| 1. |
- Glasbey, JC, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
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| 3. |
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| 4. |
- Pezzotta, A., et al.
(författare)
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Euclid preparation XLI. Galaxy power spectrum modelling in real space
- 2024
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 687
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the accuracy of the perturbative galaxy bias expansion in view of the forthcoming analysis of the Euclid spectroscopic galaxy samples. We compare the performance of a Eulerian galaxy bias expansion using state-of-the-art prescriptions from the effective field theory of large-scale structure (EFTofLSS) with a hybrid approach based on Lagrangian perturbation theory and high-resolution simulations. These models are benchmarked against comoving snapshots of the flagship I N-body simulation at z = (0.9, 1.2, 1.5, 1.8), which have been populated with H alpha galaxies leading to catalogues of millions of objects within a volume of about 58 h(-3) Gpc(3). Our analysis suggests that both models can be used to provide a robust inference of the parameters (h, omega c) in the redshift range under consideration, with comparable constraining power. We additionally determine the range of validity of the EFTofLSS model in terms of scale cuts and model degrees of freedom. From these tests, it emerges that the standard third-order Eulerian bias expansion - which includes local and non-local bias parameters, a matter counter term, and a correction to the shot-noise contribution - can accurately describe the full shape of the real-space galaxy power spectrum up to the maximum wavenumber of k(max) = 0.45 h Mpc(-1), and with a measurement precision of well below the percentage level. Fixing either of the tidal bias parameters to physically motivated relations still leads to unbiased cosmological constraints, and helps in reducing the severity of projection effects due to the large dimensionality of the model. We finally show how we repeated our analysis assuming a volume that matches the expected footprint of Euclid, but without considering observational effects, such as purity and completeness, showing that we can get constraints on the combination (h, omega c) that are consistent with the fiducial values to better than the 68% confidence interval over this range of scales and redshifts.
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| 5. |
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| 6. |
- Horsley, S. A. R., et al.
(författare)
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Removing singular refractive indices with sculpted surfaces
- 2014
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 4876-
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Tidskriftsartikel (refereegranskat)abstract
- The advent of Transformation Optics established the link between geometry and material properties, and has resulted in a degree of control over electromagnetic fields that was previously impossible. For waves confined to a surface it is known that there is a simpler, but related, geometrical equivalence between the surface shape and the refractive index, and here we demonstrate that conventional devices possessing a singularity-that is, the requirement of an infinite refractive index-can be realised for waves confined to an appropriately sculpted surface. In particular, we redesign three singular omnidirectional devices: the Eaton lens, the generalized Maxwell Fish-Eye, and the invisible sphere. Our designs perfectly reproduce the behaviour of these singular devices, and can be achieved with simple isotropic media of low refractive index contrast.
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| 7. |
- Mitchell-Thomas, R. C., et al.
(författare)
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Broadband Metasurface for Surface Wave Lenses
- 2016
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Ingår i: 2016 URSI INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC THEORY (EMTS). - : IEEE. - 9781509025022 ; , s. 605-606
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Konferensbidrag (refereegranskat)abstract
- This paper presents the design of a metasurface that exhibits glide symmetry. This allows the metasurface to support a mode that is confined to the surface for a broad band of frequencies. In addition it is shown that the mode index of such surfaces depends only weakly on the frequency over a given range. We then propose these structures as a practical solution to the fabrication of broadband surface-wave lenses designed using quasi-conformal transformation optics technique.
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| 8. |
- Rolles, D., et al.
(författare)
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Femtosecond x-ray photoelectron diffraction on gas-phase dibromobenzene molecules
- 2014
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 47:12
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Tidskriftsartikel (refereegranskat)abstract
- We present time-resolved femtosecond photoelectron momentum images and angular distributions of dissociating, laser-aligned 1,4-dibromobenzene (C6H4Br2) molecules measured in a near-infrared pump, soft-x-ray probe experiment performed at an x-ray free-electron laser. The observed alignment dependence of the bromine 2p photoelectron angular distributions is compared to density functional theory calculations and interpreted in terms of photoelectron diffraction. While no clear time-dependent effects are observed in the angular distribution of the Br(2p) photoelectrons, other, low-energy electrons show a pronounced dependence on the time delay between the near-infrared laser and the x-ray pulse.
