Strain sensing of printed carbon nanotube sensors on polyurethane substrate with spray deposition modeling

The unique mechanical and electrical properties of carbon nanotubes represent a potential for developing a piezo-resistive strain sensor for smart structures. This study demonstrated a new processing technique of multi-walled carbon nanotube strain sensors with tunable strain gauge factors. A digital-controlled spraying-evaporation deposition process that uses a 12-array bubble jet nozzle attached to a digital x-y plotter combined with a heated substrate which induces evaporation of the solvent was developed. The demonstrated fabrication technique has advantages such as high efficiency, low cost and scalability. The experimental results showed that the prepared carbon nanotube strain sensors are capable of measuring strains through highly linear electrical resistance change. The gauge factors of the fabricated strain sensors could be easily tuned by controlling the number of printed layers of carbon nanotubes. In this work, strain sensors were fabricated with printed carbon nanotube layers ranging from 10 to 50 layers and strain gauge factors were measured in a range of 0.61-6.42. Moreover, the dynamic loading test results revealed that the printed carbon-nanotube strain sensors exhibited excellent durability and stability at cyclic strain. These superior sensing capabilities of the fabricated CNT sensors make them a promising candidate for wearable smart electronics and structural health monitoring applications.