RAD Research and Education 2011

The annual report describes the main activities of the Department of Radio Science and Engineering (RAD) during the year 2011

Towards a systematic design of isotropic bulk magnetic metamaterials using the cubic point groups of symmetry

In this paper a systematic approach to the design of bulk isotropic magnetic metamaterials is presented. The role of the symmetries of both the constitutive element and the lattice are analyzed. For this purpose it is assumed that the metamaterial is composed by cubic SRR resonators, arranged in a cubic lattice. The minimum symmetries needed to ensure an isotropic behavior are analyzed, and some particular configurations are proposed. Besides, an equivalent circuit model is proposed for the considered cubic SRR resonators. Experiments are carried out in order to validate the proposed theory. We hope that this analysis will pave the way to the design of bulk metamaterials with strong isotropic magnetic response, including negative permeability and left-handed metamaterials.Comment: Submitted to Physical Review B, 23 page

Cloaking dielectric spherical objects by a shell of metallic nanoparticles

We show that dielectric spheres can be cloaked by a shell of amorphously arranged metallic nanoparticles. The shell represents an artificial medium with tunable effective properties that can be adjusted such that the scattered signals of shell and sphere almost cancel each other. We provide an analytical model for the cloak design and prove numerically that the cloak operates as desired. We show that more than 70% of the scattered signal of the sphere can be suppressed at the design wavelength. Advantages and disadvantages of such a cloak when compared to other implementations are disclosed.Comment: 14 pages, 6 figure

Simulation and data processing of GOMOS measurements

In this paper the data simulation and data inversion studies for stellar occultation measurements are discussed. The specific application is the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument which has been proposed for the first European Platform, Polar Orbiting Earth Mission (POEM-1)

Signs, curls, and time variations: learning to appreciate Faraday’s law

In this article, we present the analysis of a study on the development of conceptual understanding of dynamic electromagnetic fields of electrical engineering students in Finland. The focus of the study was teaching and understanding of Faraday’s law. A coil with two light-emitting diodes and a strong permanent magnet were used with which the induced electromotive force could be made visible. However, the field and flux directions, temporal changes, and topological constellations within this setting determine in a subtle manner the character of the resulting electric effect. The demonstration was used on electromagnetic field theory classes at Aalto University, Finland, to assess the conceptual understanding of the students. Drawing from the Peer Instruction principle, the students were asked to fill in a questionnaire concerning this experiment, first on their own, and once again after discussing with their neighbors in the classroom. They were asked about the direction of the electric force and the confidence of their answer. The results show that the answer is not very obvious: students tend to vote for the wrong answer. The Peer Instruction discussion greatly improves the situation. Also, the confidence of the students increases thanks to the discussion period with neighbors. The results, however, seem to be somewhat sensitive to the exact constellation and the administration of the experiment

Polarizability of a dielectric hemisphere

This article presents a method for solving the polarizability of a dielectric hemispherical object as a function of its relative electric permittivity. The polarizability of a hemisphere depends on the direction of the exciting electric field. Therefore, the polarizability can be written as a dyadic consisting of two components, the axial and the transversal polarizabilities, which can be solved separately. The solution is based on an analytical approach where the electrostatic potential function is written as a series expansion. However, no closed-form solution for the coefficients of the series is found, so they must be solved from a matrix equation. This method provides very high accuracy. However, it requires construction of large matrices which consumes both time and memory. Therefore, approximative expressions for the polarizabilities with absolute error less than 10−5 are also presented.Peer reviewe

Nanowire waveguide made from extremely anisotropic metamaterials

Exact solutions are obtained for all the modes of wave propagation along an anisotropic cylindrical waveguide. Closed-form expressions for the energy flow on the waveguide are also derived. For extremely anisotropic waveguide where the transverse permittivity is negative while the longitudinal permittivity is positive, only transverse magnetic (TM) and hybrid modes will propagate on the waveguide. At any given frequency the waveguide supports an infinite number of eigenmodes. Among the TM modes, at most only one mode is forward wave. The rest of them are backward waves which can have very large effective index. At a critical radius, the waveguide supports degenerate forward- and backward-wave modes with zero group velocity. These waveguides can be used as phase shifters and filters, and as optical buffers to slow down and trap light.Comment: 11 pages, 15 figures, RevTex

Longitudinal chirality, enhanced non-reciprocity, and nano-scale planar one-way guiding

When a linear chain of plasmonic nano-particles is exposed to a transverse DC magnetic field, the chain modes are elliptically polarized, in a single plane parallel to the chain axis; hence, a novel longitudinal plasmon-rotation is created. If, in addition, the chain geometry possesses longitudinal rotation, e.g. by using ellipsoidal particles that rotate in the same plane as the plasmon rotation, strong non-reciprocity is created. The structure possesses a new kind of chirality--the longitudinal chirality--and supports one-way guiding. Since all particles rotate in the same plane, the geometry is planar and can be fabricated by printing leaf-like patches on a single plane. Furthermore, the magnetic field is significantly weaker than in previously reported one-way guiding structures. These properties are examined for ideal (lossless) and for lossy chains.Comment: to appear in PR

Rainbow trout (Salmo irideus) produced in Finland VI. Free amino acid composition of refrigerated and frozen rainbow trout

Changes in the amounts of free amino acids in rainbow trout during refrigerated storage in ice at + 4 . . + 6°C and in frozen storage at –18°C were investigated. The control sample was prepared directly from the killed, bleeded, and gutted fish. The results indicated that the total amounts of free aimino acids decreased in the refrigerated and in the frozen fish. These decreases depended mostly upon the steady decrease of the three quantitatively largest components, namely histidine, tryptophane, and glycine. Histidine formed 36.1 per cent, tryptophane 25.0 per cent, and glycine 15.1 per cent of the total amount of free amino acids in the control sample. In connection with many other amino acids a decrease in their amounts was noted during storage. Changes appearing in refrigerated fish were more distinct than in frozen fish