Self-powered Wearable Sensor Research Articles

Emerging Functional Polymer Composites for Tactile Sensing.

In recent years, extensive research has been conducted on the development of high-performance flexible tactile sensors, pursuing the next generation of highly intelligent electronics with diverse potential applications in self-powered wearable sensors, human-machine interactions, electronic skin, and soft robotics. Among the most promising materials that have emerged in this context are functional polymer composites (FPCs), which exhibit exceptional mechanical and electrical properties, enabling them to be excellent candidates for tactile sensors. Herein, this review provides a comprehensive overview of recent advances in FPCs-based tactile sensors, including the fundamental principle, the necessary property parameter, the unique device structure, and the fabrication process of different types of tactile sensors. Examples of FPCs are elaborated with a focus on miniaturization, self-healing, self-cleaning, integration, biodegradation, and neural control. Furthermore, the applications of FPC-based tactile sensors in tactile perception, human-machine interaction, and healthcare are further described. Finally, the existing limitations and technical challenges for FPCs-based tactile sensors are briefly discussed, offering potential avenues for the development of electronic products.

3D-Printed Flexible PVDF-TrFE Composites with Aligned BCZT Nanowires and Interdigital Electrodes for Piezoelectric Nanogenerator Applications

Piezoelectric nanogenerators based on piezoelectric nanocomposites have attracted much interest in recent decades owing to their excellent piezoelectric properties and application in self-powered systems and wearable sensors. As a promising piezoelectric ceramic filler in composite-based generators, one-dimensional (1D) piezoelectric nanowires were filled into a polymer matrix to enhance its dielectric and piezoelectric properties. In this paper, flexible PVDF-TrFE composite films containing highly aligned Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) nanowires (NWs) have been manufactured via a direct-ink writing method. The effect of BCZT NW content on the dielectric, ferroelectric, and piezoelectric properties was investigated using multiphysics modeling and detailed experiments. An optimum composite composition was discovered, and the piezoelectric composite film with 15 wt % BCZT NWs possessed the highest energy harvesting figure of merit of 5.3 × 10–12 m2/N. Interdigital electrodes were combined with the composite to fabricate a patterned piezoelectric nanogenerator, where the piezoelectric nanogenerator can produce an open-circuit output voltage of 17 V, and the maximum output power density could reach 5.6 μW/cm2. This work provides opportunities for the optimization and fabrication of piezoelectric materials for energy-harvesting and sensing applications.

Vascular bundle-inspired MXene ion-conducting microchannels enabled tough ionic hydrogels with high-sensitivity sensing and high-efficiency mechanical-electric conversion

High-sensitivity hydrogel-based sensors with self-powered functions are becoming more and more important in wearable electronics fields. However, traditional hydrogels cannot satisfy the application requirements for high-performance self-powered wearable sensors due to their low conductivity, poor sensitivity, and limited electric output performance. Inspired by the transport effect of vascular bundles in trees on inorganic salts, unique ion-conducting microchannels are assembled by MXene nanosheets as conductive materials, cellulose nanofibrils (CNFs) as cross-linking supports, and NH4HCO3 as an inducer, which exhibits high mechanical properties, excellent conductivity, and high-sensitivity sensing. The MXene microchannels contribute to the directional transport of free ions in the polyvinyl alcohol (PVA) hydrogel with poly(diallyl dimethyl ammonium chloride) (PDADMAC) as ion source, thus endowing the MXene-CNF-PDADMAC-PVA (MCPP) hydrogel with high-sensitivity sensing and high-efficiency mechanical-electric conversion performance. The MCPP hydrogel-based sensor possesses a low detection limit (200 mg) and fast response time (120 ms). The MCPP hydrogel-based triboelectric nanogenerator can generate a VOC of 159.1 V, ISC of 24.5 µA, and QSC of 32.5 nC, and the MCPP hydrogel-based piezoelectric nanogenerator can output a voltage of 1134.3 mV. Thanks to the excellent self-powered sensing performance, a self-powered sensing indicator and tiny pressure detector based on the hydrogel are developed to realize the visual sensing in an uncomfortable state of the elderly without an external power supply and detect the heartbeat and fluttering pulse. Therefore, this ionic hydrogel with high-sensitivity sensing and high-efficiency mechanical-electric conversion performance is very promising for applications in next-generation advanced wearable electronics.

