Dan-Yang Wang

An intelligent artificial throat with sound-sensing ability based on laser induced graphene

Traditional sound sources and sound detectors are usually independent and discrete in the human hearing range. To minimize the device size and integrate it with wearable electronics, there is an urgent requirement of realizing the functional integration of generating and detecting sound in a single device. Here we show an intelligent laser-induced graphene artificial throat, which can not only generate sound but also detect sound in a single device. More importantly, the intelligent artificial throat will significantly assist for the disabled, because the simple throat vibrations such as hum, cough and scream with different intensity or frequency from a mute person can be detected and converted into controllable sounds. Furthermore, the laser-induced graphene artificial throat has the advantage of one-step fabrication, high efficiency, excellent flexibility and low cost, and it will open practical applications in voice control, wearable electronics and many other areas.

Graphene-Paper Pressure Sensor for Detecting Human Motions

Pressure sensors should have an excellent sensitivity in the range of 0-20 kPa when applied in wearable applications. Traditional pressure sensors cannot achieve both a high sensitivity and a large working range simultaneously, which results in their limited applications in wearable fields. There is an urgent need to develop a pressure sensor to make a breakthrough in both sensitivity and working range. In this paper, a graphene-paper pressure sensor that shows excellent performance in the range of 0-20 kPa is proposed. Compared to most reported graphene pressure sensors, this work realizes the optimization of sensitivity and working range, which is especially suitable for wearable applications. We also demonstrate that the pressure sensor can be applied in pulse detection, respiratory detection, voice recognition, as well as various intense motion detections. This graphene-paper pressure sensor will have great potentials for smart wearable devices to achieve health monitoring and motion detection.

High performance flexible strain sensor based on self-locked overlapping graphene sheets.

Strain sensors have been widely used in the fields of wearable devices, robot arms, medical sensing, bio-sensing, artificial skin and so on, but the existing strain sensors have some shortcomings such as a limited gauge factor (GF) or strain range. We fabricate a novel and flexible strain sensor with high performance based on self-locked overlapping graphene sheets (SOGS) which can be used for wearable devices. Polydimethylsiloxane (PDMS) is used to lock the overlapping graphene sheets, and then the graphene can be stretched and achieve an ultrahigh GF. In addition, a new theory is put forward to explain the GF changes with strain range for the SOGS strain sensor. In this work, graphene oxide (GO) film is reduced to reduced GO (rGO) by a laser. Then, the SOGS and electrodes are encapsulated by PDMS. The SOGS strain sensor has a high GF up to 400 and strain range over 7.5%, and this SOGS strain sensor achieves a balance between high sensitivity and large strain range compared with other existing strain sensors. Furthermore the theoretical equation based on the new theory agrees well with the experimental results. And this strain sensor can be used in many applications because of its high sensitivity. Some applications of the SOGS strain sensors are demonstrated for the detection of various human motions and human sounds. The SOGS strain sensor can exhibit great potential in wearable electronics because of its good balance between high sensitivity and large strain.

Fabrication techniques and applications of flexible graphene-based electronic devices

In recent years, flexible electronic devices have become a hot topic of scientific research. These flexible devices are the basis of flexible circuits, flexible batteries, flexible displays and electronic skins. Graphene-based materials are very promising for flexible electronic devices, due to their high mobility, high elasticity, a tunable band gap, quantum electronic transport and high mechanical strength. In this article, we review the recent progress of the fabrication process and the applications of graphene-based electronic devices, including thermal acoustic devices, thermal rectifiers, graphene-based nanogenerators, pressure sensors and graphene-based light-emitting diodes. In summary, although there are still a lot of challenges needing to be solved, graphene-based materials are very promising for various flexible device applications in the future.

Vortical structures of supersonic flow over a delta-wing on a flat plate

Employing the nanoparticle-based planar laser scattering (NPLS), supersonic flow over a delta-winged vortex generator on a flat plate was experimentally investigated in a supersonic quiet wind tunnel at Ma = 2.68. The fine structures of the flow field, shock waves, separation vortices, wake, and boundary layer transition were observed in the NPLS images. According to the time-correlation of the NPLS images and the measurement results of particle image velocimetry, the structural model of the flow field was improved further, and coherent wake structures were observed, which is of significance theoretically and in engineering application.

