freestanding functional structures can be built up layer by layer, which are stable and robust upon repeated stretching. The process involves printing a combination of layers of different materials with the desired functionality, onto a substrate coated with a sacrifical film that is subsequently dissolved to release the printed structure. Using this method, we demonstrate freestanding conductive wires can be used as stretchable interconnects/electrodes, and that also function as strain-sensors. We also show that a freestanding capacitive structure functions as a robust, stretchable humidity sensor, paving the way for the development of other multi-layer, multifunctional stretchable devices and sensors.

Semiconducting piezoelectric materials have attracted considerable interest due to their central role in the emerging field of piezotronics, where the development of a piezo-potential in response to stress or strain can be used to tune the band structure of the semiconductor, and hence its electronic properties. This coupling between piezoelectricity and semiconducting properties can be readily exploited for force or pressure sensing using nanowires, where the geometry and unclamped nature of nanowires render them particularly sensitive to small forces. At the same time, piezoelectricity is known to manifest more strongly in nanowires of certain semiconductors. Here, we report the design and fabrication of highly sensitive piezotronic pressure sensors based on GaAs nanowire ensemble sandwiched between two electrodes in a back-to-back diode configuration. We analyse the current–voltage characteristics of these nanowire-based devices in response to mechanical loading in light of the corresponding changes to the device band structure. We observe a high piezotronic sensitivity to pressure, of ~7800 meV MPa−1. We attribute this high sensitivity to the nanowires being fully depleted due to the lack of doping, as well as due to geometrical pressure focusing and current funnelling through polar interfaces.

Electrical polarization phenomena in GaN are important as they have significant impact on the operation of modern day energy efficient lighting and are fundamental to GaN-based high power and high frequency electronics. Controlling polarization is beneficial for the optimization of these applications. GaN is also piezoelectric, and therefore mechanical stress and strain are possible handles to control its polarization. Nonetheless, polar semiconductors in general, and GaN in particular, are weak piezoelectric materials when compared to ceramics, and are therefore not considered for characteristic electromechanical applications such as sensing, actuation and mechanical energy harvesting. Here, we examine the effect of nanoscale porosity on the piezoelectricity of initially conductive GaN. We find that for 40% porosity, the previously conductive GaN layer becomes depleted, and exhibits enhanced piezoelectricity as measured using piezoresponse force microscopy, as well as by using a mechanical energy harvesting setup. The effective piezoelectric charge coefficient of the porous GaN, d33,eff, is found to be about 8 pm/V which is 2-3 times larger than bulk GaN. A macroscale device comprising a porous GaN layer delivered 100 nW/cm2 across a resistive load under a 150 kPa mechanical excitation. We performed finite element simulations to analyze the evolution of the piezoelectric properties with porosity. The simulations suggest that increased mechanical compliance due to porosity gives rise to the observed enhanced piezoelectricity in GaN. Furthermore, the simulations show that for stress-based excitations, the porous GaN electromechanical figure of merit is increased by an order of magnitude and becomes comparable to that of barium titanate piezoceramics. In addition, considering the central role played by GaN in modern electronics and optoelectronics, our study validates a very promising research direction when considering stress-based electromechanical applications which combine GaN's semiconducting and piezoelectric properties.

Harvesting energy from ambient mechanical sources in our environment has attracted considerable interest due to its potential to power applications such as ubiquitous wireless sensors and Internet of Things devices. In this context, piezoelectric and/or triboelectric materials offer a relatively simple means of directly converting mechanical energy from ubiquitous ambient vibrating sources into electrical power for microscale/nanoscale device applications. In particular, nanoscale energy harvesters, or nanogenerators, are capable of converting low-level ambient vibrations into electrical energy, thus are vital to the realization of the next generation of self-powered devices. Polymer-based nanogenerators are attractive as they are inherently flexible and robust, making them less prone to mechanical failure which is a key requirement for vibrational energy harvesters. They are also lightweight, easy and cheap to fabricate, lead-free and biocompatible, but in many cases their energy harvesting performance is found lacking in comparison to more commonly studied inorganic materials. Recent advances have been made in developing scalable nanofabrication techniques for flexible and low-cost polymer-based nanogenerators with improved energy conversion efficiency, including the incorporation of high-quality polymer nanowires with enhanced crystallinity, piezoelectric and/or surface charge properties. In this review, we discuss aspects of nanomaterials growth and energy harvester device design, including those involving nanowires of polymers of polyvinylidene fluoride and its co-polymers, Nylon-11, and poly-lactic acid for scalable piezoelectric and triboelectric nanogenerator applications, as well as the design and performance of polymer-ceramic nanocomposite nanogenerators. In particular, we highlight the effects of growth parameters, nanoconfinement, self-poling, surface polarization, crystalline phases, and device assembly on the energy harvesting performance of a range of recently reported nanostructured polymer-based materials and devices.

