3.3 Operating Frequencies
Different RFID systems operate at a variety of radio frequencies. Each range of frequencies
offers its own operating range, power requirements, and performance. Different ranges may
be subject to different regulations or restrictions that limit what applications they can be
used for.
The operating frequency determines which physical materials propagate RF signals. Metals
and liquids typically present the biggest problem in practice. In particular, tags operating in
the ultra-high frequency (UHF) range do not function properly in close proximity to liquids
or metal.
Operating frequency is also important in determining the physical dimensions of an RFID
tag. Different sizes and shapes of antennae will operate at different frequencies. The
operating frequency also determines how tags physically interact with each other. For
instance, stacking flat foil inlay tags on top of each other may interfere or prevent tags from
reading properly. Table 2 lists standard frequencies and their respective passive read
distances.