Showing papers by "Nanjing University of Science and Technology published in 2001"

Analysis and design of L-probe proximity fed-patch antennas

Abstract: In this paper, the finite-difference time-domain (FDTD) method is employed to analyze L-probe proximity-fed rectangular patch antennas. Numerical results for the input impedance, co- and cross-polarization radiation patterns are presented and compared with the measurements. Good agreement between the computed and measured results is obtained. The effects of geometric parameters on the characteristics of the L-probe patch antenna are extensively studied. For design purposes, the variation of input impedance at resonance with different geometric parameters is plotted on a Smith chart. Mutual coupling between two L-probe patch antennas is also investigated.

H/sub /spl infin// and positive-real control for linear neutral delay systems

Abstract: This note is concerned with the H/sub /spl infin// and positive-real control problems for linear neutral delay systems. The purpose of H/sub /spl infin// control is the design of a memoryless state feedback controller which stabilizes the neutral delay system and reduces the H/sub /spl infin// norm of the closed-loop transfer function from the disturbance to the controlled output to a prescribed level, while the purpose of positive-real control is to design a memoryless state feedback controller such that the resulting closed-loop system is stable and the closed-loop transfer function is extended strictly positive real. Sufficient conditions for the existence of the desired controllers are given in terms of a linear matrix inequality (LMI). When this LMI is feasible, the expected memoryless state feedback controllers can be easily constructed via convex optimization.

Mathematical modeling of laser induced heating and melting in solids

Abstract: An analytical method for treating the problem of laser heating and melting is developed in this paper. The analytical method has been applied to aluminum, titanium, copper, silver and fused quartz and the time needed to melt and vaporize and the effects of laser power density on the melt depth for four metals are also obtained. In addition, the depth profile and time evolution of the temperature of aluminum before melting and after melting are given, in which a discontinuity in the temperature gradient is obviously observed due to the latent heat of fusion and the increment in thermal conductivity in solid phase. Additionally, the calculated melt depth evolution of fused quartz induced by 10.6 μm laser irradiation is in good agreement with the experimental results.

The perfectly matched layer boundary condition for scalar finite-difference time-domain method

Abstract: The perfectly matched layer (PML) boundary condition for the scalar finite-difference time-domain (FDTD) method is developed in this letter. It is demonstrated that the PML is suitable and effective in computation of optical waveguides. The results also show how to optimize the parameters of PML.

Vibrations of Tapered Timoshenko Beams in Terms of Static Timoshenko Beam Functions

Abstract: In this paper the free vibrations of a wide range of tapered Timoshenko beams are investigated. The cross section of the beam varies continuously and the variation is described by a power function of the coordinate along the neutral axis of the beam. The static Timoshenko beam functions, which are the complete solutions of a tapered Timoshenko beam under a Taylor series of static load, are developed, respectively, as the basis functions of the flexural displacement and the angle of rotation due to bending. The Rayleigh-Ritz method is applied to derive the eigenfrequency equation of the tapered Timoshenko beam. Unlike conventional basis functions which are independent of the cross-sectional variation of the beam, these static Timoshenko beam functions vary in accordance with the cross-sectional variation of the beam so that higher accuracy and more rapid convergence have been obtained. Some numerical results are presented for both truncated and sharp-ended Timoshenko beams. On the basis of convergence study and comparison with available results in the literature it is shown that the first few eigenfrequencies can be given with quite good accuracy by using a small number of terms of the static Timoshenko beam functions. Finally, some valuable results are presented systematically.

Optimal FLD algorithm for facial feature extraction

Abstract: In this paper, we try to extend Fisher linear discriminant analysis (FLD) to the singular cases. Firstly, PCA is used to reduce the dimension of feature space to N-1 (N denotes the number of training samples). Then, the transformed space is divided into two subspaces: the null space of within- class scatter matrix and its orthogonal complement, from which two cases of optimal discriminant vectors are selected respectively. Finally, we test our method on ORL face database, and achieve a recognition rate of 97% with a minimum distance classifier or a nearest neighbor classifier. The experimental results indicate that our approach is better than classical Eigenfaces and Fisherfaces with respect to recognition performance.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fiber optic sensor for dual measurement of temperature and strain using a combined fluorescence lifetime decay and fiber Bragg grating technique

Abstract: A fiber optic sensor device has been developed incorporating a short length of erbium doped fiber fused in close proximity to a single-fiber Bragg grating, to measure both the fluorescent lifetime decay and the wavelength shift in these respective elements, for temperature and strain determination. Calibration results obtained from this simple, low cost, intrinsic sensor scheme show standard deviation errors of 20.4 μe and 1.2 °C over strain and temperature ranges of 22–1860 μe and 25–120 °C, respectively.

