How Near Field Communication Works

While NFC technology can do many things, the task most people think of tends to be making payments with a smartphone. It's a clear, easy to understand scenario. You've finished shopping and you walk up to pay for your purchases. You whip out your smartphone, hold it up to a receiver at the register, type in a quick PIN to identify yourself and the purchase charges to your electronic credit card.

There are already applications that make this method of payment compelling. In 2011, Google announced Google Wallet and Google Offers, a pair of products that take advantage of NFC technology. The basic function of Google Wallet is what we just talked about -- replacing your physical credit card. But it can also store other information like customer loyalty cards and special offers.

Here's an example. There's a particular coffee shop I go to frequently. To encourage customer loyalty, the shop has a policy that for every 10 cups of coffee I buy, I get a free cup. But that means I have to carry a card with me so that the barista can punch it every time I buy some coffee. If the coffee shop starts to accept Google Wallet -- and if I have a phone with NFC capability and the Google Wallet app -- my technology can keep track of everything for me. I just have to use my phone to make the purchase and it will register how many cups I've bought since my last free one. When it's time for a free cup, the phone will send that information to the store and I won't be charged.

But feeding my caffeine addiction isn't the only thing NFC can do. At CES 2012, Yale Lock demonstrated another use for NFC. The company had built special electronic locks that use NFC to lock or unlock doors. Holding your phone up to a pad on the door sends a signal from the phone to the lock. The lock disengages and you can get inside. Great, now we've eliminated the need to carry credit cards, loyalty cards and house keys!

Another potential use is in marketing. It's possible to incorporate an NFC tag inside a poster, for example. So if you see an ad for something that interests you, you can hold up your smartphone with an NFC chip up to it and receive more information. The main disadvantage to this type of marketing is that you'll have to be very close to the poster to receive the signal.

Other potential uses could include using NFC to communicate health records or synchronize data between devices. In the future, a profile on your smartphone might let you pass through airport security seamlessly as you navigate NFC stations. Only the limitations of the technology itself will determine what we can or can't do with it.

Back in 2004, three big companies -- Nokia, Sony and Philips -- got together with the goal of establishing a standard for near field communication technology. While these companies worked to standardize NFC, the technology that makes it possible dates back much further. And it all begins with the relationship between magnetism and electricity.

When electrons flow through a conductor, they create a magnetic field. And when magnetic fields change, they can cause electrons to flow through a conductor. This relationship -- known as inductive coupling -- allows for some interesting applications in electronics. One of the most versatile is a transformer -- just to be clear, that's a device that converts electricity from one voltage to another, not a robot that's more than meets the eye.

It's easy to see the effects of inductive coupling with a simple experiment. Take two lengths of copper wire and coil them -- the coiling helps amplify the magnetic fields we'll be generating. Attach one length of copper wire to a battery. You now have a very simple circuit as electrons flow from one end of the battery through the wire and into the other end of the battery. Connect the second coil of wire to a voltmeter -- a device that measures voltage traveling through a circuit. Bring the two coils closer together and you should see the needle on the voltmeter move.

What's happening is that the magnetic field from the coil attached to the battery is inducing electricity to flow through the second coil of wire. Move the coils apart and the needle will come to rest at zero. The strength of inductive coupling depends on several factors, one of them being the distance between the two conductors.

Radio frequency identification (RFID) tags are one application of inductive coupling. This technology is a predecessor to NFC. With an RFID tag, an electronic reader generates a magnetic field. Bringing an RFID tag close to this field induces electricity within the RFID tag. The reader detects the new magnetic field from the RFID tag and registers it. Many transportation systems and security systems use this sort of technology -- the RFID tag is in a card or fob that you must place near a reader to activate. This method is called passive RFID. Newer RFID technology adds the capacity to have a powered RFID tag, which we call active RFID. Active RFID tags can be used to improve the range of a tag and to store more information, among other applications [source: Zebra Technologies].

Near field communication builds on this technology. It allows for two-way communication between devices at a very short range. It uses inductive coupling the same way RFID tags do.

What exactly happens when you tap two NFC-enabled devices together? It's easier to understand with a concrete example, so let's assume you're walking down the street when you see a poster for an upcoming performance by Man or Astro-man? Because you dig surf rock, you want to check it out. You also see some text on the poster that says it has an NFC tag.

You quickly whip out your smartphone and activate an NFC-reading app. Activating the app sends a signal to the NFC chip inside your phone. Electricity flows through the circuitry of the chip, generating a weak magnetic field. This means your smartphone is an active NFC device -- it's using power to generate a magnetic field. You hold your phone up to the appropriate spot on the poster.

At this point, the weak magnetic field generated by your phone induces a magnetic field in the NFC tag within the poster. The magnetic field induces electricity in the NFC tag, which doesn't have its own power supply -- it's a passive NFC tag. This creates a radio field. The radio field generated by the tag interacts with the field generated by your phone. The NFC chip in your phone detects and decodes the radio field. The information turns out to be a link to a video of the band playing live. The app gives you the option of visiting the link directly if you wish.