We present a newly designed self-powered identification system based on sliding electrification by combination of a barcode fabricated by gratings with intervals of different widths between each other and a reader consists of a layer of FEP film and a strip electrode. Introducing a reference interval and a baseline, an encoding method was established by calculating the ratio of time spent for sliding across the strip electrode and the one for the reference interval. Sliding across a reader at a constant speed rate from 10 mm/s to 100 mm/s, even swiping a card by human hands, coded information by gratings with intervals of different widths was successfully identified. This work demonstrates the practicability of a self-powered, triboelectric-based identification system, and indicates its potential applications in laboratories, libraries, and industry.

With 70% of the earth's surface covered with water, wave energy is abundant and has the potential to be one of the most environmentally benign forms of electric energy. However, owing to lack of effective technology, water wave energy harvesting is almost unexplored as an energy source. Here, we report a network design made of triboelectric nanogenerators (TENGs) for large-scale harvesting of kinetic water energy. Relying on surface charging effect between the conventional polymers and very thin layer of metal as electrodes for each TENG, the TENG networks (TENG-NW) that naturally float on the water surface convert the slow, random, and high-force oscillatory wave energy into electricity. On the basis of the measured output of a single TENG, the TENG-NW is expected to give an average power output of 1.15 MW from 1 km(2) surface area. Given the compelling features, such as being lightweight, extremely cost-effective, environmentally friendly, easily implemented, and capable of floating on the water surface, the TENG-NW renders an innovative and effective approach toward large-scale blue energy harvesting from the ocean.

A self-powered, sliding electrification based quasi-static triboelectric sensor (QS-TES) for detecting angle from rotating motion is reported. This innovative, cost-effective, simply-designed QS-TES has a two-dimensional planar structure, which consists of a rotator coated with four channel coded Cu foil material and a stator with a fluorinated ethylenepropylene film. On the basis of coupling effect between triboelectrification and electrostatic induction, the sensor generates electric output signals in response to mechanical rotating motion of an object mounted with the sensor. The sensor can read and remember the absolute angular position, angular velocity, and acceleration regardless being continuously monitored or segmented monitored. Under the rotation speed of 100 r min−1, the output voltage of the sensor reaches as high as 60 V. Given a relatively low threshold voltage of ±0.5 V for data processing, the robustness of the device is guaranteed. The resolution of the sensor is 22.5° and can be further improved by increasing the number of channels. Triggered by the output voltage signal, the rotating characteristics of the steering wheel can be real-time monitored and mapped by being mounted to QS-TES. This work not only demonstrates a new principle in the field of angular measurement but also greatly expands the applicability of triboelectric nanogenerator as self-powered sensors.

Stretchable electronics represent an emerging class of devices that can be compressed, twisted and conform to very complicated shapes. The mechanical and electrical compliances of the technology promise to open up applications for healthcare, energy and entertainment purposes. However, advancement in the field has been hindered by material related constraints. Moreover, the current microfabrication facilities are optimized for rigid substrates such as silicon, which have significant different properties compared to elastomers. In this paper, four categories of enabling technologies for stretchable electronics commercialization are critically reviewed, namely: the novel design of stretchable structures, use of non-conventional materials, state-of-art printing techniques and also the patterning of electrodes or metal interconnects via conventional manufacturing techniques.

