Magnetomechanical electronic article surveillance system and method using sideband detection

A method of enhancing the detection of a magnetomechanical electronic article surveillance (EAS) marker of a type having a magnetostrictive ferromagnetic member that resonates at a preselected frequency when exposed to a biasing magnetic field, comprising:

• transmitting a first signal alternating at a first frequency and a second signal alternating at a second frequency, said second frequency being lower than said first frequency;
• providing an EAS marker comprising a magnetostrictive ferromagnetic member adapted to resonate at said first frequency when biased by a magnetic field, wherein said second signal modulates the resonance about said first frequency forming and radiating a sideband of said first signal when said marker is exposed to said first signal and said second signal;
• and,
• detecting said sideband.

A magnetomechanical electronic article surveillance (EAS) system, comprising:

• means for transmitting a first carrier signal alternating at a first frequency and a plurality of second modulation signals alternating at a plurality of second frequencies, said plurality of second frequencies all being lower than said first frequency, each of said second plurality of signals being transmitted into a respective zone;
• an EAS marker comprising a magnetostrictive ferromagnetic member adapted to resonate at said first frequency when biased by a magnetic field, wherein each of said second plurality of signals modulates the resonance about said first frequency forming and radiating a sideband of said first signal when said marker is exposed to said first signal and each of said second signals;
• and,
• means for detecting said sideband and determining from said sideband which of said plurality of second signals was received by said marker and which zone said marker was in when detected.

A method of enhancing the detection of a magnetomechanical electronic article surveillance (EAS) marker of a type having a magnetostrictive ferromagnetic member that resonates at a preselected frequency when exposed to a biasing magnetic field, comprising:

• transmitting a first carrier signal alternating at a first frequency and a plurality of second modulation signals alternating at a plurality of second frequencies, said plurality of second frequencies all being lower than said first frequency, each of said second plurality of signals being transmitted into a respective zone;
• providing an EAS marker comprising a magnetostrictive ferromagnetic member adapted to resonate at said first frequency when biased by a magnetic field, wherein each of said second plurality of signals modulates the resonance about said first frequency forming and radiating a sideband of said first signal when said marker is exposed to said first signal and each of said second signals;
• detecting said sideband;
• and,
• determining from said sideband which of said plurality of second signals was received by said marker and which zone said marker was in when detected.