IEEE Dallas EMC Society David Johns System Level EMC Simulation Using the TLM Method.
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Transcript of IEEE Dallas EMC Society David Johns System Level EMC Simulation Using the TLM Method.
IEEE Dallas EMC Society
David Johns
System Level EMC Simulation Using the TLM Method
What is FLO/EMC…?
The first electromagnetic field simulator developed specifically for system-level EMC design in the electronics industry
Enables EMC problems to be identified and managed in the early stages of design
Good for investigating radiated & conducted emissions, immunity (susceptibility), ESD and crosstalk problems: Enclosures & EMI shields Interfaces between boards and chassis Cables and EMI filters Unintentional antennas! (heat sinks etc.)
Based on the 3D Transmission-Line Matrix (TLM) Method
TLM Method
3D space-volume divided into nodes (10th wavelength) Each node is a 12-port transmission-line junction Scattering at the nodes models coupling between E and H fields Transient E and H fields are calculated from combinations of voltages
and currents on the transmission lines Spectrum found by FFT
V8
V9
V11
V10
V4
V2
V3
V6
V12 V7
V1 V5
X
YZ
Ey= ½ (V3i + V4
i + V8i + V11
i ) / Y
TLM Coupling Matrix
YX ZY XY ZX YZ XZ YZ
ZX ZY XZ XY YX
1 2 3 4 5 6 7 8 9 10 11 12
YX 1 1 1 1 -1
ZY 2 1 1 -1 1
XY 3 1 1 1 -1
ZX 4 1 1 -1 1
YZ 5 1 1 -1 1
XZ 6 1 1 1 -1
YZ 7 -1 1 1 1
ZX 8 1 -1 1 1
ZY 9 1 -1 1 1
XZ 10 -1 1 1 1
XY 11 -1 1 1 1
YX 12 1 -1 1 1
S = ½
Reflected Pulses Vr
k+1
Incident Pulses Vi
k
Ey= ½ (V3i + V4
i + V8i + V11
i ) / w
Wave Propagation, Time 0
1
1
1
1
Wave Propagation, Time 1
-0.5
-0.5
-0.5
-0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
Wave Propagation, Time 2
-0.5
-0.5
-0.5
-0.5
0.5
0.25
0.25
0.5
0.50.5
0.25
0.5
0.25
0.5
0.25
-0.25
0.25
0.25-0.25
0.25
0.25
-0.25
0.25
-0.25
0.25
0.25
0.5
Wave Propagation, Time 3
0.25
0.25
0.25
0.25
0.25
-0.25
0.125
0.25
-0.25
0.375
0.25
-0.25
0.25
-0.25
0.375-0.125 0.375
0.375
0.3750.375
0.375
0.3750.375
0.375
0.375
0.375
0.375
0.375
0.3750.375
0.125
0.125
0.1250.125
0.125
0.125
0.125
-0.125
-0.125
-0.125-0.125
-0.125
-0.125
-0.125
0.125
0.125
0.1250.125-0.125
-0.125
-0.125
-0.125
-0.375
-0.375-0.375
-0.375
-0.375 -0.375
-0.375
-0.375
Complexity of EMC Analysis
Compact vent model
seamsair vents
Accurate modeling requires geometric detailA long narrow seam may be a good antenna!Meshing the detail is computationally impractical
connectors
FLO/EMC Smart PartsTLM method uses a TL-Matrix to model fields.Other TL’s & lumped-circuit models can be connected
into the matrix.Arrays of small holes are often necessary to provide
adequate thermal ventilation/cooling.Apertures increase emissions and decrease shielding
effectiveness of the box.Low-frequency fields are evanescent near the apertures.Extremely fine grid would be required to model the
exponential decay.FLO/EMC overcomes this difficulty by inserting a “smart
part” into the grid.
Air vent smart part
L models the current flow along the edges of the apertures C models the electric field stored inside the apertures.
For a thin panel TEM transmission can be modelled by a shunt inductor. L is like a short at DC, but allows high freq. transmission.
