UHF RFID's Key Constraints

7. In some cases, RFID passive tags received from vendors can be damaged during manufacture, in transit or when encapsulated. Thus, it would be wise to test each and every tag before placing them on objects. This way, you can avoid a reduced read rate due to damaged tags.

8. When performing a test for read rates, make a point to understand the radiation pattern of the interrogator antenna rather than just doing a trial-and-error test with the tags. An optimum combination of tag orientation, antenna direction and radiation pattern provides the best-read rates.

9. Keeping the UHF RFID tags in close physical proximity to each other can render some tags ineffective. Nevertheless, a more complex signaling algorithm, such as frequency hopping, can actually help increase performance levels.

10. If you plan to apply UHF RFID tags to liquid-based items, such as bottles of juice or water, understand that the effective read range of these tags would be drastically reduced as shorter-wave tags are more susceptible to absorption by liquids. Nevertheless, read range can be improved marginally by having a spacer between the tag and the object.

11. An RFID tag's lifespan can vary, depending on the application, business processes and other environmental factors involved. For example, in the supply chain, tag life may end once a product reaches the consumer; in cases of assembly line tracking, the end-point may be when the finished good is produced; and in asset-tracking scenarios, a tag's lifespan may be most subject to wear and tear. Whatever the lifespan, RFID solution providers need to simulate the various internal and external factors that can impact tag performance over a period of time. For example, what are the minimum and maximum temperatures that a tag can withstand, and for how long? And what would the impact be if the tag were physically handled—that is, removed from one object and reused on another—a thousand times per year? Answering these questions can help determine the kind of tag and encapsulation required.

12. Finally, when using a handheld UHF RFID reader for discrete item-level stock taking, make sure to set an optimum attenuation so the handheld interrogator doesn’t read superfluous tags. In such situations, a reader fitted with a circularly polarized antenna and set for high attenuation (low signal strength) would be ideal. In applications involving a search for out-of-sight objects, however, a linear polarized antenna with high power would be a preferable choice.

There are, of course, other parameters to consider when implementing a UHF passive RFID solution. Still, with these 12 critical constraints in mind, the process becomes that much smoother.

Vinod Kankaria is an RFID consultant based in Chennai, India.