EMC / EMI in HFSS v8

8/18/2019 EMC / EMI in HFSS v8

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EMC / EMI

in

HFSS v8

Jim ShermanAnsoft Applications Engineer

East Coast


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Summaryw What is EMC / EMI ?

w Practical Examples:

w Trace over split in ground plane(HFSS EMI Wizard)

w Heatsink Emissions(HFSS Eigenmode Analysis)

w EMI from shielding enclosures(HFSS user Exercise)

• Will be available as download or disk:

• Listing of EMI Wizard macro• Complete EMI exercise


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EMC/EMI ?

w EMC - ElectroMagnetic Compatibilityw Ability of equipment to function without error in it’s

intended EM environment

w EMI - ElectroMagnetic Interferencew

EM emissions from the equipment that interfere withnormal operation of other equipment

EMC Margin

Frequency E M

D i s t u r b a n c e

L e v e

l

Emission Limit

Immunity Limit

Equipment


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Three Elements of the EMC Problem

EM Sourc e EM Recepto r Path

Conducted(Electric Current)

Inductively Coupled(Magnetic Field)

Radiated(Electromagnetic Field)

Capacitively Coupled(Electric Field)

Antenna

Connector

Apertures

Lightning

Power Line

Electronics

Cell Phone

Grounding

Electronics

Antenna

Apertures

Cell Phone

PeopleGrounding

Transistor

Diode


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Solution

w HFSS – High Frequency Structure Simulator w Provide fast, accurate EMC/EMI predictionsw Use it early in product developmentw Understand the EM interaction

w EMI Lab bench measurementsw Uses specialized test equipmentw Test done late in product development

w EM interaction hard to understand

TestEquipment

Data

HFSSSoftware

EM Model

Data


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Practical Examples **

w ACES Standard Problem 2000-2w Trace over split in ground plane

(HFSS EMI Wizard)

w ACES Standard Problem 2000-4w Heatsink Emissions

(HFSS Eigenmode Analysis)

w ACES Model Validation Paper w EMI from shielding enclosures

(HFSS user Exercise)

** Reference:(ACES) Applied Computation Electromagnetics Society:http://aces.ee.olemiss.edu/


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Example 1:**ACES Standard Problem 2000-2

Trace Over Split in Ground Plane

** Linda Walling - Ansoft AE 1999


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Problem Description

w EMI

Dimensions:

plane size: 10” x 12”

trace: 5 mil wide; 10” long

(trace is 5mil above plane) 80 Ohm

substrate: FR4 er = 4.5

slot: 8” long; 20 mil wide.

Dimensions:

plane size: 10” x 12”

trace: 5 mil wide; 10” long

(trace is 5mil above plane) 80 Ohm

substrate: FR4 er = 4.5

slot: 8” long; 20 mil wide.

Stitching capacitor

0.1uF/470pF

with 2 nH/4.88 nH indu ctance

with 0.5 Ohm seriesres i s tance

Stitching capacitor

0.1uF/470pF

with 2 nH/4.88 nH ind uctance

with 0.5 Ohm series

res i s tance Source/Load3.3mV

100 MHz to 2 GHz

50 Ohm load

Source/Load

3.3mV

100 MHz to 2 GHz

50 Ohm load

Find:

Maximu m EMI 3m f rom c i rcu i t

acros s 100 MHz to 2 GHz Band

Find:

Maximum EMI 3m f rom c i rcu i t

acros s 100 MHz to 2 GHz Ban d

ACES Problem 2000-2


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Model Reduction Tricks

w Increase substrate thickness and strip width one order of magnitude.w This helps to relax aspect ratio for smaller mesh.w Line impedance remains the same.w Emissions are not affected.

w Use a virtual objectw Use mesh seeding to reduce number of adaptive passes.w Put virtual object in the air above the substrate.

w Simplify metal layersw Use Perfect Electrical Conductors.w Make all conductors 2D objects.

