Electromagnetic Pulse Simulator Research Articles

Optimization Design of TEM Cell Brace for an EMP Simulator

TEM Cell was widely used as the electric field generator of electromagnetic pulse(EMP)simulator. To keep the transfer characteristic and avoid wrinkling of inner conductor, the TEM Cell brace was designed basing on simulation. Structure, size and material were optimized by using HFSS and the best scheme was given. Experiment showed the output pulse waveform generated by the EMP simulator using the optimized braces was all right and met the requirement of EMP simulator.

A 6-MV Pulser to Drive Horizontally Polarized EMP Simulators

L-3 Pulse Sciences (L-3 PS) is fabricating a 6-MV biconic pulse generator to drive a horizontally polarized dipole electromagnetic pulse simulator antenna at the Naval Air Systems Command, Pax River. The L-3 PS pulser, i.e., the horizontal fast rise electromagnetic pulser (HFREMP), will replace the Maxwell Laboratories ML-5 pulser. The HFREMP project is funded through the Central Test and Evaluation Investment Program (CTEIP). The CTEIP was established by the United States Department of Defense (DoD) to provide joint initiatives, avoid unwarranted duplication of capability, and increase interoperability through capability improvement projects for the DoD Major Ranges and Test Facility Bases. Like the Physics International Fast Risetime EMP Simulator (FEMPS) 2000, which drives an identical antenna at the Centre d'Etudes de Gramat, France, the HFREMP uses two stages of pulse compression. In fact, output capacitors, output switches, intermediate capacitors, and intermediate switches all use the same type of design as the FEMPS 2000. The Marx generator is of a different lower inductance design, and where FEMPS 2000 has a 2.7-MV Marx pulser in only one side, the HFREMP has a 3-MV pulser in each side of the 150- bicone that is the central part of the antenna. When the HFREMP drives the existing Pax River antenna, which is a variable height antenna (30-18 m), it will produce a 60- to 117.5-kV/m peak at the reference sensor with a waveform similar to that of the ML-5, which produces 47-92 kV/m. The HFREMP has also been considered to drive a bounded wave antenna of a different design, which is a fixed height antenna (30 m), producing at the reference sensor a peak field of over 80 kV/m and a wider more smoothly decaying pulse. The design of the HFREMP is described and compared with the designs of ML-5 and FEMPS 2000. Predictions of its performance into both types of antennas are presented.

Lightning Electromagnetic Field Coupling to Overhead Lines: Theory, Numerical Simulations, and Experimental Validation

The evaluation of electromagnetic transients in overhead power lines due to nearby lightning return strokes requires accurate models for the calculation of both the incident lightning electromagnetic pulse (LEMP) and the effects of coupling of this field to the line conductors. Considering also the complexity of distribution networks in terms of their topology and the presence of power system components and protection devices, the implementation of the LEMP-to-transmission-line coupling models into software tools used to represent the transient behavior of the entire network is of crucial importance. This paper reviews the most significant results obtained by the authors concerning the calculation of lightning-induced voltages. First, the theoretical basis of advanced models for the calculation of LEMP-originated transients in overhead power lines is illustrated; then, the relevant experimental validation using: 1) reduced-scale setups with LEMP and nuclear electromagnetic pulse (NEMP) simulators and 2) full-scale setups illuminated by artificially initiated lightning are reported. Finally, the paper presents comparisons between simulations and new experimental data consisting of measured natural lightning-induced voltages on a real distribution network in northern Italy, correlated with data from lightning location systems.

Review of New Developments in the Modeling of Lightning Electromagnetic Effects on Overhead Lines and Buried Cables

In the last 20 years, the widespread use of sensitive electronic devices has increased the interest in transients, in particular those caused by lightning (direct and/or indirect). After a short review of the modeling methods achieved in the last 25 years for indirect lightning electromagnetic effects and the validation of these models using electromagnetic pulse simulators and triggered lightning, this paper focuses on four significant new developments in this field achieved in the last years. They concern the decontamination of the natural lightning current from measurements on elevated structures, the possibility of using statistical methods to infer lightning current values from electric field measurements of lightning-detection systems, and the calculation of field-to-transmission line coupling to complex networks and to shielded cables. These numerical calculations today permit approximative solutions and effect orders of magnitude helpful for a correct electromagnetic compatibility design for very complex configurations to be obtained.

