Geometric design optimization of polyaniline/graphite nanocomposite based flexible humidity sensor for contactless sensing and breath monitoring

Abstract

• Polyaniline-graphite nanocomposite based 2D humidity sensor was screen-printed. • Adding graphite leads to faster response, improved thermal stability and hysteresis. • Improved long term stability with high performance was demonstrated over 180 days. • Sensor geometry (inter-electrode distance and number of electrodes) was optimized. • Contactless sensing and respiration monitoring applications were demonstrated. We report a low cost flexible polyaniline-graphite nanocomposite based resistive type humidity sensor, screen printed on a PET substrate with interdigitated silver electrodes. The composite with a 3:1 ratio of polyaniline and graphite was found to be ideal with a sensing response of 93.4%, took 24 s to reach 54% RH, a maximum response/recovery time of 35/39 s and low hysteresis (1.12%). Graphite acting as the support material increased the sensor's thermal stability, allowing it to be operated at temperatures as high as 55 ⁰C. To further improve sensor performance and find an optimum device architecture, geometric parameters such as inter-electrode distance and number of electrodes were studied and optimised. Based on this, a relative humidity contactless finger sensor (1.5 cm range) and a human breath monitoring sensor to map different breathing rates were demonstrated.