Electromagnetic Environment In Payload Fairing Cavities

An accurate determination of a spacecraft’s radio frequency electromagnetic field environment during launch and flight is critical for mission success. Typical fairing structures consist of a parabolic nose and a cylindrical core with diameters of 1 to 5 meters resulting in electrically large dimensions for typical operational sources at S, C and X band where the free space wavelength varies from 0.15 m to 0.03 m. These electrically large size and complex structures at present have internal fairing electromagnetic field evaluation that is limited to general approximation methods and some test data. Though many of today’s computational electromagnetic tools can model increasingly complex and large structures, they still have many limitations when used for field determination in electrically large cavities. In this dissertation, a series of test anchored, full wave computational electromagnetic models along with a novel application of the equivalent material property technique are presented to address the electrical, geometrical, and boundary constraints for electromagnetic field determination in composite fairing cavity structures and fairings with acoustic blanketing layers. Both external and internal excitations for these fairing configurations are examined for continuous wave and transient sources. A novel modification of the Nicholson Ross Weir technique is successfully applied to both blanketed aluminum and composite fairing structures and a significant improvement in computational efficiency over the multilayered model approach is obtained. The advantages and disadvantages of using commercially available tools by incorporating Multilevel Fast Multipole Method (MLFMM) and higher order method of moments (HO MoM) to extend their application of MoM to electrically large objects is examined for each continuous wave transmission case. The results obtained with these models are ii compared with those obtained using approximation techniques based on the Q factor, commonly utilized in the industry, and a significant improvement is seen in a prediction of the fields in these large cavity structures. A statistical distribution of data points within the fairing cavity is examined to study the nature of the fairing cavity field distribution and the effect of the presence of a spacecraft load on these fields is also discussed. In addition, a model with external application of Green’s function is examined to address the shielding effectiveness of honeycomb panels in a fairing cavity. Accurate data for lightning induced effects within a fairing structure is not available and hence in this dissertation, a transmission line matrix method model is used to examine induced lightning effects inside a graphite composite fairing structure. The simulated results are compared with test data and show good agreement

Analysis and Validation of the Field Coupled Through an Aperture in an Avionics Enclosure

This work focused on accurately predicting the current response of an equipment under test (EUT) to a random electromagnetic field representing a threat source to model radio frequency directed energy weapons (RFDEWs). The modeled EUT consists of a single wire attached to the interior wall of a shielding enclosure that includes an aperture on one face. An in-house computational electromagnetic (CEM) code based on method of moments (MOM) and accelerated by the multi-level fast multipole algorithm (MLFMA), was enhanced through the implementation of first order vector basis functions that approximates the EUT surface current. The electric field integral equation (EFIE) is solved using MOM/MLFMA. Use of first-order basis functions gives a large savings in computational time over the previous implementation with zero-order Rao-Wilton-Glisson basis functions. A sample EUT was fabricated and tested within an anechoic chamber and a reverberation chamber over a wide frequency band. In the anechoic chamber measurements, the current response on the wire within the EUT due to a single uniform plane wave was found and compared with the numerical simulations. In the reverberation chamber measurements, the mean current magnitude excited on the wire within the EUT by a mechanically stirred random field was measured and compared with the numerical simulations. The measured scattering parameter between the source antenna and the EUT measurement port was used to derive the current response on the wire in both chambers. The numerically simulated currents agree very well with the measurements in both the anechoic and reverberation chambers over the measured frequency band, confirming the validity of the numerical approach for calculating EUT response due to a random field. An artificial neural network (ANN) was trained that can rapidly provide the mean induced current response of an EUT due to a random field under different aperture configurations arbitrarily placed on one face of an EUT. However, ANN proved no better than simple linear interpolation in approximating the induced currents on EUTs that give strong resonances and nulls in the response.Electrical Engineerin

Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers

Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method

Development of a composite CAD package to predict and reduce EM radiation from a PCB

