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

Abstract

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 I' 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.

Date of Award	2018
Original language	English