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.
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 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. 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). 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. 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.