RE: TLDs as Anti-Theft Devices?

[Rogers Brent <Brent.Rogers@environment.nsw.gov.au>]

Interesting reading about these gadgets.  Even more interesting to me is

what happens when I set one of these off (I'd need all my fingers and toes

to count the times).  The store clerks have just sent me on my way, with an

exasperated look on their face that says "Not again".  This would seem to

suggest that somewhere in the process of activating the devices,

deactivating the devices at the register and actually clearing the door on

the way out results in enough false-positives that store employees usually

can't be bothered to check things out.





Brent Rogers

Sydney Australia 





 -----Original Message-----

From: 	John_Sukosky@DOM.COM [mailto:John_Sukosky@DOM.COM] 

Sent:	Friday, 5 November 2004 1:27 PM

To:	radsafe@list.vanderbilt.edu

Subject:	RE: TLDs as Anti-Theft Devices?



I found an explanation (at howstuffworks.com) of the physics for these

tag-and-alarm systems, better known as electronic article surveillance

(EAS).  All EAS systems work in essentially the same way: Tags or labels

with certain characteristics are affixed to product and activated; at store

exit areas, a transmitter sends a signal to a receiver, creating a zone

that detects tags that have not been deactivated at a register; when an

active tag enters the zone, it sets off an alarm. But the systems use

varying methods and levels of detection. I've seen a report that says

WalMart uses EAS system #3 listed below, the acoustomagnetic system (I

haven't been able to find the specific EAS system used by Kmart and Home

Depot).  Acoustomagnetic systems use a transmitter that sends a signal at

58 kHz in pulses. The tag responds to the pulse. If certain characteristics

are present, it creates an alarm.  Anyone care to venture what

characteristics are present in a TLD that would create an alarm on an

acoustomagnetic EAS system?



John M. Sukosky, CHP

Dominion

Surry Power Station

(757)-365-2594 (Tieline: 8-798-2594)





Three types of EAS systems dominate the retail industry:



1) Radio Frequency (RF) Systems are the most widely used systems in the

United States today and RF tags and labels are getting smaller all the

time. A label that contains a miniature, disposable electronic circuit and

antenna is attached to a product. The label responds to a specific

frequency emitted by a transmitter antenna (usually one pedestal of the

entry/exit gate). The response from the label is then picked up by an

adjacent receiver antenna (the other pedestal). This processes the label

response signal and will trigger an alarm when it matches specific

criteria. The distance between the two gates, or pedestals, can be up to 80

inches wide. Operating frequencies for RF systems generally range from 2 to

10 MHz (millions of cycles per second); this has become standard in many

countries. Most of the time, RF systems use a frequency sweep technique in

order to deal with different label frequencies.





2) The Electromagnetic (EM) system, which is dominant in Europe, is used by

many retail chain stores, supermarkets and libraries around the world. In

this technology, a magnetic, iron-containing strip with an adhesive layer

is attached to the merchandise. This strip is not removed at checkout --

it's simply deactivated by a scanner that uses a specific highly intense

magnetic field. One of the advantages of the EM strip is that it can be

reactivated and used at a low cost. What most people refer to as an

electromagnetic tag is actually a metal wire or ribbon that has high

permeability, making it easy for magnetic signals to flow through it. A

magnetized piece of semi-hard magnetic material (basically, a weak magnet)

is put up next to the active material to deactivate it. When you magnetize

the semi-hard material, it saturates the tag and puts it in its inactive

saturated state.



The EM system works by applying intensive low frequency magnetic fields

generated by the transmitter antenna. When the strip passes through the

gate, it will transmit a unique frequency pattern. This pattern is, in

turn, being picked up by an adjacent receiver antenna. The small signal is

processed and will trigger the alarm when the specific pattern is

recognized. Because of the weak response of the strip, the low frequency

(typically between 70 Hz and 1 kHz) and intensive field required by the EM

system, EM antennas are larger than those used by most other EAS systems.

The maximum distance between entry pedestals is 40 inches. Also, because of

the low frequency here, the strips can be directly attached to metal

surfaces. That's why EM systems are popular with hardware, book and record

stores. (Check out the patent for more details!)



Magnet-based systems have a small wire or metal strip hidden in the tag.



3) Another magnetic technology is the acousto-magnetic system, which has

the ability to protect wide exits and allows for high-speed label

application. It uses a transmitter to create a surveillance area where tags

and labels are detected. The transmitter sends a radio frequency signal (of

about 58 kHz) in pulses, which energize a tag in the surveillance zone.

When the pulse ends, the tag responds, emitting a single frequency signal

like a tuning fork. While the transmitter is off between pulses, the tag

signal is detected by a receiver. A microcomputer checks the tag signal

detected by the receiver to ensure it is at the right frequency, is

time-synchronized to the transmitter, and that it is at the proper level

and the correct repetition rate. If all these criteria are met, the alarm

occurs.

In each case, an EAS tag or label is attached to an item. The tag is then

deactivated, or taken from an active state where it will alarm an EAS

system to an inactive state where it will not flag the alarm. The

disposable tag is deactivated by swiping it over a pad or with a handheld

scanner that "tells" the tag it's been authorized to leave the store. If

the item has not been deactivated or detached by the clerk, when it is

carried through the gates, an alarm will sound.



howstuffworks.com



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