How can 802.11 and phones etc go through walls?

[BoogieQ]

I had asked a different question and found the answer so this is an edit 😛 But something I was always curious about how these things can work through walls.

I mean, why does a solid block of concrete not stop the signal? How does it actually go through the wall?

🙂

 

[f95toli]

For the same reason as it goes through air. At those frequencies concrete is more or less tranparant to electromagnetic radiation, there is some attenuation so if the wall is too thíck it won't work.

 

[BoogieQ]

This still confuses me though: "At those frequencies concrete is more or less tranparant to electromagnetic radiation"

WHY?

Isn't that 'matter' going though 'matter' or am I not in the right thinking?

Maybe I should have asked how radiation works 🙂

 

[Fencer128]

Originally posted by: BoogieQ
This still confuses me though: "At those frequencies concrete is more or less tranparant to electromagnetic radiation"

WHY?

Isn't that 'matter' going though 'matter' or am I not in the right thinking?

Maybe I should have asked how radiation works 🙂

Hi again,

Electromagnetic radiation (EM) is massless - it is energy. Since it has no mass there is no "collision" to worry about. Different frequencies of EM radiation (not to be confused with the different alpha and beta radiation from radioactive elements) exist from gamma waves through x-rays through visible light waves through microwaves to radio waves and beyond. The whole range is called the electromagnetic spectrum.

Different atoms/molecules absorb different frequencies/wavelengths (frequency and wavelength are like two sides of the same coin - they are mathematically inversely related) by different amounts.

It so happens that concrete absorbs wireless networking/phone wavelengths more strongly than, say, air. Given this the EM signal strength is stronger over a certain distance of uninterupted air as compared to uninterupted concrete. Hopefully you can now see why you get better recepetion without concrete walls in the way.

Hope that helps,

Andy

EDIT: Here is a quick introductory page on EM radiation that I found on google.

 

[merlocka]

Another way to think of it would be... why can I hear someone shout through a wall? It will make the sound more quiet, but you can still hear them.

 

[sgtroyer]

Or another way to think of it... You can see through a pane of glass. Why? It's solid, right? But it's transparent at visible wavelengths. At microwave wavelengths, most materials are partially or fully transparent.

Remember that solids are really anything but solid. They're still >99% empty space. They just seem solid because big things (like you or me) can't walk through them.