While the coating of fibres with conductive compounds is a regular trick used in academia to craft flexible pressure piezoresistive sensors (with resistance decreasing when pressure is applied), the researchers toughened up the game with a specially developed deposition process that maintains the fibres' original compliance yet makes very durable and reliable pressure sensors even under repeated flex.
Instead of merely blending a conductive compound into a polymer used to coat the fibres or to draw them, the paper "Thin and Flexible Carbon Nanotube-Based Pressure Sensors with Ultrawide Sensing Range" published in the ACS Sensors journal details a scalable electrophoretic deposition (EPD) process, whereby functionalized multi-walled carbon nanotubes (positively charged in a water-based dispersion) are deposited under a direct current electric field to grow a uniform coating on a fabric strapped to the cathode.
More specifically, the nanotubes are functionalized with the dendritic polyelectrolyte polyethyleneimine (PEI) which forms covalent bonds with the oxide groups on the nanotube surface as well as functional groups on the fibres' surfaces, the paper reports. This PEI functionalization also acts as a polymer matrix, creating a porous, flexible, and electrically conductive nanocomposite film less than 750nm thick, on the treated textile.
This tight chemical integration means that pressure sensors built with such coated fibres are not subject to physical damage even under repetitive flex or high pressure loads, unlike alternative solutions.
The authors report a very wide range of pressure sensing, ranging from 0.0025 to 40 MPa, outperforming any other reported fabric-based sensors, with a sensor response fairly linear at low pressures and only becoming nonlinear at high pressures.