Modified EAS tag used as a resistive sensor platform

Abstract

In this article, a modified design of an RF Radio Frequency Electronic Article Surveillance (EAS) tag, used as a sensor platform, is manufactured and characterized. EAS tags are passive devices consisting of a capacitor and coil, tuned to a resonance frequency readable by the detector equipment, in this case 8.2 MHz. They were originally used to detect whether merchandise was being moved through the detection gates at shop exits, in which case an alarm was triggered. If the capacitance is divided in two and a resistive sensor device inserted in between, the resonant Inductor-Capacitor (LC) circuit becomes an Inductor-Capacitor-Capacitor-Resistor LCCR circuit and can be used as a sensor tag. A high sensor resistance means that one capacitor is decoupled, leading to one resonance frequency, while a low resistance will couple both capacitances into the circuit, resulting in a lower resonance frequency. Different types of resistive sensors exist that are able to detect properties such as pressure, moisture, light and temperature. The tag is manufactured in Aluminum foil on a polyetylentereftalat (PET) substrate, resulting in a cost effective RF-platform for various resistive sensors. Two types of tags are designed and manufactured, one with parallel plate capacitors and the other with interdigital capacitors. To test the tags, a resistive tilt sensor is mounted and the tags are characterized using a network analyzer. It is shown that for high resistance, the tags have a resonance frequency of morethan 10 MHz while for low values the frequency approaches 8.2 MHz.