Eli5: What component in eletonics like cellphones and computers actually “receives” and “emits” wifi signals? What is wi-fi in terms of physics?
In: Physics
When you apply a voltage to an open wire, the electromagnetic field around it changes a little. This change propagates to infinity, diminishing in magnitude as distance to the wire increases. Do that many times per second, and you have a radio wave. By superimposing additional voltages onto a radio wave of known frequency, a message (such as sound, or digital information) can be sent. This is called modulation.
Electromagnetic waves induce voltages in wires (the reverse of the process above). Precise filtering for specific frequencies allow a receiver to reproduce the signal encoded in the radio wave. This is called demodulation.
A radio antenna is just a wire of a specific length that corresponds to the wavelength (or even fraction) of the intended radio frequency. This causes it to resonate electrically at that frequency, which increases transmission and reception efficiency by attenuating frequencies other than the intended frequency.
WiFi frequencies are ultra high (UHF), meaning their antennas can be very short. This is useful in cellphones and other small devices.
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