Introduction

NFC is a short-range wireless technology that lets devices communicate when in close proximity. The devices communicate through the coupling of magnetic field rather than the energy radiation-interception process in far field communications.

The technology allows for the development of devices, including mobile phones, that can be used like contactless cards. Various features like e-ticketing, contactless transactions of all kind at payment terminals, contactless identification and authentication can be incorporated in a mobile device.

It operates within the globally available and unlicensed radiofrequency ISM band of 13.56 MHz. The supported data transfer rates include 106, 212, 424 or 848 Kbit/s.

This technology was developed by Philips, SONY and Nokia in 2002. They set up the first NFC technology standard NFCIP-1 and were approved for ISO/IEC IS 18092 international standard.

Difference between Near Field & Far Field

Thenear fieldandfar field are regions of the electromagnetic fieldaround an object, such as a transmittingantenna.

Fig: Near and Far field Zone (www.antenna-theory.com)

Theoretically for antenna aperture D Far-field starts where the distance from the antenna is > 2D2 / . Practically this distance is much greater than 5 , as aperture D of an antenna can be very small. If a sphere is imagined around an antenna and if the radius of this sphere is too small , cutting a piece we will not get planar rectangular shape. Here E and H fields will not be in phase .If radius of sphere is increased sufficiently by moving away and now a piece is cut in the size of a receiving antenna a planar rectangular shape is obtained . Thus waves here are planar and E and H- fields are orthogonal to each other . This is the Far field region. In this region, each part of the EM field is produced by a change in the other part. The ratio of electric to magnetic field strength is simply the speed of light. The radiation decreases as the square of distance, and absorption of the radiation does not feedback to the transmitter.Present communication systems are based on far field characteristics of radio waves.At a distance lesser than /2 from the antenna, we have the Non- radiative near field. The Radiating near field or Fresnel region is the region between the near and far fields. In this region, the reactive fields are not dominating and radiating fields begin to emerge. The characteristics of Non- radiative near field are different from that of far-field . In this region:1. The electric and magnetic fields can exist independently of each other, and one type of field can dominate the other.2. Absorption of electromagnetic power in the region by a second device has effects that cause feed-back to the transmitter, increasing the load on the transmitter. The antenna impedance seen by the transmitter decreases . Thus coupling can occur which is similar to the principle that applies ininduction coupleddevices, such as a transformer, which draws more power at the primary circuit, if power is drawn from the secondary circuit. This property is utilized in Near Field Communication systems .

It operates within the globally available radio frequency band of 13.56 MHz

Wavelength in meters is given by: = 300/fMHz. .Hence for a frequency

of 13.56 MHz

300/13.56 = 22.1 meters or 72.6 feet

Thus the near field is within:

/2 = 0.159 = 0.159(22.1) = 3.51m = 11.5 feet

Hence the two devices must be kept within 3.5m of each other for this form of communication to be effective . In actual scenario the effective distance is less than 1m. Thus it is a very short range communication.

As shown in the , the NFC reader on right excites current at 13.56 MHz through the reader NFC antenna (which is like an inductor). This induces a magnetic field, which further (via mutual coupling) induces an electric current in the smartphone's NFC antenna when they are closely placed. A NFC card inside the smartphone mainly has two parts: a CPU and storage. CPU can help the card to run some simple logic process program. The storage can provide data storage and memory to the application The induced electric current can be used to power the card in the smartphone . This is how communication occurs.

Modes of communication:

Initiator and Target

The initiator is the one who wishes to communicate and starts the communication. The target receives the initiators communication request and sends back a reply. This concept prevents the target from sending any data without first receiving a message.

There are two modes of communication:

1.Passive Communication Mode:

Here the Initiator device provides a carrier field and the target device answers by modulating existing field. In this mode, the Target device may draw its operating power from the Initiator-provided electromagnetic field, thus making the Target device a transponder.When operating in this mode a mobile device can conserve its battery power and operate using power of the initiator . Hence when used as smart cards no additional power is wasted .

2.Active Communication Mode:

Here Both Initiator and Target device communicate by alternately generating their own RF field. A device deactivates its RF field while it is waiting for data. In this mode, both devices typically need to have a power supply.

In passive communication mode, the passive device acts always as NFC target. Here the active device is the initiator, responsible for generating the radio field. In the case of an active configuration in which the RF field is alternately generated, the roles of initiator and target are strictly assigned by the one who starts the communication. By default all devices are NFC targets, and only act as NFC initiator device if it is required by the application. In the case of two passive devices communication is not possible.

