For example a tiny antenna in the phone, why em wave do not pass through it, but pass through concrete walls?
closed as unclear what you're asking by Alfred Centauri, Jon Custer, user191954, Cosmas Zachos, ZeroTheHero Nov 10 '18 at 1:08
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For an antenna to pick up a sufficient signal, it does not need to stop the wave - it just needs to slightly attenuate it, which it does.
In general, when radio waves pass through obstacles, they get attenuated and, given the same level of conductivity, larger obstacles will cause greater attenuation, but even a small fraction of the absorbed energy could be sufficient for an adequate reception.
I would add that an antenna of a phone is tuned to a particular frequency range and, because of that, everything else the same, it will absorb more energy in that frequency range than a randomly shaped conductor of a similar size.
Simply put, cell phone antennas are made of metal, and are designed to absorb radio waves at cell phone frequencies. Concrete does not interact with radio waves as strongly as metal does and although concrete buildings may have some big pieces of metal in them, at cell phone wavelengths that metal tends to reflect and sometimes bend the radio waves instead of absorbing them.