A novel TEM waveguide using uniplanar compact photonic-bandgap(UC-PBG) structure

A novel waveguide using a photonic bandgap (PBG) structure is presented. The PBG structure is a two-dimensional square lattice with each cell consisting of metal pads and four connecting lines, which are etched on a conductor-backed Duroid substrate. This uniplanar compact PBG structure realizes a magnetic surface in the stopband and is used in the waveguide walls to provide magnetic boundary conditions. A relatively uniform field distribution along the cross section has been measured at frequencies from 9.4 to 10.4 GHz. Phase velocities close to the speed of light have also been observed in the stopband, indicating that TEM mode has been established. A recently developed quasi-Yagi antenna has been employed as a broad-band and efficient waveguide transition. Meanwhile, full-wave simulations using the finite-difference time-domain method provide accurate predictions for the characteristics of both the perfect magnetic conductor impedance surface and the waveguide structure. This novel waveguide structure should find a wide range of applications in different areas, including quasi-optical power combining and the electromagnetic compatibility testing     

多层压电结构中声表面波特性的计算

The propagation properties of the surface acoustic waves(SAWs) in a ZnO-SiO2-Si multilayered piezoelectric structure are calculated by using the recursive asymptotic method.The phase velocities and the electromechanical coupling coefficients for the Rayleigh wave and the Love wave in the different ZnO-SiO2-Si structures are calculated and analyzed.The Love mode wave is found to be predominantly generated since the c-axis of the ZnO film is generally perpendicular to the substrate.In order to prove the calculated results,a Love mode SAW device based on the ZnO-SiO2-Si multilayered structure is fabricated by micromachining,and its frequency responses are detected.The experimental results are found to be mainly consistent with the calculated ones,except for the slightly larger velocities induced by the residual stresses produced in the fabrication process of the films.The deviation of the experimental results from the calculated ones is reduced by thermal annealing.     

Guided Waves in Moving Dispersive Media Part II: Relativistic Velocities

The detailed modal field structure has been determined for electromagnetic waves propagating in a uniform cylindrical lossIess waveguide of arbitrary cross section filled with a moving medium. The medium is assumed to be homogeneous, isotropic, and nondissipative, but may be dispersive. It moves uniformly, with a constant speed v, parllel to the axis of the waveguide. The solutions obtained are exact closed-form functions of the space variables, time, modal wave frequency, and propagation factor, and they hold for any value of the magnitude of v, from zero up to the speed of light in vacuum. The electromagnetic power flow in the waveguide is investigated and shown to display characteristics that differ considerably from those associated with the stationary medium case. The general theory is applied to several types of moving media, including nondispersive media and the idealized low-temperature plasma.     

Waveguides Containing Moving Dispersive Media

Perturbation formulas are derived for the changes in the dispersion curves and phase velocity for the modes in an arbitrary composite waveguide structure containing dispersive media in relative motion. The formulas are also valid when the media are fluids with arbitrary velocity distributions. It is shown that the relativistic transformation laws for the frequency and wave vector of uniform plane waves are also valid for waveguide modes provided that all moving media that make up the guide move with the same velocity. There are also difficulties when the moving media are dispersive. In general, one most therefore obtain the dispersion relation directly from the field equations or from the perturbation formulas. An example involving a simple surface wave along the interface of a moving plasma and a dielectric is worked out by both methods. As an interesting side result, it is found that plane waves in an unbounded isotropic plasma have phase velocities independent of the motion of the plasma.     

Propagation Constants in Rectangular Waveguide Partially Filled with Dielectric (Correspondence)

There is considerable current interest in the production of guided electromagnetic waves having phase velocities equal to or less than the speed of light in free space (for example, in the design of traveling-wave slot antennas and of devices involving electron traveling-wave interactions). Such phase velocities can be obtained conveniently by partially loading a rectangular waveguide with dielectric material. In antenna work particularly, because of the field configurations, it is usually desirable to place the dielectric interface so that it is parallel to the broad face of the waveguide, as indicated in Fig. 1. The calculation of phase velocities in such a waveguide has been considered in the literature, and there is published information on some of the cutoff frequencies, but (since in this case there is no convenient relationship between the cutoff frequencies and the propagation constants) there has been little detailed information available concerning the phase velocities as a function of waveguide proportions and dielectric material. Thus a compilation has been made of such information for the dominant (hybrid) mode.     

