Is progress being made in passive or active RFID for scanning in such high-density materials?
Active tags can be used for this purpose (see RFID Is the Cure for San Francisco Construction Project). Such tags broadcast a signal, which can usually penetrate through fairly dense materials, just as a cell phone signal can be received when you are inside a brick or concrete building. Passive transponders do not broadcast a signal, so it is much more difficult to penetrate dense materials. However, tag performance and reader sensitivity have improved a great deal during the past few years, and it is now possible to read tags embedded in asphalt and concrete. The Minnesota Department of Transportation has put passive ultrahigh-frequency (UHF) tags on sensors embedded in roads, for example, in order to locate those sensors (see RFID Takes the Strain Out of Testing Minnesota's Roadbeds). The location can be found using a standard Motorola handheld reader.
—Mark Roberti, Founder and Editor, RFID Journal
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