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This work addresses the dynamic switching of liquid crystal cells. While static measurements of the permittivity liquid crystal cells are well established, here a novel transient permittivity technique is developed and applied to several liquid crystalline substances in a variety of geometries. This technique utilises A.C. waveforms to measure the permittivity of a cell during the dynamic processes of switching and relaxing, allowing a detailed picture of the switching process to be constructed on small time scales. The results for several materials are presented and compared to theoretical predictions stemming from standard liquid crystal continuum theory. The technique is expanded to utilise frequency modulation when applied to dual frequency materials and is adapted to D.C. fields. Novel experimental results concerning surface stabilised ferroelectric liquid crystals have recently shown an unexpected second minimum in the tau-V response curve. The origin of this phenomenon is explored via a numerical simulation program and a qualitative explanation found regarding the torque generated by the surface alignment that is consistent with established theory.

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The exponentially increasing demand on operational data rate has been met with technological advances in telecommunication systems such as advanced multilevel and multidimensional modulation formats, fast signal processing, and research into new different media for signal transmission. Since the current communication channels are essentially nonlinear, estimation of the Shannon capacity for modern nonlinear communication channels is required. This PhD research project has targeted the study of the capacity limits of different nonlinear communication channels with a view to enable a significant enhancement in the data rate of the currently deployed fiber networks. In the current study, a theoretical framework for calculating the Shannon capacity of nonlinear regenerative channels has been developed and illustrated on the example of the proposed here regenerative Fourier transform (RFT). Moreover, the maximum gain in Shannon capacity due to regeneration (that is, the Shannon capacity of a system with ideal regenerators – the upper bound on capacity for all regenerative schemes) is calculated analytically. Thus, we derived a regenerative limit to which the capacity of any regenerative system can be compared, as analogue of the seminal linear Shannon limit. A general optimization scheme (regenerative mapping) has been introduced and demonstrated on systems with different regenerative elements: phase sensitive amplifiers and the proposed here multilevel regenerative schemes: the regenerative Fourier transform and the coupled nonlinear loop mirror.

All travel behavior of people in urban areas relies on knowing their position. Obtaining position has become increasingly easier thanks to the vast popularity of ‘smart’ mobile devices. The main and most accurate positioning technique used in these devices is global navigation satellite systems (GNSS). However, the poor performance of GNSS user equipment in urban canyons is a well-known problem and it is particularly inaccurate in the cross-street direction. The accuracy in this direction greatly affects many applications, including vehicle lane identification and high-accuracy pedestrian navigation. Shadow matching is a new technique that helps solve this problem by integrating GNSS constellation geometries and information derived from 3D models of buildings. This study brings the shadow matching principle from a simple mathematical model, through experimental proof of concept, system design and demonstration, algorithm redesign, comprehensive experimental tests, real-time demonstration and feasibility assessment, to a workable positioning solution. In this thesis, GNSS performance in urban canyons is numerically evaluated using 3D models. Then, a generic two-phase 6-step shadow matching system is proposed, implemented and tested against both geodetic and smartphone-grade GNSS receivers. A Bayesian technique-based shadow matching is proposed to account for NLOS and diffracted signal reception. A particle filter is designed to enable multi-epoch kinematic positioning. Finally, shadow matching is adapted and implemented as a mobile application (app), with feasibility assessment conducted. Results from the investigation confirm that conventional ranging-based GNSS is not adequate for reliable urban positioning. The designed shadow matching positioning system is demonstrated complementary to conventional GNSS in improving urban positioning accuracy. Each of the three generations of shadow matching algorithm is demonstrated to provide better positioning performance, supported by comprehensive experiments. In summary, shadow matching has been demonstrated to significantly improve urban positioning accuracy; it shows great potential to revolutionize urban positioning from street level to lane level, and possibly meter level.

Spintronics is an emergent interdisciplinary topic for the studies of spin-based, other than or in addition to charge-only-based physical phenomena, which promises not only new capabilities of electronic devices, but also abundant science. For applied materials, the spin ordering has long been investigated within the context of conventional ferromagnetic materials (FMs), while the study of spin generation, relaxation, and spin-orbit coupling (SOC) in semiconductors (SCs) took off only recently with the advent of spintronics and it is here that many novel materials and FM/SC hybrid structures can find their greatest potential in both science and technology. In the pursuit for such goals, the intrinsic material properties are important indicators and the artificially synthetized hybrid systems (layered FM/SC structures and FM-doped SCs) are valuable models for studying spindependent phenomena and could potentially be used as actual components for an eventual spintronic device. These results are expected to contribute to some of the most fundamental questions of the contemporary spintronic materials research, such as the FM/SC interfacial hybridization and magnetism, the spin and orbital ordering of ferrites, and the fundamental magnetism of doped TIs, and the proximity effects in FM/DMS and FM/doped TI heterostructures.

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Magnetic induction tomography (MIT) is an exciting yet challenging research topic. It is sensitive to all passive electromagnetic properties, and as such it has great appeal to many industries. This thesis presents an experimental investigation of MIT within two broad ar- eas of application: non-destructive evaluation (NDE) and industrial process tomography. Within both areas, MIT is presented as a low cost and non-invasive inspection tool with considerable developmental potential with regard to commercial applicability. Experi- mental investigations into the use of MIT demonstrate its versatility in imaging conduc- tive substances ranging from metallic structures, such as pipelines (s ⇡ 106 108S/m) to new composite material, such as carbon fibre reinforced polymers (s ⇡ 104 105S/m), as well as substances in a state of flow (s < 10S/m). Research innovations presented in this thesis constitute (i) the first experimental evalu- ation of MIT for pipeline inspection, an application never before attempted in the area of NDE, (ii) the development of a novel limited region algorithm, which can improve the traditional resolution from 10% to 2%, (iii) the first experimental 3D planar MIT study for subsurface imaging, which opens many opportunities for MIT as a limited access tomog- raphy technique, (iv) an in-depth experimental evaluation of the MIT system response towards various fluid measurements for the first time, while also reporting some of the first flow rig tests in this field. In addition, for each specific application, the capabilities of the prototype MIT systems are assessed with regard to (v) their flexibility in accommodating different sensor geometries, including circular, dual planar, planar and arc, (vi) situations in which the imaging subject has limited access, and (vii) their capacity to reconstruct a viable image of the subject given limited measurement data. Altogether, the results provide an evidential basis for future exploitation of this tech- nique. From the experimental investigations, it is concluded that the major limitations of this technique lie in both the hardware development in order to meet the standards of widespread commercial applications and the software capability for fully automated real time image reconstruction and structural analysis of the imaging subject. Nevertheless, with consistent development in both aforementioned areas, MIT could eventually be used as a rapid NDE technique for structural health monitoring and process tomography, as such contributing both to the social economy and public safety.