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.
Some competitive Advantages of Acousto Magnetic Systems-
Acousto Magnetic system is just like to magnetic tags that are composed of three strips, one of ferromagnetic material and the other two are of amorphous metal. What makes these strips different? These strips free to automatically oscillate, instead of bounding concurrently. Besides, the tag is activated at the time of magnetization of the material. A 58 Kilo Hertz magnetic field is used by the detectors that produce standardized resonance by magnetostriction. While turning off the excitation field, these tags remain automatically oscillating that induces a magnetic signal due to that of the 2nd strip that is magnetized. The alarm is triggered by this signal. Magnetic tags are less thick as compared to these tags and are therefore occasionally utilized for books. Despite, they are comparatively cheap and have a steadier rate of detection (with some wrong negatives & wrong positives) as compared to that of Acousto Magnetic tags.