Waves in active and passive periodic structures: A review

The theory and recent applications of waves in periodic structures are reviewed. Both the Floquet and coupled waves approach are analyzed in some detail. The theoretical part of the paper includes wave propagation in unbounded and bounded active or passive periodic media, wave scatterring from periodic boundaries, source radiation (dipole, Cerenkov, transition, and Smith-Purcell) in-periodic media, and pulse transmission through a periodic slab. The applications part covers the recent development in a variety of fields: distributed feedback oscillators, filters, mode convertors, couplers, second-harmonic generators, deflectors, modulators and transducers in the fields of integrated optics and integrated surface acoustics. We also review the work on insect compound eyes, mehanical structures ocean waves, pulse compressions, temperature waves, and cholestric liquid crystals. Particles interaction with crystals is briefly reviewed, especially in the case of zeolite crystals and supelattices. Recent advances in fabrication techniques for very fine gratings me also covered. Finally, speculations about future problems and development in the field of waves in periodic structures are given.     

Traveling wave lobe locations

A simple and reasonably accurate formula for the angular locations of traveling wave lobes has been available for many years, but the formula holds only for surface waves that travel at the speed of light. It is shown how the formula may be modified to account for propagation velocities less than the speed of light. It is shown that when the equation derived by the author is used to estimate a starting value for cosQ in the Newton-Raphson method, the solution usually requires no more than three iterations for an accuracy of 10^-6 in the solution for Q     

湍流大气中传输光波的波相位结构解析函数

在湍流大气对传输光波调制的双尺度湍涡(大尺度湍涡和小尺度湍涡)近似下,研究了用于计算描述湍流大气中传输光波相干长度变化的核心函数(互相干函数)的关键因子波结构函数(WSF),通过建立包含不同尺度湍流因子的折射率起伏谱密度函数,导出了可以用于精确理论分析平面波与球面波在湍流大气中传播时所产生的诸如到达角起伏和相干性变化等效应的波相位结构函数的精确解析式,同时给出了便于数值计算的近似误差在2%范围以内的波相位结构函数的精确渐近表达式。     

Measurement and classification of low-grazing-angle radar seaspikes

High-resolution dual-polarization X-band images of the ocean surface were obtained at a grazing angle of about 3°. Area extensive imaging allowed us to study the backscatter properties of sea spikes and to compare radar measurements with visual surface features evident from video recordings. The vertically polarized radar images consist of distributed scatter whose amplitude and Doppler velocity are modulated by larger scale gravity waves consistent with Bragg scattering and composite surface theory (CST). The horizontally polarized radar images are dominated by spatially discrete scattering centers (or sea spikes) moving at velocities comparable to the phase velocities of gravity waves beyond the spectral peak. These sea spikes also exist in the corresponding V-pol radar images, but are less prominent due to the dominant Bragg backscatter. Sea spikes are characterized by polarization ratios H/V that often exceed unity, typically by about 5 dB. Comparison of the larger spikes with simultaneous co-registered video recording of the surface indicates that approximately 30% of observed sea spikes are associated with actively breaking waves (whitecaps) while the remainder are identified with “steep” wave features. By classifying the larger sea spikes according to their corresponding surface features, we find hat the Doppler velocities for sea spikes due to whitecaps are noticeably faster (about 50%) than other sea spikes, though the distributions for both overlap significantly. We also find little measurable difference in the polarization ratios of the two classes of sea spikes as observed on the open ocean     

Negative Index Materials With Gain Media for Fast Optical Modulation

We discuss the origin of negative index behavior that is observed in certain artificial structures known as metamaterials that are periodic structures supporting backward optical waves with generally antiparallel phase and group velocities. Slab-like metamaterials, metal-dielectric, and purely dielectric ones support surface-plasmon polaritons that may be coupled into by an incident field. When this is the case, these surface waves can be pumped by the source, lead to pumping of the evanescent waves, and, as a result, enable subwavelength resolution. The main limiting factors for subwavelength resolution are losses and surface imperfections. Metal-dielectric metamaterials and systems are of special interest to nanophotonics, the focus of this paper, since they obviously provide high dielectric contrast, much larger than all-dielectric/semiconductor systems. This makes them promising for applications in dense integrated optical systems, since the mode volume is small. We consider various ways of combining metallic materials for negative dielectric constant and a gain medium to compensate for optical losses. Ultimately, one would like to make Si-compatible subwavelength optical components using metamaterials.     

