Make Wi-Fi Visible #3 – Radio Frequency Refraction

As we all know, Wi-Fi is amazing. The only thing is… it’s invisible.

So let’s start by explaining what makes Wi-Fi invisible? Wi-Fi uses radio frequencies electromagnetic waves to transfer information. These waves have wavelengths that are not within the visible space.

Light is also an electromagnetic wave. However, its wavelength is within the visible spectrum (between 330 nm and 700 nm). This is what make the light visible to the human eye. In fact, any electromagntic radiation having a wavelength between 330 nm and 700 nm is called “light” or to be precise “visible light”.

This means that we can explain Wi-Fi concepts using light analogies. In this set of articles, that is what we are going to do using simple drawings.

Episode #3 – Radio Frequency Refraction

Radio frequency refraction occurs when a radio wave is moving to a medium having a different density. The direction of the radio wave changes as it moves to the new medium as illustrated below:

The concept of light being refracted is very familiar. It is easy to demonstrated if you light up an aquarium with a flashlight. You will see the light under water going in a different direction. Light refraction is illustrated below:

Drywalls, wood, metal or plastic might each, in their own way, refract radio frequency since the density of the materials are different. This can have a little impact on indoor Wi-Fi deployment.

However, refraction is most likely to occur in outdoor site-to-site Wi-Fi links since refraction is usually the result of atmospheric conditions changes. Changes in temperature, existence of water vapor or air pressure can cause refraction. And since the outdoor point-to-point link has to be perfectly aligned in order to work properly, a little bit of refraction can have a bad impact on the Wi-Fi connection.

Written by François Vergès

“Episode #1 – Radio Frequency Propagation” is still available!
“Episode #2 – Radio Frequency Reflection” is still available!
“Episode #4 – Radio Frequency Diffraction” coming next!

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