Far field subwavelength source resolution using Phase Conjugating Lens Assisted With Evanescent-to-Propagating Spectrum Conversion

The imaging properties of a phase conjugating lens operating in the far field zone of the imaged source and augmented with scatterers positioned in the source near field region are theoretically studied in this paper. The phase conjugating lens consists of a double sided 2D assembly of straight wire elements, individually interconnected through phase conjugation operators. The scattering elements are straight wire segments which are loaded with lumped impedance loads at their centers. We analytically and numerically analyze all stages of the imaging process; i) evanescent-to-propagating spectrum conversion; ii) focusing properties of infinite or finite sized phase conjugating lens; iii) source reconstruction upon propagating-to-evanescent spectrum conversion. We show that the resolution that can be achieved depends critically on the separation distance between the imaged source and scattering arrangement, as well as on the topology of the scatterers used. Imaged focal widths of up to one-seventh wavelength are demonstrated. The results obtained indicate the possibility of such an arrangement as a potential practical means for realising using conventional materials devices for fine feature extraction by electromagnetic lensing at distances remotely located from the source objects under investigation

Frequency selective surface using nested split ring slot elements as a lens with mechanically reconfigurable beam steering capability

The design is described of a double layer frequency selective surface which can produce a differential phase shift of 180 ° as the wave propagates through it at normal incidence. The hand of an applied circularly polarized signal is reversed due to the 180° phase shift, and it is demonstrated that the exit circularly polarized output signal can be phase advanced or phase retarded by 180 ° upon rotation of the elements comprising the structure. This feature allows the surface to act as a spatial phase shifter. In this paper the beam steering capabilities of a 10 × 10 array of such elements are demonstrated. Here the individual elements comprising the array are rotated relative to each other in order to generate a progressive phase shift. At normal incidence the 3 dB Axial Ratio Bandwidth for LHCP to RHCP conversion is 5.3% and the insertion loss was found to be -2.3 dB, with minimum axial ratio of 0.05 dB. This array is shown to be able to steer a beam from -40 ° to +40 ° while holding axial ratio at the pointing angle to below 4 dB. The measured radiation patterns match the theoretical calculation and full-wave simulation results. © 2010 IEEE.

The Influence of Friction Stir Welding Process Idealization on Residual Stress and Distortion Predictions for Future Airframe Assembly Simulations

The ability to accurately predict residual stresses and resultant distortions is a key product from process assembly simulations. Assembly processes necessarily consider large structural components potentially making simulations computationally expensive. The objective herein is to develop greater understanding of the influence of friction stir welding process idealization on the prediction of residual stress and distortion and thus determine the minimum required modeling fidelity for future airframe assembly simulations. The combined computational and experimental results highlight the importance of accurately representing the welding forging force and process speed. In addition, the results emphasize that increased CPU simulation times are associated with representing the tool torque, while there is potentially only local increase in prediction fidelity.

Retrodirective Rotman Lens Constraining Factors

The mechanism by which a retrodirective Rotman lens operates is examined theoretically and prediction is compared with measurement. By deriving the reflection matrix based on the phase delay relationship between the beam ports and the array ports we show that if the phase delay difference between neighbouring ports is constrained in a particular way that the reflection matrix becomes an inverse diagonal matrix and the Rotman lens functions as a Van Atta Array hence can perform retrodirective reflection. Further, the primary factors governing the bandwidth and beam pointing error of the lens are elaborated.

Rotman lens based-retrodirective array

A new type of broadband retrodirective array, which has been constructed using a microstrip Rotman lens, is presented. Automatic tracking of targets is obtained by exploiting the conjugate phase response of the beamforming network which is exhibited when the input ports are terminated with either open or short circuits. In addition, the true time-delay property of the Rotman lens gives broadband operation of the self-tracking array when used in conjunction with Vivaldi antennas. The simulated and measured bistatic and monostatic radar cross-section (RCS) patterns of a structure consisting of 13 beamports and 12 array ports are presented at frequencies in the range 8-12 GHz. Significantly enhanced RCS within the scan coverage ±40° is demonstrated by comparing the retrodirective behavior of a 12-element Vivaldi array terminated with and without the Rotman lens. © 2006 IEEE.

Reconfigurable beam forming using phase-aligned Rotman lens

The authors describe how a standard Rotman lens design can be readily adapted in order to allow reconfigurable beam
forming. This is achieved by applying concurrent excitations to the modified Rotman lens. A rationale for the design and
underlying behaviour of the modified, phase-aligned, Rotman lens as well as the deficiencies of a conventional Rotman lens
in this mode of operation are provided. Simulated and measured results are provided in order to illustrate the feasibility of the
approach suggested.

Investigation of the effect of simulated lens yellowing, transparency loss and refractive error on in vivo resonance Raman spectroscopy

To separately investigate the impact of simulated age-related lens yellowing, transparency loss and refractive error on measurements of macular pigment (MP) using resonance Raman spectroscopy.

Surface localisation of photosensitisers on intraocular lens biomaterials for prevention of infectious endophthalmitis and retinal protection

Cataract surgery is one of the most commonly-practiced surgical procedures in Western medicine, and, while complications are rare, the most serious is infectious postoperative endophthalmitis. Bacteria may adhere to the implanted intraocular lens (IOL) and subsequent biofilm formation can lead to a chronic, difficult to treat infection. To date, no method to reduce the incidence of infectious endophthalmitis through bacterial elimination, while retaining optical transparency, has been reported. In this study we report a method to optimise the localisation of a cationic porphyrin at the surface of suitable acrylate copolymers, which is the first point of contact with potential pathogens. The porphyrin catalytically generates short-lived singlet oxygen, in the presence of visible light, which kills adherent bacteria indiscriminately. By restricting the photosensitiser to the surface of the biomaterial, reduction in optical transparency is minimised without affecting efficacy of singlet oxygen production. Hydrogel IOL biomaterials incorporating either methacrylic acid (MAA) or methyl methacrylate (MMA) co-monomers allow tuning of the hydrophobic and anionic properties to optimise the localisation of porphyrin. Physiochemical and antimicrobial properties of the materials have been characterised, giving candidate materials with self-generating, persistent anti-infective character against Gram-positive and Gram-negative organisms. Importantly, incorporation of porphyrin can also serve to protect the retina by filtering damaging shortwave visible light, due to the Soret absorption (?max) 430 nm). © 2012 Elsevier Ltd. All rights reserved.

Through the lens of the hospital magazine - Downshire and Holywell psychiatric hospitals in the 1960s and 1970s

An exploration of the pages of two psychiatric hospital magazines, Speedwell from Holywell Hospital, Antrim, and The Sketch from Downshire Hospital, Downpatrick, reveals the activity filled lives of patients and staff during the 1960s and 1970s. This was a time of great change in mental health care. It was also a time of political turbulence in Northern Ireland. With large in-patient populations, both hospitals had a range of occupational and sporting activities available to patients and staff. The magazines formed part of the effort to promote the ethos of a therapeutic community. While hospital magazines may be viewed as one aspect of an institutional system that allowed people to cut themselves from the wider society, they also provided opportunities for budding writers to express their views on life in a hospital from the service user perspective. As such they offer some valuable insights into the lives of psychiatric patients.