Flexible passive LC resonator for wireless measurement during curing of thermosets

Monitoring of fibre composites is an important task to spread the application of fibre composites. Cure monitoring of the polymer matrix of fibre composites during the fabrication can be realized with interdigital sensors. The measured impedance can be directly related to the curing process. However wiring the sensor may disrupt the material, therefore sensing should be done wireless. As many fibre composites are processed under high temperature and high pressure conditions no electronics can be used inside the material. Here we present the design, fabrication, and characterization of a wireless sensory system using a chipless strategy for online cure monitoring. For this purpose, different combinations of sensors and readers are designed, consisting of a planar inductor-capacitor (LC) resonator, where capacitance is an interdigital capacitor, and an inductor as antenna operating wirelessly through inductive coupling. The designs are realized onto flexible polyimide substrate using microfabrication technology. To characterize the coupling effect, the response of the reader antenna has been carried out when sensor is placed in its vicinity. Furthermore, the curing process of adhesive is demonstrated and results are discussed. It is shown that the curing process of a thermoset polymer can be monitored by a flexible chipless LC resonator wirelessly. (paper)