Make Wi-Fi Visible #6 - Radio Frequency Absorption

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 #6 - Radio Frequency Absorption

Let’s finish this first series of article with absorption! Absorption is the fact that a radio wave loses some of its energy going through a medium or an obstacle. A radio wave will typically lose some of its energy as it travels trough the air du to absorption.

Light waves are easily absorbed. Indeed, the simple fact of blocking a flashlight with your hand will block the light. A wall will also totally block light. Some other materials like glass will let the light pass through with less absorption.

As you probably understood, absorption depend on the material the radio wave goes through. Typically, a Wi-Fi wave will be less absorbed going through a dry wall than going through a brick wall. While deploying Wi-Fi, it is important to keep in mind what objects absorbe Wi-Fi radio wave the most in order to find the best APs locations. Performing on-site site survey will help you determining the absorption of the objects of your environment.


Written by François Vergès