869MHz RF-ID Technology
The
new UHF 869.50MHz RFID frequency range has recently been released by
ETSI for use in EUROPE and is significant for passive RFID tag technology
because it gives longer read ranges than some other technologies. (Users
in other countries outside Europe should check freq use) At Low frequencies
- (less than 400MHz) the means of coupling is by Inductive Coupling. The
magnetic component of the electromagnetic field is dominant. Power attenuates
as the cube of the distance from the antenna and at the fourth and higher
powers dependant upon Tag orientation and environmental conditions. Thus
13.56MHz series tags noteably have a short read range. At Higher Frequencies - At
frequencies above 400MHz the means of coupling is by Propagation Coupling
and the electrical component of the electromagnetic field is the dominant
component, this results in a characteristic radio wave. Power attenuation
is related to the square of the distance from the antenna, therefore
higher frequencies with lower power radiated fields offer the promise
of longer communication ranges.
RF Propagation Field
At UHF frequencies the radiated RF primary field and the reflected waves add constructively or destructively depending on path length differences, thereby causing nulls and peaks in the RF energy fields. In this example, at a certain instant in time, when a read command is issued by the fixed reader, the 3 red transponders cannot receive this command. With a fixed reader and a fixed output power stationary tags cannot always be read with 100% accuracy due to this phenomenen, but moving tags will move through troughs and peaks and so be identified. (As will tags with long enough antennae to span the troughs).The stationary tag problem can be overcome by sweeping the output power of the radiated RF field to move the peaks and troughs.This holds true for 2.4GHz range tags as well except that at the higher frequency means smaller troughs and peaks.
For further information on products in this section follow the links below: