I understand that radio waves pass through certain material (eg concrete walls), and hence we can receive cellular signals when in an apartment
However lets say I stay in a lower level of a high rise apartment (eg level 3 of a 50 storey tall building) – how does the radio waves penetrate so many walls to reach me? Does the amount of material not matter in this case?
In: Engineering
It all boils down to signal to noise ratio. As long as the remaining signal level is above background and other noise levels the system is fine. The difference between the signal that leaves your phone and that gets to the tower can drop by approximately 140 dB or 1/100000000000000 and still work.
Just as glass is transparent to visible light, your walls are transparent to radio waves.
(The walls aren’t completely transparent, more like tinted glasses. But the radio waves can travel through at least some of the walls and still be “seen” by your phone)
You may know that the electromagnetic spectrum is generally chopped up into sections based on the energy or wavelength of the wave (more energy = shorter wavelength). Really short, high frequency waves like gamma or X-rays are generally thought of as harmful because they get absorbed by almost everything they hit. Light gets absorbed by a lot of stuff, but some materials like glass let the light pass through. Sound operates similarly: high pitched noises don’t travel as far as low-pitched noises. Whale song (extremely low wavelength) can be heard across entire oceans. All waves generally work like this.
Radio waves are the section of the electromagnetic spectrum with very ~~low~~ long wavelength, and we use them for communication for exactly this reason. We don’t need a super “bright” wave that does anything on its own. Our devices are just amplifying waves of a certain wavelength and then translating it (into sound or a text message or something). We also use radio waves because they don’t get absorbed very much by most material. Really thick glass looks distorted, and radio signal can be distorted by really thick slabs of concrete or metal or even a ton of trees, but still it’s generally able to penetrate most materials. The long wavelength lets it bounce around really well too.
They go around walls. Find a large, wide building and stand in the center. Your signal will be weak or none. Stand near a window or door, it’ll be stronger.
You need to change how you think about transparancy. Things are not see through or not. Things are see through to certain wavelenghts of light.
For example those black trashbags look opague to your eyes, but they are almost completely see through to infrared.
Same with your walls. They are opague to visible light, but see through to radio waves. Imagine sitting in house with walls and floors out of glass and someone on the lower floors uses a flashlight to morse you a message. That is basically how the world looks from the perspective of radiowaves.
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