Karl F. Lindman: the last Hertzian, and a harbinger ofelectromagnetic chirality

The research career of Karl F. Lindman, who has widely been referred to as being the first to demonstrate the effect of a chiral medium on electromagnetic waves, is described. During the first half of this century, Lindman completed an extensive research career, using essentially the same methods as Heinrich Hertz did in his time. His work is reviewed, focusing on his chirality studies     

Polarizability of gyrotropic sphere

The polarizability of gyrotropic spheres is studied in this short article. Gyrotropic media are anisotropic in two respects: the symmetric part of the permittivity dyadic is uniaxial, and furthermore, there is also antisymmetric part in the permittivity. The polarizability is also dyadic with its components depending on the relations of the permittivity components of the material.     

Boosting numerical accuracy in calculation of polarizability of two-dimensional scatterers

This article presents an effective way to increase the accuracy of the numerical evaluation of the polarizability of two-dimensional scatterers. It is based on the numerical exploitation of the observation that the polarizabilities of complementary inclusions are closely related: if the permittivity is inverted, the polarizability changes sign. For anisotropic inclusions, the corresponding property cross-connects the orthogonal components, and can be used as well in the numerical calculations. The improvement of the numerical accuracy is several orders of magnitude. The method is also applied to evaluate the polarizability of split rings.     

The tangent galvanometer of Johan Jacob Nervander

J.J. Nervander designed the more- sensitive tangent galvanometer in 1834, which led to a great improvement in precise measurements of electric current. Because of its ingenuous coiling arrangements, Nervander was able to use the tangent busol to prove the validity of the law that the tangent of the deviation angle of the needle of the tangent-bussol is proportional to the electric current flowing through its coil. Exploitation of the tangent law provided a way of measuring and comparing currents. The increased sensitivity of the galvanometer was a result of the uniformity of the current-created magnetic field over the cylindrical volume inside the coils. This allowed the use of a long magnetic needle. The reconstructed galvanometer operates with a short needle. For the reconstructed galvanometer, the tangent law is valid up to deflection angles more than 50deg; Nervander reported acceptable deviations only up to 30deg.     

Analysis of a three-dimensional dielectric mixture with finitedifference method

The present paper reports the results of a numerical analysis of electric fields in random dielectric materials. The effective permittivity of a three-dimensional (3D) dielectric mixture is calculated by the finite difference method. The results show the distribution of the effective permittivity of a mixture with different random inclusion positionings. New empirical mixing models are created as least squares approximations to fit the collection of numerical results. The calculated permittivity distribution is also compared with theoretical mixture models, showing that in case of clustered inclusions, the Bruggeman model is quite reasonable. On the other hand, if the inclusions in the mixture are separate, the results are closer to the Maxwell-Garnett model     

Polarizabilities of platonic solids

This article presents results of a numerical effort to determine the dielectric polarizabilities of the five regular polyhedra: tetrahedron, cube, octahedron, dodecahedron, and icosahedron. The polarizability is calculated by solving a surface integral equation, in which the unknown potential is expanded using third-order basis functions. The resulting polarizabilities are accurate to the order of 10/sup -4/. Approximation formulas are given for the polarizabilities as functions of permittivity. Among other results, it is found that the polarizability of a regular polyhedron correlates more strongly with the number of edges than with the number of faces, vertices, or the solid angle seen from a vertex.     

Effective permittivity of mixtures: numerical validation by theFDTD method

The present paper reports the results of an extensive numerical analysis of electromagnetic fields in random dielectric materials. The effective permittivity of a two-dimensional (2-D) dielectric mixture is calculated by FDTD simulations of such a sample in a TEM waveguide. Various theoretical bounds are tested in light of the numerical simulations. The results show how the effective permittivity of a mixture with random inclusion positionings is distributed. All possible permittivity values lie between Wiener limits, and according to FDTD simulations the values are almost always between Hashin-Shtrikman limits. Calculated permittivity distribution is also compared with theoretical mixture models. No model seems to be able to predict the simulated behavior over the whole range of volume fraction     

Perfectly anisotropic impedance boundary

The concept of a perfectly anisotropic boundary (PAB) is defined in terms of a surface impedance dyadic without an isotropic component. Realisation of PAB in terms of a slab of anisotropic metamaterial is suggested. It is shown that PAB can serve as a simple rotatable polarisation transformer, transforming a linearly polarised field to a field with given elliptic polarisation and handedness, or conversely. It is also shown that, unlike at a regular impedance boundary, a PAB can simultaneously support two orthogonally polarised surface waves propagating in certain directions along the boundary