Development of a FHE Based Temperature and Humidity Sensing System for Asset Monitoring Applications

A novel flexible hybrid electronics (FHE) based system was developed to monitor temperature and humidity inside any storage container. The primary components for the fabrication of the temperature and humidity sensing system prototype include a flexible 5-mil-thick Kapton polyimide substrate with high temperature withstanding capability and high tensile strength, as well as a conductive silver ink. The conductive traces were screen printed on the Kapton substrate and the components for measuring and recording temperature and humidity were attached to the printed traces to fabricate the system. Various tests were performed on the printed traces based on IPC-TM650 and ASTM standards to investigate the capability of the system. Mechanical tests including bending and elongation deformations, moisture and insulation resistance tests were performed to understand the flexibility, durability and environmental effects on the system. The results obtained from the mechanical bending tests showed a negligible average resistance change of 0.1% in each cycle when the printed coupon was bent by 180° for 200 cycles. In addition, a Young's modulus of 2.6 GPa was calculated from the elongation test. The moisture and insulation resistance test confirmed a stable resistance of ∼18 MΩ for the PFS test coupon when temperature was varied from 25°C to 65 °C at a maximum humidity of 90% RH repeated for 20 cycles in 7 days. This printed FHE based temperature and humidity monitoring system can be employed in several applications in the food, pharmaceutical, agriculture, automotive, and defense industries.