Design, fabrication and embedding of microscale interdigital sensors for real-time cure monitoring during composite manufacturing

In this study, microscale interdigital capacitive sensors are designed, fabricated and embedded in glass fiber composite for real-time cure monitoring of resin. The microscale interdigital capacitive sensor offers great advantages due to its miniaturized size, high flexibility and high temperature stability. Most importantly, after integration, due to the small footprint and only 5 mu m thickness, the embedded sensor minimally downgrades the composite mechanical properties. Apart from all these merits, the substrate foil is perforated to provide an opportunity for the resin to go through the substrate and bridge it. The sensor consists of two interdigitated arrays. There are two different sensor designs, which offer 900 and 450 electrodes in arrays. The electrodes are made out of tantalum and are fully insulated with about 50 nm tantalum oxide. Therefore, it is possible to embed the sensor even in conductive fibers, e.g. carbon, and to use the sensor out of the Cleanroom without getting contaminated with conductive particles to shortcut the arrays. Polyimide is chosen for the substrate of the sensor. This specific polymer has excellent flexibility and its geometry stays unchanged even at high temperature. The Dielectric Analysis (DEA) measurement proves the effective and real-time tracking of resin polymerization during laminate production.