Measurement of the high-frequency giant magnetoresistance of nanostructures in the traveling-wave mode

The change that occurs under the action of an external magnetic field in the propagation constant of the H ₁₀ mode of a rectangular waveguide containing a metallic nanostructure is investigated. Expressions for the complex reflection and transmission coefficients are derived. The dependence of the reflection coefficient on the intensity of the external magnetic field is analyzed. It is shown that experimental values of the propagation constant or the reflection and transmission coefficients can be used for estimation of the value of the microwave magnetoresistance of nanostructures. Experiments on the measurement of the reflection and transmission coefficients in a waveguide with an (Fe/Cr)_n nanostructure are performed in the millimeter and centimeter wave bands.     

Diffraction of millimeter-wavelength electromagnetic waves by nanostructure material specimens based on 3D lattices of carbon nanotubes with magnetic nanoparticles and of magnetic nanowires in a waveguide

A mathematical model of the electromagnetic wave diffraction by specimens of anisotropic nanocomposite materials (3D lattices of oriented carbon nanotubes (CNTs) with magnetic nanoparticles and magnetic nanowires) in waveguides is developed. It is made with the help of a computational algorithm based on a multilevel recomposition and the method of autonomous blocks with the Floquet channels. The transmission coefficients of the H₁₀ wave with the frequency of 26 GHz that propagates through plates of magnetic nanocomposites in a waveguide are electrodynamically calculated as dependences of an external constant magnetic field (a magnetic bias field) and the number of magnetic nanoparticles filling the CNT.     

Microwave Dielectric Properties of Ceramic and Nanocomposite Titanates of Transition Metal

Ceramic and nanocomosite samples of the titanates of transition metals have been synthesized and their microwave dielectric properties have been investigated. Frequency and magnetic field dependences of the transmission and reflection coefficients in centimeter and millimeter wavebands were measured. It is established for most of studied ceramic titanates that transmission coefficient increases and reflection coefficient decreases when frequency increases. An absorption maximum has been found for ceramic sample made of Co_0.9Fe_0.1TiO₃. The real and imaginary parts of complex dielectric permittivity were determined from measurements of transmission and reflection coefficients. On the whole, real part of dielectric permittivity of nanocomposite titanates based on an opal matrix is less than for ceramic titanates.     

The dynamics of tunnel-coupled waves in a waveguide structure consisting of right- and left-handed media

An absorbing waveguide structure consisting of media characterized by refractive indices whose real parts have different signs is considered. The dynamics of forward and backward waves in such a structure is investigated. Expressions for the amplitudes of propagating waves and the reflection and transmission coefficients of the structure are obtained. It is shown that this structure can be used as a slow-wave system and that its characteristics can effectively be controlled with the help of an external magnetic field.     

The electrodynamic analysis of propagation constants of electromagnetic waves in 3D magnetic nanowire lattices under the magnetic resonance conditions at microwaves

Periodic 3G lattices made of oriented magnetic nanowires are considered under the magnetic resonance in the millimeter-wavelength range. The propagation of electromagnetic waves in anisotropic nanostructured materials based on these lattices is mathematically modeled using the method of autonomous blocks with virtual Floquet channels. The real and imaginary parts of propagation coefficients of longitudinal (clockwiseand counterclockwise polarized) and transverse (ordinary and extraordinary) waves for the zero spatial harmonic of 26 GHz are electrodynamically calculated. These waves propagate in 3D lattices of magnetic (Co₈₀Ni₂₀, Fe) nanowires. The obtained results depend on the intensity of the external constant magnetic field and the lattice period. The methods of control of the frequency dispersion in the millimeter-wavelength range under the influence of the external magnetic field and under the change of the geometry of lattices are determined. It is considered that the direction and intensity of the magnetic bias, its orientation with respect to the nanowire axis, and the mutual orientation of the constant and high-frequency magnetic fields vary.     

