Glossary: Electro-magnetic EAS

The electromagnetic EAS system creates a low frequency electromagnetic field between two pedestals at an exit or checkout aisle. The RFID equivalent returns a signal from a fixed or handheld interrogator. Frequencies between 70 Hz and 1 KHz are often used for electromagnetic EAS. The field is varied in strength and polarity, repeating a cycle from positive to negative and back to positive again. With each half cycle, the polarity of the magnetic field between the pedestals will change.

Responding to the changing magnetic field created by the transmitter, the magnetic field of the tag material switches as the field strength varies past a particular point, positive or negative, during each half of the transmit cycle. This sharp change in the magnetic state of tag material generates a momentary signal that is rich in harmonics (multiples) of the fundamental frequency. Electronic signal processing techniques are used to verify that the harmonics are at the right frequencies and levels, and that they occur at the proper time in relation to the transmitter signal. If this is the case, an alarm is triggered.

Electromagnetic EAS devices are the thinnest and fairly tolerant of bending and therefore the most suitable for thin packaging. However, they do not work with acoustomagnetic pedestals, the largest installed base and range is limited. They are the third most popular EAS technology and are losing market share.

Electromagnetic EAS employs wire (e.g. Confirm Technologies) or RF sputtered thin films of high permeability, low coercivity materials the same as that used for EAS (e.g. Flying Null). Flying Null uses the term Electromagnetic Identification EMID to distinguish it from mainstream RFID.

 

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