We recently blogged about the choice of barcode or RFID for tracking applications.
When RFID is the choice, another decision looms: passive RFID versus active. The two technologies are very similar (see
RFID Technology
for an initial discussion).
If your application is "open loop" -- for instance you exchange goods with third parties -- your choice is limited since the standards call for EPCglobal passive tags. Your choice might also be limited if your tags encounter harsh conditions -- passive tags are better survivors. But otherwise you have choice. Often, the most important factor in this decision is not a technology factor, it is a cost factor. The decision hinges on the sum of total tag cost and total reader cost.
Total tag cost is driven by the total number of objects to be tagged -- lots of objects calls for inexpensive tags. Also a short lifecycle (commission a tag, read it just a few times, then discard it) calls for inexpensive tags. Inexpensive tags usually means passive is the choice. If you are tagging relatively few objects, and if the objects are permanent and valuable, then active RFID is the choice.
Total reader cost is driven by tag readability. While there are cases where short read range is required (contactless payments), usually trying to increase readability is THE challenge. Readability of active tags is usually not an issue... for passive it’s almost always the issue. If you can tightly control tag/reader proximity you usually can solve passive readability issues -- but this may mean using lots of readers and/or novel reader placement like portals and vehicle mounts.
The cost of reader installation includes mounting readers and antennas, and connecting power, antenna, and communication cables. Reduced readability means more readers and therefore greater expense. So the trade-off between passive versus active can come down to the cost of reader installation versus tag cost.
