The general principle of operation of any RFID system is quite simple. There are always two main components in the system: it is a reader and an identifier (a map, a label, a key fob). The reader emits electromagnetic energy into the surrounding space. The identifier receives the signal from the reader and generates a response signal, which is received by the reader's antenna and processed by its electronic unit.
By the principle of the RFID system can be divided into passive and interactive. In a simpler passive system, the reader's radiation is constant in time (not modulated) and serves only as a power source for the identifier. Having obtained the required energy level, the identifier is turned on and modulates the radiation of the reader with its code, which is received by the reader. By this principle, most access control systems work, where you only need to get the serial number of the identifier. Systems used, for example, in logistics, work online. The reader in such a system emits modulated oscillations, that is, it forms a request. The identifier decrypts the request and, if necessary, generates an appropriate response.
The need for interactive systems has arisen due to the need to simultaneously work with more than one identifier. For example, if the stock is necessary to read all the labels in the package with the goods. In such situations, we cannot do without the anticollision mechanism, which provides selective sequential operation with several identifiers that are simultaneously in the reader's field. Without such a mechanism, identifier signals would overlap each other. During the anticollision process, the reader identifies all identifiers by their unique serial numbers, and then processes them in turn.
To make a decision on the admission of a person to a room or to count the number of boxes on a pallet, it is enough that each identifier has a unique number. However, there is a large class of tasks when it is necessary to place additional information on the label reflecting the process flow.
In this case, rewritable identifiers with additional non-volatile memory are used, in which information is stored even after power failure. The amount of such memory can vary from a few tens of bits to tens of kilobytes, depending on the application.
Frequency ranges and standards
There are two key definitions in RFID technology:
The proximity of the card and key chains - identifiers of short range, usually about 10 cm. Used in access systems, transport applications
proximity - identifiers of average range (about one and a half meters). Used to identify products and products mainly in logistic applications. From the point of view of operating frequencies, the main ones are the low-frequency range (125 or 134 kHz), the mid-frequency (13.56 MHz) and high-frequency (800 MHz ... 2.45 GHz).
The low-frequency range is most popular in access systems, and is also used to identify animals and metal objects (for example, beer kegs).
Currently, the mid-range is the most popular. It is used in transport and other similar applications that require rewritable cards. The basic standard is ISO 14443, and almost all smart cards are manufactured in accordance with this standard.
For labels in the mid-frequency range, two standards are relevant: ISO 15693 and EPC.
According to ISO 15693 rewritable labels are mainly produced with a fairly wide functionality. EPC (electronic product code) has a simpler structure and is an electronic equivalent of bar codes.
The high-frequency range (800 MHz ... 2.45 GHz) began to be mastered relatively recently, but it is of great interest because the existing standards for the level of radiation power in this range reach up to 4 ... 8 meters on passive identifiers, which is very important, for example , for warehouse applications. Two standards dominate this range: ISO 18000 and EPC.
Today, it can be argued that the EPC standard for the mid-frequency and high-frequency bands is very promising, especially for logistics applications.