Design, fabrication, and characterization of rubber-CNTs and paper-CNTs nanocomposite-based five-layered proximity sensors for various applications

Proximity sensors with transmitting and receiving units were designed, fabricated, and characterized. The transmitting unit was fabricated by depositing carbon nanotubes (CNT) thin film on a flexible polymeric rubber substrate. While the receiving unit consisted of five layers of cellulosic polymer (paper) substrates containing CNT films. The CNT films on both substrates were deposited using rubbing-in technology. During experiments, the transmitting and the receiving units were placed parallel (in space). Between the surfaces of the transmitting and receiving units, the effect of proximity was experiential at frequencies of 100 kHz and 200 kHz. It was found that on increasing gap between the transmitting and the receiving units (0.1 to 5 mm), the increase in sensor’s impedance was observed up to 1.73 times, whereas the reduction in the capacitance was up to 1.62 times. The fabricated proximity sensors were also assessed for tactile force (0–120 gf), humidity (69% to 96% RH), temperature (31℃ to 50℃), and ultraviolet radiation (0 uW/cm² to 354 uW/cm²) sensing. It was observed that on rising humidity and force, the sensors’ impedance decreased, whereas the capacitance increased and vice versa for the temperature and ultraviolet irradiation. These changes may be explained due to the changes of electrophysical parameters. Moreover, it was observed that on increasing frequency from 100 to 200 kHz, the sensors’ impedance decreased while the capacitance increased. It indicates that these devices may also be used as electronic filters for the correction of frequency response of the circuits as well. The low-cost materials, easy and ecologically friendly fabrication are important for educational and industrial utilization of these sensors.