Operational Description of RFID Systems

In a nutshell, RFID involves detecting and identifying a tagged object through the data it transmits. This requires a tag (a.k.a. transponder), a reader (a.k.a. interrogator) and antennae (a.k.a. coupling devices) located at each end of the system. The reader is typically connected to a host computer or other device that has the necessary intelligence to further process the tag data and take action. The host computer is often a part of a larger network of computers in a business enterprise and, in some cases, is connected to the Internet.

This basic unit of architecture can be applied to the full spectrum of RFID-enabled solutions, whether simple or complex. For example, in a clothing store where items have an RFID tag affixed, the detection of the tag by the reader simply sets off an alarm. At the other end of the complexity spectrum is a sophisticated supply chain application where detection of a pallet of cereal boxes coming into the loading dock at a supermarket updates the inventory and triggers several other actions. It generates an update to the financial system for possible bill payment, a notification to the warehouse personnel to restock shelves, and an update to the manufacturer that the shipment has been received, possibly through an Internet or Electronic Data Interchange (EDI) connection.

One key element of operation in RFID is data transfer. It occurs with the connection between a tag and a reader, also known as coupling, through the antennae on either end, as shown in Figure 3.1.

Figure 3.1. Connection Between Tag, Reader, and Antenna

The coupling in most RFID systems is either electromagnetic (backscatter) or magnetic (inductive). The method used in a particular implementation depends on the application requirements, such as the cost, size, speed, and read range and accuracy. For example, inductively coupled RFID systems typically have a short range, measured in inches. These types of systems are used mostly in applications, such as access control, where short range is advantageous. In this case a tag only unlocks an RFID-enabled door lock when it is moved within close range of the reader, not when people who may be carrying a tag in their wallet or purse are walking past the reader in a hallway in front of the door.

The element that enables the tag and reader communication is the antenna. The tag and the reader each has its own antenna.

Another important element in an RFID system is the frequency of operation between the tag and the reader. Specific frequency selection is driven by application requirements such as speed, accuracy, and environmental conditions, with standards and regulations that govern specific applications. For example, RFID applications for animal tagging have been operating in the 135 kHz frequency band, based on longstanding regulations and accepted standards.

What is backscatter modulation?

A common way the communication between a tag and a reader happens is through a physical principle known as backscatter modulation. In this process, a reader sends a signal (energy) to a tag, and the tag responds by reflecting a part of this energy back to the reader. A charge device such as a capacitor contained in the tag makes this reflection possible. The capacitor gets charged as it stores the energy received from the reader. As the tag responds back, it uses this energy to send the signal back to the reader. The capacitor discharges in the process.

Although hardware components are responsible for identifying and capturing data, software components of an RFID application are responsible for managing and manipulating the data transmitted between the tag and the reader and between the reader and the host computer.

Figure 3.2 shows the various RFID System components and their operational relationship with one another.

Figure 3.2. RFID System Components