Xiaoming Tao

Fiber-Based Wearable Electronics: A Review of Materials, Fabrication, Devices, and Applications

Fiber-based structures are highly desirable for wearable electronics that are expected to be light-weight, long-lasting, flexible, and conformable. Many fibrous structures have been manufactured by well-established lost-effective textile processing technologies, normally at ambient conditions. The advancement of nanotechnology has made it feasible to build electronic devices directly on the surface or inside of single fibers, which have typical thickness of several to tens microns. However, imparting electronic functions to porous, highly deformable and three-dimensional fiber assemblies and maintaining them during wear represent great challenges from both views of fundamental understanding and practical implementation. This article attempts to critically review the current state-of-arts with respect to materials, fabrication techniques, and structural design of devices as well as applications of the fiber-based wearable electronic products. In addition, this review elaborates the performance requirements of the fiber-based wearable electronic products, especially regarding the correlation among materials, fiber/textile structures and electronic as well as mechanical functionalities of fiber-based electronic devices. Finally, discussions will be presented regarding to limitations of current materials, fabrication techniques, devices concerning manufacturability and performance as well as scientific understanding that must be improved prior to their wide adoption.

Well-Dispersed Chitosan/Graphene Oxide Nanocomposites

Nanocomposites of chitosan and graphene oxide are prepared by simple self-assembly of both components in aqueous media. It is observed that graphene oxide is dispersed on a molecular scale in the chitosan matrix and some interactions occur between chitosan matrix and graphene oxide sheets. These are responsible for efficient load transfer between the nanofiller graphene and chitosan matrix. Compared with the pure chitosan, the tensile strength, and Youngs modulus of the graphene-based materials are significantly improved by about 122 and 64%, respectively, with incorporation of 1 wt % graphene oxide. At the same time, the elongation at the break point increases remarkably. The experimental results indicate that graphene oxide sheets prefer to disperse well within the nanocomposites.

Simultaneous strain and temperature measurement using a superstructure fiber Bragg grating

A novel and simple fiber-optic sensor based on a superstructure fiber Bragg grating (SFBG) for simultaneous strain and temperature measurement is proposed and demonstrated. The transmission spectrum of the sensor possesses several narrow-band loss peaks situated on the slope of a broad-band loss peak. By measuring the transmitted intensity and wavelength at one of the loss peaks, strain and temperature can be determined simultaneously. The accuracy of the sensor in measuring strain and temperature is estimated to be /spl plusmn/20 /spl mu//spl epsiv/ in a range from 0 to 1200 /spl mu//spl epsiv/ and /spl plusmn/1.2/spl deg/C from 20/spl deg/C to 120/spl deg/C, respectively.

In-Shoe Plantar Pressure Measurement and Analysis System Based on Fabric Pressure Sensing Array

Spatial and temporal plantar pressure distributions are important and useful measures in footwear evaluation, athletic training, clinical gait analysis, and pathology foot diagnosis. However, present plantar pressure measurement and analysis systems are more or less uncomfortable to wear and expensive. This paper presents an in-shoe plantar pressure measurement and analysis system based on a textile fabric sensor array, which is soft, light, and has a high-pressure sensitivity and a long service life. The sensors are connected with a soft polymeric board through conductive yarns and integrated into an insole. A stable data acquisition system interfaces with the insole, wirelessly transmits the acquired data to remote receiver through Bluetooth path. Three configuration modes are incorporated to gain connection with desktop, laptop, or smart phone, which can be configured to comfortably work in research laboratories, clinics, sport ground, and other outdoor environments. A real-time display and analysis software is presented to calculate parameters such as mean pressure, peak pressure, center of pressure (COP), and shift speed of COP. Experimental results show that this system has stable performance in both static and dynamic measurements.

Thin Film Field‐Effect Phototransistors from Bandgap‐Tunable, Solution‐Processed, Few‐Layer Reduced Graphene Oxide Films

Thin film field-effect phototransistors (FETs) can be developed from bandgap-tunable, solution-processed, few-layer reduced graphene oxide (FRGO) films. Large-area FRGO films with tunable bandgaps ranging from 2.2 eV to 0.5 eV can be achieved readily by solution-processing technique such as spin-coating. The electronic and optoelectronic properties of FRGO FETs are found to be closely related to their bandgap energy. The resulting phototransistor has great application potential in the field of photodetection.

