Dual-frequency planar inverted-F antenna

Cellular telephone handsets are now being designed to have dual-mode capabilities. In particular, there is a requirement for internal antennas for GSM and DCS1800 systems. This paper describes a novel planar dual-band inverted-F antenna for cellular handsets, which operates at the 0.9-GHz and 1.8-GHz bands. The dual-band antenna has almost the same size as a conventional inverted-F antenna operating at 0.9 GHz and has an isolation between bands of better than 17 dB. The bandwidths of the antenna are close to those required for the above systems. Good dual-band action is also obtained for other frequency ratios in the range of 1.3-2.4. Studies also show that the dual-band antenna can operate with one or two feeds. A finite-difference time-domain analysis has been shown to give calculated results close to those measured     

Excited-state-absorption cross sections and amplifier modeling inthe 1300-nm region for Nd-doped glasses

The performance of Nd³⁺-doped fibre amplifiers is limited by strong excited-state absorption (ESA) of the signal, and, even for fluorozirconate glasses, ESA prevents the important region below 1320 nm from being used. To quantify this limitation and explore alternative host materials, ESA and stimulated-emission cross sections have been measured for a representative group of glass compositions. These parameters have been used in an accurate fiber-amplifier model to provide the first quantitative comparisons of performance for Nd³⁺ -doped glasses in the 1300-nm band as a function of host     

One micrometre scale self-aligned cobalt disilicide Schottkybarrier diodes

CoSi₂/n-type silicon(111) Schottky barrier diodes on a 1 μm scale have been fabricated using a self-aligned silicide process incorporating magnetron sputtering and rapid thermal processing, in an industrial environment. Anneal temperatures in the range 700-1100°C have been used, and ideality factors of 1.06-1.07 were obtained in the range 700-900°C with larger values for higher temperatures. The consistency in the values of the ideality factor indicates that a wide annealing temperature window exists for the successful fabrication of CoSi₂/silicon diodes     

A Scalable Framework For Segmenting Magnetic Resonance Images

A fast, accurate and fully automatic method of segmenting magnetic resonance images of the human brain is introduced. The approach scales well allowing fast segmentations of fine resolution images. The approach is based on modifications of the soft clustering algorithm, fuzzy c-means, that enable it to scale to large data sets. Two types of modifications to create incremental versions of fuzzy c-means are discussed. They are much faster when compared to fuzzy c-means for medium to extremely large data sets because they work on successive subsets of the data. They are comparable in quality to application of fuzzy c-means to all of the data. The clustering algorithms coupled with inhomogeneity correction and smoothing are used to create a framework for automatically segmenting magnetic resonance images of the human brain. The framework is applied to a set of normal human brain volumes acquired from different magnetic resonance scanners using different head coils, acquisition parameters and field strengths. Results are compared to those from two widely used magnetic resonance image segmentation programs, Statistical Parametric Mapping and the FMRIB Software Library (FSL). The results are comparable to FSL while providing significant speed-up and better scalability to larger volumes of data.     

Full-wave aperture coupled patch antenna

An aperture coupled patch antenna with a dual-lobed (cavity mode TM/sub 200/) radiation pattern is described. The antenna employs a full-wavelength long patch fed via a butterfly-shaped aperture and a stripline feed network. This configuration provides high patch to feed network coupling and reduced back radiation. Measured return loss and pattern data are presented with proposals for several potential applications of this element.<>     

Separation of kinetics and mass-transfer in a batch alkoxylation reaction

The quantitative aspects of the role of interfacial mass-transfer and reaction kinetics in ethoxylation of lauryl alcohol were examined in a batch recirculation reactor. The liquid droplets falling through a gas column were obtained by utilizing a recirculation loop and a set of spray nozzles. The CO₂/NaOH reaction was employed to characterize the interfacial area. The alkoxylation reaction was studied at temperatures between 124°C and 171°C, at catalyst levels between 0.09 and 0.50 weight percent and at ethylene oxide partial pressures between 68 kPa and 204 kPa. A model was developed which permits the prediction of reactor performance at various operating conditions. The mass-transfer during free fall dominates the interfacial mass-transfer and the contributions during the drop formation and coalescence stages are small. The rate of ethylene oxide (EO) addition to lauryl alcohol was constant during the batch run, indicating similar activity for the unreacted lauryl alcohol and the lauryl alcohol ethoxylated to varying extents. The rate of ethoxylation is first-order in both catalyst and ethylene oxide concentrations. The liquid-phase reaction kinetics and interfacial mass-transfer occur in series, with kinetics dominating the overall ethoxylation rate. As expected, an increasing role of mass transfer is observed at higher temperatures, and/or higher catalyst concentrations where the kinetic rate becomes significantly high. The intrinsic activation energy for the ethoxylation of lauryl alcohol is 55.2 kJ/mole.     

Fabrication of planar optical waveguides by K+-ion exchange in BK7 and Pyrex glass

Planar graded index optical waveguides have been formed by K+ ion exchange in BK7 optical glass and Pyrex glass. Measurements of the mode indexes have been made and are well described by the WKB dispersion relation with a complementary error function refractive index profile for both glass types with refractive index changes (Delta n) of 0.0094 and 0.0073 for BK7 and Pyrex, respectively. A linear relation was found between the diffusion depth and the square root of the diffusion time for both materials, and effective diffusion coefficients were calculated. Diffusion times necessary to achieve a desired number of modes and diffusion depths have also been established.     

Polarisation modulation in long couplers

A simple mathematical model of long tapered couplers shows that the modulation of the output power due to polarisation has a period which varies inversely with the square of wavelength. This prediction is in agreement with experimental measurements.