The problem
Condenser microphones needed a bulky external bias supply, making them costly and impossible to miniaturise.
The innovation
A polymer film holding a permanent electrostatic charge, removing the need for an external bias voltage.
How it worked
The permanently charged electret film acts as its own bias source; sound vibrates it against a backplate, generating the signal.
Why it mattered
Microphone cost collapsed and size shrank to millimetres.
The legacy
Billions of units: telephones, hearing aids, laptops, headsets, smart speakers.
You use this today
The microphone in the phone in your pocket.
Sources
US Patent 3,118,022
Primary record
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