Wearable Flexible Pressure Sensor Based on Nitrogen-Functionalized CNT in Melamine Foam for Human Motion Monitoring

Flexible pressure sensors, with prominent applications in healthcare, human-computer interface, and motion monitoring, have garnered significant interest among researchers in recent times. Melamine foam (MF), valued for its porous structure and accessibility, is a preferred material for flexible pressure sensors. Various electrically conducting nanomaterials are incorporated into these foams to realize piezoresistive flexible sensors. Carbon nanotubes (CNTs), one of the filler materials used in these sensors, suffer from the issues of agglomeration and uneven dispersion when used as a single filler, which significantly affects the sensing properties of the piezoresistive foam-based sensors. Covalent functionalization, such as nitrogen doping, effectively addresses these issues and modifies the properties of carbon nanotubes (CNTs) to enhance their performance in various applications. In the present work, we have prepared a nitrogen-doped CNT (N-CNT) using a simple hydrothermal method and fabricated piezoresistive flexible pressure sensors using N-CNT/MF by facile dip coating method. The 4 wt% N-CNT/MF pressure sensor worked in the 0-35 kPa range and showed a sensitivity of 0.172 kPa(-1) in the 0-4 kPa range. With a low detection limit of 18 Pa, a response time of 0.4 s, and a relaxation time of 0.46 s, the sensor's performance was stable for more than 1800 cycles. The sensor was tested for monitoring wrist, elbow, finger, and knee bendings and finger pressing, demonstrating its applicability in human motion monitoring applications.