Granted Patent
Utility
US 4,910,840 · App. 07/385,150
"Electroacoustic transducer of the so-called ""electret"" type, and a method of making such a transducer"
Inventors:
Adrianus Joseph Sprenkels, Piet Bergveld
Patented Case
View Patent ↗
Granted: Mar 27, 1990
Filed: Jul 26, 1989
Inventors
Adrianus Joseph Sprenkels
Piet Bergveld
Assignee (at issue)
Microtel, B.V.
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.