Electromagnetic Wave Source Research Articles

Spherical excitons in manyelectron atoms

The theory is built of a new class of elementary excitations in manyelectron atomes or molecules-spherical excitons, that consists of an electron and a hole in definite angular momentum representation. Spherical excitons may be used as effective sources of electromagnetic high orders multipole waves.

Electromagnetic noise from an automobile and the flow of noise currents on automobile body surface

AbstractWith the widespread use of various electrical applicances in daily life, there has been an increase in unnecessary radiated electromagnetic waves influencing many spheres of social life. In addition to the radiation of unnecessary electromagnetic waves by electrical machinery, considerable noise arises from ignition systems of internal combustion engines. We assumed that the sources of electromagnetic waves were always due to the flow of radio wave currents. As an example of internal combustion engines, this paper uses an automobile engine. Also, a surface current detector was used for the generated noise currents (in the 300‐MHz band). By means of measurements over the body of an automobile (sedan type), the relationship between the noise currents and the radiated noise waves was examined. The automobile body receives various electromagnetic waves which exist in space, especially TV waves, and that flow as high‐frequency currents all over the automobile body. Naturally the reradiation if these waves is considered. On the other hand, a large amount of noise currents of the engine system flows on the bonnet near the fender part. It was observed especially that the noise currents tended to flow from the top of the ignition coil inside the engine housing. However, no noise currents were observed on the car door, roof and trunk. Based on these measurements of the radio noises actually radiated, it can be inferred that it is possible to reduce the electromagnetic radiation if the noise currents which are flowing in the bonnet and the fender part are eliminated.

Search for electromagnetic wave sources using the maximum entropy method

AbstractUndesirable electromagnetic waves radiated from various electrical and electronic apparatus recently have become social problems. Research to prevent these effects is in progress in various fields. This paper presents a method of determining the location of electromagnetic wave sources two‐dimensionally. The analysis method is based on the deduction of the power spectrum by applying the maximum entropy method to time‐series information, i.e., the location of electromagnetic‐wave sources in two‐dimension, corresponds to the power spectrum. It is confirmed by computer simulation that the location can be determined with very high accuracy. The relationship between the amount of data measured and the accuracy of location determination, and the relationship between the accuracy of a source‐location detection and the offset of the measuring position, were examined. The number of measurements was found to be almost twice the number of electromagnetic sources, and the detection of the location of a source can have a very high resolution if the measuring position is kept at a high accuracy. The results show that this method is very effective in determining the position of sources, for example, radiated from a system consisting of subsystems.

A proposal for searching for electromagnetic wave sources by using a synthetic aperture technique

AbstractUnwanted electromagnetic waves radiated from equipment making use of electromagnetic energy create numerous societal problems. The prevention of these problems has been studied extensively. In this paper, a method for estimating the location of the unwanted electromagnetic waves is studied. Since it is difficult to make the antenna aperture large especailly at low frequencies, a search for electromagnetic wave source via a synthetic aperture technique is proposed. In the estimated electromagnetic source distribution by this method, images similar to the antenna sidelobes appear. It is demonstrated by computer simulation that the images can be suppressed by use of the synthetic aperture method with subarrays or use of Mill's cross method. Discrepancies between the true source location and the estimated location have been found in regard to the synthetic aperture length and the geometrical relationship with respect to the aperture center. It has been found that the antenna configuration with the synthetic aperture length of 10 λ can estimate an electromagnetic wave source within 10 λ square with accuracy of less than 1/4 λ square. Therefore this method is sufficiently practical if the location of the source is restricted somewhat.

Experiment on searching for electromagnetic wave sources by using a synthetic aperture technique

AbstractTo control unwanted electromagnetic waves, it is important to estimate accurately the location of the electromagnetic source nearby. Based on the synthetic aperture technique and the signal processing algorithm of the spatial Fourier transform, the location of the source within a planar space of 10 wavelength square has been performed with an electromagnetic source model. It is confirmed experimentally that a satisfactory search of the source is possible using Mills' cross method. A parallel twin wire is used as the electromagnetic source model. Different types of discontinuities are placed along the transmission line and the electromagnetic wave is forced to radiate to create a source. In practice, 300 or 400 MHz is selected and 21 measurement points are selected along the x and y axes with each half‐wavelength spacing. The error of locating the measurement points is the cause of the wave source estimation error. It is demonstrated that the algorithm used here is rather insensitive to these errors.

