Power Transmission Coefficient Research Articles

Kinetic theory of electromagnetic waves obliquely incident upon a plasma slab

The problem of an electromagnetic wave obliquely incident upon a plasma slab is considered as a boundary-value problem, using a self-consistent solution of the coupled linearized Vlasov and Maxwell equations for the electrons, with the ions treated as a fixed, uniform background. Power reflection, transmission, and absorption coefficients are derived under the assumption that electrons undergo specular reflection at the surfaces of the plasma slab. Although our analysis is valid for arbitrary slab thickness, computational results are presented for slabs which are thin compared to a free-space wavelength. The results show a series of resonances which are attributed to the kinetic behavior of the plasma. The results further show that the resonances are Landau damped as the thermal velocity of the plasma electrons increases. While similar resonances can be predicted from the coupled linearized hydrodynamic Maxwell equations, such a model does not predict Landau damping. The effects of a finite collision frequency are then included via a simple Bhatnager-Gross-Krook collision term. The numerical computations vividly indicate that the resonances undergo severe damping for extremely small ratios of the collision frequency to signal frequency.

Reflection and transmission of electromagnetic waves normally incident on a plasma slab moving uniformly along a magnetostatic field

Power reflection and transmission coefficients are found for linearly and circularly polarized plane electromagnetic waves, normally incident on a plasma slab, moving uniformly along a magnetostatic field, normal to the slab boundaries. The solution is found by applying the boundary conditions in the rest frame, and then using relativistic transformations for the fields and the plasma parameters to find the reflection and transmission coefficients observed in the laboratory frame. The results for the circularly polarized incident waves are found in closed form. Numerical results are presented for linearly polarized incident waves. It is found that with an increase in the magnetostatic field, the absolute maximum of the reflection coefficient increases at different velocities. An increase in the magnetostatic field makes the slab more transparent at velocities for which the transmission coefficient with no magnetostatic field is very small. A dielectric-like behavior is observed for large magnetostatic fields. The sum of the power reflection and power transmission coefficients is found to be no longer equal to unity for velocity different from zero.

Hydromagnetic wave propagation and excitation of Schumann resonances

The possibility of excitation of the Earth-ionosphere cavity by hydromagnetic waves propagated through the ionosphere is investigated. Propagation through the ionosphere is studied at frequencies near the lowest resonant frequencies of the Earth-ionosphere cavity (7–30 c/s) by use of Epstein's method. In this method, certain mathematical functions are assumed as layer profiles and the wave equation is transformed into the hypergeometric equation. The analysis is based on macroscopic equations for a partially ionized inhomogeneous plasma embedded in the Earth's magnetic field. It is assumed that hydromagnetic waves are incident from above and propagated parallel to the Earth's magnetic field. Power transmission coefficients are calculated employing complex refractive index profiles which approximate those obtained from available ionospheric data. The transmission coefficients, calculated for various times of day, show that maximum transmission occurs around local midnight and minimum transmission around local noon. The various single particle and instability mechanisms which could possibly lead to generation and amplification of hydromagnetic waves in the ionosphere are briefly discussed. The expected characteristics of electromagnetic noise in the Earth-ionosphere cavity resulting from excitation by hydromagnetic waves and by worldwide thunderstorm activity are discussed.

Microwave Transmission through Thin Metal and Semiconducting Films

The EM power-transmission coefficients of thin films placed in the transverse plane of a rectangular waveguide are shown to be singularly dependent upon the product σd (thin-film conductivity times film thickness). An error analysis justifies the simplification of the theoretical expression for the power-transmission coefficient to the form T= | 2/[2+(ωμ0/ | γ0|)σd] |2. Excellent agreement is obtained with experimental data taken from metal, semimetal, and semiconductor films.

