High output piezo/triboelectric hybrid generator

Smart Printed Triboelectric Wearable Sensor with High Performance for Glove-Based Motion Detection

In a world increasingly driven by data, wearable triboelectric nanogenerators (TENGs) offer a convenient way to monitor and collect information about human body motions. To meet the demands of the large-scale production of wearable TENGs, material selection to realize a high conversion efficiency and simplify the fabrication process remains a challenge. To address these issues, we present a simple-structured wearable printed arc-shaped triboelectric sensor (PATS) for finger motion detection by leveraging inkjet printing technology. In this regard, pressure sensors composed of diverse materials based on dielectric-dielectric and metal-dielectric structures in contact-separation mode were fabricated and compared. Thanks to the unique characteristics of the silver nanoparticle (Ag-NP)-printed layer and silicon rubber (SR), the SR-Ag PATS shows a high peak-to-peak voltage of 14.15 V and a short-circuit current of 0.78 μA. The proposed sensor with the capability of accurately identifying finger motions at various bending angles suggests promising application potential in glove-based human-machine interface (HMI) systems.

The Preparation, Structural Design, and Application of Electroactive Poly(vinylidene fluoride)-Based Materials for Wearable Sensors and Human Energy Harvesters

Owing to their biocompatibility, chemical stability, film-forming ability, cost-effectiveness, and excellent electroactive properties, poly(vinylidene fluoride) (PVDF) and PVDF-based polymers are widely used in sensors, actuators, energy harvesters, etc. In this review, the recent research progress on the PVDF phase structures and identification of different phases is outlined. Several approaches for obtaining the electroactive phase of PVDF and preparing PVDF-based nanocomposites are described. Furthermore, the potential applications of these materials in wearable sensors and human energy harvesters are discussed. Finally, some challenges and perspectives for improving the properties and boosting the applications of these materials are presented.

Recent Advances in Carbon Nanotube-Based Energy Harvesting Technologies

There has been enormous interest in technologies that generate electricity from ambient energy such as solar, thermal, and mechanical energy, due to their potential for providing sustainable solutions to the energy crisis. One driving force behind the search for new energy-harvesting technologies is the desire to power sensor networks and portable devices without batteries, such as self-powered wearable electronics, human health monitoring systems, and implantable wireless sensors. Various energy harvesting technologies have been demonstrated in recent years. Among them, electrochemical, hydroelectric, triboelectric, piezoelectric, and thermoelectric nanogenerators have been extensively studied because of their special physical properties, ease of application, and sometimes high obtainable efficiency. Multifunctional carbon nanotubes (CNTs) have attracted much interest in energy harvesting because of their exceptionally high gravimetric power outputs and recently obtained high energy conversion efficiencies. Further development of this field, however, still requires an in-depth understanding of harvesting mechanisms and boosting of the electrical outputs for wider applications. Here, various CNT-based energy harvesting technologies are comprehensively reviewed, focusing on working principles, typical examples, and future improvements. The last section discusses the existing challenges and future directions of CNT-based energy harvesters.

A flexible organic mechanoluminophore device

A flexible mechanoluminophore device that is capable of converting mechanical energy into visualizable patterns through light-emission holds great promise in many applications, such as human-machine interfaces, Internet of Things, wearables, etc. However, the development has been very nascent, and more importantly, existing mechanoluminophore materials or devices emit light that cannot be discernible under ambient light, in particular with slight applied force or deformation. Here we report the development of a low-cost flexible organic mechanoluminophore device, which is constructed based on the multi-layered integration of a high-efficiency, high-contrast top-emitting organic light-emitting device and a piezoelectric generator on a thin polymer substrate. The device is rationalized based on a high-performance top-emitting organic light-emitting device design and maximized piezoelectric generator output through a bending stress optimization and have demonstrated that it is discernible under an ambient illumination as high as 3000 lux. A flexible multifunctional anti-counterfeiting device is further developed by integrating patterned electro-responsive and photo-responsive organic emitters onto the flexible organic mechanoluminophore device, capable of converting mechanical, electrical, and/or optical inputs into light emission and patterned displays.

Recent Progress in Piezoelectric-Triboelectric Effects Coupled Nanogenerators

Piezoelectric and triboelectric nanogenerators have been widely studied in the past years for their advantages of easy design/manufacturing, small size, and flexibility. Nanogenerators that are developed based on the coupled piezoelectric and triboelectric effects (PTCNG) can make full use of the mechanical energies and achieve both higher output and sensing performance. This review aims to cover the recent research progress of PTCNG by presenting in detail their key technologies in terms of operating principles, integration concept, and performance enhancement strategies, with a focus on their structural simplification and efficiency performance improvement. The latest applications of PTCNG in tactile sensors and energy-harvesting system are also illustrated. Finally, we discuss the main challenges and prospects for the future development of PTCNG, hoping that this work can provide a new insight into the development of all-in-one mechanical energy-scavenging and sensing devices.

NFC-Powered Implantable Device for On-Body Parameters Monitoring With Secure Data Exchange Link to a Medical Blockchain Type of Network

Implantable devices represent the future of remote medical monitoring and administration of both chemical and physical therapies to the patients. Although some of these devices are already in the market, the security mechanisms deployed inside them to withstand deliberate external influence are still decades away from the robust digital data security schemes employed in modern distributed networks these days. Medical data theft, spoofing, and disclosure pose serious threats that can ultimately lead to individual and social stigmas or even death. In this article, we present a small-form and batteryless implantable device with acquisition channels for biopotential (30-dB gain and 16-Hz bandwidth), arterial pulse oximetry, and temperature (0.12°C accuracy) recordings, suitable for cardiovascular, neuronal, and endocrine parameters assessment. The proposed device is powered by the near-field communication (NFC) interface with an external mobile phone, with a power consumption of 0.9 mW and achieving the full operation for distances close to 1 cm under the skin. In situ encryption of the acquired physiological signals is performed by a lightweight and short-term symmetric-key distribution scheme with data stream hopping, in order to ensure secure data transference over the air between the patient and trusted entities only, complemented by data storage, processing, and recovery through a medical blockchain type of network that involves the main stakeholders inside a medical community.

