17-12-2012, 04:50 PM
RFID TECHNOLOGY
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AN INTRODUCTION TO RFID TECHNOLOGY
Although the foundation of the Radio Frequency Identification (RFID) technology was laid by past generations, only recent advances opened an expanding application range to its practical implementation.
RFID is only one of numerous technologies grouped under the term Automatic Identification (Auto ID), such as bar code, magnetic inks, optical character recognition, voice recognition, touch memory, smart cards, biometrics etc. Auto ID technologies are a new way of controlling information and material flow, especially suitable for large production networks.
The RFID technology is a means of gathering data about a certain item without the need of touching or seeing the data carrier, through the use of inductive coupling or electromagnetic waves. The data carrier is a microchip attached to an antenna (together called transponder or tag), the latter enabling the chip to transmit information to a reader (or transceiver) within a given range, which can forward the information to a host computer. The middleware (software for reading and writing tags) and the tag can be enhanced by data encryption for security-critical application at an extra cost, and anti-collision algorithms may be implemented for the tags if several of them are to be read simultaneously.
One important feature enabling RFID for tracking objects is its capability to provide unique identification. One possible approach to item identification is the EPC (Electronic Product Code) , providing a standardized number in the EPCglobal Network, with an Object Name Service (ONS) pro-viding the adequate Internet addresses to access or update instance-specific data. However, currently, ONS cannot be used in a global environment, and since it is a proprietary service, its use is relatively expensive, especially for participants with limited resources such as SMEs.
As an alter-native, researchers from the Helsinki University have proposed the notation ID@URI, where ID stands for an identity code, and URI stands for a corresponding Internet address. This allows several partners to use the system and still guarantee unique identification. The project ‘Identity-Based Tracking and Web-Services for SMEs’ is currently working on further development of this concept.
RADIO FREQUENCY IDENTIFICATION
Radio Frequency Identification (RFID) is an automated identification technology that uses tags to transmit data upon RFID reader queries. Compared to barcodes identification technology, RFID tags provide a unique identifier, which raises concerns over user privacy, such as clandestine tracking and inventorying. In its original version, a RFID tag responds to a reader query with its fixed unique serial number. This fixed unique serial number enables tracking of tags and the bearers, possibly without the bearers’ knowledge or consent. In addition to the unique serial number, some tags carry information about the objects they are attached to. Thus, a retail store or a person owning such tags might be under threat of clandestine inventorying. Enormous research effort has been paid in attempt to solve the problem of consumer privacy and industrial espionage in the RFID world. However, most methods demand heavy or frequent cryptographic operations on RFID tags, which contradict the low cost demand of RFID tags.
ELEMENTS OF RFID
Briefly, RFID systems consist of two main components: Tags and readers. A tag has an identification (ID) number and a memory that stores additional data such as manufacturer name, product type, and environmental factors such as temperature, humidity, etc. The reader is able to read and/or write data to tags via wireless transmission. There are basically two types of communications between tags and readers. One is inductive coupling, which is done by antenna structures forming an integral feature in both tags and readers. The other is propagation coupling, which is done by propagating electromagnetic waves. In a typical RFID application, tags are attached or embedded in objects that need to be identified or tracked. By reading tag IDs in the neighborhood and then consulting a background database that provides mapping between IDs and objects, the reader is able to monitor the existence of the corresponding objects.
Passive tags
Passive RFID tags are fixed function devices that are powered and read by a standard RFID tag.UHF tag consist of a thin 2D printed antenna and a CMOS Application Specific Integrated Circuit (ASIC).The absence of an onboard battery means that the device can be quite small and is suitable to be used as a label or sticker. Although their read range is limited to roughly 3-10m, the lack of batteries means that the tag has an extremely long lifetime that can be measured in decades. Furthermore, the simplicity in design makes them suitable for mass manufacturing and has become a valuable method for asset tracking and control. Figure 2.1 shows a basic block diagram of RFID tag. The design goal is to maximize read range while providing compliance with the protocol. Read range is primarily limited by the amount of RF power that can be transmitted by the reader and the rate at which this RF power is attenuated as it travels through the free space. Since the tag is entirely passive, it relies on the energy provided by the incident radiation to power up. The electrical current induced in the antenna by the incoming radio frequency signal is converted into DC power by the rectification block. IC tags typically use diode connected MOS transistor configured in a multi stage, voltage doubling configuration. The regulation block powers the rest of the circuit once the minimum threshold of the rectified voltage has been met.
Active tags
Active RFID tags run the gamut from simple battery assisted identification devices to full embedded systems, such as wireless sensor network nodes. The defining factor is that the addition of a battery makes it an “active” device, which allows the possibility for extra functionality. Active RFID tags are generally fall into three categories: identification with increased reliability, sensing and monitoring, and localization. As is the case with any RF device, interference and multipath effects can cause significant performance problems. Thus, one of the advantages when considering active tags is increased readability in difficult RF environments where metal, liquids, or RF noise is prevalent. Since active tags can transmit a signal rather then simply using backscatter modulation.
RFID READER
The reader/interrogators can differ considerably in complexity depending on the type of tags being supported and functions to be fulfilled. The overall function is to provide the means of communicating with the tag and facilitating data transfer. Functions performed by readers include signal conditioning, parity error checking and correction. Once the signal from a transponder has been correctly received and decoded, algorithms can be applied to decide whether the signal is a repeat transmission and may then instruct the transponder to stop transmitting. This is known as Command Response Protocol and is used to circumvent the problem of reading multiple tags in a short span of time. Using interrogators in this way is also referred to as Hands Down Polling. A more secure, but slower tag polling technique is called Hands up polling which involves the interrogator looking for tags with specific identities and interrogating them, in turn. A further approach uses multiple readers, multiplexed into one interrogator but results in cost increase
SENSORS
The main function of a sensor is to detect some sort of physical stimulus such as temperature, heart rate, or carbon dioxide levels and then record a measurement for this stimulus. The actual “sensing” components can be electronic, chemical, mechanical, fiber optic, or a combination. A thermometer is a common example of a sensor in its most basic form. However, a basic sensor can be equipped with memory, power, and the ability to wirelessly communicate with numerous other devices that can create a smart data collection environment to provide constant, real-time feedback. Sensors come in a variety of shapes, sizes, applications, and abilities. This section will delve into the different types of sensors and how they can be applied to different data collection applications.
The sensing modalities may fall at least into the classes of stationary and non stationary sensing. Stationary sensing occurs when the measurement is performed in controlled conditions and non stationary sensing is performed at different times the things are moving. The eventual change of the reader –tag position and also the change in the environment can be a further unknown of the sensing problem, making data retrieval more difficult, if it is even still possible, but at the cost of more complicated data processing or more complex tag electronics. Self sensing tags detect the change of the thing through variation of an antennas impedance gain. This variation can be communicated to the reader by analog modulation of the backscattered power or if multiple microchips are included in the tag.