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Electronic Article Surveillance – Fig 1
GB Patent Number: GB2500134
Granted to: Redcliffe Magtronics Limited
You’ve seen them before and you know what they do, but do you know what they’re called? By this I mean the tags attached to clothing and other high-value items which shop assistants remove at the till so that you don’t end up with alarm bells ringing as you leave. These tags form part of Electronic Article Surveillance (EAS) systems that are used to stem shoplifting or ‘shrinkage’ as it is known within the retail world.
In EAS, a tag is attached to an article and a detector is placed at the entrance of the shop. If an active tag passes in the proximity of the detector an alarm is sounded. In order to prevent triggering the alarm, the tag must be neutralised by the sales assistant.
There are two types of EAS tags. The first are always active and must be removed from the item at the point of sale. The second are deactivated at the point of sale, so that they can be innocuously taken out of the store whilst still attached to an item’s packaging.
UK patent no. 2500134, granted on 12 February 2014 to Redcliffe Magtronics Limited, focuses on the latter type of tag, known as acousto-magnetic or AM tags, which are relatively inexpensive and hence widely used.
The patent addresses the following scenario. You have completed your shopping, having successfully located the perfect outfit for that special occasion. You have then waited patiently at the till while the shop assistant waves the tag deactivator over your purchase. But as you leave the store, the alarm sounds and the next thing you know, a hand firmly lands on your shoulder and a stern voice asks you to make your way back to the sales counter. You are (naturally) embarrassed and silently vow never to return to the store again.
Wouldn’t it be better if, instead of the security guard making you traipse back to the till, the tag could be deactivated at the shop’s exit once your bona fides have been verified?
The issue here is that existing, hand-held deactivators are prone to triggering the alarm themselves. Redcliffe’s invention addresses this problem and mitigates any embarrassment caused by such false alarms.
AM tags contain two strips. The first strip is made of a magnetostrictive, ferromagnetic amorphous metal and the second strip is made of a magnetically semi-hard metallic strip.
Magnetostrictive materials change their shape or dimensions during the process of magnetisation, effectively converting magnetic energy into kinetic energy. You will be familiar with the magnetostrictive effect because this is what is responsible for the low-pitched buzzing sound that can be heard near transformers and on AC carrying transmission towers. The second strip is used to bias the first strip and also to allow deactivation. These two strips are not bound together but are free to oscillate mechanically.
Redcliffe’s invention provides a portable, hand-held EAS deactivator. In order to first detect an AM tag, the deactivator emits a signal comprising a pattern of bursts. The bursts typically contain 58kHz sinewaves of electromagnetic radiation, which is the resonance frequency of the magnetostrictive strip.
The bursts cause the magnetostrictive strip of a tag in close enough proximity to the deactivator to vibrate longitudinally.
When a tag is active, the magnetically semi-hard strip is magnetised which makes the magnetostrictive strip respond more strongly to the detection bursts emitted by the deactivator. The vibration of the magnetostrictive strip causes a change in its magnetisation that, in the presence of the magnetised second metallic strip, induces at the deactivator, a detectable signal. This matches, in terms of signal frequency and burst repetition, the detection signal emitted by the deactivator.
If a detected signal has the correct signal frequency and burst pattern, tag detection is declared, and in response the deactivator emits a decaying oscillating magnetic field which de-magnetises the magnetically semi-hard metallic strip of the tag. With the second metallic strip de-magnetised, the response of the first magnetostrictive strip to any subsequent detector is too small for it to be detected by that detector and the tag is thus deactivated.
In this way, the now frustrated and possibly embarrassed shopper can be quickly sent on their way with minimal fuss – problem solved!
Michael Jaeger is a patent attorney at leading UK patent and trade mark attorneys, Withers & Rogers LLP.