For a thick panel the additional electric field inside the aperture can be modelled by a shunt capacitor
TEM
Transmission dependence on aperture shape and size, coverage and depth – empirical results
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.0
0.1
0.2
0.3
0.4
0.5
circular aperture array
square aperture array
Tra
nsm
issi
on c
oeffi
cien
t - T
Coverage
0.0 0.5 1.0 1.5 2.00.0
0.1
0.2
0.3
0.4
0.5
circular aperture array
square aperture array
Tra
nsm
issi
on c
oeffi
cien
t - T
Perforation depth / mm
Fine TLM mesh of single aperture used to calculate dependence of Transmission on aperture shape and size, coverage and depth Fit L,C air vent parameters to the Transmission results at two frequencies - 10% and 80% of aperture cut-off frequency
Air Vent Implementation
plane of screen
inductive short (vertical polarization)
inductive short (horizontal polarization)
TLM nodeTLM node
Inductor modelled by short-circuit transmission line
+ + +2Vli
Yl
V to ta l
2Vri
YrYs
2Vsi
Yo
2Voi+
a
iototal
ro
istotal
rs
irtotal
rr
iltotal
rl
VVV
VVV
VVV
VVV
osrl
oios
isr
irl
il
total YYYY
YVYVYVYVV
2
Capacitor modelled by open-circuit transmission line
1D propagation through an array of circular apertures (depth equal to diameter)
0 10 20 30 40 50 60 700.00
0.02
0.04
0.06
0.08
0.10
0.12
single L modelair-vent modelfine TLM mesh
|Ey|
in o
utpu
t poi
nt /
V/m
frequency / GHz
Validation - Plane Wave
The fine TLM mesh and air vent model give the same results at 10% and 80% of aperture cut-off frequency
Validation - Emission
r
p
t
a = 50 mmb = 20 mmc = 40 mmd = 10 mm
r = 10.0 mmp = 5.0 mmt = 1.65 mmN = 252
c
a
lossy material
.
.d
excitation
b
xz
y
lon g -w ire feed[M.Li et al,’EMI…’,IEEE Trans EMC, Vol. 42, No. 3, p265,2000]
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2-60
-50
-40
-30
-20
-10
0
10
20
30
single L model
air-vent model
measurements
|E| a
t 3m
aw
ay, d
BmV
/m
frequency / GHz
Run time on Dual Pentium Xeon with 3 GHz clock rateAir vent model
3 min
Enclosure with thick walls
r
p
t
a = 100 mmb = 80 mmc = 15 mm
r = 5.08 mmp = 0.69 mmt = 5.20 mmN = 45
y
b
c
...excitation
z
x
a.
output point
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
single L modelair-vent modelfine TLM mesh
e:ou
tput
poi
nt /
dBV
/m
frequency / GHz
Run time on Dual Xeon with 3 GHz clock rate
Fine TLM mesh Air vent model
2.5 hours 4 min
Enclosure with vents & slots
y
b
c
.
.
.excitation
z
x
a
t
w
a = 50 mmb = 20 mmc = 40 mm
= 94.92 mmw = 0.69 mmt = 0.20 mm
r
p
t
r = 5.08 mmp = 0.69 mmt = 0.20 mmN = 45
Air vents and slots
Run time on Dual Xeon with 3 GHz clock
fine TLM mesh compact models
2.5 hours 3 min
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0-60
-50
-40
-30
-20
-10
0
10
20
30
compact modelsfine TLM meshe:
fron
t1 /
dB
V/m
frequency / GHz
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0-80
-70
-60
-50
-40
-30
-20
-10
0
10
compact modelsfine TLM meshe:
fron
t /
dBV
/m
frequency / GHz
3m from air vent 3m from slot
Multi-Wire Smart Part
Compact vent model
Multi-conductor TL models of wires are connected into the TLM grid
Full coupling between wires and fieldsSupports splits, bends, multi-way connections,
circuit terminations and ports
connector pins
cable
Near Field Scan Smart Part
Emissions
Pre-determined near-field scans over entire boards or regions/components can be imported and applied as distributed frequency-dependent (time-varying) sources
Ideal for PCB with 1 or 2 layers where radiation from “exposed” nets may be important
TLM References
1. Johns P. B. & Beurle R. L., ‘ Numerical Solution of 2-Dimensional Scattering Problems Using a Transmission-Line Matrix’, Proc. IEE, Vol. 118, No. 9, Sept 1971.
2. Akhtarzad, S. and Johns, P. B., ‘The solution of Maxwell’s equations in three space dimensions and time by the TLM method of numerical analysis’, Proceedings IEE 122, 12, p.1344-1348, December 1975.
3. Johns P. B., ‘A symmetrical condensed node for the TLM method’, IEEE Trans. Microwave Theory and Techniques, Vol. MTT-35, No. 4, pp. 370-377, 1987.
4. Christopoulos C., ‘The Transmission-Line Modeling Method: TLM’, IEEE Press and Oxford University Press, 1995. A volume in the IEEE/OUP Series on Electromagnetic Wave Theory ISBN 0-7803-1017-9
If you have any questions or comments, we welcome your feedback !
Please visit the FLO/EMC web site at www.floemc.com and email us at [email protected]
Flomerics Inc.257 Turnpike Road, Suite 100Southborough MA 01772
Tel: (508) 357 2012
Flomerics Inc.1106 Clayton Lane, Suite 525W Austin, TX 78723
Tel: (512) 420 9273
Flomerics Inc.
410 South Melrose Drive, Suite 102,
Vista, CA 92083
Tel: (760) 643 4028
Flomerics Inc. 4699 Old Ironsides Drive - #390 Santa Clara, CA 95054-1860
Tel:(408) 562-9100