摘要:

The electromagnetic eigenfrequencies fnsmin a perfectly conducting spheroidal cavity are determined analytically, by a shape perturbation method. The analytical determination is possible in the case of small values of the quantity = 1- a2/b2, (|1), where 2a and 2b are the lengths of the rotation axis and the other axis of the spheroidal cavity, respectively. In this case, exact, closed-form expressions are obtained for the expansion coefficients and in the resulting relation fns(0) [1 + + There is no need for using any spheroidal eigenvectors in our solution. The electromagnetic field is expressed in a series of spherical eigenvectors, while the equation of the spheroidal boundary is given in terms of the spherical coordinates. Numerical results are given for the eigenfrequencies of the lower-order magnetic and electric modes.

ISSN:0920-5071    

DOI:10.1163/156939397X00224

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939397X00233

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

It is well known that in bi-anisotropic media, e.g., chiral media, gyrotropic media, the polarization vector of linearly polarized waves undergoes rotation. Upon reflection, the returning waves show different effects: In gyrotropic media the rotation is enhanced, while in chiral media it is unraveled and annulled. In general, these properties are not necessarily intrinsic to the media involved but depend on the reflection mechanism, as shown below. It must be emphasized at the outset that in the present study external mirroring mechanisms only are considered, so that the reflection at the interface separating the active medium (chiral or gyrotropic) from the external domain does not enter the discussion. Strictly speaking, the effect of these interfaces cannot be ignored, except in special cases. However, where our approach is valid, it leads to a simple consistent and non-trivial picture of the effects involving returned waves in the presence of external mirror mechanisms. Inasmuch as this analysis is of importance for practical applications, e.g., in ocular glucose polarimetry measurements, and because the mathematics involved here is minimal, the subject appears to be timely and worthwhile. Two different mirror mechanisms are shown to exist: The simple, conventional mirror mechanism, henceforth referred to as "reflection", and a different mechanism referred to as "retrodirection". The simplest example for retrodirection is a wave turned around by an optical fiber. A similar retrodirection effect occurs when the wave is turned around by a set of two conventional reflectors. In non-chiral non-gyrotropic media the two categories lead to identical effects, and the distinction is superfluous. Presently we consider the effect of such reflection and retrodirection mirroring mechanisms on the total rotation of the polarization vector of a wave undergoing a round trip in chiral, and in gyrotropic media. It is shown that for the case of reflection and chiral media, the rotation is canceled, while in the presence of a retrodirecting mirror, the rotation is enhanced. For gyrotropic media we have the opposite situation: A reflector will induce enhanced rotation, while a retrodirector will cause the total rotation to vanish. Various situations are considered below, involving mirroring mechanisms. Provided we stay within the limitations of the present model, simple well-known considerations relevant to the Fresnel theory of reflection of plane waves by plane interfaces, as well as simple geometrical observations, suffice for analyzing the problems and drawing the conclusions.

ISSN:0920-5071    

DOI:10.1163/156939397X00242

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The main idea of a wake field transformer is to induce a high (wake) field by a beam of high intensity but low energy per particle (called the drive beam) accelerating a second beam with low intensity but high energy gain per particle. A geometry suitable for a wake field accelerator is a beam widened to a ring passing a thin pill-box cavity (that is a cylinder with a circular base) (Weiland, Voss 1982). In this report a problem with the same circular symmetry was investigated. The problem consists of a ring-shaped line charge in a plane parallel to the plates of a plane condensor and moving in a direction perpendicular to the plates. The ring is at rest in front of one condensor plate until it starts suddenly to move with constant velocity; then the ring traverses the plane condensor until it reaches the second plate, where it stops. The field is derived from the potentials. The only non-zero component, the longitudinal one, of the vector potential is computed with the method of Green's function. The scalar potential is computed by using the Lorentz gauge. The field can be expressed as an infinite sum over complete and incomplete elliptic integrals and simpler terms. But at any given finite time only a finite number of terms of the infinite sum contributes. The field is evaluated numerically with the computer and shown in several figures.

ISSN:0920-5071    

DOI:10.1163/156939397X00251

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper a comprehensive full-wave analysis of the double-sided or bilateral microslotline both in its single slot and coupled slots configuration, is presented. First, an equivalent model of the original structure is derived upon which a variational method is applied for establishing a stationary expression for the line's dominant mode propagation constant. The electric field in the slot(s) is the trial quantity and suitable approximations of its distribution are made which are also used for calculating the characteristic impedance. Numerical results are presented for the single and for the first time for the coupled slot(s) configuration.

ISSN:0920-5071    

DOI:10.1163/156939397X00260

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Across-track Synthetic Aperture Radar Interferometry is an emerging technique for Earth monitoring capable to generate high-resolution Digital Elevation Models. The ability to achieve such mission depends on the correlation of the signals received by the two antennas and used to generate the interferometric fringes. In this paper we formulate the baseline decorrelation due to antennas spatial diversity to include the effect of surface scattering.

ISSN:0920-5071    

DOI:10.1163/156939397X00279

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A methodology to extract the effective constitutive parameters of uniaxial bianisotropic chiral (UBC) materials was presented in [1]. While the results of numerical verification studies within that paper were positive, laboratory measurements of these material types seemed warranted for further verification as well as there being no measured scattering results in the literature for this type of material. Consequently, two UBC composite material slabs were fabricated, as described in this paper, by embedding aligned helices within an epoxy host. The scattering from these slabs was measured using a free-space measurement method and compared to that predicted using our methodology in [1]. Very good correspondence was observed in these comparisons and provides convincing evidence that both the methodology in [1] is correct and that effective UBC composite materials can indeed be constructed from periodically aligned helices. An investigation on the degree of mutual coupling between helices in these fabricated slabs is also presented.

ISSN:0920-5071    

DOI:10.1163/156939397X00288

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Introducing a pseudotime variable, Tai has given recently a simple solution to the problem of the transient radiation in a uniformly moving isotropic medium. Using suitably dilated space variables and the 3D-complex formalism of electromagnetism we give an alternative solution to the same problem with the aid of the Green's function of the scalar wave equation.

ISSN:0920-5071    

DOI:10.1163/156939397X00297

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939397X00305

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939397X00314

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor