纤维基自供能电子皮肤的构建及其应用性能研究进展
Fabrication and application research progress of fiber-based self-powered electronic skins
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收稿日期: 2022-04-13 修回日期: 2022-07-5
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Received: 2022-04-13 Revised: 2022-07-5
作者简介 About authors
吕晓双(1997—),女,博士生。主要研究方向为纤维基压力传感器及智能电子皮肤。
本文结合触觉传感型电子皮肤的组成结构,首先介绍了常用构筑材料的种类、性能特点及制备工艺,然后针对致密的薄膜基和橡胶基电子皮肤透气性差,长期穿戴易导致皮肤刺痒等问题,概述了可呼吸纤维材料作为电子皮肤基底层、电极层和传感层所具有的独特优势。其次,介绍了压电式和摩擦电式电子皮肤的触觉传感原理,不仅可以实现实时的压力响应,还可收集环境中的机械能转化为电能来实现自供能,有利于制备微型、轻量、柔性的可穿戴器件。最后,从制备方法、性能表征和功能应用等方面系统总结了近年来纤维基自供能电子皮肤在运动监测、医疗检测等多个领域的应用进展,并深入探讨了目前存在的问题与未来的发展方向。
关键词:
This review introduces the categories, characteristics, and preparation processes for constructing materials with applications for electronic skins, from the perspective of composition structure of the electronic skins with tactile sensing capability. The compelling features of breathable fiber materials serving as substrate layer, electrode layer, and sensing layer in electronic skins were highlighted, in view of the poor air permeability of current dense film-based and rubber-based electronic skins that easily lead to itching during long-term wearing. The working mechanisms of piezoelectric and triboelectric electronic skins were introduced, which are not only able to achieve real-time pressure sensing response, but also able to harvest the ambient mechanical energy and convert it into electricity to power themselves. These are conducive to the fabrication of miniatured, lightweight, and flexible wearable devices. The