Natural frequency measurement of magnetic markers

An electronic article surveillance (EAS) system, comprising:

• an antenna for capturing signals generated in an interrogation zone of said EAS system during successive receive windows of a transmit and receive sequence, said captured signals from said interrogation zone including noise and, when at least one of a plurality of markers is present in said interrogation zone, a ring down signal with a characteristic frequency generated by said at least one marker responsive to a magnetic field transmitted into said interrogation zone;
• a receiver coupled to said antenna having a first signal processor for extracting amplitude information and frequency information from said captured signals, said frequency information including a measured time duration of a portion of an IF waveform signal produced as a result of said ring down signal, said measured time duration proportional to said characteristic frequency;
• and,
• a detector responsive to both said amplitude information and said frequency information for validating when said at least one marker is in said interrogation zone.