Self-powered Wearable Devices Research Articles

Thin-Film π-Type Micro TEG Using Vacuum/Insulator-Hybrid Isolation with Convex-Shape Hot-Plate Module Structure for Wearable Device Applications

Design optimization and performance of a micro thermoelectric generator (μTEG) using human body heat are investigated. A newly introduced thin-film π-type μTEG module structure using vacuum/insulator-hybrid thermal isolation with the convex-shape hot plate is useful to achieve a high thermal resistance of the module and also to suppress the unwanted heat flow passing through the supportive wall structure for the vacuum isolation. The optimum design of this μTEG module can exhibit sufficiently high output power suitable for a power source of self-powered wearable devices.

Hybrid nanomanufacturing of mixed-dimensional manganese oxide/graphene aerogel macroporous hierarchy for ultralight efficient supercapacitor electrodes in self-powered ubiquitous nanosystems

The economic production of wearable energy storage devices exhibiting mechanically-compliable form factors and reliable performance enable exciting opportunities in emerging technologies of consumer electronics, human-machine interface, and the Internet of Things. Here we report a hybrid scheme for designing and nanomanufacturing ultralight, high-performance supercapacitor electrodes through the hydrothermal growth of two-dimensional MnO2 on three-dimensional printed graphene aerogel (GA). The derived mixed-dimensional hierarchical macroporous composite electrodes exhibit superior specific capacitance and excellent cycling stability after thousands of cycles. We further explored the integration of a contact mode triboelectric nanogenerator and a mixed-dimensional MnO2/GA based supercapacitor into a self-powered system that is capable of converting mechanical signals into electrical power and further storing such scavenged power. The holistic integration of energy harvesting and storage units promises the implementation of self-powered wearable devices with greater intelligence that can scavenge and store environmental energy through sustainable pathways for ubiquitous electronics in societally-pervasive applications.

Self-Activated Electrical Stimulation for Effective Hair Regeneration via a Wearable Omnidirectional Pulse Generator.

Hair loss, a common and distressing symptom, has been plaguing humans. Various pharmacological and nonpharmacological treatments have been widely studied to achieve the desired effect for hair regeneration. As a nonpharmacological physical approach, physiologically appropriate alternating electric field plays a key role in the field of regenerative tissue engineering. Here, a universal motion-activated and wearable electric stimulation device that can effectively promote hair regeneration via random body motions was designed. Significantly facilitated hair regeneration results were obtained from Sprague-Dawley rats and nude mice. Higher hair follicle density and longer hair shaft length were observed on Sprague-Dawley rats when the device was employed compared to conventional pharmacological treatments. The device can also improve the secretion of vascular endothelial growth factor and keratinocyte growth factor and thereby alleviate hair keratin disorder, increase the number of hair follicles, and promote hair regeneration on genetically defective nude mice. This work provides an effective hair regeneration strategy in the context of a nonpharmacological self-powered wearable electronic device.

(Invited) 3D Conformal Printing of High-Performance and Flexible Thermoelectric Devices Using Colloidal Nanocrystals

The flexible thermoelectric generator (f-TEG) is a very promising technology for energy harvesting to enable self-powered wireless sensors and wearable devices, an area of exponential growth. Here, we present a scalable and cost-effective additive manufacturing process to fabricate f-TEGs using colloidal nanocrystals, and an innovative and highly efficient photonic sintering method to sinter large areas of printed films using pulsed light. Flexible TE films and devices were printed using screen printing and aerosol jet printing, followed by pulsed photonic sintering process. The pulsed sintering confines the delivered thermal energy within the printed film region without over heating the substrate, enabling TE film sintering on flexible polymer based substrates with relatively low melting point. In addition, the pulsed sintering limits grain size growth due to an ultrafast heating and cooling process, and lower thermal conductivity can be achieved than films sintered by conventional thermal processing. The p-type and n-type printed films demonstrate peak ZTs of 1 and 0.43 near room temperature along with superior flexibility, which is among the highest reported ZT values in flexible thermoelectric materials. A flexible thermoelectric device fabricated using the printed films produces a high power density above 19 mW/cm2 with 80 ºC temperature difference between the hot side and cold side. The additive printing and photonic sintering can enable a highly scalable and low-cost roll-to-roll manufacturing process to transform high-efficiency colloidal nanocrystals into high-performance and flexible TEG devices for widespread applications.