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| 9. |
- Hardisty, Alex R., et al.
(författare)
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BioVeL: A virtual laboratory for data analysis and modelling in biodiversity science and ecology
- 2016
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Ingår i: BMC Ecology. - : Springer Science and Business Media LLC. - 1472-6785. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 The Author(s).Background: Making forecasts about biodiversity and giving support to policy relies increasingly on large collections of data held electronically, and on substantial computational capability and capacity to analyse, model, simulate and predict using such data. However, the physically distributed nature of data resources and of expertise in advanced analytical tools creates many challenges for the modern scientist. Across the wider biological sciences, presenting such capabilities on the Internet (as "Web services") and using scientific workflow systems to compose them for particular tasks is a practical way to carry out robust "in silico" science. However, use of this approach in biodiversity science and ecology has thus far been quite limited. Results: BioVeL is a virtual laboratory for data analysis and modelling in biodiversity science and ecology, freely accessible via the Internet. BioVeL includes functions for accessing and analysing data through curated Web services; for performing complex in silico analysis through exposure of R programs, workflows, and batch processing functions; for on-line collaboration through sharing of workflows and workflow runs; for experiment documentation through reproducibility and repeatability; and for computational support via seamless connections to supporting computing infrastructures. We developed and improved more than 60 Web services with significant potential in many different kinds of data analysis and modelling tasks. We composed reusable workflows using these Web services, also incorporating R programs. Deploying these tools into an easy-to-use and accessible 'virtual laboratory', free via the Internet, we applied the workflows in several diverse case studies. We opened the virtual laboratory for public use and through a programme of external engagement we actively encouraged scientists and third party application and tool developers to try out the services and contribute to the activity. Conclusions: Our work shows we can deliver an operational, scalable and flexible Internet-based virtual laboratory to meet new demands for data processing and analysis in biodiversity science and ecology. In particular, we have successfully integrated existing and popular tools and practices from different scientific disciplines to be used in biodiversity and ecological research.
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| 10. |
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| 11. |
- Mitchell-Thomas, R. C., et al.
(författare)
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Lenses on curved surfaces
- 2014
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 39:12, s. 3551-3554
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Tidskriftsartikel (refereegranskat)abstract
- This Letter presents a theory that allows graded index lenses to be mapped onto arbitrary rotationally symmetric curved surfaces. Examples of the Luneburg and Maxwell fish-eye lens are given, for numerous surfaces, always resulting in isotropic permittivity requirements. The performance of these lenses is initially illustrated with full-wave simulations utilizing a waveguide structure. A transformation of the refractive index profiles is then performed to design surface-wave lenses, where the dielectric layer is not only isotropic but also homogenous, demonstrating the applicability and ease of fabrication.
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| 12. |
- Mitchell-Thomas, R. C., et al.
(författare)
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Omnidirectional surface wave cloak using an isotropic homogeneous dielectric coating
- 2016
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The field of transformation optics owes a lot of its fame to the concept of cloaking. While some experimental progress has been made towards free-space cloaking in three dimensions, the material properties required are inherently extremely difficult to achieve. The approximations that then have to be made to allow fabrication produce unsatisfactory device performance. In contrast, when surface wave systems are the focus, it has been shown that a route distinct from those used to design free-space cloaks can be taken. This results in very simple solutions that take advantage of the ability to incorporate surface curvature. Here, we provide a demonstration in the microwave regime of cloaking a bump in a surface. The distortion of the shape of the surface wave fronts due to the curvature is corrected with a suitable refractive index profile. The surface wave cloak is fabricated from a metallic backed homogeneous dielectric waveguide of varying thickness, and exhibits omnidirectional operation.
