Sub-Wavelength Profile 2-D Leaky-Wave Antennas With Two Periodic Layers

A fast and accurate analysis and synthesis technique for high-gain sub-wavelength 2-D Fabry-Perot leaky-wave antennas (LWA) consisting of two periodic metallodielectric arrays over a ground plane is presented. Full-wave method of moments (MoM) together with reciprocity is employed for the estimation of the near fields upon plane wave illumination and the extraction of the radiation patterns of the LWA. This yields a fast and rigorous tool for the characterisation of this type of antennas. A thorough convergence study for different antenna designs is presented and the operation principles of these antennas as well as the radiation characteristics are discussed. Moreover, design guidelines to tailor the antenna profile, the dimensions of the arrays as well as the antenna directivity and bandwidth are provided. A study on the radiation efficiency for antennas with different profiles is also presented and the trade off between directivity and radiation bandwidth is discussed. Numerical examples are given throughout to demonstrate the technique. A finite size antenna model is simulated using commercial software (CST Microstripes 2009) which validates the technique.

Large acoustic solitons and double layers in plasmas with two positive ion species

Large nonlinear acoustic waves are discussed in a plasma made up of cold supersonic and adiabatic subsonic positive ions, in the presence of hot isothermal electrons, with the help of Sagdeev pseudopotential theory. In this model, no solitons are found at the acoustic speed, and no compositional parameter ranges exist where solutions of opposite polarities can coexist. All nonlinear modes are thus super-acoustic, but polarity changes are possible. The upper limits on admissible structure velocities come from different physical arguments, in a strict order when the fractional cool ion density is increased: infinite cold ion compression, warm ion sonic point, positive double layers, negative double layers, and finally, positive double layers again. However, not all ranges exist for all mass and temperature ratios. Whereas the cold and warm ion sonic point limitations are always present over a wide range of mass and temperature ratios, and thus positive polarity solutions can easily be obtained, double layers have a more restricted existence range, specially if polarity changes are sought. (C) 2011 American Institute of Physics. [doi:10.1063/1.3579397]

Online Tracking of Thévenin Equivalent Parameters Using PMU Measurements

This paper presents a new method for tracking Thévenin equivalent parameters for a power system at a node using local Phasor Measurement Unit (PMU) measurements. Three consecutive phasor measurements for voltage and current, recorded at one location, are used. The phase drifts caused by the measurement slip frequency are first determined and phase angles of the measured phasors are corrected so that the corrected phasors are synchronized to the same reference. The synchronized phasors are then used to determine the equivalent Thévenin parameters of the system.

Optimisation and scaling of interfacial GeO2 layers for high-k gate stacks on germanium and extraction of dielectric constant of GeO2

Germanium is an attractive channel material for MOSFETs because of its higher mobility than silicon. In this paper, GeO2 has been investigated as an interfacial layer for high-kappa gate stacks on germanium. Thermally grown GeO2 layers have been prepared at 550 degrees C to minimise GeO volatilisation. GeO2 growth has been performed in both pure O-2 ambient and O-2 diluted with N-2. GeO2 thickness has been scaled down to approximately 3 nm. MOS capacitors have been fabricated using different GeO2 thicknesses with a standard high-kappa dielectric on top. Electrical properties and thermal stability have been tested up to at least 350 degrees C. The K value of GeO2 was experimentally determined to be 4.5. Interface state densities (D-it) of less than 10(12) CM-2 eV(-1) have been extracted for all devices using the conductance method.