NFC Near Field Communication technology provides a format for short range communication to enable low data rates to be transferred.
Using the near field, effectively induction with a frequency of 13.56 MHz data can be transmitted in an RF carrier, but by using the near field and not radiating an electromagnetic wave, the distance over which the signal is transmitted is small.
By limiting the distance over which the signal is transmitted brings a high level of security, although other forms of security are required to make sure that the system is safe from all forms of hacking and fraud.
Antennas and fields
As the frequency used by near field communication, NFC is 13.56 MHz, then using basic antenna theory it is possible to determine the approximate length for a half wave dipole as 10.5 metres. This would radiate a high level of electromagnetic field.
This is clearly impracticable for handheld devices and in fact they may have loops that may be 20 centimetres in diameter, although this will be determined by the device being used and it may be even smaller.This significantly reduces the range and limits the field to an inductive field which has a short range.
NFC technology RF interface
NFC near field communication is a wire-less technology, using radio frequencies. It operates at a frequency of 13.56 MHz within the globally available and unregulated 13.56 MHz frequency band. As a result no licenses are required for operation on these frequencies.
In addition to this the radio transmissions using NFC are half duplex as the same channel is used for both transmit and receive. Also to prevent two devices transmitting together, they operate what is termed a listen before talk protocol. The devices may only transmit if they previously listen to check that no other devices are transmitting. In view of the short ranges involved, the protocol used by NFC need not be as comprehensive as that used for other wireless protocols.
Connection is made between two NFC devices when they are brought together so there is no difficulty in associating two devices. This occurs when the two devices are brought to less than about 4 centimetres of one another, although actual distances will depend upon a variety of factors, and figures of 20 centimetres for the maximum communications distance have been seen. In this way a simple wave or touch can establish an NFC connection. Because the transmission range is so short, NFC-enabled transactions are inherently secure.
To provide the standard interfaces, the underlying layers of NFC technology follow the normal ISO standards.
NFC technology data transfer
The data transfer rate may be either 106, 212 or 424 kbps. The application itself sets up the initial communication speed, but it may be changed later dependent upon the communication environment and the requirements.
NFC technology device types
The NFC near field communication standard defines two types of NFC device. These are known as the Initiator and Target of the communication. As the names imply, the initiator is the device that initiates the communication and it controls the data exchanges. The Target device is the one that responds to the requests from the Initiator.The NFC near field communication standard defines two different modes of operation:
- Active mode of communication: In the active NFC mode of communication, both devices generate an RF signal on which the data is carried.
- Passive mode of communication: In this mode of communication, only one NFC device generates an RF field. The second passive device which is the target uses a technique called load modulation to transfer the data back to the primary device or initiator.
In addition to the NFC modes of operation, three communication modes are also defined:
- Read / Write: This mode of operation within NFC near field communication allows applications to transfer data in an NFC Forum-defined message format. It should be noted that this mode is not secure. It is also necessary to note that this mode is supported the Contactless Communication API
- NFC card emulation: This NFC mo enables the NFC device to behave as a standard Smartcard. In this mode, data transfer is secure and the mode is also supported by the Contactless Communication API.
- Peer to peer: A third mode within NFC is the peer to peer mode which supports device to device link-level communication. It is worth noting that this mode of NFC communication is not supported by the Contactless Communication API.
NFC standards and capability
With Near Field Communications set to become widely accepted in many applications, the system has been standardised by a number of globally accepted standards bodies. NFC has standards accepted by ISO (18092), ECMA (340) and ETSI. Additionally NFC is compatible with Philips' MIFARE® (ISO 14443 A) and Sony's FeliCa smart card protocols.
NFC technology is now well developed and is incorporated into many forms of contactless data transfer. One of the main uses now is within payment cards and ticketing systems where it is used to make swift and easy transactions. Although NFC technology finds its roots within RFID, NFC uses the near field to effect its communication link and in this way it is very different.
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