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An Overview of The Technologies
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What is EAS?
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Electronic Article Surveillance (EAS) is an
anti-theft system that protects merchandise from
illicit removal from a retail establishment. An
EAS system has three basic components:1)
tags-electronic sensors that are attached to
merchandise; 2) deactivators and detachers-used
to remove or inactivate the tags; and 3) systems
that detect the tags at store exits.
The EAS process begins by attaching tags to
merchandise. When an item is purchased, the tag
is removed or deactivated. If merchandise with
an active label or hard tag is carried past the
detection system, the system alarm sounds.
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How EAS Systems Work
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EAS
systems operate from a simple principle regardless
of the manufacturer or the specific type of
technology used: a transmitter sends a magnetic or
radio frequency signal at defined frequencies to a
receiver. This creates the system detection zone.
Upon entering the zone, an EAS tag creates a
disturbance, which is detected by the system
receiver.
By design the disturbed signal created by the tag
and detected by the receiver is distinctive and not
likely to be created by natural circumstances. The
tag is the key element, for it must create a unique
signal to avoid false alarms. The disturbance caused
by the tag creates an alarm that may indicate a
shoplifting event.
EAS systems range from very low magnetic frequencies
through the radio frequency range. These different
frequencies play a key role in establishing the
features that affect operation. |
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How Acousto-Magnetic (AM) Technology Works |
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Acousto-Magnetic
systems transmit a magnetic frequency signal at 58
kHz in a pulsed pattern. The transmit signal
energizes an acousto-magnetic tag in the detection
zone. When the transmit signal pulse ends, the tag
responds, emitting a single very distinctive
frequency signal. The tag signal is at the same
frequency as the transmitter signal. |
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While the
transmitter is off between pulses, a narrow band
receiver detects the tag signal. A microcomputer
checks the tag signal detected by the receiver to
ensure it is at the right frequency and defined
characteristics, occurs at a precise point in time
synchronized to the transmitter, at the proper
level, and at the correct repetition rate. If all of
these criteria are met several times in a row, an
alarm occurs. This unique tag signature and the
large tag signal produce the Acousto-Magnetic
technology's wide surveillance coverage, high tag
detection rate, and immunity to false alarms. |
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How Electromagnetic Technology Works
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The
electromagnetic system (EM) creates a low frequency
electromagnetic field. The field continuously varies
in strength and polarity, repeating a cycle from
positive to negative and back to positive again. |
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In
response to the changing magnetic field created by
the transmitter, the magnetic field of the tag
material abruptly "switches" as the field strength
varies past a particular point, whether positive or
negative. This abrupt change in the tag material
generates a momentary signal that is similar to the
systems fundamental frequency. Using electronic
signal processing techniques, the system identifies
the harmonics and causes an alarm. |
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How Swept-RF Works
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Swept-RF
uses a transmitter to create a detection zone where
tags are detected. The transmitter sends a signal
that varies between 7.4 and 8.8 MHz (millions of
cycles per second), which is why it is called swept;
it sweeps over a range of frequencies.
The transmitter signal energizes the swept-RF tag,
which is composed of a circuit containing a
capacitor and a coil, both of which store electrical
energy. When connected together in a loop, the
components can pass energy back and forth or
"resonate." |
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The tag
responds by emitting a signal that is detected by a
wideband receiver, meaning a receiver that monitors
for signals over a wide frequency range; for swept-rf
systems the bandwidth is typically about 1,400,000
Hz. By detecting a phase difference between these
two signals, the receiver recognizes the presence of
a tag, and it alarms. |
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