Multi-thread re-entrant marker with simultaneous switching

摘要

A marker for a harmonic electronic article surveillance system includes three wires of magnetic material arranged in parallel. The material has a magnetic hysteresis loop with a large Barkhausen discontinuity such that, upon exposure of the marker to an external magnetic field whose field strength in the direction opposing the instantaneous magnetic polarization of the marker exceeds a predetermined threshold value, there results a regenerative reversal of the magnetic polarization in the material. The three wires are coupled at opposite ends thereof by magnetic charge spreading elements formed of a highly permeable material so that all three wires exhibit the regenerative reversal simultaneously on exposure to the above-described magnetic field. The resulting harmonic marker can be formed with a substantially shorter over-all length than previously practical markers of the harmonic type while providing a signal of comparable amplitude.