Electromagnetic waves over half-space metamaterials of arbitrary permittivity and permeability

Most electromagnetic problems deal with media with unit permeability. However, recent interest in metamaterials necessitated studies of wave characteristics in media with arbitrary permittivity and permeability whose real parts can be positive or negative. This paper presents analysis of wave characteristics on semiinfinite metamaterials. Waves are excited by electric or magnetic line sources, and the problem is separated into the p (TM) and the s (TE) polarization, showing symmetries. The Fourier spectra of the reflection and transmission coefficients are examined and the poles, branch points, and zeros are shown in the real /spl mu/-real /spl epsi/ diagram. We clarify the location of poles in proper and improper Riemann Surfaces, and the excitation of forward and backward surface waves, forward and backward Lateral waves, and Zenneck waves, and the relations between Brewster's angle and Sommerfeld poles. We include the behaviors of the backward surface waves and the temporal backward Lateral waves.     

Reflection coefficient of a semiconductor superlattice subjected to a magnetic field

Propagation of magnetoplasma waves in a structure formed by periodically alternating semiconductor and dielectric layers is studied for the case where an external magnetic field is applied parallel to the layers; the waves traveling in the plane normal to the field are considered. Dispersion characteristics are calculated with the finiteness of the speed of light accounted for, and the features of the structure reflectivity are analyzed. It is demonstrated that the physical parameters and thicknesses of the layers composing the superlattice can be obtained from the frequency, angle of incidence, and magnetic-field dependences of the reflection coefficient.     

ERS-1 SAR images of atmospheric gravity waves

ERS-1 synthetic aperture radar (SAR) images of atmospheric gravity waves over the ocean are discussed. Several case studies are presented in detail. It is shown that the well-organized long wavelength (1 to 10 km) wave phenomena which often are seen in SAR images over the ocean may be atmospheric gravity waves. The waves appear in the SAR images because they modulate the surface wind speed which in turn modulates the surface roughness and the radar cross section. The wavelength may be measured directly from the SAR image, and the mean wind speed and wind speed modulation near the ocean surface may be estimated from the observed radar cross section modulation using a wind retrieval model. The atmospheric gravity waves usually were generated by the approach or passing of a meteorological front. Atmospheric soundings and a two-layer model for the lower troposphere indicate that, in general, the observed atmospheric wave phenomena could have been supported by accompanying temperature inversion layers and wind shears     

The snell and fresnel relationships for electromagnetic waves with the constant linear polarization

General conditions for the existence of plane electromagnetic waves with a single nonzero electric-field component (TE waves) in an anisotropic medium are established. A transformation that makes it possible to derive similar formulas for TM waves (plane electromagnetic waves with a single nonzero magnetic-field component) from the formulas expressing the properties of TE waves is considered. A general numerical algorithm is developed for calculating the amplitudes (with allowance for phases) of the TE waves formed when an external TE wave propagates through a system of plane-parallel plates consisting of media supporting TE waves. Formulas are obtained for the solution of the particular problem on the transmission of a TE wave through a plane interface between two media supporting TE waves. A series of relationships that can be interpreted as generalizations of the Snell and Fresnel relationships for media of the considered type are derived. Formulas for the transmission, reflection, and refraction coefficients are obtained. The existence conditions for TE (TM) surface waves are derived. A numerical method is proposed for computing the spectra of such surface waves formed on the interface between two media. For isotropic media, analytic expressions for the spectra of surface waves are derived. It is shown that the obtained formulas are similar to the known formulas for surface TM waves in dielectrics but, in addition, make it possible to take into account both the permittivities and permeabilities of the media.     

