No description available.

<p>Progress in miniaturized computing and connectivity has led to a plethora of smart connected electronic devices around humans, leading us towards the era of seamless human-electronics co-operation. In this connected society, radiative communication using electromagnetic fields is the backbone of inter-device connectivity. This unfortunately leads to high power usage as well as physical signals being available for malicious interceptors to snoop. To address the need of security and energy efficiency of inter-device communication for devices on and around the human body, Human Body Communication (HBC) has been proposed. The fundamental philosophy of HBC is to use the human body as a medium - thus being helped and not hurt by the body - for communication between devices. Confinement of a signal within the body implies higher security as well as efficiency. This dissertation is an analysis of these properties of different HBC modalities, through electromagnetic modelling, simulation, and experienced. Electro-quasistatic (EQS) HBC has been explored in significant detail, including a complete theoretical formulation of return path capacitance, as well as a study of inter-body coupling for interference and security management in EQS-HBC. Magnetic modes of HBC have also been analyzed, and compared with its electric counterparts. Finally, a novel HBC technique, GSW-HBC, has been proposed. GSW-HBC or a Goubau line inspired surface wave based HBC, is shown to be a viable, secure and energy efficient alternative to RF wireless communication, leading the search for Gbps communication around the body.</p><p>In reference to IEEE copyrighted material which is used with permission in this thesis, the IEEE does not endorse any of Purdue University's products or services. Internal or personal use of this material is permitted. If interested in reprinting/republishing IEEE copyrighted material for advertising or promotional purposes or for creating new collective works for resale or redistribution, please go to <a href="http://www.ieee.org/publications_standards/publications/rights/rights_link.html" rel="noreferrer" target="_blank">http://www.ieee.org/publications_standards/publications/rights/rights_link.html</a> to learn how to obtain a License from RightsLink.</p>

Following the foundation of aberration theory for rotationally symmetric optical systems established by Seidel, Schwarzschild, Burch, Conrady, Buchdahl, and in its most useful form H.H. Hopkins, Shack, Buchroeder, Thompson, and Rogers developed a vectorial form of the wave aberration theory that enables addressing optical systems without symmetry. In this research, a vectorial theory is utilized and extended for the alignment of two- and three-mirror astronomical telescopes, including the effects of pointing changes and astigmatic figure errors. Importantly, it is demonstrated that the vectorial form of aberration theory, also referred to as nodal aberration theory, not only provides valuable insights but also facilitates a quantitative description of the aberrations in optical systems without symmetry. Specifically, nodal aberration theory has been utilized to establish key insights into the aberration field response of astronomical telescopes to misalignments. Important nodal properties have been derived and discussed and the theoretical predictions have been validated with optical design software. It has been demonstrated that the removal of on-axis coma in some of the most common astronomical telescopes in use today directly leads to a constraint for one of the nodes for astigmatism to be located at the field center, which is exactly true for Cassegrain or Gregorian telescopes, and approximately true for Ritchey-Chretien (or aplanatic Gregorian) telescopes. These observations led to important conclusions concerning the alignment of astronomical telescopes. First, the correction of these telescopes on-axis for zero coma removes all misalignment induced aberrations only on-axis. Secondly, given that the image quality at the field center remains stigmatic in the presence of misalignments, for these telescopes non-zero astigmatism measured at the field-center directly reveals astigmatic mirror figure errors. Importantly, the effects of misalignments and astigmatic figure error can be clearly distinguished if present in combination, even in the presence of significant boresight errors. Having the possibility to clearly distinguish between misalignment and astigmatic mirror figure error provides an important prerequisite for the optimal operation of active/adaptive optics systems that are becoming standard in observatory class telescopes. Subsequent work on TMA telescopes revealed that even though TMAs are limited by fifth order aberrations in their nominal alignment state, third order nodal aberration theory provides accurate image quality predictions for misalignments and astigmatic figure (third order) effects in these optical systems. It has been demonstrated for the first time that analytical expressions can be devised that describe the characteristic misalignment induced aberration fields of any TMA telescope, leading to two main image quality degrading aberrations, field-constant coma and field-linear, field-asymmetric astigmatism. These new insights can be strategically leveraged in the development of alignment strategies for TMAs. The final part of this work analyzed how third and fifth order nodal aberration fields can be utilized in the alignment of wide-angle telescopes, with the specific example of the Large Synoptic Survey Telescope (LSST). In cooperation with the National Optical Astronomy Observatory (NOAO) an alignment strategy has been developed for the LSST (without camera) to expedite the commissioning of the telescope, providing for the first time analytical expressions for the computation of misalignment parameters in three-mirror telescopes, taking into account fabrication tolerances for the alignment of the tertiary mirror on the primary mirror substrate. Even though the discussion has been focused primarily on alignment strategies of astronomical telescopes, the methods and algorithms developed in this work can be equally applied to any imaging system.

Over the years, non-spreading or non-diffracting wave configurations have been systematically investigated in optics. Perhaps the best known example of a diffraction-free optical wave is the so-called Bessel beam, first suggested and observed by Durnin et al. This work sparked considerable theoretical and experimental activity and paved the way toward the discovery of other interesting non-diffracting solutions. In 1979 Berry and Balazs made an important observation within the context of quantum mechanics: they theoretically demonstrated that the Schrodinger equation describing a free particle can exhibit a non-spreading Airy wavepacket solution. This work remained largely unnoticed in the literature-partly because such wavepackets cannot be readily synthesized in quantum mechanics. In this dissertation we investigate both theoretically and experimentally the acceleration dynamics of non-spreading optical Airy beams in both one- and two-dimensional configurations. We show that this class of finite energy waves can retain their intensity features over several diffraction lengths. The possibility of other physical realizations involving spatio-temporal Airy wavepackets is also considered. As demonstrated in our experiments, these Airy beams can exhibit unusual features such as the ability to remain quasi-diffraction-free over long distances while their intensity features tend to freely accelerate during propagation. We have demonstrated experimentally that optical Airy beams propagating in free space can perform ballistic dynamics akin to those of projectiles moving under the action of gravity. The parabolic trajectories of these beams as well as the motion of their center of gravity were observed in good agreement with theory. Another remarkable property of optical Airy beams is their resilience in amplitude and phase perturbations. We show that this class of waves tends to reform during propagation in spite of the severity of the imposed perturbations. In all occasions the reconstruction of these beams is interpreted through their internal transverse power flow. The robustness of these optical beams in scattering and turbulent environments was also studied. The experimental observation of self-trapped Airy beams in unbiased nonlinear photorefractive media is also reported. This new class of non-local self-localized beams owes its existence to carrier diffusion effects as opposed to self-focusing. These finite energy Airy states exhibit a highly asymmetric intensity profile that is determined by the inherent properties of the nonlinear crystal. In addition, these wavepackets self-bend during propagation at an acceleration rate that is independent of the thermal energy associated with two-wave mixing diffusion photorefractive nonlinearity.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.