Expedient secondary functions of flexible piezoelectrics for biomedical energy harvesting

Flexible piezoelectrics realise the conversion between mechanical movements and electrical power by conformally attaching onto curvilinear surfaces, which are promising for energy harvesting of biomedical devices due to their sustainable body movements and/or deformations. Developing secondary functions of flexible piezoelectric energy harvesters is becoming increasingly significant in recent years via aiming at issues that cannot be addressed or mitigated by merely increasing piezoelectric efficiencies. These issues include loose interfacial contact and pucker generation by stretching, power shortage or instability induced by inadequate mechanical energy, and premature function degeneration or failure caused by fatigue fracture after cyclic deformations. Herein, the expedient secondary functions of flexible piezoelectrics to mitigate above issues are reviewed, including stretchability, hybrid energy harvesting, and self-healing. Efforts have been devoted to understanding the state-of-the-art strategies and their mechanisms of achieving secondary functions based on piezoelectric fundamentals. The link between structural characteristic and function performance is unravelled by providing insights into carefully selected progresses. The remaining challenges of developing secondary functions are proposed in the end with corresponding outlooks. The current work hopes to help and inspire future research in this promising field focusing on developing the secondary functions of flexible piezoelectric energy harvesters.

A Novel High-Speed Resonant Frequency Tracking Method Using Transient Characteristics in a Piezoelectric Transducer

When driving the piezoelectric transducer (PT: piezo transducer), which is a key device, it is important for the ultrasonic system (using ultrasonic waves of 20 kHz or higher) to operate at a resonant frequency that can maximize the conversion of mechanical energy (vibration) from electrical energy. The resonant frequency of the PT changes during the actual operation according to the load fluctuations and environmental conditions. Therefore, to maintain a stable output in an ultrasonic system, it is essential to track the resonant frequency in a short time. In particular, fast resonant frequency tracking (RFT: resonant frequency tracking) is an important factor in the medical ultrasonic system, i.e., the system applied in this thesis. The reason is that in the case of a medical ultrasonic system, heat-induced skin necrosis, etc., may cause the procedure to be completed within a short period of time. Therefore, tracking the RFT time for maximum power transfer is an important factor; in this thesis, we propose a new high-speed RFT method. The proposed method finds the whole system resonance frequency by using the transient phenomenon (underdamped response characteristic) that appears in an impedance system, such as an ultrasonic generator, and uses this to derive the mechanical resonance frequency of the PT. To increase the accuracy of the proposed method, parameter fluctuations of the pressure of the PT, the equivalent circuit impedance analysis of the PT, and a MATLAB simulation were performed. Through this, the correlation between the resonance frequency of the ultrasonic system, including the LC filter with nonlinear characteristics and the mechanical resonance frequency of the PT, was analyzed. Based on the analyzed results, a method for tracking the mechanical resonance frequency that can transfer the maximum output to the PT is proposed in this thesis. Experiments show that using the proposed high-speed RFT method, the ultrasonic system can track the mechanical resonance frequency of the PT with high accuracy in a short time.

Mitigating the Negative Piezoelectricity in Organic/Inorganic Hybrid Materials for High-performance Piezoelectric Nanogenerators

The conversion of ecofriendly waste energy into useable electrical energy is of significant interest for energy harvesting technologies. Piezoelectric nanogenerators based on organic/inorganic hybrid materials are a key promising technology for harvesting mechanical energy due to their high piezoelectric coefficient and good mechanical flexibility. However, the negative piezoelectric effect of the polymer component in composite devices severely undermines its overall piezoelectricity, compromising the output performance of PVDF-based piezoelectric hybrid nanogenerators. Here, to conquer this, we report a two-step poling schedule to orient the dipoles of organic and inorganic components in the same direction. The optimized nanogenerator delivers a combination of high piezoelectric coefficient, great output performance, and remarkable stability. The isotropic piezoelectricity in the composite device collaborates to output a maximum voltage of 110 V and a power density of 7.8 μW cm^-2. This strategy is also applied to elevate the piezoelectricity of other organic/inorganic-hybrid-based nanogenerators, substantiating its universal applicability for composite piezoelectric nanogenerators. This study presents a feasible strategy for enhancing the effective output capability of composite nanogenerator technologies.

Ambient Humidity-Induced Phase Separation for Fiber Morphology Engineering toward Piezoelectric Self-Powered Sensing

Electrospun polymeric piezoelectric fibers have a considerable potential for shape-adaptive mechanical energy harvesting and self-powered sensing in biomedical, wearable, and industrial applications. However, their unsatisfactory piezoelectric performance remains an issue to be overcome. While strategies for increasing the crystallinity of electroactive β phases have thus far been the major focus in realizing enhanced piezoelectric performance, tailoring the fiber morphology can also be a promising alternative. Herein, a design strategy that combines the nonsolvent-induced phase separation of a polymer/solvent/water ternary system and electrospinning for fabricating piezoelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE) fibers with surface porosity under ambient humidity is presented. Notably, electrospun P(VDF-TrFE) fibers with higher surface porosity outperform their smooth-surfaced counterparts with a higher β phase content in terms of output voltage and power generation. Theoretical and numerical studies also underpin the contribution of the structural porosity to the harvesting performance, which is attributable to local stress concentration and reduced dielectric constant due to the air in the pores. This porous fiber design can broaden the application prospects of shape-adaptive energy harvesting and self-powered sensing based on piezoelectric polymer fibers with enhanced voltage and power performance, as successfully demonstrated in this work by developing a communication system based on self-powered motion sensing.

Increasing Permittivity and Mechanical Harvesting Response of PVDF-Based Flexible Composites by Using Ag Nanoparticles onto BaTiO3 Nanofillers

The role of Ag addition on the structural, dielectric, and mechanical harvesting response of 20%(xAg − (1 − x)BaTiO₃) − 80%PVDF (x = 0, 2, 5, 7 and 27 vol.%) flexible composites is investigated. The inorganic fillers were realized by precipitating fine (~3 nm) silver nanoparticles onto BaTiO₃ nanoparticles (~60 nm average size). The hybrid admixtures with a total filling factor of 20 vol.% were embedded into the PVDF matrix. The presence of filler enhances the amount of β-PVDF polar phase and the BaTiO₃ filler induces an increase of the permittivity from 11 to 18 (1 kHz) in the flexible composites. The addition of increasing amounts of Ag is further beneficial for permittivity increase; with the maximum amount (x = 27 vol.%), permittivity is three times larger than in pure PVDF (εr ~ 33 at 1 kHz) with a similar level of tangent losses. This result is due to the local field enhancement in the regions close to the filler-PVDF interfaces which are additionally intensified by the presence of silver nanoparticles. The metallic addition is also beneficial for the mechanical harvesting ability of such composites: the amplitude of the maximum piezoelectric-triboelectric combined output collected in open circuit conditions increases from 0.2 V/cm² (PVDF) to 30 V/cm² for x = 27 vol.% Ag in a capacitive configuration. The role of ferroelectric and metallic nanoparticles on the increasing mechanical-electric conversion response is also been explained.