research progresses in fiber-based self-powered electronic skins in the fields of motion monitoring and medical detection were comprehensively summarized in terms of preparation methods, performance characterizations, and practical applications. The existing challenges and future development directions of fiber-based self-powered electronic skins were extensively discussed.
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本文引用格式
吕晓双, 刘丽萍, 俞建勇, 丁彬, 李召岭.
LÜ Xiaoshuang, LIU Liping, YU Jianyong, DING Bin, LI Zhaoling.
电子皮肤是由传感阵列所组成的具有仿生物体皮肤传感功能的精密传感系统,可模拟生物体皮肤多维感知的功能,如感知外界压力、湿度、温度,还可以感受物体的形状轮廓和表面纹理等,在医疗检测、人机交互、人工智能、智能穿戴等领域具有广阔的应用前景,已成为当前科研界研究的热点[1-2]。由于触觉传感是生物体皮肤最基本的传感功能,具有人体生理信号监测功能的触觉传感型电子皮肤备受研究人员的关注[3-4]。这类电子皮肤可实时监测人体的脉搏、心率、呼吸等生理信号,并将其转化为可识别量化的电信号,为疾病的预防和诊断提供可靠依据。目前,日益增长的应用需求对这类电子皮肤提出了更高的要求,如应具备灵敏度高、稳定性好、响应时间快、柔性化、微型化等特性[5]。压电式和摩擦电式传感系统不仅可采集量化外界物理机械刺激,还可将机械能转化为电能供自身使用[6⇓-8]。与电容式、压阻式等传感系统相比,自供能传感系统不需要额外的电源(如电池)进行供电,结构简单且质量轻,有利于实现电子皮肤的轻量化、微型化和柔性化,且不需要频繁地更换电池或反复充电,也不存在电解液泄露的问题,有利于电子皮肤等可穿戴设备的长期使用[9⇓-11],因此,采用压电式或摩擦电式传感系统是制备高性能柔性电子皮肤的理想方法。
但是,目前报道的大多数电子皮肤由致密的薄膜或橡胶材料作为基底层、电极层或传感层。虽然这些材料具有出色的柔韧性、拉伸性、耐久性,但因不透气、热湿舒适性差,不适合人体长期穿戴使用[12-13]。在纤维制备的织物、纤维膜等材料中,纤维之间存在大量的空隙,这种连通的网状结构赋予电子皮肤良好的透气性,能够满足人体对热湿舒适性的生理需求[14],因此,纤维材料是制备可呼吸电子皮肤的理想材料。而且,纤维材料本身具有优异的柔韧性和拉伸性,使电子皮肤能与各种平面、曲面以及人体皮肤紧密贴合。同时纤维材料具有质量轻、比表面积大、成本低等独特优势,可根据实际需求对其微观结构进行调控,这为制备轻薄透气的柔性电子皮肤提供了新思路[13]。
总体而言,纤维基自供能电子皮肤在制备优异灵敏度、可呼吸、柔性化、微型化电子皮肤领域展现出巨大的应用潜力,已成为目前科学研究的焦点。本文围绕压电式和摩擦电式传感系统,主要阐述了电子皮肤中基底层、电极层和传感层的材料选择,然后从制备方法、性能表征和功能应用方面,重点概述了纤维基自供能电子皮肤在运动监测、医疗检测等多个领域的研究进展,以期为相关领域研究提供有益参考。
1 材料选择
