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Carbon Nanotube-based Flexible Sensors for Human Motion Analysis



Traditionally, carbon nanotubes (CNTs) are integrated with textiles using chemical vapor deposition. Due to the high processing temperature, the use of conventional fibers such as polyester and nylon is challenging. In this research, we use electrophoretic deposition (EPD) to create a thin electrically conductive film of a nanostructured composite consisting of carbon nanotubes functionalized with a dendritic polymer polyethyleneimine (PEI). Different types of fabrics such as cotton, wool, nylon, polyester and aramid can be coated with carbon nanotubes. EPD is inherently scalable because it is performed at room temperature without using any harsh chemicals or volatile solvents. This research is focused on the development of flexible and low-cost wearable technology that can be used to create functional fabrics and smart footwear. Typically, human motion is analyzed using instrumented treadmills and motion capture cameras. Their extremely high cost and complexity make them prohibitive for large scale commercial use. Additionally, the patient/subject can be monitored only for a limited amount of time and not in their natural work/home environment. As a result, a critical need exists for low-cost, comfortable and flexible wearable sensors for human motion analysis. For developing a flexible pressure sensor, carbon nanotubes are deposited on a non-woven aramid veil with randomly oriented fibers. The pressure sensor displays a large in-plane change in electrical conductivity with applied out-of-plane pressure. Upon compression, the number of fiber-fiber contact points between the conductive carbon nanotube coated aramid fibers increases which leads to a decrease in the electrical resistance. The pressure sensors can detect a wide range of pressures from tactile (<10 kPa) to thousands of pounds (~40 MPa). Preliminary experiments of integrating a pressure sensor in the heel of footwear have shown promising results.


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