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| 13. |
- Mitchell-Thomas, R. C., et al.
(författare)
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The anti-fish eye cloak for surface wave antennas
- 2014
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Ingår i: 8th European Conference on Antennas and Propagation, EuCAP 2014. - 9788890701849 ; , s. 267-268
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Konferensbidrag (refereegranskat)abstract
- In this paper a new lens, named the anti-fish eye lens, is proposed and its relation to the Maxwell fish eye lens is described. This novel lens is then applied to cloak an object positioned underneath it, to electromagnetic waves that are confined to the surface. The performance of the lens in reforming the cylindrical wave fronts is illustrated with numerical simulations. This lens has direct applications for surface wave antennas that are conformal to curved structures to remove the influence of the curvature, the consequence of which would detrimentally affect the directivity because of the distortion of the wavefronts. Therefore, using this technique, the performance of surface wave antennas on curved surfaces can be equivalent to those on flat surfaces.
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| 14. |
- Quevedo-Teruel, Oscar, et al.
(författare)
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Conformal surface lenses from a bed of nails
- 2014
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Ingår i: 8th European Conference on Antennas and Propagation, EuCAP 2014. - 9788890701849 ; , s. 269-270
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Konferensbidrag (refereegranskat)abstract
- This paper presents a validation of a fast method for calculating the propagation constant of a periodic bed of nails structure. These results are compared to full wave simulation results, showing good agreement. This method is then employed to design a Luneburg lens which is conformal to the surface of a sphere. The index distribution required to create this conformal lens was calculated using an optical path technique. This work has applications for the design of communication systems for vehicles and airborne platforms.
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| 15. |
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| 16. |
- Benjet, Corina, et al.
(författare)
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A longitudinal study on the impact of Internet gaming disorder on self‐perceived health, academic performance, and social life of first‐year college students
- 2023
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Ingår i: American Journal on Addictions. - : John Wiley & Sons. - 1055-0496 .- 1521-0391. ; 32:4, s. 343-351
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Tidskriftsartikel (refereegranskat)abstract
- Background and objectives: Internet gaming disorder (IGD) is associated with health, social, and academic problems but whether these are consequences of the disorder rather than precursors or correlates is unclear. We aimed to evaluate whether IGD in the 1st year of university predicts health, academic and social problems 1 year later, controlling for baseline health, academic and social problems, demographics, and mental health symptoms.Methods: In a prospective cohort study, 1741 university students completed both a baseline online survey in their 1st year and a follow-up survey 1 year later. Log-binomial models examined the strength of prospective associations between baseline predictor variables (IGD, baseline health, academic and social problems, sex, age, and mental health symptoms) and occurrence of health, academic and social problems at follow-up.Results: When extensively adjusted by the corresponding outcome at baseline, any mental disorder symptoms, sex, and age, baseline IGD was associated only with severe school impairment and poor social life (risk ratio [RR] = 1.77; 95% confidence interval [CI] = 1.14-2.75, p = .011; RR = 1.22; 95% CI = 1.07-1.38, p = .002, respectively).Conclusions and scientific significance: University authorities and counselors should consider that incoming 1st-year students that meet criteria for IGD are likely to have increased academic and social impairments during their 1st year for which they may want to intervene. This study adds to the existing literature by longitudinally examining a greater array of negative outcomes of IGD than previously documented.
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| 17. |
- Chen, Qiao, et al.
(författare)
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A General Solution for Double-Layer Gradient-Index and Geodesic Lenses with Rotational Symmetry
- 2023
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Ingår i: 2023 17TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION, EUCAP. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- A double-layer lens consists of a pair of rotationally symmetric index profiles or geodesic lens shapes connected by a reflecting mirror partially covering their common periphery. Such a lens can provide a focus in each layer, and a wave travelling between the foci explores both layers. Here, we concentrate on the case with one layer being homogeneous or flat, and derive a general solution for the lens profiles by solving a Luneburg-like inverse problem with pre-specified foci inside or outside the lens, and different background indices in two layers. We demonstrate four examples of interest in ray-tracing plots. These lenses may find application in communications, sensing, and imaging from millimeter waves up to the optical bands.
