What is different between RF tag and RFID tag?
RF tags all send the same, simple signal and simply tell the receiver that something is present;
RFID tags send more complex signals that uniquely identify whatever they're attached to.
RF tag
These are the simplest RF tags and they're used mainly in what's called electronic article surveillance (EAS)—the anti-shoplifting technique I've described above. All the tags are exactly the same and none of them identify the articles to which they're attached. So in a store, RF tags set off the alarm when you try to steal something, but the alarm mechanism doesn't know what you're stealing, only that you're stealing something: there's no way of telling any one item from any another.
One of the most popular RF technologies is called acousto-magnetic (AM). A pulsed beam of radio waves from the transmitter strikes the tag, making it give off a precise frequency radio signal. The receiver picks up the signal, verifies that it's at the correct frequency, and then sets off the alarm. One big advantage of AM tags is that they can be scanned at quite a distance and at speed, making them popular in antitheft systems (which have only seconds to pick up a signal from someone walking or running through a shop doorway).
RF tags are sometimes known as transponders or chipless RFID tags.
RFID tag
These are more advanced and differ from simple RF tags in that they uniquely identify the article to which they've been attached: the radio signal that zaps from the article to the receiver contains a digitally encoded identifier. That's how self-checkout machines in libraries work: they beam radio waves into the RFID tag in the back of the book, receive the radio signal back from the book, and decode this to figure out a digital code that uniquely identifies which book you want to check out. A computer attached to the scanner does the rest (so in a library, the self-checkout machine communicates with the library's computer to update the main database whenever you check out or return a book). Unlike RF tags, RFID tags tend to work over much shorter distances. Some actually have to be held right next to a reader device, while others operate at a distance of 10cm (4 inches) or less.
Simple RFID tags are described as passive. Instead of containing batteries, they work entirely by responding to the incoming radio waves from the scanner or transmitter. There is just enough energy in those radio waves to activate the RFID chip. Passive tags typically send and receive signals only a few centimeters, but not much more. An alternative form of RFID technology, known as active tags, contain more advanced chips and tiny batteries to power them. They can send and receive signals over much greater distances.
An RFID tag held in someone's hand
Passive RFID tags contain just three components:
The antenna—catches incoming radio waves and sends them back out again.
The chip—generates a unique identifier code for the particular tag.
The substrate—the backing material (typically paper or plastic) to which the antenna and chip are fixed.
As you can see from this photo, most of the space in an RFID tag is occupied by the antenna: the oval-shaped tracks around the edge. The antenna needs to be this big both to pick up radio waves from the transmitter and (because there are no batteries) to convert them into energy to power the chip. The chip itself is tiny—sometimes as small as the point of a pencil. Anti-shoplifting RF tags are often smaller and simpler than this: instead of needing a chip to generate a unique identifier code, all they have to do is receive the incoming radio waves and retransmit the same electromagnetic energy at a different frequency.