Wearable bending wireless sensing with autonomous wake-up by piezoelectric and triboelectric hybrid nanogenerator

The Internet of Things calls for the demand for wearable self-powered sensors for human motion monitoring and interaction. However, the redundant data and large amount of power consumption limit the application in sustainable wireless sensing. In this study, a flexible hybrid nanogenerator with bridge structure design for self-powered wearable sensor is proposed. When harvesting energy from the finger bent motion, it combines contact separation mode for triboelectric nanogenerator (TENG) with bending d31 mode for piezoelectric generator (PEG). To highlight the significance, we propose an autonomous wake-up wireless sensing method by hybrid generator in wearable bending. Different from recording and transmitting data all the time, the TENG signal as a trigger to record the PEG voltage amplitude as angle sensing data for wireless transmitting. Concise and accurate sensing data with autonomous wake-up is expected to reduce the computational burden and power consumption for wireless sensing and provide more possibilities for wearable wireless monitoring and human-computer interaction. The wireless manipulator interaction experiment based on this hybrid nanogenerator as wearable bending sensor verifies the feasibility of this scheme, which has a great application prospect in wearable self-powered sensors field such as virtual reality and robot control.

MOF-derived porous Ni/C material for high-performance hybrid nanogenerator and self-powered wearable sensor

This study proposed a self-powered bio-sensing positioning system driven by MOF-derived porous Ni/C material-based hybrid nanogenerator. The porous structure of Ni/C nanoparticles provides a high specific surface area, increases the capacitance of the nano-composite, and traps more charges due to the formation of micro-capacitors, which boost the performance of TENGs. The as-fabricated enhanced TENG achieved a peak voltage of 820 V and a power density of 10.1 W/m2. An optimal bilayer structure was determined through experiments and simulations to obtain the maximum output performance. Flexible TENGs are placed on various parts of the body to achieve biomechanical energy harvesting and motion monitoring, and provide power sources for small electronics. By combining with electromagnetic generator (EMG), a wearable self-powered positioning system is constructed. This work provides a new idea to enhance the output of TENG, and broadens the application of TENG in self-powered wearable systems.

Asymmetric-elastic-structure fabric-based triboelectric nanogenerators for wearable energy harvesting and human motion sensing

With rapid advancement in wearable electronics, triboelectric nanogenerators (TENGs) have attracted great attention for energy harvesting and bio-motion sensing because of low cost, environmentally friendly, safe, sustainable and easy availability. However, the existing structure is not well suitable and desirable for ordinary apparel. There are great challenges in balancing structural and motion adaptability with high-performance output for practical wearable applications. Therefore, herein we ingeniously combine human motions and the difference in elasticity between fabrics to develop an asymmetric-elastic-structure fabric-based triboelectric nanogenerator (AesF-TENG) which can realize rapid contact and separation under small deformation or force, and can efficiently harvest the mechanical energy under the natural motion of the human body to obtain better wearable potential. The AesF-TENG is composed of nylon and doped polydimethylsiloxane (PDMS) used as positive and negative triboelectric materials respectively, and stretchable elastic fabric and conventional cotton fabric as the base. The developed AesF-TENG can efficiently harvest biomechanical energy and maintain stable electrical performance after 20 washes and 120,000 durability tests and also drive commercial electronic watch, calculator and LEDs. Additionally, it could be also utilized as a self-powered wearable sensor for wireless monitoring of human body motions. The prominent output power performance of AesF-TENG together with human motion and textiles show their great potentials for viable applications in wearable electronics and smart textiles in the near future.

Highly Stretchable and Stimulus-Free Self-Healing Hydrogels with Multiple Signal Detection Performance for Self-Powered Wearable Temperature Sensors

A flexible wearable temperature sensor is a novel electronic sensor that can monitor real-time changes in human body temperature in a variety of application scenarios and is regarded as the "crown jewel" of information collection technology. Although flexible strain sensors based on hydrogels have excellent self-healing effects and mechanical durability, their widespread application is still limited by external power sources. Herein, a novel self-energizing hydrogel was developed by embellishing cellulose nanocrystals (CNC) with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The resultant thermoelectrically conductive CNC was then employed as a booster for poly(vinyl alcohol) (PVA)/borax hydrogels. The obtained hydrogels exhibit remarkable self-healing performance (92.57%) and exceptional stretchability (989.60%). Additionally, the hydrogel was capable of accurately and reliably identifying human motion. Most importantly, it exhibits excellent thermoelectric performance, capable of generating stable and reproducible voltages. It shows a large Seebeck coefficient of 1.31 mV k-1 at ambient temperatures. When subjected to a temperature difference of 25 K, the output voltage reaches 31.72 mV. CNC-PEDOT:PSS/PVA conductive hydrogel is multifunctional with self-healing, self-powering, and temperature sensing, which has the potential to be used for the preparation of intelligent wearable temperature-sensing devices.

