Kenneth P. Spies

QUASI‐STATIC TRANSIENT RESPONSE OF A CONDUCTING PERMEABLE SPHERE

When a conducting body is immersed in a time‐varying magnetic field, eddy currents are induced. These, in turn, produce a secondary magnetic field which may be detected by an observer external to the sphere. It has been demonstrated that a measurement of the external field can be used to estimate the conductivity of the body if certain assumptions are valid. For example, Ward (1953) has shown that the conductivity and permeability of geological core specimens from diamond drill holes may be determined by examining the frequency dependence of the time‐harmonic response of the specimen. In principle, the same information should also be available from the time response of the specimen for a suddenly applied magnetic field (Wait, 1951). In this paper, we wish to discuss the transient solution when a homogeneous conducting sphere is under the influence of a transient magnetic field. Also, as suggested earlier by Wait (1951), the actual time‐domain electromagnetic response of a massive sulfide body should exhib...

Electromagnetic propagation in an idealized earth crust waveguide, part I

SummaryThe electromagnetic mode characteristics for the earthcrust waveguide are considered. The formulation allows for any depth-conductivity profile, but the specific results are only for a homogeneous sub-surface waveguide region with a finitely conducting lower layer and a perfectly conducting upper layer. Attenuation rates of the order of 1 dB/km are possible for operating frequencies of 20 kHz or lower if the crystalline rock in the waveguide has conductivities less than 10−6 mhos per meter.

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.

Radio propagation over a cylindrical hill including the effect of a surmounted obstacle

An analysis is presented for wave propagation over a smooth cylindrical surface of constant curvature when the boundary impedance is specified. High-frequency approximations are introduced which permit a universal plot of the diffraction loss as a function of a hill-height parameter. The results are extended to allow for the presence of a knife-edge obstacle located on the crest of the rounded hill. For the conditions considered, the latter produces a substantial gain which, to some extent, overcomes the diffraction loss associated with the hill. The results have direct application to HF and VHF radio propagation over heavily vegetated and forested terrain.

Range dependence of the surface impedance and wave tilt for a line-source excited two-layer earth

The integral representations for the field components are evaluated numerically and compared with often used asymptotic formulas. It is found that the latter have a limited range of validity when the substratum is highly resistive. In general, the distance to the source cable must be allowed for in the interpretation of the observed fields.

On the radiation from a vertical dipole with an inductive wire-grid ground system

The far field of a vertical electric dipole on a sectionally homogeneous ground plane is considered. The specific model used is a dielectric-like ground which is modified by using an inductive wire grid or mesh screen in a region surrounding the dipole. Attention is focused on the modification of the radiation pattern resulting from the presence of the inductive ground screen. It is demonstrated that the low-angle radiation may be greatly enhanced by a ground screen which extends out to 15 or more wavelengths.

Electromagnetic propagation in an idealized earth crust waveguide, part II

SummaryFurther calculations for the mode characteristics for an idealized model of the earth crust waveguide have been carried out. Specifically, we consider a homogeneous waveguide region bounded below by a homogeneous transition layer whose conductivity is intermediate between that of the main waveguide region and the bottom conductive region. It is shown that the presence of the transition layer usually increases the attenuation rate of the dominant modes although there are some interesting exceptions.

User-oriented performance evaluation of data communication services: measurement results

The authors report the results of the Institute for Telecommunication Sciences (ITS) measurements of a particular data communication performance parameter, block transfer time, on several public data networks. The measurements were conducted in accordance with the general requirements set out in American National Standards X3.102 and X3.141, and a specific experimental design. Issues associated with the proper interpretation of end-to-end data communication performance values are identified and discussed.<<ETX>>

Quasi-static Transient Response of a Conducting Permeable Sphere; discussion and reply

Wait and Spies have calculated the transient step-function response of a conducting permeable sphere using the harmonic response and integral transformations. The result is given as a series of exponential functions instead of the higher functions used earlier (Wait, 1951). The exponential series solution can be obtained in another way by separating the time and spatial variables.

On the Calculation of Mode Conversion at a Graded Height Change in the Earth-ionosphere Waveguide at VLF†

A multistep model is used to simulate the transition between the day and night portions of the earth-ionosphere waveguide. A convenient simplification is the justified neglect of all reflected modes. On the other hand, forward mode conversion (and reconversion) is accounted for. The analytical method involves the multiplication of square matrices which correspond individually to the conversion at the various steps. The calculations are carried through for a sharply bounded ionosphere and a perfectly conducting ground. Earth curvature is allowed for but the influence of the earths magnetic field is neglected. A calculated example for 20 kHz indicates that the transition length δd between day and night influences the amount of mode conversion.