ACES Problem 2000-2


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HFSS Model

Trace Slot

FR4 andground p lane

Virtual Object m aterial: air

surfaces us ed in EMI calculat ion

A i r Box material: air

wi th rad iat ion s ur faces

50 Ohmgap source

50 Ohmgap sourc e load

ACES Problem 2000-2


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Solution Time Reduction Tricksw

Save time solving multiple geometriesw 1.Trace centeredw 2. 0.1 pF capacitor is placed across the slot close to tracew 3. 0.1 uF capacitor is placed across the slot close to tracew 4. Slot removedw 5. Trace moved to 2” from edge of board with slot and no

capacitors

w Reuse the meshw Capacitor 3D object

w First assigned to a vacuum dielectric.w Perform a solvew Solved project is then copiedw Mesh remains the samew Materials can be changedw Boundaries can be changedw Only the fast sweep is required again

w Use EMI Wizard

ACES Problem 2000-2


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EMI Wizardw EMI Wizard:

w Field Post Processing Macrow Full complex vector field solution availablew Data spans the entire fast frequency sweep

w Allowed:w PML’sw Symmetry Walls

w Use inputs for EMI sweep customizationw Adjust frequency step to coarse or fine

w Provides results in dBuV/mw Finds maximum Etotal, Ephi, and Ethetaw Writes data to ASCII filew Requires a user supplies face list

ACES Problem 2000-2


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EMI Wizardw The macro: emiwiz.mac **

** will be available as a download or disk

ACES Problem 2000-2


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EMI Wizardw User Inputs

ACES Problem 2000-2


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EMI Wizardw Specifiy sweep range (must be within fast sweep range)

ACES Problem 2000-2


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EMI Wizardw Specifiy output file and path

ACES Problem 2000-2


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HFSS Predicted Resultsw E total vs Frequency from Emi Wizard output

Best Case: No SlotBest Case: No Slot

3.3mV source3.3mV source

Capacitoris veryfrequencydependent

Capacitoris veryfrequencydependent

ACES Problem 2000-2


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w Different cases produce modes that radiate in different directions.

Frequency (GHz)

Results forCases 1 and 2

Results for

Cases 1 and 2

Angle of

thetaor phi(deg.)

Maximum E Total

HFSS Predicted ResultsACES Problem 2000-2


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Conclusions

w HFSS can be used to simulate EMI test structures.

w Only real problem is related to aspect ratio;w i. e. 5 mil substrates with 10 inch boards.

w The circuit model can be modified to improve aspectratio.

w Scale substrate and trace width.w Has very little effect on EMI results.w Don’t change the slot width. It will change EMI

results.

ACES Problem 2000-2


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Example 2:**

ACES Standard Problem 2000-4Heatsink Emissions

** Richard Remski - Ansoft AE 2000


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Problem Description

Heat Sink: 2.5 x 3.5 x 1.5 inch block,located 6 mm above a 6.29 x 4.74 inchground plane (2D conducting sheet)

Ground configurations: 6 mm squaregrounds, located in various combinationsof one, two, four, and eight locations at atime.

Model enclosed in volume of ‘vacuum’,with Perfect_H boundary walls.

First 4 eigensolutions obtained starting at0.1 GHZ.

ACES Problem 2000-4

Test cases

Grounds

1 Only

1, 2

3, 4

1, 2, 3, 4

5, 6, 7, 8

Test cases

Grounds

1 Only1, 2

3, 4

1, 2, 3, 4

5, 6, 7, 8

1

2

6

3

4

5

7

8

Ground plane edgeGround Pins

Air Circuit


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HFSS Eigenmode Solution ?

ACES Problem 2000-4

w Eigenmode looks for natural modes in structure.

w It can be used to simulate resonance effects in EMItest structures.

w Sources are not allowed

w HFSS output:w Resonant frequenciesw Full complex vector field solution


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E-field magnitude on the ground plane for the single-ground configuration. Note that a probe too close tocenterline might not excite either Modes 3 or 4, but thisis not of too much concern since the fundamentalmode would specify the worst-case emissions threat.

