What is EAS System?

(Note: The following article is quoted from a third party website called "en.wikipedia.org". You can click here to read the full articles)

Electronic Article Surveillance(EAS) is a technological method for preventing shoplifting from retail stores or pilferage of books from libraries. Special tags are fixed to merchandise or books. These tags are removed or deactivated by the clerks when the item is properly bought or checked out. At the exits of the store, a detection system sounds an alarm or otherwise alerts the staff when it senses active tags. For high-value goods that are to be manipulated by the patrons, wired alarm clips may also be used; these, being less common and technologically less mysterious, are not covered by this article.

Types of EAS

There are four major types of electronic article surveillance systems :

  • Magnetic, also known as magneto-harmonic
  • Acousto-magnetic, also known as magnetostrictive
  • Radio frequency
  • Microwave

Magnetic systems

These tags are made of a strip of amorphous metal (metglas) which has a very low magnetic saturation value. Except for permanent tags, this strip is also lined with a strip of ferromagnetic material with a moderate coercive field (magnetic "hardness"). Detection is achieved by sensing harmonics and sum or difference signals generated by the non-linear magnetic response of the material under a mixture of low-frequency (in the 10 Hz to 1000 Hz range) magnetic fields.

When the ferromagnetic material is magnetized, it biases the amorphous metal strip into saturation, where it no longer produces harmonics. Deactivation of these tags is therefore done with magnetization. Activation requires demagnetization. Due to the system being able to deactivate and re-activate this type of system is extremely suitable for libraries.

Due to the convenient dimensions of the tags, and their very low cost, this system is popular in libraries and retail stores.

Magnetic systems are often referred to as Electromagnetic (or EM) systems. EM systems rarely appear in retail environments outside of Europe.

Acousto-magnetic systems

These are similar to magnetic tags in that they are made of two strips, a strip of amorphous metal and a strip of ferromagnetic material. They differ in that these strips are not bound together but free to oscillate mechanically. Also the tag is active when the material is magnetized. The detectors use a 58 kHz (or 66 kHz) magnetic field which induces mechanical resonance by magnetostriction. When the excitating field is turned off, these tags continue to oscillate mechanically, which produces a magnetic signal because of the magnetized second strip. This signal triggers the alarm.

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

Radio-frequency systems

These tags are essentially an LC tank circuit that has a resonance peak anywhere from 1.75 MHz to 9.5 MHz. The most popular frequency is 8.2MHz. 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. This is done by submitting the tag to a strong electromagnetic field at the resonant frequency which will induce voltages exceeding the capacitors breakdown voltage, which is artificially reduced by puncturing the tags.

Microwave systems

These permanent tags are made of a non-linear element (a diode) 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 reemitting a combination of signals from both fields. This modulated signal triggers the alarm. These tags are permanent and somewhat costly. They are mostly used in clothing stores.