Radio frequency identification is the wireless use of electromagnetic fields to transfer data for the purpose of tracking and identifying tags attached to an item. It is somewhat like a bar code, but it does not need to be within sight of the reader. Radio frequency identification is used frequently in industries. It is used to keep track of items that are on the assembly line. It is also used track goods and track airport baggage.
Radio frequency identification works by sending a signal between the tag and the reader. tags may be either read only or have serial numbers already build into them. There are two types of readers. these two types are active reader passive tag and active reader active tag. Active reader passive tag transmits interrogator signals and also receives authentication replies from passive tags. Active reader active tag uses active tags awoken with and interrogator signal from the active reader. It is signaled by using wave lengths.
Source: http://en.wikipedia.org/wiki/Radio-frequency_identification
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