Recent developments of hybrid piezo-triboelectric nanogenerators for flexible sensors and energy harvesters

Hybrid piezo-triboelectric nanogenerators constitute a new class of self-powered systems that exploit the synergy of piezoelectric and triboelectric mechanisms to improve energy harvesting efficencies and address the energy and power needs of portable and wearable electronic devices. The unique, synergistic electrical coupling mechanisms of piezoelectric and triboelectric effects increase the electric outputs and energy conversion efficiency of hybrid generators to beyond a linear summation of the contributions from individual triboelectric and piezoelectric mechanisms. Due to their large surface-area-to-volume ratios and outstanding mechanical, electronic and thermal properties, nanomaterials are favourable building blocks for constructing hybrid nanogenerators and represent a large family of flexible energy harvesting electronic structures and devices. Herein, we review the recent advances of hybrid piezo-triboelectric nanogenerators, with a particular focus on microstructure design, synergy mechanisms, and future research opportunities with significant potential for physiological monitoring, health care applications, transportation, and energy harvesting. The main strategies for improving electrical output performance are identified and examined, including novel nanostructures for increasing the contact area of the triboelectric pair, and nano-additives for enhancing the surface potential difference between the triboelectric pair and piezoelectric layers. Future applications and commercialization opportunities of these nanogenerators are also reviewed.

Triboelectric Nanogenerators for Energy Harvesting in Ocean: A Review on Application and Hybridization

With recent advancements in technology, energy storage for gadgets and sensors has become a challenging task. Among several alternatives, the triboelectric nanogenerators (TENG) have been recognized as one of the most reliable methods to cure conventional battery innovation’s inadequacies. A TENG transfers mechanical energy from the surrounding environment into power. Natural energy resources can empower TENGs to create a clean and conveyed energy network, which can finally facilitate the development of different remote gadgets. In this review paper, TENGs targeting various environmental energy resources are systematically summarized. First, a brief introduction is given to the ocean waves’ principles, as well as the conventional energy harvesting devices. Next, different TENG systems are discussed in details. Furthermore, hybridization of TENGs with other energy innovations such as solar cells, electromagnetic generators, piezoelectric nanogenerators and magnetic intensity are investigated as an efficient technique to improve their performance. Advantages and disadvantages of different TENG structures are explored. A high level overview is provided on the connection of TENGs with structural health monitoring, artificial intelligence and the path forward.

Design and optimisation of magnetically-tunable hybrid piezoelectric-triboelectric energy harvester

The demand for energy harvesting technologies has been increasing over the years that can be attributed to its significance to low power applications. One of the key problems associated with the available vibration-based harvester is the maximum peak power can only be achieved when the device frequency matches the source frequency to generate low usable power. Therefore, in this study, a magnetically-tunable hybrid piezoelectric-triboelectric energy harvester (MT-HPTEH) was designed and optimised. Four key design factors: mass placement, triboelectric surface area, extension length and magnetic stiffness were investigated and optimised. The voltage generation from piezoelectric and triboelectric mechanisms was determined individually to understand the effect of each design factor on the mechanisms. An output power of 659 µW at 180 kΩ at 44 Hz was obtained from the optimised MT-HPTEH with a theoretical-experimental discrepancy of less than 10%. The added magnetically-tunable feature enabled the harvester to work at the desired frequency range with an open circuit voltage between 7.800 and 20.314 V and a frequency range from 38 to 54 Hz. This MT-HPTEH can power at least six wireless sensor networks and can be used for low power applications such as RFID tags. Future work may include designing of energy-saving and sustainable harvester.

High-Performance Triboelectric Devices via Dielectric Polarization: A Review

Energy harvesting devices based on the triboelectric effect have attracted great attention because of their higher output performance compared to other nanogenerators, which have been utilized in various wearable applications. Based on the working mechanism, the triboelectric performance is mainly proportional to the surface charge density of the triboelectric materials. Various approaches, such as modification of the surface functional group and dielectric composition of the triboelectric materials, have been employed to enhance the surface charge density, leading to improvements in triboelectric performances. Notably, tuning the dielectric properties of triboelectric materials can significantly increase the surface charge density because the surface charge is proportional to the relative permittivity of the triboelectric material. The relative dielectric constant is modified by dielectric polarization, such as electronic, vibrational (or atomic), orientation (or dipolar), ionic, and interfacial polarization. Therefore, such polarization represents a critical factor toward improving the dielectric constant and consequent triboelectric performance. In this review, we summarize the recent insights on the improvement of triboelectric performance via enhanced dielectric polarization.

Self-Powered, Hybrid, Multifunctional Sensor for a Human Biomechanical Monitoring Device

For personal and daily activities, it is highly desirable to collect energy from multiple sources, not only for charging personal electronics but also for charging devices that may in the future sense and transmit information for healthcare and biomedical applications. In particular, hybridization of triboelectric and piezoelectric energy-harvesting generators with lightweight components and relatively simple structures have shown promise in self-powered sensors. Here, we present a self-powered multifunctional sensor (SPMS) based on hybridization with a novel design of a piezoelectrically curved spacer that functions concurrently with a zigzag shaped triboelectric harvester for a human biomechanical monitoring device. The optimized SPMS had an open-circuit voltage (VOC) of 103 V, short-circuit current (ISC) of 302 µA, load of 100 kΩ, and maximum average power output of 38 mW under the operational processes of compression/deformation/touch/release. To maximize the new sensor’s usage as a gait sensor that can detect and monitor human motion characteristics in rehabilitation circumstances, the deep learning long short-term memory (LSTM) model was developed with an accuracy of the personal sequence gait SPMS signal recognition of 81.8%.

