Wave Impedance Explained
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- เผยแพร่เมื่อ 1 ต.ค. 2024
- / edmundsj
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Wave impedance is a concept central to acoustics, mechanics, electromagnetics, and optics. In this video I describe wave impedance in terms of electromagnetics, as a ratio between the electric and the magnetic field of a traveling plane wave. If you know the electric field, amplitude, you know the magnetic field amplitude, and vice-versa.
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This is part of my graduate series on optoelectronics / photonics, and is based primarily on Coldren's book on Lasers as well as graduate-level coursework I have taken in the EECS department at UC Berkeley.
Hope you found this video helpful, please post in the comments below anything I can do to improve future videos, or suggestions you have for future videos.
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This deserve more views
Hello from India JEE ADVANCED ASPIRANT 👋🏻
Thank you so much from Indonesian Student! God Bless U sir
Stay healthy down there!
Sir here for magnetic field y component should come but you have written x
Excellent explanation, it can be easily argued that the ratio or sequence alignment contains the most important information
Yup! Exactly. Phase is only meaningful in relative terms.
Sir, Thanks you for your detailed explaination. From South Korea
Woo! I’ve always wanted to visit!
What a great lecture!! thanks
Hi, Thank you for posting the video! Can you explain how does wave impedance changes between the near field and far field?
Wave impedance is only really defined for the far-field (for transverse waves, as the ratio of the electric field to the magnetic field). In the near-field the waves aren't transverse (there's some component that doesn't propagate outward radially but sort of stays localized), so you can't really define a wave impedance in this region. You *can* define a capacitance and an inductance (by integrating all the E-fields and integrating all the H-fields) and these are usually more useful.
@@JordanEdmundsEECS In the case of a Gaussian beam, there are nearly spherical wavefronts on either side of the beam waist, where the wavefronts are nearly planar. How does wave impedance change along the axis of a Gaussian beam through these regions?
Very nice explanation. I have not found it this neatly derived anywhere so far.
I have a question though. Considering an EM wave hitting a dielectric interface at an angle, the impedance is supposed to change dependant on the polarisation and incidence angle of the wave.
I found a formula somewhere but when I plug in the brewster's angle and expect Eta(alpha_B) = Eta_0 for parallel polarisation, I get something weird instead. Since my formula does not seem to work, do you know one that does work?
It would be nice to see example on magnetic material. Few textbooks cover magnetic material properties. THX.
Wow thank you so much, this explanation is extremely well!
This was very helpful for me. Thank you.
0:19 What is the meaning of the arrows from E to H and vice versa, and the narrative "a propagating electric field and a propagating magnetic field and these two switch back and forth in their oscillations as we move through space"? In what sense are they switching back and forth? Is this saying that E somehow changes places, or exchanges energy with H?
Yeah, in a propagating electromagnetic wave the E-field and H-fields oscillate out of phase, you can indeed think of it like the energy sloshing back and forth between them.
@@JordanEdmundsEECS Thanks very much for your reply! I wondered if that was what you might mean. But when you say "E-field and H-fields oscillate out of phase", how does that relate to the plot of field intensity (exemplified by the top figure in en.wikipedia.org/wiki/Electromagnetic_radiation), where they are shown (and the caption says explicitly) _in_ phase?
@@JordanEdmundsEECS I'm still interested in this question. This video seems to contain the misconception described here: th-cam.com/video/uZnXhRgztEg/w-d-xo.html I think. My suspicion is increased by 4:45 where the phasor factors in the equation relating H0 and E0 are equal (same phase angle) and cancel. But maybe I've missed something.
Love and respect from India ❤️
Wave impedance same as intrinsic impedance?
thank you!!!!
Hi Jordan.....i just want to know...if in space nothing is there to obstruct the propagating em wave, why this impedance arises?....or it is just a misleading term😁?
Space itself has properties that conduct or betterresist electric and magnetic fields. Thats what µ and epsilon represent. Meaning space itself obstructs.
No wonder you a Hertz fellow!
Is their not an exponetial factor missing from e^(gamma*
the 377 Ohms are valid for the far field from a radiation source.. could you expand on what happens in the near field (distance from source smaller than wavelength/2Pi) ?
for that you should probably use equations for transmission lines, smith diagram, etc
Thank you very much!
Also sir which playlist does this fall under ?
So nice thanks sir
What is the physical significance of wave impedance?
One physical significance is that it determines the speed of propagation of the wave. Higher wave impedance -> lower propagation speed. When you have physical discontinuities (like between air and water for example), wave impedance is what determines how much of the wave gets reflected and how much gets transmitted.
Thank you sir !
You are welcome!