Wearable Woven Triboelectric Nanogenerator Utilizing Electrospun PVDF Nanofibers for Mechanical Energy Harvesting

Several wearable devices have already been commercialized and are likely to open up a new life pattern for consumers. However, the limited energy capacity and lifetime have made batteries the bottleneck in wearable technology. Thus, there have been growing efforts in the area of self-powered wearables that harvest ambient mechanical energy directly from surroundings. Herein, we demonstrate a woven triboelectric nanogenerator (WTENG) utilizing electrospun Polyvinylidene fluoride (PVDF) nanofibers and commercial nylon cloth to effectively harvest mechanical energy from human motion. The PVDF nanofibers were fabricated using a highly scalable multi-nozzle far-field centrifugal electrospinning protocol. We have also doped the PVDF nanofibers with small amounts of multi-walled carbon nanotubes (MWCNT) to improve their triboelectric performance by facilitating the growth of crystalline β-phase with a high net dipole moment that results in enhanced surface charge density during contact electrification. The electrical output of the WTENG was characterized under a range of applied forces and frequencies. The WTENG can be triggered by various free-standing triboelectric layers and reaches a high output voltage and current of about 14 V and 0.7 µA, respectively, for the size dimensions 6 × 6 cm. To demonstrate the potential applications and feasibility for harvesting energy from human motion, we have integrated the WTENG into human clothing and as a floor mat (or potential energy generating shoe). The proposed triboelectric nanogenerator (TENG) shows promise for a range of power generation applications and self-powered wearable devices.

Fluorinated Titania Nanoparticle-Induced Piezoelectric Phase Transition of Poly(vinylidene fluoride)

We prepared F-coated rutile titanium dioxide nanoparticles (r-TiO2 NPs) via simple thermal annealing of titania NPs in poly(vinylidene fluoride) (PVDF) and demonstrated that the F-coated r-TiO2 NP-doped composite film could efficiently induce piezoelectric phase transition of non-electroactive PVDF due to highly electronegative F bonds on the surface of these NPs. In the case of a 2.0 wt % composite film, 99.20% of the non-electroactive PVDF was transformed into the electroactive phase. Additionally, utilizing the F-coated r-TiO2 NPs for a piezoelectric device led to an enhancement of the piezoelectric performance. With the 5.0 wt % composite film, the resulting piezoelectric device exhibited voltage generation of 355 mV, whereas a device with the innate r-TiO2 NPs exhibited voltage generation of only 137 mV. Furthermore, because of optical inactivity of F-coated r-TiO2 NPs, the piezoelectric films exhibited high stability under 64 h of photoirradiation at an intensity of 0.1 W/cm2. These results indicate that the F-coated r-TiO2 NP-doped composite films could be useful for various applications, including outdoor energy-harvesting, self-powered wearable devices, and portable sensors.

Flexible heatsink based on a phase-change material for a wearable thermoelectric generator

Thermoelectric generators (TEGs) represent a promising technology for self-powered wearable systems. Since the conventional TEGs have limitation to be used on the human body due to its structural rigidity, flexible TEGs have been studied and developed so that TEGs can be attached to an arbitrarily shaped surface on the human body. However, flexible TEGs require a good heatsink with good flexibility to allow them to produce enough power for wearable devices. In this study, a high-performance flexible heatsink based on a phase-change material (PCM) was proposed. PCM blocks were arranged in an array and good flexibility was realized with an elastomer that filled the space between the PCM blocks. Given that PCM can absorb a large amount of heat at the phase-change temperature, the heatsink can hold the temperature difference across the TEG constant for a relatively long period of time. Thus, the generated power from the flexible TEG was maintained at around 20 μW/cm2 for 33 min. The flexible heatsink can be reused because the PCM solidifies at room temperature. Furthermore, the PCM-based flexible heatsink is smaller and lighter than the conventional metal heatsink. The proposed heatsink is expected to contribute to the commercialization of self-powered wearable devices.

Design and Development of a Self-Powered Wearable Device for a Tele-Medicine Application

This project aims to develop a self-powered, multipurpose system designed to measure an array of biomedical parameters like, SPO2, temperature and pulse rate which serves the need for Telemedicine application. The IOT based biomedical instrument helps in bridging the gap between a doctor and his patient by providing real time diagnosis and treatment through telecommunication technology. This instrument is designed to target individuals who are in fields which go hand in hand with high altitudes and having walking as the only means of transport. Fields like the armed forces, trekking etc. come in this bracket. Piezoelectric sensors are useful for such fields as these require a whole lot of activity but do not usually have active power sources to charge their health monitors. National defence personnel, who have to take care of their bodies in places like Siachen and other difficult terrains, require wearable health devices, now more than ever to continually monitor their health. Hence the design of a self-powered wearable health monitoring device proved to be of critical importance. As the device fulfils telemedicine requirements, it also provides sophisticated health care resources with solutions, allowing the soldier to return to duty and avoid medical evacuation.

