Electronic Article Surveillance (EAS)
What is EAS?
Electronic Article Surveillance (EAS) is an anti-theft system that protects merchandise from illicit removal from a retail establishment. An EAS system has three basic components:1) tags-electronic sensors that are attached to merchandise; 2) deactivators and detachers-used to remove or inactivate the tags; and 3) systems that detect the tags at store exits.
The EAS process begins by attaching tags to merchandise. When an item is purchased, the tag is removed or deactivated. If merchandise with an active label or hard tag is carried past the detection system, the system alarm sounds.
How EAS Systems Work
EAS systems operate from a simple principle regardless of the manufacturer or the specific type of technology used: a transmitter sends a magnetic or radio frequency signal at defined frequencies to a receiver. This creates the system detection zone. Upon entering the zone, an EAS tag creates a disturbance, which is detected by the system receiver.
By design the disturbed signal created by the tag and detected by the receiver is distinctive and not likely to be created by natural circumstances. The tag is the key element, for it must create a unique signal to avoid false alarms. The disturbance caused by the tag creates an alarm that may indicate a shoplifting event.
EAS systems range from very low magnetic frequencies through the radio frequency range. These different frequencies play a key role in establishing the features that affect operation.
How Acousto-Magnetic (AM) Technology Works
Acousto-Magnetic systems transmit a magnetic frequency signal at 58 kHz in a pulsed pattern. The transmit signal energizes an acousto-magnetic tag in the detection zone. When the transmit signal pulse ends, the tag responds, emitting a single very distinctive frequency signal. The tag signal is at the same frequency as the transmitter signal.
While the transmitter is off between pulses, a narrow band receiver detects the tag signal. A microcomputer checks the tag signal detected by the receiver to ensure it is at the right frequency and defined characteristics, occurs at a precise point in time synchronized to the transmitter, at the proper level, and at the correct repetition rate. If all of these criteria are met several times in a row, an alarm occurs. This unique tag signature and the large tag signal produce the Acousto-Magnetic technology's wide surveillance coverage, high tag detection rate, and immunity to false alarms.
How Electromagnetic Technology Works
The electromagnetic system (EM) creates a low frequency electromagnetic field. The field continuously varies in strength and polarity, repeating a cycle from positive to negative and back to positive again.
In response to the changing magnetic field created by the transmitter, the magnetic field of the tag material abruptly "switches" as the field strength varies past a particular point, whether positive or negative. This abrupt change in the tag material generates a momentary signal that is similar to the systems fundamental frequency. Using electronic signal processing techniques, the system identifies the harmonics and causes an alarm.
How Swept-RF Works
Swept-RF uses a transmitter to create a detection zone where tags are detected. The transmitter sends a signal that varies between 7.4 and 8.8 MHz (millions of cycles per second), which is why it is called swept; it sweeps over a range of frequencies.
The transmitter signal energizes the swept-RF tag, which is composed of a circuit containing a capacitor and a coil, both of which store electrical energy. When connected together in a loop, the components can pass energy back and forth or "resonate."
The tag responds by emitting a signal that is detected by a wideband receiver, meaning a receiver that monitors for signals over a wide frequency range; for swept-rf systems the bandwidth is typically about 1,400,000 Hz. By detecting a phase difference between these two signals, the receiver recognizes the presence of a tag, and it alarms.
