A 0.18-/spl mu/m SiGe BiCMOS receiver and transmitter chipset for SONET OC-768 transmission systems

A 43-Gb/s receiver (Rx) and transmitter (Tx) chip set for SONET OC-768 transmission systems is reported. Both ICs are implemented in a 0.18-/spl mu/m SiGe BiCMOS technology featuring 120-GHz f/sub T/ and 100 GHz f/sub max/. The Rx includes a limiting amplifier, a half-rate clock and data recovery unit, a 1:4 demultiplexer, a frequency acquisition aid, and a frequency lock detector. Input sensitivity for a bit-error rate less than 10/sup -9/ is 40 mV and jitter generation better than 230 fs rms. The IC dissipates 2.4 W from a -3.6-V supply voltage. The Tx integrates a half-rate clock multiplier unit with a 4:1 multiplexer. Measured clock jitter generation is better than 170 fs rms. The IC consumes 2.3 W from a -3.6-V supply voltage.     

Simulation and design methodology for a 50-Gb/s multiplexer/demultiplexer package

A 50 Gb/s package for SiGe BiCMOS 4:1 multiplexer and 1:4 demultiplexer targeting SONET OC-768 serial communication systems is introduced in this work. The package was designed to facilitate bit-error-rate tests and constructed with high-speed coaxial connectors, transmission lines on ceramic substrate, ribbon bonds for chip-to-package interconnects, and a metal composite housing. Numerical simulations were conducted to guide the package design, and both small signal measurements and operational tests were performed thereafter to verify the design and modeling concepts. To keep the model structure under the existing computing capability, the simulation was segmented into three sections - coaxial connector to transmission line, transmission line alone, and transmission line to ribbon bond, and then the results were assembled to predict the performance of the entire package. The package was operated up to 50 Gb/s with low degradation to input digital waveforms and free of error.     

The performance of multiwavelets based OFDM system under different channel conditions

In wireless communication reception, the reliability of orthogonal frequency division multiplexing (OFDM) is limited because of the time-varying nature of the channel. This causes inter-carrier interference (ICI) and increases inaccuracies in channel tracking. This can effectively be avoided at the cost of power loss and bandwidth expansion by inserting a cyclic prefix guard interval before each block of parallel data symbols. However, this guard interval decreases the spectral efficiency of the OFDM system as the corresponding amount. Recently, it was found that based on Haar-orthonormal wavelets, discrete wavelet-based OFDM (DWT-OFDM) is capable of reducing the inter symbol interference (ISI) and ICI, which are caused by the loss in orthogonality between the carriers. DWT-OFDM can also support much higher spectrum efficiency than discrete Fourier-based OFDM (DFT-OFDM). In this paper the DFT-OFDM is replaced by Multiwavelets OFDM (DMWT-OFDM) in order to further reduce the level of interference and increase spectral efficiency. It is found that proposed Multiwavelet design achieves much lower bit error rates, increases signal to noise power ratio (SNR), and can be used as an alternative to the conventional OFDM. The proposed OFDM system was modeled tested, and its performance was found under different channel conditions.     

Modeling of hermetic transitions for microwave packages

Two numerical techniques, the finite difference in time domain (FDTD) and the finite element method (FEM) in frequency domain, are employed to characterize microstrip hermetic transition geometries in an effort to investigate high-frequency effects. Measurements performed on these transitions compare favorably with theory. Two different types of transitions have been analyzed from 10 to 25 GHz and have been found to be limited in performance by higher return loss as frequency increases. It is shown that microstrip-through-CPW hermetic transitions in the shielded environment may suffer from parasitic waveguide modes which, however, can be eliminated with the use of vias at appropriate locations. The hermetic wall on top of the CPW section shows a relatively small (≤ 2 dB) effect on the original circuit performance. Similarly, the hermetic bead transition shows good performance at a lower frequency region while it degrades as frequency increases. This indicates the need for very careful characterization of transitions intended for use in microwave and millimeter-wave applications. © 1996 John Wiley & Sons, Inc.     

Stripping methods studies for HVOF WC-10Co-4Cr coating removal

The use of high-velocity oxyfuel (HVOF) cermet coatings is considered to be a valuable and innovative alternative technology to replace Cr(VI) electroplating. Among others, a WC-10Co-4Cr coating is one of the best choices for landing gear components due to its excellent tribology and corrosion properties. The stripping process of such a cermet coating was studied due to its importance for the repair and overhaul of landing gear components. Stripping solutions fulfill the following criteria: keep substrate integrity; exhibit a high strip rate (SR); lead to uniform dissolution; show no galvanic corrosion; and be environmentally friendly. Three different high-strength steel substrates (4340, 300M, and Aermet100) were studied. Five different stripping solutions were selected for the electrochemical study. Only three met the targeted criteria: the meta-nitrobenzane sulfonate-sodium cyanide solution; the Rochelle salt; and a commercial nickel stripper. It was found that the process must be electrolytic, and that ultrasonic agitation is needed to enhance the overall mass transport and removal of WC particles and metallic matrix residues. When choosing the most efficient solution and conditions, the SR was found to be as high as 162 μm h⁻¹, which is a very acceptable SR for productivity sake.     

