What Are TE/TM Modes in Electromagnetic Waves?

[dexterdev]

Hello PF,

I have a doubt. polarization refers to the plane of Electric field right?, then linearly polarized wave is TEM and circularly may be TE/TM right? Please someone clear my doubt...

What is this TE/TM (m n) modes mean...Any helpful animations other than falstad.com links...

-Devanand T

 

[the_emi_guy]

Polarization is generally associated with TEM waves and is often (if not mostly) the relationship between the E-field direction and the horizon. Polarization can be shifted from horizontal to vertical, for example, by simply rotating an antenna.

The TE and TM modes inside of waveguides are a different story. The orientations of the fields are governed by the dimensions of the waveguide and the particular mode. I cannot rotate an antenna inside of a waveguide and change the polarization of the internal fields like you can with TEM waves in free space. I can rotate the entire waveguide and the internal fields will have rotated relative to the the external horizon but this is of no interest.

Very briefly...

TE and TM occur when waves are guided (rectangular microwave waveguide, fiber optic cable).
TE means that the E-field is always orthogonal to the direction of propagation (often called z-axis of guide). H-field will have a component along z-axis.

TM means that the H-field is always orthogonal to z-axis (making closed loops in x-y axis). E-field will have component along z-axis.

The mode is analogous to the vibrational modes on a violin string. The string has a node at each end that prevents movement. The lowest frequency mode has the string motion maximum in the center between the nodes. The next mode has a node in the center of the string and maximum amplitude at the 1/4 and 3/4 points, and is at twice the frequency.

In a waveguide there are two mode indices (m,n) because there are two dimensions involved.

Do Google searching for images of modes within rectangular waveguide. Pictures really help understanding this.

 

[dlgoff]

I google searched "em modes". Here's the first hit on my list. I don't think you'll find a much better explanation IMO.

"whites.sdsmt.edu/classes/ee481/notes/481Lecture10.pdf"

 

[dexterdev]

Thank you for the help...

 

[alphysicist]

Hello Devanand T,

I am happy to help clarify your doubts about TE/TM modes. In electromagnetic theory, TE (Transverse Electric) and TM (Transverse Magnetic) modes refer to the two types of polarizations that a wave can have in a waveguide or transmission line. These modes are important in understanding the behavior of electromagnetic waves and their propagation in different mediums.

To visualize these modes, let's first understand what transverse means. Transverse refers to the direction of the electric and magnetic fields in relation to the direction of wave propagation. In TE mode, the electric field is perpendicular to the direction of wave propagation, while in TM mode, the magnetic field is perpendicular to the direction of wave propagation.

Now, let's consider a wave propagating in a waveguide or transmission line. In TE mode, the electric field is parallel to the walls of the waveguide or transmission line, while the magnetic field is perpendicular to both the electric field and the direction of wave propagation. This results in a wave with a linear polarization, where the electric field oscillates in a single plane.

On the other hand, in TM mode, the magnetic field is parallel to the walls of the waveguide or transmission line, while the electric field is perpendicular to both the magnetic field and the direction of wave propagation. This results in a circularly polarized wave, where the electric field rotates in a circular motion as the wave propagates.

The (m n) in TE/TM modes refers to the mode numbers, which determine the number of nodes in the electric and magnetic fields along the direction of wave propagation. These numbers are important in understanding the behavior of waves in different mediums and can be visualized using mathematical equations and simulations.

As for helpful animations, I recommend checking out university websites or online resources that provide interactive simulations for TE/TM modes. You can also find helpful videos on platforms like YouTube that explain these concepts visually.

I hope this helps clear your doubts and provides a better understanding of TE/TM modes. Keep exploring and learning about electromagnetic theory!

Best,