Preface

Computational electromagnetics (CEM) is witnessing a drastically changing environment with the new generation of computer processors, which are multicore instead of single-core. The change in Central Processing Units (CPU) design represents something of a cataclysmic shift for Electromagnetic (EM) software. As a result, parallel CEM programming has suddenly become relevant for all computer systems. The burden now falls on the EM software designer to add new functionality to enable computational codes to run efficiently on this new generation of multicore processors or to revamp existing codes for that purpose.

HOBBIES, which is an acronym for Higher Order Basis Based Integral Equation Solver, is a high-performance both in-core and out-of-core parallel simulation software intended for fast and accurate analysis of a wide range of EM problems, especially for the solution of electrically large and complex problems. The unique features in HOBBIES can be classified into two classes: (1) use of the higher order basis based on the Method of Moments (MoM) in a frequency domain integral equation solver, and (2) the computer-related methodologies such as an out-of-core parallel processing methodology for efficient solution of large, dense complex matrix equations. This book on HOBBIES not only contains the theory but also has an academic version of the code with a maximum of 3000 nodes for generating the geometry and 5000 samples for the post-processing. It has a capability not only for analysis but also for synthesis of various electromagnetic structures. One of the unique features of this code is that besides providing its own mesher and post-processor, one can import geometries generated on other computer aided design (CAD) formats and remesh them or repair them as needed for efficient and accurate electromagnetic simulation.

As the name implies, HOBBIES employs higher-order polynomials as the basis functions for the solution of a frequency domain integral equation. The bottleneck of traditional MoM partly comes from the storage, which is related to the amount of memory required. HOBBIES applies the higher order basis functions to overcome one of the bottlenecks of storing the impedance matrix elements in the memory, resulting in a reduction of matrix sizes at least by a factor of ten over the use of a subsectional basis for the analysis of electrically large problems. Higher-order polynomials over wires and quadrilateral surfaces are used in HOBBIES MoM as basis functions over larger subdomain segments and patches. Polynomial expansions for the basis functions over larger subdomains lead to a good approximation of the current distributions over large surfaces using approximately 20 unknowns per wavelength squared of surface area. This number is much lower than that for the piecewise RWG (Rao–Wilton–Glisson) basis functions, and thus, the use of polynomial basis functions over larger subdomains reduces significantly the number of unknowns.

In addition, using the latest computer technology, HOBBIES provides a parallel implementation of the computational kernel as a powerful tool for analysis of electrically large objects composed of metallic and dielectric structures. In this way, one can fully utilize the multicore CPUs on a Personal Computer (PC)/cluster. As is well known, MoM needs to deal with large, dense complex matrices for analyzing complex problems. This leads to a requirement of a large amount of random access memory (RAM). Most computers may not have large RAMs. To overcome such limitations of the RAM, an out-of-core solver is introduced to extend the capability of MoM by taking full advantage of the mass storage space on the hard disks. The simulation efficiency of a serial MoM code is constrained by the computing capability of the computer system at hand. To improve the efficiency of a MoM code and to integrate the trend of modern CPU development, use of parallel algorithms is the inevitable way out, and that is an important contribution of this book/computer code. Furthermore, use of parallel out-of-core solvers generates numerically accurate results within a reasonable time frame by using multicore CPUs. The main objective of developing HOBBIES is thus to provide a parallel in-core and parallel out-of-core solution methodologies to extend the capability of MoM to analyze large, complex problems.

HOBBIES provides computational methodologies to overcome these two limitations inherent in MoM by using a unique, advanced out-of-core parallel solver using the higher order basis. HOBBIES thus brings to the EM engineer's desktop computing solutions based on an out-of-core processing kernel and parallel solving capability, thereby fully exploiting the modern multicore technology. Benchmark tests have shown this software to be more accurate than other higher order basis based commercial MoM solvers. In this way, one can go beyond the limitations of RAM for solving MoM problems. It is important to note, since the software is integrated with the hardware, that the penalty for using an out-of-core solver over an in-core one with large RAM for HOBBIES is approximately ONLY 20% slower than the latter. Thus, providing numerically accurate results within a reasonable time frame makes HOBBIES unique in the area of EM solvers.

