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broadband optimization is required. In
addition, matching the coils at a single
position will cause as many problems
as it solves – strong mismatches will
occur when the antennas are moved.
Together, these two factors make
effective matching difficult.
across a wider range of frequencies,
and the effect of the optimized circuits
can be included directly in a new 3D
simulation.
The inclusion of circuit simulation
tools means that the analysis can
be more detailed than a simple
S-parameter
calculation.
The
electronic components of the chip
and reader can be combined with a
3D model of the system (Figure 7),
and using the AC Task, a realistic data
transmission can be simulated. This
will take into account distortions to
the signal caused by modulation and
demodulation, refl ection within the
system, and unwanted parasitic eff
ects such as interference from other
tags.
Full system simulation
It is not enough for an RFID tag
to work in isolation. Any practical
RFID application also needs to
take into account the effect of the
environment, including detuning,
shielding, and coupling between tags.
These effects can have many different
possible sources, including other tags,
metal structures, nearby people and
animals, and the tagged object itself.
Simulation is the only way to calculate
these complex effects before the
prototyping phase begins.
Figure 8 shows one example: sixteen
pill boxes marked with RFID tags, all
located in close proximity. These tags
are interrogated by a reader located
some distance away. Figure 9 shows
the S-parameters for one tag on each
row, ordered from those nearest to
the antenna to those furthest away.
The simulation reveals that the RFID
tag in the first row, which is closest
to the antenna, are actually more
For this, the OptenniLab tool is ideal.
Optenni Lab shares a close two-
way link with CST STUDIO SUITE,
allowing simulation results and circuit
models to be shared between the two
products. The matching circuits can
then be optimized to get a good match
Figure 6: The eff ect of diff erent possible alignment problems in a 13.56
MHz RFID-based near-fi eld communication (NFC) system.
New-Tech Magazine Europe l 55