Local monitoring of polymerization trend by an interdigital dielectric sensor

Composite materials are increasingly used for advanced applications subjected to high standards of quality that can be guaranteed by sophisticated control systems of the production process. Quality is usually controlled by monitoring temperature inside the laminate, but some researches have also evaluated the degree of cure during the thermal cycle. The goal of this work is to measure the local cure degree of thick laminates presenting a different trend as function of thickness; to achieve this aim, a suitable interdigital dielectric sensor was developed. Sensor development was carried out through FEM simulation, suited to evaluate the electric field inside the laminate: the depth of measurement of the sensor is due to its trend. The sensor was realized after having designed it and it was experimentally verified comparing the cure degree measured in a laminate polymerized in an oven with those recorded through a cure process simulation. A thick laminate was chosen because the cure degree trend is different as function of thickness and this condition is ideal to check if the sensor is able to perform local measurements.