用于人体生理信号监测的触觉传感型电子皮肤对传感性能和力学性能具有很高的要求,既要具备卓越的灵敏度、精确度和稳定性,也要具备一定的力学强度与柔性,使其在复杂形变过程中维持良好的动态监测功能,以满足人体长期穿戴的需求。众所周知,材料决定性能,基材的选择对电子皮肤的性能有着至关重要的影响。无论采用何种材料,必须保证不会对电子皮肤所具备的特性产生负面影响。电子皮肤的构筑材料按其特定功能,大致可分为柔性基底层、导电电极层和活性传感层三大类。
1.1 基底层
基底层的柔韧性、拉伸性、适形性是其重要的考察参数。按照其结构和物理特性,柔性基底层大致可分为三大类,即薄膜类、橡胶类和纤维类。薄膜类基底本身具有很多优点,如优异的柔韧性、适形性、耐久性、质轻及耐磨性,且器件集成简单、成本低,已经在柔性电子领域得到广泛应用。常用的塑料薄膜材料主要有聚酰亚胺(PI)、 聚对苯二甲酸乙二醇酯(PET)、 聚萘二甲酸乙二酯(PEN)、聚醚酰亚胺(PEI)、 聚醚砜(PES)和聚醚醚酮(PEEK)等[18⇓-20]。值得一提的是,这些薄膜材料中,PI的拉伸强度高达231 MPa,玻璃化转变温度为360~410 ℃,具有卓越的耐高温和耐化学性能,使其在热加工和化学处理过程中不受损伤,已成为电子皮肤领域优先选择的薄膜材料[18,21],但PI薄膜呈淡黄色,限制了其在透明柔性电子领域更广阔的应用。幸运的是,通过分子结构设计和其他有效调控技术,研究者已经开发出透明的PI薄膜,同时保持了其原有的力学柔性和化学特性[22]。除上述提到的薄膜类材料,具有高弹性的塑料薄膜类材料因其既具有良好的柔性和强度,又具备优异的拉伸性能,可使电子器件在拉伸应变等作用下仍保持稳定的传感性能[23],而被广泛应用于柔性可穿戴电子领域。聚氨酯(PU)是常被采用的塑料弹性体,其无毒、拉伸强度高、防水性好、生物相容性好,不仅可用来制备可穿戴电子皮肤,在可植入的医疗监护方面也具备广阔的应用前景[16,24]。脂肪族芳香族无规共聚酯(Ecoflex)也是常用的一种新型的具有高弹性的塑料薄膜[25]。
虽然薄膜类和橡胶类基底材料在柔性电子领域展现出优异的柔韧性、可拉伸性和力学稳定性,但其结构致密不透气,且长期穿戴时易滋生细菌甚至导致皮肤刺痒,不能满足人体穿戴时热湿舒适性需求。选择或设计具有舒适多孔结构的透气性材料极其重要。纤维类材料本身具有多孔透气结构,成为制备柔软和舒适电子皮肤基底的替代材料[13-14]。同时,纤维类材料具有选材范围广、加工简单、易于表面处理、成本低等优势,可直接与织物进行结合,更利于人体穿戴[28]。按照纤维集合体的结构组成,纤维类基底材料可分为纱线、织物、纳米纤维膜等形式。其中纱线的成形方式主要有传统纺纱技术、熔喷纺丝、湿法纺丝等,而织物的成形方法主要指传统的纺织品加工技术,如针织、机织、编织、非织造等方式。对于纳米纤维膜来说,静电纺丝技术是制备的主要方式,静电纺纳米纤维膜的比表面积更大,纤维形貌可调,且纺丝工艺简单,由此受到研究者的广泛关注。
1.2 电极层
电极层主要是指导电材料,对电子皮肤电信号的传输起着关键作用。电极层的导电性能取决于材料的导电率,一般导电率越高,电极层材料的导电性能越好。常见的导电材料分类及优缺点如表1所示。金属材料是地球上资源最丰富也是人们使用最早的导电材料。最常用的金属材料主要有银(Ag)和铜(Cu),其导电性能好,资源丰富且材料易获取,但其硬而脆的特质不利于制备柔性电子皮肤[24]。随着纳米技术的发展,纳米线、纳米棒、纳米颗粒的出现使得制备柔性纳米金属材料成为可能,如银纳米线(AgNWs)、金纳米线(AuNWs)等,其质量轻、柔软、导电性能好,是制备柔性可穿戴设备的理想电极材料[29]。无机碳材料也具有良好的导电性,同时具备材质轻、比表面积大、环境稳定性强等优点。无机碳材料主要包括炭黑(CB)、碳纳米管(CNTs)、石墨烯、还原氧化石墨烯(rGO)。其中 CNTs作为一维碳材料,其具有优异的导电性能和力学性能,载流子迁移率极高,而且还具备优异的导热性能,在电子皮肤领域具有广阔的应用前景[30]。