A practical self-powered velocity sensor based on the principles of a triboelectric generator for either rectified linear or rotary motion is presented. The effort represents the first successful attempt in integrating a triboelectric generator into a commercial digital circuit for the dual-mode speed sensing. Employing alternating Kapton-copper strips arranged in a spiral configuration wrapped on the inner and outer surfaces of two concentric cylinders, voltage assays for linear and rotary motions can be measured without the need for an external power source. The triboelectric generated output signals when integrated with a digital circuit and a microcontroller unit can be directly processed into remarkably stable, macro-scale output signals for measurements of (0.1−0.6) ms−1±0.5% for linear velocities and (300−700) rpm±0.9% for rotary velocities. We have also discussed the measuring sensitivities and limitations of our device in the paper. We believe our pioneering demonstration of the applied triboelectric technology will have a huge impact in the industrial commercialization of self-powered devices and sensors.

A new membrane-based triboelectric sensor (M-TES) is presented as a self-powered pressure change sensor. It generates a voltage induced by surface triboelectric charges in response to an air pressure change. Extremely high detection resolutions of 0.34 Pa and 0.16 Pa are achieved when the air pressure increases and decreases in a small region away from the ambient standard atmosphere pressure, respectively, indicating an excellent sensitivity. By integrating the M-TES with a signal processing unit, we demonstrate practical applications of the device in sensing footsteps, respirations, and heartbeat, which suggests widespread use of the M-TES in fields of security surveillance, chemical engineering, geography research, environment monitoring, and personal healthcare.

We present triboelectrification based, flexible, reusable, and skin-friendly dry biopotential electrode arrays as motion sensors for tracking muscle motion and human-machine interfacing (HMI). The independently addressable, self-powered sensor arrays have been utilized to record the electric output signals as a mapping figure to accurately identify the degrees of freedom as well as directions and magnitude of muscle motions. A fast Fourier transform (FFT) technique was employed to analyse the frequency spectra of the obtained electric signals and thus to determine the motion angular velocities. Moreover, the motion sensor arrays produced a short-circuit current density up to 10.71 mA/m(2), and an open-circuit voltage as high as 42.6 V with a remarkable signal-to-noise ratio up to 1000, which enables the devices as sensors to accurately record and transform the motions of the human joints, such as elbow, knee, heel, and even fingers, and thus renders it a superior and unique invention in the field of HMI.

U.S. Department of Energy, Office of Basic Energy Sciences [DE-FG02-07ER46394]; "thousands talents" program for pioneer researcher and his innovation team, China; NSFC [61174017]; Chinese Scholars Council

The applications of a single-layer triboelectric nanogenerator (TENG) may be challenged by its lower output current, and a possible solution is to use three-dimensional (3D) integrated multilayered TENGs. However, the most important point is to synchronize the outputs of all the TENGs so that the instantaneous output power can be maximized. Here, a multi-layered stacked TENG is reported as a cost-effective, simple, and robust approach for harvesting ambient vibration energy. With superior synchronization, the 3D-TENG produces a short-circuit current as high as 1.14 mA, and an open-circuit voltage up to 303 V with a remarkable peak power density of 104.6 W m−2. As a direct power source, it is capable of simultaneously lighting up 20 spot lights (0.6 W ea.) as well as a white G16 globe light. Furthermore, compared with the state-of-the-art vibration energy harvesters, the 3D-TENG has an extremely wide working bandwidth up to 36 Hz in low frequency range. In addition, with specific dimensional design, the 3D-TENG is successfully equipped inside a ball with a diameter of 3 inches, using which 32 commercial LEDs are simultaneously lighted up via hand shaking, exhibiting great potential of scavenging the abundant but wasted kinetic energy when people play basketball, football, baseball, and so on.

