Electronic article surveillance

A retail security label is part of an article surveillance system at retail. Attached to the goods it provides that in case of theft, either alarm is triggered or the goods are unusable. Security labels are removed or deactivated during regular payment process.

History

In the Federal Republic of Germany in late 1987 new electronic article surveillance labels were used. The label had a circumference of 62 × 19 mm and was also the pricing. When leaving the security area formed by locks it triggers a visual and / or audible alarm when it has not been previously disabled. 1987 were only 20 to 30 percent of a department store range are secured, including, mainly textiles and leather goods for more products labels were far too large and uncertain.

Mechanical security tag

Mechanical labels often include a color cartridge. They can only be removed with a special tool or a considerable amount of time. In the illustrated system, which is usually in a counter built-in strong magnet that retracts the inner sheet metal shields against the spring force and a clamped between the balls retainer pin releases. Are they broken up by force, the color cartridge emptied. Textiles are discolored in this way and make it unusable. Mechanical safety labels may prevent a repeat theft. Often mechanical safety labels also contain a coil and a RFID chip as a possible combination of mechanical and electronic security systems.

Electronic article surveillance label

An electronic article surveillance tag of an electronic article surveillance system (EAS ) triggers when approaching the secured item to an antenna of an alarm. Antenna systems for detection are usually located between the cash register and exit of the store to report unpaid goods. Modern security labels are activated and deactivated by the cashier.

The trend in retail security is to integrate the appropriate security elements already directly in the product or product packaging. This so-called source fuse restricts the manipulation and reduces the cost of installation.

There are currently four different electronic security systems on the market. There are radio-frequency, electromagnetic, high frequency and acousto-magnetic EAS systems.

Radio frequency resonance method

The picture shows a so-called RF tag. On the top side it bears a EAN ( European Article Number). On the back of a silvery coil can be seen, this is a coil which serves as the antenna at the same time. The blue bar in the picture connects the beginning and end of the coil with a capacitor. Coil and the capacitor form a resonant circuit with the tag characteristic resonant frequency.

In an external high-frequency electromagnetic field that is tuned to its resonant frequency - typically 8.2 MHz - the resonance circuit cut off the system and transmission power is detected (see resonant absorption and dipmeter ). The field generating system for detecting installed after checkout in the output area. After purchasing the product, the label must be disabled in order to trigger any false alarm. Either this is done mechanically ( the label is removed, cutting the coil) or electric ( inducing high voltages which can change the capacitor irreversible and thus the resonant circuit of tune ).

RF labels have some disadvantages, such as their size and their low selectivity. Including various mobile electronic devices such as hearing aids, radios or mobile phones can randomly display with their electrical circuits resonant circuits on the detection frequency. In such cases, an undesirable false alarm. Unfavorable orientation relative to the antenna or a manipulative shield by metal effect that only 70 percent of the active labels are detected. This argues against their safety function. By the shielding of the magnetic field no longer reaches the label coil and the resonant circuit is no longer excited, so that the label of the detection system will not be visible. The reason for this is here, among others, the eddy current effect.

Once disabled, they can not be used again. The advantage of RF tags is their low price.

In addition, there are also the so-called hard tags. They are designed as a cone-shaped plastic objects, which can be found via a safety pin preferably in textile products. In you is one of a core of a ribbon cable parabolic wound and then hot pressed coil with a ceramic capacitor located at their ends. These labels are over flat clear position-insensitive. This type of label is removed after the purchase at the box office, making it reusable.

The safety pin makes it the thief seemingly impossible at first to remove the label. In fact, such hard tags can be removed with a simple but sufficiently strong magnet. Due to the applied magnetic balls are that hold the safety pin on a spring force, retired and passed the needle free. Thus, this system represents only a false sense of security

Electromagnetic method

The picture shows two labels of the so called electromagnetic method (EM - label ). The long metal strip in the top picture is partially obscured by short strips that have slipped out of position. Below it is embedded in paper and recognizable as light gray shading. The metal strip is composed of a leichtmagnetisierbaren alloy. In a sinusoidal alternating magnetic field with a frequency of 10 Hz to 20 kHz it reaches its saturation magnetisation. The steep flanks of the magnetization generate harmonics in the alternating field, which can be readily detected.

