lecture16addition - Lecture 16 (b) Waves in Isotropic...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
1 ECE 303 – Fall 2005 – Farhan Rana – Cornell University Lecture 16 (b) Waves in Isotropic Media: Plasmas and Dispersive Media In this lecture you will learn: • Wave propagation in plasmas • Wave propagation in dispersive media • Phase and group velocities ECE 303 – Fall 2005 – Farhan Rana – Cornell University Plasmas What is a Plasma? A plasma is an assembly of positive and negative charged particles with a net zero time-average charge density Examples of Plasmas: 1) Gases in which the electrons have been stripped off the atoms – resulting in a mixture of positive ions and electrons Examples: a) Surface of the Sun b) Hydrogen ions and electrons in a fusion reactor c) Earth’s Ionosphere 2) Atoms and electrons making up solids (semiconductors, metals, etc) can also be described as a plasma - although in this case the positive charges are fixed
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 ECE 303 – Fall 2005 – Farhan Rana – Cornell University Plasmas +ve ions -ve electron cloud • In plasmas, electrons are not attached to any one particular positive ion (or atom) but move about freely • On average (spatial and temporal average), plasmas are charge neutral (i.e. electrons tend to spend more time in the vicinity of the positive ions (or atoms) than away from them – hence the pictures shown A solid state plasma A gaseous plasma ECE 303 – Fall 2005 – Farhan Rana – Cornell University In most plasmas, the positive ions (or atoms) are much heavier than the negative electrons and one may ignore the motion of the ions in response to an E-field for simplicity Waves in Plasmas – Electron Dynamics What happens when a plasma is subjected to a time-dependent E-field (like that of a plane wave)? ( ) z k j o e E x r E = ˆ r r x z Let the displacement of the electrons at the location from their average position be given by the vector ( ) t r d , r r r r Newton’s second law gives: ( ) () () t r E e t r F t t r d m , , , 2 2 r r r r r r = = +ve ions -ve electron cloud E k r H
Background image of page 2
3 ECE 303 – Fall 2005 – Farhan Rana – Cornell University Waves in Plasmas – Material Polarization x z () z k j o e E x r E = ˆ r r t r E e t t r d m , , 2 2 r r r r = r E m e r d r r r r 2 ω = Dipole moment phasor ( ) ( ) r d e r p r r r r = = () () r E e r d m r r r r = 2 Use phasors to solve the differential equation: () ( ) { } ( ) ( ) { } t j t j e r d t r d e r E t r E r r r r r
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/02/2008 for the course ECE 3030 taught by Professor Rana during the Fall '06 term at Cornell University (Engineering School).

Page1 / 9

lecture16addition - Lecture 16 (b) Waves in Isotropic...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online