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Unformatted text preview: 1 ECE 303 – Fall 2007 – Farhan Rana – Cornell University Lecture 34 Electromagnetic Scattering In this lecture you will learn: • Scattering of electromagnetic waves from objects • Rayleigh Scattering • Why the sky is blue • Radar range equation ECE 303 – Fall 2007 – Farhan Rana – Cornell University Scattering of Electromagnetic Waves from a Plane Interface z =0 z z k k i ˆ = r E i H i Incident, transmitted, and reflected waves are all plane waves The reflected and transmitted waves can also be called the scattered waves z k k i ˆ − = r E r H r z k k t ˆ = r E t H t o o µ ε o t µ ε x 2 ECE 303 – Fall 2007 – Farhan Rana – Cornell University Scattering of Electromagnetic Waves from Objects Incident plane wave: Scattered wave: ( ) r E i r r ( ) r E s r r o ε 1 ε Questions: • How does one find the scattered field? • How much power from the incident field goes into the scattered field? • In which direction(s) does the scattered power go? λ phase fronts ECE 303 – Fall 2007 – Farhan Rana – Cornell University Scattering of Electromagnetic Waves From Spherical Particles Incident plane wave: ( ) r E i r r o ε Assumption: • Assume that the particle radius is much smaller than the wavelength of the incident wave, i.e.: 1 << ka- When the above condition holds the scattering is called “Rayleigh Scattering”- When the above condition does not hold the scattering is called “Mie Scattering” • When ka << 1, the particle sees a uniform E-field that is slowly oscillating in time 1 ε a 2 λ 3...
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- Fall '06