We are looking for a long-range RFID tag and interrogator to use on vehicles (buses). What is the secure maximum distance to interrogate passive and active RFID tags? Can I integrate an RFID tag and interrogator with Wi-Fi 802.11 wireless networks? How many tags can I interrogate at the same time? And what happens if there is more than one tag in the same area of any interrogator?
The maximum reliable distance for an ultrahigh-frequency (UHF) passive tag is probably 10 to 15 feet, so in order to track buses, you would need to have readers located at key points that a bus passes at a consistent distance. For example, Montreal's transit agency, Agence métropolitaine de transport (AMT), tracks buses arriving at depots (see RFID Puts Montreal Transit on a New Route).
In addition, the Secretary of Transit and Transportation for Bogotá, Colombia, tracks buses using active tags from Identec Solutions (see RFID Speeds Up Bogotá). These can be read from more than 100 meters (300 feet) away.
Many readers currently come with Wi-Fi networking capability. Technically, you can read only one tag at a time, but tags can be read so quickly that for operational purposes, you can usually read dozens of tags within a second. If there is more than one tag in a read zone, the interrogator asks the tags to respond according to a predefined algorithm.
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