Applied research in remotely queried embedded microsensors

Sensors embedded in structural composites have been a topic of research in recent years. Embedded sensors can be used to monitor and optimize the manufacturing process, to monitor performance during use, and for structural health monitoring in high-performance applications. For several years, embedded optical fibers were the predominant type of sensor. There are well-known reasons that optical fiber sensors have not yet been fully embraced in industry including primarily the cost of equipment and sensors, the fragility of the optical fiber itself, and the need to provide ingress and egress from the structure. Recent work by the authors and others has produced prototype wireless electronic sensors of various types that address these shortcomings. The US Office of Naval Research is funding a multi-disciplinary team to consolidate progress made in earlier programs towards self- contained microsensors to be embedded in a composite structure and queried using methods that do not require physical connections. The sensors are to be left in place for the lifetime of the structure, are powered by the querying apparatus, and require no penetrations through the surface of the structure. This paper describes the integrated approach taken to realize the goal of an interrogatable strain rosette that is embedded 0.25″ into a graphite composite plate. It also describes the progress to date of the sensor system itself.