表1 导电电极层的分类与比较
Tab.1
导电电极层 | 代表材料 | 优点 | 缺点 |
---|---|---|---|
金属 | Au、Ag、Cu、Al及其纳米线、纳米棒等 | 高导电率、机械稳定性好、易于加工 | 柔性差、易于氧化和生锈 |
碳材料 | CB、石墨烯、rGO、CNTs | 高导电率、纳米多孔结构、机械稳定性好 | 溶液分散性差、结构不易控制 |
导电聚合物 | PEDOT、PEDOT:PSS、PANI、PPy | 良好的柔性、易于溶液加工处理 | 成本高、导电率低、稳定性差 |
与金属材料和碳材料相比,导电聚合物本身就具有优良的柔韧性,是制备柔性电子皮肤的重要材料[31],但导电聚合物的导电性能相对较差;因此,进一步提高导电聚合物的导电率而又不损伤其固有的柔性,是目前研究的一个主要方向。导电聚合物主要有聚吡咯(PPy)、聚苯胺(PANI)、聚(3,4-乙烯二氧噻吩(PEDOT)和聚(3,4-乙烯二氧噻吩)-聚苯乙烯磺酸(PEDOT:PSS)等[32⇓-34]。其中,PEDOT:PSS 具有良好的水溶性、高导电性、热稳定性和环境稳定性,在柔性可穿戴领域得到广泛应用[35]。为提高导电电极层的柔韧性,可通过涂层、气相沉积等方法涂覆到柔性材料的表面,也可通过纺织加工技术制备具有良好柔韧性的导电纱线、导电织物或导电纳米纤维膜。
1.3 传感层
活性传感层是电子皮肤的核心材料,具有感知外界物理机械刺激并将其转化为电信号的能力。在具有类皮肤功能的仿生电子皮肤中,传感材料的选择对器件的灵敏度起着重要作用。按照自供能电子皮肤的传感原理,活性功能材料主要分为压电材料和摩擦电材料,如表2所示。
表2 活性传感层的分类与比较
Tab.2
传感层 | 分类 | 代表材料 | 优点 | 缺点 | |
---|---|---|---|---|---|
压电材料 | 压电陶瓷 | BTO、ZnO、PZT | 压电常数高、 强度高、化学惰性 | 柔性差、硬而脆 | 选材单一、能量 转化效率低 |
压电聚合物 | PVDF、P(VDF-TrFE) | 柔性好、易于加工 | 压电常数小 | ||
摩擦电材料 | 摩擦电正性材料 | 乙基纤维素、聚酰胺 | 选材范围广、能量转化效率高 | 灵敏度低 | |
摩擦电负性材料 | PTFE、PVDF PDMS |
压电聚合物可通过物理成膜、机械牵伸、电场极化等工艺制得有机压电薄膜,具有良好的机械柔性、生物相容性、无毒和耐化学性能,是目前制备柔性自供能压电设备的主要材料[27]。聚偏氟乙烯(PVDF)的压电系数高、成本低,是柔性压电电子皮肤常用的压电聚合物[39]。PVDF是一种半结晶聚合物,有多达5种不同的晶体相,分别是α、β、γ、δ和ε相。在这些压电活性极性相中,β相的极化程度最高,压电灵敏度也最高,因此,将PVDF的其他晶相转化为 β相, 进一步提高PVDF聚合物中β相的含量,对于提高压电性能至关重要。目前,最常用的技术有原位极化法、热拉伸法、机械拉伸法、电场极化法、高压退火法等。与纯PVDF相比,其聚(偏氟乙烯-三氟乙烯)共聚物P(VDF-TrFE)具有一定的铁电性,常温下可完全极化,具有很高的压电活性,但成本较高。压电聚合物虽然具有压电陶瓷不可比拟的柔性,但其压电系数小、能量转换效率小、传感灵敏度低[38]。通过掺杂、涂层或其他技术,将压电聚合物与压电陶瓷或介电材料结合在一起制备的压电复合材料的压电常数高、柔韧性好,也是目前经常采用的压电材料。
