How many times have you walked through a
store's doors and—to your extreme embarrassment—set off the anti-theft alarm? It's surprisingly
easy to do, even when you've paid for your item and had it
"deactivated" at the checkout. Anti-shoplifting alarms use a
technology called RF (radio-frequency), while
a similar (but more advanced) technology called RFID (radio-frequency identification)
has many other uses, from tracking pets and public library stocktaking to collecting fares from bus passengers.
Let's take a closer look at this cunning technology and find out how it works!
Photo: A typical RF security gate in a shop doorway in London, England.
There's another one of these on the other side of the door. Sometimes these scanners are disguised so you can't see them, but more often they're designed to act as a very visible deterrent to shoplifters.
Radio or wireless is a way of transmitting energy
through empty space—that is, instead of using a wire cable. The energy
is carried by invisible waves of electricity
and magnetism that vibrate through the
air at the speed of light. The basic science and the practical
technology of wireless communication was developed in the second half of the 19th
century. During the early 20th century, "radio" came to mean
audio programs beamed through the air from giant transmitters to
cumbersome electronic boxes sitting in people's homes. When inventors
found a way of sending pictures, as well as audio, television was born.
Today, all kinds of things work using the same wireless technology,
from digital radio and television to cellphones (mobile phones), and wireless Internet.
Radio and television involve sending radio waves in one direction
only: from the transmitter at the radio or TV station to the receiver
(the radio or TV set) in your home. Wireless Internet and cellphones
are more sophisticated because they involve two-way communication. Your
cellphone, for example, contains both a radio receiver (to pick up an
incoming signal from the person you're speaking to) and a radio
transmitter (to send your voice back to the other person). Radar is
another technology that uses radio waves. Planes and ships fitted with
radar transmitters send out beams of radio waves and listen for
echoes—reflected radio beams bouncing back off other planes and ships
nearby. Anti-shoplifting devices are a little bit like radar: they beam
radio waves out into a store in the hope of catching a stolen book or
CD as it passes by. But how exactly do they work?
Photo: An example of the kind of RFID tag used in book labels.
It helps with automated stock control and (in some systems) might double-up as an anti-theft device. You can often see these by holding library paperbacks up to the light. This tag is a UPM Raflatac RaceTrack that can hold up to 1 kilobyte (1024 characters) of information. It operates at a relatively high radio wave frequency of 13.56 megahertz.
How RF works
Imagine your mission is to design an anti-shoplifting device using
some old radio sets you found in the garage. You could build something a bit like a
radar (with a combined radio transmitter and receiver), sit it by the shop doorway,
and point it at people passing by. Radio waves would pass out from
your transmitter, bounce off people walking past, and then reflect back
to your radio receiver. The trouble is, this wouldn't actually tell you
anything useful, because everyone would reflect the radio waves in
exactly the same way! You wouldn't know whether people were shoplifting
or not, because there would be no way to distinguish shoplifters from
ordinary customers or people who hadn't bought anything at all. What
you'd really need would be for shoplifters to reflect radio waves in a
different way to everyone else. But how?
Photo: Look closely at this price and size label from a pair of shoes and you'll see it says "RFID" on the bottom. Peel it off, turn it over, and you'll find the tell-tale antenna pattern on the back.
Anti-shoplifting devices have cracked this problem. As well as
having a transmitter and receiver at the doorway, every item in the
store contains a concealed RF "tag". In bookstores and libraries, you'll find
very discreet "soft tags," stuck to one of the inside pages. In
record stores, the plastic shrink-wrap may have an RF tag stuck
onto it, or CDs may be locked into large plastic cases with RF tags
built into them, which can be removed only be a special tool at the
checkout. In clothes stores, there is typically a "hard tag" (a chunky, round,
white plastic tag) bolted onto each item with a sharp metal spike
(sometimes the tag has ink inside it so it spills all over you and spoils
the item you're trying to steal if you attempt to remove it).
Some of these tags are cleverly concealed so you can't spot them. Others are deliberately very
obvious and easy to see—so they deter you from stealing. The gates on the doorway
(and the frequent alarms) are another very visible deterrent to shoplifters.
If you walk through the doorway without paying for something, the
radio waves from the transmitter (hidden in on one of the door gates)
are picked up by the coiled metal antenna in the label. This generates
a tiny electrical current that makes the label transmit a new radio signal of its
own at a very specific frequency. The receiver (hidden in the other door gate) picks up the
radio signal that the tag transmits and sounds the alarm. Why doesn't the alarm sound when you pay for something? You
may have noticed that the checkout assistant passes your item over or
through a deactivating device (sometimes it's incorporated into the ordinary
barcode scanning mechanism, and sometimes it's completely separate). This destroys or
deactivates the electronic components in the RF label so they no longer pick up or transmit a signal when you walk through the gates—and the alarm does not sound.
