Providing a bit more near-field sensitivity than the very small Button, the PaperClip is a versatile
choice for items allowing a slightly larger form factor.
the application at hand. In any event,
form factor is an important aspect of
tag antenna choice.
The performance of the tag is
dependent upon a very precise relationship between the tag chip, its
antenna, the application/environment,
and, of course, the tagged item itself.
Unless the RFID deployment plan
takes into account all of the critical
links in the chain, its overall performance (reliability, accuracy, flexibility,
and throughput) could be severely
compromised. Therefore, a thorough
tag evaluation process is a logical first
step. Fortunately, tag providers can
help you eliminate all of the guesswork, so you can focus on getting the
most from your serialization operations. The sections that follow shed a
little light on the process and the major
considerations we take into account.
mounted, and used in whatever manner is most advantageous to harvesting
good tag reads for the application at
hand. Applications range from items
speeding along a filling line to pallets of
cases moving through a distribution
center. (To this end, Impinj has
designed highly specialized reader
antennas to maximize read reliability,
and also to overcome the effects that
metals and liquids otherwise have on
tag performance.) Regardless of the
application, a tag must be able to
receive the reader’s transmissions and
reliably communicate the appropriate
responses—all through its antenna. So
where the RFID tag is concerned, its
performance ends up being a function
of both radio-frequency physics and the
particular tag antenna design. Of
course, the quality of the RFID chip
and the inlay assembly process have
much to do with this, as well as does the
particular protocol or standard that
manages the communications between
the tag and the interrogating reader.
With that, let’s take a closer look at tag
antennas.
FORM FOLLOWS FUNCTION
Convenient as it would be, there is
no single best tag antenna design for
every application, which is why there
has been such a proliferation of specially optimized forms and configurations. Available in a plethora of shapes
and sizes, many antenna designs also
A tag antenna must be
able to transfer energy
to the tag chip. As it turns
out, there are a number
of things that can
interfere with its ability
to do that.
feature creative geometries that, like a
Rorschach ink blot, conjure up the
images that inspire their names: Propeller, Satellite, Paper Clip, and Button,
to name a few in the Impinj line, for
example.
Fine art considerations aside, tag
antenna design is more concerned with
managing the many trade-offs—size,
cost, orientation sensitivity, range—for
A SMOOTH TRANSFER OF POWER
A tag antenna must be able to transfer energy to the tag chip. As it turns
out, there are a number of things that
can interfere with its ability to do that.
Certain types of mismatches can result
in the tag reflecting the signal back to
the reader, with very little of the power
reaching the chip. When this happens,
the tag is unable to function—at least
reliably. What conditions can cause
these mismatches? A whole host of
things, but to name a few:
• Poor antenna design.
• Poor tag chip design.
• Too-narrow tag chip bandwidth.
• Inadequate antenna-chip tuning.
• Proximity to various materials that
reflect or absorb radio waves.
• Failure to account for the properties of
the tagged item.
• Incorrect reader antenna configuration.
Attachment to any material will have
some effect on the antenna tuning, as
each antenna type has a particular near
field response that is subject to interaction with nearby objects. These are but
a few of the issues that must be accounted for in tag selection, as well as in the