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| 18. |
- Chen, Qiao, et al.
(författare)
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Double-layer geodesic and gradient-index lenses
- 2022
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- A double-layer lens consists of a first gradient-index/geodesic profile in an upper waveguide, partially surrounded by a mirror that reflects the wave into a lower guide where there is a second profile. Here, we derive a new family of rotational-symmetric inhomogeneous index profiles and equivalent geodesic lens shapes by solving an inverse problem of pre-specified focal points. We find an equivalence where single-layer lenses have a different functionality as double-layer lenses with the same profiles. As an example, we propose, manufacture, and experimentally validate a practical implementation of a geodesic double-layer lens that is engineered for a low-profile antenna with a compact footprint in the millimeter wave band. Its unique double-layer configuration allows for two-dimensional beam scanning using the same footprint as an extension of the presented design. These lenses may find applications in future wireless communication systems and sensing instruments in microwave, sub-terahertz, and optical domains. A double-layer lens consists of a first gradient-index/geodesic profile in an upper waveguide, partially surrounded by a mirror that reflects the wave into a lower guide where there is a second profile. A family of such lens profiles are derived.
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| 19. |
- Cordeddu, Viviana, et al.
(författare)
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Activating Mutations Affecting the Dbl Homology Domain of SOS2 Cause Noonan Syndrome
- 2015
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Ingår i: Human Mutation. - : WILEY-BLACKWELL. - 1059-7794 .- 1098-1004. ; 36:11, s. 1080-1087
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Tidskriftsartikel (refereegranskat)abstract
- The RASopathies constitute a family of autosomal-dominant disorders whose major features include facial dysmorphism, cardiac defects, reduced postnatal growth, variable cognitive deficits, ectodermal and skeletal anomalies, and susceptibility to certain malignancies. Noonan syndrome (NS), the commonest RASopathy, is genetically heterogeneous and caused by functional dysregulation of signal transducers and regulatory proteins with roles in the RAS/extracellular signal-regulated kinase (ERK) signal transduction pathway. Mutations in known disease genes account for approximately 80% of affected individuals. Here, we report that missense mutations altering Son of Sevenless, Drosophila, homolog 2 (SOS2), which encodes a RAS guanine nucleotide exchange factor, occur in a small percentage of subjects with NS. Four missense mutations were identified in five unrelated sporadic cases and families transmitting NS. Disease-causing mutations affected three conserved residues located in the Dbl homology (DH) domain, of which two are directly involved in the intramolecular binding network maintaining SOS2 in its autoinhibited conformation. All mutations were found to promote enhanced signaling from RAS to ERK. Similar to NS-causing SOS1 mutations, the phenotype associated with SOS2 defects is characterized by normal development and growth, as well as marked ectodermal involvement. Unlike SOS1 mutations, however, those in SOS2 are restricted to the DH domain.
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| 20. |
- Diallo, C. D., et al.
(författare)
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Parallel-plate-waveguide luneburg lens through a holey plate metasurface
- 2015
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Ingår i: 2015 9th European Conference on Antennas and Propagation, EuCAP 2015. - : IEEE. - 9788890701856
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Konferensbidrag (refereegranskat)abstract
- This paper presents a parallel plate waveguide (PPW) Luneburg lens designed using an array of subwavelength circular holes etched on a metallic plate printed on a dielectric substrate. Variation of the hole radius modulates the effective permittivity. The lens operates in the Ka band of frequencies in a quasi-TEM mode. Easy to implement and low cost, the lens could be a good candidate as a lens-like beamformer for low loss multiple beam applications.
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| 21. |
- Fernandez-Prieto, Armando, et al.
