High-frequency fields excited by a line source located on a perfectly conducting concave cylindrical surface

Alternative representations are obtained for the high-frequency surface field excited on a perfectly conducting concave circular cylinder by an axial magnetic line current located on the surface. Included are ray-optical, canonical integral, whispering gallery mode, and near-field formulations, and various combinations of these. Asymptotic evaluations in different parameter ranges lead to results with varying accuracy and physical content. Their utility is assessed by extensive numerical calculations and comparisons. Most intriguing is a form of the asymptotic solution that involves only a number of geometric optical rays and a number of whispering gallery modes.     

Excitation of surface waves on a unidirectionally conducting screen by a phased line source

The excitation of surface waves on a unidirectionally conducting screen produced by a phased line source located above the screen and perpendicular to the wire elements is considered. The screen consists of an infinite number of straight, perfectly conducting, parallel wires and conducts only in the direction of the wire elements. The phased line source consists of a periodic line current with an electric charge distributed along its length. The complete electromagnetic field is determined exactly and simple expressions are given for the scattered far field. It is shown that surface waves exist and simple expressions for the amplitudes are given. Another principal result is the determination of the magnitude of the complex Poynting vector for the radiated power. It is found that the pattern function lies on a cone independent of the presence of the screen and that the cone angle depends only on the phasing of the source. The pattern function at points below the screen is independent of the location of the source above the screen. Furthermore, the pattern function vanishes in the direction of the screen and this seems concomittant to the existence of surface waves. Two pattern functions are drawn for typical cases of interest. The power propagated by the surface waves is also determined. The method employed to solve the problem is based on the deduction that the scattered magnetic field component in the direction of the wire elements is zero. A consequence of this deduction is that the electromagnetic field can be derived from a single scalar wave function that satisfies a partial differential equation in the plane of the screen and a jump condition across the screen. This method is quite general and can be applied to a large class of interesting propagation problems arising from different types of excitation. The scattered far field is obtained using another method that is algebraic in character and does not require a complete solution of the problem.     

Radiation from a line charge source located near an air-piezoelectric interface

The ray optical solution to the problem of a time harmonic line charge source radiating acoustic energy into a semi-infinite piezo-electric half space is outlined. This ray optical technique differs from the approach employed in recent publications [1], [2], and leads to a better understanding of bulk-wave radiation in SAW devices. PZT ferroceramic materials have been chosen for this study and numerical results are obtained and given.     

Excitation of surface waves on a unidirectionally conducting screenby an arbitrary phased line source parallel to it

An exact solution is obtained for the scattering problem of a phased line source in front of a screen and parallel to it. The direction of perfect conduction forms an arbitrary angle Ω with the normal projections of the filament on the screen. The coupled surface waves and scattered far field are investigated, and alternative expressions suitable for numerical calculations are presented together with numerical results. It is found that the energy is highly localized in the neighborhood of the screen, and the closer the filament is to the screen, the larger the excitation of the surface wave. In addition, it was found that the surface waves travelling to the right and to the left of the filament are different and become identical only when either Ω=π/2 or the propagation constant γ=π/2. For the special cases γ=Ω and Ω+γ=π, a surface wave is excited in only one side of the screen. In general, the surface waves are slow waves which are circularly polarized with opposite polarization on both sides of the screen. The ordinary end fire source was found to be characterized by 100% launching efficiency     

Electromagnetic coupling between two half-space regions separatedby two slot-perforated parallel conducting screens

The problem of electromagnetic coupling between two half-space regions separated by two slot-perforated parallel conducting planes is investigated. A general moment solution for the problem is obtained. This moment solution is then specialized to the case of narrow slots and to a TE (transverse electric to the slot axis) excitation. Attention is given to the power transmitted from one half-space to the other through the slots and to its functional dependence on various problem parameters involved     

High-frequency fields excited by a line source located on a concave cylindrical impedance surface

A previous study of high-frequency currents induced by a line source on a perfectly conducting concave cylindrical surface is extended to the case of nonvanishing surface impedanceZ_{s}. Alternative field representations are formulated and evaluated asymptotically as combinations of ray-optical, whispering gallery (WG) mode, surface wave, continuous spectrum, and canonical integral contributions. Numerical calculations provide an insight into the accuracy and utility of the various formulations. Sufficiently far from the source point, a combination of ray optical fields and tightly bound WG modes was previously found to be a most appealing form whenZ_{s} = 0. As the surface impedance becomes more dissipative, the WG modes axe weakened by attenuation and eventually render the ray optical fields adequate by themselves. A representation in terms of rays and a canonical integral is found to be useful for all parameter ranges. The canonical integral has been evaluated numerically and tabulated.     

