When a customer makes a purchase, the sales clerk will either de-activate the tag by swiping the item over a label deactivator pad (you may have seen these in use at your local library as well) or simply via a specialised barcode scanner. For this reason it is generally advised that the electronic tag be located within 3 inches of the EAN or UPC barcode appearing on the product, especially in products such as CD’s and DVD’s which are commonly fitted with EAS tags. In products where a ‘hard’ tag has been used – often in the case of clothing items and the like – the sales person uses a special detacher to remove the tag entirely. If the tag is not deactivated or removed, the tag will trigger the antenna to set off the alarm when carried through the gates.
Types of EAS system:
Electronic Article Surveillance systems come in Acousto-magnetic, RF (Radio Frequency), Magnetic and microwave varieties, designed for differing retail purposes. All EAS systems work on the basis of a defined frequency being emitted by the transmitter, which is picked up by a receiver. This means that a ‘surveillance area’ is created. The type of EAS system in place will dictate how large this area is. It may span just a narrow aisle at the check-out till or a very large shop exit in the case of supermarkets and the like. The differing EAS systems work on frequencies ranging from very low all the way up to radio frequency. For example, acousto-magnetic EAS tags respond to signals sent at 58 kHz (58 thousand cycles per second), whilst swept-RF (Radio Frequency) transmitters designed for very large surveillance areas, emit from 7.4 to 8.8 MHz – or 8.8 million cycles per second. When a tag comes into an area where it’s corresponding frequency is being emitted by the EAS transmitter, it becomes activated and will respond with a matching signal. The EAS receiver will pick this up, and then verify a match via a microcomputer. If the signals matches, the alarm goes off.
Magnetic systems work off of the basis of tags made of a strip of ‘amorphous’ metal. Unlike most metals, these amorphic metals have a disordered atomic-scale structure, unlike the normal crystalline structure. This means that it has a very low magnetic saturation value, and when combined with a ferromagnetic strip, the tag can be activated and de-activated through magnetisation. This makes this system very popular in libraries where items are returned and sent out often, in addition to being very low in cost. When demagnetized, the tag becomes active and emits a low frequency (10 – 1000 Hz) harmonic signal, which will be picked up by the electromagnetic receiver.
Acousto-magnetic systems work on a similar basis, however because they are thicker and more expensive they are seldom used in library situations, although they do provide better detection rates.In up-market clothing and shoe stores, more costly microwave systems may be employed. At the shop exit, two antennae are employed – one which emits a low frequency field, and one which emits a microwave field. These tags are permanently active and therefore need to be removed with a detacher at the counter. If a tag comes in range of the antennae, it will re-emit a combination of signals from both the low range and microwave fields, triggering the alarm.
When used in conjunction with your barcode numbers these systems provide an excellent way to reduce losses and discourage shoplifters, benefiting both the suppliers and the retail outlets using them.
By Cat Robinson