File:US Patent 3118022 - Gerhard M. Sessler James E. West - Bell labs - electroacustic transducer - foil electret condenser microphone 1962 1964 - pages 1-3.png
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![File:US Patent 3118022 - Gerhard M. Sessler James E. West - Bell labs - electroacustic transducer - foil electret condenser microphone 1962 1964 - pages 1-3.png](https://upload.wikimedia.org/wikipedia/commons/thumb/a/ad/US_Patent_3118022_-_Gerhard_M._Sessler_James_E._West_-_Bell_labs_-_electroacustic_transducer_-_foil_electret_condenser_microphone_1962_1964_-_pages_1-3.png/800px-US_Patent_3118022_-_Gerhard_M._Sessler_James_E._West_-_Bell_labs_-_electroacustic_transducer_-_foil_electret_condenser_microphone_1962_1964_-_pages_1-3.png?20070901090434)
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