Advanced Structural Health Monitoring

Frequency selective surfaces (FSSs) are periodic arrays of conductive elements or patches that cause a particular reflection or transmission response when illuminated with high frequency electromagnetic energy. These arrays have been used as high frequency filters and in radar, stealth and advanced antenna applications, and more recently, as sensors. In particular, FSS-based sensing has found a home as a next-generation structural health monitoring (SHM) approach. FSS sensors are inherently wireless and passive, and are interrogated remotely via microwave energy. These sensors can be embedded in layered dielectric (non-conducting) structures during manufacture or installed during the service lifetime on the surface (conductive or dielectric). Microwaves penetrate through dielectrics, so in the case of layered structures, FSS sensors can be placed on materials/layers of interest that may be covered by additional dielectrics (such as reentry heat tiles covered with insulation). Multiple sensing parameters can be concurrently sensed through proper sensor design and interrogation, as is illustrated below through a strain and temperature sensor. This Phase I effort will focus on creating a design for a field deployable prototype that can be ruggedized for use in space environments.