Highly efficient photovoltaic energy storage hybrid system based on ultrathin carbon electrodes designed for a portable and flexible power source

Integrated perovskite solar capacitor (IPSC) systems are the new paradigm for power generation and storage. Herein, a novel configuration and combination of materials for an IPSC, theoretically affording a maximized areal capacitance of 2.35 mF cm−2 and exceeding a 25% overall photo-chemical-electricity energy conversion efficiency is reported. A ∼1 μm solid-state photocapacitor is suggested based on a CH3NH3PbI3 photoactive layer, inorganic buffer junctions, an ultrathin nanocarbon border and top electrodes. For the first time, bulk and interfacial imperfections in the perovskite layer are reckoned in simulation, realizing the recombination rate to 14-order of magnitude higher than that in the perfect perovskite structure. The simulation considers the band gap energy, the valance and conduction bands, carrier mobility and carrier density of every individual layer of the designed IPSC. Overall, the results for the areal capacitance, output voltage and photocharging efficiency under various illumination conditions, frequencies and dielectric materials show that the performance of the perovskite power pack is mildly susceptible to external and internal triggers. This ultrathin and sturdy architecture, shows promise for use in self-powered portable and wearable personal devices.

Highly transparent triboelectric nanogenerator utilizing in-situ chemically welded silver nanowire network as electrode for mechanical energy harvesting and body motion monitoring

Triboelectric nanogenerators (TENGs) functioning as energy harvester as well as body motion sensor pose great significance for oncoming wearable (opto)electronic systems. Herein, A transparent welded AgNW electrode based TENG (WA-TENG) is demonstrated. AgNWs are in-situ chemically welded with surfacial silver oxide naturally formed in air as solder and hydrazine as reductant based on epitaxial recrystallization, ensuring high transparency and conductivity of the electrode used in TENG. This welding endows AgNW electrodes with a high transmittance of 96% (at 77 Ω/sq sheet resistance) and low sheet resistance of 18 Ω/sq (at 92% transmittance), meanwhile, can effectively heal the damaged AgNW network. The WA-TENG exhibits a transmittance up to 95%, and generates an open-circuit voltage (Voc) of 66 V, short-circuit current (Isc) of 8.6 μA, and peak power density of 446 mW/m2 under single-electrode mode at 2 Hz. Besides, it can be employed to monitor human body motions, including bending of the elbow, eye blinking, and bending angle and frequency of the finger. Lastly, the WA-TENG serves as a tactile sensor to record touch control of a smart phone by the finger. The WA-TENG with standout transparency, electric output and sensing performance underscores the crucial role in self-powered wearable multifunctional devices.

Activity-Aware Wearable System for Power-Efficient Prediction of Physiological Responses

Wearable health monitoring has emerged as a promising solution to the growing need for remote health assessment and growing demand for personalized preventative care and wellness management. Vital signs can be monitored and alerts can be made when anomalies are detected, potentially improving patient outcomes. One major challenge for the use of wearable health devices is their energy efficiency and battery-lifetime, which motivates the recent efforts towards the development of self-powered wearable devices. This article proposes a method for context aware dynamic sensor selection for power optimized physiological prediction using multi-modal wearable data streams. We first cluster the data by physical activity using the accelerometer data, and then fit a group lasso model to each activity cluster. We find the optimal reduced set of groups of sensor features, in turn reducing power usage by duty cycling these and optimizing prediction accuracy. We show that using activity state-based contextual information increases accuracy while decreasing power usage. We also show that the reduced feature set can be used in other regression models increasing accuracy and decreasing energy burden. We demonstrate the potential reduction in power usage using a custom-designed multi-modal wearable system prototype.

Tactile sensor from self-chargeable piezoelectric supercapacitor

Tactile sensors that can simultaneously detect temperature and force are highly desirable for applications in health monitoring and human-machine interface. Rendering such devices the ability to harness energy from ambient environment would make them more sustainable, wearable, and even implantable. Herein, a self-powered flexible tactile sensor is developed on the base of piezoelectrically active solid supercapacitors. By conformally intercalating solid electrolyte into the piezoelectric separator, the as-designed flexible piezoelectrical supercapacitor can not only convert environmental mechanical energy into electricity and charge itself, but also detect static pressure, dynamic pressure, acceleration and even temperature with high sensitivity and wide linear range. These concomitant intelligences make the piezoelectric supercapacitor ideal platform for developing self-powered multifunctional wearable devices.

