Physical meaning of TEM, TE and TM

Why TEM cannot exist in single conductor?

Please send me some files regarding the topic (no books).

Since its a conductor, its equipotential. Hence, the 'E' term vanishes.

What is an equipotential?

Equi potential surface is a surface in which all the points have the same potential

This means the potential difference between any two points in it is always 0

What does the TEM, TM, TE modes mean?

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If a TEM wave were to exist in a waveguide, the field lines of B and H would form closed loops in a transverse plane.

What does the above statement mean?

I took it from field and wave electromagnetics text book.

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explain with diagrams if possible....

Hi,

TE, TM, TEM is simply a representation of the field. If you project Maxwell equation in rectangular coordinate and separate them into transverse and longitudinal (in general the direction on propagation but not always) components, you can verify by application of the bondaries conditions if an TE, TM or TEM mode occur.
TE mode is also a electromagnetic field whose longitidinal electric field component is null, same thing for TM expect that it is the Magnetic field whose longitudinal component is null. For TEM both electric ans magnetic longitudinal components are null.
But you bare going to say me : what is the aim of that decomposition ?
In fact in several electromagnetic problems, any field can be express by an infinite sum of this basic decomposition (think about Fourier series). Furthemore, such decomposition simplify the application of bondaries conditions : nxE=0 or nxH=0.

For TEM, imagine E field only varying along z direction and H field only vary along y direction, the propagation direction of the EM wave is x direction. This is like a 1D problem. For TE, TM, lets say TEz wave, this means Transverse E perpendicular to z direction, that means E field only exists on XoY plane, H only exists along z direction. Same for TM waves, check Balanie's book for more details

To understand EM waves, you need to start from Maxwell's equations.

Here's what it basically says:

An electric field that varies with time results in a magnetic field that varies with time.
A magnetic field that varies with time results in an electric field that varies with time.

Lets say you have an antenna. (just a long piece of wire) You connect an oscillator to it. So, electrons move back and forth in it. This induces a magnetic field in free space, which in turn results in an electric field and so forth.

Both Electric and Magnetic fields are in phase. i.e., they rise and fall together, but they are perpendicular to each other, and both are perpendicular to the direction of propagation of the wave.

This is called a TEM wave.

The TE, TM waves all exist only in waveguides. (hollow metal stuff or an optical fiber) (In optical fibers, the same thing is called with a different nomenclature)

TE- No electric field in direction of propagation.
TM- No magnetic field in the direction of propagation.

There's one more mode, which is the hybrid mode, in which there's both electric and magnetic field in the direction of propagation.

Basically, these modes exist only because of the boundary conditions imposed by the metallic walls of the waveguide.

I agree with you Ninju,

but we have to remenber that in a hollow wave guide (metalic) a field with both magnetic and electric field in the longitudinal direction could exist. This is due to the fact that Maxwell equation are linear. So we can sum the mode. Is it that you call hybrid mode ?
In fact the decomposition in mode could be done in either axis (x, y , z or another one direction), we use the best axis for boundaries conditions.

What is the "transverse" mean in transverse TE or transverse TM ?

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TE- No electric field in direction of propagation.
TM- No magnetic field in the direction of propagation.

I didn't understand the 2 statements.

Eraste, yes, the one in which both electric and magnetic fields are present in the direction of propagation are hybrid modes.

Nishanth, there's nothing, as far as I know called transverse TE or transverse TM. (I'm not an expert at waveguides)

Transverse just refers to the direction. So does longitudinal.

well,

In an electromagnetic system with an axis system choosen, in order to represent the field, you can developpe the solutions along an axis (say Oz for example). The found solutions are called TE if the field is only perpendicular to this Oz axis (magnetic field is also perpendicular and along Oz), called TM if the magnetic field is is only perpendicular to Oz (electric field is also perpendicular and along Oz). And finaly solution are called TEM if both electric and magnetic field are perpendicular to Oz.
The Oz axis is often chosen along the propagation axis but it is not an obligation. So for TE : E hasn't component along Oz.For TM : H hasn't got component along Oz and for TEM mode both E and H haven't got component on Oz.
A TEM wave is also called a plane wave. It is the case when you look at the far field of an Antenna.