Physics trivia

Microphones work

Microphones are equipment that transform sound energy into electrical energy, and this occurs through electromagnetic induction processes.

Microphones are devices that convert sound energy into electrical energy.
Microphones have the purpose of transforming sound waves into electrical signals , which will be directed to amplifiers, recorders or some other type of equipment. In other words, microphones are electroacoustic transducers, that is, they transform the energy from sound waves into electrical energy .

Existing in various formats and types, these equipments are widely used in our daily lives for recording voice and musical instruments, to amplify the voice of a speaker in front of a large audience and to capture the voice in devices such as cell phones.

Basic operating principle

Electromagnetic induction is the physical principle involved in the functioning of the microphone. Simply put, this concept states that the variation of the magnetic flux through a loop will produce an electric current , called induced current.

Sound is a type of mechanical wave , which propagates through the compression and rarefaction of molecules in the medium Naturally, sound vibrations cannot stimulate electrical circuits , so when they reach a microphone, sound waves collide with membranes that are attached to coils, for example. The coils attached to the membranes are close to a magnet , so when they receive the sound waves, they will vibrate around the magnet so that the magnetic flux is variable. The variation of magnetic flux generates an electric current that will follow the vibration patterns of sound waves.

Some other microphone types are described below:

  • Charcoal microphone: This is the oldest type of microphone. The membrane makes contact withcoal, and when sound waves make the membrane vibrate, the coal grains change their positions, generating a change in the material’s resistance, which produces a variable electrical current.
  • Piezoelectric microphone: Sound waves cause the deformation of piezoelectric substances such as barium titanate. Always when deformed, these substances produce electric currents proportional to the deformations suffered.
  • Electret microphone : Similar to piezoelectric materials, substances called electrets are charged with static electricity when undergoing mechanical deformation. In electret microphones, these substances are used in the formation of vibrating membranes, generating electrical currents when struck and deformed by sound waves.

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