(författare)
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Glide Symmetry Applied to the Design of Common-Mode Rejection Filters Based on Complementary Split-Ring Resonators
- 2023
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Ingår i: IEEE Transactions on Circuits and Systems - II - Express Briefs. - : Institute of Electrical and Electronics Engineers (IEEE). - 1549-7747 .- 1558-3791. ; 70:6, s. 1911-1915
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Tidskriftsartikel (refereegranskat)abstract
- In this brief, glide symmetry is applied to design common-mode rejection filters based on defected ground structures with bandstop response. To this aim, complementary split-ring resonators are chosen as the basic components for common-mode rejection. To illustrate the advantages of using glide symmetry, three implementations are studied and compared. The results reveal that glide symmetry offers the best performance in terms of common-mode rejection level and fractional bandwidth. Furthermore, glide symmetry barely affects the integrity of the differential mode. A prototype of each of the considered symmetries has been designed, simulated, and tested for practical validation. Good agreement is observed between the simulated and measured results, experimentally demonstrating the advantages of glide symmetry.
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| 22. |
- Kunnus, K., et al.
(författare)
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Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)(5) to Fe(CO)(4)EtOH
- 2016
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 3:4
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Tidskriftsartikel (refereegranskat)abstract
- We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)(5) in ethanol solution. We propose mechanistic explanation for the parallel ultrafast intra-molecular spin crossover and ligation of the Fe(CO)(4) which are observed following a charge transfer photoexcitation of Fe(CO)(5) as reported in our previous study [ Wernet et al., Nature 520, 78 (2015)]. We find that branching of the reaction pathway likely happens in the (1)A(1) state of Fe(CO)(4). A sub-picosecond time constant of the spin crossover from B-1(2) to B-3(2) is rationalized by the proposed B-1(2) -> (1)A(1) -> B-3(2) mechanism. Ultrafast ligation of the B-1(2) Fe(CO)(4) state is significantly faster than the spin-forbidden and diffusion limited ligation process occurring from the B-3(2) Fe(CO)(4) ground state that has been observed in the previous studies. We propose that the ultrafast ligation occurs via B-1(2) -> (1)A(1) -> (1)A'Fe(CO)(4)EtOH pathway and the time scale of the (1)A(1) Fe(CO)(4) state ligation is governed by the solute-solvent collision frequency. Our study emphasizes the importance of understanding the interaction of molecular excited states with the surrounding environment to explain the relaxation pathways of photoexcited metal carbonyls in solution.
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| 23. |
- McCall, Martin, et al.
(författare)
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Roadmap on transformation optics
- 2018
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Ingår i: Journal of Optics. - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 20:6
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Forskningsöversikt (refereegranskat)abstract
- Transformation optics asks, using Maxwell's equations, what kind of electromagnetic medium recreates some smooth deformation of space? The guiding principle is Einstein's principle of covariance: that any physical theory must take the same form in any coordinate system. This requirement fixes very precisely the required electromagnetic medium. The impact of this insight cannot be overestimated. Many practitioners were used to thinking that only a few analytic solutions to Maxwell's equations existed, such as the monochromatic plane wave in a homogeneous, isotropic medium. At a stroke, transformation optics increases that landscape from 'few' to 'infinity', and to each of the infinitude of analytic solutions dreamt up by the researcher, there corresponds an electromagnetic medium capable of reproducing that solution precisely. The most striking example is the electromagnetic cloak, thought to be an unreachable dream of science fiction writers, but realised in the laboratory a few months after the papers proposing the possibility were published. But the practical challenges are considerable, requiring meta-media that are at once electrically and magnetically inhomogeneous and anisotropic. How far have we come since the first demonstrations over a decade ago? And what does the future hold? If the wizardry of perfect macroscopic optical invisibility still eludes us in practice, then what compromises still enable us to create interesting, useful, devices? While three-dimensional (3D) cloaking remains a significant technical challenge, much progress has been made in two dimensions. Carpet cloaking, wherein an object is hidden under a surface that appears optically flat, relaxes the constraints of extreme electromagnetic parameters. Surface wave cloaking guides sub-wavelength surface waves, making uneven surfaces appear flat. Two dimensions is