Currents induced in a wire cross by a plane wave incident at an angle

The currents induced in a thin-wire cross with equal mutually perpendicular arms by an incident plane electromagnetic wave are determined when the normal to the wave front is perpendicular to the horizontal wire and is at an anglethetawith respect to the vertical wire; the direction of the electric vector in the wave front is arbitrary. The analysis is formulated in general terms but explicit formulas are obtained only for the zero-order currents which are generally adequate to determine the scattered field of very thin wires. The relatively simple formulas consist of even and odd parts for both the vertical and horizontal wires; they include components due to mutual coupling as well as those excited directly by the incident field.     

Scattering by wires near a material half-space

The currents in and the field scattered by a thin wire over a material half-space composed of earth, sea water or lake water are determined. Full account is taken of the effect of the half-space on both the currents indneed in the wire and on the scattered field. Distributions of current, back-scattering cross sections, and scattering patterns are shown for both normal and nonnormal incidence and with the incident field polarized in and perpendicular to the plane of incidence.     

Current induced on single and crossed electrically short and thin tubular cylinders by a normally incident plane electromagnetic wave

The currents induced in electrically thin conducting tubes are evaluated from the general solution of the coupled integral equations derived by C. C. Kao [5] in the form of transverse Fourier components. It is shown that on a single cylinder of length2hand radiusain a normally incidentE-polarized field with wavenumberk, the rotationally symmetric zero-order term dominates forka leq 0.1and increases in magnitude askais reduced, but only whenkh > 1. Under these conditions, supplemented with the inequalitya ll h, thin-cylinder theory is valid. The relatively small first-order term produces small departures from rotational symmetry that increase or decrease the current on the illuminated side depending on the condition of axial resonance and the location of the cross section in the standing-wave pattern. Askhis reduced so thatka < kh ll 1, the rotationaily symmetric part of the axial current decreases and becomes negligible compared to the first-order current which is proportional tocos theta. Thin-cylinder theory is then no longer useful. When two electrically thin tubes intersect, thin-wire theory and junction conditions determine only the rotationally symmetric part of the axial currents in the arms. These dominate only when the arms of the cross are not electrically short. The fast-order nonrotationally symmetric components of the axial current and the transverse currents can be determined from the incident magnetic field. They dominate when the arms of the cross are electrically short. The significance of the surface currents and charges on aircraft illuminated by an electromagnetic wave or pulse at low frequencies is pointed out.     

RCS of resonant scatterers with attached wires

The effects of wire antennas carried on aircraft for HF communication on the radar cross section (RCS) at HF frequencies are studied by comparing the RCSs of a strip, a cylinder, and a rod with and without an attached wire. The RCS is found for broadside incidence and for end-on incidence of the plane wave for scatterer lengths from 0.4 to 3.8 wavelengths, typical of aircraft size at HF frequencies. It is shown that the RCS of such fuselage-like targets with a wire antenna is quite different from that of the targets without the wire. For broadside incidence, the wire contributes a sharp peak-and-trough to the RCS are the wire's fundamental resonant frequency. For end-on incidence the wire considerably enhances the RCS at frequencies making its length odd multiples of the quarter-wave     

Electromagnetic excitation of a wire through an aperture-perforated conducting screen

Integro-differential equations are formulated for the general problem of a finite-length wire excited through an arbitrarily shaped aperture in a conducting screen. The wire is assumed to be electrically thin and perfectly conducting, and it is arbitrarily oriented behind the perfectly conducting screen of infinite extent. A known, specified incident field illuminates the perforated-screen/wire structure. The integro-differential equations fully account for the coupling between the wire and the aperture/screen. They are specialized to the case of the wire parallel to the screen with the aperture a narrow slot of general length. These special equations are solved numerically and data are presented for wire currents and aperture fields under selected conditions of wire/slot lengths and orientation. Data indicative of the coupling between the wire and slot are presented.     

A new class of resonant antennas

A new class of wire antennas called meander antennas is introduced as possible elements for size reduction. Efficiency is affected only by the ohmic losses in the wire, and cross polarization is negligible. An increase in the number of meander sections introduces less size reduction in return for an improved bandwidth. These antennas can be used to reduce the size of existing wire antennas such as Yagi-Uda antennas and log-periodic dipole arrays. A size reduction in the resonant length typically from 25-40% is obtained. More size reduction is obtained by decreasing the radius of the wire or increasing the separation of the folded arms     

On the backscattering from two arbitrarily located identical parallel wires

A study of the backscattering from two identical perfectly conducting, thin wires illuminated by a plane wave at an arbitrary angle of incidence is presented. The theory is based on an integral equation method. By decomposing the induced currents into symmetric and antisymmetric modes, the simultaneous integral equations for the induced currents are converted into independent integral equations similar to the one for a single wire for which the solution has already been carried out. The induced currents on and the backscattering cross sections of the wires are determined. Numerical examples include nonstaggered, staggered, and collinear cases of both half-wave and full-wave wires. Comparisons are made between the calculated and measured values of the echo area. The experimental results are in good agreement with theory.     

