F. Issac

Susceptibility analysis of wiring in a complex system combining a 3-D solver and a transmission-line network simulation

This paper deals with the application of electromagnetic field-to-transmission-line coupling models for large cable systems analysis. It emphasizes the use of Agrawals (1980) model applied here in a numerical simulation of an electromagnetic susceptibility problem up to 500 MHz. Based on the concepts of EM topology, the proposed methodology consists in calculating the incident fields with a three-dimensional (3-D) computer code and the coupling on cables with a multiconductor transmission-line network computer code. In order to validate the efficiency of this methodology in an industrial context, an experiment has been performed on a prototype wiring installed in a Renault Laguna car, stressed by an EM plane wave. Numerous validation configurations have been carried out. First, the prototype cable network under study has been tested on a ground plane to validate the coupling model but also, to validate the cable-network topology itself. Second, EM fields have been measured onto the structure and inside the structure. Then, they have been compared to 3-D calculations, performed with an FDTD code. Third, comparisons between measurements and calculations of bulk currents and voltages on 50 /spl Omega/ loads on the wiring have been achieved.

A Network Formulation of the Power Balance Method for High-Frequency Coupling

This paper deals with a network formulation of the power balance approach in order to estimate high frequency coupling mechanisms in complex systems. After giving the general principles of this approach found in the scientific literature, the network development of the method is presented, based on an electromagnetic topology analysis. Finally, the network formulation of this approach is applied on a simple two contiguous cylindrical structure by easily adapting a computer code initially dedicated to electromagnetic topology on cable networks.

Stability analysis including wires of arbitrary radius in FD-TD code

A thin wire formalism has been previously implemented (R. Holland et al., 1981) in FDTD (finite-difference time-domain) code by introducing an in-cell inductance model of the wire. In the present work, a stability criterion is introduced for taking into account wires of radius less than or equal to half the cell size. To confirm the validity of this criterion, results obtained with the FDTD code ALICE for current injection are compared with the results of the code CRIPTE based on transmission line concepts. The application of the stability criterion has been useful for studying complex structures including a very dense set of internal wires. One example concerns the lightning strike of a helicopter in which wire bundles have been replaced by equivalent conductors having a diameter comparable to the cell size.<<ETX>>

On the Power Dissipated by an Antenna in Transmit Mode or in Receive Mode in a Reverberation Chamber

One of the main characteristics of a reverberation chamber is its quality factor since it determines the field enhancement and the decay time of the impulse response. If a receiving antenna is placed in the room, it absorbs part of the energy which leads to a decrease of the intrinsic quality factor of the room. Such a well-known phenomenon is quantified by the quality factor of the receiving antenna, and a simple analytical formula is available in the literature. If the antenna placed in the chamber is a transmitting antenna, it also receives the waves reflected by the chamber walls and it is often supposed that its quality factor is still given by the same formula. However, it has been already outlined that the quality factor of an antenna used either in a transmitting mode or in a receiving mode is not identical, but differ by a factor of two. The objective of this contribution is to propose an analytical approach, based on the statistical properties of scattering matrices, to justify this result. Furthermore, experiments have been carried out both in the frequency domain and in the time domain to clearly point out the increase of the power dissipated in a transmit-mode antenna. Polarization effects are also studied.

Lightning-Induced Current Simulation Using RL Equivalent Circuit: Application to an Aircraft Subsystem Design

Full-wave EM simulation techniques such as finite-difference time domain (FDTD) are generally used for the calculation of lightning-induced current redistribution on complex 3-D geometries. For slow lightning waveforms, such techniques are not compatible with sensitivity analysis due to heavy preprocessing and calculation constraints. As an alternative, this paper presents an equivalent electric circuit method in which the 3-D geometry is described by conductive segments only on which resistance, self-inductance, and mutual inductance are calculated with analytical formulas. Here, this method, once known as “stick model” method, has been applied for the calculation of the lightning-induced currents on an A320 aircraft landing gear. The results have been compared with an FDTD simulation and with laboratory measurements. They demonstrate that the overall simulation cost is extremely reduced compared to FDTD while they maintain the same degree of accuracy. This paper shows how this equivalent circuit method is appropriate for design processes in which parametric calculations performed in a reasonable time are required.

FDTD application to the electrical characterization of materials by solving an inverse problem

We present a method in order to obtain the unknown permittivity and conductivity of a homogeneous object. The object is illuminated by an electromagnetic plane wave and we measure a set of near scattered fields with the EMIR (electromagnetic infrared) method. This experimental method is based on the use of photothermic film as a sensor to measure electromagnetic fields. With the field data available, we can formulate an inverse problem to evaluate the electrical characteristics of the studied object. To solve the inverse problem, we use an iterative scheme based on a finite difference time domain method for the direct problem.

Field penetration through composite material using FDTD method

Field penetration through a composite material is investigated by solving the curl Maxwells equation with the finite difference method. Use is made of the FDTD (finite-difference time-domain) code ALICE for current injection. The structure used to study field penetration is a perfectly conductive parallelepiped cavity with a square aperture on the upper side. A current injection technique with a thin conductive wire allows electromagnetic distributions outside and inside the cavity to be obtained. Analytical results are presented and discussed.<<ETX>>

FDTD formalism including a microstrip inside an elementary cell

Analysing microwave millimeter-wave integrated circuits (MMIC) with the FDTD technique can require a large computation space, and, as a consequence, a long computation time. With this technique, accurate frequency responses are obtained by the Fourier transform of very long time domain records. A classical way to lower the computation time is to apply linear, or non-linear, predictors, to short time domain records. We propose another method to lower the computation time: this method consists in reducing the computation space by introducing a formalism of a microstrip inside an elementary cell. We have applied the above formalism to the determination of the S/sub 21/ parameter for the classical double-stub filter. For the computation, the filter is enclosed in a PEC parallelepipedic cavity. This formalism is similar to the thin wire formalism previously introduced by Holland and Simpson (1981).

FDTD method for electromagnetic coupling through composite material with contact resistance

An attempt has been made to improve the FDTD (finite-difference time-domain) formalism for electromagnetic coupling through composite material by taking into account the imperfect contact between the loading material and the rim of the aperture. The low frequency domain is still assumed. The results of the FDTD code ALICE are first compared with analytical results. A code validation is then obtained with experimental data. Experimental transient electromagnetic fields were obtained on the French military Transall C 160 aircraft during in-flight lightning strikes. The measurements allowed a more precise determination of the internal magnetic field behind a composite panel located on the forward fuselage.<<ETX>>

Comparison of experimental and numerical results for transient electromagnetic fields induced on a scale model aircraft by current-injection technique

A scale model of the Transall C160 military aircraft, 1/10 of the actual, was installed above a large copper ground plate and connected to it. The entry point at the nose was hard-wire connected to a 12- mu F/5-kV capacitor bank, and the current pulse launch was made using a triggered atmospheric-pressure spark gap. The exit point at the tail or at the left wing tip, depending on the configuration, was connected to the ground plate via an 80- Omega waveshaping resistor. The transient electromagnetic fields on the outer skin of the model were measured using D-dot and B-dot sensors. Three D-dot sensors were mounted on the forward upper fuselage, on the top and the bottom of the left wing. Two B-dot sensors were mounted on the forward upper fuselage and on the top of the left wing. The current was also measured using three i-dot sensors mounted on the nose boom, on the left wing tip, and on the tail boom. A comparison of experimental and computed electromagnetic fields on the scale model was performed for two experimental configurations of current injection: nose to tail and nose to left wing. As shown for one typical case, all the data were predicted with excellent frequency agreement and very good amplitude agreement.<<ETX>>