also the setting in which conformal and complex coordinate transformations are realisable, and the possibilities in this restricted domain do not appear to have been exhausted yet. Beyond cloaking, the enhanced electromagnetic landscape provided by transformation optics has shown how fully analytic solutions can be found to a number of physical scenarios such as plasmonic systems used in electron energy loss spectroscopy and cathodoluminescence. Are there further fields to be enriched? A new twist to transformation optics was the extension to the spacetime domain. By applying transformations to spacetime, rather than just space, it was shown that events rather than objects could be hidden from view; transformation optics had provided a means of effectively redacting events from history. The hype quickly settled into serious nonlinear optical experiments that demonstrated the soundness of the idea, and it is now possible to consider the practical implications, particularly in optical signal processing, of having an 'interrupt-without-interrupt' facility that the so-called temporal cloak provides. Inevitable issues of dispersion in actual systems have only begun to be addressed. Now that time is included in the programme of transformation optics, it is natural to ask what role ideas from general relativity can play in shaping the future of transformation optics. Indeed, one of the earliest papers on transformation optics was provocatively titled 'General Relativity in Electrical Engineering'. The answer that curvature does not enter directly into transformation optics merely encourages us to speculate on the role of transformation optics in defining laboratory analogues. Quite why Maxwell's theory defines a 'perfect' transformation theory, while other areas of physics such as acoustics are not apparently quite so amenable, is a deep question whose precise, mathematical answer will help inform us of the extent to which similar ideas can be extended to other fields. The contributors to this Roadmap, who are all renowned practitioners or inventors of transformation optics, will give their perspectives into the field's status and future development.
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| 24. |
- Minelli, Caterina, et al.
(författare)
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Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles
- 2022
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 14, s. 4690-4704
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Tidskriftsartikel (refereegranskat)abstract
- We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles.
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| 25. |
- Mitchell-Thomas, R. C., et al.
(författare)
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Altering antenna radiation properties with transformation optics
- 2015
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Ingår i: 2015 9th European Conference on Antennas and Propagation, EuCAP 2015. - : IEEE conference proceedings. - 9788890701856
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Konferensbidrag (refereegranskat)abstract
- In this paper, the technique of quasi-conformal transformation optics is utilized to design lenses that can alter the radiation properties of common antennas. The performance of these lenses is simulated using numerical software and analysis shows that the directivity can be increased significantly, or the radiation patterns can be changed as desired. Therefore, using this technique, bespoke lenses can be designed that create complex radiation from simple antenna feed types, for a number of high-frequency applications.
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| 26. |
- Mitchell-Thomas, R. C., et al.
(författare)
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Transformation optics applied to antennas and focusing systems
- 2018
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Ingår i: Aperture Antennas for Millimeter and Sub-Millimeter Wave Applications. - Cham : Springer Science and Business Media Deutschland GmbH. ; , s. 387-406
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Bokkapitel (refereegranskat)abstract
- This chapter describes the way in which transformation optics can be used to design lens antennas. It begins with a brief introduction to the analytical method and describes the difficulties faced by practical applications, in terms of anisotropic material requirements and bandwidth restrictions. Two further variants of transformation optics are provided to circumvent these issues, which are the quasiconformal transformation technique, and non-Euclidean transformations for surface devices. The use of both these methods results in material property requirements that can be easily implemented with dielectrics. These two techniques are thoroughly described, with the benefits and drawbacks they present detailed. The discussion is supported throughout with a number of application examples in each section, which include planar lenses, bespoke lenses, curved surface wave lenses, and a surface wave cloak. Examples are chosen to illustrate the variety of ways in which transformation optics can be applied to antenna systems, and are all supplemented by simulation or measurement data.
