Voltage Controlled Intertwined Spiral Arrays for Reconfigurable Metasurfaces

Reconfigurable bistate metasurfaces composed of interwoven spiral arrays with embedded pin diodes are proposed for single and dual polarisation operation. The switching capability is enabled by pin diodes that change the array response between transmission and reflection modes at the specified frequencies. The spiral conductors forming the metasurface also supply the dc bias for controlling pin diodes, thus avoiding the need of additional bias circuitry that can cause parasitic interference and affect the metasurface response. The simulation results show that proposed active metasurfaces exhibit good isolation between transmission and reflection states, while retaining excellent angular and polarisation stability with the large fractional bandwidth (FBW) inherent to the original passive arrays. © 2014 A. Vallecchi et al.

Optimizing geometric accuracy of four dimensional CT scans acquired using the wall and couch mounted Varian Real-Time Position Management camera systems

Objective:

The aim of this study was to identify sources of anatomical misrepresentation due to the location of camera mounting, tumour motion velocity and image processing artefacts in order to optimise the 4DCT scan protocol and improve geometrical-temporal accuracy.

A phantom with an imaging insert was driven with a sinusoidal superior-inferior motion of varying amplitude and period for 4DCT scanning. The length of a high density cube within the insert was measured using treatment planning software to determine the accuracy of its spatial representation. Scan parameters were varied including the tube rotation period and the cine time between reconstructed images. A CT image quality phantom was used to measure various image quality signatures under the scan parameters tested.

No significant difference in spatial accuracy was found for 4DCT scans carried out using the wall mounted or couch mounted camera for sinusoidal target motion. Greater spatial accuracy was found for 4DCT scans carried out using a tube rotation speed of 0.5s rather than 1.0s. The reduction in image quality when using a faster rotation speed was not enough to require an increase in patient dose.

4DCT accuracy may be increased by optimising scan parameters, including choosing faster tube rotation speeds. Peak misidentification in the recorded breathing trace leads to spatial artefacts and this risk can be reduced by using a couch mounted infrared camera.

This study explicitly shows that 4DCT scan accuracy is improved by scanning with a faster CT tube rotation speed.

Reconfigurable frequency selective surfaces with interleaved spiral slots

A new type of active frequency selective surface (AFSS) is proposed to realise a voltage controlled bi-state (transparent and reflecting) response at the specified frequencies. The bi-state switching is achieved by combining a passive array of interleaved spiral slots in conducting screens and active dipole arrays with integrated pin diodes at the opposite sides of a thin dielectric substrate. Simulation results show that such active surfaces have high isolation between the transparency and reflection states, while retaining the merits of substantially sub-wavelength response of the unit cell and large fractional bandwidths (FBWs) inherent to the original passive interwoven spiral arrays. Potential applications include reconfigurable and controllable electromagnetic architecture of buildings.

Analytical model of interwoven spiral arrays

Interweaving planar spiral conductors in doubly periodic arrays enable substantially sub-wavelength resonant response along with broadening fractional bandwidth. A self-contained analytical model is proposed to accurately predict the characteristics of the intertwined quadrifilar spiral array near the fundamental resonance. The model, based upon a multiconductor transmission line (MTL) approach, provides physical insight into the unique properties of the distributed interactions between the interleaved counter-wound spiral arms extended beyond a single unit cell and elucidates the mechanisms underlying the array performance at normal and oblique incidence of TE and TM polarised waves. The developed MTL model is instrumental in the design of the artificial surfaces with the specified response.

Active singly and dual polarised interwoven spiral frequency selective surfaces

Reconfigurable bi-state interwoven spiral FSSs are explored in this work. Their switching capability is realized by pin diodes that enable the change of the electromagnetic response between transparent and reflecting modes at the specified frequencies in both singly and dual polarised unit cell configurations. The proposed topologies are single layer FSS with their elements acting also as dc current carrying conductors supplying the bias signal for switching pin diodes between the on and off states, thus avoiding the need of external bias lines that can cause parasitic resonances and affect the response at oblique incidence. The presented simulation results show that such active FSSs have potentially good isolation between the transmission and reflection states, while retaining the substantially subwavelength response of the unit cell with large fractional bandwidths (FBWs) inherent to the original passive FSSs.