Mutual Coupling in Infinite Planar Arrays of Rectangular Waveguide Horns

The radiation admittance and effective power transmission coefficient are derived by a field matching method for arbitrary scan of an infinite array of open rectangular waveguides. Higher order waveguide modes, as well as higher order modes in the free space cell above the array, are included in the field matching problem. The convergence of the solution was studied, and the number of external free space and internal waveguide modes necessary for an adequate answer are given. Numerical results are obtained and compared with previous theory and with experiment for rectangular grids. Comparison is also made with experiment on a triangular grid which exhibited an anomalous notch in the element pattern. The experimental results in both cases seem to substantiate the theory, at least to the extent that could be expected from the small test arrays that were used for the measurements. The comparison indicates that the method of analysis includes all of the necessary features required for the study of mutual coupling effects in infinite arrays of rectangular waveguides having thick walls.

Properties of Thin Metal Films at Microwave Frequencies

The power transmission, reflection, and absorption coefficients of thin metal films positioned in the transverse plane of a rectangular waveguide are investigated. The results are presented as a function of film thickness for iron, nickel, and silver at 9800 MHz using (a) theoretical expressions for conductivity as a function of film thickness, and (b) measured values of conductivity. Experimental transmission data were obtained and compare favorably with theory.

Scattering of Unidirectional Surface Waves

A perfectly conducting plane screen embedded in a gyrotropic medium is shown to be able to support a unidirectional surface wave. Such a surface wave is assumed to be incident on the top of a semi-infinite screen. At the edge the incident power is converted partly into a reflected surface wave which travels on the bottom of the screen and partly into a space wave. The angular distribution of the radiated energy as well as the power-reflection and the power-transmission coefficients are evaluated. Total reflection is shown to occur for a certain band of frequencies.

Wave Propagation in a Coaxial Glow Discharge

The propagation of electromagnetic radiation from 500 to 4200 Mc in a coaxial cage transmission line passing through a cylindrical discharge chamber is investigated experimentally. Measurements were conducted in argon, helium, and nitrogen gas at pressures between 0.09 mm Hg and 2 mm Hg for a discharge-electromagnetic radiation interaction length of 30.48 cm. The results are compared with theory using a Lorentzian model to describe the electron motion in the presence of the RF field. A graphical method for determining the plasma frequency and electron momentum transfer collision frequency from measurements of the power transmission coefficient at two different radio frequencies is discussed. A comparison is made between the plasma frequency determined by this method and that obtained by the use of a cylindrical Langmuir probe. The electron momentum transfer collision probability is calculated from the RF and probe data.

Scattering of Surface Waves by Discontinuities on a Unidirectionally Conducting Screen

It is shown that a plane screen consisting of closely-spaced parallel wires which are separated from one another and which are such that the radius of the wires and the spacing between them are small in comparison to wavelength, can support a surface wave, the spread of whose field components depends only on the angle which the direction of propagation makes with the direction of the wires. The problem of radiation from a discontinuity in such a semi-infinite waveguide is studied for the following three types of discontinuities: 1) when the waveguide terminates in empty space, 2) when it terminates at another such semi-infinite waveguide having different propagation characteristics, and 3) when it terminates at a perfectly conducting half-plane. In each case, the power reflection coefficient, where applicable the power transmission coefficient, the loss of power due to radiation, and its angular distribution are evaluated. The motivation for this investigation is briefly indicated.

Transmission of Electromagnetic Waves through Pairs of Parallel Wire Grids

The control and direction of electromagnetic waves is accomplished, in general, by the use of boundary materials and structures which produce desired effects on such waves when irradiated by them. An important class of boundary structure for this purpose is a surface having alternate areas of conducting and nonconducting material. Grids formed of a large number of parallel cylindrical conductors of circular cross section, uniformly spaced and lying in a common surface, are among the most generally useful of this class of boundary structure. Single layer parallel wire grids have received considerable study in the past. However, little information is available concerning the characteristics of multiple layers of such grids An analytical solution is obtained for the power transmission coefficient of a double grid system. Power transmission coefficients for various combinations of system parameters are computed from the analytical solution and tested experimentally. The solution is found to yield excellent correlation with experiment until the interwire spacing approaches the wavelength.