Is Movement or Shaking Necessary to Read 100 Percent of Fixed UHF RFID Tags?

Can a reader interrogate tags without any movement taking place?

—Hamid

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Hamid,

It depends. If you had a fixed reader pointing at a shelf containing cartons, and the tags faced out with no cartons behind others, you would likely be able to read every tag with little problem and no need to shake the tags. However, if you had a fixed reader pointing at a round rack holding 100 clothing items, you might need to move those items in order to interrogate the tags.

There are two issues with rounders. One is that you would have tags in different orientations. If a tag were facing the reader, then it could be easily read, but if it were turned sideways to the device, doing so would be more difficult. Tags have improved a lot to address this orientation issue, but occasionally it can still be a problem, particularly if you are not using a circular polarized reader antenna.

The second issue is that tags that are close to one another can prevent energy from reaching those behind them. Shaking or moving the tags helps to create separation, which enables you to achieve 100 percent read accuracy.

There is a third issue, which is null spots or dead zones in the read field. With passive ultrahigh-frequency (UHF) RFID systems, there can be areas in the field in which tags will not be energized. Moving the tags (not just shaking them) ensures that they travel out of the null spots and are read.

In general, I would say that if tags are close together and in random orientation, movement can help to ensure that all of the tags are interrogated. But in situations in which there is separation and tag antennas are oriented toward the reader, it is probably not necessary.

—Mark Roberti, Founder and Editor, RFID Journal