Granted Patent
Utility
US 4,868,504 · App. 07/013,256
Apparatus and method for locating metal objects and minerals in the ground with return of energy from transmitter coil to power supply
Inventor:
David Johnson
Patented Case
View Patent ↗
Granted: Sep 19, 1989
Filed: Feb 9, 1987
Inventor
David Johnson
Assignee (at issue)
FLR, Inc.
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.