A two-permeability approach for assessing flow properties in metal foam

One of the key properties for understanding the fluid flow and pressure drop in metal foam is the permeability. This paper investigates a non-traditional approach for evaluating this critical transport property by considering the physics of energy dissipation, i.e., the viscous dissipation and form drag and the fact that they are linked. The current work emphasizes the necessary initial step of clearly distinguishing between different flow regimes prior to evaluating the permeability. This distinction is usually either absent or overlooked in several previous studies, which may lead to significant errors. The approach presented in this study is applied to wind-tunnel steady-state unidirectional pressure-drop measurements for airflow through isotropic open-cell aluminum foam samples having different pore densities. The results show that the porous medium exhibits two different permeabilities—one is calculated and only valid in the Darcy regime, while the other is calculated and only valid in the Forchheimer regime.     

DELAYED COKING OF HYDROTREATED REDUCED CRUDE

ABSTRACT

A laboratory coking unit was designed and constructed for an experimental study of the delayed coking process of hydrotreated Kirkuk reduced crude. The yield and analysis of coke, gases and liquid products were obtained for each experiment. The gas < C₄. and gasoline yield decrease by increasing Liquid hourly space velocity (LHSV) while the yields of kerosene and gas oil increase and no effect of LHSV on petroleum coke yield was observed, The specific gravity of gasoline, kerosene and gas oil decreases by increasing LHSV. The increase in LHSV (decrease in residence time) decreases the olefinic hydrocarbons of produced gas oil and fraction 350-450^°C. Sulfur content of produced coke and coking residue increases by increasing residence time while it changes slightly for kerosene and gas oil. By increasing the recycle ratio (RR), the yield of gas decreases while the coke yield increases. Sulfur content of gas oil and coking residue increases with an increase in the recycle ratio while it decreases for coke. Metals content of coke decreases with an increase in the recycle ratio and coke with accepted properties for aluminum anode manufacture could be produced when a recycle ratio of 1.4 was used.     

Design of planar concentric circular antenna arrays with reduced side lobe level using symbiotic organisms search

This paper investigates the design of concentric circular antenna arrays (CCAAs) with optimum side lobe level reduction using the Symbiotic Organisms Search (SOS) algorithm. Both thinned and full CCAAs are considered. SOS represents a rather new evolutionary algorithm for antenna array optimization. SOS is inspired by the symbiotic interaction strategies between different organisms in an ecosystem. SOS uses simple expressions to model the three common types of symbiotic relationships: mutualism, commensalism, and parasitism. These expressions are used to find the global minimum of the fitness function. Unlike other methods, SOS is free of tuning parameters, which makes it an attractive optimization method. The results obtained using SOS are compared to those obtained using several optimization methods, like Biogeography-Based Optimization (BBO), Teaching-Learning-Based Optimization (TLBO), and Evolutionary Programming (EP). It is shown that the SOS is a robust straightforward evolutionary algorithm that competes with other known methods.

     

Effect of sample’s length on flow properties of open-cell metal foam and pressure-drop correlations

Many applications require fluid flow through the open pores of metal foam. The foam is usually treated as a porous medium for which the Darcy law and the Hazen-Dupuit-Darcy (or Forchheimer) equation are used to describe the pressure drop, and for obtaining the two important flow properties, i.e., the permeability and the form drag coefficient. Little or no attention is paid to the length (or thickness) of the porous medium in the flow direction. This paper establishes a minimum length necessary for the foam to have length-independent (or bulk) permeability and form drag coefficient. This minimum length is obtained experimentally for various types of open-cell aluminum foam subjected to airflow in the Forchheimer regime. Below this thickness values of the two key flow properties are not constant, and they include entrance/exit effects, which may explain some of the discrepancies in the reported values in the literature. The Forchheimer equation was recast in two different manners, which resulted in new non-dimensional numbers- one representing the form drag and the other the viscous drag. These numbers correlated very well with the thickness of the porous medium. The obtained correlations allow for determining the pressure drop given only the velocity and the thickness of an aluminum foam sample.