Hybrid Triboelectric Nanogenerators: From Energy Complementation to Integration

Energy collection ways using solar energy, wave, wind, or mechanical energy have attracted widespread attention for small self-powered electronic devices with low power consumption, such as sensors, wearable devices, electronic skin, and implantable devices. Among them, triboelectric nanogenerator (TENG) operated by coupling effect of triboelectrification and electrostatic induction has gradually gained prominence due to its advantages such as low cost, lightweight, high degree of freedom in material selection, large power, and high applicability. The device with a single energy exchange mechanism is limited by its conversion efficiency and work environment and cannot achieve the maximum conversion of energy. Thus, this article reviews the research status of different types of hybrid generators based on TENG in recent years. Hybrid energy generators will improve the output performance though the integration of different energy exchange methods, which have an excellent application prospect. From the perspective of energy complementation, it can be divided into harvesting mechanical energy by various principles, combining with harvesters of other clean energy, and converting mechanical energy or various energy sources into hydrogen energy. For integrating multitype energy harvesters, mechanism of single device and structural design of integrated units for different application scenarios are summarized. The expanding energy harvesting efficiency of the hybrid TENG makes the scheme of self-charging unit to power intelligent mobile electronic feasible and has practical significance for the development of self-powered sensor network.

Impact-Driven Energy Harvesting: Piezoelectric Versus Triboelectric Energy Harvesters

This work investigated the mechanical and electrical behaviors of piezoelectric and triboelectric energy harvesters (PEHs and TEHs, respectively) as potential devices for harvesting impact-driven energy. PEH and TEH test benches were designed and developed, aiming at harvesting low-frequency mechanical vibration generated by human activities, for example, a floor-tile energy harvester actuated by human footsteps. The electrical performance and behavior of these energy harvesters were evaluated and compared in terms of absolute energy and power densities that they provided and in terms of these energy and power densities normalized to unit material cost. Several aspects related to the design and development of PEHs and TEHs as the energy harvesting devices were investigated, covering the following topics: construction and mechanism of the energy harvesters; electrical characteristics of the fabricated piezoelectric and triboelectric materials; and characterization of the energy harvesters. At a 4 mm gap width between the cover plate and the stopper (the mechanical actuation components of both energy harvesters) and a cover plate pressing frequency of 2 Hz, PEH generated 27.64 mW, 1.90 mA, and 14.39 V across an optimal resistive load of 7.50 kΩ, while TEH generated 1.52 mW, 8.54 µA, and 177.91 V across an optimal resistive load of 21 MΩ. The power and energy densities of PEH (4.57 mW/cm³ and 475.13 µJ/cm³) were higher than those of TEH (0.50 mW/cm³, and 21.55 µJ/cm³). However, when the material cost is taken into account, TEH provided higher power and energy densities per unit cost. Hence, it has good potential for upscaling, and is considered well worth the investment. The advantages and disadvantages of PEH and TEH are also highlighted as main design factors.

Miniaturized Piezo Force Sensor for a Medical Catheter and Implantable Device

Real-time monitoring of intrabody pressures can benefit from the use of miniaturized force sensors during surgical interventions or for the recovery period thereafter. Herein, we present a force sensor made of poly(vinylidene fluoride)-co-trifluoroethylene (P(VDF-TrFE)) with a simple fabrication process that has been integrated into the tip of a medical catheter for intraluminal pressure monitoring, as well as into an implantable device with a power consumption of 180 μW obtained by the near-field communication (NFC) interface to monitor the arterial pulse at the subcutaneous level (≤1 cm). The pressure range supported by the sensor is below 40 kPa, with a signal responsivity of 0.63 μV/Pa and a mean lifetime expectancy of 400 000 loading cycles inside physiological conditions (12 kPa). The proposed sensor has been tested experimentally with synthetic anatomical models for the lungs (bronchoscopy) and subcutaneous tissue, as well as directly above the human carotid and radial arteries. Information about these pressure levels can provide insights about tissue homeostasis inside the body as fluid dynamics are altered in some health conditions affecting the hemodynamic and endocrine body systems, whereas for surgical interventions, precise control and estimation of the pressure exerted by a catheter over the internal walls are necessary to avoid endothelium injuries that lead to bleeding, liquid extravasation, or flow alteration associated with atheroma formation.

Measuring Piezoelectric Output-Fact or Friction?

Piezoelectric polymers are emerging as exceptionally promising materials for energy harvesting. While the theoretical figures of merit for piezoelectric polymers are comparable to ceramics, the measurement techniques need to be retrofitted to account for the different mechanical properties of the softer polymeric materials. Here, how contact electrification, including friction and contact separation, is often mistaken for piezoelectric charge is examined, and a perspective for how to separate these effects is provided. The state of the literature is assessed, and recommendations are made for clear and simple guidelines in reporting, for both sample geometry and testing methods, to enable accurate determination of piezoelectric figures of merit in polymers. Such improvements will allow an understanding of what types of material manipulation are required in order to enhance the piezoelectric output from polymers and enable the next generation of polymer energy harvester design.

Flexible and stretchable dual mode nanogenerator for rehabilitation monitoring and information interaction

Motion recognition and information interaction sensors with flexibility and stretchability are key functional modules as interactive media between the mechanical motions and electric signals in an intelligent robotic and rehabilitation training system. Nanogenerators have many useful applications in the field of intelligent interaction, with the advantages of a self-powered sensing ability, easy fabrication, considerable sensitivity and reliability. However, the singularity of the sensing mode limits its applications. Hence, in this research, a flexible and stretchable dual mode nanogenerator (FSDM-NG) for human motion sensing and information interaction, based on the integration of piezoelectric and triboelectric principles was developed. In piezoelectric mode, the FSDM-NG can effectively monitor the bending angle of joints (finger, wrist and elbow) from 30° to 90°. In triboelectric mode, text and logic information transfer are encoded using Morse code and logic gates, respectively. In addition, the device has good adhesion and biosafety, and is robust which makes it work normally even in under water environments. Combining these two sensing mechanisms, multiple modes of sensing from touch and stretch based on the FSDM-NG can be achieved for information interaction in real time. The proposed sensor has the potential to be adapted for more complex sensing, which may provide new applications for intelligent interaction of robots and in the rehabilitation training field.

