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Fields and Waves

This lesson explores the reflection and transmission of waves at an interface between two different media. It covers topics such as impedance discontinuity, boundary conditions, standing wave patterns, Smith chart usage, and power flow in lossless and lossy media.

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Fields and Waves

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  1. Fields and Waves Lesson 5.5 Wave Reflection and Transmission Lale T. Ergene

  2. Normal incident MEDIUM 2 η2 MEDIUM 1 η1 incident plane wave transmitted plane wave reflected plane wave • wave is normally incident on an infinite interface separating two different media • impedance discontinuity • similar to the transmission lines • EM waves represented with rays or wavefronts

  3. Lossless media • two lossless, homogenous, dielectric media MEDIUM 2 ε2,μ2 MEDIUM 1 ε1,μ1 . . . . . z=0 Incident wave

  4. Lossless media transmitted wave reflected wave

  5. Boundary conditions Tangential component of the electric field should be continuous across the boundary Tangential component of magnetic field should be continuous (no current source) At the boundary (z=0): or or

  6. reflection and transmission coefficients Normal incident Normal incident Γandτare real for lossless dielectric media Normal incident For nonmagnetic media

  7. transmission line analogy • One to one correspondence between the transmission line parameters and plane wave parameters • incident and reflected waves create a standing wave pattern Standing wave ratio • if η1= η2Γ=0 S=1 • η2= 0 (perfect conductor) Γ=-1 S= ∞ • Smith chart can be used • the max and min locations of the electric field intensity from the boundary are defined by the same expressions for the voltage max and min locations

  8. Power flow in lossless media The average power density flowing in medium 1 The average power density flowing in medium 2 For lossless media

  9. Boundary between lossy media • two lossy media MEDIUM 2 ε2,μ2, σ2 MEDIUM 1 ε1,μ1, σ1 . . . . . z=0 Medium 1

  10. Boundary between lossy media Medium 2 . Γandτare real for lossless dielectric media

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