Environment-tolerant versatile ion-conductive eutectic hydrogels for self-powered wearable flexible sensors

Conductive hydrogels (CHs) have been widely utilized in the design of wearable flexible sensors. The remaining issues with CHs include their propensity to dehydrate in the open air and freeze at low temperatures, which makes them significantly less functional. Additionally, the wide applications of CHs are limited by their dependence on external power sources and inadequate sensing of humidity, strain, etc. Herein, a series of versatile ion-conductive adhesive hydrogels (GAAAD) with emblematic on-demand 3D cross-network structures were nanoengineered by combining solvent exchange strategies with in-situ physical and covalent cross-linking. The GAAAD possesses exceptional properties such as integrated outstanding sensing of multiple external stimuli in harsh environments, desirable adhesive ability towards various substrates, mechanical robustness, transparency, anti-freezing and anti-dehydration performance, and self-healing capacity. Even after being frozen at −20 ℃ for 48 h, GAAAD could be utilized for effective real-time human sleeping monitoring, demonstrating preponderant environmental stability. Integrated with the versatile origins of GAAAD, a simple Cu/GAAAD/Zn self-powered flexible sensor (GAAADB) was developed based on the fundamental structure of a primary battery, which exhibits remarkable properties of stable open-circuit voltage even in extremely cold environments, sensitive response to applied tensile or compressive strain, as well as its repeatability and durability. Interestingly, based on the sensing mechanism of the potential difference between the humidity-regulating electrodes, GAAADB was substantiated to be reliable for long-term respiratory monitoring (with the humidity response/recovery time less than 1 s) under extreme cold conditions (−20 °C), indicating its great potential for extensive applications in respiratory diagnosis, sleep monitoring, electronic skin, and wearable electronics.

Flexible piezoelectric generator based on PLLA/ZnO oriented fibers for wearable self-powered sensing

Herein, PLLA/ZnO oriented fibers were prepared via orientation electrospinning towards a piezoelectric generator, omitting polarization and stretching postprocesses. The composite fibers achieved macroscopic orientation and molecular alignment, as well as higher crystallinity and more polar phase for PLLA. Collectively, the resulting generator exhibited dramatic and stable piezoelectric signals over 1000 s, boosting the open-circuit voltage to 7.9 V, nearly 4.6 times larger than that of the random neat device. With the same changing tendency, the simulated results confirmed oriented fibers and ZnO induced stress concentration, imparting better piezoelectricity. Furthermore, the generated electricity from the generator with a short-circuit current of 286nA and an output power density of 1.25 mW cm−3 charged a 10 μF capacitor up to 2 V at 210 s then illuminated a LED. Encouragingly, high flexibility and sensitivity allowed this device to function as a wearable self-powered sensor for differentiating human movement and monitoring human health.

Multifunctional smart mask: Enabling self-dehumidification and self-powered wearables via transpiration-driven electrokinetic power generation from human breath

Self-operating transpiration-driven electrokinetic power generators (STEPGs) offer an attractive approach for autonomous electricity production, but they suffer from a narrow range of applications due to the need for a highly humid environment. Herein, we introduce an efficient STEPG and its unprecedented application in the design of a multifunctional smart mask with self-dehumidification capability and self-powered wearable sensors. Our STEPG design for the smart mask comprises of (1) a carbon black-loaded cotton fiber (CB/CF) serving as a hydrophilic, electroactive platform for power generation, and (2) a moisture-absorbing desiccant layer to wet and activate the power generator. As-optimized STEPG achieves efficient energy conversion with a high VOC, ISC, and power output up to 1200 mV, 5 μA, and 687 nW/cm2, respectively, under 10 °C (simulating winter temperature) and 90 %RH. These electrical outputs are > 8-fold better than similar TEPG designs, and are also stable under a wide range of ambient temperature (e.g. 10–40 °C) and humidity (e.g. 30–90 %RH). As a proof-of-concept application, we incorporate as-designed STEPGs in series onto a N95 mask to harness electrical energy directly from human breath and use it to power inbuilt temperature/humidity sensors for real-time, wireless monitoring of breath using a smart phone. By showcasing the facile use of human breath as an energy feedstock, our work creates enormous opportunities for diverse applications in green energy production and wearable technologies.

