Would passive high-frequency (HF) tags be sufficient, or would I require ultrahigh-frequency (UHF)?
You can use any passive HF tags for taking attendance, as long as each person presents his or her RFID tag to a reader. The problem with this approach is that people sometimes forget to present their badges to the reader and are thus not counted as present when they are, in fact, on the premises. To automatically capture information about who has attended a class or meeting, you would need to use UHF RFID technology. But UHF energy is absorbed by the human body, so it is sometimes difficult to read passive UHF tags when they are close to the body, or when there is a body between the tag and the reader. This is because the human body is mostly composed of water, which absorbs RF energy in the UHF spectrum.
I would recommend utilizing battery-assisted UHF tags. The battery boosts the tag's signal, so even though the tag communicates with the reader (much like an ordinary passive UHF tag), it can be read consistently even when close to the human body. Convergence Systems Ltd. (CSL) makes a tag for precisely this purpose, and those who have used it tell me it works very well. CSL will be an exhibitor at this year's RFID Journal LIVE! conference and exhibition, which will take place in Orlando, Fla., on May 3-5, so you could connect with them at the event.
—Mark Roberti, Founder and Editor, RFID Journal
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