| The
RF in RFID: the book! by Daniel M. Dobkin Elsevier-Newnes - September 3, 2007 |
| Radio-frequency identification is a catch-all term that
covers a wide variety of technologies, from the low-cost passive
ultra-high-frequency tags used in supply-chain tracking to 13.56 MHz
tags inserted in a passport, or active WiFi-based transponders used to
locate expensive assets in a hospital. The RF in RFID, now
available from Elsevier-Newnes, focuses on UHF passive RFID, though a
brief history and general introduction to the field is provided.
The book is a greatly-expanded version of the tutorial found
elsewhere on this site. |
| The book opens with an introductory chapter describing
the general layout and approach of the book. Chapter 2 first
reviews the history of RFID. After shamelessly repeating the
internet myth about rolling fighter pilots as the first passive RFID tags (for
which an archival confirmation is still pending -- if anyone has one,
please forward it to me!), the story wends its way through the early
research on active and passive transponders, including the remarkable
early UHF work of Koelle and colleagues out of Sandia Laboratories. |
| A review of applications brings us to the
present day, where we examine the different types of RFID, categorized
by frequency, coupling, and power source, with some examples and
example applications for each type. |
| Chapter 3 surveys a potpourri of topics important to
the analysis of radio links: waves, measurement of voltage
and power, modulation and bandwidth, backscatter links, and the
important topic of link budget calculations. Within the
latter discussion we introduce the concepts of antenna gain and
polarization, and arrive at the Friis equation for received power.
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| Chapter 3 also touches briefly on propagation,
reflection, and fading. Chapter 4 deals with UHF RFID reader
radios. We examine the elements of a radio -- amplifiers,
mixers, oscillators, circulators, filters, and conversion between
analog and digital signals. The parameters characterizing the
performance of these components -- gain, power, noise, distortion, and
so on -- each receive their moment of fame. We then put these
components together to make an RFID transmitter and receiver,
highlighting the key issues faced by the designer, including those
unique to the homodyne architecture typical of such radios: specialized
modulations for bandwidth-minimization in the face of dumb tag
receivers, and conversion of phase noise to amplitude noise. |
| Chapter 5 is about passive UHF tags, peculiar beasts
with special challenges for the circuit designer. Diodes and
charge pumps serve to convert the reader's RF signal into power for the
tag IC; switching the tag impedance allows it to talk back to the
reader. This bit of analog circuitry supports a digital brain
that must make do with a high-impedance, noisy, unreliable power
supply. The circuit must be packaged on a plastic inlay and
integrated with an antenna at cost levels that make children's toys
seem expensive. |
| Chapters 6 and 7 discuss reader and tag antennas, key
components in a working system. A more detailed discussion of
antenna directivity and gain also seeks to clarify how gain arises from
the changes of distance and thus phase with angle.
Polarizations linear, circular, and undecided are introduced
and the key role they plan in tag readability examined, and the
interaction between antenna size, impedance, and bandwidth exposed.
We take a close look at the patch antenna because of its
dominant role for fixed reader applications. The last half of
Chapter 6 views the various choices for reader antennas in the light of
typical applications in portals, conveyors, and handheld
configurations. |
| Tag antennas need to be tiny, cheap, robust, and
efficient, and must power a high-impedance load (the tag IC) from a
low-impedance wave. After a brief introduction to impedance
matching, chapter 7 looks at various approaches to the problem: the
meandered dipole, tip loading, shunt inductive matching, bowtie
structures, and dual dipoles. We review antenna radar
cross-section and provide a more realistic discussion of backscatter
signaling, and look at the very important effects of the nearby
environment on tag antenna operation. A discussion of the
important scattering effects of other tag antennas includes a rather
nifty and (as far as I know) previously unpublished formula for endfire
array behavior as a function of antenna impedance. Finally,
we discuss the interesting problem of producing a useful inductive loop
(near-field) antenna at UHF frequencies. |
| Chapter 8 takes a detailed look at how tag air interface protocols circumvent the stringent limitations of tag ICs. A review of protocol history reaches back to the days of reader-talks-first and up to the original Class 0 and Class 1 EPCglobal protocols; we even make an attempt to put some punch in ISO 18000-6B, despite the source document's status as reigning champion amongst insomnia cures. The last half of the chapter dives into EPCglobal Class 1 Generation 2, the protocol that seems likely to become the de facto worldwide standard for passive UHF tags. We discuss the slotted-Aloha Q protocol, dense-reader operation, and cheerfully conceal the shameless murder of innocent tags behind 32-bit passwords. |
| Appendices discuss radio regulations around the world,
and review background electrical engineering topics ( harmonic
functions, complex numbers, impedance, reflection, and matching) in
case the reader has been privileged to relegate his or her past
experience with them to the dustbin of college history. The book comes with a CD that includes color images (like those above) of all the figures. Also on the CD are Flash animations illustrating (or at least parodying) key concepts in medium access control, and a simple one-tag Class 1 Gen 2 emulator through which the reader can watch the protocol work step-by-step. Each chapter includes a capsule summary and some suggestions for further reading, and is further adorned with exercises to test the reader's grasp of the material. The reader determined enough to peruse the exercises will meet Bob the lazy RF designer and his brilliant but too-often-ignored colleague Amy, encounter the age-old tradeoff between microwave adaptors and beer, and help Committee Chair Toulouse Track to resolve the frequent disputes surrounding the International Organization for Contention's STAR (Slothful-Tag-And-Reader) protocol. Finally, The RF in RFID sets a new standard for jokes hidden within the index, as the author continues in the Quixotic quest begun with RF Engineering for Wireless Networks to achieve the perfect balance of suspense and excitement with alphabetical reference materials. You can click on the link below to check out, and hopefully purchase, the book from Amazon. Thanks for your consideration! |
(And yes, I know those are HF, not UHF, tags on the cover. If only they would have asked me...)
FOR FOLKS WHO ALREADY HAVE THE BOOK:
 www.enigmatic-consulting.com |
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