Electronic Article Surveillance (EAS)
An Overview of the Major Technologies

What is EAS?

Electronic Article Surveillance is a system that protects merchandise from theft. An EAS system has three components: 1) labels and hard tags—electronic sensors that are attached to merchandise; 2) deactivators and detachers—used at the point of sale to electronically deactivate labels and detach reusable hard tags as items are purchased; and 3) detectors that create a surveillance zone at exits or checkout aisles.

The EAS process begins by attaching labels or hard tags to merchandise. When an item is purchased, the label is deactivated or the hard tag is removed. However, if merchandise with an active label or hard tag is carried past the detector, an alarm sounds.

Over 800,000 EAS systems are installed worldwide, primarily in the retail market. This includes Apparel, Drug, Discount, Home Centers, Hypermarkets, Food, Entertainment, and Specialty stores.

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 signal at defined frequencies to a receiver. This creates a surveillance area, usually at a checkout aisle or an exit in the case of retail stores. Upon entering the area, a tag or label with special characteristics creates a disturbance, which is detected by the receiver. The exact means by which the tag or label disrupts the signal is a distinctive part of different EAS systems. For example, tags or labels may alter the signal by using a simple semi-conductor junction (the basic building block of an integrated circuit), a tuned circuit composed of an inductor and capacitor, soft magnetic strips or wires, or vibrating resonators.

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 in the electronic environment caused by a tag or label creates an alarm condition that usually indicate someone is shoplifting or removing a protected item from the area.

The nature of the technology dictates how wide the exit/entrance aisle may be. Systems are available that cover from a narrow aisle up to a wide mall store opening. Similarly, the type of technology affects the ease of shielding (blocking or detuning the signal), the visibility and size of the tag, the rate of false alarms, the percentage of detection rate (pick rate), and cost.

The physics of a particular EAS tag and resultant EAS technology determines which frequency range is used to create the surveillance area. EAS systems range from very low frequencies through the radio frequency range. Similarly, these different frequencies play a key role in establishing the features that affect operation.

How Swept-RF Works

Like other EAS technologies, swept-rf uses a transmitter to create a surveillance area where tags and labels 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 or label, which is composed of a circuit containing a capacitor and an inductor or coil, both of which store electrical energy. When connected together in a loop, the components can pass energy back and forth or "resonate." The frequency at which the circuit resonates is controlled by matching the storage capacity of the coil and capacitor. The tag responds by emitting a signal that is detected by a receiver.

In addition to the small tag signal, the receiver also responds to the much larger transmitter signal. By detecting a phase difference between these two signals, and other properties of the tag signal, the receiver recognizes the presence of a tag and generates an alarm.

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