Transforming transformation optics via generalised refraction

Generalised refraction is a topic which has, thus far, garnered far less attention than it deserves. The purpose of this thesis is to highlight the potential that generalised refraction has to offer with regards to imaging and its application to designing new passive optical devices. Specifically in this thesis we will explore two types of gener- alised refraction which takes place across a planar interface: refraction by generalised confocal lenslet arrays (gCLAs), and refraction by ray-rotation sheets. We will show that the corresponding laws of refraction for these interfaces produce, in general, light-ray fields with non-zero curl, and as such do not have a corresponding outgoing waveform. We will then show that gCLAs perform integral, geometrical imaging, and that this enables them to be considered as approximate realisations of metric tensor interfaces. The concept of piecewise transformation optics will be introduced and we will show that it is possible to use gCLAs along with other optical elements such as lenses to design simple piecewise transformation-optics devices such as invisibility cloaks and insulation windows. Finally, we shall show that ray-rotation sheets can be interpreted as performing geometrical imaging into complex space, and that as a consequence, ray-rotation sheets and gCLAs may in fact be more closely related than first realised. We conclude with a summary of potential future projects which lead naturally from the results of this thesis.

The development of the accounting professional in a postcolonial context: evidence from Sierra Leone

Despite increasing interest in the development of the accountancy profession and constitutive professional bodies in ex-colonies, little is known about the development of professional accountants as individuals. Similarly, although the continuing influence of the legacies of colonialism and imperialism on the accounting professionalisation trajectory in ex-colonies has been recognised, little attempt has been made to theorise such continuing colonial intervention as a postcolonial condition of accommodation and resistance, with implications for the development of professional accountants. This thesis fills this vacuum by employing four aspects of the critical lens of postcolonial theory – local-global nexus, psycho-existential complex, postcolonial hybridity and diaspora - to gain an insight into the development of accounting professionals in ex-colonies with specific reference to Sierra Leone. Specifically, it examines the current model of accounting professionalisation adopted in Sierra Leone and implications for the development of professional accountants in the country; investigates the historical and ideological legacies of colonialism that shaped and continue to influence the professionalisation trajectory in Sierra Leone; explores the perceptions of Sierra Leonean chartered and aspiring accountants of their professional identity in terms of their professional development within Sierra Leone; and explores the lived experiences of Sierra Leonean chartered and aspiring accountants in the diaspora and the diaspora effect on accountancy in Sierra Leone. The empirical evidence presented here emanated from two sources: a web-based survey and semi-structured interviews with Sierra Leonean chartered and aspiring accountants both within and outside the country at the time of the study. The model for developing professional accountants in Sierra Leone comprises a partnership between the local professional body, ICASL, and the British-based global body, the ACCA. A postcolonial analysis of the empirical evidence reveals that an unintended consequence of this model is that the local is co-opted within the global while the global becomes increasingly localised. The analysis also shows that the presence of a perceived global body ‘inferiorises’ the local body to the point of undesirability among local chartered and aspiring accountants. Thus the partnership has to date done little by way of developing ICASL’s capacity to ensure the development of a localised profession and professionals. Instead, it produces, within the Sierra Leone accountancy space, professional hybrids that at once pose as global as well as local accountants. This has significant implications for the local profession because many of the hybrid professional accountants who could potentially drive the local profession forward end up in the diaspora, which leaves the local profession in a weaker state. Also, given the established link between a robust accountancy profession and sustainable economic development, such professional diasporisation could negatively impact on the country’s economic development. In sum, Sierra Leone has failed to establish an accounting professionalisation model that develops professional accountants (through contextualised professional education and training) that meets the specific accounting needs of its growing economy.

Bull's eye leaky wave antenna for terrestrial and space applications

This work presents the study of Bull's eye antenna designs, a type of leaky wave antenna (LWA), operating in the 60 GHz band. This band emerged as a new standard for specific terrestrial and space applications because the radio spectrumbecomes more congested up to the millimetre-wave band, starting at 30 GHz. Built on existing Bull's eye antenna designs, novel structures were simulated, fabricated and measured, so as to provide more exibility in the implementation of wireless solutions at this frequency. Firstly, the study of a 60 GHz Bull's eye antenna for straightforward integration onto a CubeSat is presented. An investigation of the design is carried out, from the description of the radiation mechanism supported by simulation results, to the radiation pattern measurement of a prototype which provides a gain of 19.1 dBi at boresight. Another design, based on a modified feed structure, uses a microstrip to waveguide transition to provide easier and inexpensive integration of a Bull's eye antenna onto a planar circuit. Secondly, the design of Bull's eye antennas capable of creating beam deflection and multi-beam is presented. In particular, a detail study of the deflection mechanism is proposed, followed by the demonstration of a Bull's eye antenna generating two separate beams at ±16° away from the boresight. In addition, a novel mechanically steerable Bull's eye antenna, based on the division of the corrugated area in paired sectors is presented. A prototype was fabricated and measured. It generated double beams at ±8° and ±15° from the boresight, and a single boresight beam. Thirdly, a Bull's eye antenna capable of generating two simultaneous orbital angular momentum (OAM) modes l = 3 is proposed. The design is based on a circular travelling wave resonator and would allow channel capacity increase through OAM multiplexing. An improved design based on two stacked OAM Bull's eye antennas capable of producing four orthogonal OAM modes l = (±3,±13) simultaneously is presented. A novel receiving scheme based on discretely sampled partial aperture receivers (DSPAR) is then introduced. This solution could provide a lower windage and a lower cost of implementation than current whole or partial continuous aperture.