Research and application of flexible wearable electronics based on nanogenerator in touch sensor
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摘要: 柔性可穿戴电子设备因其在人工智能、健康医疗等领域的应用而受到了人们的极大关注. 然而, 如何降低功耗或实现自供能一直是阻碍其广泛应用的瓶颈. 随着纳米发电机与自驱动技术的兴起, 尤其以摩擦纳米发电机(TENG)与压电纳米发电机(PENG)代表的研究, 为解决可穿戴传感器电源的问题提供了可行的方案. TENG和PENG分别基于摩擦起电效应与压电效应, 可以将机械能转化为电能, 同时具备可拉伸性、生物相容性和自愈性等优良特性, 已经广泛应用于自驱动的触觉传感器的设计制备中, 并作为下一代可穿戴电子设备的技术基础展现出巨大的应用潜力. 基于该领域的最新进展, 本文对TENG与PENG的机理进行概述, 对其性能优化途径进行归纳, 再结合材料、器件的设计等讨论应力应变与分布、滑移等纳米发电机自驱动传感器的制备与应用研究. 最后, 对自驱动触觉传感器目前存在的问题与挑战进行讨论, 并对未来的发展进行展望.Abstract:With the advance of the fourth industrial revolution, a wave of emerging industries and interdisciplinary research is breaking out, such as the Internet of Things, megadata, humanoid robots and artificial intelligence.The rapid development of these functional electronic devices is changing the way people communicate with each other and their surroundings, thus integrating our world into an intelligent information network. The applications of flexible wearable electronic devices in intelligent robots, health and medical monitoring and other fields have attracted great attention. Following the human skin, the device can respond to external stimuli and should also have stretchability and self-healing properties. In practical applications, a large network of sensors is needed to connect with humans or robots, so the supply of energy is crucial. Several forms of green and renewable energy have been searched for, such as magnetic energy, solar energy, thermal energy, mechanical energy and microbial chemical energy. However, high cost, limitations in the choice of materials, and other disadvantages have become serious bottlenecks.The advent of nanogenerator brings a novel and effective solution to the above problems. Here in this work, the triboelectronic nanogenerator (TENG) and the piezoelectric generator (PENG) are taken as two representative objectives, which are, respectively, based on the triboelectronic effect and piezoelectronic effect to realize the collection of mechanical energy, and each of them can be used as a self-power sensor, which can generate electrical signals, respond to environmental stimuli, and need no power supply any more.The optimization and design of nanogenerator is always a key factor to improve its performance and wide application. At present, the methods commonly adopted in optimization schemes mainly include material selection, design and optimization of structural layer and electrode. The selection of materials should be based on low cost, stretchability, transparency, stability and biocompatibility. Firstly, for the optimization of structural layer, there are mainly two ways of designing the materials, one is the microstructure of the material surface, and the other is the functionalization of materials.The performance of the nanogenerator is proportional to the charge density of the contact surface. The square of the charge density is the main parameter to quantify the performance of the nanogenerator. Therefore, increasing the charge generation has been the main strategy to improve the output power. The microstructure of materials can be realized by means of colloidal arrays, soft lithography, block copolymer components and surface nanomaterial manufacturing. The same materials can be functionalized by ion doping, plasma treatment, electrical polarization, laser induction, and the formation of nanocomposites. In practical application, more attention is paid to the electrode with excellent performance which can simplify device structure, improve device performance and expand application field. The design of the electrode more focuses on the features such as flexibility, stretchability, high transparency and excellent electrical conductivity. The touch sensors based on TENG and PENG such as pressure sensors, strain sensors, pressure distribution sensors and slip sensors have shown excellent performances in application. Self-powered pressure sensors are used most widely because they are highly sensitive to and can detect the subtle pressure changes such as respiratory or arterial pulse-related changes. Strain sensors can detect signals produced by the body during mechanical movements, such as walking and joint movements. Pressure distribution sensor and slip distribution sensor play a key role in touch screen and smart prosthesis and so on.In this article, first, we introduce the mechanism of TENG and PENG, and summarize the way of performing the optimization design of the nanogenerators. Then, we discuss the self-powered sensors based on the nanogenerators such as stress, strain and distribution and slip sensors by combining the marerials and the design of device. Finally, the problems and challenges of the tactile sensor based on the nanogenerators are discussed, and the future development is prospected.
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Key words:
- nanogenerator /
- flexiblewearable electronic device /
- touch sensor /
- flexible device
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图 3 主体结构层的设计与性能优化 (a)微纳加工技术制备的微金字塔与微柱状结构的TENG的SEM图像[15]; (b)表面具有微柱结构的PENG结构示意图[47]; (c)在FEP表面进行表面极化示意图[55]; (d) gC3N4, PANI纳米棒, DMF和PVDF链之间相互作用机制示意图[48]
Figure 3. Design and performance optimization of the main structure layer: (a) SEM images of micropyramid and microcolumnar TENG prepared by micro-nano processing techniques[15]; (b) schematic diagram of PENG structure with microcolumn structure on the surface[47]; (c) schematic diagram of negative ion implantation on the FEP surface[55]; (d) schematic diagram of the interaction mechanism between gC3N4, PANI nanorods, DMF and PVDF chains[48].