Versatile nanodot-patterned Gore-Tex fabric for multiple energy harvesting in wearable and aerodynamic nanogenerators

The ongoing expedition to harvest ambient renewable energies from the environment by wearable fabric-based nanogenerators is a promising route to sustainably drive the small electronics with unprecedented opportunities in next-generation self-powered devices. Here, we report a simple method to fabricate a washable, breathable and wearable triboelectric nanogenerator that harvests the energy of triboelectricity through an enhanced friction surface area made of the gold nanodot-pattern crafted by electron-beam sputtering on an inexpensive polyurethane surface. The gold deposition which crops-up as regular small islands, under oxygen plasma is subsequently, etched into nanodot-pattern on a polyurethane surface to convert mechanical energy into an electrical signal via in-plane sliding mode with a maximum output of ~2 μW. The nanodot engineering plays an important role to improve the active sliding frictional area, as well as the corresponding output-performance of the triboelectric nanogenerator. To demonstrate the potential applications of our approach, we designed a self-powered wearable device integrated with clothes to harvest different kinds of mechanical energies from the human motion. To elevate the power output-performance, we fabricated waterproof fiber with flutter membrane and quantified triboelectric charge against airflow speed. At mild wind speed, the fabricated triboelectric nanogenerator shows a maximum output of 70 µW. Besides, as an example of practical application, the nanogenerator constructed can produce an improved capacitor charge voltage to drive dozens of light-emitting diodes and apply them to low power consumption devices. This technology is produced in a simple and cost-effective manner and reports an easy way to produce an energy harvesting system based on triboelectric effects using a sustainable and renewable energy source of body motions and air flows. This system is expected to be one of the best green energy sources for portable and wearable electronic devices in the near future.

An air-cushion triboelectric nanogenerator integrated with stretchable electrode for human-motion energy harvesting and monitoring

Harvesting energy from human-motion can be a viable solution for developing self-powered wearable and portable electronic devices. This work presents an air-cushion triboelectric nanogenerator (ACTNG) which is entirely made of stretchable materials. ACTNG can efficiently harvest mechanical energy from intense movements like walking, running and jumping without any ambient influence. Systematic testing of different parameters like diameter (20–60 mm), frequency (1–5 Hz), and applied force (20–60 N), reveals an optimal peak power density of 44.6 mW m−2. The output performance is further validated by charging commercial capacitors, lighting LEDs, and operating as a power supply for a scientific calculator and digital thermometer. In addition, this device can operate as a human motion sensor with a detection sensitivity of 33.8 μA MPa−1 for instantaneous force. This device has potential for a wide range of applications in biocompatible, wearable, and smart sensing technologies.

A Nano-Watt ECG Feature Extraction Engine in 65-nm Technology

This brief presents an ultralow power electrocardiography (ECG) feature extraction engine. ECG signal represents the cardiac cycle and contains key features, such as QRS complex, ${P}$ -wave, and ${T}$ -wave, which provide important diagnostic information about cardiovascular diseases. The ECG feature extraction is based on combined techniques of curve length transform (CLT) and discrete wavelet transform. A novel pipelined architecture for implementing CLT is proposed. The system was fabricated using GF-65-nm technology and consumed 642 nW only when operating at a frequency of 7.5 kHz from a supply voltage of 0.6 V. Ultralow power consumption of the SoC made it suitable for self-powered wearable devices.

Wind-Driven Triboelectric Nanogenerators for Scavenging Biomechanical Energy

The wind-driven triboelectric nanogenerator (TENG), considered as one of the most important tributaries of the TENG family, possesses high-frequency signals and remarkable output power. Herein, a wind-driven TENG, employing silver nanowires (Ag NWs) and fluorinated ethylene propylene (FEP) as triboelectric materials, was designed with a purpose to act as a power unit to replace batteries in some wearable devices. Under a wind speed of 20 m/s, the as-fabricated TENG could generate an output voltage, current, and power of up to 150 V, 7.5 μA, and 0.18 mW, respectively. Wind-driven TENGs were integrated into three types of self-powered devices (i.e., shoe, bracelet, and mask) to play roles as energy sources due to the high output power and high-frequency signals. The wearable devices were utilized to monitor different motion states (e.g., walking, jogging, and running) at various body positions. These prototypes of self-powered wearable devices could offer new approaches to protecting our environment and imp...

