Saturday 6 October 2012

How EAS System Works ?

A lack of understanding about how Electronic Article Surveillance or EAS works is most often the downfall in achieving the best results. The information below will help you understand how it all works together for optimum results. 

What is an EAS System?

Electronic Article Surveillance (EAS) is a technological method for preventing shoplifting.

It usually involves three components:

  • Electronic Antenna
  • Deactivator or Detacher
  • Electronic Tag or label

Special tags and labels are fixed to merchandise. These tags or labels are removed or "deactivated" by the clerks when the item is properly bought or checked out. 

Labels are deactivate using a "Label Deactivator". 

While ringing up purchases a cashier should pass each product label across the "Deactivation Pad". 

To remove a Hard Tag a cashier uses a "Detacher" which releases the pin. 

After a label is deactivated or a tag is removed the customer can then pass by the antenna without any alarm.

At the exits of the store, a detection system sounds an alarm or otherwise alerts the staff when it senses active tags are passing by. 

Types of EAS systems and how they work.

There are several major types of electronic article surveillance systems :

  1. Radio Frequency (RFiD)
  2. Acousto-magnetic (AM)
  3. Microwave

Radio-frequency (RFiD) Systems 

These tags are essentially an LC tank circuit.

An LC circuit is a resonant circuit or tuned circuit that consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C that has a resonance 

In physics, resonance is the tendency of a system to oscillate at larger amplitude at some frequencies than at others. These are known as the system's resonant frequencies . At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system peak anywhere from 1.75 MHz to 9.5 MHz. The most popular frequency is 8.2 MHz. Sensing is achieved by sweeping around the resonant frequency and detecting the dip. Deactivation for 8.2 MHz label tags is achieved by detuning the circuit by partially destroying the capacitor.

A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force. This is done by submitting the tag to a strong electromagnetic. 

Electromagnetism is the physics of the electromagnetic field, a field that exerts a force on particles with the property of electric charge and is reciprocally affected by the presence and motion of such particles field at the resonant frequency which will induce voltages exceeding the capacitor's breakdown voltage. 

The breakdown voltage of an Insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive.The breakdown voltage of a diode is the minimum reverse voltage to make the diode conduct in reverse which is artificially reduced by puncturing the tags.


Acousto-magnetic (AM)

These tags are similar to magnetic tags in that they are made of two strips, a strip of magnetostrictive. 

Magnetostriction is a property of ferromagnetic materials that causes them to change their shape when subjected to a magnetic field. The effect was first identified in 1842 by James Joule when observing a sample of nickel called ferromagnetic. 

Ferromagnetism is the basic mechanism by which certain materials form permanent magnets and/or exhibit strong interactions with magnets; it is responsible for most phenomena of magnetism encountered in everyday life called amorphous metal. 

An amorphous metal is a metallic material with a disordered atomic-scale structure. In contrast to most metals, which are crystalline and therefore have a highly ordered arrangement of atoms, amorphous alloys are non-crystalline and a strip of a magnetically semi-hard metallic strip, which is used as a biasing magnet (to increase signal strength) and to allow deactivation. These strips are not bound together but free to oscillate mechanically.

Amorphous metals are used in such systems due to their good magnetoelastic coupling, which implies that they can efficiently convert magnetic energy to mechanical vibrations.

The detectors for such tags emit periodic tonal bursts at about 58 kHz, the same as the resonance.

In physics, resonance is the tendency of a system to oscillate at larger amplitude at some frequencies than at others. These are known as the system's resonant frequencies . At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system frequency of the amorphous strips. This causes the strip to vibrate longitudinally by magnetostriction, and will continue to oscillate after the burst is over. The vibration causes a change in magnetization in the amorphous strip, which induces an AC voltage in the receiver antenna. If this signal meets the required parameters (correct frequency, repetition etc.) the alarm is activated.

When the semi-hard magnet is magnetized, the tag is activated. The magnetized strip makes the amorphous strip respond much more strongly to the detectors, because the DC magnetic field given off by the strip offsets the magnetic anisotropy. 

Magnetic anisotropy is the direction dependence of a material's magnetic properties. A magnetically isotropic material has no preferential direction for its magnetic moment in zero field, while a magnetically anisotropic material will align its moment to an easy axis.-Sources of magnetic within the amorphous metal. The tag can also be deactivated by demagnetizing the strip, making the response small enough to that it will not be detected by the detectors.

These tags are thicker than other tags and are thus seldom used for books. However they are relatively expensive and have better detection rates (fewer false positives and false negatives) than RFiD tags.

Acousto-Magnetic EAS System

Microwave EAS Systems 

These permanent tags are made of a non-linear element called a Diode.

In electronics a diode is a two-terminal electronic component which conducts electric current asymmetrically or unidirectional; that is, it conducts current more easily in one direction than in the opposite direction. The term usually refers to a semiconductor diode, the most common type today, coupled to one microwave and one electrostatic antenna. 

At the exit, one antenna emits a low-frequency (about 100 kHz) field, and another one emits a microwave field. 

The tag acts as a mixer re-emitting a combination of signals from both fields. This modulated signal triggers the alarm. These tags are permanent and somewhat very costly. They are mostly used in clothing stores.

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