Sensing mechanism of hierarchical carbon nanocomposite sensors and their applications in structural health monitoring and human health support
Date
2023
Authors
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Publisher
University of Delaware
Abstract
Carbon nanotubes are an excellent choice for hierarchical multiscale composites and nanocomposite films due to their extraordinarily high specific strength and stiffness, high electrical and thermal conductivities, and large aspect ratios (length/diameter). Research into using carbon nanotubes in a wide range of novel applications has significantly been sparked by improvements in processing science and characterization techniques for nanomaterials. Advancements in the computation capability added to the increased usage of simulation in research. This research combines computation, multi-scale testing, and prototyping to investigate the underlying sensing mechanism of knit fabric sensors and develop multifunctional applications using carbon nanocomposites with non-woven and knit fabric. ☐ Aqueous electrophoretic deposition and dip coating processes are used to create conductive nanocomposite films of carbon nanotubes on non-conductive fabrics such as non-woven aramid and commercial knit fabric. The multifunctional performance of carbon nanotube-based multiscale composites and nanocomposite-coated textiles is assessed for potential uses in structural health monitoring and wearables. The strain sensing response of carbon nanotube-coated sensing skins fabricated using multiple processing techniques and parameters are studied. ☐ Non-woven aramid carbon nanotube sensors are developed and tested for structural health monitoring applications. Characterization of piezoresistive sensing skins under variety of loading conditions is performed comprehensively. The carbon nanotube-based sensor is also employed for hybrid metal and composite structures adherently bonded to detect damage due to unexpected loading and service conditions. A prototype is developed and tested using a data acquisition system to record real-time data from remote locations without much manual intervention. ☐ The strain sensing response of carbon nanocomposite-coated knit fabric is significantly higher than typical polymer-based carbon nanotube strain sensors. When the sensor is used over the elbow or knee, a resistance changes of 3,000% is recorded during flexion/extension. This ultrahigh sensing response is due to the combined effect of carbon nanotube tunneling and micromechanical deformation of fibers and yarns of knit fabric on the application of strain. The electromechanical response of the knit fabric coated with nanotubes is studied at different length scales, from individual yarns to fabric levels, to investigate and explain the unique sensing response. A computational finite element model is developed to study the behavior of yarn when elongated in the wale direction. Ultrahigh sensitivity is due to the combined effect of micromechanical deformation of the carbon nanotube-coated knit fabric and the tunneling gap of carbon nanotubes. ☐ The stretch sensors are breathable (allow perspiration to diffuse) and easy to wear because of the extremely thin nanocomposite coating, which prevents the fabric's properties such as flexibility and stretchability from changing. Collaborating with biomedical and computer science researchers, a comprehensive study is performed with a carbon nanocomposite-coated flexible sensor on the compression sleeve on the elbow. The sensor is tested for repeatability and variability on KinArm for controlled movement. Virtual reality (VR) games for upper extremity exercise are developed, and the wearable sensor’s response is studied with KinArm and VR together. The response of the sensor is similar in both tests. The sensor's response is independent of the path of the hand movement and depends on the change in the elbow angle during the hand movements. A calibration curve prepared beforehand can be used to measure the angle of the elbow based on resistance change in the sensor. These novel wearable sensors can inspire research in human-computer interaction, gesture recognition, and the rehabilitation monitoring progress after an injury.
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Keywords
Carbon nanotubes, Fabric based sensors, Human machine interaction, Multifunctional composite, Structural health monitoring, Wearable sensors