Among today’s bustling lifestyles, the demand for autonomous, durable, and low-maintenance healthcare systems has surged, surpassing that of earlier periods. Nanostructured and environmentally friendly materials employed in nanogenerator technology offer a novel avenue for biomedical applications by harnessing biomechanical energy. Triboelectric Nanogenerators (TENGs) have emerged as comprehensive solutions, furnishing self-sustaining, eco-conscious, and compact devices. Recognizing the immense potential of TENGs, this paper presents a comprehensive overview of its motion detection. Our analysis delves into the versatility of TENG-based motion detection systems, providing wearable, user-friendly solutions powered by human motion. Recent advancements in triboelectric devices are cataloged, elucidating their structural intricacies, capabilities, performance metrics, and future prospects. In addition, the article also outlines the applications of different TENGs in motion monitoring, including contact, non-contact, and single-electrode mode. The evolution of intelligent wearable technologies has extended our capacities in communication, healthcare, and various other domains beyond our biological limits. Apart from the Internet of Things, the concept of Internet of bodies or beings is poised for rapid advancement, promising further transformation of our lifestyles. Conclusively, we present insights into forthcoming opportunities and plausible strategies to address anticipated hurdles.

In personalized medicine, wearable health detection systems leverage sensors to interface with the body, capturing real-time physical and physiological signals. These signals are then wirelessly relayed to mobile apps and cloud platforms for processing. Through extensive big data analysis and artificial intelligence algorithms, the raw signals are transformed into actionable health insights,1 enabling motion monitoring, remote disease diagnosis, and treatment for users,2 as shown in Fig. 1.3–6 The cornerstone of motion monitoring lies in portable/wearable devices, which enable continuous data acquisition and instantaneous wireless transmission.7,8 The power requirements for numerous distributed sensors pose a challenge to the sustained and reliable operation of health detection devices,9 alongside comfort issues associated with wearability.10 The demand for energy supply is amplified by the continuous need for data acquisition, processing, and wireless transmission in motion monitoring systems.11–13 Historically, rigid batteries such as lithium-ion ones have served as the primary power source for most wearable electronics.14–16 Despite advancements in battery flexibility and size reduction,17–20 the need for frequent recharging and replacement hampers its broader adoption.21–25 

FIG. 1.

Big data for exercise and health monitoring.

FIG. 1.

Big data for exercise and health monitoring.

Close modal

Given the diverse contexts in which motion detection devices are deployed, harnessing the mechanical energy from human motion to power such systems emerges as a potentially optimal energy solution.26,27 The triboelectric nanogenerator technology, serving as a novel energy acquisition and information sensing technology, presents several advantages, including low cost, ease of production, high stability, and efficient conversion rates,28,29 thereby drawing considerable interest.30–33 Since its initial report in 2012,34 the triboelectric nanogenerator has garnered significant interest. Operating through the combination of contact electrification and electrostatic induction, this device demonstrates the capability to transform diverse mechanical energies into electrical power.35,36 Such mechanical energies encompass body movements, water waves,37 wind currents, and vibrations.38,39 Combining with the electromechanical conversion characteristics of Triboelectric Nanogenerators (TENGs), various forms of energy are collected, which provides a promising method for the further development of self-driven wearable electronic and health detection devices.40,41 In addition to being used for power supply,42,43 TENG is also widely used as an active sensor for the detection of physical indicators of human health, such as heart rate, pulse, and respiration44, due to its unique electromechanical conversion characteristics. Sensors that can sense human physical signals are essential for motion detection.45 Therefore, it is of great significance to construct self-driving devices for biochemical index detection and physical index detection based on TENG.

This research update presents a categorization of triboelectric-based motion detection into three main sections. First, in Sec. I, we provide an overview of triboelectric methods employed for safeguarding human health against external factors. Following this, Sec. II delves into the applications of TENG devices for sensing and monitoring purposes. Finally, we conclude our discussion by outlining future directions for the integration of TENG in motion detection.

TENGs are becoming the center of attention for wearable sensing systems,46 offering considerable potential in both sensing and energy generation through diverse mechanical stimuli associated with human motion.47,48 These devices are renowned for their simplicity, affordability, efficiency, wearability, and biocompatibility.49–51 Given their versatility, TENGs are poised to propel advancements in this field.

In 2012, Wang reported on the first TENG and explained its working mechanism as that when two materials with different friction polarities contact under external force or bending, the surfaces of the two materials will generate friction charges with different polarities; when the mechanical action is released or reapplied, in order to provide a continuous AC output, the separation or recontact of the surface with charge causes the two metallic back electrodes to have an opposing potential difference, which forces electrons to flow across the external load.

