Highly Sensitive Flexible Sensor Over a Wide Linear-Range Based on Carbon Nanotube Toward Physiological Monitoring

The capacity of flexible sensors to transform mechanical and chemical signals into electrical impulses has attracted much attention, exhibiting potential for various applications in human-machine interaction. Nonetheless, it remains challenging to maintain their high sensitivity over a wide operating range. Herein, we present an efficient strategy to expand the sensor's linear range at high sensitivity performance by using polyvinylidene fluoride (PVDF) in combination with thermoplastic polyurethane (TPU) with a moderate Young's modulus as a composite substrate for the sensitive layer. In addition, we filled the dielectric layer with multi-walled carbon nanotubes (MWCNTs) to enhance the sensor's sensitivity. To better the carbon nanotubes' dispersion in polymer substrates, we also capped them using dopamine (DA), which can participate in a self-polymerization reaction. The sensitivity (1.21 kPa(-1)) of this capacitive pressure sensor (CPS) can be maintained over a wide pressure range (2-50 kPa), which far exceeds the linear detection range of the one-component substrate sensors (0-2 kPa), with a linearity of 0.995. Meanwhile, the CPS was characterized by fast response and recovery times (156/153 ms), low detection limit (100 Pa), and excellent cyclic stability (>2000 cycles). Furthermore, the CPS was also tested for human physiological monitoring, confirming its potential for applications in wearable electronics and giving rise to ideas for developing tactile sensing features in intelligent robots.