What's the difference between RF and RFID tags?
It's all a bit more complex than I've made it sound so far because there are, in fact, two quite different types of RF tags and they work in a slightly different way. Often the term "RFID" is loosely used to describe both, but
there's a big difference between them: RF tags all send the same, simple signal and simply tell the receiver that something is present; RFID tags send more complex signals that uniquely identify whatever they're attached to.
These are the simplest RF tags and they're used mainly in what's called electronic article surveillance (EAS)—the anti-shoplifting technique I've described above. All the tags are exactly the same and none of them identify the articles to which they're attached. So in a store, RF tags set off the alarm when you
try to steal something, but the alarm mechanism doesn't know what you're stealing, only that you're stealing
something: there's no way of telling any one item from any another.
One of the most popular RF technologies is called acousto-magnetic (AM). A pulsed beam of radio waves from the transmitter strikes the tag, making it give off a precise frequency radio signal. The receiver picks up the signal, verifies that it's at the correct frequency, and then sets off the alarm. One big advantage of AM tags is that
they can be scanned at quite a distance and at speed, making them popular in antitheft systems (which have
only seconds to pick up a signal from someone walking or running through a shop doorway).
RF tags are sometimes known as transponders or chipless RFID tags.
These are more advanced and differ from simple RF tags in that they uniquely identify the article to which they've been attached: the radio signal that zaps from the article to the receiver contains a digitally encoded identifier. That's how self-checkout machines in libraries work: they beam radio waves into the RFID tag in the back of the book, receive the radio signal back from the book, and decode this to figure out a digital code that uniquely identifies which book you want to check out. A computer attached to the scanner does the rest (so in a library, the self-checkout machine communicates with the library's computer to update the main database whenever you check out or return a book). Unlike RF tags, RFID tags tend to work over much shorter distances. Some actually have to be held right next to a reader device, while others operate at a distance of 10cm (4 inches) or less.
Simple RFID tags are described as passive. Instead of containing
batteries, they work entirely by responding to the incoming radio waves from the
scanner or transmitter. There is just enough energy in those radio waves
to activate the RFID chip. Passive tags typically send and receive signals
only a few centimeters, but not much more. An alternative form of RFID technology, known as active tags, contain more advanced chips and tiny batteries
to power them. They can send and receive signals over much greater distances.
Photo: Passive RFID: You can see the metal tracks of the antenna in this RFID tag quite clearly. This is the sort of tag used in library self-checkout systems.
Passive RFID tags contain just three components:
The antenna—catches incoming radio waves and sends them back out again.
The chip—generates a unique identifier code for the particular tag.
The substrate—the backing material (typically paper or
plastic) to which the antenna and chip are fixed.
As you can see from this photo, most of the space in an RFID tag is occupied by the antenna: the oval-shaped
tracks around the edge. The antenna needs to be this big both to pick up radio waves from the transmitter
and (because there are no batteries) to convert them into energy to power the chip. The chip itself is
tiny—sometimes as small as the point of a pencil. Anti-shoplifting RF tags are often smaller and simpler than this: instead of needing a chip to generate a unique identifier code, all they have to do is receive the incoming radio waves and retransmit the same electromagnetic energy at a different frequency.
How EAS anti-shoplifting systems work
Picture a shoplifter trying to steal a book from a store. What he doesn't
realize is that the store's using electronic article surveillance (EAS):
the book has an RF tag stuck just inside the back cover.
Here's the sequence of steps that triggers the alarm:
The gate on one side of the doorway contains a radio transmitter.
This constantly beams out radio waves to the gate on the opposite side
of the doorway, which contains a radio receiver.
A shoplifter walks through the doorway carrying a stolen book.
The book contains a hidden RF tag stuck to a label inside,
which picks up the radio waves.
Once activated, the RF tag transmits a radio wave of its own at a very precise frequency.
The receiver gate picks up the radio waves and identifies their frequency.
If the frequency is correct, the gate figures out that a stolen item is moving through and sounds
Other uses for RF tags
Photo: The US military is now using RFID tags to track its huge reserves of equipment. Here a military technologist is holding up some examples of RFID tags in front of a poster advertising the benefits of the technology.
Photo by Vicky Falcon courtesy of US Navy and Wikimedia Commons.
You can't blame stores for wanting to
install systems like this—especially when you hear that around 10
percent of all "shoppers" commit theft. But stopping shoplifters is
only one of the things for which we can use RF technology—especially
RFID technology, which is much more sophisticated.
Some cities are already using active RFID tags embedded in car windshields
to collect tolls automatically on bridges or highways as people drive by.
