NOVEL FEATURES OF SHORT PULSE ELECTROMAGNETICS

Transcription

1 NOVEL FEATURES OF SHORT PULSE ELECTROMAGNETICS Shahid Ahmed Thomas Jefferson National Accelerator Facility, Newport News, VA 1

2 Sources of UWB Electromagnetics Natural Lightning Artificial ESD Fast Switches 2

3 Waveform & Spectrum t r 10 ns E (a.u.) Pulse-width 100 s Time Power (db) 100 MHz Frequency 3

4 Coupling with Electrical/Electronic Equipment Overhead Cable EMP Field Telephone Cable Current Antenna Utility Ducts Window Underground Cable 4

5 Effects on Biological Tissues Duration, Intensity Disadvantage Advantage Tumor Growth Reduction Neuropsychological Damage Cardiopulmonary Arrest 5

6 Major Challenges Design and Optimization of EMP Simulator for Desired EMP Environment Modeling of a Complex 3D Test-object Self-Consistent Full-Wave Simulations 6

7 Experimental Setup 10th IEEE International Pulsed Power Conference C P = 82 pf, 1 MV, 90 horn, risetime 7ns, 1ns 7

8 Modern High Speed ICs and Interconnects High Density IC V Ideal Pulse V 0 Slow Clock 0.9V 0 0.1V 0 Time Real Pulse t r Fast Clock Spectrum High Density Interconnects (Micro Micro-strip Lines) db F 8

9 Effects of High Speed Clocks Ringing Waveform Waveform Distortion Distortion Information Information Loss Loss Radiation Leakage Parasitic Coupling 9

10 Need For Modelling EMP Simulators are big and expensive Multi-physics: EM scattering, reflections, absorption, radiation, heating etc High power switch Complex geometry and multiple materials Wide range of frequencies in a single problem Need full 3D time-domain simulations before construction 10

11 3-D Finite Difference Time-Domain Code Solves Maxwell s curl equations in time-domain: B D E - ; B (Free Space) t t Divergence Equations Are Inherent To These Curl Equations. Model: Arbitrary 3-D Object With Multiple Materials (Conductor / Dielectric) USES: 1. Antenna Radiation, EMP Simulators 2. EMP Coupling to Electronic & Electrical Equipment 3. Radar Cross-Section of Objects 11

12 Computational Domain Z H z H x E z H y H y H x H z E y H z E B - B t D t J E x H y H x Y 100 x 156 x 600 X = Y= Z = 1.85 cm X t = 35.6 ps t 1 c 1 x 2 1 y 2 1 z 2 Platform : Shared Memory Linux Clusters Run Time : 15 Hrs 12

13 Simulation Setup 13

14 Validation Check Switch : (t) = 0 exp[ - (t s ) 2 ] ; 0 t ( 0 + s ) Q (pc) Capacitor Charging Discharging Time (ns) 14

15 Validation Check --- Cont d Input impedance of TEM Structure -- Design Confirmation Impedance (Ω) R in X in F (MHz) 15

16 E-fields Near Feed Rise-Time (20-90)% x E 0 = 1.4 ns Main Pulse Pre-Pulse Reflected Pulse 16

17 Pre-Pulse Almost all pulsed power experiments -- source coupled with load through a switch -- R. S. Clark, Sandia Nat. Lab. Physical Significance τ chgsrc ~ τ clswt Method I D (t) = C sw dv(t)/dt E P (t) = I D (t) Z in / g 17

18 Simulation Setup = 40 11m 5.5m 18

19 Induced E-field Opt * E 0 = 500 kv/m t r = 1.4 ns 19

20 Mode Structures Inside Tapered Section TOP VIEW 20

21 Mode Structures Inside Tapered Section SIDE VIEW 21

22 Singular Value Decomposition (SVD) Physical quantity E : E ij i Channels, j times SVD [E] = [U][S][V T ] Temporal Vectors Singular Values Spatial Vectors TM m Mode Waveform inside a parallel-plates waveguide: E x (x) = E x0 Cos[m x/ h(z)], f c = mc/2h(z) h(z) = inter-plate separation (h ~ 1.5 m), i = 25, j = (t s = time step size) 22

23 Setup for Modal Analysis 23

24 Illustration of SVD 24

25 Evolution of Modes Without Test Object 25

26 Cross-Correlation Correlation Coefficient : C() = y 1 (t) y 2 (t - )dt y 1 = u(t) / u, y 2 = V(t) / v σ u std(u(t)) 1 N 1 j N 1 u t j u t 2 Advantage : Prediction of Coupling 26

27 Prediction of Radiation Leakage = 10 (a), 15 (b) and 20 (c). Far-field strongly correlated with TM 1 & TM 2 and weakly 27 correlated with TEM.

28 Cross-Correlation TM 1 and TM 2 are strongly correlated and TEM is weakly correlated 28

29 Simulation Setup σ = nq e μ, J = σe, Heat = J 2η τ p = μm*/qe, τ d = ε / σ τ p t τ d and E << E Br Example: Si at 300K n = 1.0 x m 3, m* = 0.19m e μ e = m 2 /V-m σ = 2.32 x 10-4 Sm -1, τ d = 0.45 μs τ pe = 1.6 x Sec. σ Semiconductor Dielectric Excitation Waveform: Ey (t) E e ( t ) 2 y0 ; 0 t 2τ 29 α = (4/τ) 2

30 Pulses on Printed Coupled Lines Z= Z= Z= A S = w / h = 1, τ = ps, ε r = 4, Dashed Curves -- SMSL & Solid Curves CMSL Distortion and Coupling Increases (d < <) 30

31 Pulses on Printed Coupled Lines 31

32 Pulses on Printed Coupled Lines 32

33 Cross-Correlation Near End 33

34 Cross-Correlation Far End 34

35 Conclusion Short Pulse electromagnetics is potentially challenging Provides wealth of information need thorough investigation 35