7 research outputs found
Phonon deficit effect and solid state refrigerators based on superconducting tunnel junctions
Thin film devices have the advantage of being extremely compact, operate in a
continuous mode, dissipate little power, and can easily be integrated in
cryogenic detectors. Motivated by such possibilities, we investigate the phonon
deficit effect in thin film (superconductor--insulator--superconductor)
and tunnel junctions. Under certain circumstances, the phonon absorption
spectra of such tunnel junctions have spectral windows of phonon
absorption/emission. We propose to use phonon filters to select the phonon
absorbtion windows and thus to enhance the cooling effect. Membranes attached
to such tunnel junctions can be cooled in this way more effectively. We discuss
a particular superlattice design of corresponding phonon filters.Comment: 8 pages 7 figure
Immittance Matching for Multi-dimensional Open-system Photonic Crystals
An electromagnetic (EM) Bloch wave propagating in a photonic crystal (PC) is
characterized by the immittance (impedance and admittance) of the wave. The
immittance is used to investigate transmission and reflection at a surface or
an interface of the PC. In particular, the general properties of immittance are
useful for clarifying the wave propagation characteristics. We give a general
proof that the immittance of EM Bloch waves on a plane in infinite one- and
two-dimensional (2D) PCs is real when the plane is a reflection plane of the PC
and the Bloch wavevector is perpendicular to the plane. We also show that the
pure-real feature of immittance on a reflection plane for an infinite
three-dimensional PC is good approximation based on the numerical calculations.
The analytical proof indicates that the method used for immittance matching is
extremely simplified since only the real part of the immittance function is
needed for analysis without numerical verification. As an application of the
proof, we describe a method based on immittance matching for qualitatively
evaluating the reflection at the surface of a semi-infinite 2D PC, at the
interface between a semi-infinite slab waveguide (WG) and a semi-infinite 2D PC
line-defect WG, and at the interface between a semi-infinite channel WG and a
semi-infinite 2D PC slab line-defect WG.Comment: 8 pages, 6 figure
Unified Homogenization Theory for Magnetoinductive and Electromagnetic Waves in Split Ring Metamaterials
A unified homogenization procedure for split ring metamaterials taking into
account time and spatial dispersion is introduced. The procedure is based on
two coupled systems of equations. The first one comes from an approximation of
the metamaterial as a cubic arrangement of coupled LC circuits, giving the
relation between currents and local magnetic field. The second equation comes
from macroscopic Maxwell equations, and gives the relation between the
macroscopic magnetic field and the average magnetization of the metamaterial.
It is shown that electromagnetic and magnetoinductive waves propagating in the
metamaterial are obtained from this analysis. Therefore, the proposed time and
spatially dispersive permeability accounts for the characterization of the
complete spectrum of waves of the metamaterial. Finally, it is shown that the
proposed theory is in good quantitative and qualitative agreement with full
wave simulations.Comment: 4 pages, 3 figure
Effect of transition layers on the electromagnetic properties of composites containing conducting fibres
The approach to calculating the effective dielectric and magnetic response in
bounded composite materials is developed. The method is essentially based on
the renormalisation of the dielectric matrix parameters to account for the
surface polarisation and the displacement currents at the interfaces. This
makes it possible the use of the effective medium theory developed for
unbounded materials, where the spatially-dependent local dielectric constant
and magnetic permeability are introduced. A detailed mathematical analysis is
given for a dielectric layer having conducting fibres with in-plane positions.
The surface effects are most essential at microwave frequencies in
correspondence to the resonance excitation of fibres. In thin layers (having a
thickness of the transition layer), the effective dielectric constant has a
dispersion region at much higher frequencies compared to those for unbounded
materials, exhibiting a strong dependence on the layer thickness. For the
geometry considered, the effective magnetic permeability differs slightly from
unity and corresponds to the renormalised matrix parameter. The magnetic effect
is due entirely to the existence of the surface displacement currents.Comment: PDF, 33 pages, 10 figure