How do RFID and RF tags work?

Radio Frequency Identification (RFID) is the wireless non-contact use of radiofrequency waves to transfer data. RFID takes auto-ID technology to the next level by allowing tags to be read without a line of sight and, depending on the type of RFID, having a read range between a few centimeters to over 20+ meters. RFID has come a long way from its first application of identifying airplanes as friends or foes in World War II. Not only does the technology continue to improve year over year, but the cost of implementing and using an RFID system continues to decrease, making RFID more cost-effective and efficient.

An RFID tag in its most simplistic form is comprised of two parts – an antenna for transmitting and receiving signals, and an RFID chip (or integrated circuit, IC) which stores the tag’s ID and other information. RFID tags are affixed to items in order to track them using an RFID reader and antenna. RFID tags transmit data about an item through radio waves to the antenna/reader combination. RFID tags typically do not have a battery (unless specified as Active or BAP tags). They receive energy from the radio waves generated by the reader. When the tag receives the transmission from the reader/antenna, the energy runs through the internal antenna to the tag’s chip. The energy activates the chip, which modulates the energy with the desired information, and then transmits a signal back toward the antenna/reader.

Now let us see some practical approaches to the solution of our second problem – Maintaining and checking a database for members of an institution, using an RFID system. The basic idea involves each person of the institution having an id card and when this card is swiped against the reader, the person’s info is matched with the existing system in the database and his/her attendance is marked. The whole system uses the passive RFID system with the inductive coupling method. 

Let us consider another example for better understanding. Picture a shoplifter trying to steal a book from a store. What he doesn't realize is that the store's using Electronic Article Surveillance (EAS): the book has an RF tag stuck just inside the back cover. Here's the sequence of steps that trigger the alarm:

• The gate on one side of the doorway contains a radio transmitter. This constantly beams out radio waves to the gate on the opposite side of the doorway, which contains a radio receiver.
• A shoplifter walks through the doorway carrying a stolen book.
• The book contains a hidden RF tag stuck to a label inside, which picks up the radio waves.
• Once activated, the RF tag transmits a radio wave of its own at a very precise frequency.
• The receiver gate picks up the radio waves and identifies their frequency.
• If the frequency is correct, the gate figures out that a stolen item is moving through and sounds the alarm.