Radiometric sensor for temperature control of food processing

This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented.     

Finite element analysis of advanced multilayer capacitors

We establish a systematic methodology to design and analyse electromagnetic components such as advanced multilayer ceramic capacitors (MLCCs) using the finite element (FE) method. We employ a coupled formulation to compute the interaction between the electric and magnetic fields. Unlike a linear distribution of current assumed in the circuit model, an accurate electrostatic solution to model the entire advanced MLCCs (4 × 4 × 27 = 432 cells) is presented. The FE solution is used to compute the lumped parameters for a range of frequencies. These lumped parameters are then used to compute the parasitic elements of the MLCCs. We introduce two algorithms to efficiently analyse the behaviour of a capacitor with changing frequency. The lower frequency (much below the self‐resonant frequency of the capacitor) algorithm separates the effect of the electric and magnetic fields and reduces the computational effort required to solve the FE problem, whereas, the high‐frequency algorithm couples the effect between the electric and the magnetic fields. We use these algorithms in conjunction with a new multiple scale technique to effectively determine the small values of R, L and C in MLCCs. The formulation, the implementation, and the numerical results demonstrate the efficacy of the present FE formulation and establish a systematic methodology to design and analyse advanced electromagnetic components. Copyright © 2003 John Wiley & Sons, Ltd.     

Pack cementation process for the formation of refractory metal modified aluminide coatings on nickel-base superalloys

The vapour phase compositions of a series of pack powder mixtures containing elemental Al and Hf or W powders as depositing sources and CrCl₃·6H₂O or AlF₃or CrF₃as activators were analysed in an attempt to further develop the pack cementation process to codeposit Al and Hf or W to form diffusion coatings on nickel base superalloys. The results suggested that Al could be codeposited with Hf, but not with W, from the vapour phase. Compared with both AlF₃and CrF₃, CrCl₃·6H₂O has been shown to be a more suitable activator for codepositing Al with Hf. The optimum coating temperature was identified to be in the range of 1050°C to 1150°C. Based on the thermochemical analysis, a series of coating deposition studies were undertaken, which confirmed that codeposition of Al and Hf could be achieved at a deposition temperature of 1100°C in the CrCl₃·6H₂O activated packs containing elemental Al and Hf powders. The coating obtained had a multilayer structure consisting of a Ni₇Hf₆Al₁₆top layer and a NiAl layer underneath, followed by a diffusion zone, which revealed that the coating was formed by the outward Ni diffusion. It is suggested that the compositions suitable for codeposition of Al and Hf could be effectively identified by comparing the vapour pressures of HfCl₄and HfCl₃with that of AlCl in the packs activated by chloride salts. It has also been experimentally demonstrated that, although W could not be deposited from the vapour phase, a high volume of fine W particles can be entrapped into the outer NiAl coating layer formed by the outward Ni diffusion using a modified pack configuration. This leads to the formation of a composite coating layer with W particles evenly distributed in a matrix of NiAl. It is suggested that this modified pack process could be similarly applied to develop nickel aluminide coatings containing other refractory metals that may not be codeposited with Al from the vapour phase.     

Asymptotic performance of single parity-check product codes

This article investigates the asymptotic performance of single parity-check (SPC) product codes (PCs) from a decoding point of view. Specifically, the probability of bit error is bounded before and after the decoding of each dimension, similar to the analysis of "iterated codes" by Elias (1954). It is shown that the asymptotic probability of bit error can be driven to zero as the number of dimensions, and hence the block length, increases at signal-to-noise ratios (SNRs) within 2 dB of capacity over the additive white Gaussian noise (AWGN) channel.     

High-efficiency LEDs of 1.6–2.4 µm spectral range for medical diagnostics and environment monitoring

High efficient LED structures covering the spectral range of 1.6–2.4 μm have been developed on the basis of GaSb and its solid solutions. The electroluminescent characteristics and their temperature and current dependences have been studied. The radiative and nonradiative recombination mechanisms and their effect on the quantum efficiency have been investigated. A quantum efficiency of 40–60% has been obtained in the quasi-steady mode at room temperature. A short-pulse optical power of 170 mW was reached. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 8, 2003, pp. 996–1009. Original Russian Text Copyright ? 2003 by Stoyanov, Zhurtanov, Astakhova, Imenkov, Yakovlev.     

The extended quadratic residue code is the only (48,24,12) self-dual doubly-even code

An extremal self-dual doubly-even binary (n,k,d) code has a minimum weight d=4/spl lfloor/n/24/spl rfloor/+4. Of such codes with length divisible by 24, the Golay code is the only (24,12,8) code, the extended quadratic residue code is the only known (48,24,12) code, and there is no known (72,36,16) code. One may partition the search for a (48,24,12) self-dual doubly-even code into three cases. A previous search assuming one of the cases found only the extended quadratic residue code. We examine the remaining two cases. Separate searches assuming each of the remaining cases found no codes and thus the extended quadratic residue code is the only doubly-even self-dual (48,24,12) code.     

Why does it pay to be selfish in a MANET?

Routing protocols for a mobile ad hoc network have assumed that all mobile nodes voluntarily participate in forwarding others' packets. This was a reasonable assumption because all MNs in a MANET belonged to a single authority. In the near future, however, a MANET may consist of MNs that belong to many different organizations since numerous civilian applications are expected to crop up. In this situation, some MNs may run independently and purposely decide not to forward packets so as to save their own energy. This could potentially lead to network partitioning and corresponding performance degradation. To minimize such situations in MANETs, many studies have explored the use of both the carrot and the stick approaches by having reputation-based, credit-payment, and game theory schemes. This article summarizes existing schemes, identifies their relative advantages, and projects future directions     

Application of extended boundary conditions and the Haar wavelets in the analysis of wave scattering by thin screens

A recent approach to solution of 2D scattering problems for electromagnetic waves scattered by thin screens is analyzed. With the use of examples of scattering by a strip and an unclosed cylindrical surface, it is shown that the proposed approach has no advantages in terms of the efficiency of numerical solution over a well-known approach based on exact integral equations for currents that have singular kernels and that are solved with the Krylov-Bogoliubov method.