Transmission Frequency.

Frequency is the number of occurrences of a repeated event per unit of time, is measured in Hertz. And wavelength (lambda), is the distance between repeated units of a wave pattern.

The frequencies are grouped in bands of frequencies with similar characteristics. There are different versions of RFID that operate at different radio frequencies. The choice of frequency is dependent on the requirements of the application.

Three primary frequency bands have been allocated for RFID use.

· Low Frequency (LF) – 125/134 Khz. Short read range (1mm to 10mm)
· High Frequency (HF) – 13.56 Mhz. Read range less than 1 meter.
· Ultra High Frequency (UHF) – 850 to 950 Mhz and 2.4 to 2.5 Ghz. Long read range up to 6 meters.
 

Low Frequency and High Frequency tags operation principle is magnetic coupling (explained below), while UHF principle is back scattering.

Inductive Coupling.

An inductively coupled transponder comprises an electronic data-carrying device, usually a single microchip, and a large coil that functions as an antenna.


Inductively coupled transponders are almost always operated passively. This means that all the energy needed for the operation of the microchip has to be provided by the reader. For this purpose, the reader’s antenna coil generates a strong, high frequency electromagnetic field, which penetrates the cross section of the coil area and the area around the coil. Because the wavelength of the frequency range used (<135kHz:2400m, 13.56Mhz:22.1m) is several times greater than the distance between the reader’s antenna and the transponder, the electromagnetic field may be treated as a simple magnetic alternating field with regard to the distance between transponder and antenna.