| This thesis proposes the use of Frequency Selective Surfaces (FSSs) as an embedded structural health monitoring (SHM) sensor. FSSs are periodic arrays of conductive elements that filter certain frequencies of incident electromagnetic radiation. The behavior of this filter is heavily dependent on the geometry of the FSS and local environment. Therefore, by monitoring how this filtering response changes when the geometric or environmental changes take place, information about those changes may be determined. In previous works, FSS-based sensing has shown promise for sensing normal strain (a stretching or compressing geometrical deformation). This concept is extended in this thesis by investigating the potential of FSSs for sensing shear strain (a twisting deformation) and detection of delamination/disbond (defined as an air gap that develops due a separation between layered dielectrics, and herein referred to as delamination) in layered structures. For normal strain and delamination sensing, monitoring of the FSS's resonant frequency is shown to be a reliable indicator for each phenomena, as verified by full-wave simulation and measurement. For shear strain, simulation results indicate that an FSS may cross-polarize incident radiation when under shear strain. Additionally, FSS was applied as a normal and shear strain sensor within a steel-tube reinforced concrete column, where it was found to provide reliable normal strain detection (as compared to traditional strain sensors), but was not able to detect shear strain. Lastly, in order to improve the design procedure by reducing computation time, an algorithm was developed that rapidly approximates the response of an FSS to delamination through use of conformal mapping and existing frequency response calculations. |
