Miniaturized Circular-Waveguide Probe Antennas Using Metamaterial Liners

This work presents the radiation performance of open-ended circular-waveguide probe antennas that have been miniaturized by the introduction of thin metamaterial liners. The liners introduce an HE$_{11}$ mode well below the natural cutoff frequency, which provides substantial gain improvements over a similarly sized waveguide probe. A new feeding arrangement employing a shielded-loop source embedded inside the miniaturized waveguide is developed to efficiently excite the HE$_{11}$ mode and avoid the excitation of other modes across the frequency reduced band while maintaining the antenna's compactness. A metamaterial-lined circular-waveguide probe antenna operating over 42% below its natural cutoff frequency is designed to provide a radiation efficiency of up to 28.8%. A simple, printed-circuit implementation of the metamaterial liner based on inductively loaded wires is proposed and its dispersion features are discussed.Comment: The manuscript has been revised for publication as a 6 page communication in the IEEE Transactions on Antennas and Propagation. This included a reduction of material in the theory section, removal of all discussion on anisotropic theory, and introduction of a novel excitation sourc

Free-Space Imaging Beyond the Diffraction Limit Using a Veselago-Pendry Transmission-Line Superlens

Focusing using conventional lenses relies on the collection and interference of propagating waves, but discounts the evanescent waves that decay rapidly from the source. Since these evanescent waves contain the finest details of the source, the image suffers a loss of resolution and is referred to as 'diffraction-limited'. Superlensing is the ability to create an image with fine features beyond the diffraction limit, and can be achieved with a 'Veselago-Pendry' lens made from a metamaterial. Such a Veselago-Pendry superlens for imaging in free space must be stringently designed to restore both propagating and evanescent waves, but meeting these design conditions (isotropic n = epsilon_r = mu_r = -1) has proven difficult and has made its realization elusive. We demonstrate free-space imaging with a resolution over three times better than the diffraction limit at microwave frequencies using a Veselago-Pendry metamaterial superlens based on the negative-refractive-index transmission-line (NRI-TL) approach, which affords precise control over its electromagnetic properties and is also less susceptible to losses than other approaches. A microwave superlens can be particularly useful for illumination and discrimination of closely spaced buried objects over practical distances by way of back-scattering, e.g. in tumour or landmine detection, or for targeted irradiation/hyperthermia.Comment: 19 pages, 7 figures, submitted to IEEE Transactions on Antennas and Propagatio

The Effect of Silica Nanoparticles on Corrosion of Steel by Molten Carbonate Eutectics

The effect of silica nanoparticles on corrosion of steel by molten carbonate eutectic (42.7 percent Li2CO3, K2CO3) was investigated. The experimental design was based on static coupon immersion methodology where a coupon (material under study, in this case a rectangular stainless steel specimen of SS304 with dimensions approximately 5X20X.6mm and weight .5gm) is exposed to a static corroding environment for predetermined periods of time. The testing times were 2, 4 and 6 weeks. The temperature during testing was maintained at a constant 520C. The instantaneous corrosion rates were determined by normalizing the mass loss with respect to time and area. The mass loss was determined by descaling the corroded steel coupons using concentrated hydrochloric acid. The instantaneous corrosion rates obtained from all three times showed a reduction in corrosion of steel by molten carbonate eutectics when doped with silica 1 percent by weight in comparison to the molten base carbonate eutectics. The results showed that doping the carbonate eutectic with silica nanoparticles (1 percent by weight) reduced the corrosion of steel by half in comparison to the corrosion without doping

Study of transformer explosion prevention with bushing turret protection

Liquid-filled power transformers typically contain thousands of liters of flammable insulation. When this insulation breaks down, there is a high risk of transformer failure that would endanger human life, generate environmental hazards, and destroy valuable assets. Because live tests involving arcing are expensive and potentially dangerous, numerical simulations are a useful alternative to study faults over a wide range of transformers. Since bushings are common sources of transformer failure, we examine the role of deploying a transformer fast depressurization system on two simulated transformer designs, with protections localized in the bushing turret region, to ensure that the transformer is robust to internal arcs