Propagation Of Electromagnetic Signals Research Articles

Reply to `Remarks on ``Optical pulses in an optically active moving Tellegen medium'' '

Professors Weiglhofer and Lakhtakia make use of Post as the the ancient scholastics of Aristotle. I have proved elsewhere [1] that his equation (6.18) is unnecessarily restrictive. Strictly speaking all media are dispersive but in many cases, dispersion may be neglected, for example, for nonanalytic waves propagating with the wave front velocity. Professors Harmuth and Hussain [2] have rightly argued that `periodic waves are outside the causality law'. [1] Hillion P 1996 Remark on the constitutive relations of linear bi-isotropic media IEEE Antennas Propag. Mag. 48 93 - 4 [2] Harmuth H F and Hussain M G M 1994 Propagation of Electromagnetic Signals (Singapore: World Scientific)

Electromagnetic Step Signal Propagation in Lossy Waveguide

Electromagnetic Step Signal Propagation in Lossy Waveguide

Lightning transient fields in the atmosphere—low ionosphere

The complexity of the electric properties of the atmosphere, which influences the excitation and propagation of electromagnetic signals generated by lightning discharges, gives rise to a diversity of the typical signal wave forms and amplitudes in the various space-time domains. This causes difficulties and controversies in the interpretation of the experimental data. In geophysical problems of such a kind, considerations accounting for a broadband spectrum are particularly important. In the present paper, lightning induced ULF-VLF fields in the daytime inhomogeneous atmosphere and D-region of the ionosphere above the thundercloud are analyzed for a standard model of the vertical return stroke. The developed analytical approach makes it possible to unite the canonical model of the electromagnetic radiation into a free-half-space, the discharge (ELF-VLF spectrum) and ‘post-discharge’ (ULF spectrum) low-frequency models and to clarify the temporal scales in the mechanism of lightning coupling with the atmosphere and low ionosphere with respect to the local relaxation time, discharge characteristic time scales and observer location.

Borehole Radar - Why it is Different from Lower Frequency DHEM Techniques

Borehole radar is a geophysical technique which uses high to ultra-high frequency radio waves generated and detected in boreholes to produce a high resolution image of the subsurface. The physics of the propagation of radio frequency electromagnetic signals in the earth is quite different to the physics of audio frequency electromagnetic signals used in most other drillhole electromagnetic techniques. The difference is due to the difference in value of the loss tangents of geological materials at these two frequencies. The loss tangent is equal to the ratio of conductivity to the angular frequency multiplied by real permittivity. At audio frequencies the loss tangent of geological materials is much greater than 1. Consequently, the full damped wave equation that describes the propagation of electromagnetic reduces to a minor variation on the diffusion equation and electromagnetic signals travel predominantly by diffusion. At radio frequencies the loss tangent is much less than 1 and the damped wave equation reduces to a minor variation on the standard undamped wave equation and electromagnetic signals travel predominantly as waves.As a result of the wave behaviour of electromagnetic signals at radio frequencies, borehole radar can be used to produce high resolution images of the subsurface, albeit at smaller ranges. Sample measurements of the electrical properties of the host rock from two large Australian base metals mines (Mt Isa, Broken Hill) suggest that borehole radar can be used to obtain reflections from interfaces up to 25 m away at 50 MHz and up to 70 m away at 20 MHz. The wave behaviour of electromagnetic signals at radio frequencies makes it possible to obtain very detailed images of rock structure with borehole radar. At 20 MHz, structures as small as 2.5 metres in size may be detected, and at 50 MHz, structures may be detected down to a size of about 1 m.

Using spacecraft range data and radar observations for the improvement of the orbital elements of planets and parameters of Mars rotation

The extremely precise Viking (1972–1982) and Mariner data (1971–1972) were processed simultaneously with the radar-ranging observations of Mars made in Goldstone, Haystack and Arecibo in 1971–1973 for the improvement of the orbital elements of Mars and Earth and parameters of Mars rotation. Reduction of measurements included relativistic corrections, effects of propagation of electromagnetic signals in the Earth troposphere and in the solar corona, corrections for topography of the Mars surface. The precision of the least squares estimates is rather high, for example formal standard deviations of semi-major axis of Mars and Earth and the Astronomical Unit were 1–2 m.

