Reprint of: Triboelectric nanogenerator-based wearable electronic devices and systems: Toward informatization and intelligence

Highlights

• Applications and optimal design of TENG-based wearable devices are summarized.

• Signal processing methods are investigated for information mining of output signals.

• Challenges and routes on “fully self-powered wearable microsystem” are discussed.

Abstract

Nowadays, wearable electronic devices with rich functions have significantly facilitated individual combat in the military and daily lives of people. To achieve implanting and sustainable wearable electronic systems, it is necessary to develop self-powered sensors utilizing environmental energy harvesting with superior mechanical stretchability and flexibility. Triboelectric nanogenerators (TENGs) can capture the low-frequency mechanical energy in human motion and convert it into electricity, which is expected to be a potential solution for this urgent need. In this review, based on advanced applications, the rich functions of TENG-based wearable devices are thoroughly discussed, including human body perception and human-machine interaction, personnel identification, as well as generation and recognition of coded information. Then, we elaborate on three crucial strategies for achieving an optimal design of TENG-based wearable devices, including selection and optimization of flexible materials, structural design and optimization, and synergistic information acquisition using multiple sensors. The representative signal processing methods are investigated to exploit the potential information behind the output signals, 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. The review concludes with an overview of the remaining key challenges and potential technologies that can achieve the ultimate goal of a “fully self-powered wearable microsystem”.

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.