I am doing a project on RFID technology, and I have a few questions regarding tags. If there is a thick concrete wall, or some other barrier, between a tag and a reader, can the tagged object still be read? And what are the differences between active, passive and semi-passive tags?
It is difficult to answer your question without more detail. How thick do you consider "thick?" Is it 1 foot thick or 10 feet thick? And is there a great deal of metal rebar in the wall? These issues will have an impact.
In general, radio frequency identification cannot penetrate a wall with a lot of metal reinforcement, or that has great density or thickness. Whether or not an object will affect a passive tag's readability depends on that item's size, as well as whether it is composed of metal or contains a high volume of water, which absorbs ultrahigh-frequency (UHF) energy.
A passive tag has no power source and cannot broadcast a signal; it simply reflects a signal back to a reader. An active tag has a power source—typically, a battery—and can broadcast a signal, like a cell phone. It has a much longer read range than a passive tag.
A semi-passive or battery assisted tag has a battery that is used to power a sensor and run the chip, but it still reflects back a signal to the interrogator, rather than broadcasting a signal. The read range is longer than for a purely passive tag, but not much longer.
—Mark Roberti, Founder and Editor, RFID Journal
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