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Passive or Active RFID: The Choice Isn't Always Obvious
Blount Island Command, which performs preprositioning for the U.S. Marine Corps, is switching from active to passive technology, for the purpose of tracking vehicles.
I recently visited Blount Island Command (BIC), located in Jacksonville, Fla., which manages the prepositioning process for the U.S. Marine Corps (USMC). The island comprises 33 acres of reinforced concrete, on which tanks, munitions, food, spare parts and myriad other items that the Marines use overseas are staged before being placed onto a ship. As part of its efforts to improve asset visibility and equipment accountability, BIC has evaluated passive RFID technology, and is now applying passive RFID tags to the equipment transported on what are known as maritime prepositioning ships (see U.S. Marines' Blount Island Command Attaches Passive Tags to Containers).
Tracking everything being moved onto ships bound for overseas ports—as well as retrograde material from Iraq and Afghanistan—is a huge task. In fact, it takes 40 to 60 days to unload and reload a ship. How workers track vehicles going onto and off of vessels has changed over time. At first, workers would manually write down serial numbers to track vehicles, but this was a slow and error-prone process. Then, BIC introduced bar codes, which was better, but they were often damaged in the theater of operations. So a few years ago, the command began putting active RFID transponders on vehicles, so that they could be tracked while moving onto and off of ships.
This makes perfect sense. Active tags can be read from a longer distance than passive tags, and since the vehicles are often in large open spaces (such as parking areas), active technology would seem the most obvious choice. But I learned, during my visit, that the command is switching to passive tags. The main reason is maintenance—active tags have a battery that needs to be replaced every three to five years. That might not be a huge deal within a hospital setting, but when a vehicle is located within a war zone, no one wants to worry about changing batteries.
Another reason for the switch is that the Marines do not require real-time visibility into their vehicles' locations. They simply need to read the tags and identify the vehicles as they are moved onto and off of ships. Portals set up near a ship's entry ramp make this possible. When employees need to take inventory of vehicles located within a particular lot, they can drive around in a car equipped with a fixed ultrahigh-frequency (UHF) RFID reader, thereby enabling them to conduct inventory in a fraction of the time that it would take to perform this task manually.
Finally, USMC can switch to passive tags because their read range has greatly improved. During my visit, BIC demonstrated how an Omni-ID Ultra tag could be read from a distance of 75 feet. That's not as good as the distance for an active tag, which can be read from 300 feet or more, but the Marines are finding that it's more than sufficient for their need.
I'm not suggesting that passive tags will replace active tags. Certainly, the longer read range is necessary for many applications, and the ability to triangulate on a beaconing active tag is very valuable when locating assets. But the point here is that there is no hard and fast rule regarding when to employ active or passive tags. The specific application, environment and situation involved all have an impact on choosing the proper RFID solution for a particular problem.
Mark Roberti is the founder and editor of RFID Journal. If you would like to comment on this article, click on the link below. To read more of Mark's opinions, visit the RFID Journal Blog, the Editor's Note archive or RFID Connect.
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