Reciprocating motion is a widely existing form of mechanical motion in natural environment. In this work we reported a case-encapsulated triboelectric nanogenerator (cTENG) based on sliding electrification to convert reciprocating motion into electric energy. Patterned with multiple sets of grating electrodes and lubricated with polytetrafluoroethylene (PTFE) nanoparticles, the cTENG exported an average effective output power of 12.2 mW over 140 kΩ external load at a sliding velocity of 1 m/s, in corresponding to a power density of 1.36 W/m(2). The sliding motion can be induced by direct-applied forces as well as inertia forces, enabling the applicability of the cTENG in addressing ambient vibration motions that feature large amplitude and low frequency. The cTENG was demonstrated to effectively harvest energy from human body motions and wavy water surface, indicating promising prospects of the cTENG in applications such as portable and stand-alone self-powered electronics.

A harmonic-resonator-based triboelectric nanogenerator (TENG) is presented as a sustainable power source and an active vibration sensor. It can effectively respond to vibration frequencies ranging from 2 to 200 Hz with a considerably wide working bandwidth of 13.4 Hz. This work not only presents a new principle in the field of vibration energy harvesting but also greatly expands the applicability of TENGs.

We introduce an innovative design of a disk triboelectric nanogenerator (TENG) with segmental structures for harvesting rotational mechanical energy. Based on a cyclic in-plane charge separation between the segments that have distinct triboelectric polarities, the disk TENG generates electricity with unique characteristics, which have been studied by conjunction of experimental results with finite element calculations. The role played by the segmentation number is studied for maximizing output. A distinct relationship between the rotation speed and the electrical output has been thoroughly investigated, which not only shows power enhancement at high speed but also illuminates its potential application as a self-powered angular speed sensor. Owing to the nonintermittent and ultrafast rotation-induced charge transfer, the disk TENG has been demonstrated as an efficient power source for instantaneously or even continuously driving electronic devices and/or charging an energy storage unit. This work presents a novel working mode of TENGs and opens up many potential applications of nanogenerators for harvesting even large-scale energy.

By combining contact-mode atomic force microscopy (AFM) and scanning Kevin probe microscopy (SKPM), we demonstrated an in situ method for quantitative characterization of the triboelectrification process at the nanoscale. We systematically characterized the triboelectric charge distribution, multifriction effect on charge transfer, as well as subsequent charge diffusion on the dielectric surface: (i) the SiO2 surface can be either positively or negatively charged through triboelectric process using Si-based AFM probes with and without Pt coating, respectively; (ii) the triboelectric charges accumulated from multifriction and eventually reached to saturated concentrations of (-150 ± 8) μC/m(2) and (105 ± 6) μC/m(2), respectively; (iii) the charge diffusion coefficients on SiO2 surface were measured to be (1.10 ± 0.03) × 10(-15) m(2)/s for the positive charge and (0.19 ± 0.01) × 10(-15) m(2)/s for the negative charges. These quantifications will facilitate a fundamental understanding about the triboelectric and de-electrification process, which is important for designing high performance triboelectric nanogenerators. In addition, we demonstrated a technique for nanopatterning of surface charges without assistance of external electric field, which has a promising potential application for directed self-assembly of charged nanostructures for nanoelectronic devices.

Synchronization in classes of continuous-time dynamical networks with different topologies is investigated. A synchronization-optimal algorithm based on the synchronization criterion is proposed so as to get the appropriate topology such that complex network has the optimal synchronizability. It has been argued that heterogeneity suppresses synchronization in unweighted networks. However, it is shown in this work that synchronizability of Type I networks is independent of heterogeneity in the degree distribution, while synchronizability of Type II networks is dependent of both heterogeneity and scale of networks. It is presented the more heterogeneous and larger scale, the poorer synchronizability of Type II networks.

Harnessing random micromeso-scale ambient energy is not only clean and sustainable, but it also enables self-powered sensors and devices to be realized. Here we report a robust and self-powered kinematic vector sensor fabricated using highly pliable organic films that can be bent to spread over curved and uneven surfaces. The device derives its operational energy from a close-proximity triboelectrification of two surfaces: a polytetrafluoroethylene film coated with a two-column array of copper electrodes that constitutes the mover and a polyimide film with the top and bottom surfaces coated with a two-column aligned array of copper electrodes that comprises the stator. During relative reciprocations, the electrodes in the mover generate electric signals of ±5 V to attain a peak power density of ≥65 mW m−2 at a speed of 0.3 ms−1. From our 86,000 sliding motion tests of kinematic measurements, the sensor exhibits excellent stability, repeatability and strong signal durability., Kinematic sensors are required in many industrial applications, but the current sensor designs rely on power input from external sources. Here, Jing et al. harness the micro-meso scale ambient energy via a triboelectric generator to self-power sensors for one- and two-dimensional motion vector sensing.

