Re: anti-theft strips

[brian whatcott <inet@INTELLISYS.NET>]

At 08:50 3/12/99 -0700, you wrote:
> Hi,
>        There is a 1 page article inside the back cover of the May 97
> Scientific American about these things.
>
>        The description goes like this.  The door unit transmits a pulsed
> 58 kHz radio.
> signal.  The antishoplifting stickon contains a resonator made of a
> magnetic material the right size to mechanically vibrate at 58 kHz.  The
> vibrating resonator produces its own 58 kHz radio signal.  So, the pulse
> from the door unit starts the device vibrating, the pulse stops, and then
> the door unit looks for a 58kHz signal.
>
> Thanks
> Roger Haar

Roger described an example of a hybrid technology system.
New England J Medicine carried a cautionary piece in Nov 6 1998
concerning the adverse effects to people with heart pacemakers who
pause in the near field of this kind of equipment.

This is a slightly shortened web note from a Dutch producer of such devices:
(CrossPoint)
----------------------------------------------------------------------------

Electronic Article Surveillance or EAS systems are becoming  widely
accepted as an effective means to eliminate theft.

Basically there are 3 types of systems which electronically detect theft
 at the exit of retail outlets.  All systems operate in conjunction with
 tags or labels attached to the product to be protected. Electronic or
electric components conceiled in the label will respond with a more or
less unique small signal when passing the EAS antenna('s):

 RF systems:
RF systems are the most common and widely applied systems.
A label which is attached to a product, will respond to a specific frequency
 emitted by a transmitter antenna. The response from the label is in turn
being picked up by an adjacent receiver antenna.
The label response signal is 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. 8.2 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 receiver antenna (RX).
In most cases RF systems use a frequency sweep technique in order to
cope with tolerances in label frequencies.
The so-called hard and soft labels which are attached to the products
have a special lock mechanism in order to remove the label only at the
cash register, by using a special detacher.
Other so-called paperlabels or stickertags are not removed from the
product but electrically destroyed by an electronic deactivator.
Sometimes both the receiver (RX) and transmitter (TX) are combined
in one antenna frame, a so-called Mono system, 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 separate 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 the centre of the antenna.
Mono systems are applied in conjunction with fine-tuned (hard) labels
which are slightly more expensive than normal labels 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 conjunction with
 paperlabels.



.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 receiver antenna, the small signal is being processed and
 will trigger an alarm when the specific pattern is being recognized.
In some cases transmitter and receiver are combined in both antennas
whereby alternating reception and transmission will provide a more
omnidirectional field which increases the detection hit-rate.
The EM strip is not removed at the cash register but simply deactivated
by a specific highly intensive magnetic field.
EM strips are insensitive 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 antennas are rather big when
 compared to other EAS systems. The maximum distance between two
antennas is limited to 1 meter (40").

.Electro-Acoustic systems:
Produced solely by Sensormatic USA, Electro-Acoustic systems will
activate a small label when passing an electromagnetic field, emitted
by a transmitter antenna.
The label will in turn start to resonate, thereby producing a particular
ultrasonic noise, which is consequently picked up and detected by
an adjacent receiver with an ultrasonic microphone.

brian whatcott <inet@intellisys.net>
Altus OK