Eugene A. Aronson

Resistive receiving and scattering antenna

This work is a sequel to two earlier papers devoted to detailed theoretical and numerical analyses of the imperfectly conducting cylindrical transmitting antenna [1], [2]. A knowledge of the driving-point impedance of the transmitting antenna, as previously reported, and the short-circuit current, as derived in this paper, completely determine the receiving properties of the resistive antenna. It is assumed that an internal impedance per unit length may be defined for the resistive cylinder. This study was prompted primarily by the desire to determine the current distribution along an ionized column of gases when the dielectric constant and conductivity are known, and also along imperfectly conducting missiles in free flight following burnout. The radar cross section of a gas column is readily obtained from the induced current distribution. Current distributions along several representative resistive cylinders as well as scattering cross sections are computed considering broadside illumination by a plane-wave field. The analysis yields accurate results when k_{0}a \ll 1, h \gg a , and k_{0} h \leq 5\pi /4 . Here k_{0} is the free-space wave number; h and a are the antenna half length and radius, respectively.

Magnetic torque or force calculation by direct differentiation of finite element coenergy

A vector-potential finite-element method for calculating magnetic force or torque by direct analytic differentiation of coenergy is derived and applied to two- and three-dimensional actuators. The results are shown to agree well with calculations using the conventional difference between coenergies at two positions and with experimental measurements. Another method of force calculation, Maxwells stress tensor, is also derived by differentiating the coenergy, resulting in a formula that is applicable on the surface of nonlinear materials. >

Theory of coupled monopoles

Accurate numerical values of mutual and self-admittances are obtained for an array consisting of two monopoles having different lengths and radii. The monopoles are actually protrusions of the inner conductors of coaxial cables. The sheaths of the cables are connected to a perfectly conducting ground screen. Restrictions in the theory are the following: the monopoles must be thin, a/\lambda \ll 1 where a is the radius and \lambda the wavelength, b where b is the radius of the coaxial cable sheath, and d > 10a where d is the separation of the monopoles. The procedure employed to obtain the mutual and self-admittances is to derive simultaneous integral equations for the current distributions and to solve the integral equations numerically. The results are given for the most part in graphical form. Comparisons are made with existing theory and with experimental data. Excellent agreement in all cases is observed.

On the Response of a Missile with Exhaust Trail of Tapered Conductivity to a Plane Wave Electromagnetic Field

The current distribution along and scattering cross section of a missile with plume (ionized trail) is found, using numerical techniques when the conductivity of the plume tapers with increasing distance from the exhaust nozzles. In the theory no restrictions are imposed on the length of either the missile or plume, and the variation of conductivity along the entire scattering obstacle may be arbitrary. A model of cylindrical geometry is assumed. Curves for the current distribution along the missile and its ionized trial are presented for several missile and plume lengths at selected frequencies. A table is provided for the scattering cross sections.

Passive levitation in alternating magnetic fields

In this paper we analyze the stability of a levitated axisymmetric top carrying a system of permanent magnets in an alternating magnetic field. We show that there are stable configurations where the top is stationary, and the alternating magnetic field stabilizes the equilibrium position. We show that one mechanism for achieving stability is to periodically change the coupling between the rotational and translational degrees of freedom.