Interwoven spiral arrays on ferrite-dielectric substrates for high-impedance metasurfaces

A high impedance metasurface (HIMS) composed of the arrays of intertwined planar spirals on thin (~0.1λ) ferrite-dielectric substrate is proposed. The HIMS exhibits fractional bandwidth in excess of 10% and excellent angular and polarisation stability of the circular polarised waves at oblique incidence.

Performance of Archimedean spiral antenna backed by FSS reflector

The use of a backing cavity composed of a frequency selective surface (FSS) above a metal plate as a means to suppress the back lobe radiation and increase the gain of an Archimedean spiral antenna that operates from 3 to 10 GHz is investigated. The FSS is designed to reflect signals in the upper band (7-10 GHz) with a loss of <;0.25 dB, and allow transmission in the lower band (3-6 GHz). Good impedance match and bidirectional to unidirectional beam transformation is obtained when the FSS and metal plate are inserted at a distance λ/4 below the spiral at the centre of the upper and lower bands, respectively. Simulated and measured radiation patterns are employed to show the performance enhancement, which is attributed to the FSS reflector.

On-line cone beam CT image guidance for vocal cord tumor targeting

Background and purpose: We are developing a technique for highly focused vocal cord irradiation in early glottic carcinoma to optimally treat a target volume confined to a single cord. This technique, in contrast with the conventional methods, aims at sparing the healthy vocal cord. As such a technique requires sub-mm daily targeting accuracy to be effective, we investigate the accuracy achievable with on-line kV-cone beam CT (CBCT) corrections. Materials and methods: CBCT scans were obtained in 10 early glottic cancer patients in each treatment fraction. The grey value registration available in X-ray volume imaging (XVI) software (Elekta, Synergy) was applied to a volume of interest encompassing the thyroid cartilage. After application of the thus derived corrections, residue displacements with respect to the planning CT scan were measured at clearly identifiable relevant landmarks. The intra- and inter-observer variations were also measured. Results: While before correction the systematic displacements of the vocal cords were as large as 2.4 ± 3.3 mm (cranial-caudal population mean ± SD Σ), daily CBCT registration and correction reduced these values to less than 0.2 ± 0.5 mm in all directions. Random positioning errors (SD σ) were reduced to less than 1 mm. Correcting only for translations and not for rotations did not appreciably affect this accuracy. The residue random displacements partly stem from intra-observer variations (SD = 0.2-0.6 mm). Conclusion: The use of CBCT for daily image guidance in combination with standard mask fixation reduced systematic and random set-up errors of the vocal cords to <1 mm prior to the delivery of each fraction dose. Thus, this facilitates the high targeting precision required for a single vocal cord irradiation. © 2009 Elsevier Ireland Ltd. All rights reserved.

Four-dimensional CT analysis of vocal cords mobility for highly focused single vocal cord irradiation

Background and Purpose: To quantify respiratory motion of the vocal cords during normal respiration using 4D-CT. The final goal is to develop a technique for single vocal cord irradiation (SVCI) in early glottic carcinoma. Sparing the non-involved cord and surrounding structures has the potential to preserve voice quality and allow re-irradiation of recurrent and second primary tumors. Material and methods: Four-dimensional CTs of 1 mm slice thickness from 10 early glottic carcinoma patients were acquired. The lateral dimensions of the air gap separating the vocal cords were measured anteriorly, at mid-level and posteriorly at each phase of the 4D-CTs. The corresponding anterior-posterior gaps were similarly measured. Cranio-caudal vocal cords movements during breathing were derived from the shifts of the arythenoids. Results: The population-averaged mean gap size ± the corresponding standard deviation due to breathing (SD_B) for the lateral gaps was 5.8 ± 0.7 mm anteriorly, 8.7 ± 0.9 mm at mid-level, and 11.0 ± 1.3 mm posteriorly. Anterior-posterior gap values were 21.7 ± 0.7 mm, while cranio-caudal shift SD_B was 0.8 mm. Conclusion: Vocal cords breathing motions were found to be small relative to their separation. Hence, breathing motion does not seem to be a limiting factor for SVCI. © 2008 Elsevier Ireland Ltd. All rights reserved.

