Plasma and dielectric barrier discharge actuator radar cross section

Abstract

Plasma actuators for aerodynamic applications are receiving significant research attention and it is necessary to know the effects of this plasma on the vehicle radar cross section (RCS). This study identifies the critical parameters affecting the RCS of plasma along with experimental techniques and numerical techniques for determining the effects of plasma on RCS. A review of plasma physics is presented along with the background of cavity design, cavity-waveguide coupling, choke design and the microwave perturbation technique. A cylindrical dielectric barrier discharge (DBD) plasma under five different pressures is generated in an evacuated glass tube. The microwave perturbation method is used to measure permittivity and loss factor of the plasma and then the plasma frequency, electron-neutral collision rate and electron density are determined for these five pressures. Simulations by a commercial microwave simulator are comparable to the experimental results which show little effect at sea level and increasing effects with increased elevation. Plasma has a capability that its refractive index can be controlled by changing parameters such as the electron density profile, plasma frequency or collision rate so the RCS becomes controllable. However controlling the aforementioned parameters practically in order to decrease RCS is not as simple as the theoretical simulations. From the various methods of plasma generation, our focus is on the DBD because this method has shown benefits like aerodynamic drag reduction noticed in the last decade. The effect of a plasma slab on the RCS of a conductive sheet is investigated. The RCS is simulated and measured to verify the validity of the model used for simulations. Moreover, we show the DBD actuator generates extra scattering because of Bragg diffraction phenomenon not previously reported in the DBD literature. A comprehensive study on dispersive media RCS using Finite-Difference Time-Domain (FDTD) method is done. The method used to generate the plane wave is the discrete plane wave (DPW) method. However, by plane wave we mean a wave packet which can behave like a plane wave not a real plane wave. A 12-layer split-field perfectly matched layer (PML) is used for the Absorbing Boundary Conditions (ABC). The dispersive media is modelled by shift-operator FDTD. Near-to-Far Field transformation (NTFT) is applied to calculate RCS in the far-field. This NTFT method is based on the surface equivalence theorem (Huygens’s principle). Finally the Fast Fourier Transform (FFT) is used to transform time domain signals to the frequency domain. Moreover, the simulation was extended for anisotropic dispersive media for two general profiles of exponential and polynomial. The results show that by choosing the right profile the RCS can be reduced to a large extent; however, achieving such a profile practically is very challenging.