09-21-2007, 11:14 AM
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Passive RFID Tags Active in Asset Tracking
Issue #116 | Sept. 21, 2007 | by Venkat Krishnamurthy
For many years, active tags were the only RFID game in town for most industrial asset tracking applications. While their expense limited some practical uses, the alternative – passive tags – simply weren’t robust enough to meet stringent accuracy needs. In other applications requiring real-time location sensing (RTLS), passive tags don’t provide the required functionality.
So given the lack of alternatives, organizations have avoided using RFID in cases where the cost of active tag technology could not be justified. For example, active tags can cost from $20 to more than $150 each, because of their proprietary protocols and their need for batteries. There are plenty of asset tracking applications where ROI is achievable at these prices.
For many companies, though, that is simply too expensive to justify their use. Consider, for example, a manufacturer I spoke with recently that has over 2 million assets that require tracking through a closed loop supply chain. Using active tags, the cost of deploying RFID would have been prohibitive.
Don’t choke on active RFID
Let me first debunk the popular misconception that active tag technology is only used in cases where one needs the precise X, Y, Z location of an asset. In fact, the most common uses of active tags (60-70% of the uses cases we've seen) tend to be the "choke-point" model, i.e. the use of a low frequency exciter to place a tag in a zone.
The way it works is that the exciter "wakes" up an active tag. Upon "waking up", the tag sends an update on its location which is mapped to a "zone." In these cases you are using exactly the same functionality as a passive tag. The specific coordinates (X, Y and Z) are not being used in these cases. The question then becomes, why spend $20 on an active tag where you can spend 20¢? Even if you have an existing wi-fi infrastructure, the cost differential on the tags will pay for your RFID reader installation in short order.
Passive RFID reliability up, price down
With the advent of Gen 2 technologies and standards, passive tags are now both economically viable ($.20 to $.40 each) and accurate (100%) for applications such as asset tracking and work-in-process, which do not require continual (RTLS) RFID transmissions. Ruggedized cost from $1 to $3 each, including the plastic casing. A profusion of form factors and backing materials accommodate assets containing metal and liquids.
Consider bar code-based asset tracking implementations. Before the viability of passive tags, individuals had to read bar codes at specific points during the receipt, shipment and delivery of goods (i.e. typical supply chain). With the advent of robust Gen 2 passive RFID technology, tags can be read automatically, saving costs, time and human error.
The active RFID advantage
So if two-thirds of asset-tracking use-cases can use passive RFID, why not use these cheaper tags all the time? The answer is:
Readability & Physics: In many cases where the surroundings are RF noisy (e.g. too much metal in products/areas, liquids, etc.) active tags are the only choice. In the last year we've seen Gen 2 UHF tags perform superbly in many environments which previously were thought to be "difficult." So I recommend careful testing before deciding whether the environment is overly difficult.
Tag functionality: Active tags are battery assisted and permit features beyond just identity e.g. we've seen the use of tags with buttons. The buttons could be used, for instance to call a supervisor upon a certain event being observed. Because the back-haul for active tags has greater bandwidth (usually), it's also easier to send back temperature & pressure information that has been logged to the tag.
Real-time locationing: If there is a need to know the location of a tag in a relatively real-time manner, then active is a preferred route. While it's cool to see "dots on a map", most real-world applications don't need it. But for applications such as location awareness and safety of personnel in unsafe environs, this becomes a must.
Don’t get me wrong, there remain powerful applications for active tags, such as location and safety of personnel in dangerous environs, real-time patient tracking within hospitals, etc. It’s just that organizations now have the luxury of choosing the right tag for the right application. And in doing so, they can both expand the use of RFID tags in their organizations and enable additional savings.
Venkat Krishnamurthy is chief technology officer for OATSystems, a provider of RFID solutions (www.oatsystems.com). Dr. Krishnamurthy holds a Ph.D. in Computer Science from Stanford University and a Bachelor of Technology from the Indian Institute of Technology, Kanpur, where he was a President's Gold Medalist.
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