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Cai J.,Nanjing University of Aeronautics and Astronautics | Shi L.-H.,Nanjing Engineering Institute | Yuan S.-F.,Nanjing University of Aeronautics and Astronautics
Zhendong yu Chongji/Journal of Vibration and Shock | Year: 2011

Adjacent multi-damages imaging is a difficult point in the research of Lamb wave imaging. Based on the traditional "delay-and-sum" method, an improved adjacent multi-damages imaging method was proposed. To avoid or reduce the overlapping between neighboring damage scattered signals, double side excitation was adopted in the method to generate single mode Lamb wave monitoring signals with higher spatial resolution. Meanwhile, according to the energy attenuation in the propagation of Lamb waves, a compensation factor was introduced to reduce the monitoring distinctions of monitoring signals at different locations. Both theoretical analysis and experiment show that the above two improvements can make the imaging results of adjacent multi-damages better.

Mao Y.,Nanjing Engineering Institute
2010 IEEE International Conference on Ultra-Wideband, ICUWB2010 - Proceedings | Year: 2010

In this paper, uniaxial perfectly matched layer (UPML) is applied in weakly conditionally stable finite-difference time-domain method for periodic structures. In order to solve the special non-tridiagonal matrix, the Sherman-Morrison formula is applied, so the computational efficiency is improved. The reflection error of the proposed UPML absorber can be almost the same as the UPML absorber in the conventional FDTD method when the UPML is 16-layer. Even when the UPML is 4-layer, the reflection error can below -50 dB. Numerical results of reflection coefficient for the periodic array of metallic patches are calculated, so as to verify the accuracy and efficiency of the proposed method. © 2010 IEEE.

Chen J.,Nanjing University of Science and Technology | Zhou B.,Nanjing Engineering Institute | Zhao F.,Nanjing University of Science and Technology | Qiu S.,Nanjing Engineering Institute
IEEE Transactions on Electromagnetic Compatibility | Year: 2010

When a building is directly struck by lightning, the electromagnetic environment in the structure is very severe, and the conducted and radiated electromagnetic disturbances are dangerous to the information technology equipment in the building. In this paper, instead of the equivalent circuit method and method of moment used by the former researchers, the finite-difference time-domain method is applied to calculate the impulse response in a reinforced steel structure struck by lightning. Besides a reasonable concordance between the calculation results of current distribution among the vertical columns and those of former experiments, the oscillations superimposed on the current flowing along the reinforced bars, and the relation between the oscillation intensity and the soil conductivity are discussed. Furthermore, the role of a ring conductor to stabilize its interior electromagnetic field is discussed in detail. © 2010 IEEE.

Duan Y.-T.,Nanjing Engineering Institute | Chen B.,Nanjing Engineering Institute | Fang D.-G.,Nanjing University of Science and Technology | Zhou B.-H.,Nanjing Engineering Institute
IEEE Transactions on Microwave Theory and Techniques | Year: 2011

When the Laguerre-based finite-difference time-domain (FDTD) method is used for electromagnetic problems, a huge sparse matrix equation results, which is very expensive to solve. We previously introduced an efficient algorithm for implementing an unconditionally stable 2-D Laguerre-based FDTD method. We numerically verified that the efficient algorithm can save CPU time and memory storage greatly while maintaining comparable computational accuracy. This paper presents new efficient algorithm for implementing unconditionally stable 3-D Laguerre-based FDTD method. To do so, a factorization-splitting scheme using two sub-steps is adopted to solve the produced huge sparse matrix equation. For a full update cycle, the presented scheme solves six tri-diagonal matrices for the electric field components and computes three explicit equations for the magnetic field components. A perfectly matched layer absorbing boundary condition is also extended to this approach. In order to demonstrate the accuracy and efficiency of the proposed method, numerical examples are given. © 2010 IEEE.

Shi L.-H.,Nanjing Engineering Institute | Zhou Y.-H.,Nanjing Engineering Institute | Qi Z.,Nanjing Engineering Institute
2010 Asia-Pacific Symposium on Electromagnetic Compatibility, APEMC 2010 | Year: 2010

The analysis of transmission line under non-uniform incident field and with nonlinear loads is discussed in this paper. A test system is established according to IEC 61000-4-24, which consists of fast pulse generator and SPD (Surge Protection Device) test fixture. By using this system, the nonlinear Volt-Ampere characteristics of SPD can be measured and the nonlinear model of SPD is established. The response voltage of SPD to EMP with different rising time is also measured and discussed. A time-domain transmission line model is then employed to calculate the terminal response of transmission lines under nonlinear loads. Calculation results show the estimated response voltage is in good accordance with the measured one. This kind of method provides a systemic approach for evaluating the EMP protection ability of electronic and electrical systems. © 2010 IEEE.

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