Electromagnetic
or EM systems
A strip consisting of a alloy of magnetic and ferrous material with
an adhesive layer is attached to a product to be secured.
By applying intensive low frequency magnetic fields generated by
an EM transmitter antenna, the strip, when passing the field, will
transmit a unique frequency pattern, which is in turn being picked
up by an adjacent EM reciever antenna, the small signal is being
processed and will trigger an alarm when the specific pattern is
being recognized.
In some cases transmitter and reciever are combined in both antenna's
whereby alternating reception and transmission will provide a more
omnidirectional field wich increases the detection hit rate.
The EM strip is not removed at the cash register but simply deactivated
by a specific highly intensive magnetic fields.
EM strips are intensive to direct mounting on metal surfaces.
A unique feature of an EM strip is that it can be (re-) activated,
and in this way be used as a very low cost one bit read/write transponder,
applied in libraries.
Because of the weak response signal of the strip and due to the
low frequency and intensive field needed, EM antenna's are rather
big when compared to other EAS systems. The maximum distance between
two antennas is limited to 1 meter (40"). Radio Frequent or
RF systems:
RF systems are the most common and widely applied systems. A label
which is attached to a product, will respond to specific frequency
emitted by a transmitter antenna. The response from the label is
in turn being picked up by an adjacent reciever antenna. The label
response signal is being processed and will trigger an alarm when
it matches specific criteria.
The distance between the antenna's can in most cases be up to 2
meters (80").
Operating frequencies range from 2 till 10 MHz is the most widely
used frequency and has become more or less standard in most countries.
Most RF systems are so called dual systems using a separate transmitter
(TX) and reciever antenna (RX).
In most cases RF systems use a frequency sweep technique in order
to coop with tolerances in label frequencies.
The so called hard and soft lables which are attached to the products
have a special lock mechanism in order to remove the label only
at the each register, by using a special detached.
Other so called paperlables or stickertags are not removed from
the product but electrically destroyed by an electronic deactivator.
Sometimes both the reciever (RX) and transmitter (TX) are combined
in one antenna frame, a so called mono systems, whereby the system
can apply pulse or continuous sweep technique or a combination of
both . Pulse technique used in mono systems has the advantage that,
when using more than one transmitter no synchronization through
seperate coaxial cables is needed, resulting in easier installation.
An advantage of mono systems is that for small entries one antenna
will be sufficient, the area covered or detection zone is about
+ and -1 meter (+/-40") from center of the antennaa.
Mono systems are applied in conjuction with fine tuned (hard) lables
which are slightly more expensive than normal lables used with sweep
techniques. Mono systems are in general more direction sensitive
and have a lower sensitivity, decreasing slightly the detection
hit rate.
Because of tolerances and a lower (direction) sensitivity than dual
systems, mono systems are normally not applied in conjuction with
paperlabels.
Tag
Types:
- Mini Tag
- Wafer Tag
- Soft Tag
- Clip Tag
- 4x4 Sticky Labels
- Adhesiv Permanent
- Deactivateable.
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