Kinds of RFID tags
RFID tags come in three general varieties:- passive , active , or semi-passive (also known as battery-assisted ). Passive tags require no internal power source, thus being pure passive devices (they are only active when a reader is nearby to power them), whereas semi-passive and active tags require a power source, usually a small battery.
RFID backscatter.
To communicate, tags respond to queries generating signals that must not create interference with the readers, as arriving signals can be very weak and must be differentiated. Besides backscattering , load modulation techniques can be used to manipulate the reader's field. Typically, backscatter is used in the far field , whereas load modulation applies in the nearfield , within a few wavelengths from the reader.
Passive
Passive RFID tags have no internal power supply. The minute electrical current induced in the antenna by the incoming radio frequency signal provides just enough power for the CMOS integrated circuit in the tag to power up and transmit a response. Most passive tags signal by backscattering the carrier wave from the reader. This means that the antenna has to be designed both to collect power from the incoming signal and also to transmit the outbound backscatter signal. The response of a passive RFID tag is not necessarily just an ID number; the tag chip can contain non-volatile , possibly writable EEPROM for storing data.
Passive tags have practical read distances ranging from about 10 cm (4 in.) ( ISO 14443 ) up to a few meters ( Electronic Product Code (EPC) and ISO 18000-6 ), depending on the chosen radio frequency and antenna design/size. But thanks to deep-space technology, that distance is now 600 feet [6] . Due to their simplicity in design they are also suitable for manufacture with a printing process for the antennas. The lack of an onboard power supply means that the device can be quite small: commercially available products exist that can be embedded in a sticker, or under the skin in the case of low frequency (LowFID) RFID tags.
In 2007, the Danish Company RFIDsec developed a passive RFID with privacy enhancing technologies built-in including built-in firewall access controls, communication encryption and a silent mode ensuring that the consumer at point of sales can get exclusive control of the key to control the RFID. The RFID will not respond unless the consumer authorizes it, the consumer can validate presence of a specific RFID without leaking identifiers and therefore the consumer can make use of the RFID without being trackable or otherwise leak information that represents a threat to consumer privacy.
In 2006, Hitachi, Ltd. developed a passive device called the μ-Chip measuring 0.15×0.15 mm (not including the antenna), and thinner than a sheet of paper (7.5 micrometers ). [7] [8] Silicon-on-Insulator (SOI) technology is used to achieve this level of integration. The Hitachi μ-Chip can wirelessly transmit a 128-bit unique ID number which is hard coded into the chip as part of the manufacturing process. The unique ID in the chip cannot be altered, providing a high level of authenticity to the chip and ultimately to the items the chip may be permanently attached or embedded into. The Hitachi μ-Chip has a typical maximum read range of 30 cm (1 foot). In February 2007 Hitachi unveiled an even smaller RFID device measuring 0.05×0.05 mm, and thin enough to be embedded in a sheet of paper. The new chips can store as much data as the older μ-chips, and the data contained on them can be extracted from as far away as a few hundred metres. The ongoing problems with all RFIDs is that they need an external antenna which is 80 times bigger than the chip in the best version thus far developed. Further, the present costs of manufacturing the inlays for tags has inhibited broader adoption. As silicon prices are reduced and new more economic methods for manufacturing inlays and tags are perfected in the industry, broader adoption and item level tagging along with economies of scale production scenarios; it is expected to make RFID both innocuous and commonplace much like Barcodes are presently.
