Next-Generation Embedded Printed Sensors for Near-Field Monitoring of High-Performance Composites

Monitoring the structural health of composites during manufacturing and in-service is desirable to alert against damage or deterioration of conditions beyond an acceptable level. Wireless sensors embedded into materials that can endure the forming and curing of carbon fiber-reinforced polymer laminates will open the door to automated near-field detection of key metrics such as temperature, strain, and manufacturing defects. Current sensing technologies are generally too intrusive and fragile to be reliably embedded into laminates or too expensive to be applied commercially. The development of embedded, low-weight, small-footprint sensors is reported here, and how these sensors can be used to monitor ply movement during the manufacturing process is demonstrated. These screen-printed sensors consist of closed-loop spiral coils excited externally with an AC magnetic field to generate a secondary field, which alerts on the change of relative position of each ply. This proof-of-concept work demonstrates how printed coil sensors can be fabricated to generate a high electromagnetic response, while minimizing their footprint in the laminate. It is determined that stacked silver coils, which are subsequently plated with copper to increase the conductance, are capable of producing signals that can be detected through over 3 mm of composite material.