An overview on the innovate loss prevention technology - Electronic Article Surveillance (EAS)

What is EAS?
Electronic Article Surveillance (EAS) or Source Tagging is an anti-theft system that protects merchandise from illicit removal from a retail establishment. The EAS process begins by attaching tags or labels to the merchandise. When an item is purchased, the tag is removed or the label is deactivated. If the merchandise with an active label or hard tag is carried past the detection system, the system alarm sounds.

AM tags are composed of two strips, a strip of magnetostrictive, ferromagmetic amorphous metal and a strip of magnetically semi-hard metallic strip. To increase the signal strength and permit detection or deactivation, they are unbounded together but free to oscillate mechanically. AM metals are of good magnetoelastic coupling that can transform magnetic energy to mechanical vibrations effectively.

EAS has three components:

1. Security tags or labels that attached to the merchandise
2. Detachers and deactivators used to remove tags or labels at the point of sale
3. Detection system which detects tags of labels at store exits

The EAS process starts from fixing security tags or labels to the merchandises. They are removed at cashiers when being bought out. At the exit of stores, there is a detection system to sound alarm alerting in case of unremoved or active tags.


Major types of EAS systems:

Acousto-Magnetic (AM) Technology
AM systems transmit a magnetic frequency signal at 58kHz in pulses which energize a tag in the detection zone. The tag responds when the pulse finishes, emitting a single frequency signal. The tag signal is at the same frequency as the transmitter signal.

While the transmitter is off between pulses, a receiver detects the tag signal. To ensure the correct frequency and features, a microcomputer is functioned to check the receiver's detection of tag signal. And occurring at an exact point in time synchronized to the transmitter, at the appropriate level and correct repetition rate. If all the above criteria are matched several times in a row, the alarm occurs. This unique tag signature and the large tag signal contribute to the wide detection coverage, high detection rate, and immunity to false alarms.

When the AM tag is demagnetized, it is deactivated. While it is magnetized, it is activated.


Radio Frequency (RF) Technology
RF labels have a resonance peak from 7.4 to 8.8MHz, sensing is achieved by sweeping around the resonant frequency and detection, this is why it is also called swept-RF.

The RF label is basically a miniature, disposable circuit (contain a capacitor and a coil to store electrical energy) and antenna. RF systems use a frequency sweep technique and the bandwidth is about 1,400,000 Hz. The label reacts when emitting a signal detected by a receiver, implying that the receiver monitors a wide frequency range. The label responses signal and will actuate an alarm if specific criteria are matched. The distance between the two pedestals can be up to 80 inches wide.

To implement the RF system, the label has a helical antenna etched from thin aluminum bonded to a piece of paper. At the end of the antenna, there is a small diode or RC network to emit a radio signal it receives. To disarm the label, a strong RF pulse (much stronger that the pedestals emit) blasts the label and burns out the diode or RC components. Between the pedestals, a burned out label does not emit a signal, so they let it passes without alarming.