摩擦电效应主要是指2种不同材料相互接触或摩擦时,由于材料对电子的亲和力不同,而在材料表面产生等量相反电荷的过程。这一效应普遍存在于不同的材料之间,因此,任何2种不同的材料都可作为自供能传感系统的摩擦电材料,这一特点使得制备摩擦电式电子皮肤变得方便可行。与选材比较单一的压电材料相比,摩擦电材料具有选材范围广、电输出性能高等优点,但由于摩擦过程中传感层易磨损,导致其传感性能不稳定,同时传感灵敏度相对较低。材料在摩擦序列表中的位置是摩擦电式电子皮肤选材的主要参考依据,如图1所示。根据材料对电子的亲和能力,一般摩擦过程中易获得电子而带负电荷的材料称为摩擦电负性材料,倾向于失去电子带正电荷的为摩擦电正性材料。2种材料在摩擦电序列中的距离越远,在接触或摩擦过程中产生的电荷就越多,电能输出越高,灵敏度也就越高[40-41]。根据摩擦电序列表,并综合考虑摩擦电极性、柔韧性等要求,PTFE、PVDF和PDMS是吸引电子能力强的主要代表材料,是最常用的摩擦电负极材料[10],而摩擦电正极材料主要采用聚酰胺66(PA66)、金属材料和乙基纤维素等。
图1
2 压电式电子皮肤研究进展
2.1 压电式传感原理
压电效应是介电性质和弹性性质的耦合作用,利用压电材料特有的压电效应,可将压力、应变、振动等外界机械作用准确而有效地转化成可识别的电信号,同时还可收集机械能并转化为电能。压电效应是指压电材料在外力作用下会产生偶极矩的变化,从而产生电信号的变化[25]。在初始阶段(见图2 中(i)[30]),压电材料正负电荷的中心相互重合,不存在电势差。当压电材料在压力作用下发生形变时会产生内部极化,导致正负电荷中心相互分离,且具有相反电性的电荷积累在材料的2个表面,因而产生偶极矩的变化;当压电材料通过电极与外电路相连时,由于压电势的形成会产生电流(见图2中(ii))。当上下两个电极充分接触时,压电材料达到最大受压状态,产生最大电势差(见图2中(iii))。当外力逐渐撤去,电流沿相反方向流动,以平衡由于压力所产生的电荷(见图2中(iv))。当材料完全分离时,相反电荷的中心相互重叠,压电材料最终变成电中性,回到图2中(i)所示的状态。压电式传感器具有灵敏度高、动态响应时间快、自供电能力强等优点,同时也存在不适合静压力传感、易受温度影响等缺点,需要进一步改进。
图2
2.2 压电式电子皮肤
随着纺织技术的发展与进步,纤维材料在柔性电子皮肤领域得到广泛关注。纳米纤维膜具有质量轻、比表面积大、压电活性高、透气性好、结构可调等优点,在压电式传感系统中展现出巨大的应用潜力。静电纺丝具有设备简单、成本低、工艺可调等优势,是制备纳米纤维膜的主要途径之一,且纺丝过程结合了机械牵伸和电场极化过程,使PVDF的内部晶型更多的转变为β相,提高了压电灵敏度,因此,静电纺丝技术是制备高压电活性纤维的有效方式。李召岭课题组[42]采用同轴静电纺丝工艺以PVDF/GO为壳层,PVDF/BTO溶液作为芯层,制备了高性能核壳结构压电纤维膜,然后将导电织物分别作为上下电极,PU作为基底层进行封装,构筑三明治结构柔性电子皮肤,如图3(a)所示。得益于纤维本身的良好柔性,这种电子皮肤可很好地贴附在人体关节部位,对人体的各种运动姿态和运动频率进行检测。由于同轴结构的协同效应,该形状自适应电子皮肤表现出优异的传感性能,在80~230 kPa 压力范围内,灵敏度可达 10.89~0.5 mV/kPa, 即使在超过8 500次的工作循环后,电子皮肤的传感灵敏度依然保持相对稳定,展现出卓越的机械耐久性。
图3
图3
纤维基压电式电子皮肤
Fig.3
Fiber-based piezoelectric electronic skins.
