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Module 4 a

# Module 4 a - Module 4 Lecture 1 Thin film coatings...

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Page 1 Module 4 Lecture 1 Thin film coatings: Reflection properties

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Page 2 On the program today An EM wave incident at normal incidence on two boundaries in a row. What for? Antireflection coatings for media with different dielectric constants: optical glasses, cameras, computer and cell displays, radar cloaking Lossless weather shields for radars Passband filters with “designed” filtering shapes Using wave interference effects to “trick” Maxwell’s equations
Page 3 Generic case: time harmonic x -polarized TEM wave Z=0 Z=-L Medium 0 Medium 1 Medium 2 Take m r =1 in all media. Linearly polarized TEM wave allows us to use scalar equations for E Question: for a given wave incident from the left onto boundary 01, what is the reflected wave in 0 and transmitted wave in 2

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Page 4 Write down the E-field phasors in the three regions of space Z=0 Z=-L Medium 0 Medium 1 Medium 2 z j i e E 0 z j r e E 0 z j t e E 2 z j i e E 1 1 z j r e E 1 1
Page 5 Write down the E-field phasors in the three regions of space Z=0 Z=-L Medium 0 Medium 1 Medium 2 z j i e E 0 z j r e E 0 z j t e E 2 z j i e E 1 1 z j r e E 1 1 + + We have ten unknowns (5 E-fields and 5 H-fields) minus 1 arbitrary (the amplitude of the incident E-field). But we also have 4 boundary conditions (2 for tangential E and 2 for tangential H), and 5 equations for the E/H ratios in all media (the local wave impedance). SO THERE IS A UNIQUE SOLUTION!

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Module 4 a - Module 4 Lecture 1 Thin film coatings...

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