2.    Applications of RFID

RFID technologies are already widely employed.  In many regions of the United States and other countries, automobile tolls are efficiently and accurately collected with minimal traffic delays using radio-enabled toll booths (Figure 3) and compact, inexpensive transponders that can be readily mounted to the car windshield (Figure 4).  In the US, the transponders usually contain an identifying number, which is read by a reader antenna mounted on the gantry above the toll booth.  A network is used to verify that the number corresponds to an active toll account, a debit entered in the account, and the car allowed to pass, all within a much shorter time than that required for manual collection of cash and distribution of change.       

RFID-enabled toll booths

Figure 3:  Tollbooths equipped for automated toll collection.



typical auto tolling tag

Figure 4:  Typical toll transponder.


A more elaborate system for wireless traffic management is used in the city-state of Singapore.  All automobiles must be equipped with a transponder, and during peak hours a toll is charged to enter the crowded downtown areas of the city.  Since the transponders are universally available, the system can also be used for private purposes such as paying parking garage fees.  

Rail transport is widely used in the US and Europe.  Identification of railcars is particularly well-suited to wireless techniques, since trains run on rails whose location is fixed, and can make changes only at well-known switching points.  Thus, complete location information can be obtained with a few identifying operations at key points along the line.  Railcars are valuable, and their contents often more so, so a cost of a few tens of dollars per car for identification is tolerable.  As a consequence, wide adoption of RFID in the rail industry took place some time ago. Since the early 1990's most rail cars in the US have been tracked using small RFID tags placed on the car frame, and readers located near the tracks (Figure 5).  

AEI images

Figure 5:  Automated Equipment Identification (AEI) tag and reader antenna for railcar tracking.


With the appropriate selection of tags and readers, RFID can be used to track livestock (Figure 6).  Ear tags like those shown cost a few US dollars.  RFID tags are immune to dirt and superficial damage, and unlike a brand the animal's hide is not defaced.  Tracking of individual animals can be useful in minimizing the cost and maximizing the effectiveness of recalls in the case of disease and other health issues, as well as providing  benefits in improved inventory visibility.  However, the cost and size of the tags used makes them impractical for tracking smaller, lower-value livestock like chickens or turkeys.  

cow tracking

Figure 6:  Cows with ear tags passing by reader antennas.


Smaller glass-encapsulated tags can also be implanted in pets to provide unambiguous and robust identification of a lost companion.  In a few cases such tags have been used for identifying people, although such applications are potentially controversial; we will discuss issues related to privacy and security below.  

Certain types of tags can be so small that they can readily be embedded in adhesive labels (Figure 7), and are so inexpensive that the resulting "smart" label cost is only around US$0.25.  (The tag itself can cost as little as US$0.10 in large volume.)  


label with embedded tag

Figure 7:  Adhesive label with embedded RFID tag.


These tags can be used to track cartons of items in transit from vendors to distribution centers and retailers, improving inventory visibility and reducing cost and out-of-stock conditions.  Some large retailers -- notably Wal-Mart and Target in the United States, and Metro Group in Europe -- require their key suppliers to tag cartons and pallets of goods (Figure 8).  Reports to date indicate that the greatest utility of these techniques is currently found in the retailing environment, allowing improved tracking of inventory, management of special marketing displays, and reduction in out-of-stock conditions.  Integration of tags with temperature sensors and data logging adds cost, but offers improved tracking of the "cold chain" for fresh meats and produce, providing longer shelf life and improved food safety.  RFID tags can also be used to simplify the laborious and time-consuming process of counting inventory, a costly necessity for many businesses. 

tagged cartons

Figure 8:   Cartons of produce identified with "smart" labels.