The computer keyboard is one of the most common, reliable, accessible, and effective tools used for human--machine interfacing and information exchange. Although keyboards have been used for hundreds of years for advancing human civilization, studying human behavior by keystroke dynamics using smart keyboards remains a great challenge. Here we report a self-powered, non-mechanical-punching keyboard enabled by contact electrification between human fingers and keys, which converts mechanical stimuli applied to the keyboard into local electronic signals without applying an external power. The intelligent keyboard (IKB) can not only sensitively trigger a wireless alarm system once gentle finger tapping occurs but also trace and record typed content by detecting both the dynamic time intervals between and during the inputting of letters and the force used for each typing action. Such features hold promise for its use as a smart security system that can realize detection, alert, recording, and identification. Moreover, the IKB is able to identify personal characteristics from different individuals, assisted by the behavioral biometric of keystroke dynamics. Furthermore, the IKB can effectively harness typing motions for electricity to charge commercial electronics at arbitrary typing speeds greater than 100 characters per min. Given the above features, the IKB can be potentially applied not only to self-powered electronics but also to artificial intelligence, cyber security, and computer or network access control.

Piezoelectric polymers are capable of interconverting mechanical and electrical energy, and are therefore candidate materials for biomedical applications such as sensors, actuators, and energy harvesters. In particular, nanowires of these materials are attractive as they can be unclamped, flexible and sensitive to small vibrations. Poly-l-lactic acid (PLLA) nanowires have been investigated for their use in biological applications, but their piezoelectric properties have never been fully characterised, even though macroscopic films and fibres have been shown to exhibit shear piezoelectricity. This piezoelectric mode is particularly interesting for in vivo applications where shear forces are especially relevant, and is similar to what has been observed in natural materials such as bone and DNA. Here, using piezo-response force microscopy (PFM), we report the first direct observation of shear piezoelectricity in highly crystalline and oriented PLLA nanowires grown by a novel template-wetting method. Our results are validated using finite-element simulations and numerical analysis, which importantly and more generally allow for accurate interpretation of PFM signals in soft nanostructured materials. Our work opens up the possibility for the development of biocompatible and sustainable piezoelectric nanogenerators and sensors based on polymer nanowires.

The first bionic membrane sensor based on triboelectrification is reported for self-powered physiological and behavioral measurements such as local internal body pressures for non-invasive human health assessment. The sensor can also be for self-powered anti-interference throat voice recording and recognition, as well as high-accuracy multimodal biometric authentication, thus potentially expanding the scope of applications in self-powered wearable medical/health monitoring, interactive input/control devices as well as accurate, reliable, and less intrusive biometric authentication systems.

We invented a triboelectric nanogenerator (TENG) that is based on a wavy-structured Cu-Kapton-Cu film sandwiched between two flat nanostructured PTFE films for harvesting energy due to mechanical vibration/impacting/compressing using the triboelectrification effect. This structure design allows the TENG to be self-restorable after impact without the use of extra springs and converts direct impact into lateral sliding, which is proved to be a much more efficient friction mode for energy harvesting. The working mechanism has been elaborated using the capacitor model and finite-element simulation. Vibrational energy from 5 to 500 Hz has been harvested, and the generator's resonance frequency was determined to be ∼100 Hz at a broad full width at half-maximum of over 100 Hz, producing an open-circuit voltage of up to 72 V, a short-circuit current of up to 32 μA, and a peak power density of 0.4 W/m(2). Most importantly, the wavy structure of the TENG can be easily packaged for harvesting the impact energy from water waves, clearly establishing the principle for ocean wave energy harvesting. Considering the advantages of TENGs, such as cost-effectiveness, light weight, and easy scalability, this approach might open the possibility for obtaining green and sustainable energy from the ocean using nanostructured materials. Lastly, different ways of agitating water were studied to trigger the packaged TENG. By analyzing the output signals and their corresponding fast Fourier transform spectra, three ways of agitation were evidently distinguished from each other, demonstrating the potential of the TENG for hydrological analysis.