Some NFC transactions will involve two powered devices. You may want to exchange some contact information from your phone with another person's phone. In an exchange, both devices act as active and passive components -- when active, a device sends information and when passive, it accepts information. It takes just a moment for the two phones to send information to each other. Before you know it, your contact information is in the other person's phone and vice versa.

An active NFC device can only communicate with one target device at a time -- you can't broadcast a message to multiple devices over NFC. The active device will send information to the target and will only accept a response from that target. Other NFC devices will ignore the communication.

It's important to remember that NFC just covers the actual transmission technology. It doesn't determine the content of those transmissions. The various hardware and apps that incorporate NFC chips will dictate what information changes digital hands. While the transmission technology is standardized, the content that can move across it isn't.

Because NFC is a standard, it has particular specifications. The transmission frequency for data across NFC is 13.56 megahertz. Like all radio signals, these travel in waves, with peaks and troughs. The distance from the peak of one wave to the next is a wavelength. At 13.56 megahertz, that means the signal moves 13.56 million wavelengths in the span of a second.

The NFC forum, an organization that establishes and promotes the NFC standard, designed NFC to send data in three different transmission speeds. Currently, an NFC device can send data at a rate of 106, 212 or 424 kilobits per second. These speeds are fine for short bursts of information, but aren't suitable for heavy-duty tasks like watching videos or playing games.

There are three modes of operation for NFC. The read/write mode allows an NFC device to read a tag like the kind you'd find in a poster. The peer-to-peer mode makes it possible for two NFC-enabled devices to exchange information. This lets you do things like tap your phone to another person's phone to exchange contact information. Finally, there's the card emulation mode. This is what lets NFC emulate -- or imitate -- a smart card like the kind you use in public transportation or ticketing systems.

It's important to remember than NFC is a developing standard. It will evolve as time goes on. While the standard dates back to 2004, it's still a young technology. Adoption of NFC has been slow in the United States -- only a few smartphone manufacturers and retail organizations support it. In other parts of the world, notably Japan, it's much more popular.

One risk we run with NFC is that it will fall out of favor before it sees widespread adoption. It's possible some other competing technology will sweep in and take up the niche NFC would otherwise fill. But that's just one hazard we could face with this technology.

Whenever radio frequencies are involved, there's a potential security risk. Could it be possible for an unscrupulous person to eavesdrop on communications between NFC devices? The answer is a resounding yes. With the right antenna, hardware and software, it's possible to snoop on transactions.

Even though NFC transmissions must take place over very short ranges -- 10 centimeters is the maximum distance, with many applications requiring even shorter ranges -- it's possible to pick up transmissions from much further away. Defining exactly how far away an eavesdropper can be isn't easy. It relies on several factors, including whether the information is being sent in active or passive mode, the type of antenna and receiver the eavesdropper is using and how much power the active component pours into the transmission. It's possible that someone trying to listen in on an active component could get a signal as far away as 10 meters [source: Haselsteiner and Breitfuß].

It's harder to detect transmissions from passive components. Even so, an eavesdropper could detect signals from about a meter away with the right equipment. To prevent someone from getting valuable data -- including your financial information -- hardware and software manufacturers use encryption to keep valuable information away from prying eyes. With encryption, both components need a specific type of key to decrypt information into something useful. An outsider without access to the key would only see gibberish.

Another way NFC devices could prevent eavesdroppers from stealing information is if both devices involved information simultaneously. Here's how it works: Both devices begin to transmit a random series of bits, which are either 0s or 1s. An eavesdropper would be able to tell if both devices transmitted a 0 or a 1 at the same time. But what if one device transmits a 1 and the other a 0? The two devices know which is which, but an eavesdropper would be unable to tell. At that point, the two devices could simultaneously communicate and mask communications so that the eavesdropper can't make out what is being transmitted -- there's no way to know who's sending which bit.

Another potential problem with NFC is that someone could attempt to disrupt communications by broadcasting radio signals in the NFC spectrum during transactions. While this isn't the same as eavesdropping, it could be a source of annoyance.

Before we have to worry about these kinds of problems, we'll have to adopt NFC technology on a wider basis. It remains to be seen if NFC will take off. If it does, you may be able to ditch most of your gear and rely primarily on your smartphone. The utility belt industry could be headed for some lean years pretty soon.

I've been interested in NFC technology since I first heard about it being used in Japan. At the time, even the idea of a smartphone was exotic. Now it seems like smartphones are the new standard, and it surprises me we haven't moved toward an NFC-based transaction system yet. Part of the problem may be that different financial institutions want to establish their own payment standards and retail organizations must choose which ones to support. It could be a few more years before we see this tech rolled out into our neighborhood stores.

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