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One of the most popular ways to record sound is RF condenser microphone (RF = radio frequency). It is used in telephones and high-fidelity recording microphones. RF condenser microphone can produce very good sound quality. It doesn’t need a big mass to be moved by the soundwave. This means that RF condenser microphone needs a separate power source.
How does sound move through matter?
Sounds is a vibration that moves wave. It moves through matter as a longitudinal wave. Sound can move through gas, liquid and solid, but certain materials propagate sounds better than others. The vibration of particles transport the sound vibrations as a wave. Some materials (mostly solids) will not do this very well. Sound has to have a medium (the matter) to move through. It can not travel through a vacuum.
The matter the sounds moves through effects the sound waves. The density and pressure (and temperature) effects the speed of sound in the matter. That means that sound moves through cold and hot air at different speeds. This is unnoticeable at short distances. If the matter is in motion when sound moves through it has an effect on the sound. For example sound moving through windy air. Depending on the direction it may attenuate more or less compared to non windy air. Also the viscosity of the matter affects how fast the sound attenuates.
How antenna works in phones?
In the mobile phones of today, there are different kind of antennas needed in order to receive and transmit the signal from the phone to the link tower. All the different antennas are needed, because the frequencies differ from countries and different carriers. Usually the frequencies mostly used are from 800MHz to 2700 MHz. The frequencies used are radio waves, part of the electromagnetic radiation.
In the transmitting end, the antenna transforms the electric current into radio waves. Then in the receiving end, the antenna transforms these radio waves back into electric current and to voice that can be heard from the phones speaker. When the radio waves goes from the phone, they don’t go directly to the person you're calling to. Instead the phone connects to a link tower which then connects forward to another link and then finally to the phone you’re calling to.
By: Iiro Sivula, Janne Järvinen & Hester Verwej
References:
ftp://cm.bell-labs.com/cm/amg/Physics_Com_wFig.pdf
http://astarmathsandphysics.com/o-level-physics-notes/o-level-physics-notes-the-telephone.html
http://www.connected-earth.com/Learningresources/Howitworks/Telephone/Howthetelephoneworks/index.htm
http://en.wikipedia.org/wiki/Telephone
http://electronics.howstuffworks.com/telephone.htm
http://en.wikipedia.org/wiki/Microphone
http://en.wikipedia.org/wiki/Sound
http://en.wikipedia.org/wiki/Telephone