Biomedical subjects

A J Viitanen

Publications and source records attributed to A J Viitanen.

4 recordsLinked to original sources

PubMed2005

Resonator mode in chains of silver spheres and its possible application.

A transversal mode with zero group velocity and nonzero phase velocity that can exist in chains of silver nanospheres in the optical frequency range is theoretically studied. It is shown that the external source radiating a narrow-band nonmonochromatic signal can excite in the chain a mixture of standing and slowly traveling waves. The standing-wave component (named the resonator mode) is strongly dominating. The physical reason for such a regime is a sign-varying distribution of power flux over the cross section of the chain. A possible application of the resonator mode for evanescent-wave enhancement and for subwavelength imaging in the visible is discussed.

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PubMed2005

Propagating and evanescent modes in two-dimensional wire media.

Electromagnetic waves in an artificial medium formed by two mutually orthogonal lattices of thin ideally conducting straight wires (referred to as a two-dimensional wire medium) are considered. An effective medium approach and a full-wave method based on the dyadic Green's function and the method of moments are developed. Effects of spatial dispersion, such as the appearance of anisotropy in a square lattice and an additional extraordinary wave, as in crystal optics, are demonstrated. Evanescent waves with complex propagation constants are found. The case when both forward and backward extraordinary waves with respect to an interface exist simultaneously is observed and discussed. The effect of birefringence, so that one extraordinary wave has the wave vector making a positive angle to the interface and the other has the wave vector making a negative angle to the interface, is illustrated.

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PubMed2002

Nonreciprocal microwave band-gap structures.

An electrically controlled nonreciprocal electromagnetic band-gap material is proposed and studied. The new material is a periodic three-dimensional regular lattice of small magnetized ferrite spheres. In this paper, we consider plane electromagnetic waves in this medium and design an analytical model for the material parameters. An analytical solution for plane-wave reflection from a planar interface is also presented. In the proposed material, a new electrically controlled stop band appears for one of the two circularly polarized eigenwaves in a frequency band around the ferrimagnetic resonance frequency. This frequency can be well below the usual lattice band gap, which allows the realization of rather compact structures. The main properties of the material are outlined.

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PubMed2000

Plane waves in regular arrays of dipole scatterers and effective-medium modeling.

A simple analytical theory for finding eigensolutions for plane electromagnetic waves propagating along an axis in infinite regular arrays of small dipole particles is presented. The spacing between dipoles in every plane is assumed to be smaller than the wavelength; separation between the planes is arbitrary. The influence of evanescent modes is taken into account. This theory gives a model for an effective propagation constant that can be applied in a wide frequency range from the quasi-static regime to the Bragg reflection (photonic bandgap) region.

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