Integrated Flexible Polyimide Sensor for Monitoring Compressive Force in Sealings

This article is an extension of the IEEE Sensor Conference 2022 paper and presents a study on the fabrication and integration of pressure sensors into rubber sealings. The sensors were used to continuously measure the applied pressure and monitor the sealing’s condition. The sensors are made using a single-layer polyimide-based piezoresistive material with gold interdigital electrodes. The working principle is the material conductivity change due to the rearrangement of conductive carbon nanotubes (CNTs) within the polymer caused by the applied pressure. The sensors were integrated into rubber sealings during their vulcanization process and it was found that higher vulcanization pressures suggest better integration as the air gap between the sensors and sealing is reduced. The sensor’s performance is characterized by measurements of its resistance change due to the pressure response. The study shows that sensors with a 50-
$\boldsymbol {\mu }\text{m}$
interdigital electrode distance have a linear sensitivity up to a pressure of 55 N, while sensors with a larger (
$200 \boldsymbol {\mu }\text{m}$
) interdigital electrode distance have a lower linear region up to almost 10 N, but higher sensitivity. The thickness of the piezoresistive layer also affects the sensors’ sensitivity, with thinner layers showing increased sensitivity but with a limited effective pressure region. The study shows that the relaxation phenomena of the rubber sealing can be measured with the sensor. Overall, the integration of sensors into sealings provides a real-time condition monitoring system that can detect faults and reduce the risk of environmental damage caused by fluid leakage, damage, and corrosion.