RFID is an automatic identification method for remote storage and data retrieval on RFID tags. RFID tags can be attached on people, products, animals and merchandise. RFID tags support a larger set of unique IDs than bar codes and can incorporate additional data (e.g., manufacturer, product type) and measure environmental factors (e.g., temperature). RFID tags have a memory capacity of 16-64 kbytes whereas bar codes only 1 - 100 bytes. A RFID system can discern many different tags in the same area without human assistance.
The tag consists of an integrated circuit and antenna. The data rate is up to 115 kbps with signal from 915 MHz and 868 MHz (at the higher end of the spectrum) to 315 MHz and 27 MHz (at the lower end of the spectrum). RFID does not require line-of-sight.
RFID involves two components, namely a tag and a reader (also known as an interrogator). Some reader not only read, but also remotely write to, the tags. Chip tags consist of a microchip and a coupling element (an antenna). A tag is activated when they are within the interrogation zone of the reader. Otherwise, it sleeps. Chip tags can be read-only (programmed during manufacture) or read-write. Chip tags contain memory. The size of the tag depends on the size of the antenna, which increases with range of the tag and decreases with frequency.
RFID devices can be grouped into two types: active and passive. An active tag requires a power source — either it is connected to a power source or uses energy stored in an integrated battery. In the latter case, a tag's lifetime is limited by the stored energy, which determines how many read operations the device can undergo. The use of battery makes the cost, size and lifetime of active tags impractical for the retail trade.
A passive tag does not require batteries or maintenance, therefore, it has indefinite operational life. It is also small enough to fit into a practical adhesive label. It consists of an antenna, a semiconductor chip attached to the antenna and some form of encapsulation. The power to activate the tag's microchip is supplied by the reader through the tag's antenna when the tag is in the interrogation zone of the reader. The antenna captures energy and transfers the tag's ID (the chip coordinates this process). The encapsulation maintains the tag's integrity and protects the antenna and chip from environmental conditions.
There are two ways to transfer power from the reader to tag: magnetic induction and electromagnetic (EM) wave capture. Both makes use of the EM properties, i.e., near field and far field. Enough power is transferred to power a remote tag to sustain its operation, usually between 10 μW to 1 mW, depending on the type of tag.
Near-field RFID is the most straight forward approach for implementing a passive RFID system. It uses Faraday's principle of magnetic induction. A reader passes a large alternating current through a reading coil, resulting in an alternating magnetic field in its locality. When you place a tag in this field, an alternating voltage appears across it. If this voltage is rectified and coupled to a capacitor, a reservoir of charge accumulates, which can be used to power the tag chip. Data is sent back to the reader using load modulation.
Far-field RFID tags capture EM waves propagating from a dipole antenna attached to the reader. A small dipole antenna in the tag receives this energy as an alternating potential difference that appears across the arms of the dipole. A diode rectifies this potential and links it to a capacitor, which results in an accumulation of energy in order to power its electronics. Because the tags are beyond the reader's near field, data cannot be transmitted to the reader using load modulation. Data is sent back to the reader using back scattering. A far-field reader can interrogate tags 3 to 6 meters away.
Tags that use far-field principle operate at greater than 100 MHz, usually in the ultra high-frequency (UHF) band, such as 2.45 GHz. RFID near-field coupling operates below this frequency.
What is RFID & How RFID Works
RFID In Manufacturing
Source:
R. Want, "An Introduction to RFID Technology", Pervasive Computing, Volume 5 Issue 1, 2006
S. Ahuja, P, Potti, "An Introduction to RFID Technology", Communications and Network, Volume 2 Issue3, 2010
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