Radio-frequency systems
These tags are essentially an LC tank circuit. An LC circuit is a resonant circuit or tuned circuit that consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C that has a resonance In physics, resonance is the tendency of a system to oscillate at larger amplitude at some frequencies than at others. These are known as the system's resonant frequencies . At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system peak anywhere from 1.75 MHz to 9.5 MHz. The most popular frequency 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 achieved by detuning the circuit by partially destroying the capacitor. A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric. When a voltage potential difference exists between the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force. This is done by submitting the tag to a strong electromagnetic. Electromagnetism is the physics of the electromagnetic field, a field that exerts a force on particles with the property of electric charge and is reciprocally affected by the presence and motion of such particles field at the resonant frequency which will induce voltages exceeding the capacitor's breakdown voltage. The breakdown voltage of an Insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive.The breakdown voltage of a diode is the minimum reverse voltage to make the diode conduct in reverse which is artificially reduced by puncturing the tags.
Microwave systems
These permanent tags are made of a non-linear element called a Diode. In electronics a diode is a two-terminal electronic component which conducts electric current asymmetrically or unidirectional; that is, it conducts current more easily in one direction than in the opposite direction. The term usually refers to a semiconductor diode, the most common type today, coupled to one microwave and one electrostatic antenna. At the exit, one antenna emits a low-frequency (about 100 kHz) field, and another one emits a microwave field. The tag acts as a mixer reemitting a combination of signals from both fields. This modulated signal triggers the alarm. These tags are permanent and somewhat costly. They are mostly used in clothing stores.