Perturbation analysis and modeling of curved microstrip bends

The curved microstrip bend consisting of a microstrip ring segment between two microstrip lines is analyzed for its transmission properties. The microstrip lines are modeled by equivalent ideal magnetic wall waveguides for which the electromagnetic field solutions are known. The field solutions in the microstrip ring segment are derived by using a perturbation analysis of a modified (magnetic wall) curved waveguide model. Other techniques have been formulated to evaluate the fields inside curved metallic waveguides. These include the use of an equivalent nonuniformly loaded straight waveguide and rectangular and annular model analysis. The perturbation solution for the fields in the equivalent curved waveguide model presented is readily adaptable to the mode-matching procedure, and is used to calculate the properties of the curved microstrip bend discontinuities. The frequency-dependent reflection and transmission coefficients of curved microstrip bends are determined and compared with those of the right-angle and chamfered right-angle microstrip bends     

Mutual Coupling Between Parallel-Plate Waveguides

The radiation field and mutual coupling between two identical parallel-plate waveguides having the same axis of symmetry are investigated. Jones' method of formulation is applied and a modified Wiener-Hopf equation is obtained. Expressions for the radiated field in free space, reflected field in the exciting waveguide, and transmitted field in the coupled waveguide are obtained and the reflected and transmitted fields are expressed in terms of waveguide modes. The reflection coefficient for each mode is represented by three terms, two of which are due to reflections at the open end of the exciting waveguide and are constant along the waveguide. The third term is the contribution from the field scattered by the open end of the coupled waveguide and decays along the waveguide according to the radiation condition. Similarly, the transmission coefficient of each mode is represented by three terms, two of which decay along the coupled waveguide and the third one is constant. The radiation field is also divided into three terms. One of them is due to the radiation from the open end of the exciting waveguide and the other two are the contribution of multiple interactions between the two waveguides. Computed results for the reflection and transmission coefficients and the radiation field are shown for TE/sub 0,1/ excitation and various separation distance of the waveguides. The results for the reflection and transmission coefficients are oscillating functions of period /spl pi/, and approach gradually the well-known final values of a single excited wavegnide.     

Transmission line models for lossy waveguide interconnections in VLSI

At high frequencies the waveguide nature of interconnections in VLSI circuits becomes important. Moreover, losses in interconnection are a major feature, not a perturbation. Here it is shown that even for such lossy waveguide structures an exactly equivalentRLGCtransmission line can be found. Equations are given determining these transmission line parameters in terms of the waveguide propagation constant and complex average power, and also in terms of integrals over the electric and magnetic field varibles. The resultingL,C, andGparameters differ from the usual static values when losses are important, and R is not restricted to the usual formula based upon a perturbation treatment of the skin effect. Consequently, semiconductor substrates can be treated. "Current" and "voltage" are found to have an abstract meaning in the equivalent transmission line. For a waveguide in a medium where conductivity and permittivity vary with position (such as a many-layered medium) an explicit formula relating "current" and "voltage" to weighted averages of transverse waveguide fields is given. A brief discussion of the reformulation of Thevenin equivalent circuit parameters in terms of reflection coefficients avoids terms such as "open circuit voltage" that are difficult to interpret for the equivalent transmission line. The framework presented allows construction of equivalent circuits for lossy waveguide interconnections, drivers, and terminations that provide correct spatial dependence in the direction of propagation and correct power relations despite the abstract nature of "current" and "voltage" in these lines.     

Scattering by a Cylindrical Post of Complex Permittivity in a Waveguide

An exact solution of the discontinuity problem of a circular cylindrical post of arbitrary complex permittivity centered in a rectangular waveguide with the axis parallel to the electric field vector of the dominant mode has been set up and numerical results based directly on this solution have been found rising an electronic computer. The method used divides the waveguide up into three different regions by introducing two imaginary plane walls perpendicular to the waveguide walls. In the center region, which contains the cylindrical rod, the electromagnetic field is expanded in cylindrical waves and in the outer regions the field is expanded in waveguide modes. By setting up the boundary conditions at all discontinuity surfaces and performing numerical matching of the fields at the two imaginary walls, a system of linear equatious determining the coefficients of reflection, transmission, and absorption of the field due to the cylindrical rod is found. The structure which is of most interest in the case of a plasma column is a coaxial structure consisting of an inner dielectric cylinder with complex permittivity (the plasma) surrounded by a dielectric sleeve with real, positive permittivity (the glass tube). The theory is therefore developed to apply generally for such structures. From the numerical results, curves have been obtained showing the relationship between the coefficients of reflection and transmission and the (complex) permittivity of the rod material. Such curves maybe used for deducing the microwave properties of a cylindrical rod from measurements of the reflection and transmission coefficient of the rod.     

Full-wave analysis of dielectric frequency-selective surfaces using a vectorial modal method

A novel vectorial modal method is presented for studying guidance and scattering of frequency-selective structures based on lossy all-dielectric multilayered waveguide gratings for both TE and TM polarizations. The wave equation for the transverse magnetic field is written in terms of a linear differential operator satisfying an eigenvalue equation. The definition of an auxiliary problem whose eigenvectors satisfy an orthogonality relationship allows for a matrix representation of the eigenvalue equation. Our proposed technique has been applied to the study of lossy all-dielectric periodic guiding media with periodicity in one dimension. This method yields the propagation constants and field distributions in such media. The reflection and transmission coefficients of a single layer under a plane-wave excitation can be obtained by imposing the boundary conditions. Study of the scattering parameters of the whole multilayered structure is accomplished by the cascade connection of components as characterized by their scattering parameters. Results obtained with this method for the propagation characteristics of a one-dimensional periodic dielectric medium are compared with those presented by other authors, and results for the scattering of several dielectric frequency-selective surfaces (DFSS) are compared with both theoretical and experimental results presented in the literature, finding a very good agreement. A symmetrical band-stop filter with a single waveguide grating is also demonstrated theoretically.     

FDTD Analysis of Electromagnetic Reflection by Conductive Plane Covered with Magnetized Inhomogeneous Plasmas

A novel finite-difference time-domain (FDTD) methodology which incorporates both anisotropy and frequency dispersion at the same time is developed for electromagnetic wave propagation in anisotropic magnetoactive plasmas in this paper. The numerical verification of the method are confirmed by computing the reflection and transmission of right-handed/left-handed circularly polarized (RCP/LCP) wave through a magnetized plasma layer, with the direction of propagation parallel to the direction of the biasing field. And, the right-handed / left-handed polarized wave reflection coefficients for electromagnetic signals normally incident upon a conductive plane covered with a layer of magnetized plasma are computed using the new FDTD method. The parabolic electron-number density profile varies only in the direction perpendicular to the plane. The function dependence of reflection coefficients on the number density, collision frequency and external magnetic field is studied.     

Numerical simulation of evolution of electron-hole avalanches and streamers in silicon in a uniform electric field

Numerical simulation of origination and evolution of streamers in Si is performed for the first time. It is assumed that an external electric field E ₀ is constant and uniform, the avalanche and streamer are axially symmetric, and background electrons and holes are absent. The calculations have been performed in the context of the diffusion-drift approximation with impact and tunneling ionization, Auger recombination, and electron-hole scattering taken into account. The most realistic values of the ionization and recombination rates, diffusion coefficients, and drift mobilities of electrons and holes have been used. It is shown that the features of evolution of avalanches and streamers are generally consistent with the result obtained previously for a hypothetic semiconductor with equal kinetic coefficients for electrons and holes. Asymmetry of these coefficients (mostly, the impact-ionization coefficients) manifests itself only at the initial stage of evolution. However, with time, two exponentially self-similar streamers are formed, differing only in the sign of charge of fronts and directions of their propagation. Empirical dependences of the main parameters of streamers on E ₀ in the range of 0.34–0.75 MV/cm have been derived for this most important stage of evolution.     

Moment method solution of double step discontinuities in waveguides

The problem of scattering of a double step waveguide discontinuity is investigated. Two coupled sets of equations in terms of the unknown magnetic current sheets on the apertures are obtained and solved for the electric field distribution using the moment method. The scattering matrix coefficients describing reflection, transmission, and mode conversions at a symmetric double step waveguide discontinuity are obtained and presented graphically for specific junctions.     

