RFID technology is not a single technology. It has many implementations that vary
according to frequency, protocol, and antenna design. But most RFID variants have two
things in common: (1) Communication is bi-directional and takes place between a very
inexpensive RFID tag and a considerably more sophisticated RFID reader; and (2) the
information exchanged tends to be 2 Kbits or less – usually much less. In the vast
majority of cases, the tag has no power supply – it harvests energy from the reader to
transmit its identification information. In most cases, energy is transferred though
inductive coupling, which could be thought of as a transformer with an air core created
by the distance between the tag and the reader. Reading range is determined by carrier
frequency and the power generated by the reader. RFID systems that operate at UHF
frequencies can achieve a considerable greater reading range through a phenomenon called
backscatter coupling and in some instances by providing an energy source to the tag.
The design challenges posed by RFID systems are considerable, but quite different
from those of high-performance computing and communications designs. Performance is
often measured by the number of tags that can be read simultaneously, reading
accuracy, and ease–of-use. RFID design challenges also arise from considerations
such as system cost, reading range, the multiplicity of protocols that could be
used, antenna design, and the system’s operating environment: wet, dirty, dusty,
hot, noisy, etc. By far the most difficult challenges would be posed by the
application itself, which may be as simple as the exchange of a few hundred bits of
identification information, or as demanding as keyless access that requires
authentication. Other high-end applications include point-of-sale activities,
pharmaceutical tracking that is subject to regulatory oversight, ePassports, and
factory automation in which a tag can activate a programmable logic controller.
Although RFID systems can use many carrier frequencies, three dominate the market:
LF, which uses the 125 to 135 KHz band; HF, which operates at 13.56 MHz; and UHF,
which primarily is used in the 865 to 955 MHz band. The 2.4 GHz band may also be
included in UHF. Semiconductor companies design the transponders that are embedded
in the tags. Inlay manufacturers (including IC companies) integrate the transponder
into a tag that typically includes little more than the transponder, memory, and an
antenna, of which there are many designs.
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