Tai T. Wu

Comment on ‘‘Focus wave modes in homogeneous Maxwell’s equations: Transverse electric mode’’

The recent formulation by Brittingham [J. Appl. Phys. 54, 1179 (1983)] of a solitary electromagnetic wave called a ‘‘focus wave mode’’ in terms of three regions with discontinuities is found not to satisfy Maxwell’s equations across the discontinuities.

The complete electromagnetic field of a three‐phase transmission line over the earth and its interaction with the human body

The electromagnetic field at all points near a high‐voltage transmission line is determined in analytical form. Account is taken of the presence of the earth below the three‐wire, three‐phase power line. The electric and magnetic fields, the total axial current, and the current and power densities in the interior of a human body are determined when the body is standing on the ground under or near the line, is in an elevated basket under the line, or is reclining in bed near the height of the line. The fields are very weak and the current and power densities so small that thermal effects are ignorable, but not necessarily possible effects on nerve action, the functioning of cells, or on certain secretions.

The dipole antenna with eccentric coating in a relatively dense medium

In a medium of high permittivity or conductivity, such as sea water, lake water, or wet earth, a dielectric coated antenna can produce a directional radiation pattern when the coating is eccentric. The current distribution on a finite or infinite dipole with such a coating is obtained. Formulas for the directivity and the radiation pattern of an infinitely long dipole with eccentric coating are also derived.

Lateral waves: Formulas for the magnetic field

New simple formulas are obtained as an approximation of the exact general integrals for the components of the magnetic field generated by a horizontal electric dipole in a half‐space of water or earth near its boundary with air. These formulas supplement the earlier derivation of the three components of the electric field which are repeated here for completeness. The formulas for the transverse and vertical components are needed in treating the reflection of lateral waves from plane or cylindrical boundaries.

The tapered antenna and its application to the junction problem for thin wires

When electrically thin conductors of different cross sectional size meet, the continuity of current is assured by Kirchhoffs current law. Additional conditions must be imposed on the derivatives of the currents or the charges per unit length. The nature of the required conditions is determined from an analysis of the tapered antenna.

First Correction to the Geometric‐Optics Scattering Cross Section from Cylinders and Spheres

The total scattering cross section in the short wavelength limit is considered in this paper. The problems treated include diffraction of a plane electromagnetic wave by a conducting cylinder (two possible polarizations) or a conducting sphere, acoustic scattering by a rigid sphere, and quantum‐mechanical scattering by an impenetrable sphere. The first correction term to the geometric optics result is computed. In each case, this term is proportional to (ka)−2/3. The constant of proportionality depends on the specific geometry.

Lateral electromagnetic pulses generated by a vertical dipole on the boundary between two dielectrics

An exact solution in terms of elementary functions is obtained in the time domain for the vertical electric field Ez(ρ,t) and the transverse magnetic field Bφ(ρ,t) of a dipole located on the plane boundary z=0 between air (region 2, z 0) when the dipole is excited by a single delta‐function current pulse. The vertical electric field on the boundary consists of a delta‐function pulse that travels in the air with the velocity c, an oppositely directed delta‐function pulse that travels in the dielectric with the smaller velocity c/e1/2, an amplitude structure that varies in time between the two pulses, and a final static electric field due to the charges left on the dipole. The horizontal magnetic field is similar. For comparison, the vertical electric field in the equatorial plane of the same dipole in a homogeneous dielectric is also derived. The comparison indicates that the field along the boundary is a surface‐wave or lateral pulse.

Cylindrical Antennas Immersed in Arbitrary Homogeneous Isotropic Media

The cylindrical antenna is potentially useful as a probe for studying the properties of any material in which it is immersed. Examples of possible media are the earth, plasmas, and organic tissues. Such applications presuppose a knowledge of the detailed behavior of the currents and charges along an antenna in a medium with very general properties. In this paper the integral equation for the current along a highly conducting center‐driven cylinder of length 2h and radius a when immersed in a homogeneous isotropic medium is solved analytically and simple, and quite accurate formulas are obtained for the distribution of current, the distribution of charge, and the admittance. The lengths 2h may range from zero to over a wavelength; the radius a is assumed to satisfy the condition a≪h. The real effective conductivity of the medium may extend from zero to arbitrarily large values, the real effective permittivity from large negative values (as in certain plasmas) to large positive values (as in ordinary dielec...

The propagation of a radar pulse in sea water

The propagation in sea water of an electromagnetic field in the form of a semi‐infinite wave train or a radar pulse generated by an electric dipole is investigated analytically for low frequencies. The frequency‐domain formula for the downward‐traveling field of a horizontal electric dipole excited by a sinusoidally modulated electric‐current pulse is Fourier transformed to obtain an explicit expression for the field at any distance in the time domain. Specific application is made to a wave packet of 25.5 cycles in a time duration of 1 s. The amplitude and phase velocity of the wave packet are determined together with the amplitudes of the initial and final transients. Graphs are displayed and discussed for a range of distances; these show that the amplitude of the wave packet decays more rapidly than the amplitudes of the transients. Possible application to remote sensing in the ocean is considered.

The horizontal-wire antenna over a dissipative half-space: Generalized formula and measurements

It is shown and verified by experiment that a horizontal resonant or traveling wave antenna placed in air close to a dense halfspace with the properties of lake or sea water or earth behaves like a terminated lossy transmission line. The terminal impedance is related to the radiation of the antenna into the air and the complex wavenumber and characteristic impedance are those of an infinitely long line. The complex wavenumber takes account of both dissipation in and radiation into the dense half-space.