Reprint of: Triboelectric nanogenerator-based wearable electronic devices and systems: Toward informatization and intelligence☆
Graphical abstract
Introduction
With the rapid development of an informational and intelligent society, wearable electronic devices and smart microsystems perform an increasingly important role in military and civilian applications. In military scenarios, wearable sensor devices can achieve real-time physical status monitoring of soldiers [1], [2], [3]; wearable detectors can help soldiers perceive battlefield situations and dangerous factors in the battlefield environment [4], [5]. Moreover, wearable communication microsystems can achieve the interconnection of information between individual soldiers [6], [7] and enable commanders to formulate the deployment of resources across the entire battlefield. In office and home scenarios, wearable sensors can achieve long-term monitoring of important health indicators, such as blood pressure [8], [9], [10], [11] and blood sugar [12], [13], [14], for people with health problems; moreover, wearable signal generators can help people with disabilities utilize human-machine interaction conveniently [15], [16], [17], [18]. Wearable biometric information recognition systems [19], [20], [21] can effectively identify the users and authenticate permissions.
The normal operation of the above-mentioned wearable electronics is based on the availability of a reliable power source. However, the power supply based on batteries and other energy storage devices is restricted by the battery life and other problems, which causes several inconveniences [22], [23]. In military applications, such as in the wilderness or battlefield, it is difficult and sometimes impossible to replace batteries on time, which has become a bottleneck that restricts the continuous long-time combat activity of individual soldiers. In office and home applications, battery replacement causes a waste of resources and environmental problems for the long-term daily use of wearable devices, and the inconvenience also becomes an important factor restricting its practical commercial promotion. Therefore, the limitation pertaining to self-powering of wearable electronics must be solved urgently.
Currently, the mainstream technology focusing on the self-powering issues of wearable electronics is the harvesting of mechanical energy based on triboelectricity [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], piezoelectricity [35], [36], [37], and other effects, which can achieve long-term independent operation of wearable electronic devices and their integrated microsystems. Among these, the triboelectricity-based technology, which uses the charge transfer between materials with different electronegativities to achieve the generation of electrical signals and the collection of energy, has become the most important field because of its advantages of low cost [38], [39], biocompatibility [40], [41], [42], [43], improvement of human comfort [44], and fitness for energy harvesting of low-frequency movements such as human movement [45], [46], [47], [48].
Self-powered wearable electronic devices based on triboelectric nanogenerators (TENGs) have been extensively studied in recent years, and a series of practical devices have been systematically developed, which has strongly promoted the development of wearable electronics and is worthy of review and further development prospects [49], [50], [51], [52], [53], [54], [55], [56], [57], [58]. In this review, first, various functions implemented by TENG-based self-powered wearable electronic devices are summarized, such as human body perception and human-machine interaction, personnel recognition, as well as generation and recognition of coded information. To achieve the above functions, the devices have been delicately optimized for specific application scenarios, including selection and optimization of flexible materials, structural design and optimization, and synergistic information acquisition using multiple sensors. Next, the signal processing methods of wearable electronic devices are summarized, including basic qualitative waveform features and quantization thresholds, anti-interference processing and joint processing of multiple signals, and implementation of complex functions based on artificial intelligence. Finally, for achieving a “fully self-powered wearable microsystem”, three urgently required technologies are discussed, i.e., wireless communication without external power supply, power management (PM) modules, and self-powered logic devices. Their integration with various existing TENG-based devices is also analyzed and discussed.
Section snippets
Wearable electronic devices: smart sensing, recognition, and informatization
TENG-based wearable electronics have flourished in recent years and have become the basic devices for intelligent sensing, identification, and informatization. In this section, the various functions that these devices can achieve and the convenience they bring are summarized. TENG-based wearable electronic devices can sense human body movements and status, such as gait, breathing, pulse, and gestures, which are further utilized to achieve complex functions such as health monitoring and
Design and optimization of the devices: material, structure, and multisensors
To better achieve the functions of human perception and human-machine interaction, personnel identification, as well as coded information generation and its recognition, the TENG-based electronic devices are optimally designed in terms of material system, sensitive structure, and multisensor synergy. In terms of the material system, the electrode materials, friction-layer materials, and their processing technologies are optimized, forming a flexible device, enhancing the sensitivity, and
Signal processing for TENG-based wearable electronics: from threshold judgment to neural network
The implementation of the various functions of TENG-based electronic devices relies on the processing of acquired signals. In this section, the signal processing methods used for these devices are summarized from simple to complex methods. In the simplest case, the signal processing of TENG-based electronic devices is based on the observation of waveforms with identifiable features, such as the presence or absence of signals, strength, peak, and pulse width; further, quantitative judgments and
Future work: fully self-powered wearable microsystems
Till now, wearable TENG devices have been elaborately studied, achieving a wealth of functions in various scenarios, and the structure, material, and signal processing algorithms have been specially designed and optimized. To achieve a fully self-powered wearable microsystem, research in the following three fields still needs to be promoted.
