An electronic security system adapted for use in a controlled area such as a retail store and employing a multi-frequency resonant tag circuit having distinct frequencies for detection and discrimination. An electromagnetic field is provided within the controlled area at a frequency which is swept through...http://www.google.de/patents/US3967161?utm_source=gb-gplus-sharePatent US3967161 - A multi-frequency resonant tag circuit for use with an electronic security system having improved noise discrimination
A multi-frequency resonant tag circuit for use with an electronic security ...