(a) Sandwich-structured electronic skin and core-shell piezoelectric fiber; (b) Structural design and optical photograph of dual-modal piezoelectric electronic skin
在上述研究工作基础上,李召岭课题组[43]还开发了纤维基双模式感知电子皮肤,既可检测人体的体温和环境温度,也可感知外界物体的压力和人体的脉搏等。所制备的多功能电子皮肤由压力传感层和温度传感层在空间方向上垂直排列而成,如图3(b)所示。对于温度传感层,采用柔软的静电纺碳纳米纤维膜作为热阻传感的活性材料,其在25~100 ℃的范围内温度分辨率可达到0.381%。对于压电传感层,采用掺杂ZnO纳米颗粒的PVDF纳米纤维膜为压电材料,由于纳米掺杂和纺丝过程都在一定程度上提高了压电材料的压电系数,表现出优异压力传感性能,在4.9~25 kPa和25~45 kPa的压力范围内,传感灵敏度分别为15.75和52.09 mV/kPa。
3 摩擦电式电子皮肤研究进展
3.1 摩擦电式传感原理
图4
该压力传感系统由摩擦电负性材料和摩擦电正性材料分别连接导电电极组成。在初始状态时,2种不同的材料之间存在一定的间隙,处于静态平衡状态。当在外界压力的作用下,2种材料相互接触,由于二者对电子的亲和能力存在差异,在摩擦起电或接触起电的作用下,相互接触的2个表面上产生等量相反的摩擦电荷(见图4中(i)[4])。当外力释放后上下2个表面逐渐分离,由于中间夹杂着空气层,2个表面上的电荷不能完全中和,从而形成电势差;为平衡电势差,在静电感应作用下,上下两层摩擦材料的背面电极层感应出相反的电荷,同时在电势差的驱动下外部的电路形成瞬时电流(见图4中(ii))。当2种材料完全分离时,电极层分别带有与摩擦层等量相反的异电荷,传感系统又回到静态平衡的状态(见图4中(iii))。再次施加外力时,上下两个摩擦层又相互接触,摩擦电荷产生的电势差不断降低,电极层的感应电荷逐渐减少,感应电荷通过外电路沿相反方向运动(见图4中(iv)),直至 2种材料重新接触回到图4中(i)的状态。综上,随着摩擦电负性和电正性两层材料接触和分离的循环,传感器可感知到刺激并获取能量,这使得摩擦电传感器只能检测动态信号而不能检测静态信号。尽管如此,由于具备灵敏度高、自供电、绿色环保等优点,摩擦电式传感系统备受研究者的关注。
3.2 摩擦电式电子皮肤
图5
图5
纤维基摩擦电式电子皮肤
Fig.5
Fiber-based triboelectric electronic skins.
(a) Washable and highly stretchable electronic skin with silver-coated polyamide yarn; (b) All-nanofiber structured breathable electronic skin; (c) Transparent and antibacterial electronic skin constructed with conductive composite nanofibrous membranes; (d) Biodegradable and antibacterial electronic skin fabricated with nanofibers;(e) Highly sensitive electronic skin for respiratory monitoring
所制备的电子皮肤表现出优异的电输出性能和传感性能,其最大能量密度为230 mW/m2,可用来检测人体的脉搏和声音振动,还可作为传感器应用在人工假肢领域。
李召岭课题组[12]利用静电纺技术制备了一种基于摩擦电传感机制的全纤维结构自供能电子皮肤,如图5(b)所示。该电子皮肤以强电负性的PVDF纳米纤维膜为摩擦传感层,导电碳纳米纤维膜为电极层,柔性PU纳米纤维膜为基底层组成单电极式压力传感系统。在0~175 kPa的压力范围内,该电子皮肤表现出良好的传感性能,其灵敏度高达0.18 V/kPa。得益于纳米纤维膜丰富连通的多孔结构,组装而成的器件表现出优异的透气性,水蒸气透过率为10.26 kg/(m2·d),保证了这种全纤维结构电子皮肤穿戴时的热湿舒适性;且该电子皮肤具有优异的力学稳定性,即使拉伸变形达到50%,可穿戴设备的传感性能依然保持相对稳定。
李召岭课题组[46]将AgNWs与PVDF纳米纤维膜复合,制备了导电复合纳米纤维膜,如图5(c)所示。为进一步提高摩擦层的有效接触面积,还提出“模板牺牲法”的制备方法,来调节玫瑰花模板的微纳结构,克服花瓣微纳结构的不均一性,得到更均匀的高灵敏传感层。采用AgNWs 复合纳米纤维膜为导电电极层,以含有抗菌剂的PDMS弹性体为基底层,制备了柔性、透明、抗菌的纤维基电子皮肤,具有优异的传感性能,在0~75 kPa和75~250 kPa的压力范围内,灵敏度分别为71.52和10.87 mV/kPa。同时该电子皮肤具有优异的力学稳定性和耐久性,在23 000个循环后其传感性能依然保持相对稳定。利用纤维集合体作为摩擦传感层,由于其本身的高比表面积、高柔韧性等独特优势,可进一步提高摩擦电式电子皮肤的传感性能。