Electromagnetic coupling between two half-space regions separatedby multiple slot-perforated parallel conducting screens

Considers the problem of electromagnetic coupling between two half-space regions separated by multiple slot-perforated parallel conducting screens. The fields are considered to be excited by either a transverse electric (TE) or a transverse magnetic (TM) plane wave. A characteristic mode solution is used for the computation of the fields in each half-space. Special attention is given to the power transmitted from one half-space to the other through the slots and to its functional dependence on various parameters. Numerical examples are presented for illustration and comparison     

Scattering by a moving unidirectionally conducting screen

The problem of scattering that results when an arbitrary field is incident on a unidirectionally conducting screen undergoing translational motion is analyzed. The screen is assumed to move at a constant speed in its own plane and in a direction perpendicular to that of conduction. A relativistically exact solution is obtained in the (stationary) frame of the observer via representing the screen as a plane where boundary conditions must be met plus a field constraint to be applied everywhere. The solution is presented in integral form and applied to the case of plane wave incidence for which low velocity effects are displayed     

Current induced on a conducting cylinder located near the planar interface between two semi-infinite half-spaces

An analysis is described for determining the current induced by a known excitation on a conducting cylinder located near the planar interface between two semi-infinite, homogeneous half-spaces of different electromagnetic properties. The perfectly conducting cylinder of general cross section is of infinite extent and the excitation is transverse magnetic to the cylinder axis. An integral equations for the induced current is derived and a numerical method for solving it is developed. The kernel of the integral equation contains a term corresponding to the usual open-space Green's function plus a term proportional to a Sommerfeld-type integral in two dimensions. Various forms of the Sommerfeld-type integral are given and the choices of form amenable to efficient evaluation are discussed. For a flat strip, a circular cylinder, and a rectangular cylinder, data are presented and discussed for selected parameters. Data are presented for cylinders above and below the interface as well as for a cylinder resting on the interface.     

EM fields of a phased line current over a conducting half-space

The need often arises to predict the electromagnetic field of power and communication lines over the earth. A simple and explicit derivation is given for the electromagnetic fields of a travelling current line source located over a layered conducting half-space. Special attention is paid to the case of a homogeneous half-space where analytical closed-form expressions can be obtained. Of some interest is the radiation of a vertically polarized radio ground wave which would not be present if the line source was uniform     

Guidance of waves by a moving unidirectionally conducting screen

The scattering problem for a moving, unidirectionally conducting screen excited by a conical wave is analyzed using the exact relativistic integral representation previously derived by the author (see ibid., vol.37, no.1, p.64-70, Jan. 1989). The screen is in uniform motion in its own plane and in a direction perpendicular to that of conduction. The screen is found to respond with a conical scattered field and a certain type of surface waves which are of a different nature from that which a stationary screen allows. An equivalent image source is found, and low-velocity effects are show explicitly     

Diffraction by a circular aperture in a unidirectionally conducting screen

The diffraction of a normally incident plane electromagnetic wave with wave numberkby a circular aperture of radiusain a unidirectionally conducting plane screen of zero thickness and infinite extent is considered. In the limit of largeka, the ratio of the transmission cross section to the geometrical optics valuepi a^{2}, is found up to the order(ka)^{-3/2}.     

Radiation patterns for two monopoles on a perfectly conducting sphere

A general numerical technique for analyzing monopole antennas protruding from a conducting sphere is suggested. Computed results for special cases of antenna locations are compared to known and approximate solutions showing that the method is practical and accurate.     

Maximum field criteria for a line current source in a conducting medium

Criteria are presented for the maximum amplitudes of the electric and magnetic fields that can be produced at various distances by a line current source immersed in a conducting medium of infinite extent.     

Current induced by TE excitation on a conducting cylinder located near the planar interface between two semi-infinite half-spaces

An analysis is presented for determining the current induced by a known transverse electric excitation on a perfectly conducting cylinder located near the planar interface separating two semi-infinite, homogeneous half-spaces of different electromagnetic properties. The conducting cylinder of general cross section is of infinite extent and the excitation is transverse electric to the cylinder axis. Two types of integral equations, the magnetic field integral equation and the electric field integral equation, are formulated, and the Green's functions for the integral equations are derived in an appendix. Numerical solution methods for solving the integral and integrodifferential equations are presented. For a strip parallel or perpendicular to the interface, a circular cylinder, and a rectangular cylinder, data are presented and discussed for selected parameters, including the case of a cylinder resting on the interface.     

Detailed FD-TD analysis of electromagnetic fields penetratingnarrow slots and lapped joints in thick conducting screens

The physics of electromagnetic-wave transmission through narrow slots and tapped joints in thick conducting screens is examined in detail by applying numerical models to compute both field distributions within the slots and joints, and fields transmitted to the shadow region. The primary modeling tool is the finite-difference time-domain (FD-TD) method, using a Faraday's-law contour integral approach to modify the basic FD-TD algorithm to properly model the slot physics, even when the slot gap width is much less than one space lattice cell. Finely sampled method-of-moments (MM) models are used to validate the FD-TD tool for relatively simple straight slots; FD-TD is then used to explore properties of more complicated lapped joints which are widely used for shielding purposes at junctions of metal surfaces. It is found that previously reported slot resonances occur in a more general sense for lapped joints as path-length resonances. In addition to greatly enhanced power transmission, path-length resonances can result in total fields within the joint exceeding the incident fields by more than one order of magnitude. Sample field distributions for this case are given     

Asymptotic solution for line source radiation from a curved perfectly conducting wedge

An asymptotic solution is presented for the radiation of an infinite line source located on a convex face of a perfectly-conducting curved cylindrical wedge. The solution employs a pair of new universal functions. Excellent agreement with a moment method solution is demonstrated for radiation from an original cylinder.<>     

The transient electromagnetic field of a pulsed line source located above a dispersively reflecting surface

An exact representation for the transient field of a pulsed line source above a plane reflecting surface is obtained as a finite integral over the transient plane-wave solution for complex angles of incidence. When applied to the reflection from a conducting half-space, a solution for the transient field is obtained as a finite double integral, which permits accurate calculations in a minimum of computer time. Comparison with early-time and late-time approximations available in the literature shows that there is a wide range of times for which neither is accurate.