A composite CAD package to predict and reduce radiation from a printed circuit board (PCB) is presented in this thesis. The composite CAD package is implemented using an electromagnetic (EM) computation tool linked with other circuit design packages (CDPs) such as ORCAD (a schematic design package), PSPICE (a circuit simulation package) and Boardmaker (a board layout tool). Software is developed to link all the packages so that one can incorporate EMC verification in the design process of an electronic product. The well-known Numerical Electromagnetic Code (NEC) version 2 is used as an EM computation tool. In using NEC-2 to predict PCB radiation, the PCB is simulated as a loaded thin wire structure just above (but not contacting) the surface of an imperfect ground. An algorithm is developed and implemented to automate the geometrical modelling of a wire structure for NEC-2. The data required by NEC-2 ( geometrical, load and electrical) for prediction of PCB radiation can be obtained from various CDPs. The development and implementation of data extraction algorithms are presented in this thesis. Single and double sided PCBs can be accommodated and the work can be extended to handle multilayer PCBs. The use of NEC-2 for this type of application has been validated experimentally and theoretically (by comparing NEC-2 predicted radiation with that obtained where the EM radiation from a pair of parallel PCB tracks running between two components/devices is computed using transmission line modelling-TLM). Both methods of evaluation are described in detail in this thesis and results showing good agreement are presented. TLM is employed by considering, (i) the effective dielectric constant of the medium (air and substrate) surrounding the PCB tracks and (ii) the displacement current between the two PCB tracks. The effect of displacement current in near field radiation is highlighted. The use of TLM for prediction of PCB radiation is verified experimentally. Measured radiation is in good agreement with prediction. In the developed composite CAD package, one can compare the predicted radiation with the mandatory EMC requirement laid down by the regulating bodies and "close the loop" to modify the design where these requirements have not been met. Various techniques to reduce radiation can also be employed. Reduction of radiation by providing shielding in some section of the circuit is proposed. An algorithm is developed and implemented to find the section of the circuit where shielding is necessary. The optimum layout (track separation to width ratio) that can minimise radiation is found theoretically. An optimum layout is also determined experimentally and compared with the theoretical value. A good agreement is found in this comparison. Thus a guideline to choose optimum layout for minimum radiation is provided

Simplified equivalent modelling of electromagnetic emissions from printed circuit boards

Characterization of electromagnetic emissions from printed circuit boards (PCBs) is an important issue in electromagnetic compatibility (EMC) design and analysis of modern electronic systems. This thesis is focused on the development of a novel modelling and characterization methodology for predicting the electromagnetic emissions from PCBs in both free space and closed environment. The basic idea of this work is to model the actual PCB radiating source with a dipole-based equivalence found from near-field scanning. A fully automatic near-field scanning system and scanning methodology are developed that provide reliable and sufficient data for the construction of equivalent emission models of PCB structures. The model of PCB emissions is developed that uses an array of equivalent dipoles deduced from magnetic near-field scans. Guidelines are proposed for setting the modelling configuration and parameters. The modelling accuracy can be improved by either improving the measurement efforts or using the mathematical regularization technique. An optimization procedure based on genetic algorithms is developed which addresses the optimal configuration of the model. For applications in closed environments, the equivalent model is extended to account for the interactions between the PCB and the enclosure. The extension comprises a dielectric layer and a ground plane which explicitly represent the necessary electromagnetic passive properties of a PCB. This is referred to as the dipole-dielectric-conducting plane (DDC) model and provides a completely general representation which can be incorporated into electromagnetic simulation or analysis tools. The modelling and characterization methodology provides a useful tool for efficient analysis of issues related to EMC design of systems with PCBs as regards predicting electromagnetic emissions in both free space and closed environment. The proposed method has significant advantages in tackling realistic problems because the equivalent models greatly reduce the computational costs and do no rely on the knowledge of detailed PCB structure

Applied Computational Electromagnetics Society Journal / Volume 15, Number 1

Approved for public release; distribution is unlimited

Electromagnetic Modeling and Simulation of Anisotropic Structures Using the Equivalent Source Method

