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RFID: tagging the world


Uniquely identifying specific objects is a powerful capability, useful in classifying, counting, and organizing anything. These abilities are essential to many aspects of modern life, including manufacturing, the logistics of distribution, and the various stages of supply chains, from manufacturing to retail. Before the electronic era, identification had to be done visually—explicitly by humans observing and noting the characteristics of objects. When dealing with objects that appeared to be identical or very similar, people were forced by necessity to add distinguishing markings. They could then recognize them in order to determine the identity of the marked object.

Even today, identification systems consist of identifying markings and ways to read them. The first readers were humans; technical innovations subsequently yielded photo-detectors, cameras, and lasers that were adapted and transformed into readers. The markings evolved into the fantastically popular bar code printed on almost every conceivable piece of packaging moved and sold worldwide.

Radio-frequency identification (RFID) is the latest technology to be useful for precisely identifying objects [3]. It uses radio waves to read an object's markings in the form of a unique identifying number stored on an attached or embedded silicon chip. There are two types of RFID tag: active and passive. Active tags are similar to the wireless nodes of sensor networks. The difference is in their usage models, not in their capabilities. Sensor-network nodes include sensors to measure and report on properties (such as temperature and movement) of their environments, while active tags focus on providing only an identification number and possibly some information (such as a description or transportation history) relating to the tagged object.

We can imagine a future where passive RFID tags are in every manufactured object and maybe even in some non-manufactured ones (such as natural resources, animals, and people).

Unlike active tags, passive tags provide only an identifying number when the tags themselves are "illuminated" by the radio waves emitted by a specialized reader. The electric field radiated by the reader's antenna serves two purposes: provide the tag with power and function as an asymmetric communication link between reader and tag. The tag harvests all the power it needs from the reader's emanations and communicates by modulating the reflected electric field. This ability to wirelessly draw power is what makes passive RFID tags particularly appealing; they operate without batteries or an autonomous radio, so they can be very small and very cheap while opening up entirely new and interesting design possibilities.

We can imagine a future where passive RFID tags are in every manufactured object and maybe even in some non-manufactured ones (such as natural resources, animals, and people). The technology promises orders-of-magnitude greater efficiency and accuracy than was possible with previous identification technologies. Although RFID is not a recent development [2], advances in semiconductor technology have now made it practical and much more cost-effective. So much so that RFID tags are beginning to compete with printed bar codes in supply chain management.

It is also important to keep in mind that passive RFID tags are much more than bar code replacements in terms of both the base technology and its applications. They are, for example, more flexible for tracking items in modern highly complex automated supply chains, because they are readable without a line-of-sight requirement and from much farther away, as well as being easily embedded in objects without marring their appearance. In addition, they are capable of holding orders of magnitude more data that can be written by RFID transponders (so readers become potential writers), enabling objects to carry their own database information. Moreover, new generations of RFID tags include sensing capabilities that make it possible to expand the scale of sensor networks by providing cheap and numerous sensing points.

Finding more and more uses in supply chain applications, RFID tags are likely to revolutionize distribution networks, permitting crates and pallets of goods to be traced from the manufacturer through the global transportation system and into retail stores worldwide. Many industries and government agencies, including some of the biggest retailers in the U.S. (such as Wal-Mart and Target), as well as the biggest agency in the U.S. Government (the Department of Defense) mandate the use of RFID tags at the pallet level by all of their suppliers. Pilot projects in these and other organizations are beginning to evaluate the use of passive tags even at the item level.

Passive RFID tags deliver much more than identification capabilities. That's why this special section includes a set of articles that highlight emerging RFID uses of and challenges in sensing, mobility, personal privacy, data security, and consumer applications. While deliberately not including RFIDs in the manufacturing supply chain (it's been covered extensively in the industry's literature), we instead emphasize what will happen when RFID tags, readers, and related databases start being commonplace in the consumer sphere—beyond the retail counter, as well as behind it.