Hillion's proof of the nonexistence of certain solutions of Maxwell's equations

The author notes that P. Hillion (see ibid., vol.33, no.2, p.144-5, 1991) has greatly simplified the author's proof that Maxwell's equations have generally no solution in the case of propagation of electromagnetic signals in lossy media. He clarifies some remarks on conservation of energy and causality law.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dominance of resistive losses over hysteretic losses in ferromagnetic conductors

In the presence of ferromagnetic conductors, electromagnetic signal propagation might be seriously degraded through hysteretic losses. It is shown, however, that independent of frequency, such losses are always smaller than the ordinary resistive losses that would be calculated for a similarly resistive, equivalent paramagnetic material. This indicates that measurements of conductivity and permeability suffice to bound hysteretic losses, obviating the necessity for measurements of hysteresis at operating frequencies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Propagation effects for electromagnetic pulse transmission

We review past research on the propagation of electromagnetic pulse signals over the surface of the earth with emphasis on analytical methods to predict waveforms. The best example is the electromagnetic field radiated from a lightning stroke that can be observed at global distances or very close in if one has sufficient motivation. In any case, the propagation channel will distort the signal wave shape because of the strong frequency dependence of the attenuation factors and the phase velocities of the modes. We begin with a flat earth model that has the virtue of simplicity particularly when displacement currents in the earth are relatively small compared with the conduction currents. Here we see that the rise time of the ideally radiated step function signal is of the order of a few microseconds at a range of 50 km over average land paths. Such a prediction is in accord with published experimental data. At greater ranges, earth curvature comes into play and we show here how various analytical and numerical methods can be used in overlapping time regions which serves as a good consistency check. Other complicated effects such as mixed land-sea paths and ionospheric influences are also reviewed.

Covariant electromagnetic theory for inertial frames with substratum flow

Based on the Galilean relativity principle and Maxwell's equations, electromagnetic field equations are derived for inertial frames, in which the substratum of the electromagnetic waves flows with arbitrary velocity | w | &lt; c (velocity of light). It is demonstrated that the electromagnetic field equations with electromagnetic substratum flow are strictly covariant against Galilei transformations. Wave equations, conservation and invariance theorems, and boundary conditions are derived for the electrodynamic fields in presence of electromagnetic substratum flow. Initial‐boundary‐value problems are solved for electromagnetic signal propagation and induction in the substratum by an integral equation method. Physical effects for the measurement of the velocity field of the electromagnetic substratum are discussed. Maxwell's conception that his equations refer to a frame of reference with resting electromagnetic substratum is confirmed, and it is shown that Maxwell's equations are also applicable to inertial frames with small substratum velocities, | w | ≪ c.

Theory of the electromagnetic transient response of the ionosphere for plane wave excitation

The reflection and transmission of a transient plane wave by an ionosphere with a linear electron density profile and constant collision frequency are calculated. The exact frequency domain solution is inverted numerically, and the resultant reflected and transmitted waveforms are found to satisfy causality. A linearly varying, nondispersive dielectric half-space is also considered, but the nonphysical nature of the model causes the reflected waveform to be noncausal. Using convolution the waveforms for a step modulated sinusoid excitation are also obtained from the impulse response of the ionosphere. The results provide insight into the physical mechanism involved in the ionospheric propagation of HF electromagnetic pulsed signals.

A CAD Tool For The Analysis OfComplex-geometry Microwave Circuits

In this abstract, the development of a microwave-circuit CAD tool is described, which accomplish the full-wave analysis of the electromagnetic signal propagation through complex-geometry domains. The simulation relies on the extension of the well-known Finite-Difference Time-Domain (FDTD) integration algorithm to non-orthogonal, unstructured discretization meshes. In the present approach, a highly flexible discretization strategy is exploited, which allows for intermixing different kinds of elements and field-mapping strategies. Through such a technique, the analysis of complex-geometry structure is made possible at a computational expense close to that of conventional, orthogonal-grid FDTD technique. A set of simple examples is discussed, which illustrates the main capabilities of the proposed method.

Propagation of ground wave electromagnetic signal, with particular reference to a pulse of nuclear origin

The physical phenomena of the theory of propagation of an electromagnetic pulse at low radiofrequencies are scrutinized from the viewpoint of detection systems. Methods for tagging a point in time on the pulse are described theoretically. The filter action of the propagation medium together with various select receiver filters are considered in the analysis. A particular electromagnetic pulse observed and recorded at a short distance from the source (44.6 km) is propagated theoretically to a great distance ( > 2000 km) as a ground wave. The behavior of the tagged point in time on the pulse is studied both as a function of distance and as a function of the conductivity of the ground. The computer method is also used to determine the attenuation vs. distance function of the pulse. This study provides information of general interest on the subject of low radiofrequency pulse propagation. In addition, the results of this study form a basis for the determination of the effects of ground conductivity on location finding systems, based on the theory of propagation of an electromagnetic pulse.