RÉSUMÉ Le développement de nouvelles technologies de fabrication ouvre de nouvelles possibilités au niveau du développement de matériaux possédant des anisotropies complexes. Les caractéristiques anisotropes, comparativement aux caractéristiques isotropes, permettent de contrôler aisément aux ondes électromagnétiques. Ces propriétés pourraient s’avérer intéressantes pour la conception de futurs dispositifs faisant partie de systèmes de communication sans-fil. Jusqu’à maintenant, les méthodes de simulations intégrées dans les logiciels commerciaux se basent sur la discrétisation volumétrique comme la méthode des éléments finis (FEM) et la méthode des différences finies dans le domaine temporel (FDTD). Ces méthodes permettent de traiter la plupart des cas généraux de matériaux anisotropes, mais elles nécessitent une discrétisation de l’entièreté du volume de l’objet. Cela représente un fardeau de calcul important lorsqu’un matériau plus volumineux est traité. La méthode des moments basée sur les équations intégrales de surface (SIE-MoM) peut simplifier le problème en restreignant le problème à la surface du volume. Cette méthode se heurte toutefois aux problèmes de singularités. Pour surmonter ceux-ci et dans le but de fournir un outil de simulation efficace, nous présenterons une méthode d’équivalence de source (ESM) qui est une solution par moments permettant l’évaluation électromagnétique de matériaux anisotropes. Les fonctions de Green tensorielles en deux et trois dimensions des matériaux analysés seront abordées en détails et appliquées dans la formulation de la ESM qui permet d’analyser les diffuseurs anisotropes. Le placement de sources filamentaires et des points de test qui jouent un grand rôle dans la méthode ESM seront détaillés car il favorise l’obtention de solutions stables. Le problème des singularités, un problème majeur de la SIE-MoM, peut facilement être résolu par la ESM. De plus, les conditions frontières anisotropes, plus spécifiquement les conditions aux frontières d’impédance tensorielle (TIBC) utilisées dans la représentation de matériaux composites en fibre de carbone multicouche et la condition des feuilles de transition généralisée (GSTC) utilisée dans la caractérisation de métasurfaces cylindriques sont aussi intégrées dans la ESM pour analyser les évaluations électromagnétiques. Comparativement aux logiciels commerci-aux et aux recherches déjà publiées, la ESM possède clairement l’avantage au niveau de la performance de la simulation. En outre, dans cette thèse, on s’intéressera aux limitations de la ESM dans les cas en trois dimensions. Même si la simulation par ESM d’objets en trois dimensions possédant des géométries complexes engendrent un coût de calcul important, la ESM demeure un outil de simulation puissant dans les cas de géométries en deux et trois dimensions possédant des frontières lisses.----------ABSTRACT The development of manufacturing technology provides possibility to build artificial materials possessing complex anisotropy. The anisotropic characteristic, compared with the isotropic one, provides additional freedom to control electromagnetic waves. This property makes the anisotropic material a competitive alternative in the design of devices for future wireless communication systems. So far, the simulation methods integrated in commercial software packages for anisotropic materials are volumetric discretization-based, such as Finite-Element Method (FEM) and Finite-Difference Time-Domain (FDTD). These methods can handle the most general case of anisotropic materials whereas they require to discretize the entire volume of an object, therefore it generates computational burden when a larger scatterer is encoun-tered. The surface integral equations-based method of moment (SIE-MoM) can simplify the problem by formulating the problem only on the physical surface. Yet the complexities, especially on the singularity issue, are still there. To overcome mentioned problems and to provide an eÿcient simulation tool, this thesis presents the equivalent source method (ESM), a moment solution, to analyze anisotropic materials. The dyadic Green’s functions in two-dimensional and three-dimensional cases of investigated anisotropic materials are discussed in detail, and subsequently deployed in the formulation of the ESM to analyze electromagnetic phenomena involving anisotropic scatterers. The placements of filamentary sources and the testing points, playing the key role in the ESM, are discussed and specified in detail to provide a stable solution. The singularity issue, usually a tough problem in SIE-MoM, can be solved easily by using the ESM. In addition, the anisotropic boundary conditions, specifically the tensorial impedance boundary condition (TIBC) used for representing multilayered carbon-fiber composite materials and the generalized sheet transition condition (GSTC) used for characterizing cylindrical metasurfaces, are also incorporated in the ESM. In comparison to commercial software packages and published researches, the ESM has a clear advantage on the simulation performance. For example, the CPU time and required memory are 611 s/7.50 GB for the FEM (CST) whereas only 1.58 s/0.00037 GB for the ESM when computing the field on the surface of an elliptical cylinder in two-dimensional (2D) case under the illumination of a TM plane wave, and in three-dimensional (3D) case, the CPU time and required memory are 82980 s/170.2 GB for the FEM (HFSS) whereas only 4421.52 s/2.40 GB for the ESM when computing scattering from an uniaxial sphere with a 2� radius

13th Annual Review of Progress in Applied Computational Electromagnetics at the Naval Postgraduate School, Monterey, CA, March 17-21, 1997, Conference Proceedings Volumes I & II

Includes Volumes 1 &