Antennas come in a variety of shapes and sizes; I explain how to choose the right one from a physics perspective in Chapter 5. This diversity in size and shape allows antenna placement in a wide variety of locations — from ware- house doors to highway tollbooths.
Readers tell the antennas what to do
An antenna is connected to a transceiver (which is generally known as a reader). Typically, one to four antennas are attached to a single reader, and those antennas send out the reader’s signals. Basically, the reader tells the antennas how to generate the proper RF field, which can cover an area as small as 1 inch to as large as 100 feet or more, depending on the power output and the frequency. When an RFID transponder (or tag) moves into the antenna’s radio field, it becomes active and sends back to the antenna what- ever information has been programmed into its memory. A reader receives the tag’s signal through its array of antennas, decodes the signal, and sends the information to the host computer system. A reader can also transmit spe- cial signals to a tag — telling a tag to come alive, synchronizing a tag with the reader, or interrogating all or part of the tag’s contents.
The middleware transforms the system into a network of objects
The basic elements of an RFID system are rarely useful in isolation. They gain value as part of a production or logistics system. In this way, the use of more than one system in an industrial process becomes a local network. The con- nection of local networks constitutes a global network. You can think of the local networks as a node of hardware (a reader, antennas, and tags) that interacts within itself to exchange information over RF waves. A bunch of nodes connected together creates a global network that connects to an appli- cation that creates useful information out of the data.
In order to move data from a single node to the local network and/or to the global network, you need the data-collection component, which ties readers, antennas, and tags together. This component is called by many names — middleware, reader interface layer, Savant — all describing the very simple glue that sticks together each node in an RFID system.
Middleware connects the data coming into a reader to the client’s host soft- ware systems. The middleware provides a coherent and stable interface between the RFID hardware operations and the flow of data elements, such as EPC (electronic product code) numbers, into inventory, sales, purchasing, marketing, and similar database systems distributed throughout an enterprise.
The elements of middleware include the following:
Reader and device management:RFID middleware allows users to con- figure, monitor, deploy, and issue commands directly to readers through a common interface.
Data management:As RFID middleware captures EPC data or other data from readers, it can intelligently filter and route it to the appropriate destinations.
Application integration:RFID middleware solutions provide messaging, routing, and connectivity features required to integrate RFID data into existing supply-chain management (SCM), enterprise resource planning (ERP), warehouse management (WMS), or customer relationship man- agement (CRM) systems.
Partner integration:Middleware can provide collaborative solutions like business-to-business (B2B) integration between trading partners.
The basic elements provide the data source or the local node to generate data. A series of these are linked into a local network that can connect to either a larger network or even a global network by employing middleware.
An RFID network is a peer-to-peer architecture capable of aggregating highly actionable data to a central location. See Chapter 10 for more details about middleware.
Imagine this: The use of a single tag, no larger than a book of matches, is mul- tiplied millions of times over within a global supply chain, which creates a peer-to-peer network that shares data in real time across a limitless number of boundaries. The image of the single millimeter-sized chip quickly expands to comprise a warehouse; a company; an industry; and a world of rapidly changing, automatically updated, real-time information. From that tiny chip blossoms the power to know where every object is at all times in a global net- work. Pretty cool, huh?
Time to Make Some Waves — Electromagnetic Waves
To understand today’s new RFID technology and equipment, it is important to understand the fundamentals of the science. RFID is all about physics.
Laws and mathematical equations that describe the behavior of this technol- ogy have been around for decades, even centuries. Although some people might have you believe that a successful RFID deployment requires you to wear sacred shells, sacrifice a chicken, and walk across hot coals, black magic usually isn’t required.
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The best RFID engineers understand where the technology originated, what its limitations are, and how the laws of physics can be leveraged as an asset in the design and deployment of an RFID network. The following sections explain basic principles of electromagnetic waves, how they’re measured, and how they affect each other.
Plowing the fields for electromagnetic radiation: A timeline
As far back as science knows, various fields of electronic and magnetic radiation have existed.
But the field of radio frequency communication didn’t really take off, from the perspective of RFID, until the late 1800s:
In the 1860s,while all his friends were out playing golf, James Clerk Maxwell, a Scottish physicist, predicted the existence of radio waves and postulated uses for those waves.
A short while later, in 1886,German scientist Heinrich Rudolf Hertz skipped Oktoberfest to prove that rapid variations of electric current could be projected into space in the form of radio waves similar to light waves, and that this current was measurable and repeatable.
In 1902,Italian physicist Guglielmo Marconi sparked a signal from England across the Atlantic to the shores of Newfoundland, demonstrating the first long-range use of radio waves as a form of communication. He broadcast the letter Sin Morse code. He was trying to transmit SOS(with the classy Italian accent that worked so well for Sophia Loren) but left the folks in Newfoundland hanging.