Electromagnetic Acoustic Wave Source and Measurement and Calculation of Vertical and Horizontal Displacements of Surface Waves

Source d'ondes acoustiques etalon produite en utilisant une force electromagnetique. Application a l'etalonnage d'un capteur d'emission acoustique

EXPERIMENTS STUDY ON SOIL-PILE DYNAMICS USING ELECTROMAGNETIC INDUCTION TYPE SHOCK WAVE SOURCE

In order to clarify soil-pile dynamics, a new experimental method using an electromagnetic induction type shock wave source was developed. In the experiment, a ground model was made of water-cured urethane polymer, and a pile of urethane was buried in this gel-like ground. An impulse with duration time of 0.5ms was given to the pile head by the shock wave source. This device consists of an aluminium circular plate and a flat solenoid coil close to this plate. A capacitor discharge through the solenoid serves as the energy source. Using this device makes it possible not only to estimate exact response characteristis of soil-pile systems pretty well but also to follow sharp wave fronts by photoelastic experiments.

Estimation of wave vector characteristics

In the realistic case of multiple electromagnetic plasma wave sources and multiple propagation paths, auto-correlation and cross-correlation products of the six wave components can be utilized to fit model parameters for the wave normal vector and Poynting vector distribution functions. With the complete wave vector characteristics, the wave mode can be identified, the index of refraction derived and the wave ray traced back towards the wave source region. Plasma wave instrumentation suitable for estimating some wave vector characteristics has been carried on satellites starting with FR-1 in 1964 and has evolved in various configurations on OGO-5, Injun-5, GEOS, Voyager, ISEE, Dynamics Explorer and the proposed OPEN spacecraft. Plasma wave research needs to advance along two parallel lines: (a) developing more sophisticated computer techniques for extracting the wave vector information from extensive data sets and (b) utilizing microprocessor technology in flight instruments to recognize specified phenomena and to capture the appropriate wave data for further on-board or ground processing.

The application of artificial electron beams to magnetospheric research

In the last decade, more than 25 large research rockets have injected electron beams into the ionosphere and magnetosphere to probe the magnetosphere or to investigate various basic problems in space plasma physics. The problem of vehicle neutralization has been studied in the altitude region 100–300 km, and it is now known that the beam injection produces a hot plasma extending possibly as much as 100 m from the vehicle. Vehicle neutralization is enhanced by a discharge associated with the beam or with the return current. The neutralization current may be locally enhanced by neutral gas. Beams have been projected for long distances and appear to be stable in many cases. However, certain beam‐plasma discharges similar to those observed in laboratory experiments may have also occurred in space, tending to thermalize high‐energy beams. Several types of experiments search for beam echoes from field‐aligned potential differences thought to cause auroras. Others have made observations at conjugate regions in the opposite hemisphere for magnetic geometry studies. In the Minnesota ‘Echo’ technique, conjugate hemisphere beam echoes are detected on board the source rocket. From the Echo experiments it was found that ionospheric electric fields map along auroral zone field lines as equipotentials through the equatorial plane. Echo bounce times can be fitted in some cases to model fields, but in other cases the field may be distorted or extended in the night region. Examples from the Echo program at Minnesota are used to illustrate electron beams as magnetospheric ‘probes.’ The injection of such beams creates rich sources of plasma and electromagnetic waves, which have been detected by ejected subsystems near the mother rocket or at ground level. The frequency range extends from a few kilohertz to at least 50 MHz and includes lower hybrid, whistler mode, electron cyclotron harmonics, upper hybrid, and plasma frequency emission. Electron beams have been used to produce artificial auroras that were observed by sensitive television techniques, by other optical methods, and by radar reflections. The scattering, energy loss, and magnetic reflection of beams in the 100‐km atmosphere region have also received detailed study. Future programs including Space Shuttle are discussed. Summaries of the current experimental programs and complete literature references are included.

Prospects for precision physical experiments in optics

Until recently the sources of electromagnetic waves in the radio and γ-ray bands were much more monochromatic than optical sources. The advent of stable lasers with frequency reproducibility ~1014 has uncovered new possibilities of performing experiments of interest in physics. To illustrate these possibilities, results are cited of the measurements of the quadratic Doppler effect in a gas, the magnetic hyperfine structure of a vibrational-rotational transition of methane, and the recoil effect. A number of experiments that lasers will make possible in the near future are discussed, namely, high-accuracy measurements of the Rydberg constant using two-photon absorption, measurement of the quadratic Doppler shift, measurements of the gravitational frequency shift of the earth's field, and the possibility of observing parity nonconservation in atomic transitions.

