qian xu project 139: developing eco-friendly radio absorbing materials (ram) for anechoic chambers
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Qian Xu
Project 139: Developing Eco-friendly Radio Absorbing Materials (RAM) for
Anechoic Chambers
http://www.cgeinnovation.org/http://www.rainfordemc.com/
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Qian Xu, 2
Outline
• Background Information
• Research Questions
• Systematic Solutions
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Qian Xu, 3
Background Information
Pictures from: ETS LINDGRENhttp://www.ets-lindgren.com/
Micro-level Macro-level
How to design the chamber?
Pictures from: www.cst-china.cn
Γ , , ?
RAM Type?
RAM
Thickness?
Field Uniformity?
Chamber Shape?RAM Arrangement?
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Qian Xu, 4
William H. Emerson, IEEE Trans. on Antenn. And Propag., Vol. AP-21, No. 4, July, 1973.
• Mid 1930’s: Theoretical and experimental work.• 1936: First patented absorber.• WWII(1939-1945): Germany:
Schornsteinfeger(Wesch material & Jauman absorber ), US: HARP(Halpern-anti-radar-paint) by Halpern at MIT Radiation Laboratory, Salisbury screen.
• 1945-1950: Broad-band absorber.• The early 1950’s: First “dark rooms”.• The late 1950’s: New generation of broad-band.
absorbers(-40dB normal), antenna pattern comparison method, new chamber shape, shielded anechoic chambers.
• 1960’s: Low frequency absorber(-40dB 100MHz), 3rd generation RAM (-60dB normal), improved absorber measurement(Free-space VSWR), tapered chamber by Emerson.
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Qian Xu, 5
S. M. J. Razavi, M. Khalaj-Amirhosseini, and A. Cheldavi, PIER B, Vol. 19, 367-383, 2010.
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Qian Xu, 6
Outline
• Background Information
• Research Questions
• Systematic Solutions
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Qian Xu, 7
Research Questions
Pictures from: http://www.rainfordemc.com/anechoic-materials.html
1. How to choose/analyse/optimise RAM?
Ferrite tiles Hybrid Pyramid
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Qian Xu, 8
Research Questions
Picture from: http://www.rainfordemc.com/aircraft-chamber.html
2. How to design/analyse/optimise the whole chamber?
Picture from: http://www.mobilemag.com/2010/07/16/apples-100-million-test-chamber-droid-eris-and-blackberry-bold-9700-suffer-the-same/
Tapered Chamber Aircraft ChamberCompact Chamber
Picture from: http://gtresearchnews.gatech.edu/gtri-compact-range/
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Qian Xu, 9
Outline
• Background Information
• Research Questions
• Systematic Solutions
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Qian Xu, 10
Systematic Solutions: Macro-level
• Key problem: Whole chamber design
• Commercial Software: CST (FEM, FITD), HFSS (FEM), Feko (MoM)
• Friendly GUI, General simulation software, Pricy, High performance computers(cluster), Time consuming
Trial and error/cut and try Ray Tracing Full wave simulation
Accuracy
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Qian Xu, 11
Trial and error• Empirically based, mostly determined by lower frequency limit.• Thickness~Reflectivity
• Extraneous energy level~Reflectivity (Free Space VSWR
Method)
Picture from: Electromagnetic Anechoic Chambers A Fundamental Design and Specification Guide, Leland H. Hemming, Chapter 9.3.2
22DL
1~3
TestArea WW=1/2L
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Qian Xu, 12
Free Space VSWR Method
Repeated again for horizontal and vertical polarisation.
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Qian Xu, 13
Free Space VSWR Method
If a 0.3dB ripple is observed 20dB down from the peak, the extraneous signal level is -55dB
Ripple: max
min
20log d r
d r
E E E
E E E
/20
/20
10 120log 20log
10 1r
d
E
E
Extraneous signal :
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Qian Xu, 14
Full Wave Method• Algorithm limit
• Consider lossy(inhomogeneous) material
FEM, FDTD, GO
Frequency Electrical Size/Physical Size
Electrical Volume
10MHz 0.5λ/15m 0.125λ3
100MHz 5λ/15m 125λ3
1GHz 50λ/15m 125E3λ3
10GHz 500λ/15m 125E6λ3
40GHz 2000λ/15m 8E9λ3
N3 MoM N2 FEM
N1.1~1.2 FDTDN*log(N) MLFMM
N PO/SBR/GO
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Qian Xu, 15
Ray Tracing/GO(Geometric Optics)
• High frequency approximation
T=R+G+P(dB) normalized to direct ray in dB
T=Total strength R=reflection coefficientG=Antenna pattern gain P=Propagation parameter
0ik L rE r Ee 0ik L rH r He
0
n iL r H E H
k
0k c
0
iL r E n H E
k
n c
0
limk
2 2L r n
Ref: Electromagnetic Wave Theory, J. A. Kong, p.722.
Ref: Electromagnetic Anechoic Chambers A Fundamental Design and Specification Guide, Leland H. Hemming, Chapter 5.2.3
1st
orde
r
2 nd order
0
iL r E E
k g g
0
iL r H H
k g g
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Qian Xu, 16
Ray Tracing/GO Workflow
Mesh Generation,Material/Boundary Assignment
Ray Tracing Code
Field Distribution
Performance & Cost
Preprocessing: Modeling (.stl)
, ,
GND, side-wall, back-wall….different area with different reflectivity
GPU,Parallel
1st order, 2nd order, 3rd order reflection(Propagation direction, Amplitude, Phase)
Modified rectangular, Compact Range, Tapered
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Qian Xu, 17
Expected Results• Performance
Field uniformity (±?dB)
• Cost
• Debug/Optimize
Area Price
1st order, 2nd order, 3rd order reflection can be used to find the source of extraneous signal.
Ref: Minimum usage of ferrite tiles in anechoic chambers, S. M. J. Razavi, M. Khalaj-Amirhosseini, and A. Cheldavi. PIER B, Vol. 19, 367-387, 2010.
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Thank you!