SbSI Composites Based on Epoxy Resin and Cellulose for Energy Harvesting and Sensors-The Influence of SBSI Nanowires Conglomeration on Piezoelectric Properties

In this paper, ferroelectric antimony sulfoiodide (SbSI) nanowires have been used to produce composites for device fabrication, which can be used for energy harvesting and sensors. SbSI is a very useful material for nanogenerators and nanosensors in which the high values of the piezoelectric coefficient (d₃₃ = 650 pC/N) and the electromechanical coefficient (k₃₃ = 0.9) are essential. Alternatively, cellulose and epoxy resin were matrix materials in these composites, whereas SbSI nanowires fill the matrix. Piezoelectric response induced by vibrations has been presented. Then, a composite with an epoxy resin has been used as an element to construct a fiber-reinforced polymer piezoelectric sensor. For the first time, comparison of piezoelectric properties of cellulose/SbSI and epoxy resin/SbSI nanocomposite has been presented. The influence of concentration of SbSI nanowires for properties of epoxy resin/SbSI nanocomposite and in a fiber-reinforced polymer based on them has also been shown. Results of aligning the SbSI nanowires in the epoxy matrix during a curing process have been presented as well.

Smart Textile-Integrated Microelectronic Systems for Wearable Applications

The programmable nature of smart textiles makes them an indispensable part of an emerging new technology field. Smart textile-integrated microelectronic systems (STIMES), which combine microelectronics and technology such as artificial intelligence and augmented or virtual reality, have been intensively explored. A vast range of research activities have been reported. Many promising applications in healthcare, the internet of things (IoT), smart city management, robotics, etc., have been demonstrated around the world. A timely overview and comprehensive review of progress of this field in the last five years are provided. Several main aspects are covered: functional materials, major fabrication processes of smart textile components, functional devices, system architectures and heterogeneous integration, wearable applications in human and nonhuman-related areas, and the safety and security of STIMES. The major types of textile-integrated nonconventional functional devices are discussed in detail: sensors, actuators, displays, antennas, energy harvesters and their hybrids, batteries and supercapacitors, circuit boards, and memory devices.

Fiber/Fabric-Based Piezoelectric and Triboelectric Nanogenerators for Flexible/Stretchable and Wearable Electronics and Artificial Intelligence

Integration of advanced nanogenerator technology with conventional textile processes fosters the emergence of textile-based nanogenerators (NGs), which will inevitably promote the rapid development and widespread applications of next-generation wearable electronics and multifaceted artificial intelligence systems. NGs endow smart textiles with mechanical energy harvesting and multifunctional self-powered sensing capabilities, while textiles provide a versatile flexible design carrier and extensive wearable application platform for their development. However, due to the lack of an effective interactive platform and communication channel between researchers specializing in NGs and those good at textiles, it is rather difficult to achieve fiber/fabric-based NGs with both excellent electrical output properties and outstanding textile-related performances. To this end, a critical review is presented on the current state of the arts of wearable fiber/fabric-based piezoelectric nanogenerators and triboelectric nanogenerators with respect to basic classifications, material selections, fabrication techniques, structural designs, and working principles, as well as potential applications. Furthermore, the potential difficulties and tough challenges that can impede their large-scale commercial applications are summarized and discussed. It is hoped that this review will not only deepen the ties between smart textiles and wearable NGs, but also push forward further research and applications of future wearable fiber/fabric-based NGs.

Integrated Triboelectric Nanogenerators in the Era of the Internet of Things

Since their debut in 2012, triboelectric nanogenerators (TENGs) have attained high performance in terms of both energy density and instantaneous conversion, reaching up to 500 W m-2 and 85%, respectively, synchronous with multiple energy sources and hybridized designs. Here, a comprehensive review of the design guidelines of TENGs, their performance, and their designs in the context of Internet of Things (IoT) applications is presented. The development stages of TENGs in large-scale self-powered systems and technological applications enabled by harvesting energy from water waves or wind energy sources are also reviewed. This self-powered capability is essential considering that IoT applications should be capable of operation anywhere and anytime, supported by a network of energy harvesting systems in arbitrary environments. In addition, this review paper investigates the development of self-charging power units (SCPUs), which can be realized by pairing TENGs with energy storage devices, such as batteries and capacitors. Consequently, different designs of power management circuits, supercapacitors, and batteries that can be integrated with TENG devices are also reviewed. Finally, the significant factors that need to be addressed when designing and optimizing TENG-based systems for energy harvesting and self-powered sensing applications are discussed.

NFC-Powered Flexible Chest Patch for Fast Assessment of Cardiac, Hemodynamic, and Endocrine Parameters

Cardiac-related diseases are still the number one cause of death worldwide. Methods and technologies to suppress this problem are currently being investigated by integrating electrocardiographic (ECG) monitoring with other sensing modalities in order to detect these diseases more accurately and in due course of time. In this paper, we propose a battery-less and flexible device to be worn as a chest patch for monitoring cardiac and hemodynamic parameters through electrical and acoustic measurements, combined with sweat pH level estimation and skin temperature, by swiping a smartphone over the patch area for enough time (≃5 seconds) to allow adequate acquisition and estimation of the aforementioned parameters. Fast screening of vital signals from patients in ambulatory or emergency scenarios can thus be achieved by this Near Field Communication (NFC) powered device, as well as home or office monitoring for those individuals suffering from diseases affecting the hemodynamic, cardiac and endocrine parameters detected by the proposed technology. Current consumption of the device is 1 mA for harvested levels of 1.8 V, yielding a power requirement of 1.8 mW. Within these conditions, the sensitivities achieved by each sensing modality are 42 mV/unit for pH, 0.12 °C for temperature, 48 dB SNR for ECG and -56 dBA for acoustic measurements.

A flexible self-poled piezoelectric nanogenerator based on a rGO–Ag/PVDF nanocomposite

A self-poled rGO–Ag/PVDF nanocomposite based nanogenerator is shown with proper material characterization that can light twenty commercial blue LEDs, charge capacitors and harvest biomechanical energy.

Ultrahigh Output Piezoelectric and Triboelectric Hybrid Nanogenerators Based on ZnO Nanoflakes/Polydimethylsiloxane Composite Films

We demonstrated a hybrid nanogenerator (NG) exploiting both piezoelectric and triboelectric effects induced from ZnO nanoflakes (NFs)/polydimethylsiloxane (PDMS) composite films through a facile, cost-effective fabrication method. This hybrid NG exhibited not only high piezoelectric output current owing to the enhanced surface piezoelectricity of the ZnO NFs but also high triboelectric output voltage owing to the pronounced triboelectrification of Au-PDMS contact, producing a peak-to-peak output voltage of ∼470 V, a current density of ∼60 μA·cm^-2, and an average power density of ∼28.2 mW·cm^-2. Without additional energy storage devices, the hybrid NGs with an area of 3 × 3 cm² instantaneously lit up 180 commercial green light-emitting diodes through periodic hand compression. This approach may provide an innovative design for constructing high-performance and portable energy harvesting devices with enhanced power output, scavenging ambient mechanical energy from human motions in our daily life.

