A semi-passive tag is an RFID tag that has a battery but communicates with a reader using back scatter, like a passive tag without a battery. The battery is usually used to power a sensor, and to run the circuitry on the chip. That allows more energy from the reader antenna to be reflected back to the interrogator, thereby giving semi-passive tags a longer read range than ordinary passive tags.
The terms “semi-active” and “battery-assisted” are also applied to this type of tag. “Battery-assisted” is probably the best term, since it most clearly explains how this type of tag functions.
—Mark Roberti, Founder and Editor, RFID Journal
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