Backstepping control of discrete-time chaotic systems with application to the Henon system

Abstract: This brief investigates backstepping and adaptive-backstepping design for the control of a class of discrete-time chaotic systems with known or unknown parameters. The proposed method presents a systematic procedure for the control of a class of discrete-time chaotic systems. It can be used for the stabilization of discrete-time chaotic systems to a steady state as well as tracking of any desired trajectory. Moreover, dead-beat control and tracking, exact stabilization at a fixed point and tracking of any desired trajectory in finite time can be achieved. The chaotic Henon system with known or unknown parameters is taken as an example to illustrate the applicability and effectiveness of the backstepping design.

Broadband quarter‐wavelength patch antennas with a U‐shaped slot

Abstract: A broadband quarter-wavelength patch antenna with a U-slot is presented. Using a foam layer of thickness ∼0.07λ0 as a supported substrate, an impedance bandwidth of 27% (SWR≤2) has been obtained. The far-field patterns are stable across the passband. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 328–330, 2001.

Studies on the molecular structures, vibrational spectra and thermodynamic properties of organic nitrates using density functional theory and ab initio methods

Abstract: The molecular structures, vibrational spectra, standard thermodynamic functions and heats of formation of methyl nitrate, ethyl nitrate, propyl nitrate, isopropyl nitrate, butyl nitrate, ethylene glycol dinitrate and nitroglycerin have been calculated at the levels of HF, MP2 and B3LYP theories in conjuction with the 6-31G* basis set. The molecular geometries and scaled frequencies calculated at the MP2 and B3LYP levels are comparable to the available experimental results in gas phase, and furthermore, the B3LYP results are slightly better than the MP2 results. The standard thermodynamic functions of NEs increase while the total energies decrease at constants with increasing number of carbon atoms and ONO 2 groups in molecules. The heats of formation obtained from the isodesmic reactions at the B3LYP and HF levels and from the atomization reactions at the B3LYP level are in reasonable agreement with the experimental results. The average absolute deviations are 4.21, 7.72 and 8.47 kJ mol −1 , respectively. But the heats of formation obtained from the atomization reaction at the HF and MP2 levels are much too higher.

Application of the multifrontal method to the vector FEM for analysis of microwave filters

Abstract: The multifrontal method is applied for solving a large system of linear equations resulting from the use of the edge-based finite-element method (FEM). The finite-element method combined with the perfectly matched layers (PMLs) is given for the simulation of microwave filters, and the algorithm of the multifrontal method is described in detail. The reflection loss and insertion loss of several filters are analyzed as examples, and the obtained results are compared with those obtained from the literature. In order to demonstrate the efficiency of the multifrontal method, the computational time is compared with that of both the symmetric successive overrelaxation (SSOR) preconditioned conjugate-gradient (PCG) and conjugate-gradient methods (CG) for a thick-iris waveguide bandpass filer. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 465–470, 2001.

The analysis and design of modern Low Probability of Intercept radar

Abstract: In the modern battlefield, radar faces more and more serious threats from ECM and ARM, etc. Only the Low Probability of Intercept (LPI) radar can survive. In this paper, the principle of LPI radar is introduced first. Then the effects of radar parameters on LPI performance are discussed in detail. Finally, some advice is proposed for the design of the ideal LPI radar system.

Anodic oxidation behaviour of Al–Ti alloys in acidic media

Abstract: The anodic oxidation behaviour of Al–Ti alloys in several acidic solutions was investigated. The influence of conditions such as alloy composition, electrolytic solution, electrolyte temperature and formation current density on the formation rate of oxides on Al–Ti alloys and the dielectric properties of the anodic films were analysed. It was shown that the oxide formation rate for the Al–Ti alloy containing 54 at % aluminium was the highest and the dielectric property of its anodic oxide was also the best. In addition, by means of several surface analytical techniques, the chemical composition of the films were determined as (TiO2) n (Al2O3) m . AES (Auger electron spectroscopy) profiling analysis data showed that Al–Ti alloys had preferential oxidation behaviour, that is, the aluminium was oxidized preferentially.

Angular superresolution for phased antenna array by phase weighting

Abstract: In this paper, a new angular superresolution technique called Phase Weighting Superresolution Method (PWSM) is proposed. The method combines a phase weighting method and a nonlinear spectral estimation algorithm. It is used in conventional phased array radar for improving angle resolution. The motion compensation of radar target and an analysis of influence of component imperfection in the realization of the method are presented. To evaluate the performance of the proposed method, Monte Carlo simulation has been conducted to estimate the root mean square error (RMSE) of the angle estimates and the spatial resolution signal-to-noise ratio (SNR) threshold in the cases of both non-fluctuating targets and fluctuating targets. The simulation results have been compared to those of beam space MUSIC method and the Cramer-Rao lower bound (CRLB). Numerical and experimental results show that good angular superresolution and high estimation accuracy can be achieved provided that the radar pulse repetition time is small enough so that the echoes can be considered sufficiently correlated. For an X band conventional phased array radar with 139 antenna elements, by using PWSM the angular resolution is improved by a factor of 2 when SNR equals 15 dB.