Many sensor-network researchers believe the addition of sensing to RFID tags will make them the ideal node for increasing the physical coverage of these networks. The idea is to use an RFID reader that is part of a larger sensor network to query a much larger (and cheaper) collection of RFID tag-based sensors. Joshua R. Smith et al. describe an approach to integrating basic movement-sensing with tags and how they might be used to infer human activity, specifically, which objects people manipulate.

Ramesh Raskar et al. take this concept further by integrating light sensors into tags to add location- and geometric-reasoning to RFID tag/reader combinations. Applications range from identifying warehouse contents, to shelving books in libraries, to assisting robotic assembly procedures, to detecting obstructions on remote railroad tracks.

Pairing mobile devices is an annoying task involving numerous configuration steps. If consumers would be willing to let their mobile devices communicate continuously and consume their batteries, then accomplishing it would be relatively straightforward. Devices could discover each other without having the user in the loop pressing buttons. Trevor Pering et al. address the problem of how mobile devices might seamlessly discover and integrate with other devices in the environment (such as displays and kiosks), without expending their limited, precious power.

Abundantly clear to practically any RFID technology researcher or application developer is that the threat to the data privacy of millions of consumers worldwide will be a major impediment to the technology's widespread adoption. No consumers would want anyone else to be able to follow their every move by tracking the objects they carry or wear. RFID-based applications could make tracking especially easy because the tags embedded in increasing numbers of consumer products can be observed without the consumer's knowledge by a hidden reader some distance away.

Sherry Hsi and Holly Fait focus on a particularly interesting application involving the Exploratorium in San Francisco, a science museum using RFID tags to help visitors interact with exhibits within the museum, allowing them to register and document their interests, then extend the visit after they've gone home. However, as appealing as such extended scientific discovery may be to most of us, many museum visitors, in fact, forgo this potentially rewarding experience, fearing it could open them up to violations of personal privacy.

Miyako Ohkubo et al. address the problem of lost personal privacy head on, providing a way to continuously scramble a tag's ID after every read so that only the tag's authorized users are able to keep track of their scrambled IDs.

Oliver Günther and Sarah Spiekermann take on the consumer's view of the inherent risks to their personal data privacy in RFID-based applications and why solutions (such as scrambled IDs) are only the first of a series of measures to ensure consumer participation in RFID-based retail deployments. The goal is to win consumer trust by giving them some amount of control—possibly legally mandated—over the RFID infrastructure and its uses. Otherwise, RFID vendors and RFID-enabled retailers risk losing them as customers.

And, finally, Bruce Eckfeldt cautions RFID-enabled retailers everywhere that they risk the same fate if they fail to consider—in advance—how the consumer might directly benefit or lose from their technology investment.

This sampling of RFID technologies and their applications will help show what is possible and what is promised in consumer uses of passive RFID tags. Moreover, as tags get cheaper, smaller, and more capable, we can expect many as-yet unimagined beneficial yet potentially invasive uses in areas as diverse as health care and entertainment. As RFID technologists, application developers, and consumers, we must all be vigilant as to how these systems are designed not only for the sake of efficiency and cost but also to safeguard consumers' privacy and instill their trust in the technology [1].

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1. Borriello, G., Cuff, D., Diorio, C., Schilit, B., Shafer, S., and Zipkin, P. Radio Frequency Identification Technologies: A Workshop Summary. Computer Science and Telecommunications Board, National Research Council, Washington, D.C., 2004.

2. Stockman, H. Communicating by means of reflected power. Proceedings of the Institute of Radio Engineers (Oct. 1948), 1196–1204.

3. Want, R. RFID: A key to automating everything. Scientific American (Jan. 2004), 56–65.

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Gaetano Borriello ( is a professor of computer science and engineering at the University of Washington, Seattle.

©2005 ACM  0001-0782/05/0900  $5.00

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The Digital Library is published by the Association for Computing Machinery. Copyright © 2005 ACM, Inc.


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