The first three modes carry most of the E-field beneaththe heat sink, while Mode 4 carries most energy on theground plane edges around the sink. Judging from theMode 4 distribution, mid-side grounds would not likelyterminate this mode.

E-field magnitude on the ground plane for the single-ground configuration. Note that a probe too close tocenterline might not excite either Modes 3 or 4, but thisis not of too much concern since the fundamentalmode would specify the worst-case emissions threat.

The first three modes carry most of the E-field beneaththe heat sink, while Mode 4 carries most energy on theground plane edges around the sink. Judging from theMode 4 distribution, mid-side grounds would not likelyterminate this mode.

F1=603 MHz F2=1.34 GHz F3=1.41 GHz

F4=1.48 GHz

ACES Problem 2000-4

HFSS Predicted E field:Eigensolution with 1 ground only


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E-field magnitude on the ground plane with twogrounds along the short sides. Peak forfundamental mode is beneath heat sink, likelypermitting good coupling in a probe-excitedanalysis. Modes 2 and 3 however have nulls alongcenterline of heat sink and could get missed (again,not a concern if the fundamental mode is found).

As expected, Mode 4 appears identical to that for thesingle ground case, and carries more energy on theground plane edges than beneath the heat sink.

E-field magnitude on the ground plane with twogrounds along the short sides. Peak forfundamental mode is beneath heat sink, likelypermitting good coupling in a probe-excitedanalysis. Modes 2 and 3 however have nulls alongcenterline of heat sink and could get missed (again,

not a concern if the fundamental mode is found).As expected, Mode 4 appears identical to that for thesingle ground case, and carries more energy on theground plane edges than beneath the heat sink.

F1=1.04 GHz F2=1.37GHz F3=1.40 GHz

F4=1.48 GHz

ACES Problem 2000-4

HFSS Predicted E field:Eigensolution with grounds on 1 and 2


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E-field magnitude on the ground plane with two groundsalong the long side. Here the fundamental mode has arelative null at the heatsink center; therefore none of themodes might be excited by a probe feed too close to thecenter. The reference paper‘s feed location likely did notexcite Mode 1, but did excite Mode 2. This would explainwhy this configuration was reported to have an“advantage” better than that of the other 2-ground case,while HFSS shows the first resonance mode frequency isactually lower.

Again, Mode 4 is the same as for the single-ground andthe other two-ground case, as the ground locations donot prevent it from forming.

E-field magnitude on the ground plane with two groundsalong the long side. Here the fundamental mode has arelative null at the heatsink center; therefore none of themodes might be excited by a probe feed too close to thecenter. The reference paper‘s feed location likely did notexcite Mode 1, but did excite Mode 2. This would explainwhy this configuration was reported to have an“advantage” better than that of the other 2-ground case,while HFSS shows the first resonance mode frequency isactually lower.

Again, Mode 4 is the same as for the single-ground andthe other two-ground case, as the ground locations donot prevent it from forming.

F1=994 MHz F2=1.18 GHz F3=1.46 GHz

F4=1.48 GHz

ACES Problem 2000-4

HFSS Predicted E field:Eigensolution with grounds on 3 and 4


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E-field magnitude on the ground for all fourside grounds. Fundamental mode hasrelative null beneath ground plane centeragain, and may have been missed in a probe-excited analysis. Modes 2 and 3 similarlyhave large nulls beneath one or the other

axis of the heat sink, making it easy to seehow a radiation model with a fixed probelocation as specified in the refererence papermight not couple well to them, either.

Mode 4 again appears the same as for theprior three cases illustrated, as anticipated.

E-field magnitude on the ground for all fourside grounds. Fundamental mode hasrelative null beneath ground plane centeragain, and may have been missed in a probe-excited analysis. Modes 2 and 3 similarlyhave large nulls beneath one or the otheraxis of the heat sink, making it easy to seehow a radiation model with a fixed probelocation as specified in the refererence papermight not couple well to them, either.

Mode 4 again appears the same as for theprior three cases illustrated, as anticipated.

