James R. Wait

On the electromagnetic field of a dielectric coated coaxial cable with an interrupted shield

A boundary value treatment is used to derive field expressions for a dielectric coated coaxial cable with a gap in the shield. Specific results are given for an incident TEM mode in the interior coaxial region. For example, it is shown that, for the VHF region, as much as 18 percent of the incident power is radiated into the external region via a single circumferential gap in the shield. Comparable amounts of power are transferred to a reflected TEM mode in the cable and into surface waves in the dielectric jacket.

Electromagnetic Surface Wave Propagation over a Bonded Wire Mesh

The electromagnetic surface wave that can propagate over a square mesh of intersecting parallel wires is considered. A combined analytical and numerical method developed earlier is employed to deal with the interacting wire currents. For small mesh spacings, the propagation constant is found to be almost independent of the azimuthal direction of propagation. This is in agreement with previous results obtained by Soviet investigators who utilize averaged boundary conditions for analyzing such bonded wire meshes. However, for larger wire spacings, greater than about one tenth of a wavelength, there is a significant dependence on the direction of propagation over the mesh. The validity of describing the wire mesh in terms of an effective transfer inductance and related questions are discussed briefly in the Appendix.

Electromagnetic surface fields produced by a pulse‐excited loop buried in the earth

A transient excited magnetic dipole immersed in a conducting half‐space is considered. Explicit results for the field waveforms observed on the surface are obtained for the case where the exciting current is an exponential time function. It is shown that the shape of the waveform is diagnostic of the relative location of the buried source. The results have possible application in mine rescue operations.

Determining electrical ground constants from the mutual impedance of small coplanar loops

Curves are presented for inverting measured mutual impedance to yield the conductivity and permittivity of an equivalent half-space. The displacement currents are allowed for and the loop separation is specified to be either one tenth or one twentieth of a free-space wavelength.

Electromagnetic Transient Response of a Spherical Conducting Shell over a Conducting Half-Space,

Abstract The quasi-static response of a thin spherical conducting shell over a conducting half-space is derived for plane-wave illumination. The waveform of the transient scattered field consists of two decaying exponentials whoso time constants uniquely specify the shell radius and conductivity-thickness product. The coupling between the shell and the ground is also examined.

Electromagnetic interaction between a conducting cylinder and a solenoid in relative motion

An analysis is presented for the mutual impedance between two solenoids that are coaxial with a conducting cylinder in relative motion. The formulation is based on the first‐order Lorentz transformation and the results obtained are sufficiently general to encompass any such situation that could arise in nondestructive‐testing schemes. A numerical example, relevant to steel‐wire ropes of 2‐cm radius used in mine hoists, indicates that even with relative velocities as high as 10 m/s, the mutual impedance at 10 Hz differs little from that calculated for zero velocity. However, the nonreciprocal effects could be significant for higher velocities and/or for more highly conducting and larger ropes.

Theory of the Terrestrial Propagation of VLF Electromagnetic Waves

There is now a vast literature on the subject of radio propagation of long electromagnetic waves in the waveguide formed by the earth’s surface and the lowest ionosphere. The attention is focused most heavily on the VLF (very low frequency) band, which corresponds to frequencies from 3 to 30 kHz,, the principal reason being that the attenuation of the waves is very low and the phase stability of the waves is very high. Thus, these waves find numerous applications in global communications and in long-range navigation systems.

Normal mode model for electromagnetic propagation in the earth crust waveguide

Propagation of modes in an idealized model of the earth-crust waveguide is considered. The two-layer region is bounded above and below by a perfectly conducting plane. For this structure, there are an infinite number of discrete modes without any contribution from a continuous spectrum. The excitation factor for the structure is derived for voltage-type and electric, current line sources. Specific numerical results for 1 to 1000 Hz are given for the case where the lower conductive region is effectively of infinite depth. It is found that the conductivity of the upper region is the main controlling factor on the attenuation rate.