ISSN 2311-6706 e-ISSN 2150-5551 CN 31-2103/TB ARTICLE https://doi.org/10.1007/s40820-021-00621-7 Fully Fabric‑Based Triboelectric Nanogenerators as Self‑Powered Human–Machine Interactive Cite as Nano-Micro Lett. Keyboards (2021) 13:103 1,2 2,3 2 2,3 2,3 2,3 Received: 3 December 2020 Jia Yi , Kai Dong , Shen Shen , Yang Jiang , Xiao Peng , Cuiying Ye , * Accepted: 9 February 2021 Zhong Lin Wang2,3,4 © The Author(s) 2021 HIGHLIGHTS • A fully fabric-based mechanical energy harvester with a sandwich structure is developed, which can respond to the pressure change by the fall of leaves. • A self-powered keyboard with the ability of biometric recognition is demonstrated, which is able to resist illegal intrusion by judging the keystroke behaviors. ABSTRACT Combination fexible and stretchable textiles with self-powered sensors bring a novel insight into wearable functional electronics and cyber security in the era of Internet of Things. This work presents a highly fexible and self-pow- ered fully fabric-based triboelectric nanogenerator (F-TENG) PTFE-dacron with sandwiched structure for biomechanical energy harvest- CNT-cotton Ag electrode ing and real-time biometric authentication. The prepared F-TENG can power a digital watch by low-frequency motion signal analysis and respond to the pressure change by the fall of leaves. A self-powered wearable keyboard (SPWK) is also fabricated by integrating large-area F-TENG sensor arrays, which not only PRINT PASSWORD TENG Login Interface PRINT PASSWORD TENG Login Interface Password: can trace and record electrophysiological signals, but also can welcome TENG Password: identify individuals’ typing characteristics by means of the erroerrorr Haar wavelet. Based on these merits, the SPWK has promising applications in the realm of wearable electronics, self-powered sensors, cyber security, and artifcial intelligences. KEYWORDS Triboelectric nanogenerators; Self-powered keyboard; Human–machine interface; Wearable electronics; Fully fabric- based Jia Yi and Kai Dong have contributed equally to this work. * Zhong Lin Wang, [email protected] 1 School of Physical Science and Technology, Guangxi University, Nanning 530004, People’s Republic of China 2 CAS Center for Excellence in Nanoscience, Beijing Key Laboratory of Micro-Nano Energy and Sensor, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, People’s Republic of China 3 School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China 4 School of Material Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA Vol.:(0123456789) 1 3 103 Page 2 of 13 Nano-Micro Lett. (2021) 13:103 1 Introduction breakdown phenomenon of clothes, can light up 416 seri- ally connected light-emitting diodes [7, 9]. In addition, the It is following a general trend of functionality, portability stretched yarns were embedded into TENGs can be used and self-security with the massive development of the ffth- for motion monitoring [34, 41]. However, there are rarely generation electronic technology, especially when it comes reports on devices that integrate TENGs and sensors based to wearable electronics. A superb feature of this trend is the on fully textiles, most of them were just assembled into tremendous demand in electronic devices/systems, in a total the shape of fabric, which was lack of air permeability of billions to trillions, each of which needs a mobile power and comfortability. On the other hand, some intelligent source. The traditional mobile power sources have some human–computer interface devices have been developed defects, such as bulky volume, overbalance weight, and lim- based on fully fabrics, but their too simple functions to ited lifetime [1–4], which hinder the practical and sustain- meet the needs of people’s daily life and production. able applications of wearable electronics. Fortunately, since Thus, a device, composed of fully textile-based TENG, is the invention of the triboelectric nanogenerator (TENG) in required to implement the merits of comfortability, wear- 2012 [5–7], wearable electronics provide new dawn and ability, human–computer interaction, and multifunctional reengineering for sensing and energy harvesting [8–10]. On biosensing. account of the advantages of TENGs, such as easy structural Here, a fully fabric-based pressure sensor array was design [11, 12], low cost [13], high conversion efciency manufactured via a simple and efective route, which was [14, 15], and broad range of applications [16], the coupling further assembled into a biometric SPWK to efectively efect of contact electrifcation (CE) and electrostatic induc- prevent unauthorized computer access. The developed tion can be achieved between any materials [6, 17]. There- F-TENG prototype has appropriate stretchability and sta- fore, the integration of general-purpose TENG technology bility as well as high-pressure sensitivity, and can generate with smart fabrics brings new vitality and more possibilities electrical signals to detect external keystroke. A