Talk:Mode (electromagnetism)

Reference page

In the references, the "Electromagnetic Theory for Microwaves and Optoelectronics" By Zhang & lee, which is cited for the LSE and LSM modes, is found in page 322 rather than 294 as written here.

"Zhang & Lee, p. 294" ---> "Zhang & Lee, p. 322" — Preceding unsigned comment added by 132.68.75.162 (talk) 08:00, 25 March 2019 (UTC)

Not according to the the contents section, and here's page 294 if gbooks will serve it to you. Maybe you are looking at a different edition.. SpinningSpark 14:39, 25 March 2019 (UTC)

Talk:Waveguide#Needs_beirf_explanation_of_modes

The Waveguide article mentions modes, including ones like TE1,3, but doesn't explain at all the numbers. And they aren't explained here, either. It seems that this is where they should be explained first, and linked from waveguide. Gah4 (talk) 20:56, 8 June 2023 (UTC)

Move to "Mode (wave)" or "Wave mode" or "Waveguide mode"?

Acoustic modes are not mentioned and AFAICT modes are solutions of the wave equation with (finite) boundary conditions (guides). I suppose we could have "Mode (acoustic)" but that would obscure the commonality. If we moved this article to "Mode (wave)" or "Wave mode" or "Waveguide mode", then both could be covered and the commonality discussed.

• "This same wave equation occurs (although, generally also as an approximation) in a variety of other contexts: electromagnetic theory, gravity waves in shallow water, dilatational and shear elastic waves in solids, transverse vibrations in stretched membranes, Alfvén waves in magnetohydrodynamics, pressure surges in liquid-filled tubes with elastic walls, e.g., blood vessels, and electromagnetic transmission lines." Pierce, A.D., Acoustics: An Introduction to its Physical Principles and Applications, McGraw Hill, 1981, NYC, NY.

@Constant314 Johnjbarton (talk) 01:11, 8 September 2024 (UTC)

A closed resonator has modes that are not waveguide modes. Modes spewing out of an aperture are not waveguide modes. Waveguide (electromagnetic) mode is a subtopic of Mode (electromagnetism).

Perhaps create Waveguide modes as a subpage to this page? As Mode (electromagnetism)/Waveguide modes. Constant314 (talk) 01:46, 8 September 2024 (UTC)

OK thanks, so forget "waveguide mode". I was trying generalize, to group wave "modes" across electromagnetic/acoustic etc. per the Pierce quote above. Johnjbarton (talk) 03:09, 8 September 2024 (UTC)

Normal modes.

"Modes in waveguides and transmission lines. These modes are analogous to the normal modes of vibration in mechanical systems."

This seems incorrect since normal modes in the normal mode article do not travel. I see that the note referres to a cavity. Constant314 (talk) 14:05, 13 September 2024 (UTC)

(I'm not a fan of the "normal" modifier, since I do not believe there are any "abnormal" modes.)

Isn't a "mode" in EM stationary in some sense, eg in directions orthogonal to the transmission?

Maybe add something on cavity modes if we can't find some source about traveling vs normal. Johnjbarton (talk) 16:55, 13 September 2024 (UTC)

I am not source what normal means. But stationary (or standing) vs traveling is clear. Ther latter transports energy and the former does not.

The following are citations documenting some of the uses of "mode". This is intended as a resource for discussion. No need to respond to each item.

• Wadell defines a mode as a solution of the wave equations in a wave guide.

• Jackson, defines a mode as an orthogal solution of the wave equations in a wave guide with further stipulation that the modes have associated eigenvalues. I think this would be called an eigen mode, but he does not use the term in 1975.

• Harrington, "Elementary wave functions corresponding to specific eigen values are called eigen functions".

• ngram veiwer for \ eigenmode shows an uptick of usage in the 1950s.

• ngram veiwer for | eigenmode,eigenfunction,eigenvector

References

Normal modes (con't)

(The Normal modes post no longer has a Reply button).

Your standing wave vs traveling wave is also my understanding, and I assume (cavity mode, standing wave) vs (waveguide, traveling wave).

There are traveling vibrational waves in solids called phonons and they are referred to as normal modes: "The normal mode vibrations of solids are referred to as phonons." https://sites.science.oregonstate.edu/~grahamat/COURSES/ph427/Chap2.pdf But I think that sentence could be written: The vibrational modes of solids are referred to as phonons. But multiple sources use "normal mode" in this way but never seem to define it.

I'm ok removing the sentence about normal modes here. Rather than have an analogy that is unclear in its scope I think we would be better off pointing out the parallel articles on acoustic/vibrational modes in this article. Johnjbarton (talk) 23:02, 13 September 2024 (UTC)

Agree and thanks for pinning the references down. Constant314 (talk) 00:53, 14 September 2024 (UTC)

A couple of more hints if not a smoking gun. Classical Mechanics (Goldstein) in the section on small oscillations, he talks about the eigenvalue equation and the principal axis coordinates as "normal coordinates of the system", each of which corresponds to a single vibration frequency: the corresponding oscillations are "normal modes of vibration". So the "normal mode" gets its 'normal' from normal coordinates.

In Classical Electricity and Magnetism by Wolfgang Panofsky and Melba Phillips 22.6 discusses black body radiation and says the field equations for the bounded radiation field can be related to equations for simple harmonic oscillators. "In fact there is one-to-one correspondence between the equivalent oscillators and the normal modes of the field in the enclosure." This much is the your observation about cavity modes. But the new bit is the forward ref from 22.6 to their chapter 24 on the Hamiltonian formulation of Maxwell's equations, that is a model based on a limit of continuous mechanical oscillators as in the field theory of QED. That's where an analogy between EM and mechanics comes again. Johnjbarton (talk) 00:09, 15 September 2024 (UTC)