It is important to note that there is another electromagnetic analysis code called WIPL-D in the market, of which one of the present authors was also a coauthor. The similarity between the two codes, WIPL-D and HOBBIES, is that both use similar higher order basis functions. And there the similarity ends as HOBBIES uses a professional pre- and post-processing Graphical User Interface (GUI) called GiD, which can be executed either on a Microsoft Windows (Microsoft Corporation, Redmond, WA) or a Linux platform. In addition to generating its own mesh, GiD can also deal with almost any of the geometry generator CAD meshers available and most importantly can take the geometry generated by any of the other generators and translate it into a geometry generated by Non-Uniform Rationale B-Spline (NURBS) surfaces and then rediscretize the structure with a given pre-specified degree of accuracy between the NURBS model and the discretized structure. The second unique feature of HOBBIES is that it can deal with a parallel out-of-core solution of large matrix equations making it possible to solve large problems on personal desktop computers. Therefore, the similarity between WIPL-D and HOBBIES is only in the physics, use of a higher order basis, but the rest including the GUI and the solution procedure is totally different, making HOBBIES a unique, efficient, and accurate user-friendly tool for the analysis of complex, large electromagnetic problems on personal desktop computers.

The pre- and post-processors are developed by HOBBIES and GiD groups, which enable flexible and convenient geometric modeling, meshing, data input/output, and visualization of the results. The NURBS and parametric lines/surfaces are allowed in geometric modeling. HOBBIES can import and export geometric models or meshes in many formats, such as IGES, DXF, and ACIS. For post-processing, the software has two-dimensional (2D) and three-dimensional (3D) modes for evaluating near-field, far-field, current distribution on structures, and so on. GiD is a pre/postprocessing system developed by the International Center for Numerical Methods in Engineering (CIMNE) and Compass Ingenieria y Sistemas.

HOBBIES can deal with problems of scattering analysis, antenna design, Electromagnetic Compatibility (EMC) analysis, microwave circuit design, and much more. Applications of HOBBIES include electrically large and complex objects composed of multiple metallic and dielectric structures. For example,

• Scattering analysis: monostatic and bistatic Radar Cross Section (RCS) simulation of aircrafts, missiles, ships, and other large objects.
• Antenna design: wire antennas, reflector antennas, aperture antennas, helix/spiral antennas, printed antennas, broadband antennas, antenna arrays, and the like.
• On-board antenna analysis: radiation and coupling simulation of antennas mounted on airplanes, ships, and other platforms; antenna placement on those large platforms; and so on.

This book summarizes the theory and applications of HOBBIES. Here is a thumbnail outline of what is unique in this book:

1. The mathematical form of the integral equations using the higher order basis functions and models used for the EM excitations are discussed.
2. Both parallel in-core and out-of-core EM integral equation solvers are presented to illustrate how to utilize computer resources efficiently.
3. Both the EM methodology of the HOBBIES kernel and the user friendly GUI in the pre- and post-processing software are presented.
4. The geometry modeling technique in GiD and the mesh generation including a mesh repair methodology are introduced for HOBBIES. NURBS and parametric curves and surfaces are introduced to model complicated structures. Generation of both structured and unstructured meshes is described.
5. Both EM analysis (simulation) and EM synthesis (optimization of a typical design) are emphasized.

Another important objective of this book is to provide a user guide of HOBBIES to the academic research scientists, postgraduate students, and in particular, for those undertaking numerical analysis using HOBBIES software. To this end, the book covers installing HOBBIES, setting up of the HOBBIES parallel environment, introduction to HOBBIES projects, drawing geometry models, meshing the models, setting up solution projects, post-processing, and optimizing in HOBBIES.

As a step-by-step guide for the users of HOBBIES, this book provides all the detailed information through some simple modeling examples. Advanced modeling in HOBBIES and various applications are also presented, involving antenna design, EMC prediction, scattering analysis, antenna placement, and Electromagnetic Interference (EMI) simulations.

The content of this book is organized as follows:

Chapters 1 and 2 provide the basic theory of the HOBBIES software. The fundamental theory of HOBBIES is described in Chapter 1, in relation to the EFIE (electric field integral equation) and the PMCHW (Poggio–Miller–Chang–Harrington–Wu) formulation. The geometry modeling and the CEM modeling in HOBBIES are also discussed. Then, the higher order basis functions and the formation of the impedance matrix in MoM are presented, followed by a discussion of the methods of excitation and post-processing calculations.