与上述2个研究工作类似,王中林研究组[14]报道的可降解、可呼吸的抗菌电子皮肤也由 3层纳米纤维膜组成,如图5(d)所示。该单电极式电子皮肤的上层用可降解的聚乳酸-羟基乙酸(PLGA) 作为摩擦层,下层用可降解、疏水的柔性聚乙烯醇(PVA)作为基底层,中间夹着银纳米线作为导电电极层。层层堆叠的纤维膜构建的微纳米孔洞网络结构使得电子皮肤具有大量的热湿传递通道,能够及时动态交换和平衡水蒸汽和液态水分子,并可根据周围条件可逆地保持穿着热湿舒适性。得益于采用AgNWs作为电极,电子皮肤不仅具有良好的导电性能,还赋予其良好的抗菌性能,对金黄色葡萄球菌的抑菌率达到88%。PLGA和PVA作为常用的生物可降解材料,也赋予了电子皮肤一定的生物降解性,使其能够在规定的时间范围内发挥作用,然后降解为无害成分,这对电子皮肤的可持续发展具有重要意义。该电子皮肤具有优异的传感性能和能量转化效率,其最大功率密度为130 mW/m2,电压响应压力灵敏度为0.011 V/kPa。同时,该电子皮肤具有良好的柔性和可拉伸性,能够与人体皮肤紧密贴合,实时对人体的生理信号和关节运动进行监测。王中林研究组[47]还以多层静电纺PAN和PA66纳米纤维膜为摩擦层,物理沉积金层为电极层,报道了一种垂直接触-分离式可呼吸自供能电子皮肤,如图5(e)所示。该全纤维基摩擦式电子皮肤具有优异的电输出和传感性能,其最大能量密度和传感灵敏度分别为330 mV/m2和0.217 V/kPa,可实时监测睡眠时的人体呼吸系统,来预防和诊断阻塞性睡眠呼吸暂停低通气综合征,有效改善人体的睡眠质量。
4 混合式电子皮肤研究进展
图6
图6
纤维基压电-摩擦电混合式电子皮肤
Fig.6
Fiber-based piezoelectric and triboelectric hybrid electronic skin
该电子皮肤压电层采用MWCNTs掺杂的PVDF纳米纤维膜,电极层和基底层分别采用导电织物和PDMS。摩擦层模仿荷叶表面的微纳米结构,采用微图案模板法制备多孔粗糙结构的PDMS膜,与平滑的膜结构相比,多孔结构有效提高了摩擦电部分的传感性能。同时,静电纺丝过程和MWCNTs掺杂也在一定程度上提高了压电层的压电活性。所制备的电子皮肤在0~80 kPa 和80~240 kPa范围内,灵敏度分别为54.37和9.80 mV/kPa,且具有良好的机械耐久性,可稳定工作14 000个工作循环。该混合式电子皮肤既可识别人的说话声音,监测人体的脉搏跳动,还可实现鼠标点击等各种模式的传感,对多功能电子皮肤的进一步发展提供了新思路。
5 结束语
随着社会的飞速发展和生活水平的不断提高,人们对人体生理信号监测的需求日益增加,健康监测用智能可穿戴设备成为未来科技发展的重要方向。智能可穿戴设备不仅局限于智能手表、智能手环、智能假肢等形式,还不断向轻薄化、微型化、柔性化、贴片化等趋势发展。多功能电子皮肤可实时对人体生理信号进行动态监测,对呵护生命健康起着重要作用。本文从触觉压力传感的原理入手,论述了纤维基自供能电子皮肤的材料选择,然后从制备方法、性能表征和功能应用等方面,介绍了纤维基压电式和摩擦电式电子皮肤在运动监测、医疗检测等多个领域的研究进展。综述当前的研究成果发现,纤维材料特别是纳米纤维材料具有比表面积大、微观结构可调、柔韧性好等独特优势,在自供能柔性电子皮肤领域展现出巨大的应用潜力。
相比于其他薄膜类和橡胶类材料,纤维材料更有利于制备可呼吸、可水洗的电子皮肤,且纤维材料易与其他材料进行复合,能够赋予电子皮肤更多附加功能(如抗菌性等),但是纤维基电子皮肤的力学响应性能较差,导致传感灵敏度相对较低。另外,虽然纤维材料的多孔结构使电子皮肤具备优良的透气性,但多孔结构对电子皮肤传感性能的影响规律还缺乏深入研究,进一步加强对传感机制的探索是提高传感性能的重要途径。
纤维材料的制备技术具有设备简单、操作方便等优点,但纺丝过程易受纺丝工艺参数和周围环境的影响,因此,提高纺丝过程的可控性和稳定性是实现纤维材料稳定制备的关键。同时,压电式和摩擦电式电子皮肤各有优缺点,将2种传感类型进行结合制备混合式电子皮肤,也是提高纤维基自功能电子皮肤触觉传感性能的重要手段。
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[J].DOI:10.1002/adma.201504150 URL [本文引用: 1]
Multifunctional smart electronic skin fabricated from two-dimensional like polymer film
[J].
3D fiber-based hybrid nanogenerator for energy harvesting and as a self-powered pressure sensor
[J].
DOI:10.1021/nn504243j
PMID:25268317
[本文引用: 1]
