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Page 1 of 3 Tags An RFID tag is a uniquely identifiable object, that can be embedded or attached to any physical body to track it's position or location. Tags are of various kinds, covering the entire spectrum from passive tags powered in the presence of a reader, to a continuously signal-emitting active tag.
Both active as well as passive RFID tags consist of a small microchip that contains a unique ID encoded within it. The rest of the tag consists of a mechanism to transmit this unique ID to an “Interrogator” or a reader that can identify this tag.
In the case of a passive RFID tag, the construction consists of an antenna that serves a dual purpose - it acts as a “coil” that generates enough electric current when placed within an electromagnetic field (i.e. Close to a passive reader) to “power” the microchip. The unique ID encoded within the microchip is then transmitted in an elecromagnetic pulse, that uses the antenna to broadcast the pulse back to the reader.
In the case of an Active tag, an internal power source (battery) is used to power the transmission - which broadcasts the tag's unique ID to all sensors/receivers that are listening on the specified frequency. The signals are non-directional, and may be received by one or more sensors. These signals then need to be interpreted by the system to determine the location of the tag within a facility.
Both active as well as passive tags fall within a range of frequencies that are used according to the international ISO specifications for air interface (ISO-18000 2-7). Some of these specified frequencies are more suitable to passive operation (i.e. Shorter range, larger bandwidth, lower power) while some are more suitable to active RFID technology. Passive tags operating at LF are commonly found in the 125Khz range and the tags operating at HF are in the 13.56Mhz range. Some of the newer tags are also available in the UHF range, with larger bandwidth, read speeds, as well as larger read ranges. However, these technologies also require higher power readers than those with correspondingly lower frequencies.
Most active RFID badges usually work between 420 - 450 Mhz. Some of the tags (e.g from Versus technologies) also work between the 63.57 Mhz frequency range, which compensate for the lower range (90m) with much longer battery life, which is a very practical consideration for an actual deployment. 
Features
• All tags use some kind of FM modulation in order to transmit the tag's unique ID to the Interrogator
• Interrogated remotely via RF/inductive signals (passive) and direct broadcast (active)
• Long life - can withstand mechanical shocks, dirt etc
• Non-directional, with non line-of-sight functioning that enables complete automation of RFID enabled (or supported) systems and processes.
• Non-contacting (tamperproof) and non-obtrusive (transparent to user)
• Robust protocol - fault tolerant transmission, inherently engineered for error-handling and recovery
• Flexible with minimal interference
• Unique identification number allows stronger authentication of personnel and systems.
Comparison of Active vs. Passive Tags | Feature | Active Tag
| Passive Tag
| | Frequency | 420-450 Mhz, 63.57 Mhz (Versus)
| 125Khz, 13.56Mhz, 920-930Mhz, 2.4-5.8Ghz
| | Typical usage | Position tracking, location-based computing, “Aware” systems that can react to specified physical signals and stimuli
| Object identification, process automation, Retail | | Typical environment | Hospitals and healthcare facilities, Warehouses & Freight management facilities, Defense and high-security installations | Retail sales, Warehouse and freight management, Logistics, Manufacturing & Supply chain management, Agriculture | | Cost | Medium, Re-usable for long-term cost recovery | Low |
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