Alberto Scarlatti

On the use of fitting models for the time-domain analysis of problems with frequency-dependent parameters

The use of fitting models in the time-domain analysis of electromagnetic problems is of great interest. The aim of this paper is to describe the main features of different fitting models, and the key issues related to their use and practical implementation in computational codes. Equivalent circuit representations of such models are also presented, and numerical applications are shown in order to provide guidelines for the choice of the method that is the most suitable to solve a specific problem.

An equivalent transmission-line model containing dispersion for high-speed digital lines-with an FDTD implementation

The increase in processor speeds in the last few years has created a growing need for the accurate characterization of waveform propagation on lossy printed-circuit-board (PCB) transmission lines. Due to the dispersive nature of pulse propagation on lossy transmission lines, approximations of the classic transmission-line model can fail in this application (i.e., lossless or DC losses approximations). This paper shows how an equivalent transmission-line model can be used to analyze dispersive transmission lines for high-speed digital applications. The equivalent-circuit elements of this transmission-line model incorporate the frequency dependence of the per unit length impedance and admittance caused by the finite conductivity of the conductors as well as the dielectric losses. We show that these equivalent circuit elements can be readily implemented into finite-difference time-domain (FDTD) transmission-line codes, and we present such a FDTD implementation. S-parameters and pulsed waveforms for a circular wire, coplanar waveguides (CPW) and microstrip lines are shown. Finally, we present approximate expressions for analytically obtaining the resistance and inductance per length of a microstrip line.

Modeling of magnetic-field coupling with cable bundle harnesses

A field-to-line coupling model is developed for cable bundle harnesses in terms of the scattering currents and total line voltages. The equivalent distributed sources representing the effects of electromagnetic coupling are expressed as a function of the incident magnetic-field components. Such a formulation is particularly suitable to be used for the analysis of multiconductor transmission lines excited by a transient field, when data for the incident electric field are either inaccurate or not available. This model allows the accurate calculation of the induced voltages and currents on complex cable bundles. The effects on the induced voltages and currents due to ground losses and to the presence of the dielectric sheath in shielded and unshielded cables is discussed, considering bundles excited by either slow or fast transient fields. Numerical applications demonstrate the validity of the proposed procedure.

Suppression of late-time instabilities in 3-D-FDTD analyses by combining digital filtering techniques and efficient boundary conditions

A new computational procedure is developed to suppress late-time instabilities in three-dimensional finite-difference time-domain analyses. The method combines low-pass filtering schemes with absorbing boundary conditions. The computational domain is truncated at only a few cells from the scattering object. Applications concern the analysis of long transients exciting frequencies up to a few megahertz.

Theoretical analysis of radiated emission from modal currents in multiconductor transmission lines above a lossy ground

A procedure is proposed for the accurate calculation of the modal currents that propagate along each wire of excited multiconductor transmission lines (MTLs), having whatever configuration. The radiated electromagnetic (EM) field from each modal current is predicted by using rigorous formulations, which are valid for lines of finite length and a dissipative ground plane. The developed approaches are applied to the analysis of the modal electromagnetic interference (EMI) radiated from a two-wire signal line and of a signal carrier channel on a multiconductor power line.

Radiated susceptibility of wiring system aboard lightning struck aircraft. Part I: sensitivity to the p.u.l. external parameters

The sensitivity of the radiated susceptibility of cable bundles aboard lightning struck aircraft, against variations of the p.u.l. external parameters is analyzed. The influence that these parameters have on the short-circuit currents and open-end voltages induced on cable bundles, as regards variations of the installation configuration and geometrical set-up is investigated. A strategy is proposed for the classification of the numerous cable bundle configurations aboard aircraft within a limited set of simplified installation typologies, thus reducing the complexity and computational efforts of the harness simulation.

Integral equation boundary conditions for the efficient FDTD analysis of low-frequency transient problems

Innovative boundary conditions are proposed for the efficient truncation of FDTD grids in the analysis of low-frequency transient problems, in which the minimum excited wavelength is hundreds times greater than the space discretization step. The electromagnetic transient source is coupled inside the discretized FDTD domain by enforcing electric- and magnetic-field integral-equations on the grid borders. Critical aspects of the numerical implementation are discussed. Numerical applications demonstrate the validity of the proposed procedure.

Efficient numerical calculation of integral equations-boundary conditions for the finite-difference time-domain method

An efficient integration scheme is proposed for the numerical implementation in the FDTD approach of integral equations-boundary conditions (IE-BCs). The method is based on the use of a self-adapting integration step. The procedure allows great saving of computational resources. Numerical results demonstrate the validity of the method.

Radiated susceptibility of wiring system aboard lightning struck aircraft. II. Sensitivity to the distributed induced sources

Radiated susceptibility of the wiring system aboard a lightning struck aircraft is analyzed considering the reduced order model involving only the critical cable bundles connected to apparatus that are defined to be critical for the flight safety. Correction factors of the induced sources on the critical bundles are proposed in order to take into account the shielding effect produced by the noncritical bundles in the same harness.