During World War II,the British developed the first RFID tagging system in order to rapidly discriminate between their own
returning aircraft and squadrons of the German Luftwaffe. British fighters were equipped with tags that replied to an interro- gation signal with a special “I am a friend”
code — routinely changed so that the enemy could not use it. Snoopy should have had this in his battles against the Red Baron.
In the late 1960s,the need for security and safety of nuclear materials drove further development of RFID tagging, such as elec- tronic article surveillance (EAS).
In 1977,Los Alamos Scientific Laboratories (LASL) transferred the RFID technology that had been developed in government labs to the public sector. Commercial RFID appli- cations beyond EAS began to appear in the early 1980s: railroad freight car tagging, the tagging of cattle and rare dog breeds, auto- mobile immobilizers, keyless entry systems, and automatic highway toll collection.
As the 1980s drew to a close,the primary focus in RFID commercialization shifted from new applications to issues of performance improvement and cost reduction, as well as reader, tag, and antenna miniaturization. The success is evident in the variety of RFID applications and system components now available in stores like Radio Shack.
Understanding everything that happens in the environment is critical to the success of your RFID system; that’s why we spend all of Chapter 7 talking about the site assessment. But knowing the root cause of problems will help you fix issues that crop up during that assessment.
Your “new” experiences are grounded in history. Problems you are con- fronting for the first time have likely been solved before. I always say it’s great to learn from mistakes — as long as they are someone else’s.
Frequency is a measurement
Electromagnetic radiation may have begun when the quark and leptronic soup became transparent to photons (the electromagnetic carrier particle), but the ability to measure all that radiation arrived relatively recently in the 19th cen- tury. Scientists like James Joule and James Maxwell were the first to figure out that you can measure the invisible. The ability to quantify frequency began with the advent of modern physics and the development of wave and particle theories. It is the principles behind wave and particle theory that led to the use of electronic and magnetic waves to communicate data.
Frequency is an important topic in the understanding of RFID. In Chapter 3, I introduce the three main types of frequency in RFID: low frequency (LF), high frequency (HF), and ultrahigh frequency (UHF). As you begin to under- stand the physics of RFID, you need to understand how frequency works as a measurement:
Frequencyis a measure of how many times an electromagnetic wave goes from one crest to the next crest in a unit of time (such as a second) as it moves through space.
This movement from crest to crest (or trough to trough) is called a cycle.
Frequency is measured in Hertz (Hz), which tells you how many cycles per second occur in an electromagnetic wave.
When ultraviolet radiation burns our skin at the beach, X-rays take pictures of broken bones, light glows from a neon sign outside your hotel window, or sig- nals are sent to antenna arrays in RFID networks, different frequencies are at work. All these sources belong to the family called the electromagnetic spec- trum.As the name spectrumsuggests, radio-frequency emissions form a series starting at extremely low frequencies (such as your car radio), going through the familiar visible wavelengths at higher frequencies, and finally to X-rays, gamma rays, and cosmic rays at extremely high frequencies. For example, the visible region of the spectrum is around 1014Hz, and the UV rays that burn us are at 1016Hz. Cosmic rays are 1021Hertz. RFID normally uses a portion of this spectrum from 125 kHz (kilohertz) to 5.3 GHz (gigahertz).
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History may repeat itself, but virginity comes only once
In 1902, when the Marconi team sent out the first transatlantic RF signal, that sole signal had the world’s airwaves to itself. Lightning was the only possible competition. Fortunately, the skies over the northern Atlantic were clear that day, and long-range radio was born. That signal was received 1,500 miles away because no competing RF signals were around to create interference.
In the late 1990s, when modern RF engineers from the Marconi Corporation (named after the famed engineer) proposed a reenactment of the original event, it turned out to be impossible due to RF crowding or noise.A small signal discharged today is completely drowned in the vast sea of radio fre- quency noise. The lesson here is that the human eye couldn’t detect a change in the radio wave patterns in the last hundred years; the invisible noise is what creates the biggest stumbling blocks to any radio system.
You need to be aware of all RF sources in and around your environment and also of any other sources that might interfere with the RF transmission once your network is operational. I show you how to check this in Chapter 7.
Fields: Electrical and magnetic, near and far
An electrical current gives rise to a surrounding magnetic field. A common example of the effect of this field is the effect of a current on a compass needle: The electrical current generates a magnetic field, which causes the compass needle to align with the magnetic field. A magnetic field can also generate an electrical current. This dual relationship between electrical and magnetic fields is a basic and fundamental physical property.
The region close to the source of the electrical current, where the magnetic or electrostatic forces can be detected, is called the induction field.Outside the induction field is the radiation field.Depending on which type of fre- quency your system uses (LF, HF, or UHF, which I introduce in Chapter 3), either the induction field or the radiation field will power the tags:
In LF and HF systems,the induction field has sufficient power to drive an electromagnetic field in the tag so that the chip is activated. Outside the induction field, the radiation field is too weak to do the same to other chips. This means a reader won’t activate tags in neighboring LF or HF systems.
