Jianfeng Xu

Missouri University of Science and Technology, Missouri, United States

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Publications (8)2.65 Total impact

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    ABSTRACT: A methodology to efficiently design products based on magneto-dielectric (ferrite) materials with desirable frequency responses that satisfy electromagnetic compatibility and signal integrity requirements over RF and microwave bands is presented here. This methodology is based on an analytical model of a composite magneto-dielectric material with both frequency-dispersive permittivity and permeability. A procedure for extracting complex permittivity and permeability of materials from experimental data is based on transmission line measurements. The genetic algorithm is applied for approximating both permittivity and permeability of materials by series of Debye frequency dependencies, so that they are represented as “double-Debye materials” (DDM). The DDM is incorporated in the finite-difference time-domain numerical codes by the auxiliary differential equation approach.
    IEEE Transactions on Electromagnetic Compatibility 12/2010; · 1.33 Impact Factor
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    ABSTRACT: The paper describes a methodology for an efficient design of novel products based on magneto-dielectric (ferrite) materials with desirable frequency responses that satisfy EMC and SI requirements. The methodology starts from estimating complex permittivity and permeability of these materials. This requires measurement techniques, approximation resultant frequency characteristics for permittivity and permeability using a curve-fitting procedure, and development of a full-wave numerical simulation tool that could deal with frequency-dispersive materials. An example of a ferrite material measurement, constitutive parameters extraction using a genetic algorithm, and corresponding FDTD modeling over the frequency range from 10 to 500 MHz is provided.
    Electromagnetic Compatibility, 2009. EMC 2009. IEEE International Symposium on; 09/2009
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    ABSTRACT: Transient thermal responses of GaAs field-effect transistors (FETs) in the presence of an electromagnetic pulse (EMP) are investigated in this paper. The numerical methodology employed is an efficient nonlinear finite-element method (FEM) that combines the element-by-element FEM and the preconditioned conjugate gradient technique. Parametric studies are carried out to show different pulse parameters on the transient thermal responses as well as maximum channel temperatures of some typical GaAs FETs, with silicon FETs also taken into account for comparison. It is numerically proven that the thermal impact caused by medium EMP will be the most serious compared with fast EMP or ultra-wideband pulse, and the captured maximum channel temperature is proportional to the input power density, approximately of the EMP injected. This research can serve as a base for taking further protection measures to prevent on-chip device from breakdown by the attack of an EMP.
    IEEE Transactions on Electromagnetic Compatibility 06/2008; · 1.33 Impact Factor
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    ABSTRACT: In this paper, the transient thermal characteristics of GaAs field-effect transistors (FETs) in the presence of high- power electromagnetic pulses (HP-EMP) are investigated. By hybrid finite element methods which combining element-by- element finite element method (EBE-FEM) with the preconditioned conjugate gradient (PCG) technique, transient thermal responses including the maximum channel temperature of GaAs FETs and the maximum input power density of the thermal sources are extracted which will be useful for further taking thermal protection so as to prevent on-chip device breakdown from the attack of a HP-EMP.
    Microwave and Millimeter Wave Technology, 2008. ICMMT 2008. International Conference on; 05/2008
  • Jianfeng Xu, Wen-Yan Yin, Junfa Mao
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    ABSTRACT: In this paper, numerical investigation on GaN HFETs is carried out using hybrid finite element method (FEM) which combines the FEM with the preconditioned conjugated gradient technique. The maximum temperatures of the HFETs operating under continuous-waves (CW) and pulsed-waves (PW) are both captured accurately. The effects of temperature- dependent thermal conductivities of the materials on the temperature distribution are also studied and compared for different substrate materials, such as sapphire, silicon, and SiC.
    Microwave Conference, 2006. APMC 2006. Asia-Pacific; 01/2007
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    ABSTRACT: The element-by-element finite element method (EBE-FEM) combined with the preconditioned conjugate gradient (PCG) technique is employed in this paper to calculate the coupling capacitances of multi-level high-density three-dimensional interconnects (3DIs). All capacitive coupling 3DIs can be captured, with the effects of all geometric and physical parameters taken into account. It is numerically demonstrated that with this hybrid method in the extraction of capacitances, an effective and accurate convergent solution to the Laplace equation can be obtained, with less memory and CPU time required, as compared to the results obtained by using the commercial FEM software of either MAXWELL 3D or ANSYS.
    01/2007;
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    ABSTRACT: In this paper, the thermal characteristic of the GaN HFETs has been analyzed using the hybrid finite element method (FEM). Both the steady and transient state thermal operations are quantitatively studied with the effects of temperature-dependent thermal conductivities of GaN and the substrate materials properly treated. The temperature distribution and the maximum temperatures of the HFETs operated under excitations of continuous-waves (CW) and pulsed-waves (PW) including double exponential shape PW such as electromagnetic pulse (EMP) and ultra-wideband (UWB) signal are studied and compared.
    01/2007;
  • Jianfeng Xu, Wen-Yan Yin, J. Mao
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    ABSTRACT: In this paper, the element-by-element technique in conjunction with preconditioned conjugate gradient (PCG) solver is adopted for fast parameter extraction of multi-layer and multi-conductor interconnects in VLSI circuit. In order to partially implement parallel computation, the proposed technique takes advantage of Fortran 95 in the array manipulation, and the efficiency of this technique is verified by numerical examples. Compared to some reference solutions, both the memory requirement and the CPU time are significantly reduced while maintaining a relatively high accuracy.
    Microwave Conference Proceedings, 2005. APMC 2005. Asia-Pacific Conference Proceedings; 01/2006