This saves drivers having to slow down, stop, or fumble for the right
change. Smartcards used on buses, subways (the underground or metro), and other forms
of public transportation also contain RFID chips. As you touch your
smart card on the reader, the card automatically debits your account
with the cost of the journey. Smartcards fall into two categories known
as contact and contactless according to whether you have to hold your
card to the reader or a short distance away (and that depends on
the type of RFID technology it's using). While some contactless credit and debit
cards use RFID, others use a rival technology called near-field communication (NFC),
which is briefly explained in the box below.
Photo: Contactless: RFID and related technologies like NFC power most of the contactless payment and
ID cards you carry around—but not all of them. Here, we have an Android smartphone running Google Pay (left),
and some "contactless" bank cards and an ITSO smartphone bus payment card (right). Can you spot the odd one out? It's the red card
("thank you") on the bottom right. Instead of using wireless RF technology, it uses a QR code—a completely different, optical technology.
Libraries make extensive use of RF and RFID: RF tags to secure their stock and
RFID tags to make it possible for people to use self-service checkout machines. When you
check books in or out of a library using one of those machines, you've probably wondered
how it knows which book you're borrowing without you having to scan a barcode.
The answer is that there is an RFID chip stuck inside the book's cover.
When you place your book on the glass plate, the machine reads the book's details
instantly and automatically by sending a radio signal to the chip. Since radio
waves pass straight through cardboard and paper, you don't even have to open
up the book!
RFID tags are likely to become even more popular in the future.
Soon, you might have an RFID chip embedded in your passport to speed
your passage through ports and airports. An RFID chip implanted under
your skin might save your life in an accident by transmitting your
medical information to an emergency team.
Doctors would simply wave a reader over your hand (or wherever the chip
was implanted) to gain immediate access to your
medical records. Systems like this obviously raise huge concerns about
people's privacy. Implanted identity chips would mark the
arrival of the Big Brother state, capable of monitoring everything we
do and everywhere we go. Although there might be enormous benefits,
most people would need a great of persuading to accept such a drastic
invasion of their privacy!
NFC versus RFID
Just when you're getting used to one technology, something new comes along instead!
RFID has been around for years and, as its name suggests, it's generally been focused
on identifying things (and people) using radio waves. But it was never really
designed for the 21st-century world where people need to identify or connect to things in a very ad-hoc way, often by going online to authenticate data or make payments. And anyway, now most of us carry smartphones, why should we also need a bunch of RFID smartcards that we have to keep charging up with credit? Why not just carry one device that does everything using a set of secure apps and connects to the Internet whenever it needs to?
For this, we have near-field communication (NFC), which
allows smartphones (or other devices) with embedded chips to read, write, and connect to other nearby NFC devices
(card readers on buses or access turnstiles at sports stadiums, for example).
Using 13.56 megahertz-frequency radio waves over distances of 10cm (4in) or less,
it's a bit like a cross between RFID and Bluetooth "pairing"
(the way two nearby Bluetooth devices connect together).
Screenshot: Android Pay works using NFC. When NFC is enabled on an Android phone, you see a little "N" icon appear at the top of the screen alongside things like the battery and signal status. You can switch off NFC completely to make your phone more secure. On my LG phone, I do this under Settings→ Networks→ Share&Connect→ NFC.
So far, the best-known use of NFC is in contactless smartphone payment systems like Android Pay, but there are likely to be many more applications in future, from smart house keys (where you unlock your door with a phone app) and public transportation passes
to electronic rock concert tickets and ATM cards. One of the advantages of NFC over RFID is that it can be used much more
intelligently by automated devices like smartphones to do a whole range of different things more or less automatically. Sony, for example, has fitted NFC chips into many of its new products so they can talk to one another and swap data more easily. That makes
it easier to upload photos from your digital camera to social media or to view photos from your camera on your TV.
Just as NFC brings more convenience, so it brings extra problems of security and privacy. What if other people's NFC devices start reading data from the smartphone in your pocket when you're standing nearby? What about malware (viruses and other malignant code) passing into your smartphone from someone else's? Ah well, it seems every new technology has to bring drawbacks as well as benefits!
Beginning NFC by Tom Igoe, Don Coleman, and Brian Jepson. O'Reilly, 2014. A hands-on guide to near-field communication using Arduino, Android, and PhoneGap. There's some introductory information about RFID in Chapter 2.
RFID Implementation by Dennis E. Brown. McGraw-Hill Professional, 2007. A longer and more detailed introduction than the books above, but with a similar practical approach.
RFID-Enabled Sensor Design and Applications by Amin Rida, Li Yang, Manos M. Tentzeris. Artech House, 2010. A more technical guide to using RFID tags. Compares RFID with other security systems, explains the fundamental principles of RFID sensor systems, then considers applications in logistics (such as warehouse distribution), cars (such as automatic toll collection), space, and navigation.
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