F1=1.35 GHz F2=1.38 GHz F3=1.46 GHz

F4=1.48 GHz

ACES Problem 2000-4

HFSS Predicted E field:Eigensolution with 4 side grounds


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Emissions Testing: Eigensolution Example:Results (Corner Grounds)

E-field magnitude on the groundplane for the cornergrounded case. Here, only the first mode carriessignificant energy beneath the heat sink, while the othersstrongly excite the ground plane edges, but may notcouple to a probe beneath the sink.

The first mode should likely be excited by a probe feedlocated beneath the heat sink, but may not radiate as itcarries very little energy to the ground plane edgesunlike the prior fundamental modes. Therefore this is agood example of a potential on-board (component tocomponent beneath the sink) EMI issue which mightnever show up in radiation measurements or analysis.

E-field magnitude on the groundplane for the cornergrounded case. Here, only the first mode carriessignificant energy beneath the heat sink, while the othersstrongly excite the ground plane edges, but may notcouple to a probe beneath the sink.

The first mode should likely be excited by a probe feed

located beneath the heat sink, but may not radiate as itcarries very little energy to the ground plane edgesunlike the prior fundamental modes. Therefore this is agood example of a potential on-board (component tocomponent beneath the sink) EMI issue which mightnever show up in radiation measurements or analysis.

F1=1.36 GHz F2=1.43 GHz F3=1.48 GHz

F4=1.49 GHz

ACES Problem 2000-4


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Conclusions

w HFSS Eigensolution results appear to fit fairly well with reported Emission Effectivenessw In first 3 cases, fundamental resonance is above frequency where emissions were not

improved by the groundsw However, HFSS appears to imply that the (3, 4) configuration isn’t quite as good as the (1, 2)

w Field plots show how probe may have missed case (3,4)’s fundamental modew HFSS also indicates that there is a lower frequency resonance for the 4-side and corner

grounded cases than shown in the referencew One should have been excited, but does not couple much to the ground edges to

radiate. The other has a relative null at the reported probe location and may not havebeen excited by that technique.

w Solutions took very little time (approx 1 hr total on PI450 for 5 combinations)

Grounds F1 F2 F3 F4 Reported ‘Effectiveness’1 Only 603 MHz 1.34 GHz 1.41 GHz 1.48 GHz to 450 MHz

1, 2 1.04 GHz 1.37 GHz 1.40 GHz 1.48 GHz to 750 MHz

3, 4 994 MHz 1.18 GHz 1.46 GHz 1.48 GHZ to 850 MHz

1, 2, 3, 4 1.35 GHZ 1.38 GHz 1.46 GHz 1.48 GHz to 1.5 GHz

5, 6, 7, 8 1.36 GHz 1.43 GHz 1.48 GHz 1.49 GHz to 2.5 GHz

Grounds F1 F2 F3 F4 Reported ‘Effectiveness’

1 Only 603 MHz 1.34 GHz 1.41 GHz 1.48 GHz to 450 MHz

1, 2 1.04 GHz 1.37 GHz 1.40 GHz 1.48 GHz to 750 MHz

3, 4 994 MHz 1.18 GHz 1.46 GHz 1.48 GHZ to 850 MHz

1, 2, 3, 4 1.35 GHZ 1.38 GHz 1.46 GHz 1.48 GHz to 1.5 GHz

5, 6, 7, 8 1.36 GHz 1.43 GHz 1.48 GHz 1.49 GHz to 2.5 GHz

ACES Problem 2000-4


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0.085 semi- rigid coaxial feed

50 ohm source

3 cm x 4 cmAperature

SMT Termination47 ohm

Metal Enclosure

Example 3:**

ACES Validation Paper (Min Li)EMI from shielding enclosures

** Jim Sherman - Ansoft AE 2001

ACES Validation Min Li 1


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Problem Description**

w Shielding enclosures require apertures (holes).w Heat dissipationw Unused or open I/O connector portsw Weight reductionw Non-metal shielding

w Compute EMI at distance from aperture.w FCC Class B radiation limits

w Write Post Processing Macros:w

Compute magnitude of E Field 3m from aperture vs frequencyw Compute power dissipated in load resistor in cavity


