Is there one type of RFID that works better than others?
It depends on what you are trying to achieve. If you are collecting tolls, most transportation agencies employ active RFID technology to ensure that tags can be read 100 percent of the time. Because an active tag broadcasts a signal, it is easier to capture the serial number of a transponder mounted on a windshield.
More recently, some toll-collection agencies have been introducing passive ultrahigh-frequency (UHF) systems (see RFID Puts Salt Lake City Drivers in the Fast Lane and Efforts to Aid Adoption of ISO 18000-6C RFID for Toll Collection Move Forward). Passive UHF transponders have improved a great deal during the past few years, so they can be read more consistently than they could, say, five years ago. The advantage of a passive UHF system is that the transponder is less expensive and does not need to be replaced when the battery dies.
If you are seeking to use RFID to monitor the conditions of bridges, you will likely require active RFID technology. Researchers in South Korea have developed a system to monitor corrosion (see Wireless Sensors Monitor Troubled Bridges).
—Mark Roberti, Founder and Editor, RFID Journal
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