It's an invisible part of our everyday lives, but in today's world, we can't get by without it. Short-range wireless is one of the most pervasive and important radio communications technologies. Ranging from 125 kHz to infrared (IR), applications are all over the place, from IR remote control to wireless broadband. And that just scratches the surface.
The slew of standards and protocols includes 802.11 Wi-Fi, Bluetooth, Zig-Bee, Gen2 RFID, Z-Wave, IrDA, and WiMAX, so there's something for everyone. One of the newer options, near-field communications (NFC), fills the gap from 0 to 20 cm and lives up to its designation as a short-range radio technology.
EMFs DEFINE RADIO
The term near field refers to the near field of a radio wave. Radio waves comprise electric and magnetic fields at right angles to one another. At a distance of about 10 wavelengths and beyond the antenna, at the operating frequency, radio waves behave the way Maxwell's equations say they would.
The two fields exchange energy and reinforce one another as they travel from the transmitting antenna to the receiving antenna. This is called the far field. Inside that 10 wavelengths is the near field, where you see individual electric and magnetic fields. The electric field isn't too useful, but the magnetic field can be used for short-range communications.
Consider NFC a transformer with a very low coefficient of coupling because of a large distance between primary (transmitter) and secondary (receiver) windings (antennas). The main problem with near-field magnetics is that the signal strength drops off at a rate of about 1/d6, where d is the distance or range, truly making it a short-range technology. The far field, what we all know as a radio wave, drops off at a 1/d2 rate.
Philips and Sony invented NFC. Ecma International adopted it as a standard first (NFCIP-1 or ECMA-340) and submitted it to the International Organization for Standardization/International Electrotechnical Commission (ISO/IEC), which standardized it as ISO/IEC 18092. The European Telecommunications Standards Institute (ETSI) also has recognized it. Semiconductor companies have since begun making compatible and interoperable chips.
This standard is similar to and compatible with the same NFC technology used in smartcards, whose internal chip lets consumers pay by passing them over a point of sale (POS) terminal reader. In some modes, NFC also resembles radio-frequency identification (RFID). ISO 14443, the well established smartcard standard, is implemented in Philips' MIFARE and Sony's FeliCa products.
The standard specifies an operating frequency of 13.56 MHz, the international no-license band and one of the ISM band Part 15/18 frequencies in the U.S. The data transfer rate is 106, 212, or 424 kbits/s. The speed depends upon the range, which has a maximum of 20 cm or about 8 in. In most cases, the actual range will be only a few inches or no more than 10 cm. Also, the standard specifies several operational modes.
In the active mode, both parties have powered transceivers. Either party may initiate a half-duplex transmission with a "listen before transmit" protocol. This feature prevents collisions when more than one NFC-enabled device tries to access a reader. One of the devices is the initiator, and the other device becomes the target.
In the passive mode, the target is a passive device like an RFID tag. The tag gets its operational power from the field transmitted by the initiator. It then transmits data back to the initiator by modulating the magnetic field (backscatter modulation, a kind of AM).
As with any new wireless technology, security is an issue. But the very short range of NFC devices keeps hackers out. At that distance, all you have to do is show intent and you're safe—for the most part. If you need more security, use NFC with smartcard technology, which has heavy-duty encryption and authentication built in.
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