Developing a Finite Difference Time Domain Parallel Code for Nuclear Electromagnetic Field Simulation

A two dimensional finite-difference time-domain code has been developed for complete simulation of nuclear electromagnetic pulse (NEMP) originating from an atmospheric nuclear detonation. The modules of NEMP simulation code describing various physics aspects are discussed. Typical results of the serial code for Compton current estimated from detailed neutron-gamma transport, induced air conductivity and electromagnetic fields are presented. The need for parallelizing such code has been explained. The parallel implementation using domain decomposition technique of message passing interface paradigm is described. The efficiency of the parallel code has been studied with increasing number of processors. The limitations of speed-up due to communication times are discussed.

Currents Induced in a Human Body Standing Inside a Metallic House Near a Large Wire-Array Transmission-Line NEMP Simulator

This paper describes the time-domain moment method (TDMM) and image method that have been developed for calculations of current densities induced in a human body standing inside a metallic rectangular house located near a large wire-array transmission-line nuclear electromagnetic pulse (NEMP) simulator. The TEM-mode transmission line theory and the quasi-static theory are applied in the analysis of electric fields irradiated from the NEMP simulation. The maximum current density induced on the human body with body impedance of 100 MΩ standing inside a perfectly grounded metallic house is found to be 19.7 μA/cm 2 for a distance of 30 m between the metallic house and the NEMP simulator. The value of maximum current density of 19.7 μA/cm 2 is about two times the threshold levels of neuromuscular stimulation under steady-state current flow cases. From study results, it is also found that an average shielding effect of 90% is obtained for the distance between the metallic house and the NEMP simulator when over 30 m. Remarks on health effects based on the calculated data, other scientific sources, and community public health reports are made in the conclusion.

On Wire-Grid Representation of Solid Metallic Surfaces

This work deals with the wire-grid representation of metallic surfaces in numerical electromagnetic modeling. We discuss in particular the adequacy of the well known and widely used equal area rule (EAR) to calculate the radii of wire-grid models. We show that the EAR is accurate as long as the wire grid consists of a simple rectangular mesh. For more complex body-fitted meshes, using other polygons such as triangles, the EAR appears to be less accurate in reproducing the electromagnetic field scattered by metallic bodies. The conclusions of the paper are supported by numerical simulations performed using a parallel version of the numerical electromagnetics code and experimental data obtained on a vehicle illuminated by an electromagnetic pulse simulator.

Modal Analysis for a Bounded-Wave EMP Simulator—Part I: Effect of Test Object

We have analyzed the electromagnetic-mode structure inside a bounded-wave electromagnetic pulse (EMP) simulator. This has been done by the application of the singular value decomposition method to time-domain data generated by self-consistent, three-dimensional finite-difference time-domain simulations. This combination of two powerful techniques yields a wealth of information about the internal mode structure which cannot be otherwise obtained. To our knowledge, this is the first time such a comprehensive study has been done. In the absence of a test object, the transverse electromagnetic (TEM) mode is dominant throughout the simulator length. TM/sub 1/ dominates over other transverse electromagnetic (TM) modes over most of the length. Close to the termination, the TEM mode weakens marginally, while higher order TM modes become stronger. The enhancement of TM/sub 2/, and the weakening of TEM near the termination, have been explained in physical terms. Placement of a perfectly conducting test object in the parallel-plate section increases the strength of higher order TM modes, at the cost of TEM. Hence, the object is subjected to electromagnetic fields that deviate significantly from the desired TEM form. A physical interpretation has been provided for this phenomenon. The enhancement of electromagnetic fields near the top and bottom faces of the object are explained in terms of the Poynting flux distribution.

Modal Analysis for a Bounded-Wave EMP Simulator—Part II: Radiation Leakage and Mode Suppression

Radiation leakage from a high-power bounded-wave electromagnetic pulse simulator can cause severe electromagnetic interference (EMI) with surrounding equipment. In Part I, we analyzed the electromagnetic mode structure inside a simulator. In Part II, we examine the relative contribution of these modes to radiation leakage. We have calculated the temporal cross correlation between the electromagnetic modes inside the simulator and the temporal waveform of the forward-radiated far field. The TM1 and TM2 modes show strong cross correlation over a range of switching times. For the TEM mode, on the other hand, this holds true only for larger values of the switching time. Hence, for a given mode amplitude, higher order TM modes tend to produce more leakage than the TEM mode. However, since TEM is far stronger than TM throughout the simulator, it may still contribute more in absolute terms. Increasing the angle between simulator plates excites more higher order modes and increases their strength, thereby enhancing leakage. Pulse compression with respect to time increases the relative strength of higher order modes. Placing a spatial mode filter inside the simulator significantly reduces TM/sub 1/ without modifying the desired TEM mode. However, TM/sub 2/ remains largely unchanged. The reduction in TM/sub 1/ depends sensitively upon the parameters of the filter. These observations illustrate a new method of understanding and improving simulator design from the point of view of EMI.