Rayonnement de réseaux périodiques avec conducteurs et diélectrique

This paper describes a numerical analysis of the electromagnetic behaviour of dielectric panels. These dielectric panels are very large comparatively to the wave length and can be seen as infinite and plane array of dielectric cylinders, illuminated by a plane wave. These dielectric cylinders can have any cross section and can include metallic wires. The conduction currents on the metallic wire and deplacement currents in the dielectric cylinders are determinated by a system of linear equations obtained by the application of vectors potential formalism. The use of Poisson summing gives the possibility to explicite over squared or rectangular boundaries the integrals relative to the deplacement currents. The knowledge of the currents permits to calculate the transmission coefficient of the array. The comparison between the numerical results and experimental measure shows a good agreement.     

Fast iterative approach to difference scattering from the target above a rough surface

The difference field radar cross section (d-RCS) has been defined to analyze the scattering from the target above a rough surface, which takes account of scattering from the target and multiinteractions of the target and underlying rough surface. The d-RCS removes the effect of the finite illuminated surface length under the tapered wave incidence. In this paper, the electric field integral equations (EFIEs) of the difference-induced current J/sub sd/ on the rough surface and the induced current J/sub o/ on the target are derived. A small section of rough surface toward the target in the specular direction is taken to speed up computation of the scattering contribution E/sub s0/ from the moderate rough surface to the target. Then, an iterative approach is developed to solve the EFIEs of the induced currents, directly, and yields the bistatic d-RCS. A finite rough surface length for numerical iteration is taken, corresponding to the dependence on the maximum scattering angle. Using the Monte Carlo method to generate rough surface, the bistatic d-RCS of the target, e.g., a cylinder or a square column, above a Pierson-Morkowitz rough surface is numerically simulated. The induced currents on the target and the d-RCS are discussed, and compared with the case of the target in free-space.     

Wire antennas in the presence of a dielectric/ferrite inhomogeneity

A moment method solution for treating thin-wire antennas in the presence of an arbitrary dielectric and/or ferrite inhomogeneity is presented. The wire is modeled by an equivalent surface current density, and the dielectric/ferrite inhomogeneity is modeled by equivalent volume polarization currents. The conduction currents on the wire and the polarization currents in the dielectric/ferrite inhomogeneity are treated as independent unknowns and determined in the moment method solution. The method is applied to the problem of a loop antenna loaded with dielectric or ferrite. Numerical results are presented, and are in good agreement with measurements and previous calculations.     

Plane wave reflection from a rectangular-mesh ground screen

The theory of scattering of electromagnetic plane waves of arbitrary incidence and polarization from an infinite rectangular-mesh ground screen is treated. The screen is composed of thin wires of circular cross section, and is parallel to the interface between two homogeneous media. The theoretical results for parallel-wire screens are obtained in the limit of large wire spacing for one dimension of the mesh screen. Results presented for incident parallel polarized plane waves indicate that both the parallel-wire and mesh screens may exhibit a change in reflecting properties as the plane of incidence is varied from the wire axis direction. In addition, it is shown that the parallel-wire screen can produce appreciably higher cross-polarized fields than a square-mesh screen of the same wire spacing.     

Monte Carlo study of electron relaxation in quantum-wire laserstructures

Very-low threshold currents are expected to be achieved in quantum-wire lasers owing to the singularity in the density of states occurring at the bandedge. On the other hand, the high-speed modulation of quantum-wire lasers may be limited by carrier relaxation processes that are greatly affected by the reduction in the momentum space. In this paper, we calculate the electron relaxation times for GaAs/AlGaAs wires of various cross sections assuming that electrons are injected in a thermal distribution at the edge of the potential well formed by the barrier. The relaxation times are extracted from the time evolution of the carrier distribution as the electrons come to thermal equilibrium with the lattice. The Monte Carlo method is used to simulate the details of the relaxation process with the inclusion of electron-bulklike phonon, electron-electron and electron-hole interactions. We find that the electron relaxation times range from 120 ps for the 100×100 Å wire to 30 ps for the 200×200 Å wire for a carrier density of 10¹⁸ cm^-3. When the electron-hole interaction is included into the calculations, the equilibration time for the 100×100 Å wire is reduced to ≈50 ps. Screening effects are incorporated using the Thomas-Fermi formalism. At a carrier concentration of 10¹⁶ cm^-1, the equilibration times for the corresponding wire sizes are 20 and 5 ps. Thus, the relaxation time calculated within the limits of our model decreases with an increased wire cross section. This trend indicates the presence of a trade-off between speed and efficiency in quantum-wire lasers considering that the threshold current is decreased by reducing the wire cross section     

Analysis of Crossed Wires in a Plane-Wave Field

The currents and charges induced in a pair of electrically thin crossed wires by a normally incident plane electromagnetic wave are derived by analytical methods. The boundary conditions at the ends and at the junction are explained. The solution of a new integro-differential equation for the currents is obtained in terms of trigonometric and integral-trigonometric functions. Depending on the electrical lengths of the crossed elements and location of their junction a variety of quite different distributions of current and charge obtain. These determine the scattered near and far fields. Graphs of computed currents and charges per unit length on the four arms of several important cases are displayed. The accurate determination of the induced currents and charges on a mathematically tractable structure-the thin-wire cross-is an early step in a study that will proceed to electrically thick cylinders, wide strips, and their junctions in crossed configurations in an effort to gain a meaningful approximate understanding of the currents and charges induced on an aircraft by an electromagnetic pulse.     

