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

Background Information Micro-level Macro-level RAM Type? RAM Thickness? How to design the chamber ? Field Uniformity? Chamber Shape? RAM Arrangement? Pictures from: ETS LINDGREN http://www.ets-lindgren.com/ Pictures from: www.cst-china.cn

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.

S. M. J. Razavi, M. Khalaj-Amirhosseini, and A. Cheldavi, PIER B, Vol

Outline Background Information Research Questions Systematic Solutions

Research Questions 1. How to choose/analyse/optimise RAM? Ferrite tiles Hybrid Pyramid Pictures from: http://www.rainfordemc.com/anechoic-materials.html

Research Questions 2. How to design/analyse/optimise the whole chamber? Tapered Chamber Compact Chamber Aircraft Chamber Picture from: http://www.mobilemag.com/2010/07/16/apples-100-million-test-chamber-droid-eris-and-blackberry-bold-9700-suffer-the-same/ Picture from: http://gtresearchnews.gatech.edu/gtri-compact-range/ Picture from: http://www.rainfordemc.com/aircraft-chamber.html

Outline Background Information Research Questions Systematic Solutions

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

Trial and error Empirically based, mostly determined by lower frequency limit. Thickness~Reflectivity Extraneous energy level~Reflectivity (Free Space VSWR Method) W=1/2L Picture from: Electromagnetic Anechoic Chambers A Fundamental Design and Specification Guide, Leland H. Hemming, Chapter 9.3.2

Free Space VSWR Method Repeated again for horizontal and vertical polarisation.

Free Space VSWR Method If a 0.3dB ripple Extraneous signal : If a 0.3dB ripple is observed 20dB down from the peak, the extraneous signal level is -55dB

Full Wave Method Algorithm limit Consider lossy(inhomogeneous) material FEM, FDTD, GO 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

Ray Tracing/GO(Geometric Optics) High frequency approximation 2nd order 1st order 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

Ray Tracing/GO Workflow Preprocessing: Modeling (.stl) Modified rectangular, Compact Range, Tapered Mesh Generation, Material/Boundary Assignment GND, side-wall, back-wall…. different area with different reflectivity Ray Tracing Code Field Distribution 1st order, 2nd order, 3rd order reflection (Propagation direction, Amplitude, Phase) GPU, Parallel Performance & Cost

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, 367-387, 2010.

Thank you!