A newly-designed triboelectric nanogenerator is demonstrated which is composed of a grating-segmented freestanding triboelectric layer and two groups of interdigitated electrodes with the same periodicity. The sliding motion of the grating units across the electrode fingers can be converted into multiple alternating currents through the external load due to the contact electrification and electrostatic induction. Working in non-contact mode, the device shows excellent stability and the total conversion efficiency can reach up to 85% at low operation frequency.

Tactile/touch sensing is essential in developing human-machine interfacing and electronic skins for areas such as automation, security, and medical care. Here, we report a self-powered triboelectric sensor based on flexible thin-film materials. It relies on contact electrification to generate a voltage signal in response to a physical contact without using an external power supply. Enabled by the unique sensing mechanism and surface modification by polymer-nanowires, the triboelectric sensor shows an exceptional pressure sensitivity of 44 mV/Pa (0.09% Pa(-1)) and a maximum touch sensitivity of 1.1 V/Pa (2.3% Pa(-1)) in the extremely low-pressure region (0.15 KPa). Through integration of the sensor with a signal-processing circuit, a complete tactile sensing system is further developed. Diverse applications of the system are demonstrated, explicitly indicating a variety of immediate uses in human-electronics interface, automatic control, surveillance, remote operation, and security systems.

Harvesting mechanical energy is an important route in obtaining cost-effective, clean and sustainable electric energy. Here we report a two-dimensional planar-structured triboelectric generator on the basis of contact electrification. The radial arrays of micro-sized sectors on the contact surfaces enable a high output power of 1.5 W (area power density of 19 mW cm(-2)) at an efficiency of 24%. The triboelectric generator can effectively harness various ambient motions, including light wind, tap water flow and normal body movement. Through a power management circuit, a triboelectric-generator-based power-supplying system can provide a constant direct-current source for sustainably driving and charging commercial electronics, immediately demonstrating the feasibility of the triboelectric generator as a practical power source. Given exceptional power density, extremely low cost and unique applicability resulting from distinctive mechanism and structure, the triboelectric generator can be applied not only to self-powered electronics but also possibly to power generation at a large scale.

An unstable mechanical structure that can self-balance when perturbed is a superior choice for vibration energy harvesting and vibration detection. In this work, a suspended 3D spiral structure is integrated with a triboelectric nanogenerator (TENG) for energy harvesting and sensor applications. The newly designed vertical contact-separation mode TENG has a wide working bandwidth of 30 Hz in low-frequency range with a maximum output power density of 2.76 W/m(2) on a load of 6 MΩ. The position of an in-plane vibration source was identified by placing TENGs at multiple positions as multichannel, self-powered active sensors, and the location of the vibration source was determined with an error less than 6%. The magnitude of the vibration is also measured by the output voltage and current signal of the TENG. By integrating the TENG inside a buoy ball, wave energy harvesting at water surface has been demonstrated and used for lighting illumination light, which shows great potential applications in marine science and environmental/infrastructure monitoring.

We report human skin based triboelectric nanogenerators (TENG) that can either harvest biomechanical energy or be utilized as a self-powered tactile sensor system for touch pad technology. We constructed a TENG utilizing the contact/separation between an area of human skin and a polydimethylsiloxane (PDMS) film with a surface of micropyramid structures, which was attached to an ITO electrode that was grounded across a loading resistor. The fabricated TENG delivers an open-circuit voltage up to -1000 V, a short-circuit current density of 8 mA/m(2), and a power density of 500 mW/m(2) on a load of 100 MΩ, which can be used to directly drive tens of green light-emitting diodes. The working mechanism of the TENG is based on the charge transfer between the ITO electrode and ground via modulating the separation distance between the tribo-charged skin patch and PDMS film. Furthermore, the TENG has been used in designing an independently addressed matrix for tracking the location and pressure of human touch. The fabricated matrix has demonstrated its self-powered and high-resolution tactile sensing capabilities by recording the output voltage signals as a mapping figure, where the detection sensitivity of the pressure is about 0.29 ± 0.02 V/kPa and each pixel can have a size of 3 mm × 3 mm. The TENGs may have potential applications in human-machine interfacing, micro/nano-electromechanical systems, and touch pad technology.