Electric Fields Coupling into a Vehicle Placed Inside a Large Wire-Array Transmission-Line NEMP Simulator

The time-domain moment method is used to investigate electric fields coupling into a vehicle placed inside a large wire-array transmission-line Nuclear Electromagnetic Pulse (NEMP) simulator. The Transverse Electromagnetic Mode (TEM-mode) transmission-line theory, image technique, and quasi-static condition are applied in calculations of coupled electric fields in the vehicle. Simulation results show that the best shielding effectiveness occurs with the condition of a perfectly grounded vehicle. It is also found that the coupled electric field inside the vehicle increases as the impedance between the vehicle and the ground plane increases.

Mitigation of Lightning-Induced Overvoltages in Medium Voltage Distribution Lines by Means of Periodical Grounding of Shielding Wires and of Surge Arresters: Modeling and Experimental Validation

In this paper, we investigate the effect of periodically-grounded shielding wires and surge arresters on the attenuation of lightning-induced voltages. We discuss the adequacy of the commonly made simplification of assuming the shielding wire at ground potential, instead of being treated as one of the conductors of the multiconductor system. We also compare then the mitigation effect of shielding wires with that achievable by the insertion of surge arresters along the line. The computation results are first validated by means of calculations obtained by other authors referring to a simple line configuration, and then by means of experimental results obtained using a reduced-scale line model illuminated by a nuclear electromagnetic pulse (NEMP) simulator. One of the main conclusions is that the effectiveness of shielding wires and surge arresters depends mostly on the spacing between two adjacent grounding points or surge arresters.

Nanosecond Rise Time Generator for Electro-Magnetic Pulse

We have developed an electro-magnetic pulse simulator for the radiated susceptibility tests that can generate three kinds of electro-magnetic pulses including nanosecond rise time and high electric field pulse. This paper describes simulated and measured results for the fastest rise time voltage generator of this simulator. A new circuit of the voltage generator has developed to stabilize the output voltage waveform and the effect of the connection geometry between the generator and an antenna is estimated by using transient electro-magnetic analysis program based on method of moment by triangular patch modeling.

A parallel implementation of nec for the analysis of large structures

We present a new, parallel version of the numerical electromagnetics code (NEC). The parallelization is based on a bidimensional block-cyclic distribution of matrices on a rectangular processor grid, assuring a theoretically optimal load balance among the processors. The code is portable to any platform supporting message passing parallel environments such as message passing interface and parallel virtual machine, where it could even be executed on heterogeneous clusters of computers running on different operating systems. The developed parallel NEC was successfully implemented on two parallel supercomputers featuring different architectures to test portability. Large structures containing up to 24000 segments, which exceeds currently available computer resources were successfully executed and timing and memory results are presented. The code is applied to analyze the penetration of electromagnetic fields inside a vehicle. The computed results are validated using other numerical methods and experimental data obtained using a simplified model of a vehicle (consisting essentially of the body shell) illuminated by an electromagnetic pulse (EMP) simulator.

Modeling of an EMP simulator using a 3-D FDTD code

Performed self-consistent, three-dimensional (3-D), time-domain calculations for a bounded-wave electromagnetic pulse simulator. The simulator consists of a constant-impedance transverse electromagnetic structure driven by a charged capacitor, discharging through a fast closing switch. These simulations yield the detailed 3-D electromagnetic field structure in the vicinity of the simulator. The prepulse seen in these simulations can be explained quantitatively in terms of capacitive coupling across the switch and the known charging waveform across the capacitor. Placement of a test object within the simulator significantly modifies the electric fields within the test volume, in terms of field strength as well as the frequency spectrum. This means that, for a given simulator, larger objects would be subjected to somewhat lower frequencies. The E-field waveform experienced by a small test object is reasonably close to that for free-space illumination, but the mismatch increases with object size. The use of a resistive sheet as a matching termination significantly reduces radiation leakage as compared to two parallel resistive rods. For a given termination, larger test objects marginally reduce leakage. A physical interpretation of these conclusions is also included. This work is a first step toward full-fledged optimization of such simulators using 3-D modeling.

