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Project 139: Developing Eco-friendly Radio Absorbing Materials (RAM) for Anechoic Chambers Qian Xu http://www.cgeinnovation.org/ http://www.rainfordemc.com/ Outline • Background Information • Research Questions • Systematic Solutions Qian Xu, 2 Background Information Micro-level Macro-level How to design the chamber ? Pictures from: ETS LINDGREN http://www.ets-lindgren.com/ Pictures from: www.cst-china.cn Qian Xu, 3 William H. Emerson, IEEE Trans. on Antenn. And Propag., Vol. AP21, 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(Halpernanti-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. Qian Xu, 4 S. M. J. Razavi, M. Khalaj-Amirhosseini, and A. Cheldavi, PIER B, Vol. 19, 367-383, 2010. Qian Xu, 5 Outline • Background Information • Research Questions • Systematic Solutions Qian Xu, 6 Research Questions 1. How to choose/analyse/optimise RAM? Ferrite tiles Hybrid Pyramid Pictures from: http://www.rainfordemc.com/anechoic-materials.html Qian Xu, 7 Research Questions 2. How to design/analyse/optimise the whole chamber? Tapered Chamber Picture from: http://www.mobilemag.com/2010/07/16/apples100-million-test-chamber-droid-eris-andblackberry-bold-9700-suffer-the-same/ Compact Chamber Aircraft Chamber Picture from: http://gtresearchnews.gatech.edu/gtricompact-range/ Picture from: http://www.rainfordemc.com/aircraftchamber.html Qian Xu, 8 Outline • Background Information • Research Questions • Systematic Solutions Qian Xu, 9 Systematic Solutions: Macro-level • Key problem: Whole chamber design Trial and error/cut and try Ray Tracing Full wave simulation Accuracy • Commercial Software: CST (FEM, FITD), HFSS (FEM), Feko (MoM) • Friendly GUI, General simulation software, Pricy, High performance computers(cluster), Time consuming Qian Xu, 10 Trial and error • Empirically based, mostly determined by lower frequency limit. • Thickness~Reflectivity W=1/2L • 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 Qian Xu, 11 Free Space VSWR Method Repeated again for horizontal and vertical polarisation. Qian Xu, 12 Free Space VSWR Method Ripple: Extraneous signal : If a 0.3dB ripple is observed 20dB down from the peak, the extraneous signal level is -55dB Qian Xu, 13 Full Wave Method • Algorithm limit N PO/SBR/GO N*log(N) MLFMM N1.1~1.2 FDTD N2 FEM N3 MoM 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 • Consider lossy(inhomogeneous) material FEM, FDTD, GO Qian Xu, 14 Ray Tracing/GO(Geometric Optics) • High frequency approximation T=R+G+P(dB) normalized to direct ray in dB Ref: Electromagnetic Wave Theory, J. A. Kong, p.722. T=Total strength R=reflection coefficient G=Antenna pattern gain P=Propagation parameter Ref: Electromagnetic Anechoic Chambers A Fundamental Design and Specification Guide, Leland H. Hemming, Chapter 5.2.3 Qian Xu, 15 Ray Tracing/GO Workflow Modified rectangular, Compact Range, Tapered Preprocessing: Modeling (.stl) Mesh Generation, Material/Boundary Assignment GND, side-wall, back-wall…. different area with different reflectivity Ray Tracing Code GPU, Parallel Field Distribution 1st order, 2nd order, 3rd order reflection (Propagation direction, Amplitude, Phase) Performance & Cost Qian Xu, 16 Expected Results • Performance Field uniformity (±?dB) • Cost • Debug/Optimize 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, 367387, 2010. Qian Xu, 17 Thank you!