Lead-Free Perovskite Nanowire-Employed Piezopolymer for Highly Efficient Flexible Nanocomposite Energy Harvester.

In the past two decades, mechanical energy harvesting technologies have been developed in various ways to support or power small-scale electronics. Nevertheless, the strategy for enhancing current and charge performance of flexible piezoelectric energy harvesters using a simple and cost-effective process is still a challenging issue. Herein, a 1D-3D (1-3) fully piezoelectric nanocomposite is developed using perovskite BaTiO3 (BT) nanowire (NW)-employed poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) for a high-performance hybrid nanocomposite generator (hNCG) device. The harvested output of the flexible hNCG reaches up to ≈14 V and ≈4 µA, which is higher than the current levels of even previous piezoceramic film-based flexible energy harvesters. Finite element analysis method simulations study that the outstanding performance of hNCG devices attributes to not only the piezoelectric synergy of well-controlled BT NWs and within P(VDF-TrFE) matrix, but also the effective stress transferability of piezopolymer. As a proof of concept, the flexible hNCG is directly attached to a hand to scavenge energy using a human motion in various biomechanical frequencies for self-powered wearable patch device applications. This research can pave the way for a new approach to high-performance wearable and biocompatible self-sufficient electronics.

Structural design of a flexible thermoelectric power generator for wearable applications

Self-powered wearable electronic devices are expected to be one of the mainstream technologies for future portable electronic systems. As an energy harvester to power wearable electronic devices, a flexible thermoelectric generator (f-TEG) can utilize human body heat as the energy source, creating an ideal solution. The f-TEG can make conformal contact to the human skin and fully utilize body heat with minimal energy loss, while also being comfortable to wear. However, to maximize the power generated by an f-TEG attached to the human body, a careful thermal and structural design analysis of the f-TEG must be carried out. Here, we fabricated flexible thermoelectric generators (f-TEGs) with different device parameters and evaluated their power generating performance using an artificial arm, which was carefully designed to mimic a real human arm. We demonstrated the impact of the f-TEG device parameters on the power generation performance under various circumstances. The experimental results were compared with the theoretical model, and guidelines for an optimum device design in terms of maximizing the generated power density are also presented. Finally, we show that the optimum device structure varies when the efficiency of the power management IC (PMIC) is included in the analysis of the power generation system, which is practically important.

Wearable triboelectric nanogenerators based on hybridized triboelectric modes for harvesting mechanical energy.

In this paper, we demonstrate a newly designed hybridized triboelectric nanogenerator (TENG) fabric incorporating multiple working modes, which can effectively harvest ambient mechanical energy for conversion into electric power by working in a hybridization of a contact–separation mode, a sliding mode and a freestanding triboelectric layer mode. The power generation of each mode of the TENG fabric was systematically investigated and compared along different directions, under different frequencies and at different locations. Owing to the advanced structural design, the as-fabricated TENG fabric could be switched between multiple working modes according to its real working situation. High output voltage and current of about 140 V and 0.6 μA, respectively, were obtained from a larger size of TENG fabric, which could be used to light up 120 LEDs in series. Compared to the previously reported TENGs, such a hybridized TENG fabric based on hybridized modes has much better adaptability for harvesting energy (such as human walking, running, and other human motion) in different directions. This work presents the promising potential of hybridized TENG fabric for power generation and self-powered wearable devices.

An Effective Wind Energy Harvester of Paper Ash-Mediated Rapidly Synthesized ZnO Nanoparticle-Interfaced Electrospun PVDF Fiber

In this paper, we report an innovative technique for the rapid and simple synthesis of ZnO-containing paper ash (ZPA) within 30 min. It is demonstrated that as-synthesized ZPA can be an alternative for conventional semiconducting filler that is used to improve the electroactive β-phase content in the electrospun PVDF nanofiber (NF). Furthermore, the PVDF nanofiber-based nanogenerator (NFNG) that enables a high output voltage of 4.8 V under an exerted wind pressure of 145 Pa is fabricated. In addition, the detection capability of minute wind pressure, even from human mouth blowing, makes the NFNG an active sensor that might be utilized for charging a mobile phone during conversation. Thus, this strategy is expected to be a promising platform for harvesting wind energy that is beneficial for the design of integrated self-powered wearable electronic devices.