Application of Embedded Dual-Loaded Modulated Scatterer Technique (MST) to Multilayer Structures

Health monitoring of infrastructure and other critical components composed of complex composite materials is an important ongoing concern. The embedded modulated scatterer technique (MST) has shown potential for evaluating electrical (i.e., complex dielectric) properties of bulk materials. This paper investigates its potential utility for evaluating properties of layered composite structures. The approach is based on irradiating an MST probe with an electromagnetic wave. This incident wave induces a current along the length of the thin dipole probe as a function of its load impedance and the material surrounding it, including boundaries within a layered structure. Consequently, the MST sensor may be placed at a specific location or boundary such that the probe response can be monitored over time for critical changes in the geometrical or the material property of the structure. In order to use MST for evaluating important characteristics of layered structures, this application must be fully investigated, and its limitations established. This paper presents an inclusive study of the application of MST for the evaluation of layered materials through pertinent electromagnetic simulations as well as experimental corroboration of the simulation results. The experimental results show that embedded MST is capable of detecting boundaries between layers within a layered structure and is also sensitive to the distance to the boundary

Application of embedded frequency selective surfaces for structural health monitoring

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\u27s 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 --Abstract, page iii

Dielectric resonator antennas for wireless powering of sensors embedded in civil structures

Wireless power transmission (WPT) is currently being used in a number of applications, including monitoring the health of concrete infrastructure such as bridges, buildings, tunnels, and dams, where antennas of different types, geometries and sizes have been designed for powering sensors that are embedded in concrete structures. However, dielectric resonator antennas (DRAs), which have shown great potential in free-space for microwave WPT applications, have not been investigated in concrete. In this thesis, different DRAs are designed and their performance in the X-band frequency range for the WPT in concrete is investigated using an electromagnetic computational tool: CST Microwave Studio (MWS). In addition, selected DRAs are manufactured and measurement results are compared to simulation results. Furthermore, CST MWS is utilised to design and investigate surface-mountable electromagnetic sensors that can be used for concrete characterisation, crack location and crack width estimation. Firstly, rectangular DRAs of different lengths operating in the X-band are designed, and a two-antenna setup with an external transmitting antenna and an embedded receiving antenna is used to investigate WPT to embedded sensors in concrete. It is found that, the designed DRAs can be used for WPT to the embedded sensors in concrete. However, it is also found that some of the electromagnetic energy from the external transmitting antenna radiates away from the embedded antenna. Short and long DRAs are fabricated and measured in free-space and a good agreement with simulation results is observed. The short DRA has better WPT performance than long DRA over the entire X-band. To achieve a reliable WPT system, the sensitivity of the WPT to variations in the electrical (loss tangent tan δ and the relative dielectric constant) of concrete is investigated. It is found that WPT ii using the long and short DRAs appear to be more sensitive to the electrical properties of concrete at frequencies that are closer to the lower and upper frequency limits, respectively. Secondly, gratings techniques are used to redirect the radiated electromagnetic energy from the transmitting antenna towards the receiving antenna. For this purpose, rectangular-, hexagon-, and octagon-shaped DRAs with metal loaded dielectric gratings are designed, investigated, and optimised to maximise microwave WPT to embedded sensors in concrete. These antennas are suitable for wireless powering of multiple sensors, which is illustrated by changing the positioning of the embedded/receiving antenna with respect to the transmitting antenna. Furthermore, the sensitivity of WPT using these antennas to variations in the electrical properties of concrete is investigated and the simulation results are recorded. The obtained results show that reliable WPT can be obtained with the octagon-shaped DRA because it is less sensitive to variations in the electrical properties of concrete. Finally, surface-mountable electromagnetic sensors using dual-port rectangular DRA, hexagon-, and octagon-shaped planar DRAs are designed and investigated for characterisation of concrete and crack detection. It is found that the surface-mountable electromagnetic sensor using the rectangular DRA has the highest sensitivity to variations of the electrical properties of concrete and can be used to approximate the loss tangent and the relative dielectric constant of concrete, whereas hexagon-shaped planar DRA is highly sensitive to the crack width at different locations, and can be used to estimate crack width and position remotely