Maxwell’s displacement current is the essential conceptual basis of electricity generation. It differs from conduction current, which is formed from the rotation of free charges, as it originates from a changing electric field.52–54 Conduction current is induced by stationary charges of electricity on dielectric surfaces during the interaction electrification process. A time-varying displacement current, however, is produced when the electrical charge of these static charges is changed by the mechanical motion of charged surfaces. The movement of the current is linked to surface charge or electrostatic polarization (Ps), which is generated by mechanical motion, as opposed to medium polarization (P) caused by a field of electricity applied (E). Ps is mechanically driven, but P depends on the supplied electric field. Therefore, Wang added the polarization term Ps to the displacement vectors in order to calculate the electrical outputs of TENG and clarify its physical meaning. This allowed for the rewriting of Maxwell’s current of displacement (JD),55 
JD=Dt=εEt+Pst
where t is the time, ε is the value of the dielectric constant, and D is the electrical displacement vector. The external strain field or mechanical motion is the source of the phrase Pst.

The initial term in the formula, the induced current created by the oscillating electric field, establishes the theoretical basis for electromagnetic waves. The second, which is the source of the fundamental theory of nanogenerators, is the current that emerges from the polarization field produced by the surface’s electrostatic charge. The precise source of this current is the strain-induced piezoelectric polarization charge in the electromechanical nanogenerator. In TENG, this current comes from the surface polarization charge formed by the change of static charge with displacement after the friction electrification of two contact materials.

As an emerging category of energy conversion tools, TENGs primarily rely on the principle of “contact electrification”56 to induce electrostatic charges, thereby converting mechanical force into electrical energy.57 Over recent years, through ongoing research and development, TENGs have evolved from singular operational modes to combinations of various modes. Through a fundamental examination of working modes and structural analysis, four primary configurations have been identified:58,59 the vertical contact-separation mode,60–62 lateral sliding mode,63 single electrode mode,64 and freestanding triboelectric-layer mode.

Contact-separation mode: the fundamental TENG mode is the contact separation mode. Two materials with various friction electrode characteristics make up its construction. As shown in Fig. 2(a), the electrode is situated at the rear of the friction material. Under the influence of external pressure, two distinct materials come into touch with one another. The surfaces of the two materials hold equal quantities of positive and negative charges as a result of the friction electrification effect, which transfers surface charge and creates a potential difference. The two distinct triboelectric materials split with the removal of external pressure. In order to establish charge balance, electrons go via the external circuit from a high potential to a low potential because of the potential difference. Reapplying the external tension will cause the induced charge to return to the original electrode and cause a reverse current. Periodic AC output may be produced by TENG upon separating the repeating cycle contact.

FIG. 2.

Four TENG modes. (a) Vertical contact-separation mode. (b) Lateral sliding mode. (c) Single-electrode mode. (d) Free-standing triboelectric-layer mode.

FIG. 2.

Four TENG modes. (a) Vertical contact-separation mode. (b) Lateral sliding mode. (c) Single-electrode mode. (d) Free-standing triboelectric-layer mode.

Close modal

Later-sliding mode: as shown in Fig. 2(b), the structure of TENG in the horizontal sliding mode is identical to that of TENG in the vertical contact separation mode.

Single-electrode mode: the predecessors of TENG in single wire mode are TENG in contact separation mode and horizontal sliding mode. Its schematic is shown in Fig. 2(c). The opposite side of the polymer sheet is covered with a metal conducting electrode. When the conducting electrode is connected to an external load, it is instantly grounded to form a circuit. Due to the various friction polarity of the polymer sheet and the free-moving friction item, an equal amount of opposing friction charge is produced during contact.

Freestanding triboelectric-layer mode: two fixed electrodes and a friction layer that can move freely make up the TENG of the autonomous friction layer mode. Figure 2(d) shows the little space that exists between the two electrodes. In the air, two types of friction materials come into contact and get charged. One friction material serves as an independent friction layer, while the other serves as an induction layer by being fastened to the two electrodes. The electrons are propelled to travel, and the charge is altered. AC output is produced by the independent friction layer’s periodic movement and the electron’s periodic movement between the two electrodes.

TENGs can transform mechanical energy into electrical; mechanical input data may be retrieved by analyzing electrical signals. These autonomous sensors, which are based on TENGs, are employed in a variety of fields, such as biomedical monitoring, human–machine interface, and physiological signal sensing.