Alien Technology 's Fluidic Self Assembly and HiSam machines, Smartcode's Flexible Area Synchronized Transfer (FAST) and Symbol Technologies ' PICA process are alleged to potentially further reduce tag costs by massively parallel production [ citation needed ] . Alien Technology and SmartCode are currently using the processes to manufacture tags while Symbol Technologies ' PICA process is still in the development phase. Symbol was acquired by Motorola in 2006. Motorola however has since made agreements with Avery Dennison for supply of tags, meaning their own Tag production and PICA process may have been abandoned. Alternative methods of production such as FAST, FSA, HiSam and possibly PICA could potentially reduce tag costs dramatically, and due to volume capacities achievable, in turn be able to also drive the economies of scale models for various Silicon fabricators as well. Some passive RFID vendors believe that Industry benchmarks for tag costs can be achieved eventually as new low cost volume production systems are implemented more broadly. (For example, see )
Non-silicon tags made from polymer semiconductors are currently being developed by several companies globally. Simple laboratory printed polymer tags operating at 13.56 MHz were demonstrated in 2005 by both PolyIC ( Germany ) and Philips (The Netherlands). If successfully commercialized, polymer tags will be roll-printable, like a magazine, and much less expensive than silicon-based tags. The end game for most item-level tagging over the next few decades may be that RFID tags will be wholly printed – the same way a barcode is today – and be virtually free, like a barcode. However, substantial technical and economic hurdles must be surmounted to accomplish such an end: hundreds of billions of dollars have been invested over the last three decades in silicon processing, resulting in a per-feature cost which is actually less than that of conventional printing.
Active
Unlike passive RFID tags, active RFID tags have their own internal power source, which is used to power the integrated circuits and to broadcast the response signal to the reader. Communications from active tags to readers is typically much more reliable (i.e. fewer errors) than from passive tags due to the ability for active tags to conduct a " session " with a reader.
Active tags, due to their on board power supply, also may transmit at higher power levels than passive tags, allowing them to be more robust in "RF challenged" environment with humidity and spray or with dampening targets (including humans/cattle, which contain mostly water), reflective targets from metal (shipping containers, vehicles), or at longer distances: Generating strong responses from weak reception is a sound approach to success. In turn, active tags are generally bigger, caused by battery volume, and more expensive to manufacture, caused by battery price. However, their potential shelf life is comparable, as self discharge of batteries competes with corrosion of aluminated printed circuits.
Many active tags today have operational ranges of hundreds of meters, and a battery life of up to 10 years. Active tags may include larger memories than passive tags, and may include the ability to store additional information received from the reader.
Special active RFID tags may include temperature sensors. Temperature logging is used to monitor the temperature profile during transportation and storage of perishable goods as fresh produce or certain pharmaceutical products. Other sensor types are combined with active RFID tags, including humidity, shock/vibration, light, radiation, temperature, pressure and concentrations of gases like ethylene.
The United States Department of Defense (DoD) has successfully used active tags to reduce search and loss in logistics and improve supply chain visibility for more than 15 years (concept of in-transit-visibility ITV, .
Semi-passive
Semi-passive tags are similar to active tags in that they have their own power source, but the battery only powers the microchip and does not power the broadcasting of a signal. The response is usually powered by means of backscattering the RF energy from the reader, where energy is reflected back to the reader as with passive tags. An additional application for the battery is to power data storage.
If energy from the reader is collected and stored to emit a response in the future, the tag is operating active
Whereas in passive tags the power level to power up the circuitry must be 100 times stronger than with active or semi-active tags, also the time consumption for collecting the energy is omitted and the response comes with shorter latency time. The battery-assisted reception circuitry of semi-passive tags leads to greater sensitivity than passive tags, typically 100 times more. The enhanced sensitivity can be leveraged as increased range (by one magnitude) and/or as enhanced read reliability (by reducing bit error rate at least one magnitude).
The enhanced sensitivity of semi-passive tags place higher demands on the reader concerning separation in more dense population of tags. Because an already weak signal is backscattered to the reader from a larger number of tags and from longer distances, the separation requires more sophisticated anti-collision concepts, better signal processing and some more intelligent assessment which tag might be where. For passive tags, the reader-to-tag link usually fails first. For semi-passive tags, the reverse (tag-to-reader) link usually collides first.
Semi-passive tags have three main advantages 1) Greater sensitivity than passive tags 2) Longer battery powered life cycle than active tags. 3) Can perform active functions (such as temperature logging) under its own power, even when no reader is present for powering the circuitry.
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