Surface-modified liquid metal nanocapsules derived multiple triboelectric composites for efficient energy harvesting and wearable self-powered sensing

Liquid metal (LM) has been widely used as flexible electrodes for triboelectric nanogenerators (TENGs). However, the development of high-performance triboelectric composites based on LM droplets is still challenging due to the mismatched surface tension. Here, copolymer surface-modified LM nanocapsules (CPLM NCs) with core–shell structure are successfully synthesized via two-step method containing chelation reaction and in situ free-radical polymerization. The as-synthesized NCs can be incorporated into various polymers to fabricate diverse flexible polymer/NCs nanocomposites. Based on surface engineering, CPLM will not leak and drop off from nanocomposites when they suffer severe deformations, exhibiting good interfacial compatibility and robust mechanical properties. The introduction of NCs can improve the charge storage capability and electric outputs of various nanocomposites owing to more interfacial polarization sites, showing a versatile strategy for manufacturing high-powered triboelectric composites. The optimized polydimethylsiloxane/NCs-based TENG (PDMS/NCs-TENG) delivers a significant enhancement of power density by 28.3-fold and can availably power wearable electronics. PDMS/NCs-TENG can be also developed as a wearable self-powered sensor to detect physiological signals and joint-related motions in a real-time, rapid, and noninvasive way. This work not only renders a versatile strategy for the development of high-performance triboelectric materials but also provides a sustainable energy solution for wearable electronics.

Investigated a PLL surface-modified Nylon 11 electrospun as a highly tribo-positive frictional layer to enhance output performance of triboelectric nanogenerators and self-powered wearable sensors

Although the development of self-powered triboelectric sensors (TES) is growing very rapidly, fabricating ultra-flexible, highly sensitive, lightweight and energy-sustained TES remains a tremendous challenge. Here, we report a facile poly-L-lysine (PLL) post-surface-modification technique to enhance the positive polarity of Nylon 11 electrospun membranes for the first time. Ecoflex was used as the tribo-negative layer of the triboelectric nanogenerator (TENG). The effect of the Nylon 11 electrospun membrane with PLL modification (PNy11) used as the positive layer was compared with the experimental results of the membrane without PLL modification (Ny11). The triboelectric output performances of open circuit potential and short circuit current significantly increased by more than five times (from 26 to 137 V) and four times (from 0.8 to 3.4 µA) for PNy 11. Further, various dielectric materials (MXene and SrTiO3 with different wt%) were incorporated into the Ecoflex counter layer to minimize the triboelectric loss and enhance the triboelectric performance. The 10 wt% SrTiO3-embedded Ecoflex (EC10S) and PNy 11 pair showed maximum triboelectric performance (270 V and 7.2 µA) at a working load of 8.5 N than others. The optimized EC10S+PNy 11 TENG showed a power density of 2 Wm−2, which is sufficient to operate low-power electronics. Furthermore, the proposed EC10S+PNy 11 wearable triboelectric sensor (without spacer) exhibits high shape adaptability with a sensitivity of 9 V.Pa−1 due to the imported micro-nano hierarchical roughness on the frictional layers. The proposed idea with excellent performance is expected to show great potential for use in the field of wearable electronics.

Self-Powered Wearable Breath-Monitoring Sensor Enabled by Electromagnetic Harvesting Based on Nano-Structured Electrochemically Active Aluminum

Self-powered sensors are gaining a lot of attention in recent years due to their possible application in the Internet of Things, medical implants and wireless and wearable devices. Human breath detection has applications in diagnostics, medical therapy and metabolism monitoring. One possible approach for breath monitoring is detecting the humidity in exhaled air. Here, we present an extremely sensitive, self-powered sensor for breath humidity monitoring. As a power source, the sensor uses electromagnetic energy harvested from the environment. Even electromagnetic energy harvested from the human body is enough for the operation of this sensor. The signal obtained using the human body as a source was up to 100 mV with an estimated power of 1 nW. The relatively low amount of energy that could be harvested in this way was producing a signal that was modulated by an interdigitated capacitor made out of electrochemically activated aluminum. The signal obtained in this way was rectified by a set of Schottky diodes and measured by a voltmeter. The sensor was capable of following a variety of different respiration patterns during normal breathing, exercise and rest, at the same time powered only by electromagnetic energy harvested from the human body. Everything happened in the normal environment used for everyday work and life, without any additional sources, and at a safe level of electromagnetic radiation.