By successfully preventing physical contact between friction materials and reducing friction, the non-contact TENG (NC-TENG) ensures the steady and effective functioning.65 

In 2021,66 a new self-powered sandwiched non-contact triboelectric nanogenerator (NTENG) was introduced. The device is composed of a graphene/shear stiffening gel (SSG) electrode and a shear stiffening elastomer (SSE) shell. It functions through the principles of electrostatic induction and triboelectric phenomena. The intrinsic capacity of NTENG to produce its own electrical power allows it to precisely gauge the distance and speed of moving objects. Furthermore, the NTENG successfully mitigated 41.6% of the impact force. Furthermore, NTENGs possess the capacity to be converted into diverse configurations of 3D sensing devices. The NTENG, in its initial form, exhibited properties of elasticity, self-repair, and shape adaptability. Hence, it possesses the ability to be attached to uneven surfaces as a contactless sensor for observing the surrounding environment. In order to aid humans in navigating through darkness, a linear sensor array comprising three NTENG units was integrated and securely attached to a walking stick [Fig. 3(a)]. Three units possess the capacity to discern the orientations of left, forward, and right. The stick, powered by NTENG, emits electric impulses when it comes close to obstacles, giving users guidance. Similarly, the NC-TENG device made by Xi et al. could automatically detect the distance and speed of moving objects in addition to clearly and accurately indicating the cycle of movement (lifting leg), proceeding direction, running or strolling speed, and also the path,67 without requiring an additional amplification circuit,32 as shown in Fig. 3(b).

FIG. 3.

(a) Hand lever and elevator button have the ability to automatically gauge the velocity and distance of items in motion. Reproduced with permission from Yuan et al., Nano Energy 86, 106071 (2021). Copyright 2021 Wiley. (b) Self-powered human motion speed sensor. Reproduced with permission from Xi et al., Nano Energy 69, 104390 (2020). Copyright 2020 Elsevier. (c) The NC-TENG can be seen in the following schematic diagrams. Reproduced with permission from Cao et al., Small Methods 6(8), 2200588 (2022). Copyright 2022 Wiley. (d) The current generation is interrupted by the presence of a human crossing. Reproduced with permission from Anaya et al., Nano Energy 90, 106486 (2021). Copyright 2021 Elsevier.

FIG. 3.

(a) Hand lever and elevator button have the ability to automatically gauge the velocity and distance of items in motion. Reproduced with permission from Yuan et al., Nano Energy 86, 106071 (2021). Copyright 2021 Wiley. (b) Self-powered human motion speed sensor. Reproduced with permission from Xi et al., Nano Energy 69, 104390 (2020). Copyright 2020 Elsevier. (c) The NC-TENG can be seen in the following schematic diagrams. Reproduced with permission from Cao et al., Small Methods 6(8), 2200588 (2022). Copyright 2022 Wiley. (d) The current generation is interrupted by the presence of a human crossing. Reproduced with permission from Anaya et al., Nano Energy 90, 106486 (2021). Copyright 2021 Elsevier.

Close modal

Unfortunately, these two types of NC-TENG position recognition systems are not yet sophisticated enough to be employed in everyday life;68 they can only provide input on a specific location and behavior of surrounding objects in an experimental setting.69 

A self-powered non-contact motion vector sensor (NMVS) based on the NC-TENG with multi-channel signal collection was created by Cao et al.;65 it has the ability to detect motion in both direction and magnitude at the same time. A schematic representation of the signal acquisition process is shown in Fig. 3(c), where the polytetrafluoroethylene (PTFE) rod is the moving object. The linear motor controlled the motion parameter and supplied the driving power; the PTFE rod had a sensing distance of 5 mm and a motion velocity of 10 cm s−1. The figures display four different motion routes together with the corresponding output signals, showing that the beginning places of the four motion pathways of the PTFE rod are all located above electrode 2. The four different output signal groups are represented by the four ending locations.

Anaya et al.70 introduced a position monitoring platform that has the ability to differentiate intricate human movements without the need for wearable equipment, as shown in Fig. 3(d). The platform gathered electric charges by harnessing the triboelectric connection between boots and the floor to track the location, velocity, frequency, and motion of the human body in a two-dimensional plane. It has the ability to not only recognize various activities such as running, walking, or leaping, but also effectively achieve close-range remote monitoring of individuals at a distance of up to 1.5 m.

Although most of the friction losses can be avoided, the non-contact triboelectric nanogenerator also has its limitations. It is sensitive to environmental conditions, such as temperature, humidity, and other factors may affect its performance, its design and manufacturing costs may be high, and its maintenance is more complex. With the development of biomedicine, it can monitor the tiny movements of the human body, such as respiration and heartbeat, so as to realize health monitoring and medical diagnosis.

Zhang et al. introduced a triboelectric nanogenerator built on the contact-separation mode between an Al foil formed between clothes and a patterned polydimethylsiloxane (PDMS) screen in order to capture body motion energy in 2013. The maximal voltage and current density under normal walking conditions are 17 V and 0.02 µA/cm, respectively. However, additional development is unquestionably required for biological detection based on TENG.

