ELECTROMAGNETIC TOPOLOGY: ANALYSIS OF RF EFFECTS ON ELECTRICAL SYSTEMS

1. F. M. Tesche Prepared UnderAFOSR MURI Grant with University of Illinois at Chicagoand Clemson University University of Houston University of Illinois at Urbana-Champaign University of Michigan June 13, 2001 ELECTROMAGNETIC TOPOLOGY: ANALYSIS OF RF EFFECTSON ELECTRICAL SYSTEMS

2. Outline of Presentation • Overview • Introduction to EM Topology • Applications of Topology for the MURI Project • Summary

3. Requirement is to determine behavior of the digital circuitry to the EM excitation Statement of the Project • To evaluate the response of electrical systems to radiated EM field environments • Focus is on upset or damage of digital systems • For fast transient or pulsed CW excitations at GHz frequencies Source IncidentEM Fields IlluminatedSystem Internal Circuitry Digital Components

4. Problem Statement (con’t.) • Pertinent issues to be addressed in the MURI project: • To develop EM interaction models for high frequency/fast transient environments, • To obtain fundamental insight into the interaction of these EM environments with digital circuitry, • Considering both components and subsystems • For both upset and damage • To develop methods for testing digital systems, • To develop mitigation techniques for digital systems, • To document and distribute MURI results, • Through development of specifications and standards • Liaisons with government and industry partners • To develop and maintain and basic EM capability for DOD and industry.

5. Outline of Presentation • Overview • Introduction to EM Topology • Applications of Topology for the MURI Project • Summary

6. How to Represent an Electrically Complex System ? • The analysis of electrically large systems is difficult. • This is due to the complexity of the system and the different ways that EM energy can interact with the system: • Inductive, capacitive and galvanic coupling to conductors, • Direct EM radiation coupling, • Current and charge propagation on conductors, • EM field penetration through apertures, • Diffusive penetrations through imperfect conductors, and • Cavity-mode resonances. • Early attempts at developing analysis models for such systems were hampered by not having a structured way of decomposing the system into smaller parts. • This led to models with errors frequently exceeding 30 dB. (See Carter, J. M., and W. L. Curtis, “Common Mode Model Development for Complex Cable Systems”, Boeing Company, AFWL-TR-74-60, 1974.)

7. Modeling Can Be Based on EM Topology • The system can be thought of as consisting of several layers of conducting surfaces which shield the interior. • Known as the “onion” concept of shielding (as described by Ricketts, et. al., EMP Radiation and Protective Techniques, John Wiley & Sons, New York, 1976.) • This idea was initially developed by C. E Baum and later formalized in the literature: • Baum, C. E., “How to Think About EMP Interaction”, Proceedings of the 1974 Spring FULMEN Meeting, Kirtland AFB, April 1974. • Tesche, F. M., et. al., “Internal Interaction Analysis: Topological Concepts and Needed Model Improvements”, Interaction Note Series, IN-248, October 1975. • Tesche, F. M., "Topological Concepts for Internal EMP Interaction," IEEE Trans. AP, Vol. AP-26, No. 1, January 1978. • Baum, C. E., "Electromagnetic Topology for the Analysis and Design of Complex Electromagnetic Systems", Fast Electrical and Optical Measurements, Vol. I, eds. I.E. Thompson and L.H. Luessem, Martinus Nijhoff, Dordrecht, 1986.

8. Models in Electromagnetics • In EM applications, models are based on Maxwell's equations • and the EM topology of the system • From these equations, many different solution approaches are possible: Topology is a key element to the model development

9. Analysis Using EM Topological Concepts is Conceptually Simple • The system is examined for the principal shields or EM “barriers” • Imperfections in these shields are noted and categorized • A signal flow diagram is constructed • Models are developed for important aspects of the signal path • An analysis is performed

10. The First Step in Model Development is to Determine the Topological Diagram • This is a description of the principal shielding surfaces in the system and their interrelations • Real shields are not perfect, and the external EM energy can enter by one or more of the following mechanisms: • hard-wired penetrations, formed by wires, cables or other conductors • aperture penetrations through holes in the shield, and • diffusion through the barrier material

11. Example of the Topological Approach • Simplified illustration of a hypothetical facility excited by an external EM field.

