Highly-Sensitive Humidity Sensors for Condition Monitoring of Hybrid Laminates

In recent years fibre-reinforced polymers (FRPs) gained importance in a wider field of application due to such favourable properties as low mass and tailorable mechanical strength. However, water penetrating into the lightweight material can lead to a loss of shear strength and finally to a collapse of the whole mechanical structure. Consequently, the integration of humidity sensors into compound materials is able to promote the reliability via online condition monitoring. An innovative concept is the use of ceramics-polymer-composites, which are well suited for the integration into lightweight structures during inline production. Composite and polyimide based humidity sensors have been manufactured by flexographic printing and spin-coating processes. A 5-fold increase in sensor’s capacity related to a humidity change from 10 to 80 % r.h. manifests the outstanding sensitivity of manufactured composite sensors. In addition, FRP-integrated polyimide sensors showed a significant response to water penetration, whereby the capability of condition monitoring could be confirmed.