One of the first decisions to be made in designing an RFID system is whether to use active or passive RFID tags. Because active tags have a battery in them, they have certain advantages over passive tags. Their signal is stronger, and they emit a signal without activation by an RFID reader, so they can constantly “chirp” their identity.
The additional power can overcome interference from surrounding electromagnetic fields, which means that for use on metals, active tags were the only option until a few years ago, when on-metal passive tags were introduced.
In recent years, active tags have been developed with improved functionality, enabling the tag to capture and broadcast pedigree data -- time, temperature, or GPS location -- in addition to a simple identity signal. There are also features of passive tags that are superior to active tags.
The most significant is cost; the initial per-tag cost is much lower for passive tags. Passive tags also have a much longer lifespan, lasting indefinitely, while active tag batteries typically must be replaced within two-to-three years, adding both infrastructure and labor costs. The lower overall cost – both in installation and maintenance – is responsible for the popularity of passive tags today.
Another important differentiation between passive and active tags is tag size. Passive tags are generally smaller than active tags, and will therefore physically fit on a smaller surface area. As with active tags, many new capabilities have been developed for passive tags in recent years.
Most notably, passive tags are now able to work on metals and liquids, and the memory storage capacity has been increased substantially to store pedigree data.
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