12. The interaction diagram shows the paths that EM energy can take in the system to provide a response at equipment Propagation occurs as energy moves from one location to another in the system Penetrations of the EM energy occur at imperfections in the shielding surfaces The topological diagram shows the shielding surfaces of the system and their interrelations Topological Representation of the Facility • An EM interaction model is developed using the system topological and interaction diagrams:

13. The Interaction Sequence Diagram Describes the Entire Interaction Process • Illustrated here is a more complete representation of an interaction diagram for a complex facility

14. A Transmission Line Approximation to the EM Interaction Process • The most important EM interaction paths are usually the conductive paths (transmission lines consisting of cables and wires) • A common low frequency approximation is to neglect the EM field couplings and treat only the conductors

15. The network consists of interconnected single-wire or multiconductor transmission lines Impedance elements represent the equipment loads I inc Forward and backward traveling waves exist on each transmission line “tube” in the network Incident and scattered waves exist at each junction (or node) in the network I + I - I sca The BLT Equation – A Solution for the Transmission Line Network • The BLT equation† describes the voltage or current responses on a network of transmission lines † Baum, C.E., Liu, T.K, & Tesche, F.M.,”On the Analysis of General Multiconductor Transmission Line Networks”, Interaction Note 350, Kirtland AFB, NM, 1978

16. Supermatrix multiplication Source supervector containing the excitations of each transmission line tube Identity supermatrix Response supervector containing all wire currents at each node in the network Propagation supermatrix for all tubes (suitably re-ordered) Voltage scattering supermatrix for all nodes The BLT Equation – A Solution for the Transmission Line Network (con’t.) • The current at all nodes in the network is described by the BLT equation • This is a matrix equation involving matrices as elements – a supermatrix equation

17. The BLT Equation – A Solution for the Transmission Line Network (con’t.) • A similar BLT equation can be developed for the voltages at each wire at the nodes of the network

18. Numerical Realizations of the BLT Equation • The initial BLT analysis code, QV7TA, was developed by Tesche and Liu in 1978 † • Has been used for aircraft, missile and satellite analysis for DOD programs • More recent work by Parmantier in France has resulted in the CRIPTE code † † • Presently being marketed commercially by ESI in France • Both codes operate in the frequency domain and use numerical matrix inversion techniques to solve the BLT equation †Tesche, F. M., and T.K. Liu, “User Manual and Code Description for QV7TA: a General Multiconductor Transmission Line Analysis Code”, LuTech, Inc. report, August 1978. † † CRIPTE Code Users Guide, ESI/ONERA, France, 1997.

19. The Topological Approach Has Been Used Extensively in the Past • Tesche, F. M, et. al., "Application of Topological Methods for Electromagnetic Hardening of the MX Horizontal Shelter System", LuTech, Inc. report prepared for Air Force Weapons Laboratory and Mission Research Corporation under Contract F29601-78-C-0082, January 1981. • Tesche, F. M., et. al., "Summary of Application of Topological Shielding Concepts to Various Aerospace Systems", LuTech, Inc. report prepared for Air Force Weapons Laboratory and Mission Research Corporation under Contract F29601-78-C-0082, February 1981 • Tesche, F.M., "Introduction to Concepts of Electromagnetic Topology as Applied to EMP Interaction With Systems", NATO/AGARD Lecture Series Publication 144, Interaction Between EMP, Lightning and Static Electricity with Aircraft and Missile Avionics Systems, May 1986. • Parmantier, J. P., V. Gobin, and F. Issac, “Application of EM Topology on Complex Systems”, Proceedings of the 1993 IEEE EMC Symposium, Dallas, TX. August 1993. • Parmantier, J. P., et. al. “An Application of the Electromagnetic Topology Theory to the EMPTAC Test-Bed Aircraft”, Proceedings of the 6th FULMEN Meeting, Phillips Laboratory, November 29, 1993.