Using on the contact-separation mode of the TENG, Huang et al. created a novel self-powered pressure sensor in 2021 for the detection of human joint motion and assessment of sports health.71 Positive and negative triboelectric materials were composed of bacterial cellulose (BC)/chitosan (CS)composites and PDMS/Cu films, respectively. It is interesting to note that the resulting electrical signal of BC/CS aerogels (BC/CSA)-based TENGs was less than that of BC/CS membrane (BC/CSM)-based TENGs. The output performance may be improved by a particular concentration of Cu NPs; 3 wt. % doped polyvinylidene fluoride (PVDF) films demonstrated the highest open-circuit voltages (VOC) and short-circuit currents (ISC), averaging around 23 V and 500 nA, correspondingly. The TENG showed outstanding mechanical strength and long-term durability. Furthermore, a sensitivity of 0.24 V kPa−1 was demonstrated by the triboelectric pair in an atmospheric pressure range of 10.5–96.25 kPa. The output voltage is shown in Fig. 4(a) after the triboelectric materials have been attached to the shoe bottoms to track leaping motion at various rope-skipping speeds. In order to measure the movement of several joints during sports, triboelectric materials were developed and attached to different body areas as self-powered pressure sensors.72 

FIG. 4.

(a) Equivalent output current obtained during exercise by using TENGs on various body areas. Reproduced with permission from Huang et al., Composites, Part A 146, 106412 (2021). Copyright 2021 Elsevier. (b) The simulation results of the CS-TENG obtained using COMSOL are presented. (c) A graph illustrating the simulated surface potential of CS-TENG at different distances between TENG layers. Reproduced with permission from Bhatta et al., Nano Energy 103, 107860 (2022). Copyright 2022 Elsevier. (d) Finger motion detection device. Waveforms in different walking states: (e) jumping and (f) jogging. Reproduced with permission from Xu et al., Nano Energy 102, 107719 (2022). Copyright 2022 Elsevier.

FIG. 4.

(a) Equivalent output current obtained during exercise by using TENGs on various body areas. Reproduced with permission from Huang et al., Composites, Part A 146, 106412 (2021). Copyright 2021 Elsevier. (b) The simulation results of the CS-TENG obtained using COMSOL are presented. (c) A graph illustrating the simulated surface potential of CS-TENG at different distances between TENG layers. Reproduced with permission from Bhatta et al., Nano Energy 103, 107860 (2022). Copyright 2022 Elsevier. (d) Finger motion detection device. Waveforms in different walking states: (e) jumping and (f) jogging. Reproduced with permission from Xu et al., Nano Energy 102, 107719 (2022). Copyright 2022 Elsevier.

Close modal

Bhatta et al. used dual-mode TENGs and electromagnetic generators (EMG) to develop a self-sustaining wireless device for sensing random motion.73 In addition, they incorporated a magnetic repulsion mechanism to enhance the autonomous movement of the sliding TENG (S-TENG) and contact-separation mode TENG. The self-driving system on CS-TENG utilizes a double-layer flexible film made of PDMS FeSiCr/PDMS. In Figs. 4(b) and 4(c), this film functions as both the active TENG layer and the actuating layer, streamlining the total process. The autonomous CS-TENG system provides accurate identification of the direction of motion. The dual-mode TENG possesses the capability to accurately quantify the random motion characteristics and orientation in scenarios involving linearity, rotation, and tilt. In addition, the self-powered motion sensor exhibits remarkable sensitivity in terms of acceleration (1.966 m/s2), frequency (14.099 Hz), and tilt angle (0.257°).

Xu et al. have introduced a TENG that operates in conjunction with the vertical contact-separation mode TENG (CS-TENG) and the lateral-sliding mode TENG (LS-TENG). The open circuit voltage of the hybrid mode triboelectric nanogenerator is determined by CS-TENG. The peak-to-peak open circuit voltage of the hybrid TENG can reach 1169 V. The CS-TENG has an estimated unidirectional short-circuit current of 80 μA. The self-powered human motion sensors, based on CS-TENG technology, were created to detect signals associated with finger bending, locomotion, and somatic joint bending. A finger motion detection device was constructed using CS-TENG, as shown in Fig. 4(d). During the experiment, the finger was inserted inside the ring, and the main body of the sensor was attached to the hand. Figure 4(e) shows the signals recorded while the index finger was bent at angles of 20°, 45°, 60°, and 90°. As the curvature of the object increases, the voltage undergoes a significant increase. This is directly linked to the amount of pressure applied by the finger on the sensor. The compressive force increases in direct proportion to the extent of finger bending, hence enhancing the electrical potential produced by the self-powered sensor. Figure 4(f) shows the configuration of a stepping detecting device that employs a contact-separation triboelectric nanogenerator. Figure 4(e) shows the three-dimensional simulation diagram of it. The photograph offers a distinct perspective on the internal construction of the self-powered stepping detecting mechanism situated at the rear of the insole. With its maximum output power of 14.02 mW, it can easily light 50 high-brightness LEDs.74 

The contact separation triboelectric nanogenerator has its unique advantages and application prospects in motion detection. It uses the friction in the process of contact and separation to generate energy and can achieve relatively high energy conversion efficiency. Because of its simple working principle, the contact separation triboelectric nanogenerator can be applied to a variety of materials, including hard materials, soft materials and even biological tissue surfaces; however, there are also some limitations, such as sensitivity to contact pressure and vulnerability to damage, so the specific application requirements and environmental conditions should be considered when selecting.

