Thread: Eric P. Dollard
View Single Post
 
Old 04-03-2012, 09:41 PM
Kokomoj0's Avatar
Kokomoj0 Kokomoj0 is offline
Senior Member
 
Join Date: Jul 2011
Posts: 426
Quote:
Originally Posted by lamare View Post
Yes, the tm mode is actually short for TM,LD mode, whereby the magnetic component is perpendicular with respect to the propagation direction of the wave, and the electric is in the same direction as the propagation direction of the wave, hence longitudinal.

With the TEM mode, both are perpendicular with respect to the propagation direction of the wave and in that situation both are spiralling around the propagation direction of the wave.

Note that in all cases the electric field and the magnetic field are perpendicular with respect to one another.



When you cancel them, they cease to exist. Just like you can cancel sound with anti-sound.

How do you cancel them since as you can see from your picture that they simply superimpose?


No, the lmd is a distincly different propagation mode from the TEM. It is one and the same as the TM,LD mode whereby you have the magnetic perpendicular with respect to the propagation direction of the wave and the electric longitudinal with respect to the propagation direction.

This is the mode used commercially these days by Elmore, as I posted some time ago:




What is confusing, is that with a coil you have multiple modes being present at the same time:

1) You have the TEM mode propagating more or less around the coil; and
2) the LDM or TM,LD mode propagating more or less in the length direction of the coil.

These two together result in an energy flow spiralling around the coil. At low frequencies (below the natural resonance frequency of the coil), the LDM mode is insignificant, so all you see then is the TEM mode.

At much higher frequencies, the LDM mode sticks its head out of the dirt, and you get a mix of both.

ONLY in the specific situation that the TEM mode spiralling around the coil cancels itself out, you are left with a pure longitudinal mode, whereby all magnetic fields are cancelled out.

you talk about that as if it were an absolute fact do you have any data on that? tem is set up as a result of a boundary condition so I am not sure what you are driving at.



Quote:
Types of modes

Transverse modes are classified into different types:
  • TE modes (Transverse Electric) no electric field in the direction of propagation.
  • TM modes (Transverse Magnetic) no magnetic field in the direction of propagation.
  • TEM modes (Transverse ElectroMagnetic) neither electric nor magnetic field in the direction of propagation.
  • Hybrid modes nonzero electric and magnetic fields in the direction of propagation.
Some authors use an alternate notation;
  • H modes have a magnetic field component in the direction of propagation. H modes are equivalent to TE modes.
  • E modes have an electric field component in the direction of propagations. E modes are equivalent to TM modes.
you have not posted any evidence of the existence of an LD mode
__________________
 

Last edited by Kokomoj0; 04-03-2012 at 09:47 PM.