Metamaterials display unusual electromagnetic properties, such as, a negative effective permeability and negative effective permittivity. This has sparked much interest due to possibility of negative refraction which was later confirmed by experiments. The ability of magnetically coupled resonant circuits to display an effective permeability lead to the discovery of magneto-inductive waves. These waves are only supported on arrays of magnetically coupled resonant circuits. Research into magneto-inductive waves has been largely concentrated on their use in filters and their potential use in magnetic resonance imaging. However, some work has proposed the use of magneto-inductive waveguides as a data transfer medium. This report builds on previous work which found that an optimum existed for terminal-waveguide coupling, and aims to investigate the application of magneto-inductive waves in data transfer systems. A brief overview of the topic is given along with a description of the underlying characteristics. Factors that affect the capacity of magneto-inductive wave data transfer systems, such as inter element coupling, were identified. Two novel structures, both with the intent of increasing the bandwidth via different methods, are studied. One, by making a pseudo one-dimensional channel from a two-dimensional structure, and the other by using a dual-layer design to increase the coupling between adjacent elements. Both systems are modelled, using simple circuit theory and the impedance matrix method, and a comparison between simulated behaviour and experimental observation was made. There is discussion about the differences between experiment and simulation as well as their limitations. Magneto-inductive wave data transfer systems are eventually expected to support multiple terminals and as previous research only considered two-terminal systems, an investigation into the response of a one- and two-dimensional system with a blocking terminal was undertaken. The system was modelled, again using simple circuit theory and the impedance matrix method, and simulation and experiment were compared. As a whole, the simulations showed good agreement with experiments, after some initial adjustments. Both one- and two-dimensional systems showed that their performance was not severely effected by a blocking terminal. This suggests that magneto-inductive waveguides could support more terminals.

This thesis summarizes ongoing work to develop low-cost, wireless, resonant sensor array that can be used to monitor corrosion in infrastructure systems. A magnetically coupled sensor array is presented and analyzed using circuit model. The array acts as a magneto-inductive waveguide and the impedance discontinuities caused by corrosion (or other defects) lead to reflection. The relationship between the relative position of defects and pass band characteristics is investigated, providing a technique to determine the location of targets. A configuration for increased sensitivity and a method for defect localization are presented. / text

This dissertation has been motivated by the increasing application of sensing technologies in structural health monitoring. Many wireless sensor techniques exist for structural health monitoring while a challenge faced is the finite lifetime of batteries. The objective of this dissertation is to develop passive wireless technology to provide early warning of conditions that damage the structure. In this dissertation, sensing mechanism is proposed based on time and frequency domain characteristics of magneto-inductive (MI) waves. Experimental results are also presented to demonstrate the sensing mechanism. MI waves are predominantly magnetic waves that are supported in periodic arrays of magnetically coupled resonators and propagate within a narrow frequency band around the resonant frequency. The array is to be embedded in a structure and different types of transducers can be integrated for different sensing applications. With the onset of structure defect, the transducer introduces an impedance discontinuity that generates reflected MI waves along the array, which are monitored and processed by Smoothed Wigner-Ville distribution (WVD) to extract time-of-flight for frequency components in the narrow passband. The transmission and reflection coefficients of MI waves are also investigated based on the lumped-element circuit model of the array. Based on MI waves travel time, amplitude and group velocity, the position and severity of structure defect are decided. The sensing mechanisms for different distribution of defects are proposed. The validity of the sensing mechanism is examined in experiments. The guided wave testing is implemented in one-dimensional square-shaped printed spiral resonators with Q-factor of 161 at 13.6 MHz. It demonstrates that low MI waves propagation loss is achieved with value of 0.098 dB per element at mid-band with center-to-center distance of half an inch. A pitch-catch measurement system is built to capture traveling MI signal in resonant element and extract group velocity, and a pulse-echo measurement system is designed to monitor reflected MI signal and locate structure discontinuity. In both measurement systems, MI waves are excited with wide bandwidth voltage pulse, and a digitizer is attached to sense the MI signal in a specific resonant element circuit. A baseline signal is obtained from the healthy state to use as reference and comparison with the test case using pitch-catch system. The test signal subtracted from baseline signal infers the structure damage information with time and frequency domain characteristics. It can offer an effective method to estimate the structure discontinuity location, severity and type of damage. The experimental results are consistent with the theoretical predictions. At the end, future directions for the research to integrate with other technologies are suggested. / text