We report a single-electrode-based sliding-mode triboelectric nanogenerator (TENG) that not only can harvest mechanical energy but also is a self-powered displacement vector sensor system for touching pad technology. By utilizing the relative sliding between an electrodeless polytetrafluoroethylene (PTFE) patch with surface-etched nanoparticles and an Al electrode that is grounded, the fabricated TENG can produce an open-circuit voltage up to 1100 V, a short-circuit current density of 6 mA/m(2), and a maximum power density of 350 mW/m(2) on a load of 100 MΩ, which can be used to instantaneously drive 100 green-light-emitting diodes (LEDs). The working mechanism of the TENG is based on the charge transfer between the Al electrode and the ground by modulating the relative sliding distance between the tribo-charged PTFE patch and the Al plate. Grating of linear rows on the Al electrode enables the detection of the sliding speed of the PTFE patch along one direction. Moreover, we demonstrated that 16 Al electrode channels arranged along four directions were used to monitor the displacement (the direction and the location) of the PTFE patch at the center, where the output voltage signals in the 16 channels were recorded in real-time to form a mapping figure. The advantage of this design is that it only requires the bottom Al electrode to be grounded and the top PTFE patch needs no electrical contact, which is beneficial for energy harvesting in automobile rotation mode and touch pad applications.

We demonstrate a cylindrical rotating triboelectric nanogenerator (TENG) based on sliding electrification for harvesting mechanical energy from rotational motion. The rotating TENG is based on a core-shell structure that is made of distinctly different triboelectric materials with alternative strip structures on the surface. The charge transfer is strengthened with the formation of polymer nanoparticles on surfaces. During coaxial rotation, a contact-induced electrification and the relative sliding between the contact surfaces of the core and the shell result in an "in-plane" lateral polarization, which drives the flow of electrons in the external load. A power density of 36.9 W/m(2) (short-circuit current of 90 μA and open-circuit voltage of 410 V) has been achieved by a rotating TENG with 8 strip units at a linear rotational velocity of 1.33 m/s (a rotation rate of 1000 r/min). The output can be further enhanced by integrating more strip units and/or applying larger linear rotational velocity. This rotating TENG can be used as a direct power source to drive small electronics, such as LED bulbs. This study proves the possibility to harvest mechanical energy by TENGs from rotational motion, demonstrating its potential for harvesting the flow energy of air or water for applications such as self-powered environmental sensors and wildlife tracking devices.

Harvesting mechanical energy is becoming increasingly important for its availability and abundance in our living environment. Triboelectric nanogenerator (TENG) is a simple, cost-effective, and highly efficient approach for generating electricity from mechanical energies in a wide range of forms. Here, we developed a TENG designed for harvesting tiny-scale wind energy available in our normal living environment using conventional materials. The energy harvester is based on a rotary driven mechanical deformation of multiple plate-based TENGs. The operation mechanism is a hybridization of the contact-sliding-separation-contact processes by using the triboelectrification and electrostatic induction effects. With the introduction of polymer nanowires on surfaces, the rotary TENG delivers an open-circuit voltage of 250 V and a short-circuit current of 0.25 mA, corresponding to a maximum power density of ~39 W/m(2) at a wind speed of ~15 m/s, which is capable of directly driving hundreds of electronic devices such as commercial light-emitting diodes (LEDs), or rapidly charging capacitors. The rotary TENG was also applied as a self-powered sensor for measuring wind speed. This work represents a significant progress in the practical application of the TENG and its great potential in the future wind power technology. This technology can also be extended for harvesting energy from ocean current, making nanotechnology reaching our daily life a possibility in the near future.