EM- labels can enable and disable reversible. The short metal strip to see in the picture above, are magnetically hard and unmagnetized in the active state. To disable the label they are liberated from a magnetic field, which they themselves are magnetic. Then press and hold the soft magnetic long metal strip into saturation, then a reversal of magnetization by an external field can no longer follow.

Harmonic systems

Just as the acousto-magnetic systems are harmonious systems of amorphous metal strips. The term is derived from the vibrations which generate the labels. The transmitter in a stationary detection unit continuously transmits a fundamental and receives the harmonics generated by the label. Through their analysis can be determined whether there is an active label is in the sphere of influence of the detection system.

The metal strip with these systems is up to 10 cm long and 2 mm wide and has permanent-magnetic properties with shorter strips, which are incorporated during manufacturing. Depending on the geometric arrangement of the hard magnetic properties of the metal strip is obtained in the range of a typical harmonic arrangement that can be analyzed.

Also, the label can be enabled or disabled as needed magnetically: In active label these strips are demagnetized at label disabled, the hard magnetic structures are magnetized and thus shift the spectral distribution of the harmonics.

While in this system, only a strip of metal is required, although more than outweigh article surveillance system, the following disadvantages:

• A length of up to 10 cm long strip of metal is too high for many products.
• The elaborate structure of the amorphous metal strip in combination with hard- magnetic portions drives the price per label into the air.
• The necessary receiving antennas must be very closely situated and allow only one lock maximum width of 1 m.

The benefits include:

• The lighter feasibility of selective systems. Different arrangements of the hard magnetic sections along the metal strip, other arrangements of the pattern of harmonics, which can be used to distinguish, for example, result in different product groups.
• The very thin labels, as these consist only of the 0.02 mm thin metal strip and need not be installed in a plastic carrier box.
• The insensitivity kinks in the metal band.

Harmonic security systems are mainly in the range of libraries for securing the stock of books in open stacks for use.

Acousto-magnetic method

In the left image a acousto-magnetic tag is seen ( AM label ), which had already incorporated the manufacturer in the context of source tagging in a Textilschildchen. If you cut on the label, right picture, arrive at the so-called current DR labels two ( older so-called LE- labels ) loosely inserted (r ) amorphous (r ) metal strip to light. The third metal strip, seen in the picture the front, holding a plastic sheet at a distance from the loose strips. In an alternating magnetic field, the amorphous metal strip advised by magnetostriction (contraction in the magnetic field ) into mechanical vibrations. At resonance, they vibrate briefly on, even if the external field is interrupted. The ringing in turn, generates an alternating magnetic field, register the antennas from the outside.

The resonant frequency of the metal strip, and thus the frequency of the alternating magnetic field is typically 58 kHz, and the break frequency at about 45 Hz, the alternating field is switched off after 2 ms. 5 ms try the antennas to detect ringing signals to broadcast after another 15 ms again for 2 ms, the alternating magnetic field.

The integral with the housing third (second in LE Etikektten ) metal strip consists of a magnetically hard material. If it is magnetic, the mechanical resonance frequency coincides with that of the alternating magnetic field, the tag is active. A demagnetization of the metal strip tune the label, it is disabled. Unlike EM- labels you can choose it here if an AM - label should be enabled or disabled in magnetization. Determining the resonant frequency followed by the consideration that for a potential thief demagnetization significantly more difficult to achieve than the magnetization.

RFID process

While the labels above tell only one bit of information, namely, activated or deactivated, an RFID tag can for example send a stored number, which is often not only for the group, but for the individual products. The receiving system can therefore compare this number with the read number when paying or drawn from them logistical information.

The label consists of an antenna with a resonant circuit, and a microchip. The resonant circuit provides the microchip via the RF radiation of the detection system with energy. The same data between the microchip and the detection device are transmitted. The RFID chip stores often also own data, in the simplest case, the information "paid" in the deactivation at checkout.

However, these chips can be read even after payment of the goods and leave the business, which, depending on the stored data can be a privacy issue.