Department of Electrical and Computer EngineeringECSE 352 Electromagnetic Waves and Optics3.7 Dispersive materials and group velocityReferences: Hayt and Buck 3.7 and 3.8@Andrew Kirk3.7-1OverviewIn most real materials, and also in waveguides, the phasevelocity is not constant but instead varies with frequency. Thishas very important consequences for the propagation of signalsthat are carried by electromagnetic waves in these materialsdtWillth t thiltiil diiand systems. We will see that this results insignal dispersion,which is a type of distortion. In order to describe this effectwe will introduce the concept ofgroup velocity.ECSE 352 3.7-2Learning outcomesAfter taking this class you should be able to:•Define group velocity and explain how it differs from phase velocity•Explain why the group velocity is also called the energy transport velocity•Explain why signals are distorted in dispersive systems•Estimate signal dispersionECSE 352 3.7-3Contents•Dispersive materials•Introduction to group velocity•Relationship between group velocity and signal dispersion•Definition of energy transport velocity•Estimation of signal dispersionECSE 352 3.7-4
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