Lecture 3f -- Scattering from an Interface -- Normal Incidence

This lecture describes the scattering of waves at an interface between two materials where the angle of incidence is 0 degrees (i.e. normal incidence). Equations for reflection and transmission are derived.

[@meghjitmajumder3468]

The best thing about your lecture is, if one knows any particular topic very well even after that if he/she looks your lecture about that topic, he/she will surely gain some new insights.

[@empossible1577]

Thank you very much!!!

[@hemantj675]

Amazing lectures. Hats off to you sir.

[@empossible1577]

Thank you!

[@troya.8094]

*chef kiss* amazing description

[@tejraj444]

Excellent.....no word to say

[@karielf8947]

OMG! thanks a lot dear sir

[@empossible1577]

Our pleasure!

[@ChiliBass]

Well done! I wish you had taught my undergrad EM class :)

[@empossible1577]

Ha ha. Thank you! Glad I can help.

[@serden8804]

full of thx and love from turkey

[@empossible1577]

Hello Turkey!! Very glad the videos are helping you!

[@fuzzyelectrons]

Again, awesome explanations! What happens if you have material 2 only between 0 < z < L and material 1 everywhere else? My intuition says you could solve this by using impedance transformation so that the impedance one "sees" when looking into the x-y plane (looking in +z direction), is the impedance one gets by taking impedance of material 1 (from zone z > L), transformed by a transmission line of impedance from material 2 and length L. Is this correct? Thank you so much for your very helpful lectures.

[@empossible1577]

You have described the classical dielectric slab. First, let me point you to the course website that I recommend you use as your portal to the videos. They contain downloadable notes, links to the latest videos and other learning resources. empossible.net/academics/emp3302/ Lecture 7f talks about the dielectric slab and derives analytical equations you can use to calculate transmission and reflection for any arrangement of materials. The procedure you described using impedance transformation to calculate reflection from the slab can also be used. I talk about that technique in Lectures 8f and 8g. You will see that there are more things you can apply that technique to! Hope this helps!

[@CanErtugay]

Hi all. I always make benefit of this channel and suggest everybody. Thanks thousands to your channel. I have a question. I guess, It might be possible that "t" is greater than 1 when impedance 1 less than impedance 2. I am not talking about "T", I am talking about "t". Am I right or not?

[@empossible1577]

Thank you! I am very glad the lectures are helping you!! Yes, the transmission coefficient t can be greater than 1. For example, if a wave is passing from a medium with impedance 100 ohms into a medium of impedance 300 ohms, the transmission coefficient would be around 1.5. This does not violate conservation of power because the transmission coefficient deals with wave amplitude and not power.

[@CanErtugay]

@@empossible1577 Thanks for the quick answer. You are excellent

[@GhostDocs]

Thank you

[@harshitgupta2872]

Is impedance for denser medium is greater or less than to the rarer medium

[@empossible1577]

In general, impedance will go down as refractive index increases. This ignores permeability.

[@kiranpadakanti4998]

super sir

[@karielf8947]

I have a question, in lossy dielectrics, could we have a transmission factor gretter than 1 because of internal constructives interferences?

[@empossible1577]

The transmission coefficient can be greater than 1, but not the transmittance (i.e. fraction of power transmitted).

[@karielf8947]

@@empossible1577 actualy I m simulating on CST à rebar grid, and I found à transmissions coefficient greatter than 1. Wonder if ot is correct, or there is à problem in my simulation, may be réflexions from the grid to thé plane wave source influent thé inner excitations, or périodicité conditions for infinité grid influence excitations ?

[@empossible1577]

@@karielf8947 I am not sure what you mean by transmission coefficient. Are you talking about the Fresnel coefficient that quantifies field amplitudes? This can be greater than 1. Are you talking about transmittance (i.e. fraction of power transmitted)? If so, that cannot be greater than 1 unless you are simulating materials with gain. If you are seeing that, a common reason is your absorbing boundary condition on the transmitted is not working and is producing some reflections. You will get T>1 due to there being a standing wave.

[@karielf8947]

@@empossible1577 i m talking about the ratio between thé field with and without thé rebar grid.

[@karielf8947]

I have an other question, if a sinus wave is injecter through à lossy dielectric, the output will be thé samedi sinus or I could have other fréquences because of the interferences inside the dielectric ?