Human sweat contains a myriad of biomarkers that may be used to diagnose life-threatening illnesses, including diabetes, cancer, and cystic fibrosis. These biomarkers are regulated by a variety of physiological parameters.75–77 Song et al. has created a TENG-based portable sweat sensor that runs only on human motion. This innovative system, called the freestanding-mode TENG (FTENG)-powered wearable sweat sensor system (FWS3), is made up of components designed for certain tasks, such a sweat sensor patch and a flexible FTENG sensor that is connected to circuitry. The FTENG is powered by a combination of inside the plane sliding-induced transfer of charge and contact electrification. PTFE is tribo-negative, meaning that during the sliding process, electrons collect on its surface as opposed to copper. This one-way sliding generates a current between each of the stator electrodes until the mesh slider covers the additional stator electrode entirely. The FTENG stator, which serves for walking energy harvesting and quick storage in a capacitor, is integrated with a low-dropout voltage regulator, instrumentation amplifiers, a power management integrated circuit (PMIC), and a Bluetooth low energy (BLE) setup system on a chip (PSoC) module for evaluation purchase, oversight, amplifiers, and transmission to a smartphone via Bluetooth. This wearable, cordless sensor system relies on TENG technology, has a minimum charging period of 416 W m−2, and an ultimate power draw of 0.94 mW. This system is utilized to measure the pH and Na+ ion levels in sweat at a frequency of 1.5 Hz. The method has a lot of potential for independent, personalized health monitoring.

A self-powered triboelectric band that collects gait data using electric signal data to identify humans was developed in 2019.78 

Using the upper arm band as an example, the triboelectric effect causes the rubber to be charged negatively and the skin to receive a positive charge when they come into contact. Compared to rubber, the skin has a lower affinity for electrons. An electric potential difference forms among the ground (the human being’s body or others conductive items) and the band’s electrodes (physiological saline) in an open-circuit scenario as a result of the electrical effect of the biceps muscles contracting and relaxing increasing and decreasing the contact area among the rubber and the arm skin, as shown in Fig. 5(a). The short-circuit current density of the band occurs at 89.4 V, 7.1 µC/m2, and 0.62 mA/m2, respectively. The band’s power density allows it to stably power an electronic watch. Even with a tensile tension of up to 300%, the band may still play well. The band is soft, flexible, and reasonably priced. It is composed of a rubber tube that has been filled with physiological saline. It might be attached to the body to monitor various human motions. It may also be used to deduce quantitative motion details, such step and velocity, from the motion signal it generates as shown in Fig. 5(b). In addition, with an equal error rate (ERR) of 15.9%, the band can identify and authenticate human identification in real time when linked with a certain algorithm, thanks to the identified unique gait pattern of each individual. This study creates new opportunities for human–machine interface and self-powered motion sensors.

FIG. 5.

(a) Schematic depiction of the system in action. (b) The typical TENG band structure. Reproduced with permission from Han et al., Nano Energy 56, 516–523 (2019). Copyright 2019 Elsevier. Electrical output characteristics of LS-TENG. (c) open circuit voltage. (d) Short circuit current. Reproduced with permission from Xu et al., Nano Energy 102, 107719 (2022). Copyright 2022 Elsevier.

FIG. 5.

(a) Schematic depiction of the system in action. (b) The typical TENG band structure. Reproduced with permission from Han et al., Nano Energy 56, 516–523 (2019). Copyright 2019 Elsevier. Electrical output characteristics of LS-TENG. (c) open circuit voltage. (d) Short circuit current. Reproduced with permission from Xu et al., Nano Energy 102, 107719 (2022). Copyright 2022 Elsevier.

Close modal

CS-TENG and LS-TENG are merged and function together in a coordinated manner as described in Ref. 74. Xiu et al. conducted a rudimentary assessment to gauge the efficiency of LS-TENG’s output after determining the optimal triboelectric layer. Figure 5(c) shows the magnitude of the voltage produced by the LS-TENG when there is no external load connected. The open circuit voltage of the LS-TENG remains consistently steady at around 212 V for the whole 625 s testing duration. The inset illustrates that the output voltage exhibits a nearly sinusoidal waveform. Figure 5(d) shows the magnitude of the short circuit current of the LS-TENG, which is ∼74 µA. LS-TENG is mostly employed to enhance the electric current.

The horizontal sliding triboelectric nanogenerator has its unique advantages and application prospects in motion detection. The horizontal sliding process is relatively stable and can provide continuous and stable energy output, which is conducive to real-time monitoring and long-term operation; The sliding process can be controlled by adjusting the surface roughness and material selection so that the performance of the horizontal sliding friction nanogenerator can be optimized according to the demand. However, its limitation is that it is limited by the specific motion mode and surface requirements and needs to be optimized according to the specific application requirements.

