Algorithms Increase Operational Reliability of UHF RFID Systems

A modern and efficient supply chain can no longer be imagined without an automatic-identification system. Due to cost reasons, radio frequency identification in the ultrahigh-frequency (UHF) band is increasingly employed during production, with industrial environments posing difficult challenges for radio technology. For industrial use, new readers were specifically equipped with a number of groundbreaking functions.

A radio frequency identification solution is always made up of two elements: a data medium (a transponder or smart label) and a read-write device (a reader, also called an interrogator). The transponder is the information carrier, and is attached to the object to be identified. The reader interrogates the information on the transponder, forwards it to higher-level systems—such as controllers—and, if needed, writes data back to the transponder. With UHF RFID systems, the information transfer between reader and transponder takes place by means of radio waves, as is the case with a radio or mobile phone.

Due to the long transmission range of several meters, UHF systems were, until now, typically employed for logistics applications. Increasingly, though, these systems can also be found within industrial production facilities. The reasons behind this trend are the continuous identification of objects throughout the production process, as well as the availability of inexpensive transponders (labels) that are disposed of at the end of the process. Since there is no need to monitor and look after reusable transponders, maintenance is greatly reduced. In vehicle production, for example, stripping paint off transponders is an expensive step that can be eliminated when switching to UHF RFID with disposable labels.

Difficult Radio Conditions in the Production Environment
For radio-based systems, however, industrial production facilities pose special challenges. Typically, readers at materials-handling or production machines are positioned very close together. Due to this proximity, radio crosstalk cannot be ruled out. The physical distance between the objects being manufactured—such as motors—is also very small. Parallel production lines make it more difficult to distinguish between a local object and an object on a neighboring line. What's more, the metallic environment encountered causes problems for radio transmission.

Siemens' RFID SIMATIC RF600 portfolio of UHF readers, antennas and transponders.

The UHF signal sent by the reader is repeatedly reflected by metallic objects—such as machine enclosures, steel girders, grates or the actual object to be captured (a crankcase, a car body and so forth). These reflections can cause the radio waves to spread in different paths and overlap, thereby leading to undesirable effects, such as dead spots, created by waves canceling each other out, and overshoots (an unwanted extension of the transmission range). As a result, a transponder may not be detected, even if it is located within the reader's coverage area. Conversely, a transponder located outside the coverage area may unexpectedly be read.

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