Electro-magnetic systems(EM System)
These tags are made of a strip of amorphous metal (metglas) which has a very low magnetic saturation value. Except for permanent tags, this strip is also lined with a strip of ferromagnetic material with a moderate coercive field (magnetic "hardness"). Detection is achieved by sensing harmonics and sum or difference signals generated by the non-linear magnetic response of the material under a mixture of low-frequency (in the 10 Hz to 1000 Hz range) magnetic fields.
When the ferromagnetic material is magnetized, it biases the amorphous metal strip into saturation, where it no longer produces harmonics. Deactivation of these tags is therefore done with magnetization. Activation requires demagnetization.
This system is suitable for items in libraries since the tags can be deactivated when items are borrowed and re-activated upon return. It is also suitable for merchandise in retail stores, due to the small size and very low cost of the tags (Tattle-Tape).
Electro-magnetic systems are no longer common in food or apparel retail environments, most having been replaced by radio frequency, acousto-magnetic or even RFID platforms. The technology is still popular in library environments where the need to deactivate and reactivate tags is a necessity; however here too RFID platforms have been gaining ground in the last 10 years due to their greater range of use.
Acousto-magnetic systems(AM System)
These are similar to magnetic tags in that they are made of two strips: a strip of magnetostrictive, ferromagnetic amorphous metal and a strip of a magnetically semi-hard metallic strip, which is used as a biasing magnet (to increase signal strength) and to allow deactivation. These strips are not bound together but free to oscillate mechanically.
Amorphous metals are used in such systems due to their good magnetoelastic coupling, which implies that they can efficiently convert magnetic energy into mechanical vibrations.
The detectors for such tags emit periodic tonal bursts at about 58 kHz, the same as the resonance frequency of the amorphous strips.This causes the strip to vibrate longitudinally by magnetostriction, and it continues to oscillate after the burst is over. The vibration causes a change in magnetization in the amorphous strip, which induces an AC voltage in the receiver antenna. If this signal meets the required parameters (correct frequency, repetition, etc.), the alarm is activated.
When the semi-hard magnet is magnetized, the tag is activated. The magnetized strip makes the amorphous strip respond much more strongly to the detectors, because the DC magnetic field given off by the strip offsets the magnetic anisotropy within the amorphous metal. The tag can also be deactivated by demagnetizing the strip, making the response small enough so that it will not be detected by the detectors.
AM tags are three dimensional plastic tags, much thicker than electro-magnetic strips and are thus seldom used for books. However, they are relatively inexpensive and have better detection rates (fewer false positives and false negatives) than magnetic tags.
Called Emtag by B&G International, this type tag is often attached to the inside of a plastic surround permanently attached to the power cords of hand tools and equipment.
Radio frequency systems(RF System)
These tags are essentially an LC tank circuit that has a resonance peak anywhere from 1.75 MHz to 9.5 MHz. The standard frequency for retail use is 8.2 MHz. Sensing is achieved by sweeping around the resonant frequency and detecting the dip.
Deactivation for 8.2 MHz label tags is typically achieved using a deactivation pad. In the absence of such a device labels can be rendered inactive by punching a hole, or by covering the circuit with a metallic label, a "detuner". The deactivation pad functions by partially destroying the capacitor. Though this sounds violent, in reality both the process and the result are unnoticeable to the naked eye. The deactivator causes a micro short circuit in the label. This is done by submitting the tag to a strong electromagnetic field at the resonant frequency, which induces voltages exceeding the capacitor's breakdown voltage.
In terms of deactivation Radio Frequency is the most efficient of the 3 technologies (RF, EM, AM - there are no microwave labels) given that the reliable "remote" deactivation distance can be to 30 cm. It also benefits the user in terms of running costs since the RF deactivator only activates to send a pulse when a circuit is present. Both EM and AM deactivation units are on all the time and consume considerably more electricity. The reliability of "remote" deactivation (i.e. non contact or non proximity deactivation) capability makes for a fast and efficient throughput at the checkout.
Efficiency is an important factor when choosing an overall EAS solution given that time lost attempting to deactivate labels can be an important drag of cashier productivity as well as customer satisfaction if unwanted alarms are caused by tags that have not been effectively deactivated at the point of sale.
Deactivation of RF labels is also dependent on the size of the label and the power of the deactivation pad (the larger the label, the greater the field it generates for deactivation to take place. For this reason very small labels can cause issues for consistent deactivation). It is common to find RF deactivation built into barcode flat and vertical scanners at the POS in food retail especially in Europe and Asia where RF EAS technology has been the standard for nearly a decade. In apparel retail deactivation usually takes the form of flat pads of approx. 30x30 cm in retail apparel environments.