图 4 电极的设计与优化 (a)VHB胶带上的透明及可拉伸双层CG照片[56]; (b)制造的石墨烯/聚合物混合透明电极的照片[57]; (c)具有自愈合功能的可拉伸导体照片[66]
Figure 4. Design and optimization of electrode: (a) The photo of stretch image and double layer CG transparency on VHB tape[56]; (b) the photo of fabrication of the graphene/polymer hybrid transparent electrode[57]; (c) the photo of stretchable conductor with a self-healing function[66].
图 5 基于TENG的压力传感器 (a)TES的结构示意图[67]; (b), (c)通过手指按压TES的无线报警系统与实际输出电压[67]; (d) TATSA结构示意图[68]; (e)不同年龄段人群脉搏输出信号[68]; (f)健康参与者的呼吸信号和PTT[68]
Figure 5. The pressure sensor based on TENG: (a) Schematic diagram of TES[67]; (b), (c) press TES wireless alarm system with finger and actual output voltage[67]; (d) schematic diagram of TATSA[68]; (e) pulse output signals of different age groups[68]; (f) respiratory signals and PTT of healthy participants[68].
图 6 基于PENG的压力传感器[69] (a)TVH/COC压电纳米发电机实物图; (b), (d)食指敲击, 拇指按压, 重击桌面所检测到的压力与商用测力计所对应的压力对比图
Figure 6. The pressure sensor based on PENG[69]: (a) Physical picture of TVH/COC piezoelectric nanogenerator; (b), (d) the diagram comparing the pressure detected by tapping the index finger, pressing the thumb, and thumping the table with the pressure corresponding to a commercial dynamometer.
图 7 基于TENG的应变传感器 (a)TENG与机械手结合的的照片与示意图[72]; (b)在一个接触和分离过程中反向电流信号曲线[72]; (c)中指的两个不同随机运动的转移电荷曲线[72]; (d)仿生可拉伸纳米发电机(BSNG)(填充红色墨水)的一个工作周期的照片[73]; (e)BSNG工作机制示意图[73]; (f)基于仿生伸缩性纳米发生器(BSNG)水下无线多站点人体运动监控系统的示意图[73]
Figure 7. Strain sensor based on TENG: (a) Photos and schematic diagram of the combination of TENG and manipulator[72]; (b) reverse current signal during a contact and separation process[72]; (c) the transfer charge curves of two different random motions in the middle finger[72]; (d) a photo of a working cycle of the bionic stretchable nanogenerator (BSNG) (filled with red ink)[73]; (e) schematic diagram of the working mechanism of BSNG[73]; (f) schematic diagram of underwater wireless multi-site human motion monitoring system based on bionic flexible nanogenerator (BSNG)[73].
图 9 基于TENG的压力分布传感器 (a) 16 × 16阵列器件结构示意[81]; (b)压力分布监测过程的示意图[81]; (c) 36 × 20矩阵交叉型电极的器件结构示意图[81]; (d)基于TENG的压力分布传感器在商用智能手机中的应用[81]; (e) SETY的阵列结构示意图[82]; (f), (g)单点触碰时压力分布信号示意图及 3D输出信号示意图[82]; (h)昆虫接触传感器时的信号输出曲线[82]
Figure 9. Pressure distribution sensor based on TENG: (a) The schematic diagram of device structure of 16 × 16 arrys[81]; (b) the process diagram of pressure distribution detection[81]; (c) schematic diagram of device structureof 36 × 20 matrix crossed electrode[81]; (d) pressure distribution sensor based on TENG appllied for a commercial smart phone[81]; (e) schematic diagram of the array structure of SETY[82]; (f), (g) schematic diagram of pressure distribution signal and 3D output signal in single point contact the device[82]; (h) signal output curve of ainsect contact the sensor[82].
图 11 基于TENG的滑动传感器 (a)指纹结构启发的TENG及其工作原理, 包含四个螺旋电极的示意图和照片[88]; (b)外部物体沿着不同方向接触传感器时的电压信号变化图[88]; (c) TENG传感器结构设计示意图和照片[89]; (d)检测施加斜侧45°方向切向力的动态输出关系曲线[89]
Figure 11. The sliding sensor based on TENG: (a) A schematic diagram and photograph of a fingerprint-structure-inspired TENG and how it works, including four spiral electrodes[88]; (b) the signal of the voltage when the external object is in contact in different directions[88]; (c) the schematic diagram and photo of the TENG sensor structure and of real product[89]; (d) detection of dynamic output of the tangential force in the 45° direction[89].
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