The acousto-magnetic system, which has the ability to protect wide exits with high tag detection, uses a transmitter to create a surveillance area where tags and labels are detected. The transmitter sends a radio frequency signal (of about 58 kHz) in pulses, which energize a tag in the surveillance zone. When the pulse ends, the tag responds, emitting a single frequency signal like a tuning fork. 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, is time-synchronized to the transmitter, at the proper level and at the correct repetition rate. If all these criteria are met, the alarm occurs.
Because AM systems are suited to protecting merchandise with a high metal/foil content, AM systems are commonly found in consumer electronic, hardware and pharmacies. AM systems are also suited for apparel stores because they cover wider entrances with fewer detection systems. Hard Tags are traditionally smaller and lighter than other technologies.
Radio Frequency (RF) Systems are widely used, as RF tags and labels are getting smaller all the time. RF EAS system works like this: A label -- basically a miniature, disposable electronic circuit and antenna -- attached to a product responds to a specific frequency emitted by a transmitter antenna (usually one pedestal of the entry/exit gate). The response from the label is then picked up by a receiver antenna. This processes the label response signal and will trigger an alarm when it matches specific criteria. Operating frequencies for RF systems generally range from 2 to 10 MHz (millions of cycles per second); this has become standard in many countries. Most of the time, RF systems use a frequency sweep technique in order to deal with different label frequencies.
Due to the lower cost of RF systems, they are better suited to retailers with large quantites of merchandise which requires a flat paper label that can even be printed on, such as supermarkets, discount stores, pharmacies and video stores. This is a more cost effective option for apparel stores.
The Electromagnetic (EM) system, which is dominant in supermarkets and libraries around the world. In this technology, a magnetic, iron-containing strip with an adhesive layer is attached to the merchandise. This strip is not removed at checkout -- it's simply deactivated by a scanner that uses a specific highly intense magnetic field. One of the advantages of the EM strip is that it can be re-activated and used at a low cost.
Also, because of the low frequency here, the strips can be directly attached to metal surfaces. That's why EM systems are popular with hardware, book and record stores.