Propagation of magnetostatic surface waves in a ferrite plate magnetized by a spatially periodic transverse field

Propagation of magnetostatic surface waves (MSSWs) in a ferrite plate magnetized by a spatially periodic transverse field has been considered. The parameters of MSSW propagation have been calculated by the Hamilton-Auld method. It is shown that only noncollinear MSSWs, whose wave-beam trajectories as well as wave numbers and angles, which determine the directions of the vectors of the phase and group velocities, are described by functions that are periodic in the direction of the wave propagation, can exist in this field. The period of these functions is determined by the period of the spatially periodic field. The frequency range of existence of the collinear waves is narrower than that of the waves in a uniformly magnetized plate. The characteristics of wave propagation in a nonuniform spatially periodic field are compared to the characteristics of wave propagation in nonuniform fields of known types.     

Group velocity and power flow relations for surface waves in plane-stratified anisotropic media

Two aspects of power flow associated with electromagnetic waves in plane-stratified, dispersive, anisotropic media that are also lossless and linear are considered. One aspect is the relation between group velocity and the velocity of energy transport of surface waves in such media. It is shown that the group velocity of surface waves is equal to the ratio of the real part of the complex Poynting vector, integrated over the coordinate of stratification, to the corresponding integral of the stored energy density. The second aspect is the relation between the dyadic surface impedance representing either a slab of plane-stratified medium above a perfectly conducting plane or a semi-infinite region, the latter for the case of evanescent fields, and the power flow in the respective structures. The significance of the surface impedance and power relations for surface waves is discussed.     

Transformation of surface waves in homogeneous absorbing layers

Surface waves in homogeneous absorbing layers are studied. The transformation of surface waves into other types of guided waves with frequency or layer's parameters variations is analyzed. It is found that in absorbing layers the standing damped surface waves do not exist and continuous transformation of surface waves into leaky waves is forbidden. Surface waves can only transform continuously into nonphysical waves with field strengths increasing exponentially in both the direction of propagation and in normal direction away from the layer into free-space. The frequency at which surface waves transform into nonphysical waves can be considered as cutoff frequency of surface waves. New and more general definitions previously proposed by the authors for the phase and energy velocities of guided waves are analyzed. It is shown that these velocities are identically equal to each other and never exceed the lightspeed in free-space. Several new physical phenomena are discovered. These are the upper frequency cutoff, its shifting to higher frequencies for materials with lower losses and the merging of high TE wave modes     

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.     

A surface wave interpretation for the resonances of a dielectric sphere

The calculated radar and bistatic cross sections of dielectric spheres exhibit numerous resonances when plotted versus frequency. These resonances may be related to the excitation of electromagnetic eigenvibrations of the sphere, with resonance frequencies calculable from a characteristic equation. It is shown that the resonances may be viewed as originating from families of circumferential (surface, or creeping) waves that are generated during the scattering process; at each eigenfrequency of the sphere, one of these surface waves matches phases after its repeated circumnavigations around the sphere, with the ensuing resonant reinforcement leading to the given scattering resonance. This mechanism explains the existence of electromagnetic eigenvibrations of a general smooth dielectric object; for the case of a sphere, it is shown that the surface waves suffer a phase jump ofpi/2at each of their two convergence points. We calculated numerical values of the eigenfrequencies of dielectric spheres, and obtain dispersion curves for the phase velocities of the surface waves.     

Guided Waves on an Infinite Cylindrical Cavity in a Magneto-ionic Medium II. Dipolar Modes†

The characteristics of the guided waves supported by an infinitely long cylindrical cavity of free-space immersed in a magneto-ionic medium are investigated for the case of the magnetostatic field in the direction of the axis of the column. The dipolar case for which the fields have an exp (imφ) azimuthal variation, where φ is the angular variable and m ± 1, is treated. The characteristics of the transition, the resonance and the cut-off frequencies of the guided waves ore discussed with particular reference to their dependences on the radius of the free-space column. The dispersion characteristics under propagating conditions are studied in detail both for the special case of vanishing static magnetic field and for the general case of finite magneto-static field corresponding to the two typical values of the ratio R of the gyromagnetic to the plasma frequencies. The lowest-order mode is found to be of the modified TE type and has special features such as that it can have forward or backward wave and fast or slow wave regions in certain portions of its characteristics, depending on the radius of the free-Space column and the azimuthal variation of the fields. All the other higher-order modes are found to be fast forward waves, whose phase velocity monotonically decreases as the frequency is increased and approaches the free-space velocity of electromagnetic waves. For an extremely small radius of the free-space column, the group velocity is vanishingly small for a major portion of the range of propagation of the only existing, lowest-order surface wave.