Tri-Band HIS Backed Spiral Antenna for Wireless LAN Applications

This study reports the performance of an Archimedean spiral antenna, which exhibits unidirectional circularly polarized radiation patterns with a peak gain >8 dBic in the lower (2.4–2.485 GHz) and upper (5.15–5.35 and 5.725–5.875 GHz) Wireless local area network frequency bands. The required backlobe suppression and impedance match are obtained by placing a multiresonant high impedance surface (HIS) in close proximity to the radiating aperture. Simulated and measured radiation patterns are shown at the center frequency of all three channels and a comparison of the key performance metrics is made with free space and metal backed antenna arrangements to demonstrate the enhancements which are attributed to the HIS reflector.

Caught in a 'spiral': barriers to healthy eating and dietary health promotion needs from the perspective of unemployed young people and their service providers

The number of young people in Europe who are not in education, employment or training (NEET) is increasing. Given that young people from disadvantaged backgrounds tend to have diets of poor nutritional quality, this exploratory study sought to understand barriers and facilitators to healthy eating and dietary health promotion needs of unemployed young people aged 16-20 years. Three focus group discussions were held with young people (n=14). Six individual interviews and one paired interview with service providers (n=7). Data were recorded, transcribed verbatim and thematically content analysed. Themes were then fitted to social cognitive theory (SCT). Despite understanding of the principles of healthy eating, a ‘spiral’ of interrelated social, economic and associated psychological problems was perceived to render food and health of little value and low priority for the young people. The story related by the young people and corroborated by the service providers was of a lack of personal and vicarious experience with food. External, environmental factors such as the proliferation and proximity of fast food outlets and the high perceived cost of ‘healthy’ compared to ‘junk’ food rendered the young people low in self-efficacy and perceived control to make healthier food choices. Agency was instead expressed through consumption of junk food and substance abuse. Both the young people and service providers agreed that for dietary health promotion efforts to succeed, social problems needed addressed and agency encouraged through (individual and collective) active engagement of the young people themselves.

PET/CT imaging for target volume delineation in curative intent radiotherapy of non-small cell lung cancer: IAEA consensus report 2014

This document describes best practice and evidence based recommendations for the use of FDG-PET/CT for the purposes of radiotherapy target volume delineation (TVD) for curative intent treatment of non-small cell lung cancer (NSCLC). These recommendations have been written by an expert advisory group, convened by the International Atomic Energy Agency (IAEA) to facilitate a Coordinated Research Project (CRP) aiming to improve the applications of PET based radiation treatment planning (RTP) in low and middle income countries. These guidelines can be applied in routine clinical practice of radiotherapy TVD, for NSCLC patients treated with concurrent chemoradiation or radiotherapy alone, where FDG is used, and where a calibrated PET camera system equipped for RTP patient positioning is available. Recommendations are provided for PET and CT image visualization and interpretation, and for tumor delineation using planning CT with and without breathing motion compensation.

Conical Horn Antenna with Spiral Phase Plate for Difference Pattern Generation

This paper describes the performance characteristics and experimental validation of a compact conical horn antenna with a dielectric cylinder spiral phase plate attached at its aperture. This performs the function of a spatial phase imprinting device creating a helical wave-front which results in a null in the far field radiation pattern of the antenna assembly.