What are the advantages and disadvantages for each type of technology?
Schools have used both ultrahigh-frequency (UHF) and active tags operating in the microwave range. One of the first proposed deployments in a school was at Brittan Elementary School, in Sutter, a small town northeast of Sacramento, Calif. The school tested a passive UHF system, but ultimately did not deploy the solution due to privacy concerns raised by parents (see RFID Takes Attendance—and Heat). The same year, a Japanese school tested a system using Wi-Fi tags operating at 2.4 GHz (see RFID Watches Over School Kids in Japan).
I think the important question is not which frequency works best, but rather whether passive or active tags work best. Passive UHF tags are less expensive than active tags, which is their chief advantage. They have a read range of 30 feet when not attached to anything, but water absorbs RF energy in the UHF range, and the human body is mostly composed of water. That means it can be difficult to read tags consistently when they are close to the human body—this is the chief drawback for this application.
It might be possible to design tags that can be attached to a school bag or something else that children carry around with them, thus keeping the tag away from the body. The short read range also means that portal readers must be installed around doorways in order to capture data. If you want to know which room a child is in at any given time, that means installing interrogators around every doorway, which can be expensive.
Active tags have a long read range and broadcast their signal. As such, it is easier to capture information regarding a tagged object's location. Real-time location systems (RTLS) can pinpoint a student's location by triangulating on the beacon emitted by the tag he or she is wearing. However, it can sometimes be a challenge to determine whether a child is standing inside a room or outside, so the proper system really depends on exactly what information you need to collect.
Wi-Fi tags communicate with Wi-Fi access points, so schools that already have Wi-Fi systems installed will need only to add some access points to be able to locate students. The primary disadvantage is that active tags are more expensive than passive tags ($20 apiece or more), so the initial outlay and replacement costs can be high.
—Mark Roberti, Editor, RFID Journal
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