** Complete user exercise will beavailable as download or disk.


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Model and Solution Reduction Tricks

w Use 2D conductors for all metal.

w Make all metal Perfect Electrical Conductor (PEC).

w Use symmetrical H wall to reduce model in half.

w Replace complex coax feed with lumped gap port.

w Model the resistor load as a 2D surface impedance.

w Model the aperture as a simple 2D H boundary.

w Model the input probe as a narrow 2D rectangular strip.

w Use Fast Frequency Sweep with post processor macro.



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HFSS Model

Half modelHalf model

airbox

cavity

probe

port1

res_47

hole

50 ohmGap source



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HFSS vs Measured ResultsACES Validation Min Li 1

HFSS predicted

after 6 adaptivepasses

Measured Data

TMy101

TMy111

TMy201


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sV

Source voltage 1mV

0 Z Coax Input

Input Probe

= 50 Ohm

11S

Inside the enclosure

w Use the Maxwell Plot Utility to generate plots of delivered power

( )2

110

2

18

S Z

V P s −=

Power delivered to the enclosure:

HFSS vs Measured ResultsACES Validation Min Li 1

Measured Power Delivered vs Frequency


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w Create and save S11 magnitude plot

w From Maxwell Executive Commandsw Select Post Process > Matrix Plot

w Plot > New Plotw Data Type S Matrixw Quantity

w Port1,Mode1;Port1,Mode1 (S11)w Cartesian vs frequencyw Plot scaling: Unscaled

w Plot > Save: s11mag.dat

Using The Plot Utility Calculator ACES Validation Min Li 1


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w Modify S11 plot to show Delivered Power

w From Maxwell Control Panelw Select Utilitiesw

Select PlotData

w Plot > Open : s11mag.dat(located in project directory)

The plot data program will open

ASCII text files that containcolumns of data that are spacedelimited. You can import yourmeasured data simply byopening the ASCII text file.

The plot data program will openASCII text files that containcolumns of data that are spacedelimited. You can import yourmeasured data simply byopening the ASCII text file.



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w Use plot calculator to modify plot

w Select Tools > Calculator w Perform steps:

w copy s11 to stackw 2 Enter, Y x

w 1 CHS Enter, *

w 1 Enter, +w 1e-3 Enter w 1e-3 Enter, *, *w 8 Enter, 50, Enter,w *w /w

1e-9 Enter, /w Load , Donew Plot > New

( )2110

2

18

S Z

V P s −=

Calculate Del ivered Pow er



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HFSS vs Measured Results

HFSS predictedafter 6 adaptivepasses

Measured Data


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Conclusions

w Simplify the model for faster solution and reduced model space.

w Repetitive steps can be performed automatically with macros.

w Macro’s can be used to produce additional post processing

results.

w The Maxwell Plot Utility Calculator includespowerful math functions.

w The HFSS predicted results are very close after 6 passes.w However,

additional passes are required for pinpoint results.


EMC


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EMC / EMI References

[1] (ACES) Applied Computation Electromagnetics Society:http://aces.ee.olemiss.edu

[2] EMC at Univ. of Hamburg:http://www.tu-harburg.de/et1/Emc/index.html

[3] Henry W Ott., Noise Reduction Techniques in Electronic Systems, WileyInterscience, 2nd edition, 1988

[4] Tim Williams, EMC for Product Designers , Butterworth-Heinemann, 1992.

[5] C. R. Paul.(Introduct ion to) Electromagnetic Compatibi l i ty, Wiley Interscience, 1992.

[6] Tsaliovich, A., Cable Shielding for Electromagnetic Com patibi l ity , Van NostrandReinhold, 1995.

[7] Perez, Handbook of Elec t romagnet ic Compat ib il i ty , Academic Press, 1995

Documents

EMC / EMI in HFSS v8