The currents on a cylinder illuminated by a generalobliquely-incident plane wave

A relation is presented that determines the total current induced by a general plane wave obliquely incident or a perfectly electrically conducting cylinder of arbitrary cross section from the total current induced by a normally incident plane wave. Remarkably, this same relation ran also be used to determine the physical optics (PO) and nonuniform (NU) currents for oblique incidence directly from the PO and NU currents, respectively, for normal incidence     

A review of analytically determined electric fields and currents induced in the human body when exposed to 50-60-Hz electromagnetic fields

In this review paper, analytical methods are used to determine the electric field and current induced in the conducting human body when this is exposed to an electromagnetic field at extremely low frequencies (ELFs) or very low frequencies (VLFs). This is done by treating it as a parasitic antenna when this is modeled successively as a sphere, an ellipsoid, and a cylinder. Because the body is electrically very short at ELF and VLF, the axial current depends primarily on the length of the body. Comparison with the ellipsoidal shape shows that the induced current is virtually independent of the cross-sectional shape. It is concluded that the axial current induced in the cylinder is a good approximation of the current induced in an actual body with the same length and mean cross sectional area. References to persons standing on the earth and with the arms raised are given. The significance of the accurate knowledge of induced currents and fields for biomedical purposes is discussed.     

The backscattered field of a thin wire loop for H-polarization

For a thin wire loop illuminated by a plane electromagnetic wave, the backscattered field is determined when the incident magnetic vector is parallel to the plane of the loop. The complete second-order geometrical theory of diffraction (GTD) solution is obtained and found to be in excellent agreement with numerical data at angles close to normal incidence on the loop. At wide angles, however, the data exhibit a significant lobe that is not predicted by GTD. Analysis of the data shows that the lobe is due to currents circulating around the loop and the properties of these currents are deduced. Using a simple model for the current, the corresponding contribution to the backscattered field is determined. When this is added to the GTD solution, the resulting expression for the backscattered field is in good agreement with the numerical data for all angles of incidence and all loop diameters greater than a wavelength.     

Radiation and scattering from thin wires in chiral media

The effect of chirality on thin wire antennas and scatterers in unbounded chiral material is examined through the application of fundamental principles and the examination of several canonical examples. In particular, the interplay between normalized chirality and wire length is investigated to classify radiation and scattering patterns. Chirality induces rapid decay in the currents on such wires, resulting in mountain-peak-shaped current distributions characteristic of wire antennas and bow-tie-shaped distributions characteristic of wire scatterers of sufficient length. These current distributions, in turn, cause radiation and scattering patterns which exhibit a chirality-dependent forbidden zone for both antennas and scatterers. In this zone, the fields are greatly reduced. These distinctive results lead naturally to the classification of wire scattering and radiation into subchiral, chiral, and superchiral regimes. All results are understood from the underlying physical principles of electromagnetic chirality, and are related to values of a dimensionless parameter involving normalized chirality and normalized wire length     

Electromagnetic response of two crossing, infinitely long, thinwires

The electromagnetic coupling of two crossed thin wires of infinite length is considered. Two coupled integral equations are obtained, given in terms of generalized impedance functions, for the spectral currents flowing in each wire. The wires may be in a homogeneous medium or over a half-space. The numerical implementation focuses, however, only on the former. The numerical solution may be obtained by either applying moment or multiple scattering methods. The solution obtained from the method of moments is applicable for any wire spacing. Obversely, the multiple scattering method leads to a convenient matrix series solution, which shows that the coupling between wires is proportional to 1/d ² (where d is the wire separation) plus higher order scattering terms     

Scattering from a perfectly conducting cube

The cube epitomizes the complex, three-dimensional scatterer with its multiple interactions and vertex diffraction playing a critical part in the far-field patterns of some bistatic planes. the results presented are for a cube on the order of 1.5-3 wavelengths on edge which is illuminated by a plane wave at broadside incidence. The method employed is the hybrid iterative method (HIM) which utilizes an initial approximation of the surface currents on the cube faces. These currents are inserted into the magnetic-field integral equation (MFIE) to produce improved or updated approximations to these surface currents. This process is repeated to convergence by the method of successive approximations. These currents are then used to find the bistatic radar cross section (RCS) for an arbitrary plane of measurement (emphasis has been placed upon the H-plane and the E-plane). Of particular interest is the development of cross-polarized currents, which are initially approximated by zero. As the iteration process progresses, it is seen that all physical scattering processes present in this body are introduced by enforcing the MFIE     

High-frequency admittance of a thin circular metal wire

The high-frequency admittance is calculated of a linear metal wire with circular cross section in the case where the radius is much less than the length. Different values of electron specularity are considered. Particular attention is given to limiting cases. Calculated data are compared with published experimental results. The respective specularities of copper and silver are evaluated on this basis.