using feko for electromagnetic simulations in the

Using FEKO forElectromagnetic Simulations

in the Automotive Environment

Dr. Ulrich Jakobus and Dr. Markus Schick

EM Software & Systems GmbH, Germanywww.emss.de

www.feko.infoEHTC 2008, Strasbourg, 30.09.2008

Contents

• Introduction– Electromagnetic environment

• Computational methods– Overview– Method of Moments (MoM)– Multi-Level Fast Multipole Method (MLFMM)

• Application Example

• Summary and Conclusion

Introduction


Real-World EM Problems

• Antenna analysis in complex environments.

Computational Methods


Complexity of Materials

UTD

PO/GO

MOM

FEM

MLFMM

Ele

ctrica

l Siz

e3D EM Simulation Map


• CAD geometry model created.

• Surface mesh created.• Equivalence principle

applies, i.e. electric and magnetic currents on mesh is assumed to be unknown.

• RWG basis functions forms linear set of equations:

Z I = V• Linear set of equations

solved to find vector magnitude of currents on each mesh triangle.

MoM solution process:

Method of Moments in the Frequency Domain

Geometry Surface mesh

Linear basis functions on wire segments.

RWG basis functions on triangles.


Method of Moments in the Frequency Domain

• Near- and far-fields• Input impedance• S-parameters

Radiation characteristics derived from surface currents:

Surface currents Near fields Radiation patterns


Fast multipole method (FMM)

• Multilevel implementation:– Divide space into boxes– Aggregation A– Translation T– Disaggregation D

Source region Observer region

A DT


Multilevel Fast Multipole Method (MLFMM)

• Memory requirement O(N2)

• CPU-time O(N3)

• Memory requirement O(N log N)• CPU-time O(N log2 N)

N N

Two levels

Conventional MoM MLFMMvs.

HUGEMemory & Runtime

Savings

• The MLFMM is as accurate as the MoM.• More generally applicable than asymptotic high frequency techniques PO and UTD.• For very large or electrically huge problems MLFMM might still be insufficient and PO or UTD required.


MLFMM application example: Mobile phone in a car

• Memory requirement:MLFMM 1.17 GByteMoM 209.08 GByte

• Run-time (P4 1.8 GHz):MLFMM 4 hoursMoM not solved

Mobile phone analysis in a car model at 1878 MHz

N=118 452 unknowns

Computational Examples


Fender Antenna for VW Beetle

Creation of a computational model from the CAD data:• Which details are necessary (e.g. door handle)?• Transition resistances at hinges and door locks.• Lossy dielectric ground (wet, dry)• Plastic parts (e.g. bumper, seat)• Glass windscreen


Fender Antenna for VW Beetle

Creation of a computationalmodel from the CAD data:• Which details are

necessary (e.g. door handle)?

• Transition resistances at hinges and door locks.

• Lossy dielectric ground (wet, dry).

• Plastic parts (bumper, seats).

• Glass windscreen.

Surface current distribution(transmitting case using

reciprocity)

Horizontalfar-fieldpattern


Complex Antennas: Integrated into Windshield

• TV, FM, GSM antenna integrated into multilayered glass.

• Too complex to do a full 3D analysis (i.e. cannot discretise the wire strips, glass and car).

• Solution: Use coated wire equivalents.

• Solution caters for the effect of:– Multiple glass layers– Curvature of windscreen– 3D car body (important for

far- and near-field computations)

Equiv. FEKO model of a metallic wire with dielectric coating.


Effect of Conducting Windows

• Conductive layer for thermal protection

• Effect modelled using thin dielectric sheet formulation

Far Field Gain vs Angle

Phi [Deg] at Theta = 90.00 [Deg]

With windows No Windows

0º 345º330º

315º

300º

285º

270º

255º

240º

225º210º

195º180º165º150º

135º

120º

105º

90º

75º

60º

45º30º

15º 0º0

-2

-4

-6

-8


ICNIRP Compliance for TETRA Radio System

Low current density

High current density Maximum localised SAR

High E-field values

Low E-field values


Tyre Pressure Sensor Radiation Analysis

Front tire antenna excitation Rear tire antenna excitation

Opposite side -53.8 dBV/m

True side -49.7 dBV/m

Opposite side -61 dBV/m

True side -55 dBV/m

Y. Yamada, K. Tanoshita, K. Nakatani, S. Horiuchi, “FEKO Simulations and Measurements of Electrical Field Distributions around a Car,” ACES 2007, Verona, Italy, March 2007


Optical Controller

Spectrum Analyser

Field Distributions Inside a Vehicle - VerificationM

easu

red

Sim

ula

ted

Y. Yamada, K. Tanoshita, K. Nakatani, S. Horiuchi, “FEKO Simulations and Measurements of Electrical Field Distributions around a Car,” ACES 2007, Verona, Italy, March 2007


EMC Coupling Problem (Exhaust Pipe)

Coupling between engine area and the receiving antenna at the rear of vehicle (resonance on exhaust at 24 MHz).

f = 24 MHz

f = 27 MHz

Summary and Conclusions


Summary and Conclusion

• Introduction– Antenna Design– Electromagnetic Environment

• Computational methods– Overview– Method of Moments (MoM)– Acceleration with Multi-Level Fast Multipole Method (MLFMM)

• Application Example– Different Antennas– Tyre Pressure System– EMC Applications

using feko for electromagnetic simulations in the

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