Plasma stealth

Abstract: The radar cross section (RCS) of a flat plate covered with a cold collisional inhomogeneous plasma has been studied using a 3-D finite-difference time-domain (FDTD) method for electromagnetics. Two problems have been considered. In problem 1, using experimentally reported plasma density profiles, we have observed some interesting features in the bistatic RCS and provided simple physical interpretations for some of these features. The simulations confirm that a plasma shroud can successfully be used for reducing the RCS of a flat plate at almost all scattering angles, although the RCS could increase at some other angles. This is a novel extension of the FDTD method for the calculation of the bistatic RCS of an object shielded by a nonuniform collisional plasma. Problem 2 involves an optimization study for the input power required to achieve a desired RCS reduction (RCSR), examining a variety of plasma density levels and spatial profiles. For this optimization study, we have considered a helium plasma produced by a high-energy electron beam. We find that the maximum achievable reduction increases monotonically with power up to an optimum point, beyond which the RCSR decreases, finally showing some tendency to saturate. This is of practical importance and indicates the usefulness of FDTD simulations in identifying the optimal point. Furthermore, at a given power level, there can be a considerable scatter in the RCSR achievable. This is because various combinations of the plasma parameters, differing considerably in their RCSR abilities, could require the same power to sustain them. Simulations would be of great use in helping to identify the best profiles to be used for a given input power level.

Abstract: A bounded plasma stealth model is proposed in this paper. The method of impedance transformation with multiple dielectrics is used to study the propagation properties of electromagnetic (EM) waves in this plasma slab. The relations between the plasma parameters and the reflection which is a combination of the power reflected from the wall-plasma interface, the partial reflections from the bulk plasma, and the collisionally attenuated waves reflected by the conductive plane are derived. In addition, the reflections of the incident wave power dependence on the thickness of plasma are presented for different incident wave frequencies and various plasma parameters. The numerical calculation results show that, due to the presence of the walls, the mechanism of EM-wave attenuation is a combination of the collisional absorption and cavity resonance effects. It is demonstrated that detailed numerical analyses are useful in practical applications pertaining to the control of the reflection of EM waves through a uniform plasma slab covering the conductive plane.

Abstract: To overcome the limitations of radar cross section characteristic, a method using detection probability as an indicator to evaluate plasma stealth effectiveness is proposed in this paper. Based on shift operator finite-difference time-domain method, the distorted waveform of linear frequency modulation radar echo is obtained when the targets coated with plasma. Then, by making a comparison between outputs of pulse compression with and without plasma, the peak instantaneous signal-to-noise ratio (SNR) loss is calculated. According to the signal detection theory, the relationship between plasma parameters and radar detection probability is built up through the SNR loss, in which the attenuation of radar echo and the mismatch loss of pulse compression are both considered. Finally, effects of plasma parameters including electron density, collision frequency, and radar frequency on the probability of detection have been studied systematically. By adopting detection probability $P_{d }\le 0.1$ as a valid criterion, the effective plasma parameters for different radar frequencies are given as a guide when using plasma for stealth application.

Abstract: The reflection characteristic of EM-wave (Electromagnetic Wave) incidence in non-magnetized closed plasma with uniformed multi-layer and outer envelope is discussed accordingly to plasma stealth technology applying practically to aircrafts. Based on wave impedance matching principle, the reflection coefficient of the composed structure including outer envelope dielectric and plasma plus metal plate is deduced and completed. Furthermore, the reflection loss is also yielded when double-pass attenuation is concerned. The reflection loss varying pinciples are given by adopting numerical method as EM-wave incidence angle and plasma temperature vary in the case of different plasma electronic density profiles, which provides a certain reference to plasma stealth technology applied to aircrafts and missiles.