How Can Radio Waves Travel Through Walls?

Radio waves can travel through walls that absorb all light, because light waves and radio waves have different frequencies.

Light has frequencies of several hundred THz, corresponding to 1014 vibrations per second. Radio waves typically have frequencies under 1 GHz, or fewer than 109 vibrations per second. When electromagnetic waves, such as light or radio waves, make contact with matter, such as a wall, they cause the matter’s electrons to vibrate. When a wave makes contact with an atom containing electrons, the electron reacts almost as if it were sitting on the end of a small spring.

All springs have resonance frequencies. and if you push a spring whose frequency is close to the resonance frequency, even a small push can have a great effect. If, on the other hand, the spring frequency is far from the resonance frequency, it is very hard to make the spring vibrate and thus transfer energy to it.

Radio waves have frequencies that are very far from the resonance frequency of the electrons in the wall. The waves thus only transfer a small amount of energy to the atoms and travel more or less freely even through thick walls. There is, however, some absorption, meaning that radio reception can be poor in places like tunnels.

The frequency of light waves is close to many atoms’ resonance frequencies. Consequently, the light quickly transfers energy to the atoms and is absorbed. The same goes for high-frequency radio waves, which may be absorbed by normal rainy weather. This is a problem for many modern satellites, which use still higher frequencies to quickly transfer large quantities of data.

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