Full-wave simulation of overland radar pulse propagation

A simple and efficient method of high-frequency electromagnetic pulse simulation is proposed. An asymptotic solution yields a paraxial version of geometric optics with complex eikonals and amplitudes determined from numerical solution of the parabolic wave equation. As an example, radar pulse propagation over realistic irregular terrain is considered.

Transient radiation of traveling waves by wire antennas

A simple analytic method is suggested for calculating radiation fields from traveling current waves propagating along curvilinear wires. The solutions obtained are valid in both the near and the far zones. The results are used to calculate the radiation of linear and V-antennas, as well as those composed of rectilinear segments. The radiation of a wire placed over a conducting plane is calculated when the wire is an element of an electromagnetic pulse (EMP) simulator. An engineering method of EMP simulator design is put forward and justified. >

Modeling of Army Research Laboratory EMP simulators

Presents the capabilities and limitations of a variety of EMP (electromagnetic pulse) simulator models useful for the Army's EMP survivability programs. Comparisons among frequency- and time-domain models are provided for two US Army Research Laboratory EMP simulators, AESOP (Army EMP Simulator Operations) and VEMPS II (Vertical EMP Simulator II). The models discussed have been developed to predict the field levels, waveshapes, and peak field contours for the VEMPS II and AESOP simulators. Each model has features that make it attractive for different applications. Detailed FDTD (finite-difference time-domain) models allow accurate close-in predictions. These models have been invaluable in the design of the VEMPS II, as well as in gaining a basic, physical understanding of the detailed field structure. The FDTD models have also been used to provide the sources for and to validate the simpler models. These simpler models have been extremely useful in estimating fields at large distances from the simulators. They also serve as a convenient engineering tool in support of simulator tests.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electromagnetic Pulse (EMP), Part I: Effects on Field Medical Equipment

The electromagnetic pulse (EMP) from a high-altitude nuclear detonation has the potential to cover an area as large as the continental United States with damaging levels of EMP radiation. In this study, two of seven items of medical equipment were damaged by an EMP simulator. Computer circuit analysis of 17 different items showed that 11 of the 17 items would be damaged by current surges on the power cords, while two would be damaged by current surges on external leads. This research showed that a field commander can expect approximately 65% of his electronic medical equipment to be damaged by a single nuclear detonation as far as 2,200 km away.

An efficient method for the performance analysis of bounded-wave nuclear EMP simulators

The author discusses an approach for analyzing the electromagnetic performance of bounded-wave nuclear electromagnetic pulse (NEMP) simulators. This method is extremely efficient and enables even the largest simulators to be analyzed. Typical bounded-wave EMP simulators are composed of flat-plate transmission-line sections approximated by wires. Using a priori knowledge as much as possible, the method presented obtains the current in the wave launcher's wires from an approximation of the current in a conical-plate wave launcher that generates a spherical TEM wave propagating along the radial direction. This method uses TEM-like currents obtained by approximating the TEM-mode current in the conical-plate wave launcher. The transient electromagnetic fields within the simulator's working volume are then readily computed by using efficient and analytical time-domain expressions for the fields generated by the wires. Expressions for the early-time fields and the impedance of a conical wire-mesh wave launcher are derived. Numerical results are presented for EMPSIS, a triangular-plate simulator for ships.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dipole models for the far-field representation of EMP simulators with application to estimates of human RF exposure

The authors present dipole modeling techniques which are useful for calculations of far fields from vertically or horizontally polarized electromagnetic pulse (EMP) simulators. Vertically polarized simulators are modeled with a single dipole above a finitely conducting half-space. Three dipoles were used in the case of a horizontally polarized simulator. Effects of soil models with both frequency-dependent and frequency-independent values for soil conductivity and dielectric constant are included in the study. Calculations with dipole models compare reasonably well with measurements conducted at the AESOP facility and finite-difference calculations of free fields near the VEMPS II simulator. Integrals of the Poynting vector are used to obtain an upper limit for whole body specific absorption in a prolate spheroidal human model. The results suggest that EMP simulator thermal effects at the cellular level are small in comparison to random thermal agitation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>