If you’re interested in why the induction field can power the tag, research the inverse square law.
Measuring the strength necessary to actually activate a tag in the induc- tion field is how you focus your RFID system’s detection areas. This detection distance in the induction field is called the near field.
In UHF systems,the radiation field powers up the tag. This detection distance is known as the far field.Because you’re working in the far field, the antennas are shaped and work differently than antennas in LF and HF systems (more on antennas in the next section).
Creating resonance between the antennas and the field
Antennas are made of conductive material and couplethe RF waves for com- munication purposes. Couplingis the matching of the tag and the reader so that they can communicate effectively together at the same frequency. Every piece of electrically conductive material has some degree of coupling with radiation fields out in the real world. Only when the conductor is designed to provide high coupling efficiency between certain media is it called an antenna.
A key feature of antenna design is the idea of a resonance frequency. Resonance means that two things are moving in unison or in lock step. Ignoring for the moment the underlying mathematics and physics of this event, you can easily demonstrate how resonance works. Fill a long, low basin with water. If you put your hand into the water and, with large strokes, move it back and forth, the water becomes turbulent and you splash water out of the basin. But, if you gradually change the length and frequency of your strokes, you will eventually find a rate at which the entire body of water moves in unison with your hand.
This is the resonance frequency. Your hand has matched the resonance fre- quency of the water in a basin of those particular dimensions.
Antennas work the same way. They need to match the frequency of the incom- ing field in order to set up a resonance between the antenna and the field.
Resonance is based on a multiple of the wavelengths; thus you will notice that tags (which are tiny transceivers with their own antennas) have a size that is generally proportional to the size of the reader’s antenna.
The shape of the antenna is also matched to the frequency it is intended to interact with. Thus LF and HF tags are shaped like coils, which resonate better in the near field, and UHF tags have a flatter shape, which works better in the far field. The simplest antenna design of this nature is an antenna called a half-wave dipole antenna(a good term to remember for cocktail par- ties when someone asks you about RFID). Essentially, the idea is to match half of the wavelength (half wave) with the resonant frequency, and it will
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It makes sense to relate the physical concepts of resonance to some practical RFID issues:
When a tag antenna is immersed in the field of a reader antenna (in which both antennas are tuned to couple at the same frequency), the tag absorbs the radio frequency energy at a particular wavelength — the wavelength that makes it move at the same rate as the reader antenna.
This is how resonance works in an RFID system.
The UHF antenna design is proportional to about the wavelength of the signal. Knowing the wavelength of UHF systems (about 33 cm) is impor- tant when designing your RFID system because anything conductive that is about that length can act as an antenna and cause problems with your system. Tags that are some multiple of that wavelength will also receive a better signal.
ODIN technologies’ top engineer was doing a site assessment at a company that made cable racks for data centers, among other products. The engineer was trying to figure out why all the RF from a signal generator was going hay- wire in a particular part of the warehouse. After looking around, he noticed that the metal ladder racks for cabling were made with a bunch of 1-x-1-foot sections. He realized that 1 foot is about 33 centimeters, which is a perfect wavelength for UHF. The ladder racks were absorbing all the RF signals intended for RFID tags and needed to be relocated to make the system work properly.
Chapter 5
Understanding How Technology Becomes a Working System
In This Chapter
Peeking at the components of an RFID tag Discovering the inner workings of a reader Understanding the different kinds of antennas Looking at the various tag protocols
If you want to know a thing or two about setting up a great RFID system, take a look at Lance Armstrong, one of the greatest athletes of all time.
What does Lance have to do with RFID? Well, you can make even the simplest and most well-proven systems better by paying painstaking attention to the minutest details. You also need to understand every component that makes up the entire system. The simple system in Lance’s case is a bicycle. If you add a little oil to a rusty chain, an old neglected bicycle can take you around the neighborhood or through the countryside in far less time than you can walk. Lance’s team in the Tour de France, by contrast, has spent countless hours understanding the effects of wind, speed, tire pressure, clothing, and so on, using that knowledge to fine-tune their clothing and bicycles so they don’t lose a second to the competition. Sure, the cyclists look ridiculous in their pointy helmets, but their efforts do illustrate the benefit of understand- ing every component of a system, how the system functions, and the effect that the system can have on overall performance.
In this chapter, you come one step closer to crafting the Tour de France bicy- cle of RFID. I walk you through the basics of RFID tags and readers, talk to you about different aspects of design and performance, and show how they interoperate. After you understand the technology, I take you through a crash course in understanding the protocols that allow tags to communicate with readers.
With a more in-depth understanding of the individual subcomponents of an RFID system, you’ll be much better able to create a high-performing, efficient RFID network. If you understand how the system works on the basic level,