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| 27. |
- Osipov, A. V., et al.
(författare)
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Flattened generalized Maxwell fish-eye lens limiting sub-unity refractive index regions
- 2015
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Ingår i: 2015 9th European Conference on Antennas and Propagation, EuCAP 2015. - : IEEE conference proceedings. - 9788890701856
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Konferensbidrag (refereegranskat)abstract
- In this paper we propose the designs of three wide- band flattened generalized Maxwell fish-eye lenses. The designs were performed using transformation optics with quasiconformal mapping. This transformation allows not only to arbitrarily shape the lenses preserving the same electromagnetic response, but also to reduce the sub-unity regions which limit the bandwidth of operation. These devices have practical applications as wide-angle scanner and power divider matched in terms of the shape with conventionally planar receiver/transceiver arrays.
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| 28. |
- Prado, Daniel R., et al.
(författare)
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Implementation of transformed lenses in bed of nails reducing refractive index maximum value and sub-unity regions
- 2015
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 40:6, s. 926-929
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Tidskriftsartikel (refereegranskat)abstract
- Transformation optics with quasi-conformal mapping is applied to design a Generalized Maxwell Fish-eye Lens (GMFEL) which can be used as a power splitter. The flattened focal line obtained as a result of the transformation allows the lens to adapt to planar antenna feeding systems. Moreover, sub-unity refraction index regions are reduced because of the space compression effect of the transformation, reducing the negative impact of removing those regions when implementing the lens. A technique to reduce the maximumvalue of the refractive index is presented to compensate for its increase because of the transformation. Finally, the lens is implemented with the bed of nails technology, employing a commercial dielectric slab to improve the range of the effective refractive index. The lens was simulated with a 3D full-wave simulator to validate the design, obtaining an original and feasible power splitter based on a dielectric lens. (C) 2015 Optical Society of America
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| 29. |
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| 30. |
- Valerio, Guido, et al.
(författare)
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Multimodal Transmission-Matrix Analysis of Microstrip Lines with Symmetric and Glide-Symmetric Periodic Loads
- 2023
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Ingår i: 2023 17th European Conference on Antennas and Propagation (EuCAP). - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- We perform a dispersive analysis of periodic microstrip lines by simulating a single unit cell and making use of the multimodal transmission matrix method. Transmission matrices involving one or more higher-order modes are used, and the results are compared with the analysis of a large number of unit cells and with a commercial electromagnetic software. The use of higher-order modes is found to be relevant in geometries with strong asymmetric cross sections, as happens in glide-symmetric microstrip lines.
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| 31. |
- Wernet, Philippe, et al.
(författare)
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Mapping chemical bonding of reaction intermediates with femtosecond X-ray laser spectroscopy
- 2013
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Ingår i: XVIIIth International Conference on Ultrafast Phenomena. - : EDP Sciences. - 9782759809561 ; , s. 05025-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We determine the pathways in the photo-dissociation reactions of Fe(CO)5 both in the gas phase and in solution by mapping the valence electronic structure of the reaction intermediates with femtosecond X-ray laser spectroscopy.
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| 32. |
- Zetterström, Oskar, et al.
(författare)
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Reducing the Dispersion of Periodic Structures with Twist and Polar Glide Symmetries
- 2017
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- In this article, a number of guiding structures are proposed which take advantage of higher symmetries to vastly reduce the dispersion. These higher symmetries are obtained by executing additional geometrical operations to introduce more than one period into the unit cell of a periodic structure. The specific symmetry operations employed here are a combination of p-fold twist and polar glide. Our dispersion analysis shows that a mode in a structure possessing higher symmetries is less dispersive than in a conventional structure. It is also demonstrated that, similar to the previously studied Cartesian glide-symmetric structures, polar glide-symmetric structures also exhibit a frequency independent response. Promising applications of these structures are leaky-wave antennas which utilize the low frequency dependence.
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