Implantable Energy-Harvesting Devices

The sustainable operation of implanted medical devices is essential for healthcare applications. However, limited battery capacity is a key challenge for most implantable medical electronics (IMEs). The human body abounds with mechanical and chemical energy, such as the heartbeat, breathing, blood circulation, and the oxidation-reduction of glucose. Harvesting energy from the human body is a possible approach for powering IMEs. Many new methods for developing in vivo energy harvesters (IVEHs) have been proposed for powering IMEs. In this context energy harvesters based on the piezoelectric effect, triboelectric effect, automatic wristwatch devices, biofuel cells, endocochlear potential, and light, with an emphasis on fabrication, energy output, power management, durability, animal experiments, evaluation criteria, and typical applications are discussed. Importantly, the IVEHs that are discussed, are actually implanted into living things. Future challenges and perspectives are also highlighted.

Hand-Driven Gyroscopic Hybrid Nanogenerator for Recharging Portable Devices

With the rise of portable and wearable electronics, a fast-charging, long-lasting power solution is needed; thus, there are attempts to harvest energy from the ambient environment. Mechanical energy harvesting through piezoelectric and triboelectric nanogenerators (PENG and TENG) is a promising approach due to their light weight, low cost, and high-power density in comparison to other technologies. Both types of generators are capable of charging portable and smart devices on their own by converting mechanical energy into electricity. However, most previous methods have excessive input conditions, such as high rpm and input frequency, that can be only applied with other actuators. Here, a hand-held gyroscopic generator is presented that uses the gyroscopic principle to reach a rotation rate above 8000 rpm with only hand input. The generator comprises a rotating flywheel inside a casing. Both the flywheel and casing have a TENG, and with a hybrid generator, electrical power is produced from rotation, vibration, and centrifugal force during operation. The device shows a consistent open-circuit voltage (V OC) of 90 V and a closed-circuit current (I CC) of 11 µA with a frequency of 200 Hz. As a stand-alone device, this generator can power portable sensors and smartphones through hand rotation.

Poly(dimethylsiloxane)/ZnO Nanoflakes/Three-Dimensional Graphene Heterostructures for High-Performance Flexible Energy Harvesters with Simultaneous Piezoelectric and Triboelectric Generation

Herein, we report the successful synthesis of poly(dimethylsiloxane)/ZnO nanoflakes/three-dimensional graphene (PDMS/ZnO NFs/3D Gr) heterostructures using Ni foams as the template substrate via a facile route, while adapting a rational material design for a high-performance energy-harvester application. The PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester simultaneously exploits the piezoelectric effect and triboelectrification and shows peak-to-peak output voltages up to 122 V and peak-to-peak current densities up to 51 μA cm^-2, resulting in an ultrahigh power density of 6.22 mW cm^-2. Furthermore, we have evaluated the performance of the PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester by demonstrating its capacity to instantaneously power up 68 commercially available light-emitting diodes without the need for an additional energy-storage device. The excellent performance of these energy harvesters suggests that PDMS/ZnO NFs/3D Gr heterostructures present a viable strategy for the development of high-performance, flexible, wearable energy-harvesting devices.

Piezoelectric-Induced Triboelectric Hybrid Nanogenerators Based on the ZnO Nanowire Layer Decorated on the Au/polydimethylsiloxane-Al Structure for Enhanced Triboelectric Performance

Here, we demonstrate a novel device structure design to enhance the electrical conversion output of a triboelectric device through the piezoelectric effect called as the piezo-induced triboelectric (PIT) device. By utilizing the piezopotential of ZnO nanowires embedded into the polydimethylsiloxane (PDMS) layer attached on the top electrode of the conventional triboelectric device (Au/PDMS-Al), the PIT device exhibits an output power density of 50 μW/cm², which is larger than that of the conventional triboelectric device by up to 100 folds under the external applied force of 8.5 N. We found that the effect of the external piezopotential on the top Au electrode of the triboelectric device not only enhances the electron transfer from the Al electrode to PDMS but also boosts the internal built-in potential of the triboelectric device through an external electric field of the piezoelectric layer. Furthermore, 100 light-emitting diodes (LEDs) could be lighted up via the PIT device, whereas the conventional device could illuminate less than 20 LED bulbs. Thus, our results highlight that the enhancement of the triboelectric output can be achieved by using a PIT device structure, which enables us to develop hybrid nanogenerators for various self-power electronics such as wearable and mobile devices.

Toward Wearable Self-Charging Power Systems: The Integration of Energy-Harvesting and Storage Devices

One major challenge for wearable electronics is that the state-of-the-art batteries are inadequate to provide sufficient energy for long-term operations, leading to inconvenient battery replacement or frequent recharging. Other than the pursuit of high energy density of secondary batteries, an alternative approach recently drawing intensive attention from the research community, is to integrate energy-generation and energy-storage devices into self-charging power systems (SCPSs), so that the scavenged energy can be simultaneously stored for sustainable power supply. This paper reviews recent developments in SCPSs with the integration of various energy-harvesting devices (including piezoelectric nanogenerators, triboelectric nanogenerators, solar cells, and thermoelectric nanogenerators) and energy-storage devices, such as batteries and supercapacitors. SCPSs with multiple energy-harvesting devices are also included. Emphasis is placed on integrated flexible or wearable SCPSs. Remaining challenges and perspectives are also examined to suggest how to bring the appealing SCPSs into practical applications in the near future.

A flat-panel-shaped hybrid piezo/triboelectric nanogenerator for ambient energy harvesting

Recently, many researchers have been paying attention to nanogenerators (NGs) as energy sources for self-powered mirco-nano systems, and studying how to achieve their higher power generation. Hence, we propose a hybrid-type NG for harvesting both the piezoelectric and triboelectric effect simultaneously. In the proposed hybrid NG, the piezoelectric NG (PNG) and triboelectric NG (TENG) are fabricated using polydimethylsiloxane (PDMS) and perovskite zinc stannite (ZnSnO₃) nanocubes with a high charge polarization of 59 uC cm^-2 composite (PDMS + ZnSnO₃) and UV surface-treated PDMS, respectively. To effectively combine a high output current of PNG and a high voltage of TENG, these two NGs are stacked upon each other, and separated by sponge spacers providing a uniform air gap for the triboelectric effect. In particular, this fabricated structure has a low Young's modulus for piezoelectricity. The proposed hybrid NG device effectively achieves a combined peak voltage of 300 V on an open circuit, a power density of 10.41 mW cm^-2 at 1 MΩ load, and a maximum short circuit current density of 16 mA cm^-2 at 50 Ω load. It is feasible that the proposed NG can be utilized as a source for various self-powered systems.

