A ferrite-filled cavity resonator for electronic article surveillance on metallic packaging (article)

Abstract

Conventional electronic article surveillance (EAS) tags are ineffective on metallic packaging. The component of RF magnetic field perpendicular to the surface of the packaging induces eddy currents that suppress the magnetic flux linking the inductive element of the tag. In this work an inductive quarter-wavelength planar cavity, formed by wrapping aluminum foil around a ferrite core, was extended by wrapping additional capacitive layers of foil/dielectric around the ferrite-filled central region. This so-called ‘wrapped tag’ exhibits the frequency, Q-factor, and read distance characteristics of existing EAS tags, but is instead driven by RF magnetic fields parallel to the surface of the metallic packaging. In this article we compare the observed frequency response of the wrapped tag with a simple LC-resonator model that takes account of the tag’s geometrical features, and use the model to describe how the design and construction of the tag can be optimized. Finite element method modeling is used to reveal how the current flows in the wrapped foil of the tag. Prototype tags show good reproducibility, demonstrating the potential of the design as a solution to the problem of tagging metallic packaging in the EAS industry.