A reconfigurable glow discharge plasma lattice structure is examined for its ability to interact with and suppress electromagnetic (EM) wave energy with wavelengths on the order of centimeters. The plasma lattice is formed in the air gap between a double dielectric electrode arrangement that formed a rectangular cross-section channel. The lattice consists of columns that span the gap between the electrodes. The spacing between the plasma columns in the lattice results from a surface charge instability that is controllable by a combination of channel height, AC voltage, and gas pressure. The lattice number is highly repeatable and predictable following packing theory. The effect of the plasma lattice spacing on the transmittance of O(cm) wavelength EM waves was investigated. Excellent agreement was found between the experiments and simulations, with S21 transmittance reduced by up to 75%. In addition, experiments in which the EM waves were oriented at an oblique angle to the plasma lattice incident axis were performed. This documented a narrow-band absorption that was predicted from an anisotropic medium permittivity tensor analysis. These experiments also indicated a negative index of refraction of the oblique EM waves for the plasma lattice that provided further evidence of its anisotropic behavior.

The effect of plasma flow control on reducing aerodynamic drag for ground vehicles is investigated. The experiments were carried out for a simplified ground vehicle using single dielectric barrier discharge (SDBD) plasma actuators. The plasma actuators were designed to alter the flow structure in the wake region behind the vehicle. The Ahmed body was modified to allow eight different vehicle geometries (with backlight or slant angles of 0° and 35°). Each of these were further modified by rounding the edges with different radii. Flow visualizations such as particle streams and surface oil were used to quantify features of the local flow field. The drag on the models was measured using a force balance as well as by integrating the mean velocity profiles in the model wakes. The results indicated that flow modifications needed to be applied symmetrically (upper to lower and/or side to side). This was demonstrated with the 0° backlight angle (square-back) that had all four side-corners rounded. Plasma actuators were applied to all four of the rounded edges to enhance the ability to direct the flow into the wake. Wake measurements showed that steady actuation at a fixed actuator voltage reduced the drag by an average of 20% at the lower velocities (below 15 m/s) and by 3% at the highest velocity tested (20 m/s). Model constraints prevented increasing the plasma actuator voltage that was needed to maintain the higher drag reduction observed at the lower speeds.

An experimental investigation of the three-dimensional flow through an urban-type array (four rows of three cuboid Plexiglas blocks) in a laboratory modelled neutrally stratified atmospheric boundary layer is presented. We concentrate on the effect of the streamwise spacing between adjacent rows defining two different flow regimes (wake interference and skimming flow) as well as the effect of the incident angle of the approaching boundary layer. Stereoscopic particle image velocimetry measurements provide all three components of the velocity field in closely spaced two-dimensional planes in a region located in the middle row downstream of the centre block. It is found that the maximal exchange rate between the fluid within the street and the flow above is for the wake interference regime. Two regions are apparent: one influenced by streamwise velocity fluctuations, the other by spanwise fluctuations. In addition, the incidence angle of the incoming flow has a much more dramatic effect for the wake interference regime that would greatly favour dispersion. Coherent-structure identification tools are applied to obtain information on the shape, extent and localisation of vortical structures.

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This research investigated the feasibility of a plasma lens for wavefront control of coherent light sources. The approach is based on the relation between a plasma electron density and its index of refraction. The plasma was encapsulated in a hollow glass cylinder with at optical glass at its ends. Air in the glass cylinder was ionized using a dielectric barrier discharge (DBD). The wavefront distortion produced by the ionized air was characterized by placing the plasma lens in one leg of a Michelson interferometer setup. The eect of gas pressure and plasma power were investigated. The results were compared to a derived analytic model that related the electron density and optical path dierence (OPD) to the plasma power. The agreement between the experiment and analytic model was very good, especially at the higher plasma power levels. The maximum OPD increased with the gas pressure inside the lens. A maximum OPD of approximately 1.5 µm was achieved in the experiments. This brackets OPD levels that are typical of aero-optic applications, and otherwise corrected using electro-mechanical deformable mirrors. Although air was used as the gas in the plasma lens in these feasibility experiments, the use of Penning mixtures would further increase possible OPD levels and provide greater dynamic range.