Millimeter wave sensor using cylindrical Luneberg lens with flatsides

The cylindrical lens with flat sides, which has the focal point just on the surface of the lens, is developed by using an artificial low-loss dielectric material, and the design of the lens is also given. The characteristics of the cylindrical lens fabricated in Teflon, and a millimeter-wave sensor, consisting of a millimeter-wave (MMW) antenna mounted at the focus, are also investigated at 40 GHz band. MMW sensors with the beam width of 16° and gain of 15.6 dB were obtained     

Luneberg lens formed from cubes: Geometric-optics calculations

An analysis is made of the focusing by a spherical Luneberg lens composed of discrete dielectric cubes with different permittivities. Geometric-optics calculations are used to determine the degree of focusing of rays by a lens consisting of 2600 cubes. It is shown that the degree of focusing is considerably inferior to that obtained for a continuous distribution of ε. Pis’ma Zh. Tekh. Fiz. 24, 69–72 (August 12, 1998)     

The characteristics of layers for stratified Luneberg lens

The dependence of characteristics of a stratified Luneberg lens on the layer parameters has been studied in numerical experiments using a mathematical model based on the rigorous solution of the electrodynamic problem of diffraction on a multilayer sphere.     

Taking into account the radiation pattern of a practical feed for a Luneberg lens

A method of taking into account the real feed radiation pattern for a Luneberg lens is proposed. According to this, the field of a feed with the given radiation pattern is expanded into series in spherical harmonics. Using this approach, it is possible to introduce the radiation patterns of real feeds into strict electrodynamic solution for a Luneberg lens, thus significantly refining a mathematical model of the antenna.     

Interface waves along an anisotropic imperfect interface between anisotropic solids

First and second order asymptotic boundary conditions are introduced to model a thin anisotropic layer between two generally anisotropic solids. Such boundary conditions can be used to describe wave interaction with a solid-solid imperfect anisotropic interface. The wave solutions for the second order boundary conditions satisfy energy balance and give zero scattering from a homogeneous substrate/layer/substrate system. They couple the in-plane and out-of-plane stresses and displacements on the interface even for isotropic substrates. Interface imperfections are modeled by an interfacial multiphase orthotropic layer with effective elastic properties. This model determines the transfer matrix which includes interfacial stiffness and inertial and coupling terms. The present results are a generalization of previous work valid for either an isotropic viscoelastic layer or an orthotropic layer with a plane of symmetry coinciding with the wave incident plane. The problem of localization of interface waves is considered. It is shown that the conditions for the existence of such interface waves are less restrictive than those for Stoneley waves. The results are illustrated by calculation of the interface wave velocity as a function of normalized layer thickness and angle of propagation. The applicability of the asymptotic boundary conditions is analyzed by comparison with an exact solution for an interfacial anisotropic layer. It is shown that the asymptotic boundary conditions are applicable not only for small thickness-to-wavelength ratios, but for much broader frequency ranges than one might expect. The existence of symmetric and SH-type interface waves is also discussed.     

Transient pressure response in an anisotropic formation

In this paper we study the evolution of pressure of a single-phase, slightly compressible fluid in a porous medium where a non-permeable wellbore is present. The flow is induced by a single probe on the side of an otherwise sealed wellbore which is drilled at an angle to the vertical into the anisotropic rock formation.The formulation is derived by giving a transient correction due to the presence of the wellbore to the time dependent free space source field solution (the probe). Using the divergence theorem and the zero flux condition on the wellbore surface, a boundary element formulation is derived and solved numerically in the Laplace and Fourier transformed domain before being inverse-transformed to give the real time behaviour.     

Collinear periodic cracks in an anisotropic medium

The problem of collinear periodic cracks in an anisotropic medium is examined in this paper. By means of Stroh formalism and the conformal mapping method, we obtain general periodic solutions for collinear cracks. The corresponding stress intensity factors, crack opening displacements and strain energy release rate are found.     

Josephson current in an anisotropic d-wave model

There should be no Josephson current between a CuO₂ plane with a gap of d-wave symmetry and a conventional s-wave superconductor. Nevertheless such a current is observed to exist between YBCO and Pb although with a reduced magnitude. Penetration depth measurements have revealed a large anisotropy between a- and b-directions presumably due to the existence of the CuO chains. Using a simple anisotropic tight binding model in qualitative agreement with the measured penetration depths and a standard model for the spin susceptibility we obtain, on solution of the BCS gap equations, a gap function with a mainly d-wave symmetry but with a minor extended s-wave component. The resultant Josephson current for YBCO-Pb junctions is in good agreement with experiment.     

Minor distortions with major consequences: correcting distortions in imaging spectrographs

Projective transformation is a mathematical correction (implemented in software) used in the remote imaging field to produce distortion-free images. We present the application of projective transformation to correct minor alignment and astigmatism distortions that are inherent in dispersive spectrographs. Patterned white-light images and neon emission spectra were used to produce registration points for the transformation. Raman transects collected on microscopy and fiber-optic systems were corrected using established methods and compared with the same transects corrected using the projective transformation. Even minor distortions have a significant effect on reproducibility and apparent fluorescence background complexity. Simulated Raman spectra were used to optimize the projective transformation algorithm. We demonstrate that the projective transformation reduced the apparent fluorescent background complexity and improved reproducibility of measured parameters of Raman spectra. Distortion correction using a projective transformation provides a major advantage in reducing the background fluorescence complexity even in instrumentation where slit-image distortions and camera rotation were minimized using manual or mechanical means. We expect these advantages should be readily applicable to other spectroscopic modalities using dispersive imaging spectrographs.     

Magnetic dipole interaction in an anisotropic type-II superconductor

The effect of the electromagnetic interplay between the supercurrent and localized magnetic moments is incorporated into the calculation of the magnetic dipole interaction in an anisotropic superconductor. The anisotropy of the magnetic field screening leads to an anisotropic cutoff of the dipole interaction with the radius which depends on the arrangement of magnetic moments with respect to the crystal anisotropy axis and varies between the principal-axis magnetic field penetration depths _ab and _c. The features of the modified lowest energy configuration of two magnetic moments are discussed as well.     

Scattering of radiation in an anisotropic turbulent medium

Scattering of laser radiation on density fluctuations in propagation of radiation through an anisotropic turbulent medium is analyzed. It is shown that the deviation angles in turbulent gas flows at atmospheric pressure equal ∼10⁻⁵–10⁻⁴ rad and can be detected by means of speckle photography. A statistical analysis of two-dimensional fields of deviation angles makes it possible to evaluate three-dimensional density correlation functions in a turbulent flow. It is shown that taking account of the turbulence anisotropy leads to distributions of the laser-radiation intensity over deviation angles that deviate substantially from the Gaussian distribution. Academic Scientific Complex “A. V. Luikov Institute of Heat and Mass Transfer of the National Academy of Sciences of Belarus,” Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 72, No. 1, pp. 96–101, January–February, 1999.     

Electro-optic modulation in an anisotropic artificial Kerr medium

We describe the performance of intensity and phase modulators that use an aqueous suspension of polytetrafluoroethylene (PTFE) microparticles. In this medium, the electro-optic effect is caused by the reorientation of anisotropic microparticles in an applied electric field. The intensity modulator was constructed in the Kerr geometry by the use of a sample path length of 20 μm. The response time of the modulator is less than 25 ms, and the depth of modulation was measured to be 28 dB for a switching voltage of 134 V(rms). The switching voltage necessary to achieve a π-phase shift with the phase modulator is less than 30 (Vrms).