Cellulose-based fibrous materials for self-powered wearable pressure sensor: a mini review

Cellulose-based fibrous materials for self-powered wearable pressure sensor: a mini review

Flexible Te/PEDOT:PSS thin films with high thermoelectric power factor and their application as flexible temperature sensors.

Flexible, lightweight, and low-cost thermoelectric thin films are promising for self-powered wearable electronics and sensors. In this work, we report on flexible Te nanostructures/PEDOT:PSS composite thin films with high power factor and their application as flexible temperature sensors. Te nanostructures with high crystallinity and high aspect ratios were synthesized through an environmentally friendly method without using highly toxic chemicals. Individual Te nanostructures achieve a thermoelectric figure of merit (ZT) of 0.13 at 300 K, indicating good potential as inorganic fillers for nanostructures/polymer hybrid materials. Based on the synthesized Te nanostructures, flexible p-type Te/PEDOT:PSS thin films were fabricated through a simple dilution and vacuum filtration method. The power factor of the as-prepared composite thin film outperforms that of either a Te or DMSO-treated PEDOT:PSS thin film, and importantly, it can be further enhanced to 149 μW m-1 K-2 by hot pressing, which is nearly threefold enhancement compared to the values reported for the vacuum-filtered flexible Te/PEDOT:PSS thin films in the literature. The hot-pressed composite thin film shows high flexibility with the electrical conductivity remaining almost unchanged after 1000 bending cycles under a bending radius of 5 mm. Flexible temperature sensors were fabricated based on the hot-pressed Te/PEDOT:PSS thin film, which exhibited high sensitivity in detecting temperature stimuli. The developed temperature sensors were applied onto a two-finger flexible mechanical claw for identifying hot/cold objects in robotic grasping. This work demonstrates an effective approach to enhance the thermoelectric power factor of flexible Te nanostructures/polymer composites and their promising application in flexible thermal sensing.

Recent Advances in Self-Powered Wearable Sensors Based on Piezoelectric and Triboelectric Nanogenerators.

Early clinical diagnosis and treatment of disease rely heavily on measuring the many various types of medical information that are scattered throughout the body. Continuous and accurate monitoring of the human body is required in order to identify abnormal medical signals and to locate the factors that contribute to their occurrence in a timely manner. In order to fulfill this requirement, a variety of battery-free and self-powered methods of information collecting have been developed. For the purpose of a health monitoring system, this paper presents smart wearable sensors that are based on triboelectric nanogenerators (TENG) and piezoelectric nanogenerators (PENG), as well as hybrid nanogenerators that combine piezoelectric and triboelectric nanogenerators (PTNG). Following the presentation of the PENG and TENG principles, a summary and discussion of the most current developments in self-powered medical information sensors with a variety of purposes, structural designs, and electric performances follows. Wearable sensors that generate their own electricity are crucial not only for the proper development of children and patients with unique conditions, but for the purpose of maintaining checks on the wellbeing of the elderly and those who have recently recovered from illness, and for administering any necessary medical care. This work sought to do two things at once: provide perspectives for health monitoring, and open up new avenues for the analysis of long-distance biological movement status.

Conductance-stable and integrated helical fiber electrodes toward stretchy energy storage and self-powered sensing utilization

Highly conductive and stretchable fibers are of great significance for wearable applications. Practical applications usually require high robustness and repeatability for these electronics under various mechanical deformations, which is a contradiction for most of existing strain-sensitive fibers conductors. In this work, core–shell hydrogel fiber with adjustable three-dimensional (3D) helical structure was fabricated, in which Ti3C2Tx (MXene)/poly(3,4-ethylenedioxythiophene) (PEDOT) were modified onto the surface of helical sodium alginate/polyacrylic acid (SA/PAA) hydrogel fibers via the combination of in situ polymerization and electrostatic assembly. The hybrid fiber possess a insensitive conductance (<5% resistance change) under various deformation, including stretching (0–800 %), bending (0-180°), pressuring and twisting, attributed to both the double tortuous conductive network and pre-strain release from helical structure. Moreover, conductance-stable helical fibers could be appropriately assembled into coaxial energy fibers and integrated into fabric, both acting as strain-insensitive energy storage device and self-powered wearable sensor.