Broadband Energy Harvester Using Non-linear Polymer Spring and Electromagnetic/Triboelectric Hybrid Mechanism

Over the years, several approaches have been devised to widen the operating bandwidth, but most of them can only be triggered at high accelerations. In this work, we investigate a broadband energy harvester based on combination of non-linear stiffening effect and multimodal energy harvesting to obtain high bandwidth over wide range of accelerations (0.1 g–2.0 g). In order to achieve broadband behavior, a polymer based spring exhibiting multimodal energy harvesting is used. Besides, non-linear stiffening effect is introduced by using mechanical stoppers. At low accelerations (<0.5 g), the nearby mode frequencies of polymer spring contribute to broadening characteristics, while proof mass engages with mechanical stoppers to introduce broadening by non-linear stiffening at higher accelerations. The electromagnetic mechanism is employed in this design to enhance its output at low accelerations when triboelectric output is negligible. Our device displays bandwidth of 40 Hz even at low acceleration of 0.1 g and it is increased up to 68 Hz at 2 g. When non-linear stiffening is used along with multimodal energy-harvesting, the obtained bandwidth increases from 23 Hz to 68 Hz with percentage increment of 295% at 1.8 g. Further, we have demonstrated the triboelectric output measured as acceleration sensing signals in terms of voltage and current sensitivity of 4.7 Vg⁻¹ and 19.7 nAg⁻¹, respectively.

A wave-shaped hybrid piezoelectric and triboelectric nanogenerator based on P(VDF-TrFE) nanofibers

A wave-shaped hybrid nanogenerator (NG) with mutually enhanced piezoelectric and triboelectric output is presented in this work. By sandwiching piezoelectric P(VDF-TrFE) nanofibers between wave-shaped Kapton films, the device forms a three-layer structure, which can generate piezoelectric and triboelectric outputs simultaneously in one press and release cycle. Through systematic situational analysis and experimental validation, the three-layer structure can achieve obvious improvement of the output performance for both parts. When triggered with 4 Hz external force, the piezoelectric part generates a peak output and current of 96 V and 3.8 μA, which is ∼2 times higher than its initial output. Meanwhile, the performance of triboelectric parts also increases 8 V and 16 V with the assistance of piezoelectric potential. The enhanced high output enables the hybrid nanogenerator to instantaneously light up LEDs and charges capacitors quickly, which shows extensive application prospects in the field of self-powered systems or sensor networks.

Piezoelectric and Triboelectric Dual Effects in Mechanical-Energy Harvesting Using BaTiO3/Polydimethylsiloxane Composite Film

Piezoelectric and triboelectric nanogenerators have been developed as rising energy-harvesting devices in the past few years to effectively convert mechanical energy into electricity. Here, a novel hybrid piezo/triboelectric nanogenerator based on BaTiO₃ NP/PDMS composite film was developed in a simple and low-cost way. The effects of the BTO content and polarization degree on the output performance were systematically studied. The device with 20 wt % BTO in PDMS and a 100-μm-thick film showed the highest output power. We also designed three measurement modes to record hybrid, triboelectric, and piezoelectric outputs separately with a simple structure that has only two electrodes. The hybrid output performance is higher than the tribo- and piezoelectric performances. This work will provide not only a new way to enhance the output power of nanogenerators, but also new opportunities for developing built-in power sources in self-powered electronics.

A flexible triboelectric-piezoelectric hybrid nanogenerator based on P(VDF-TrFE) nanofibers and PDMS/MWCNT for wearable devices

This paper studied and realized a flexible nanogenerator based on P(VDF-TrFE) nanofibers and PDMS/MWCNT thin composite membrane, which worked under triboelectric and piezoelectric hybrid mechanisms. The P(VDF-TrFE) nanofibers as a piezoelectric functional layer and a triboelectric friction layer are formed by electrospinning process. In order to improve the performance of triboelectric nanogenerator, the multiwall carbon nanotubes (MWCNT) is doped into PDMS patterned films as the other flexible friction layer to increase the initial capacitance. The flexible nanogenerator is fabricated by low cost MEMS processes. Its output performance is characterized in detail and structural optimization is performed. The device’s output peak-peak voltage, power and power density under triboelectric mechanism are 25 V, 98.56 μW and 1.98 mW/cm³ under the pressure force of 5 N, respectively. The output peak-peak voltage, power and power density under piezoelectric working principle are 2.5 V, 9.74 μW, and 0.689 mW/cm³ under the same condition, respectively. We believe that the proposed flexible, biocompatible, lightweight, low cost nanogenerator will supply effective power energy sustainably for wearable devices in practical applications.

Self-Positioned Nanosized Mask for Transparent and Flexible Ferroelectric Polymer Nanodiodes Array

High density arrays of ferroelectric polymer nanodiodes have gained strong attention for next-generation transparent and flexible nonvolatile resistive memory. Here, we introduce a facile and innovative method to fabricate ferroelectric polymer nanodiode array on an ITO-coated poly(ethylene terephthalate) (PET) substrate by using block copolymer self-assembly and oxygen plasma etching. First, polystyrene-block-poly(2-vinylpyridine) copolymer (PS-b-P2VP) micelles were spin-coated on poly(vinylidene fluoride-ran-trifluoroethylene) copolymer (P(VDF-TrFE)) film/ITO-coated PET substrate. After the sample was immersed in a gold precursor (HAuCl₄) containing solution, which strongly coordinates with nitrogen group in P2VP, oxygen plasma etching was performed. During the plasma etching, coordinated gold precursors became gold nanoparticles (GNPs), which successfully acted as self-positioned etching mask to fabricate a high density array of P(VDF-TrFE)) nanoislands with GNP at the top. Each nanoisland shows clearly individual diode property, as confirmed by current-voltage (I-V) curve. Furthermore, due to the transparent and flexible nature of P(VDF-TrFE)) nanoisland as well as the substrate, the P(VDF-TrFE) nanodiode array was highly tranparent, and the diode property was maintained even after a large number of bendings (for instance, 1000 times). The array could be used as the next-generation tranparent and flexible nonvolatile memory device.