Fiber Bragg grating cavity sensor for simultaneous measurement of strain and temperature

A novel and short (5 mm long) fiber grating based sensor with a fiber grating Fabry-Perot cavity (GFPC) structure was fabricated and tested for simultaneous measurement of strain and temperature. The sensor exhibits unique properties that it possesses two spectral peaks within its main reflection band and the normalized peak power difference, in addition to its peak wavelength shift, changes linearly with strain or temperature. The accuracy of this particular sensor in measuring strain and temperature are estimated to be /spl plusmn/30 /spl mu/s in a range from 0 to 3000 /spl mu/s and /spl plusmn/0.4/spl deg/C from 20/spl deg/C to 60/spl deg/C, respectively.A novel and short (5 mm long) fiber grating based sensor with a fiber grating Fabry-Perot cavity (GFPC) structure was fabricated and tested for simultaneous measurement of strain and temperature. The sensor exhibits unique properties that it possesses two spectral peaks within its main reflection band and the normalized peak power difference, in addition to its peak wavelength shift, changes linearly with strain or temperature. The accuracy of this particular sensor in measuring strain and temperature are estimated to be /spl plusmn/30 /spl mu/s in a range from 0 to 3000 /spl mu/s and /spl plusmn/0.4/spl deg/C from 20/spl deg/C to 60/spl deg/C, respectively.

RETRACTED: On the microstructure of three-dimensional braided preforms

This paper describes a study of the microstructure of 3D braided preforms produced by the four-step 1 x 1 method. An analytical approach is employed in conjunction with experimental investigation to establish the relationship between the braid structure and braiding parameters. Microscopic evidence of the microstructure of preforms reveals the different configurations of the yarns in the interior, surface and corner regions of a braided preform. On the basis of microscopic observations, three types of microstructural unit cell models are established for the three regions. By using these three unit cell models, the structural geometry of the preforms is analyzed and the mathematical relationships among the structural parameters, such as the yarn packing factor, fiber orientation, fiber volume fraction, braiding pitch, are derived. From the preforms to the finial composites, if the RTM process is utilized, the unit cell size and shape will be changed. The modification of the relationships among the structural parameters has been made. Good agreement has been obtained between the calculated and measured values of the geometric characteristics of braided composite samples.

Manageable N-doped Graphene for High Performance Oxygen Reduction Reaction

Catalysts for oxygen reduction reaction (ORR) are at the heart of key green-energy fuel cell technology. N-doped graphene is a potential metal-free electrode with much better electrocatalytic activity, long-term stability, and tolerance to crossover effect than expensive platinum-based electrocatalysts. Here, we report a feasible direct-synthesis method in preparing N-graphene with manageable N contents in a large scale. The resultant N-graphene used as electrocatalysts exhibits similar catalytic activity but superior stability compared to commercial Pt/C for ORR in an alkaline solution. It was found that their electrocatalytic activities were demonstrated to depend largely on N-doping content. When nitrogen content reaches a high value at about 24–25%, ORR reaction exhibits a favorable formation of water via a four-electron pathway. Furthermore, the effect of pyrolysis temperature and precursor on the activity of N-graphene is systematically analyzed, and may shed some light on the principle of choosing appropriate way for preparing N-graphene.

Wearable electronics and photonics

Electrostatically generated nanofibres for wearable electronics Electroceramic fibres and composites for intelligent apparel applications Electroactive fabrics and wearable man-machine interfaces Electromechanical properties of conductive fibres, yarns and fabrics Integration of fibre optic sensors and sensing networks into textile structures Wearable photonics based on integrative polymeric photonic fibres Communication apparel, optical fibre fabric display Wearable computing systems i?½ electronic textiles Data transfer for smart clothing: requirements and potential technologies Interaction design in smart textiles clothing and applications.

Edge Structural Stability and Kinetics of Graphene Chemical Vapor Deposition Growth

The energetics and growth kinetics of graphene edges during CVD growth on Cu(111) and other catalyst surfaces are explored by density functional theory (DFT) calculations. Different from graphene edges in vacuum, the reconstructions of both armchair (AC) and zigzag (ZZ) edges are energetically less stable because of the passivation of the edges by the catalytic surface. Furthermore, we predicated that, on the most used Cu(111) catalytic surface, each AC-like site on the edge is intended to be passivated by a Cu atom. Such an unexpected passivation significantly lowers the barrier of incorporating carbon atoms onto the graphene edge from 2.5 to 0.8 eV and therefore results in a very fast growth of the AC edge. These theoretical results are successfully applied to explain the broad experimental observations that the ZZ egde is the dominating edge type of growing graphene islands on a Cu surface.