Article recognition and verification

A method of making a verifiable article which is to be detected by subjecting it to an alternating magnetic field to determine whether there is at least one specific harmonic response generated by interaction between the article and the field due to the non-linear response of the flux density with the applied field from randomly dispersed metal fibers of magnetic material associated with the article, said method comprising the step of selecting the magnetic material properties and the shape of the metal fibers so that they have a magnetic saturation field greater than 100 A/m so as to prevent triggering off electronic article surveillance (EAS) systems which also include magnetic fields, and incorporating said randomly dispersed metal fibers of magnetic material into the said article.

A system by which security articles can be verified, wherein authentic articles have incorporated therein randomly dispersed metal fibers of a selected magnetic material and of a selected shape, said randomly dispersed metal fibers being saturable by an alternating magnetic field thereby to generate at least one harmonic of a fundamental frequency of the alternating field;

• and wherein a sensor is provided, a first part of which generates a local alternating magnetic field to which articles as aforesaid are to be subjected for verification, and a second part of which generates by induction electric signals indicative of the response of the material making up the article to the said alternating field;
• a signal analysing device is provided, configured to determine if a particular harmonic or a spectrum of harmonics, is present in the generated signals;
• the selection of the said magnetic material and the selection of the said shape is restricted to metal fibers which require magnetic fields in excess of 100 A/m before they become saturated, to prevent authentic articles as aforesaid from triggering electronic articles surveillance alarms, and the first part of the sensor generates a local field of sufficient strength to saturate any such metal fibers if in close proximity to, or in contact with, the sensor.