Flexible, highly sensitive pressure sensor with a wide range based on graphene-silk network structure

In this paper, a flexible, simple-preparation, and low-cost graphene-silk pressure sensor based on soft silk substrate through thermal reduction was demonstrated. Taking silk as the support body, the device had formed a three-dimensional structure with ordered multi-layer structure. Through a simple and low-cost process technology, graphene-silk pressure sensor can achieve the sensitivity value of 0.4 kPa − 1, and the measurement range can be as high as 140 kPa. Besides, pressure sensor can have a good combination with knitted clothing and textile product. The signal had good reproducibility in response to different pressures. Furthermore, graphene-silk pressure sensor can not only detect pressure higher than 100 kPa, but also can measure weak body signals. The characteristics of high-sensitivity, good repeatability, flexibility, and comfort for skin provide the high possibility to fit on various wearable electronics.

Epidermis Microstructure Inspired Graphene Pressure Sensor with Random Distributed Spinosum for High Sensitivity and Large Linearity

Recently, wearable pressure sensors have attracted tremendous attention because of their potential applications in monitoring physiological signals for human healthcare. Sensitivity and linearity are the two most essential parameters for pressure sensors. Although various designed micro/nanostructure morphologies have been introduced, the trade-off between sensitivity and linearity has not been well balanced. Human skin, which contains force receptors in a reticular layer, has a high sensitivity even for large external stimuli. Herein, inspired by the skin epidermis with high-performance force sensing, we have proposed a special surface morphology with spinosum microstructure of random distribution via the combination of an abrasive paper template and reduced graphene oxide. The sensitivity of the graphene pressure sensor with random distribution spinosum (RDS) microstructure is as high as 25.1 kPa-1 in a wide linearity range of 0-2.6 kPa. Our pressure sensor exhibits superior comprehensive properties compared with previous surface-modified pressure sensors. According to simulation and mechanism analyses, the spinosum microstructure and random distribution contribute to the high sensitivity and large linearity range, respectively. In addition, the pressure sensor shows promising potential in detecting human physiological signals, such as heartbeat, respiration, phonation, and human motions of a pushup, arm bending, and walking. The wearable pressure sensor array was further used to detect gait states of supination, neutral, and pronation. The RDS microstructure provides an alternative strategy to improve the performance of pressure sensors and extend their potential applications in monitoring human activities.

Improved electrothermal performance of custom-shaped micro heater based on anisotropic laser-reduced graphene oxide

In this paper, a flexible heater based on anisotropic laser-reduced graphene oxide (LRGO) is established. Attributing to precision and shape design of laser processing and excellent adhesion of graphene oxide, the LRGO-based heater can be microminiaturized with custom patterns and integrated on various substrates, which is what the existing film heaters cannot do and can be widely used for wearable heating devices, flexural warming systems in medical science, and light deicing equipment and heaters for aero vehicles. The electrothermal performance of the anisotropic LRGO is investigated systematically through a series of experiments including Raman spectra, SEM, white-light interferograms, IV testing, and infrared thermography. The electrothermal performance of the LRGO with the parallel aligned direction is better than the LRGO with the vertical aligned direction. The electrothermal performance can be improved greatly through radiating repeatedly. The saturated temperature and heating rate of the LRGO ra...

High-performance graphene-based flexible heater for wearable applications

In this paper, a high-performance large-scale flexible heater based on graphene and silver particles is described. The graphene-based heater can be integrated into various systems without having to be too selective about the substrate used. When silver particles are mixed with graphene, the sheet resistance is greatly reduced to 158.7 Ω sq−1. A time-dependent temperature profile under an applied voltage of 18 V exhibits a steady-state temperature of up to 220 °C within 5 s. The high steady-state temperature and ultrafast response time are superior to those of most of the existing heaters. The infrared pictures show a uniform temperature distribution whether the graphene-based heater is flat or curved. Therefore, with the advantages of a low driving voltage, high steady-state temperature, ultrafast response and excellent flexibility, the graphene-based heater is expected to be a promising potential candidate for various wearable heating applications.

Flexible, wearable, and functional graphene-textile composites

In this paper, a flexible, wearable, and functional graphene-textile composite is demonstrated. Laser scribing technology is applied to fabricate a graphene film. The thin layer of polydimethylsiloxane is covered on the surface of the graphene-textile film evenly, which would improve the abrasive resistance of the film, enhance the ability to adapt to environmental changes, and extend the service life, while maintaining the devices excellent flexibility and comfort. The graphene-textile composite can achieve constant temperature heating by controlling the input voltage, detect the human movement, and perceive the human pulse signal. The composite presents great commercial prospects and a large value in the medical, daily wear, and other areas that are closely related to human lives.