20. Application of Topology to System Design and Analysis • Topological concepts were used for the ground-up design of the Peacekeeper (MX) Missile system in the 1980’s.

21. Application of Topology to System Design and Analysis (con’t.) • Parmantier† has analyzed aircraft cabling in the 1990’s Aircraft and cable configuration Measured and computed voltages Network topology † Parmantier, J-P, “First Realistic Simulation of Effects of EM Coupling in Commercial Aircraft Wiring”, IEE Computing & Control Engineering Journal, April 1998.

22. Outline of Presentation • Overview • Introduction to EM Topology • Applications of Topology for the MURI Project • Summary

23. Role of EM Topology in the MURI Program • Provides the framework for decomposing a complex system into manageable “pieces” • Provides the methodology for integrating results from simple canonical problems (pieces) into the overall system response. • Helps to identify the appropriate interface location between the EM and circuit problems.

24. Load Equipment Incident EM Field EM analysis at this point is much more complicated, with many interaction paths needed; however, the circuit analysis is at the load equipment is simpler. A compromise is needed to decide on where the EM field/circuit interface will be located in the system analysis EM analysis at this point is relatively simple; circuit analysis down to the load equipment is more complicated  An intermediate interface point is a compromise between the EM field analysis and the circuit analysis Interface Definition • A crucial decision is where to locate the interface between the EM and circuit problems Shielded Enclosure with EquipmentTopological Diagram Incident EM Field Load Equipment

25. Needed Extensions of EM Topological Methods • Improvements are needed to the basic transmission line models used for analysis using the BLT equation. • This is the basis for the “pieces” of the MURI project that will be discussed later by other team members. • Extensions of the BLT equation to higher frequencies and for non-conducting propagation paths are needed. • Numerical implementation improvements are required. These issues will be discussed in the following slides

26. Improvements to the Basic Transmission Line Models • Transmission line tubes entering into cavities, including the effects of cavity resonances • Random-lay transmission line tubes located over a ground or penetrating into an enclosure

27. Improvements to the Basic Transmission Line Models (con’t.) • Multiconductor tubes with a vertical run over a ground plane • Cross-coupling betweenmultiple tubes in a network

28. Conventional BLT conducting interaction path New, non-conductive BLT interaction path Extensions of the BLT Equation to Higher Frequencies • Include non-conductive paths in interaction sequence diagram • To model aperture or diffusive penetrations

29. Extensions of the BLT Equation to Higher Frequencies (con’t.) • Consider cross coupling between cables through apertures in enclosures • Treatment of multiple apertures in enclosures • Many other conductor and source configurations can be envisioned, and some will be discussed in other presentations for our MURI team

30. Improvements in Numerical Implementation • The solution of the BLT equation is numerically intensive • The main problem is the inversion of the matrix {[]-[S]}-1 • Specific improvements to speed solution can include: • Implementation of fast matrix solvers • Development and use of network reduction (collapsing) techniques • Use of spectral estimation (interpolation) techniques • In addition, inclusion of norm measures in the BLT responses is desired • Development and implementation of the singularity expansion method (SEM) for BLT solvers is needed

31. Outline of Presentation • Overview • Introduction to EM Topology • Applications of Topology for the MURI Project • Summary

32. Summary • Basic EM topological concepts have been reviewed and illustrated • The application of EM topology to the MURI project has been discussed • Provides a structured way of representing the EM interaction process with complex systems • Forms the basis for system decomposition into smaller “pieces” • Aids in defining a suitable interface between the EM and the circuit-level analysis • Provides a mechanism for computation, using the BLT formalism