In single-electrode mode, the benefit is that one sole electrode is grounded. By removing the electrical energy needed for various biomechanical movements, TENG has significantly expanded its applications in the areas of pressure sensors, movements trackers, position/trajectory detectors, health devices, automated machinery, catastrophe consciousness machinery, and intelligent identification systems.79 

Fang et al. have developed a triboelectric sensor (TES) that functions with a single electrode and can accurately detect the motion of a moving item or body in two dimensions without requiring additional power.80 The motion of an object on the upper surface of a polytetrafluoroethylene (PTFE) layer results in alterations in the electrical potential of the pattern aluminum electrodes beneath, as a result of the combination of the triboelectric effect with the action of electrostatic induction. The motion characteristics of the item, such as its path, speed, and rate of change of speed [Fig. 6(a)], are determined by analyzing the output performance data, specifically the voltage in the open-circuit and short-circuit current, using the predefined settings. In addition, the TES has the capacity to simultaneously detect the motion of many objects. Moreover, the practical applications of the TES can be demonstrated by utilizing LED illuminations as immediate visual cues to indicate the movement of a rolling object and the footfall of an individual.

FIG. 6.

(a) Recorded the short-circuit current when an aluminum ball moves along a specific route. Reproduced with permission from Yi et al., Adv. Funct. Mater. 24(47), 7488–7494 (2014). Copyright 2014 Wiley. (b) Principles of operation and optimization of electrical output in yarn-based triboelectric nanogenerators. Reproduced with permission from Bai et al., Nano Energy 94, 106956 (2022). Copyright 2022 Elsevier. (c) After 300 repeated stretches and releases and the output voltage, current, and instantaneous output power density as a function of load resistance at a contact separation frequency of 2 Hz and a vertical force of 18 N. Reproduced with permission from Cao et al., Nano Energy 92, 106689 (2022). Copyright 2022 Elsevier.

FIG. 6.

(a) Recorded the short-circuit current when an aluminum ball moves along a specific route. Reproduced with permission from Yi et al., Adv. Funct. Mater. 24(47), 7488–7494 (2014). Copyright 2014 Wiley. (b) Principles of operation and optimization of electrical output in yarn-based triboelectric nanogenerators. Reproduced with permission from Bai et al., Nano Energy 94, 106956 (2022). Copyright 2022 Elsevier. (c) After 300 repeated stretches and releases and the output voltage, current, and instantaneous output power density as a function of load resistance at a contact separation frequency of 2 Hz and a vertical force of 18 N. Reproduced with permission from Cao et al., Nano Energy 92, 106689 (2022). Copyright 2022 Elsevier.

Close modal

Bai et al. achieved a high voltage of 137 V and a power density of 2.25 MW/m using an optimized yarn TENG in single electrode mode shown in Fig. 6(b).81 They achieved this by adjusting the alliin content and managing the thickness of friction composites. This performance surpasses that of previously reported fiber shape TENGs. The gadget must demonstrate excellent electrical output stability and durability when subjected to repetitive dynamic deformation or long-term use. The yarn may be seamlessly included into the elastic fabric to harvest motion energy and can also function as a pressure/strain sensor to provide comprehensive detection of physiological signals throughout the entire body. This allows for perception of human–computer interaction in the virtual reality environment.

In 2022,82 scientists achieved the creation of a self-sustaining pressure and strain sensor by utilizing a crumpled MXene film within a SE-TENG. The MXene TENG demonstrated the highest areal stress of 2150% and a linear tensile ratio of 400% because to its flexible crumpled structure. In Fig. 6(c), the MXene TENG with micro-crumples exhibited a substantial 36-fold enhancement in output power density as a result of the enlarged contact area within the triboelectric layers. Therefore, the developed sensor exhibited a remarkable sensitivity of 2.35 V kPa−1 when exposed to pressures that ranged from 0.3 to 1.0 kPa. This sensitivity exceeds that of the majority of sensors that are dependent on tribo-/piezo-electrical mechanisms. Moreover, the sensor could be easily attached to human joints in order to capture and collect complex movement signals.

