Maxwell's Eqns: EM Basis Functions Explored

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Discussion Overview

The discussion centers on the exploration of basis functions that are useful for solving Maxwell's equations, with a focus on various mathematical approaches and their applicability to different problems within electromagnetism.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that Fourier basis functions may not be convenient for Maxwell's equations due to challenges with curl and divergence operations.
  • Others propose that cylindrical and spherical harmonics are particularly useful for scalar potential and Green function problems in magneto- and electro-statics, mentioning different types of cylindrical and spherical harmonics.
  • A participant notes that vector spherical harmonics are beneficial for full electromagnetic wave problems that include polarization.
  • One contribution discusses the potential of spin functions and quaternions as basis functions, suggesting that they may provide a reduced form of transformations relevant to special relativity and Maxwell's equations.
  • Another participant shares their experience with vector spherical harmonics, indicating a preference for a derivation found in a different text compared to Jackson's.
  • A later reply acknowledges that while Fourier basis can represent divergence and curl operations, the need for a basis that simplifies the inverse of these operations remains unresolved.

Areas of Agreement / Disagreement

Participants express a variety of views on the usefulness of different basis functions for Maxwell's equations, with no consensus reached on a single preferred basis. Multiple competing models and approaches are discussed.

Contextual Notes

Some limitations include the dependence on specific coordinate systems and the unresolved nature of the inverse operations for curl and divergence in the Fourier basis.

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Are there any sets of basis functions that are particularly useful for Maxwell's equations? I was thinking about Fourier just because it is the first basis I always think of, but I don't know that it would actually be a convenient basis. For example, I don't know that curl or divergence would be easy in the Fourier basis.
 
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"Maxwell's Equations" are pretty open ended. There are bases that are useful for solving certain problems.
1. For scalar potential and Green function problems in magneto- and electro-statics, cylindrical and spherical harmonics come to mind as particularly useful. There are two different cylindrical harmonic bases as well, those with cosine/sines and ordinary Bessels, and those with cosh/sinh and modified Bessels. There are different versions of the spherical expansions, too. The alternate expansions sometimes have particular advantages, see
http://physics.princeton.edu/~mcdonald/examples/EM/cohl_apj_527_86_99.pdf"
and
http://iopscience.iop.org/0022-3727/19/8/001?ejredirect=migration"
for two interesting applications.
2. Similar harmonics exist of course for spheroidal and all the other 8 or so coordinate systems that are separable under Laplace's equation.
3. The harmonic bases are useful for radiation problems as well (e.g., multipoles). For full EM wave problems that include polarization, the vector forms of the harmonic bases are used. Vector spherical harmonics are the best known of these.
4. Sines and cosines (your Fourier bases) are useful for problems in rectangular coordinates.
 
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Spin functions seem to be basis functions of the equations. I've heard it expressed that quaterions can be reduced to a pair of complex-valued 2 component spinors. And quaterions are the most reduced form of transformations for SR. Any combination of rotations or boosts, inclusive or exclusive, can be performed most simply with spinors and quaterions.

Since SR is a particular analysis of Maxwell's Equations regarding time and length (minus the conjectural things Einstein added) spinors and quaterions must be the most reduced form of transformations of variables with the Maxwell Equations.

Quaterions function in that way apparently because they encode symmetry properties which vectors do not. At least that is my understanding.
 
I happen to use the vector spherical harmonics recently. They are the basis functions to describe the electric and magnetic field in the spherical coordinate. However, I find the derivation of the vector spherical harmonics in Jackson's a little awkward. Bohren's book on absorption and scattering of light by small particles has a different derivation I find easier to chew.
 
Thanks for the replies so far! I looked into Fourier a bit more and I found that divergence and curl can be represented by reasonably straightforward operations on the Fourier domain, but then I realized that what is really needed is a basis where the inverse of the curl and divergence has a simple representation. Unfortunately, I got stuck there. I will look into the details of what you have all posted over the next day or so.
 

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