Common EAS Systems

EAS Systems generally fall into 3 categories:

1 Acousto-Magnetic - commonly referred to as; AM Systems.

2 Radio Frequency - commonly referred to as; RF Systems

- the most popular system for supermarkets and other checkout based retailers

3 Electromagnetic - commonly referred to as; EM Systems

- once popular with retailers of small products, such as; pharmacies, CD & DVD retailers . .

- today, EM System sales are almost exclusively limited to Book Lending Libraries

Acousto-Magnetic Technology Works – AM Systems

Acousto-magnetic EAS systems use a transmitter to create a surveillance area where tags and labels are detected. The transmitter sends a radio frequency signal at a frequency of 58 kHz (thousands of cycles per second), but the frequency is sent in pulses. The transmit signal energizes a tag in the surveillance zone. When the transmit signal pulse ends, the tag responds, emitting a single frequency signal like a tuning fork. The tag signal is at about the same frequency as the transmitter signal.

While the transmitter is off between pulses, the tag signal is detected by a receiver. A microcomputer checks the tag signal detected by the receiver to ensure it is at the right frequency, occurs in time synchronized to the transmitter, at the proper level, and at the correct repetition rate. If the criteria is met, an alarm occurs.

Electromagnetic Technology Works – EM Systems

The electromagnetic EAS system creates a low frequency electromagnetic field (fundamental frequencies between 70 Hz and 1 kHz are typically used) between two pedestals at an exit or checkout aisle. The field continuously varies 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 changes.

In response to the changing magnetic field created by the transmitter, the magnetic field domain of the tag material abruptly "switches" as the field strength varies past a particular point, whether positive or negative, during each half of the transmit cycle. This abrupt change in the magnetic state of tag material generates a momentary signal that is rich in harmonics (multiples) of the fundamental frequency. Using electronic signal processing techniques, the system identifies 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 the criteria are met an alarm occurs.

How Swept-RF Works – RF Systems

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 often called swept; it sweeps over a range of frequencies.

The transmitter signal energizes the 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.

More advanced RF Systems, emit a low-energy RF pulse, which "listens" for the tag. This technology, known as Digital Signal Processing, pulse based systems are meant to be more accurate and less susceptible to false alarms.