# Confusion about what EM fields really look like, and how that relates to data transmission, waveguides etc

After a discussion at work a few days ago, I realized I don't have a very good understanding of what RF energy is truly like. I've always thought, via physics and EE classes, that all EM waves (including RF) was a nice set of electric and magnetic fields oscillating perpendicular to each other, with the direction of propagation in the third axis like the picture below shows.

I realized it is not so simple. I understand the last answer in the thread, how the EM waves actually look like they are 'ballooning' out of the antenna and the frequency is actually the flux-density, that is where the 'sine wave' comes from. That makes perfect sense. Check out this simulationvideo

What doesn't make a lot of sense to me is how to visualize the amplitude with this simulation. The reason for my confusion is this:

Take a microwave oven for example, where the outer mesh holes are essentially acting as a waveguide and blocking the microwaves from escaping. This is said to be because the wavelength of the RF is too large. Ok.

In the picture below, I've tried to illustrate my confusion. I've always thought the waves travel like picture 1, and in that case the amplitude would cause the wave to not pass through the hole. My coworkers are telling me in reality it is like picture 2, where the sine wave is actually moving to the side and that is why the wavelength is what causes it to be blocked.

I just don't understand how #2 could be true, based on the simulation video above. If the frequency is based on the flux density, it would seem the sine waves are 'in-line' with the direction of propagation just like picture 1 in my drawing. I also don't understand how a receiving antenna could make sense of any data if the sine wave component is perpendicular to it, to my understand the data must be in-line, with each bit moving towards the antenna like picture 1.

I hope this makes sense, I am awfully bothered by my confusion and would love some clarification. Thanks!

• When it comes to waves, quantum mechanics and stuff, you better give up visualizing and focus on mathematics. When getting down there, the stuff is getting weird and unlike anything we can actually imagine or visualize accurately. It is just going to confuse you even more. Jun 7, 2018 at 18:38
• Take a microwave for example .... what are you talking about here ... that is an unclear statement Jun 7, 2018 at 19:03
• Sorry I meant microwave oven Jun 7, 2018 at 19:15

It really depends on the structure of your wavegide at microwave frequencies, you can imagine the fields like the waves in a wave pool, there is a resonant frequency depending on the width and length. But it's more complicated than that because it's a 3 dimensional problem.

The first picture you show applies to all EM waves, because any EM wave is just a collection of photons super imposed together, but when you get to lower frequencies like microwaves the waves are larger with respect to other things and the effects are different (ie a light photon will bounce off of a atom, but a radio wave will not, conversely a radio wave will reflect or be absorbed into a conductor of fractions of a wavelength)

To really visualize the fields you need a 3 dimensional field solver (or be really handy with a calculator with lots of time). The picture below shows a hollow rectangular waveguide, and shows the different modes. There are vertical and horizonal modes and first and second order modes, which in reality are superimposed on top of each other. For design it can be easier to consider one mode at a time.

The modes can be calculated on paper and look like this for a 2-d cross section: Source: http://www.wikiwand.com/en/Waveguide_filter

I think your problem is you need to think of wavelength as a characteristic of EM waves

As far as your other question goes if you think of the wave traveling perpendicular to the aperture, the hole edge on would be paper thin, and the wave wouldn't see it (as soon as you add conductors around the hole things get more complicated because waves do change with conductors, but you get the idea)

• I think I understand what you're saying. Can TE and TM waves exist outside of waveguides or is it the waveguide that creates the TM and TE waves and therefore they only exist inside the waveguide? Jun 11, 2018 at 22:46
• Transverse modes only occur in waveguides. It helps that the waveguides are designed to have modes at particular wavelengths Jun 11, 2018 at 22:58