Lect35EMscattering

Lect35EMscattering - 1 ECE 3030 Electromagnetic Fields and...

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Unformatted text preview: 1 ECE 3030 Electromagnetic Fields and Waves Fall 2009 Lecture 35 2009/11/18 Electromagnetic Scattering From Objects Rayleigh Scattering 1 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 35: Instructor: Dr. Wesley E. Swartz Rayleigh Scattering Mei scattering Why the Sky is Blue Radar Range Equation in P out P Announcements • Prelim 3 tomorrow night, starting at 7:30 in Phillips 101 – Covers • Dielectric interfaces • Impedance matching with dielectrics and transmission line stubs • Transmission line transients • Antenna patterns from radiating elements • Smith Chart usage • Waveguides – Bring a calculator, straight-edged ruler, 3 sheets of notes. 2 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 35: • No Workshop Sections tomorrow. Scattering of Electromagnetic Waves from a Plane Interface z k k i ˆ E i H i k k ˆ E r H r z k k t ˆ E t H t o o o t x 3 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 35: • Incident, transmitted, and reflected waves are all plane waves. • The reflected and transmitted waves can also be called the scattered waves. z =0 z z k k i Scattering of Electromagnetic Waves from Objects Incident plane wave: Scattered wave: r E i r E s o 1 4 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 35: • 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? phase fronts Scattering of Electromagnetic Waves From Spherical Particles • Assume that the particle radius is much smaller than the wavelength of the incident wave, i.e.: ka << 1 . – 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 5 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 35: oscillating in time . Incident plane wave: r E i o 1 a 2 Rayleigh Scattering: Basic Mechanism Incident plane wave: r E i o 1 a 2 + + + + +----- 6 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 35: • One way to understand scattering is as follows: – The incident E-field induces a time-varying dipole moment in the sphere (recall the electrostatics problem of a dielectric sphere in a uniform E-field from Demo 4 and Workshop 4. – The time-varying dipole radiates like a Hertzian dipole, and this radiation is the scattered radiation. 2 Rayleigh Scattering: Induced Dipole Incident plane wave: r E i o 1 a 2 + + + + +----- z 7 Swartz 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 35: • Suppose the z-directed E-field phasor for the incident plane wave at...
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This note was uploaded on 11/26/2009 for the course ECE 3030 at Cornell.

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Lect35EMscattering - 1 ECE 3030 Electromagnetic Fields and...

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