Propagation of Electromagnetic Waves in Rectangular Guides Filled with a Semiconductor in the Presence of a Transverse Magnetic Field

The characteristics of electromagnetic waves propagating in a semiconductor filled rectangular waveguide in the presence of a transverse magnetic field are studied. It is shown that only TE mode waves having y-independent field components (y being the direction of the steady magnetic field) and anomalous modes having all six field components can propagate. The propagation constant of waves characterized by a sinusoidal y dependence of fields is derived. Asymptotic expressions for the fields and the propagation constant are then obtained for the limiting case of a small external magnetic field and some recent experimental results are analyzed in this context.     

Electromagnetic wave propagation in magnetic multilayers— Non-reciprocal reflections

A theory of EM wave propagation through magnetic multilayers and superlattices is presented based on the propagation matrix of a magnetic film. By using theP matrix, the transmission and reflection coefficients of layered magnetic media, including: (1)semi-infinite magnetic surfaces, (2) magnetic multilayers, (3) semi-infinite magnetic superlattices are obtained. The numerical results show that the EM modes of a magnetic layer system is excited and manifested as the sharp dips in theS-polarized reflection and the dispersion curves of the magnetic polaritons can be measured by a method similar to the attenuated total reflection (ATR) technique. Supported by the National Natural Science Foundation of China     

Propagation Characteristics of a Rectangular Waveguide Containing a Cylindrical Rod of Magnetized Ferrite

With an axially magnetized cylindrical ferrite rod inserted into a rectangular waveguide parallel to the E-field of the dominant (TE/sub 10/) mode, the electromagnetic field amplitudes inside the ferrite rod and the transmission and reflection coefficients are numerically obtained by means of a digital computer and their results are shown in figures. At resonance, the distributions of RF magnetization and electric field have good symmetrical patterns in the cross section of the rod. The experimental results of the transmission and reflection coefficients agree well with the theoretical values.     

A computation of the reflection and transmission coefficients for dielectric coated waveguides

A previously developed variational technique for finding the approximate solution to the electromagnetic field inside waveguides of varying shapes and containing non-uniform dielectric and magnetic materials is applied to the specific case of an axisymmetric waveguide containing three layers of different dielectric materials. The magnetic permeability is taken equal to unity. The method enables the problem to be reduced to a two point boundary value problem for a pair of second order, linear, ordinary differential equations. The values of the reflection and transmission coefficients obtained by this method are in good agreement with those derived from solving the partial differential equations for the field.     

Radio waves in an irregular spheroidal model of the earth-ionosphere waveguide

Describes a program to compute the amplitude and phase anomalies of the electromagnetic fields in a perturbed spheroidal model of the Earth-ionosphere waveguide characterized by an effective height that varies along the propagation path, and also to trace the loci of the mode numbers in the irregular region of the spheroidal waveguide and to compute the transmission and reflection scattering coefficients. The language used is Fortran IV     

A Method for Determination of Alcohol Content in Dielectric Liquids by a Longitudinal-Slot Waveguide

A new method is proposed to determine the content of alcohol in dielectric liquids. The method is based on measuring the attenuation of a wave propagating in a rectangular waveguide with a longitudinal slot in its narrow wall, immersed in a liquid under test. The propagation constant of the H ₁₀ mode in such a waveguide is calculated numerically for various parameters of the medium and the waveguide. It is shown that the attenuation of the wave depends on the parameters of the dielectric medium outside the waveguide. Experiment is carried out on two different types of waveguide at frequencies from 29 to 37 GHz with a solution of ethyl alcohol in water as the external medium. The results of the measurements show that the method can be used for the on-line measurement of alcohol concentration during fermentation.     

VLF propagation across discontinuous daytime-to nighttime transitions in anisotropic terrestrial waveguide

Discontinuity effects are analyzed after referring the ionospheric surface impedance of daytime and nighttime waveguide portions to the same common altitudeh. The properties of the waveguide junction are determined by field matching, and the resulting linear equations are rearranged in a form that permits a sequential determination of transmission and reflection coefficients. Simple dominant mode approximations of the transmission and reflection coefficients are also developed. Field calculations of reciprocal geometries illustrate the consistency of the formulation and reflection coefficients are found to be of negligible magnitudes. The discontinuous surface impedance tends to excite higher order waveguide modes of larger amplitudes than a ground based source in homogeneous waveguide.