Full-wave simulations of electromagnetic cloaking structures

Based on a coordinate transformation approach, Pendry {\it et al.} have reported electromagnetically anisotropic and inhomogeneous shells that, in theory, completely shield an interior structure of arbitrary size from electromagnetic fields without perturbing the external fields. We report full-wave simulations of the cylindrical version of this cloaking structure using ideal and nonideal (but physically realizable) electromagnetic parameters in an effort to understand the challenges of realizing such a structure in practice. The simulations indicate that the performance of the electromagnetic cloaking structure is not especially sensitive to modest permittivity and permeability variations. This is in contrast to other applications of engineered electromagnetic materials, such as subwavelength focusing using negative refractive index materials. The cloaking performance degrades smoothly with increasing loss, and effective low-reflection shielding can be achieved with a cylindrical shell composed of an eight (homogeneous) layer approximation of the ideal continuous medium

Design of Electromagnetic Cloaks and Concentrators Using Form-Invariant Coordinate Transformations of Maxwell's Equations

The technique of applying form-invariant, spatial coordinate transformations of Maxwell's equations can facilitate the design of structures with unique electromagnetic or optical functionality. Here, we illustrate the transformation-optical approach in the designs of a square electromagnetic cloak and an omni-directional electromagnetic field concentrator. The transformation equations are described and the functionality of the devices is numerically confirmed by two-dimensional finite element simulations. The two devices presented demonstrate that the transformation optic approach leads to the specification of complex, anisotropic and inhomogeneous materials with well directed and distinct electromagnetic behavior.Comment: submitted to "Photonics and Nanostructures", Special Issue "PECS VII", Elsevie

Cut-wire-pair structures as two-dimensional magnetic metamaterials

We study numerically and experimentally magnetic metamaterials based on cut-wire pairs instead of split-ring resonators. The cut-wire pair planar structure is extended in order to create a truly two-dimensional metamaterial suitable for scaling to optical frequencies. We fabricate the cut-wire metamaterial operating at microwave frequencies with lattice spacing around 10% of the free-space wavelength, and find good agreement with direct numerical simulations. Unlike the structures based on split-ring resonators, the nearest-neighbor coupling in cut-wire pairs can result in a magnetic stop-band with propagation in the transverse direction

Optical design of reflectionless complex media by finite embedded coordinate transformations

Transformation optics offers an unconventional approach to the control of electromagnetic fields. A transformation optical structure is designed by first applying a form-invariant coordinate transform to Maxwell's equations, in which part of free space is distorted in some desired manner. The coordinate transformation is then applied to the permittivity and permeability tensors to yield the specification for a complex medium with desired functionality. The transformation optical structures proposed to date, such as electromagnetic "invisibility" cloaks and concentrators, are inherently reflectionless and leave the transmitted wave undisturbed. Here we expand the class of transformation optical structures by introducing finite, embedded coordinate transformations, which allow the electromagnetic waves to be steered or focused. We apply the method to the design of several devices, including a parallel beam shifter and a beam splitter, both of which exhibit unusual electromagnetic behavior as confirmed by 2D full-wave simulations. The devices are designed to be reflectionless, in accordance with a straightforward topological criterion.Comment: submitted to the journal on Sep 10 2007, abstract changed to make it more accessible, keywords adde

Social, systemic, individual-medical or cultural? Questionnaire on the concepts of disability among teacher education students

The individual-medical concept of disability, whereby disability is believed to be caused by some intractable impairment, is perhaps the most widely held view in society. However, other concepts exist with which teachers in inclusive schools should be familiar (e.g., social, systemic), to better inform teacher behavior, attitudes and understanding. We therefore developed an instrument to capture education students’ concepts of disability. We constructed the questionnaire according to four theoretical models of disability (individual-medical, social, systemic, and cultural concepts), which are commonly used in inclusive teacher education, and validated this on a sample of 775 education students. Additionally, we administered the Attitudes towards Inclusion Scale (AIS) and measured key demographic variables. The instruments, data and analysis code used are available online at https://osf.io/dm4cs/. After dropping redundant items, a shortened form of the questionnaire contained 16 items, with satisfactory psychometric values for scales pertaining to four concepts of disability (CFI = 0.963, TLI = 0.955, RMSEA = 0.037, SRMR = 0.039). These four concepts of disability showed small correlations with the AIS, indicating that our questionnaire measured an independent construct. The more experience education students had with disability and the more courses they had attended on inclusive education, the more likely they were to agree with the social concept of disability. The questionnaire shows promise in measuring concepts of disability and might be used to stimulate students’ critical reflection during teacher education

Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators

Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies. We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance, and tested these on organic light-emitting diodes. By exploiting both the fundamental and higher-harmonic modes of the resonators we cover almost five octaves in resonance frequency within a single setup. The measurements with a common pi-conjugated polymer as the active material reveal small but non-negligible effects of spin-orbit interactions, which give rise to a broadening of the magnetic resonance spectrum with increasing frequency

Sonderpädagogische Diagnostik. Eine Einführung

Sonderpädagogische Diagnostik greift auf unterschiedliche Theorien, Konzepte und Methoden aus den Bereichen der Medizin, Psychologie und Pädagogik zurück. Daher liegen den meisten Einführungswerke zur pädagogischen und zu sonderpädagogischen Diagnostik Konzepte der klinischen, pädagogischen oder entwicklungsbezogenen Psychologie zugrunde, welche in den Bereich der Schule oder der Sonderpädagogik übertragen werden. Diese Konzepte werden im Einführungskapitel dargestellt

Unleashing renewable energy power in developing countries: Proposal for a global renewable energy policy fund

The document argues that renewable energy policies have not been implemented in the developing world due to financial costs, and also that the Clean Developing Mechanism of the Kyoto Protocol has been ineffective. The document proposes the use of Feed-In Tariff policies, and the use of a renewable energy policy fund

Broadband Wide Angle Lens Implemented with Dielectric Metamaterials

The Luneburg lens is a powerful imaging device, exhibiting aberration free focusing for parallel rays incident from any direction. However, its advantages are offset by a focal surface that is spherical and thus difficult to integrate with standard planar detector and emitter arrays. Using the recently developed technique of transformation optics, it is possible to transform the curved focal surface to a flat plane while maintaining the perfect focusing behavior of the Luneburg over a wide field of view. Here we apply these techniques to a lesser-known refractive Luneburg lens and implement the design with a metamaterial composed of a semi-crystalline distribution of holes drilled in a dielectric. In addition, we investigate the aberrations introduced by various approximations made in the implementation of the lens. The resulting design approach has improved mechanical strength with small aberrations and is ideally suited to implementation at infrared and visible wavelengths