Self-Powered Triboelectric Micro Liquid/Gas Flow Sensor for Microfluidics

Liquid and gas flow sensors are important components of the micro total analysis systems (μTAS) for modern analytical sciences. In this paper, we proposed a self-powered triboelectric microfluidic sensor (TMS) by utilizing the signals produced from the droplet/bubble via the capillary and the triboelectrification effects on the liquid/solid interface for real-time liquid and gas flow detection. By alternating capillary with different diameters, the sensor's detecting range and sensitivity can be adjusted. Both the relationship between the droplet/bubble and capillary size, and the output signal of the sensor are systematically studied. By demonstrating the monitoring of the transfusion process for a patient and the gas flow produced from an injector, it shows that TMS has a great potential in building a self-powered micro total analysis system.

Flexible Nanogenerators for Energy Harvesting and Self-Powered Electronics

Flexible nanogenerators that efficiently convert mechanical energy into electrical energy have been extensively studied because of their great potential for driving low-power personal electronics and self-powered sensors. Integration of flexibility and stretchability to nanogenerator has important research significance that enables applications in flexible/stretchable electronics, organic optoelectronics, and wearable electronics. Progress in nanogenerators for mechanical energy harvesting is reviewed, mainly including two key technologies: flexible piezoelectric nanogenerators (PENGs) and flexible triboelectric nanogenerators (TENGs). By means of material classification, various approaches of PENGs based on ZnO nanowires, lead zirconate titanate (PZT), poly(vinylidene fluoride) (PVDF), 2D materials, and composite materials are introduced. For flexible TENG, its structural designs and factors determining its output performance are discussed, as well as its integration, fabrication and applications. The latest representative achievements regarding the hybrid nanogenerator are also summarized. Finally, some perspectives and challenges in this field are discussed.

Conductive Fabric-Based Stretchable Hybridized Nanogenerator for Scavenging Biomechanical Energy

We demonstrate a stretchable hybridized nanogenerator based on a highly conductive fabric of glass fibers/silver nanowires/polydimethylsiloxane. Including a triboelectric nanogenerator and an electromagnetic generator, the hybridized nanogenerator can deliver output voltage/current signals from stretchable movements by both triboelectrification and electromagnetic induction, maximizing the efficiency of energy scavenging from one motion. Compared to the individual energy-harvesting units, the hybridized nanogenerator has a better charging performance, where a 47 μF capacitor can be charged to 2.8 V in only 16 s. The hybridized nanogenerator can be integrated with a bus grip for scavenging wasted biomechanical energy from human body movements to solve the power source issue of some electric devices in the pure electric bus.

A flexible and biocompatible triboelectric nanogenerator with tunable internal resistance for powering wearable devices

Recently, triboelectric energy nanogenerators (TENGs) have been paid the most attention by many researchers to convert mechanical energy into electrical energy. TENGs usually have a simple structure and a high output voltage. However, their high internal resistance results in low output power. In this work, we propose a flexible triboelectric energy nanogenerator with the double-side tribological layers of polydimethlysiloxane (PDMS) and PDMS/multiwall carbon nanotube (MWCNT). MWCNTs with different concentrations have been doped into PDMS to tune the internal resistance of triboelectric nanogenerator and optimize its output power. The dimension of the fabricated prototype is ~3.6 cm³. Three-axial force sensor is used to monitor the applied vertical forces on the device under vertical contact-separation working mode. The Prototype with 10 wt% MWCNT (Prototype I) produces higher output voltage than one with 2 wt% MWCNT (Prototype II) due to its higher dielectric parameter measured by LRC impedance analyzer. The triboelectric output voltages of Prototype I and Prototype II are 30 V and 25 V under the vertical force of 3.0 N, respectively. Their maximum triboelectric output powers are ~130 μW at 6 MΩ and ~120 μW at 8.6 MΩ under vertical forces, respectively.

A Low Input Current and Wide Conversion Ratio Buck Regulator with 75% Efficiency for High-Voltage Triboelectric Nanogenerators

It is meaningful to research the Triboelectric Nanogenerators (TENG), which can create electricity anywhere and anytime. There are many researches on the structures and materials of TENG to explain the phenomenon that the maximum voltage is stable and the current is increasing. The output voltage of the TENG is high about 180-400 V, and the output current is small about 39 μA, which the electronic devices directly integration of TENG with Li-ion batteries will result in huge energy loss due to the ultrahigh TENG impedance. A novel interface circuit with the high-voltage buck regulator for TENG is introduced firstly in this paper. The interface circuit can transfer the output signal of the TENG into the signal fit to a lithium ion battery. Through the circuit of the buck regulator, the average output voltage is about 4.0 V and the average output current is about 1.12 mA. Further, the reliability and availability for the lithium ion battery and the circuit are discussed. The interface circuit is simulated using the Cadence software and verified through PCB experiment. The buck regulator can achieve 75% efficiency for the High-Voltage TENG. This will lead to a research hot and industrialization applications.

Triboelectric generator for wearable devices fabricated using a casting method

We fabricate an efficient triboelectric generator (TEG) using inexpensive materials that are readily available in our surroundings. By casting PDMS, we perform micropatterning on the surface of sandpaper.

Wearable Fall Detector using Integrated Sensors and Energy Devices

Wearable devices have attracted great attentions as next-generation electronic devices. For the comfortable, portable, and easy-to-use system platform in wearable electronics, a key requirement is to replace conventional bulky and rigid energy devices into thin and deformable ones accompanying the capability of long-term energy supply. Here, we demonstrate a wearable fall detection system composed of a wristband-type deformable triboelectric generator and lithium ion battery in conjunction with integrated sensors, controllers, and wireless units. A stretchable conductive nylon is used as electrodes of the triboelectric generator and the interconnection between battery cells. Ethoxylated polyethylenimine, coated on the surface of the conductive nylon electrode, tunes the work function of a triboelectric generator and maximizes its performance. The electrical energy harvested from the triboelectric generator through human body motions continuously recharges the stretchable battery and prolongs hours of its use. The integrated energy supply system runs the 3-axis accelerometer and related electronics that record human body motions and send the data wirelessly. Upon the unexpected fall occurring, a custom-made software discriminates the fall signal and an emergency alert is immediately sent to an external mobile device. This wearable fall detection system would provide new opportunities in the mobile electronics and wearable healthcare.