A narrow beam antenna system using an air column having a central conductor and surrounded by an anisotropic plasma column

The radiation pattern of a magnetic ring source of electromagnetic waves in an air column having a central conductor along its axis and surrounded by an annular axially magnetized plasma column is studied. This configuration gives rise to a radiation peak or peaks near, before, or beyond the critical angle depending upon the value of the magnetic field. The direction of the radiation peak depends upon the inner and outer diameters of the annular plasma column, the diameter of the central conductor, the plasma density, and the magnetic field. The direction of the radiation peak is independent of the diameter of the ring source. For very high magnetic fields the peak shifts toward the end fire direction. Based upon these results it is proposed to develop an electronically scannable narrow beam plasma antenna system.

Narrow-beam antennas using cylindrical columns of isotropic plasma†

It has been reported earlier (Gupta 1970) that a radiation pattern with single or multiple narrow beams may be obtained when a column of isotropic plasma is excited by a ring source of electromagnetic waves placed inside the column. This investigation has been extended to the case where the waves on plasma column are excited by a waveguide source. Also the TE- and TM-modes of propagation for both the excitation schemes have been discussed. Narrow beams of radiation may be obtained in all these four eases. It is observed that the small beamwidths (1° to 5°) are obtained for high plasma densities (∊p = 01) and large plasma column radii (k 0b≥15.0)

The Vavilov-Cerenkov Effect and the Doppler Effect in the Motion of Sources with Superluminal Velocity in Vacuum

It is customary to consider only light sources, or sources moving with a velocity v lower than the velocity of light in vacuum (c). It is assumed in this connection that the Vavilov-Cerenkov effect and the anomalous Doppler effect are possible only in media and waves for which the refractive index n(ω) > 1. For this reason, the phase velocity of the waves is cph = [c/n(ω)] cph. Yet, as is well known, there exist also sources, with velocity v > c. Examples are light spots produced on a remote screen by a rotating source of light or particles. The spot velocity is v = ΩR, where Ω is the angular velocity of source rotation and R is the distance to the screen. The condition v > c can be realized on the Earth, and is practically always realized under astronomical conditions for pulsar radiation. It is emphasized in the article that superluminal sources are equivalent in a wide range to subluminal ones, and, concretely, can generate Cerenkov radiation in vacuum and in a medium with n(ω) < 1. The article considers several corresponding possibilities. From this point of view of radiation theory, a major difference between the superluminal and subluminal sources is that the former can not be individual particles (electrons, protons, etc.), since their velocity is always smaller than c. Superluminal sources, which must thus consist of aggregates of particles, must thus have nonzero dimensions, and this leads to a corresponding formation of a spectrum of the radiated frequencies on the short-wave side. Regardless of whether superluminal sources will find interesting applications in physics and astronomy, a study of the radiation of superluminal sources of electromagnetic and gravitational waves (and possibly also neutrinos) is in the authors' opinion of undisputed physical interest.

Electromagnetic Wave Radiation by Bremsstrahlung, Process from Weakly Ionized Plasma

The Bremsstrahlung radiation from electron-atom collisions in weakly ionized plasma has been considered as a source of electromagnetic waves. The dispersive effect of the ambient plasma on the emission of electromagnetic waves has been studied. The solution of Boltzmann transport equation with collision term has been used to evaluate the emission coefficient for the laboratory plasma. The total electromagnetic wave power in the frequency range ωp<ω<10ωp has been calculated. The effect of the energy of in—coming electrons and the pressure of the ambient plasma on the emission characteristics has been studied.

A multiple narrow beam antenna system using a column of isotropic plasma†

It has been found that a system consisting of a plasma column and a ring source of electromagnetic waves placed inside the column, may give rise to a radiation pattern with single or multiple narrow beams. The direction of these narrow beams of electromagnetic radiation depends upon the column diameter and the plasma density. The amplitude of the peaks depends also upon the position of the ring source. The effect of varying these parameters on the radiation pattern is discussed. It is suggested that the result, presented could be used to design an electronically scannable antenna system.

Statistics of a random plus constant vector with application to acoustic and electromagnetic-wave scattering

A two-dimensional random-walk problem is investigated, where a vector fixed in amplitude (magnitude) is added to one that is random in phase (direction angle). This problem can arise from a study of the effect of multipath interference from an acoustic or electromagnetic-wave source, where an arrival of constant amplitude is combined with an incoherent background of randomly scattered components of the incident field. The source is considered to have harmonic time dependence. This study follows from an earlier paper, in which the required properties of the incoherent background were derived. In the present study, the joint distribution of the resultant amplitude and of the phase angle between the resultant and the fixed arrival is determined. Further, expressions are developed for the first and second moments of the resultant phase, amplitude, decibel-amplitude, and intensity. Many properties of these moments are described.