Patent ID: 6018296
Filing Date: 2000-01-25
Classification: C21D,C22C,G08B,H01F

Abstract:
A magnetomechanical electronic article surveillance system comprising:a marker comprising a bias element which produces a bias magnetic field H.sub.b and a resonator, said resonator formed by a planar strip of an amorphous magnetostrictive alloy having a composition Fe.sub.a Co.sub.b Ni.sub.c Si.sub.x B.sub.y M.sub.z wherein a, b, c, x, y, and z are at % and a+b+c+x+y+z=100, a+b+c>75, a>15, b<20, c>5 and z<3, wherein M is at least one element selected from the group consisting of C, P, Ge, Nb, Mo, Cr and Mn, said amorphous magnetostrictive alloy having a resonant frequency f.sub.r which is a minimum at a field strength H.sub.min and having a linear B-H loop up to at least a field strength which is about 0.8 H.sub.min and a uniaxial anisotropy perpendicular to the plane of said strip with an anisotropy field strength H.sub.k which is at least as large as H.sub.min and, when driven by an alternating signal burst in the presence of a bias field H.sub.b, producing a signal having an amplitude which is a minimum of approximately 50% of a maximum obtainable amplitude relative to said bias field H.sub.b in a range of H.sub.b between 0 and 10 Oe;transmitter means for exciting said marker for causing said resonator to mechanically resonate and to emit said signal at said resonant frequency;receiver means for receiving said signal from said resonator at said resonant frequency;synchronization means connected to said transmitter means and to said receiver means for activating said receiver means for detecting said signal at said resonant frequency at a time after said transmitter means excites said marker; andan alarm, said receiver means comprising means for triggering said alarm if said signal at said resonant frequency from said resonator is detected by said receiver means.