Topics: Passive RFID, Antenna, Active RFID
RFID stands for Radio Frequency Identification. It is a technology that enables not only the contactless identification of objects but also data exchange. An RFID-tag or transponder contains the current workpiece data that can be updated during the ongoing production process, and accompanies the workpiece from the beginning of production to delivery. This data could include part number, material name, etc. An RFID read-write device has access to the transponder data and forwards it to a PLC or simultaneously to a host computer. Each transponder has its own RFID number. This allows for flexible activities during the production process. Yes, even a production size of one is possible. RFID is one of the important enablers for Smart Factory or Industry 4.0. Here users see the basic components of a typical RFID-system. The RFID-Reader sends a constant radio wave via an antenna. The tag, also called a transponder, receives this signal, and responds with its own radio signal containing the information stored in its memory. The reader decodes this information and passes it on further, typically to a host computer. The problem was that it could only detect the objects at a certain fairly short distance. Today users see RFID almost every day, from the location chips in dog, to automated toll-collection systems, to Apple Pay. One reason this RFID technology, which users also use in daily lives, is so successful is that the tags can be built very small and cheaply. But wait. Each electronic device must have an energy source, batteries are bulky, and users have to recharge them. Passive RFID transponders resolved this problem by receiving their required energy completely via an electromagnetic energy field from the RFID read-write device. Furthermore, data can also be transmitted bi-directionally via this energy field. Because energy and data are transmitted via one coil simultaneously, users need a demodulator to extract data from the energy during an upload. The new information can then be stored in the memory, which has to be, in this case, an EEPROM, as users have a Read-Write transponder. The encoder and modulator are active when the tag is read-out. Small in size, cheap, and with an almost unlimited lifetime, these passive RFID transponders are the most commonly used. What users see from this draft is that the distance range and data transfer mainly depend on the frequency. These frequencies are fixed and the components are not interchangeable. That’s also because each frequency range requires its own antenna. In general, it can be said: The higher the frequency, the smaller the antenna. If RFID technology is used in logistics, larger distances must be covered, sometimes up to several 100 meters. Here, so-called active transponders must be used. The transponder is normally in so-called “sleep mode” and is only activated by the RFID read-write unit when a data transfer is to take place. This can increase the service life of the transponder’s battery up to several years. Advantages are for example, increased range, lower signal run time, higher data transfer and the option to read several tags at one time. But on the other hand, the tags are large, costly and have a limited lifespan due to their battery. The last type of RFID-tags are the so-called semi-active tags. As the name suggests, this device incorporates some active RFID features, such as a battery to provide power for its memory and passive RFID features for data transmission purposes. These tags have a longer lifespan than active tags and are less costly. How can passive RFID tags with a low-power chip transmit data? One possibility is the so-called backscatter modulation.