D7.7: RFID, Profiling, and AmI

Title: TRANSMISSION FREQUENCIES AND RELATED EFFECTS

RFID systems* can operate over a large range of frequencies depending on the mode of operation and the application, see .

Figure : Illustration showing the broad range of frequencies within the electromagnetic spectrum that RFID systems* can utilise.

RFID transmission frequencies are roughly classified into the three ranges: 

• LF (low frequency, 30-300 kHz),  

• HF (high frequency)/RF radio frequency (3-30 MHz) 

• UHF (ultra high frequency, 300 MHz-3 GHz)/microwave (>3 GHz).

RFID systems* that utilise frequencies between approximately 100 kHz and 30 MHz operate using inductive coupling, whereas microwave based systems in the frequency range 2.45–5.8 GHz are coupled using electromagnetic fields. However, the specific absorption rate (i.e. how much energy is lost as it passes through an object) of non-conductive substances (and water) is smaller by a factor of 100 000 at 100 kHz than it is at 1 GHz, so practically no energy is lost. The result of this is that systems operating at these frequencies will typically have a greater range. That said, lower frequency systems are noted for their improved object penetration over higher frequency ones. It should also be noted that the ranges achievable at higher frequencies are suitable for data transfer, but not for supplying power from the reader*, and as such these typically utilise active devices.

RFID systems* are also classified by range into: 

• Close-coupling (0-1 cm),  

• Remote-coupling (0-1 m), 

• Long-range (>1 m) systems.

The achievable range is dependent not only on the frequency utilised, but also factors such as the positional accuracy of the transponder*, the minimum distance between several transponders* in practical operation and the speed of the transponder* in the interrogation zone of the reader* (Finkenzeller, 2003).