Chapter 2 gives a detailed discussion of the parallel in-core and out-of-core LU factorization methodology for solving the matrix equations in MoM. The data distribution of the Scalable Linear Algebra Package (ScaLAPACK) is explained in detail since this is the key to understanding how the MoM matrix in HOBBIES is distributed among many processes. Then, the development of one slab left-looking out-of-core algorithm is discussed. As is well known, filling the complex impedance matrix in parallel is greatly determined by the parallel matrix equation solvers. Therefore, both the parallel matrix filling and the parallel solution of large, complex matrices are both discussed in this chapter.

How to set up and use HOBBIES for the solution of challenging problems on modern personal desktop computers is described in Chapters 3–7.

Chapter 3 discusses how to install and set up the environment for HOBBIES. The description presented is for the Windows operating system. For a Linux operating system, the procedure is very similar. The menus and toolbars of HOBBIES are introduced in this chapter. At the end of this chapter, the flowchart of making a typical HOBBIES project is shown.

When one attempts a HOBBIES simulation, the first step is to generate the geometry model in HOBBIES. This is explained in detail in Chapter 4. Readers can use the Structure menu to create simple shaped structures, use the Geometry menu to create arbitrarily shaped structures, or use both methods if so desired. How to create, operate, and manipulate models is described in detail with examples, including use of NURBS curves and surfaces modeling methodology.

Meshing is necessary for the electromagnetic analysis of the problem. Linear segments for wires and quadrilateral patches for surfaces can be easily generated in HOBBIES. Chapter 5 describes how to generate the meshes automatically, transparent to an user using different methodologies for the computational kernel of HOBBIES.

Chapter 6 continues to describe how to set up and execute a typical HOBBIES simulation. The settings of a HOBBIES project include Operation Mode, Units, Frequency Range, Domains, Loadings, Excitation, Symmetry, Edge, Output Settings, and Options. One can run a simulation in one of the four different ways, namely, serial in-core, serial out-of-core, parallel in-core, and parallel out-of-core.

Chapter 7 describes the user-friendly GUI for post-processing. Users can view the meshes, 2D and 3D radiation/scattering patterns, Y/Z/S network parameters, 2D and 3D near-fields, and electric/magnetic current distributions. Customizing a 2D or 3D plot is available such as changing the line color for a 2D plot or setting the transparency for a 3D plot.

Typical examples and applications of HOBBIES are presented in Chapters 8 and 9.

Sample applications are presented in Chapter 8, which involve excitations, domains, loadings, symmetry planes, analysis of metallic and composite metallic/dielectric structures, and so on.

The final goal is to come up with a professional EM simulation tool for practicing engineers. Complicated models and simulations of real-life applications and comparison of computed results with measured data are presented in Chapter 9 to show the accuracy and versatility of HOBBIES.

Optimization is a process to find the best available values of some objective functions for defined domains through changing parameters in a model. Setting up of the optimization process involving several optimization methods is discussed in Chapter 10. The HOBBIES optimizer is an useful tool in EM system design. One of the unique features of this chapter is that it presents an optimization methodology that can simultaneously deal with over hundreds of variables without requiring any partial derivative of the objective function with respect to the variables.

It is hoped that this book will provide an insight into the theory of a parallel MoM methodology using higher order basis functions and a professional software with a user-friendly GUI connected with a powerful kernel, for solution of EM problems in the frequency domain. In the near future, it is envisioned that HOBBIES will have a parallel time domain integral equation solver capability under the same GUI and the same pre- and post-processing kernels.

A different version of HOBBIES is available from the authors which can be executed on the Microsoft Windows Azure Platform which is an open and flexible Microsoft cloud computing platform. Also other versions of HOBBIES can be executed on any hardware platforms containing either AMD or INTEL multicore processors and operating with any Windows or Linux operating systems.

Every attempt has been made to guarantee the accuracy of the materials presented in the book. We would, however, appreciate readers bringing to our attention any errors that may have appeared in this version. Errors and/or any comments may be e-mailed to [email protected].