The figure below shows the possible combinations:

References:

Capacity performance of an inductively coupled near field communication system . Jing, H.C. 5-11 July 2008 . San Diego, CA : Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE , 5-11 July 2008 . 978-1-4244-2042-1

Active load modulation for contactless near-field communication. Gebhart M, Wobak M,Chlestil C. 5-7 Nov. 2012. Nice: RFID-Technologies and Applications (RFID-TA), 2012 IEEE International Conference on, 5-7 Nov. 2012. 978-1-4673-4658-0. Cloud architecture based on Near Field Communication in the smart city . Yangyang Wang, Yanhui Zhou. 14-17 July 2012 . Melbourne, VIC : Computer Science & Education (ICCSE), 2012 7th International Conference on , 14-17 July 2012 . 978-1-4673-0241-8 .

http://www.nfc-forum.org.

http://www.antenna-theory.com

Operating modes of NFC

NFC Devices are capable of three different operating modes:

1.Peer-to-peer mode :

This mode is used for device pairing, networking and file transfer operations by just bringing the devices near to each other. Once the device is linked up using NFC, they can continue communication using long range and faster protocols such as Bluetooth or wireless Internet(WiFi). Thus additional authentication and setup time which is required for Bluetooth and WiFi is bypassed.

2. Reader/writer mode :

Increasing power of mobile and improving its internet access have helped making this mode more attractive in many applications. NFC enabled mobile devices can be used as a reader/writer for tags and smart cards. In this case the NFC device acts as an initiator and the passive tag is the target.

3. Card emulation mode :

In this mode the NFC device emulates an ISO 14443 Smart Card .Asmart card chip integrated in the mobile devices is connected to the antenna of the NFC module. A card reader cannot distinguish a mobile phone operating in tag emulation mode from an ordinary smart card.This is an important advantage and a unique feature of NFC technology as already existing reader infrastructures do not need to be replaced..

Applications of NFC :

Various features like e-ticketing, contactless transactions of all kind at payment terminals, information exchange ,contactless identification and authentication can be incorporated in a mobile device using this technology.

Different company use different card to promote their own competiveness in the market which bring about that everyone have a lot of smart cards. Simple imagine, we should take the entrance card of your office, bus card, ID card, various bank cards, discount cards and other different cards. Since NFC device can integrate , instead of all kinds of smart cards when one gets out, just one NFC device can help to enter office, take a bus, and other application.

Possible application of an NFC device can be divided into threecategories: 1.Contactless confirmation.

It can be used to identify ones identity and other authentication. User just need to move the card contained user information to the card reader, then all the need information will be read from the NFC device and confirm the users authority. Item tracking feature can be implemented from production to end user .

2.Contactless payment.

Secure and fast mobile transactions are possible . A single device can implement all payment cards . User moves the device over a payment terminal machine to complete transaction. One doesnt need to wait in a queue for payment. It will help to increase the use of digital currency and the need to print paper currency will be reduced.

3. Contactless browse and download:

This can be used in municipal services, advertising and internet browsing . The device can be used to get weather forecast, traffic information and other services when we move it over the terminal equipment providing such service. It can provide a convenient way to get a new application based on NFC. We can get a new NFC application through communication with a download terminal machine. Practical utility of the above category is limited.

Limitation and disadvantage:

1. Security is a big issue when mobile phone is integrated as a single device implementing various smart cards. If the phone gets lost or stolen the user is in risk of losing everything . So, the very feature that it can embed various smart card into one mobile is a major drawback in case of theft . So secure and faster authentication protocols and quick deactivation of all features with a single notification is very much essential. Secure applications must be protected through the user interface features of the device.

2. In a NFC tag all the information is stored in the tag. Ensuring proper safety against data modification and data destruction by unauthorized systems is essential.

3. The data transfer rate is very less compared to other standards such as Bluetooth and Wi-fi. Maximum achieved data rate is only 848 Kbit/s , thus will take more time for file transfer.

Conclusion

Near Field Communication is an efficient technology for communication within short distance. Different modes of communication are possible. Passive mode can conserve battery power of the mobile device. A significant advantage of this technology is compatibility with existing contactless infrastructure. It can give a huge boost to mobile based transactions in the future.

But it suffers from security issues in case of theft. So more secure features need to be incorporated in the device . Otherwise using single device for smart cards is risky. Unless the security issues are addressed benefits of Near Field Communication cannot be practically realized . Data transfer rate also needs to upgraded to make it more competitive.For this different antenna configurations and designs for more powerful coupling may be researched. Also it needs to be researched whether operating frequency other than the current 13.56 MHz , gives better performance .

Thus with other forms of communication already existing , its capabilityand reliability needs to be further improved to make this technology competitive and effective.

NEAR FIELD COMMUNICATION

Name: Soham Dey

Roll No: 001010801063

Department Of Electrical Engineering ,Jadavpur University