Xie et al. introduce a spongy triboelectric sensor (SSTS) composed mainly of a spongy composite film of multi-walled carbon nanotubes (MWCNT) and polydimethylsiloxane (PDMS),83 along with a conductive fabric. The sensor may simultaneously produce contact electrification and electrostatic induction coupling by utilizing a single-electrode contact-separation mode. The SSTS employs the triboelectric effect, properties of doping material, and a porous structure with a spongy texture, where soft sugar serves as a sacrificial template. The solid-state temperature sensor (SSTS) with a composition of 10% weight of multi-walled carbon nanotubes (MWCNT) and porosity of 64% exhibits remarkable sensitivity, a wide measurement range, and excellent linearity. The device has two sensitivity zones (slopes): 1.324 V/kPa for pressures ranging from 1.5 to 28 kPa in the low-pressure range and 0.096 V/kPa for pressures ranging from 28 to 316.5 kPa in the high-pressure range. The linearities for these zones are 0.980 and 0.979, respectively. Furthermore, the SSTS offers a higher degree of effectiveness and reliability, hence enhancing the tracking of changes in hand pressure, human movement, personalized spatial perception, and other detection tasks.

Yu et al. created a new TENG that uses cotton fabric as a flexible and stretchable single electrode.84 This TENG is specifically engineered to gather mechanical energy and autonomously identify human motion behavior through self-powered sensing. The flexible electrode of the TENG is composed of a composite fabric of 95% cotton and 5% spandex. This fabric is both breathable and contains ammonia. The fabric undergoes in situ polymerization using polypyrrole and is subsequently coated with silver nanowires. Afterward, a coating of PTFE is placed over the surface as a substance that minimizes friction. When the TENG is prepared, it can reliably sustain an output voltage of around 0.3 V when a force of 4 N is applied to it at a frequency of 2.5 Hz. The generated TENG demonstrates an air permeability of 1329.134 mm/s, a moisture permeability of 399.7 g/m2·24 h, and a cycle stability over 4000 times. This feature renders it appropriate for utilization as a portable and environmentally friendly energy supply for electronic gadgets.

To sum up, the single-electrode mode TENG has its unique advantages and application prospects in motion detection, especially in scenes requiring high sensitivity and simple integration. However, compared to other nanogenerators, their output power may be low, and they are vulnerable to electrostatic discharge and environmental factors, so the selection needs to be considered according to the specific application requirements.

Flexible and wearable sensors are an inevitable future trend in human–machine interface (HMI) systems, as shown in Fig. 7. These devices allow for the real-time collection of human physiological or environmental signals by using HMI systems. The combination of self-powered TENG sensors with artificial intelligence (AI) techniques has the potential to significantly advance intelligent life.85,86 Zhou et al. constructed the inaugural sensor array that utilizes machine learning to facilitate sign-to-speech translation. Hand motions can generate electrical impulses by attaching fiber-shaped sensors based on TENGs to each finger. In order to enhance the precision of translation, a machine-learning system is employed to identify the voltage signals. Ultimately, these gestures can be translated into verbal expressions and shown on mobile devices, enabling more efficient communication between sign language users and non-users. A triboelectric smart glove has been developed for the purpose of VR communication and detecting sign language. In this case, sensors based on Triboelectric Nanogenerator technology are positioned strategically on each joint of the hand to detect the flexing or extending of fingers. These sensors generate distinct electrical signals that correspond to different phrases. By wearing this glove, users can interact with virtual actors in virtual reality environments effectively. TENG-based sensors have the capability to do lip reading and hand-gesture sign language.87 Lip reading is particularly beneficial for individuals experiencing difficulties with their vocal cords, larynx, or tongue, as it enables them to communicate nonverbally without manual gestures. Nevertheless, individuals lacking formal training may encounter challenges while attempting to decipher lip language. The development of lip-language decoding technology using triboelectric sensors was a direct reaction to this issue. The aforementioned sensors detect lip movements when they are included into a mask, and a dilated recurrent neural network model, trained on more than 20 classes with 100 samples in each class, achieves an impressive test accuracy of 94.5%.

FIG. 7.

TENGs that can be worn for human–machine communication.8,90 Reproduced with permission from Wang et al., InfoMat 4(2), e12262 (2022). Copyright 2022 Wiley.

FIG. 7.

TENGs that can be worn for human–machine communication.8,90 Reproduced with permission from Wang et al., InfoMat 4(2), e12262 (2022). Copyright 2022 Wiley.

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The advent of 5G technology marks the commencement of the Internet of Things (IoT) era, enabling the use of TENGs as a feasible choice for IoT infrastructure sensors. Pu et al. introduced a sensor that is activated by eye movements and can sustain itself. This sensor is designed for communication systems that rely on the sense of touch.88 This sensor utilizes a contact-separation construction that incorporates latex and fluorinated ethylene propylene (FEP) as triboelectrification layers. The eyewear contains a built-in sensor that recognizes the wearer’s eye blinks. This sensor allows for the contact between natural latex and FEP, resulting in the generation of voltage signals with a maximum amplitude of 750 mV. The sensor’s connection with a microprogrammed control unit allows it to regulate a range of devices, such as electric fans, table lights, and bells. Grippers are necessary for performing tasks, such as assembling, sorting, and transportation, in industrial settings. The development of flexible and responsive grippers is highly significant. Soft grippers have been equipped with triboelectric nanogenerator sensors. A sliding triboelectric nanogenerator is capable of detecting sliding speed, contact location, and gripping mode, while a rotating TENG is capable of detecting joint angles. The soft gripper uses machine learning technology to identify objects and assess their suitability for gripping. These grippers exhibit potential for digital twin applications in virtual reality environments, facilitating intelligent forecasting of industrial scenarios and management of production. Pu et al.89 developed a triboelectric quantization sensor for gesture-controlled robot arms. While the slider moves unidirectionally, this TENG generates impulses that can be either positive or negative. For example, applying voltage pulses to the fingers can indicate the bending and straightening of the finger. In addition, pulse counting allows for precise manipulation of robot arms by accurately identifying the angular position of the finger, with an accuracy as low as 3.8°.

