23-05-2012, 04:52 PM
Near Field Communication (NFC) for Mobile Phones
Near Field Communication.pdf (Size: 4.29 MB / Downloads: 175)
Introduction
This report describes the RFID technology in general and the NFC technology in
detail. It also presents the project research, construction, testing and development of
various components, circuits, constructions and software.
The report starts with a description of the RFID technology and the applications based
on the technology. It continues by describing the basic theories that the technology is
based upon. The NFC standard is then described in detail, followed by the test
standard specified for NFC. Part of this project is focused on developing a test
assembly for NFC circuits. The construction of these components and NFC modules
used in the testing are described. Finally, the various tests and the corresponding
results are presented followed by the description of the C programs developed to
control the reader and the communication in test programs and applications.
Three appendixes are enclosed: two manuals that describe how to use the test
assembly and the Demo application programs and one appendix, containing the
complete source code developed throughout the project.
Introduction to RFID
A communication system using RFID technology consists of a reader/interrogator
device and one or several transponders/tags. The tags always function as sleeping
markers regardless of the type of RFID system or application. The reader initialises
the communication by sending a signal, which is replied to in different ways by the
tags. Really simple tags like the ones used in some anti theft systems in stores do not
contain any real electronics. They consist of a diode-connected antenna, which
reflects harmonics of the transmitted reader signal frequency. In these systems the
reader transmits continuously and listens for harmonics at the same time. When it
detects a harmonic of the signal it sets of the alarm. Other, still very simple tags
receive the reader signal and then replies with a data signal containing its
identification number or other data stored in the tag. The tags mentioned above are
called read tags since they contain information that can be read only, regardless if the
information is a block of data, an identification number or simply a reflected signal
telling the reader that a tag is within reading range. More advanced tags can also be
written to by the reader. These tags are referred to as read/write tags. Examples of
simple read/write tags are the ones used in the anti theft system at libraries which can
be activated/deactivated when the book has been registered by the librarian for
lending.
Some read/write tags that need to process large amounts of data contain a
microprocessor. A disadvantage is that such a tag is quite energy consuming.
Most RFID technology use induction. When a current flows through a coil, a
magnetic field is generated around it. If another conductor or even better, another coil
is placed within this magnetic field a current is induced in it.This is used in the RFID
system. The reader antenna works as a coil providing a magnetic field, which induces
a current in the antenna coil in the tag.
This is where RFID differs from classic radio transceivers. Most RFID tags are
passive since they have no power supply of their own. Instead, they use the induced
current from the field generated by the reader to process the information and send a
reply. The signal can be represented in various ways.
The different distances the reader and the tags can communicate on are divided into
three areas. The reason for this is that there are distinct differences in what amounts of
energy that can be extracted from the field generated by the reader depending on the
distance to the tag [1].
Close coupling systems
RFID systems communicating on very short range are commonly known as close
couple systems. The range where communication is considered to be close coupled is
between 0 and 1 cm. This means that the tag has to be placed either in the reader or
more or less pressed against the reader device. The benefit from these short distances
is that a rather large amount of energy can be extracted from the magnetic field by the
tag. More energy is available for signal processing in the tag at this distance without
the need for a power supply in the tag. Close coupling is also preferred for systems
with high security requirements.
Remote coupling systems
Remote coupling systems operate typically in the range up to 1 m. This is the most
commonly used area for RFID systems with passive tags.
Long range systems
The distances in long range RFID systems are between 1 m and 10 m although
systems with significantly greater distances exist. Long range systems use the higher
frequencies specified for RFID. These systems are typically used for keeping track of
goods or marking products ready for distribution. Tags operating in long range
systems are either very simple low power consuming read only tags or active tags
containing an internal power source, e.g., a battery.
Frequency bands and regulations
RFID systems are classified as radio systems since they radiate electromagnetic
waves. The radio spectrum is strictly regulated with great difference between different
continents and even countries. Some frequency bands are license free and therefore
more attractive for RFID technologies. Further, a manufacturer of a system wants the
products to function at as many locations at possible. Some license free frequency
bands in Europe are not license free in North America and vice versa. However, some
bands are more common to be license free than others. The most important frequency
bands for RFID systems are 0 – 135 kHz, ISM frequencies around 6.78 MHz, 13.56
MHz (NFC), 27.125 MHz, 40.68 MHz, 433.92 MHz, 869.0 MHz, 915 MHz (not in
Europe), 2.45 GHz, 5.8 GHz and 24.125 GHz [1].