First, the signal transmission of most devices still requires a wired connection or battery-powered wireless transmission. In terms of wireless
Conclusion
This paper reviewed the development of TENG-based wearable electronic devices in recent years and provided an exhaustive and in-depth summary of their functions, optimized design, and signal processing methods. TENG-based wearable electronic devices have achieved rich functions such as human body perception and human-machine interaction, personnel identification, as well as generation and recognition of coded information, which significantly facilitate individual combat in the military and
CRediT authorship contribution statement
Qingyu Li: Conceptualization, Investigation, Writing – original draft, Writing – review & editing. Keren Dai: Conceptualization, Investigation, Writing – original draft, Writing – review & editing. Wenling Zhang: Conceptualization, Writing – review & editing. Xiaofeng Wang: Supervision, Writing – review & editing. Zheng You: Supervision. He Zhang: Supervision.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Qingyu Li received the B.E. and ph.D. degrees from the Department of Electronics Engineering, Tsinghua University, Beijing, China, in 2014 and 2019 respectively. She is now an engineer at the North Information Control Research Academy Group Company, Ltd., Nanjing, China. Her research interests include communication systems, IoT nodes and networks, information theory and signal processing.
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Cited by (1)
Qingyu Li received the B.E. and ph.D. degrees from the Department of Electronics Engineering, Tsinghua University, Beijing, China, in 2014 and 2019 respectively. She is now an engineer at the North Information Control Research Academy Group Company, Ltd., Nanjing, China. Her research interests include communication systems, IoT nodes and networks, information theory and signal processing.
Keren Dai received the B.E. and Ph.D. degrees from the Department of Precision Instrument, Tsinghua University, Beijing, China, in 2014 and 2018, respectively. He is currently an Assistant Professor with the School of Mechanical Engineering, Nanjing University of Science and Technology. His research interests include triboelectric nanogenerators, power management systems, micro power devices and signal processing.
Wenling Zhang received her Ph.D degree from Inha University, Korea in 2015 and joined University of Alberta, Canada as a postdoc (2018–2019). She is currently a professor at the School of Mechanical Engineering, Nanjing University of Science and Technology. Her research interests focus on Interfacial Science, Nanotribology (adhesion, friction and lubrication) and Soft Matters.
Xiaofeng Wang received the B.S. degree from Qingdao Science and Technology University and the master's and Ph.D. degrees from the University of Science and Technology Beijing. He is currently a Professor with the Department of Precision Instrument, Tsinghua University. His research interests include supercapacitor, energy harvesting, and self-power sensor.
Zheng You received the B.S., master's, and Ph.D. degrees from the Huazhong University of Science and Technology University. He is currently an Academician with the China Engineering Academy and also a Professor with the Department of Precision Instrument, Tsinghua University. His research interests include MEMS and sensors.
He Zhang was born in Henan, China. He received the Ph.D. degree in measurement technology and instruments from the Nanjing University of Aeronautics and Astronautics, Nanjing, China. He is currently a Professor with the School of Mechanical Engineering, Nanjing University of Science and Technology (NJUST), Nanjing. He is the Director of the Institute of Mechanical and Electrical Engineering, NJUST, where he is also the Associate Director of the ZNDY of Ministerial Key Laboratory. His research interests include mechatronics and IoT systems. He is on the Editorial Board of the journal of Detection and Control.
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This work was supported in part by the National Natural Science Foundation of China (Grant No. 52007084), and in part by the Natural Science Foundation of Jiangsu Province (Grants No. BK20190470).