Radio Frequency Identification (RFID) was born in the early years of World War II as a form of airplane identification. Allied aircraft were equipped with a transponder that returned an identification code when triggered by a radar signal. Despite this early start date, it was still several decades before RFID as implemented today came into common applications.
Perhaps the first commercial application familiar to most people is the electronic article surveillance (EAS) system used in department stores to reduce the theft of garments. These are simple one bit RFID systems that are attached to the item to be protected. They sound an alarm if an article is removed from the store without being paid for. When an article is purchased, the clerk removes the EAS tag, thus allowing the article to pass through the exit without triggering the alarm. Modern systems still have such a device, but now the clerk simply scans the tag over an electronic field, turning the tag off.
RFID systems consist of readers and tags. The reader radiates a signal that is responded to by the tag. The response may be as simple as a pre-recorded serial number in the tag or as complex as a set of data that has been recorded during the operation of the unit that is tagged. For example, the data could be that from a vehicle and include an odometer reading, fuel level, oil pressure, and other items of interest to the operator.
Readers may operate in one of a number of frequencies ranging from 125 KHz to 5.8 GHz. Tags may be classed as passive or active, read only or read-write, and with or without batteries. The range and speed at which a tag may be read will vary according to the frequency, power, and the number of bits of intelligence being passed. As a result, access control badges will typically have a read range of a few inches, while a toll road application will need to have a read range of 100 feet, or more, and at highway speeds.
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