Modes in Waveguide

Different modes in a waveguide roughly equate to the number of bounces the energy has to make to travel a given distance (yes, my E&M theory _is_ rusty). Different modes travel at different speeds, so if you have multiple modes they'll disperse the signal, which slows your achievable data rate (or bandwidth).

No bounces in free space means there's only one 'mode'.

Which goes to show you that a *solution* to the equations that reflect a physical law do not have to have common properties with each other or even with the law itself. (A law may have a symmetry that the solution does not.) Boundary conditions form additional constraints to the solution.

PD

Oh, right. Hermetians and all that. But the free-space modes all go the same speed so it's not the Big Deal that it is with waveguides, unless you're trying for a perfectly circular spot out of a laser.

Now I'm less rusty.

Thanks.

Boundary conditions for the Maxwell equations...

Rusty is the word. There is a continuum of modes in free space, because a mode is just a propagating solution of Maxwell's equations in the given geometry. A metal guide has a whole number of modes (a positive integer or zero), and dielectric guides have at least one guided mode and a continuum of unguided modes. (There's no analogue of a waveguide-below-cutoff filter in the dielectric guide world.)

Cheers,

Phil Hobbs

One word: Resonance. Waveguides, optical fibres, coaxial cables, antennae, tuning forks, pipe organs, flutes and oboes and even violins. Resonance.

The symmetry is there, you just have to find it.

Androcles.

You've omitted "sinus cavities" and "exhaust headers". ;-)

Ever see that "Blue Man Group" bit where they've got a telescoping piece of about 6" PVC pipe, and one guy beats on it with drumsticks while another slides the telescoping part of the pipe in and out? Resonance. :-)

Planetary orbits, electronic orbitals, NMR/MRI, etc, etc, etc...

Cheers! Rich

No. I do know what a trombone is. Androcles.

Resonance. :-)

The what mode? Cites?

Betcha it can't propagate in free space.

Mark L. Fergerson

One of the more interesting modes (in a waveguide) is the "smoke ring" mode...apparently not very stable but capable of handling vast amounts of power. Now just figgure how to launch energy in such a mode, and....ray gun!

EZ, no problem, done all the time. But it aint called "smoke ring" U can use your microwave oven, put a "structure" on it and cook a hotdog at

Err...at Stanford Linear Accelerator Center, they wer using higher power klystrons, and to handle the power without arcing, was to use the "smoke ring" mode. That is what they called it because of the shape of the E-H mode. Argue with them.

All the stuff between electrons and protons is free space. For words and music:

Treat dielectric and conductive wave guide just as you treat dielectric and conductive mirrors.

Sue...

The cooking cavity in a microwave oven is not free space.

Cite please? Google gives no relevant returns.

Mark L. Fergerson