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only be readable in certain directions
– or worse still, not at all.
A full-wave simulation of the system
can calculate the farfi eld of the RFID
tag (Figure 11) in order to fi nd the
transmission peaks and nulls, to allow
the engineer to decide where the
best location for the reader antenna
is. When compared to Figure 2, it is
evident that the environment has
altered the tag’s farfi eld drastically.
The time domain solver in CST STUDIO
SUITE supports GPU computing,
which can dramatically speed up
the simulation of large or complex
models. This makes it possible for
big sections of the environment to
be simulated and, especially when
combined with distributed computing
(DC) for solving systems with multiple
tags, can be a very useful extension
to the simulation tool.
Conclusion
Traditional RFID design methods can
be complemented by EM simulation in
order tobetter understand thebehavior
of the device. Parameterization and
optimization means that multiple
design variations can be investigated
as part of a what-if analysis, and the
antennas can be tuned and matched
for better efficiency. The whole system
can also be simulated, including the
reader, multiple tags, and the device’s
surroundings, allowing engineers
to examine how the system will
behave in a realistic environment.
These environmental effects can be
very hard to detect without using
simulation.
Author Marc Rütschlin, Market
Development Manager for Microwave
and RF Applications, CST AG
simulation is useful is shown in Figure
10. Here, the RFID tag is embedded
in a complex metal environment,
consisting of several spools of a cable
contained in a crate reinforced by a
metal cage. All this metal will shield
the RFID tag, which means that it may
weakly coupled than the RFID tags
located in the center of the pallet,
due to constructive interference. This
effect would be extremely difficult
to calculate without carrying out a
fullwave simulation.
Another situation where a full
Figure 7: Schematic view of a full tag-and-reader simulation, showing the
time-domain signals at various points throughout the system. The 3D model
is the large block on the center-right.
Full sYstEM siMulAtion
56 l New-Tech Magazine Europe