trigger to the next generation of wearable electronics [18, 19], per- voltage threshold of 2 V was designed for the wearable sonal healthcare [20, 21], and human–computer interfaces keyboard system, so that it could work stably even in a [22–24]. severe noise environment. Furthermore, the Haar wavelet With the development of flexible human–machine was employed to successfully classify and identify the typ- interface devices, intensive progress has been realized by ing signal. More importantly, on the basis of the electrical utilizing deformable conductors [25, 26], stretchable sen- output signal obtained from diferent users, a biometric sors [27, 28], or fexible flms [29–31]. However, poly- authentication system could access to the system by biom- mer substrates, such as polyethylene terephthalate (PET), etrics recognition not just the digital passwords were estab- polyimide (PI), and polydimethylsiloxane (PDMS), were lished. Upon the user logs into the system, the self-security used for most fexible human–machine interface devices function through matching specifc users’ electrical signals [32, 33], have the disadvantage of low ft and unsatisfy- was also verifed. ing comfort for human body. Textiles, due to their mer- Owning to the unique woven structure and advanced self- its of hygroscopic, soft, breathable, and comfortable to powered function, the SPWK has the characteristics of self- human, are considered as ideal vehicles to design fex- powered ability, self-assignment-safe and wearability. And ible human–machine interfacing devices, especially for it is portable due to the combination SPWK with fabrics, wearable electronics with personal healthcare/biomedi- achieving "zero space" occupation. The SPWK is an intel- cal monitoring or biometrics [10, 34–36]. Recently, self- ligent device to convert mechanical energy into electrical powered smart textiles combined with TENGs for accom- energy through typing movement. Due to the high-pressure modating the era of IoTs have been reported [37–40]. For sensitivity of the sensor, it can dynamically identify and pre- example, a 3D honeycomb structure woven fabric tribo- vent unauthorized access. And it can make signifcant pro- electric nanogenerator based on fame-retardant wrap- gress in biometric systems, which has versatile applications ping yarn was developed for fre escape and rescue [11]. in wearable electronic, artifcial intelligence, cyber security, A DC fabric TENG, which takes advantage of electrostatic and human–machine interaction. © The authors https://doi.org/10.1007/s40820-021-00621-7 Nano-Micro Lett. (2021) 13:103 Page 3 of 13 103 2 Experimental Section 2.2 Characterizations 2.1 Fabrication of F‑TENG The surface morphology was observed by SEM, and the electrical output performance was measured by the 6,514 Fabrication of Ag conducting layer: The polymer fber was electrometer and the linear motor. The NI USB-6218 was polished into NaOH solution and rinsed with deionized used to be convert electrical signals into digital signals. water to remove impurities [42]. The processed polyester cloth was plated with a layer of Ag electrode by screen print- 3 Results and Discussion ing method. Finally, the polyester fabric was dried at room temperature. 3.1 Fundamental Measurement of F‑TENG Fabrication of CNT coating: The SDBS was dissolved in the deionized water, and the concentration of the solu- The overall schematic of the developed F-TENG is shown tion was fxed to 10 wt%. At the same time, CNT/SDBS in Fig. 1a. Firstly, the prepared polyester cloth which acts dispersion liquid with diferent contents is prepared by as friction layer was immersed into 60% polytetrafuoroeth- adding CNTs to them. By using the layer-by-layer self- ylene (PTFE) solution to obtain a uniformly mixed PTFE/ assembly approach, a cotton cloth was put in the CNT/ polyester fabric. According to the SEM images of the poly- SDBS dispersion liquid, then removed and dried for 8 ester fabric (Fig. 1b, c) soaked in the PTFE solution, it can times. be seen that the PTFE particles are evenly distributed on the Fabrication of Frictional layer: The polyester fabric, surface of the polyester fabric, the original air permeabil- which was cleaned with deionized water, was put into ity and mechanical fexibility are well retained. In addition, PTFE solution for 3 min and then placed in a vacuum dry- carbon nanotubes (CNTs) were used to mix with the disper- ing oven at 70 °C to dry for 5 min. After repeating the sant of sodium dodecylbenzene sulfonate (SDBS) to prepare above steps three times, the samples were dried at 150 °C CNT solution. A CNT/cotton conductive fabric was manu- for two hours. factured via a layer-by-layer self-assembly method until the (a) (b) (c) (d) (e) i (f) (g) PTFE-dacron ii CNT-cotton Ag electrode Fig. 1 Structural design of the F-TENG. a Schematic diagram of the F-TENG. The insets i and ii show the molecular structure diagram and screen-printing process diagram of CNTs, respectively.