In the past years, scientists have shown that development of a power suit is no longer a dream by integrating the piezoelectric nanogenerator (PENG) or triboelectric nanogenerator (TENG) with commercial carbon fiber cloth. However, there is still no design applying those two kinds of NG together to collect the mechanical energy more efficiently. In this paper, we demonstrate a fiber-based hybrid nanogenerator (FBHNG) composed of TENG and PENG to collect the mechanical energy in the environment. The FBHNG is three-dimensional and can harvest the energy from all directions. The TENG is positioned in the core and covered with PENG as a coaxial core/shell structure. The PENG design here not only enhances the collection efficiency of mechanical energy by a single carbon fiber but also generates electric output when the TENG is not working. We also show the potential that the FBHNG can be weaved into a smart cloth to harvest the mechanical energy from human motions and act as a self-powered strain sensor. The instantaneous output power density of TENG and PENG can achieve 42.6 and 10.2 mW/m(2), respectively. And the rectified output of FBHNG has been applied to charge the commercial capacitor and drive light-emitting diodes, which are also designed as a self-powered alert system.
Highly-efficient, flexible piezoelectric PZT thin film nanogenerator on plastic substrates
[J].DOI:10.1002/adma.201305659 URL [本文引用: 1]
Wearable multimode sensors with amplified piezoelectricity due to the multi local strain using 3D textile structure for detecting human body signals
[J].
A hydrophobic, self-powered, electromagnetic shielding PVDF-based wearable device for human body monitoring and protection
[J].
Triboelectric series of 2D layered materials
[J].
Quantifying the triboelectric series
[J].
Highly shape adaptive fiber based electronic skin for sensitive joint motion monitoring and tactile sensing
[J].
A dual-mode electronic skin textile for pressure and temperature sensing
[J].
Stretchable triboelectric-photonic smart skin for tactile and gesture sensing
[J].
A stretchable yarn embedded triboelectric nanogenerator as electronic skin for biomechanical energy harvesting and multifunctional pressure sensing
[J].
Bioinspired transparent and antibacterial electronic skin for sensitive tactile sensing
[J].
All-nanofiber self-powered skin-interfaced real-time respiratory monitoring system for obstructive sleep apnea-hypopnea syndrome diagnosing
[J].
Energy autonomous hybrid electronic skin with multi-modal sensing capabilities
[J].
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