Robust superhydrophobic wearable piezoelectric nanogenerators for self-powered body motion sensors

Self-powered wearable sensors have attracted extensive attention in tactile sensing, motion-detecting, and biomedical signal monitoring. The practical application of these devices, however, requires not only their high sensitivity, flexibility, and breathability, but also mechanical durability and long-term resistance to humidity, liquid, and bacteria. Herein, a robust superhydrophobic antibacterial self-powered piezoelectric nanogenerator (PENG) sensor is reported. The PENG sensor is comprised of flexible electrospun poly(vinylidene fluoride-co-trifluoroethylene) piezoelectric nanofiber membrane with spray-coated interdigitated carbon nanotube electrodes, which were subsequently encapsulated by a crosslinked conformal hydrophobic nanocoating wrapping around each individual fiber through initiated chemical vapor deposition (iCVD). The obtained sensor could accurately monitor various human behaviors such as breathing and different motions. The iCVD nanocoating provides excellent protection to the sensor, imparting self-cleaning, superhydrophobicity, and more than 90% anti-fouling rate against bacteria. As a result, the sensor shows reliable and durable sensing performance under harsh environments such as high humidity, chemical exposure, and mechanical impact. Finally, owing to its extraordinary long-term durability and stability, the PENG sensor was successfully integrated into shoe insoles to realize human gait monitoring.

PVDF/AgNP/MXene composites-based near-field electrospun fiber with enhanced piezoelectric performance for self-powered wearable sensors.

336MXenes, as highly electronegative and conductive two-dimensional nanomaterials, are extensively studied for their use in sensors and flexible electronics. In this study, near-field electrospinning was used to prepare a new poly(vinylidene difluoride) (PVDF)/Ag nanoparticle (AgNP)/MXene composite nanofiber film as a self-powered flexible human motion-sensing device. The composite film displayed highly piezoelectric properties with the presence of MXene. Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy revealed that the intercalated MXene in the composite nanofibers was evenly spread out, which not only prevented the aggregation of MXene but also enabled the composite materials to form self-reduced AgNPs. The prepared PVDF/AgNP/MXene fibers displayed exceptional stability and excellent output performance, enabling their use for energy harvesting and powering light-emitting diodes. The doping of MXene/AgNPs increased the electrical conductivity of the PVDF material, improved its piezoelectric properties, and enhanced the piezoelectric constant of PVDF piezoelectric fibers, thereby allowing the production of flexible, sustainable, wearable, and self-powered electrical devices.

Direct-current, long-lasting and highly efficient electret energy harvesting from ultra-low-frequency motions using toothed clutch mechanism

Generally, most wearable energy harvesters generate only a small amount of electrical energy from the low-frequency motions of human body and immediately stop working when the activity ends, resulting in low energy extraction efficiency. Here, we propose an electret rotatory energy harvester (e-REH) with a mechanical tooth-clutch transmission system, converting the ultra-low-frequency irregular human motion (< 0.1 Hz) into a high-speed and long-lasting rotation for boosted energy conversion efficiency. The tooth-clutch transmission system is designed with a compact integration of a linear-to-rotation unit, a tooth-clutch transmission unit and an energy storage unit to generate continuous, stable and highly efficient electrical output. Triggered by impulse excitation of gentle hand tapping, the flywheel can continuously rotate for about 45 s inertially, and the maximum speed of the flywheel can reach about 1500 rpm, indicating the frequency is increased up to 4500 times from 0.022 Hz to 100 Hz. In addition, by introducing the multi-layer phase-shift electrode design, a constant direct-current output with a crest factor down to 1.09 is obtained by the phase coupling effect, avoiding the complicated signal processing circuit. Experimental results show the fabricated e-REH can produce an overall coupling current of 22.1 μA and average output power of 3.95 mW. Thanks to the lightweight, compact and high-efficient transmission design, the e-REH is further integrated into a shoe for wearable energy harvesting and self-powered underground environmental monitoring applications. The research is of considerable significance to the practical applications of e-REH in powering sensors and building self-powered wearable sensor networks.