Tagging of individual items is of special interest when those items are medicines.  Substantial quantities of drugs distributed in the United States and other countries are believed, and in some cases known, to be imitations or fakes.  Some counterfeit drugs are produced by conventional manufacturers (though not those represented in the packaging), and actually contain the appropriate medicine; others are produced in illicit facilities that at best do not meet quality standards for pharmaceutical manufacturing, and some contain no medicines at all.  The Food and Drug Administration, and several states, are considering means to establish the "pedigree" of pharmaceuticals -- that is, to trace every step of a drug's path from the manufacturer to the consumer -- in order to reduce or eliminate the opportunity for insertion of counterfeit products.  One possible approach will employ RFID tags embedded in the drug packaging.  

Very-low-cost tags, with antennas built into a silicon integrated circuit, are under consideration for labeling documents, photographs, and currency.  These tags may have a read range of only a few millimeters (a few tenths of an inch), but may contain useful information to authenticate a document, or enhance its value.  For example, a tag added to a photograph may contain a record of the date and location at which the photograph was taken, as well as notes about the people and events depicted.  

A large distribution center or warehouse yard may have hundreds of trailers parked outside; a major port can have tens of thousands of containers on site.  Containers are themselves worth a few thousand US$, and their contents are worth tens or hundreds of thousands of dollars. Tracking the identity and location of each container by manual means is time-consuming and unreliable.  Today various RFID-based approaches can be used to provide real-time location and identity information for shipping containers and trailers in storage, and in some cases for trucks in transit (Figure 9).  In addition to reducing labor spent searching for specific trailers or containers, accurate yard information allows loads to be processed more rapidly, thus helping trailers and containers to spend more time moving goods and less time waiting.  

RFID tag on truck trailer

Figure 9:   An RFID tag can be attached to a truck trailer to provide near-real-time location information.


Hospitals characteristically have large numbers of expensive mobile assets, and are beginning to employ RFID technologies, often in conjunction with related approaches such as infrared or ultrasonic communications, to improve tracking.  Expensive disposable items like stents can be tagged and stored in RFID-enabled cabinets to provide real-time stock tracking.  Hospital staff can also be located in real time.  At some hospitals, newborn children are identified with RFID tags to help nursery staff keep track of their location at all times (Figure 10); an alert can be sounded if the baby is removed from the nursery without prior approval. 

baby with tag

Figure 10:   A newborn baby with RFID tag.


Non-contact RFID tags embedded in a credit-card-sized substrate (Figure 11) are widely used for controlling access to buildings and other secured areas.  These cards typically have a read range of a few tens of centimeters (a few inches) and cost a dollar or two.  In the figure, the antenna and tuning structures are clearly visble, but these are normally hidden between two layers of plastic in commercial products.  Similar approaches are used for non-contact "smart" credit or debit cards entering wide distribution in the United States and other counries.  Some states in the US are considering incorporation of RFID capability into driver's licenses, and new passports from the United States and other countries (ePassports) incorporate an RFID tag containing a digitized photograph and other data related to the holder.  RFID tags are also incorporated in lift passes for ski resorts and some event tickets, in both cases to speed entry while preserving authentication.  


RFID-enabled card

Figure 11:   A credit-card-sized RFID inlay.



In the applications discussed so far, a reader is used to find the identity and in some cases location of an RFID tag.  RFID techniques can also be used for the opposite purpose: to identify the location of the reader by examination of the tags it can read.  RFID tags with read range of a few meters can be placed in known locations in a building or facility.  By combining knowledge of the sequence of tags read with other location data, such as the results of a laser scanning system, a robot can establish its position to a few centimeters, achieving much better reliability than when using laser scanning alone (Figure 12).  Such techniques may be able to assist blind people to get around, and may be useful to firefighters seeking to navigate in unfamiliar buildings with impaired visibility due to smoke and fire.  


robot with RFID navigation

Figure 12:  A robot equipped with RFID reader and two antennas to assist navigation.


The reader may infer that the wide variety of applications depicted here could require distinct technological approaches, and this is indeed the case.  Let's take a look at the different approaches used to obtain the identity of an object using radio communications.