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Results of an investigation of the interaction of electromagnetic fields with plasmas, including the development and use of appropriate non-linear modeling techniques, are presented. Expressions for density distributions in the sheath and potential induced on a conducting plate in the presence of a plasma (moving or stationary) are found. The potential at one temperature in the sheath is non-linearly modeled to give the potential at another temperature. Correction terms are found for the standard treatments of the interaction of electromagnetic fields with collisionless plasmas and weakly ionized gases. These corrections are functions of field intensity and give significant results for high intensity fields. The current induced in the plasma with a low intensity field is non-linearly modeled to the high intensity case. Expressions for the conductivity (both a.c. and d.c.) are found for various plasmas and incident field intensities. (Author)

This is the final report under contract F19628-70-C-0072 and summarizes the research performed in the Department of Electrical Engineering and Systems Science, Michigan State University. Topics investigated were (1) the radiation and circuit properties of backfire antennas and open-cavity radiators, (2) the characteristics of impedance loaded slot antennas, (3) the properties of a multi-loaded cylindrical antenna, and (4) the modification of scattering by a multi-loaded slotted cylinder. (Author)

A numerical-physical optics method is applied to study the circuit (impedance) and radiation characteristics of the short-backfire antenna. This radiator, developed through extensive experimentation by AFCRL, consists of a dipole exciter located between a large rimmed reflector and a small secondary reflector. It has wide bandwidth and high directivity comparable to sophisticated reflector antennas. In the numerical-physical optics method, the following steps are followed: (1) a set of coupled integral equations for the currents excited in the dipole and on the surface of the secondary reflector are formulated and solved numerically, assuming for this step that the large reflector is infinite; (2) the surface currents of the large reflector are approximated by a truncated form of those calculated for the infinite conducting sheet; (3) the radiation field maintained by the currents of the steps (1) and (2) is calculated; and (4) a diffracted field correction is made to account for the finite dimensions of the large reflector and its rim. This method has the advantage, relative to earlier studies, that it can successfully predict the antenna's circuit characteristics. Excellent results are obtained for both square and circular geometries. Comparison is made with experimental measurements made by AFCRL. (Author)

A simple, flush-mounted antenna consists of a slot cut in a ground plane and excited by a potential maintained between its edges at a point along its axis. The circuit and radiation properties of electrically small slot antennas doubly loaded by lumped impedances connected between their edges are investigated. In the theoretical investigations, integral equations for the electric field distributions excited in the impedance loaded slots by a delta-function current source are formulated and solved numerically. In terms of these slot fields, the input impedances and the radiation fields of the loaded slot antennas are calculated. These analytical results are confirmed qualitatively by those of complementary experimental studies. It is demonstrated that the electrically small slot can be forced into a near antiresonant condition by the selection of an optimum purely reactive loading. A large input resistance is subsequently obtained. This optimum reactance is found to be usually capacitive while the antenna input impedance is inductive. Low loss capacitive loading and tuning impedances can thus be utilized to implement a high efficiency, small antenna. A second optimum reactance loading leads to radiation field patterns which can be highly directive in the case of the rectangular slot or greatly modified for the annular slot radiator. (Author)

This research investigates the radiation and circuit properties of an open-cavity radiator. This antenna consists of a simple, open-ended circular cavity with a primary radiator, placed at an appropriate location inside the cavity. If a reflecting disk is placed at the aperture of this radiator, it becomes a short 'backfire' antenna. The waveguide excitation theory is employed to find the field excited in the cavity. The aperture field is then determined by summing the propagating modes at the open end of the cavity, and the radiation field is calculated based on the aperture field. The input resistance of the radiator is obtained from the total radiated power carried by the propagating modes and the input current of the primary radiator. Various primary radiators such as a dipole, a dipole array, a transmission line, and a circular loop are considered. An experimental study has been conducted parallel with the theoretical analysis and a satisfactory agreement has been obtained between theory and experiment. (Author)

The feasibility of minimizing the back scattering of a conducting cylinder by attaching a parallel thin, loaded wire is investigated. When the cylinder and wire are illuminated by an electromagnetic wave, currents are induced on them. If the induced current on the wire is modified by a proper impedance loading, it may cancel the effect of the induced current on the cylinder in such a way that the total back-scattered field p1oduced by the cylinder and the wire is minimized. /n the analysis, a solid cyl/nder and a thin, cente1-loaded wire are placed parallel to one another and a plane wave is assumed to be incident on them at an angle. The /nduced currents on them and t0e scattered field from them are calculated, and the optimum impedance to be loaded at the wire to achieve zero total back scattering is obtained. This method should have d/rect application to radar camouflage for space veh/cles. (Author)

A theory on the minimization of the back scattering of a cylinder by loading a cylinder at two points with lumped impedances is presented. The induced current on a doubly loaded cylinder when illuminated by a plane electromagnetic wave at an arbitrary angle is obtained. The optimum loading to eliminate the broadside back scattering which is caused by the symmetrical component of the induced current is established. A suitable loading to reduce the off-broadside back scattering, due to the antisymmetrical component of the induced current, is also determined. A proper choice of the impedance and the position of double loading can lead to the reduction of the back scattering over a wide aspect range. The useful formulas for optimum loading the some graphical illustrations are included. The advantages of double loading over central loading are discussed. (Author)

The induced current on a center-loaded cylinder illuminated by a plane wave at an arbitrary angle was obtained. It was found that when a cylinder is illuminated by an obliquely incident plane wave the induced current has a symmetrical and an antisymmetrical component. The symmetrical component can be modified greatly by central loading but the antisymmetrical component is not affected. In a resonant cylinder the symmetrical component of the induced current dominates the antisymmetrical component. In an antiresonant cylinder the antisymmetrical component is dominant. Therefore, the scattering cross section of a resonant cylinder can be greatly reduced by central loading while the cross section of an antiresonant cylinder can be modified only slightly. The back scattered field of a center-loaded cylinder illuminated by a plane wave at an arbitrary angle was obtained. The scattering cross section of a resonant cylinder can be reduced more than 30 db by an optimum loading. The scattering cross section of an antiresonant cylinder can be reduced only in the broadside direction but the large cross section in the offbroadside direction can not be reduced by central loading. (Author)

An approximate theoretical study of a sandwichwire antenna is presented. The two outer conductors are in parallel and the center conductor is bent into triangular form with a period equal to the wavelength. The attenuation constant is obtained. The radiation pattern of an array consisting of a number of sandwich-wire antenna is evaluated. The theoretical results are compared with the existing experimental data. (Author)

Several methods are given for determining the type of conductivity and location of P-N junctions in silicon and germanium semiconductors. These techniques are: Staining with HF; staining with HF-HNO3; preferential precipitation of Cu; preferential precipitation of Au; preferential precipitation of Ag; Electrolytic action; anodic etching., Edited trans. of Hua Hsueh T'ung Pao (Chinese People's Republic) n2 p38-40 1963.