Frequency selective surfaces (FSSS) are periodic arrays of conductive elements/patches that cause a particular reflection response when illuminated with high frequency electromagnetic energy. These…

This is a $749,994.00 Small Business Innovation Research (SBIR) Phase II contract awarded by the National Aeronautics and Space Administration (NASA) to Texas Research Institute - Austin, Inc., a division of Texas Research International Inc. The contract is for the research and development of frequency selective surface (FSS) sensors that can be used for wireless, passive monitoring of strain and temperature on structures. The sensors are designed to be embedded or surface-mounted and can be interrogated through non-conductive materials. This Phase II effort builds on prior Phase I work to improve sensor designs, materials, and bonding methods, as well as to test the complete prototype system on various structures. The goal is to deliver the final sensor system to NASA Langley and develop a commercialization plan.

Frequency selective surfaces (FSSS) are periodic arrays of conductive elements/patches that cause a particular reflection response when illuminated with high frequency electromagnetic energy. These arrays are used for high frequency filters and in antenna applications. We propose to use FSSS as multi-functional sensors. FSS sensors are unpowered, low-profile (THIN), wireless and passive, and are interrogated remotely via low power microwave energy. These sensors can be embedded in non-conductive structures or surface mounted on conductive or non-conductive surfaces. They can be surface mounted at any point in the service life of a structure. Microwaves penetrate through dielectrics, so FSS sensors can be interrogated through non-conductive materials such as paint, insulation, fiberglass, kevlar etc. Multiple sensing parameters can be concurrently sensed through proper sensor design and interrogation, as was illustrated in phase I via both simulation and experimental measurement of a prototype strain and temperature sensor. Phase I work included: completing a study on the effect of FSS dimensions and illumination footprint on achievable resolution; miniaturization was applied and shown to improve sensor response and resolution; modeling correctly predicted sensor ability to measure temperature and strain; FSS sensors and tensile test samples were constructed and bonded together; and thermal and mechanical testing were completed to empirically confirm capabilities and limitations. In phase II we plan to improve sensor materials and designs; address measuring ranges of strains and temperatures on varying surfaces; optimize FSS bonding methods; build and test a complete strain/temperature measurement prototype; test the system on structures (both visually available and covered by nonconductive materials) undergoing various loads and temperature changes; quantify capabilities and limitations; deliver the system to NASA langley; and develop a commercialization plan.