Plenty of important factors need to be taken into account while producing wearable TENGs for HMI.90 First and foremost, it is critical to guarantee that TENGs are sufficiently flexible and stretchable in order to facilitate joint motion detection and account for notable body deformations. Second, for HMIs to function effectively—especially when handling minute movements—a good signal-to-noise ratio in TENGs is necessary. Third, in order to protect TENGs from external impacts, appropriate encapsulation must be implemented.

In this paper, we give a thorough summary of the advancements in TENG monitoring, emphasizing applications in motion detection and materials physics. A health monitoring system is embedded in the insole to monitor gait, evaluate walking mode and posture, or integrated into a chest strap or bracelet to monitor heart rate changes through the movement of the chest or wrist. It can also detect respiratory rate and mode through the movement of the chest or abdomen. A sports tracking system is embedded in sports clothes or equipment to monitor sports intensity and frequency in real time. It is also integrated into wearable devices to detect and record various motion gestures, such as running and jumping. A rehabilitation training system is embedded in rehabilitation training equipment to provide real-time feedback on patient’s movements and exercise quality, assisting in rehabilitation training. Through continuous monitoring of patient’s exercise data, the progress and effectiveness of rehabilitation can be evaluated.

Even while TENG technology has advanced significantly in terms of materials, device designs, and smaller power management circuits, there are still a lot of challenges to be solved, particularly with regard to applications in health monitoring. In order to go closer to an autonomous motion detecting system, several barriers must be removed. It is imperative to tackle the critical challenges of optimizing device design, size, and material manufacture in order to ensure in vivo applications are flexible, affordable, and sustainable. TENGs also have significant potential for use as tissue stimulators, cardiac pacemakers, physiological sensors, and other implanted medical devices (IMDs) for the monitoring and treatment of internal organs. However, there are still many challenges to be solved, such as problems with the device’s performance, power supply, and material compatibility. Among the potential solutions are wireless, non-intrusive external power sources, electrical performance-enhancing film surfaces, and biodegradable polymers that are safe for biological use. Further advancements in the marketing of self-powered devices based on TENG technology are necessary. Further research must concentrate on both the optimization of TENG devices and their seamless integration with emerging technologies, such as disposable and bio-implantable materials. To shield the gadget from the harsh in vivo environment, a sturdy, long-lasting encapsulating covering must be developed. Moreover, developing very efficient, portable, and reasonably priced wireless signal transmission techniques will be crucial. Before TENG-based healthcare and biological devices are manufactured and marketed, extensive animal testing and thorough study are necessary to fine-tune them for modern detecting applications.

Triboelectric nanogenerator technology is expected to become increasingly common in self-driven medical diagnostic and motion detection devices in the future due to its ongoing advancements and expanding application scenarios. For example, the combination of artificial intelligence and big data analysis technology can realize the personalized monitoring and diagnosis of individual health status and provide more reliable data support for motion detection.

In general, the application prospect of triboelectric nanogenerator in self-driven medical diagnosis and motion detection device is broad, which is expected to bring revolutionary changes in the field of medical diagnosis, treatment, and health management as well as improve people’s quality of life and health level.

The evolution of intelligent wearable technologies has extended our capacities in communication, healthcare, and various other domains beyond our biological limits. Apart from the Internet of Things (IoT), the concept of the Internet of bodies or beings is poised for rapid advancement, promising further transformation of our lifestyles. For realizing these advancements, energy provisioning and information gathering are essential. Given the potential utility of TENGs, their significant role in driving these technological developments is anticipated, necessitating increased efforts to propel their advancement.

This work was supported by the Shandong Provincial Natural Science Foundation Youth Project (Grant No. ZR2021QH325).

The authors have no conflicts to disclose.

Hongyuan Jiang: Conceptualization (equal); Investigation (equal); Methodology (equal); Writing – original draft (equal). Xin Lv: Conceptualization (equal); Investigation (equal); Writing – original draft (equal). Kai Wang: Conceptualization (equal); Investigation (equal); Methodology (equal); Project administration (equal); Supervision (equal); Writing – original draft (equal); Writing – review & editing (equal).

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

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