According to the RFID journal, the idea of Radio Frequency Identification (RFID) has been around since World War II. When approaching a friendly radar position German pilots would roll their planes, which would change the signal reflection and alert the radar operators that a friendly craft was approaching; this is something like a passive RFID system. The British meanwhile, fixed transmitters to their craft to send signals to special receivers at their radar stations alerting the operators that a friendly craft was approaching (more like an active RFID system).[1]
RFID systems consist of two parts: a reader (like the radar station in the examples) and a tag (like the airplanes, or the airplane’s transmitters). An RFID tag can be as simple as a microchip and an antenna. The tag transmits information to the reader via radio waves and the reader intercepts and interprets the information.
RFID tags can further be defined as passive, battery assisted passive (BAP), or active. BAP and active tags use a power source to enhance the signal so it can be read from much further away.
- Passive RFID tags are comprised of two components: a chip and a radio antenna. The reader is used to send out a signal that 'wakes up' the chip in the tag. The tag sends back the signal ('backscatters') to the reader, transmitting the information on the chip. Passive chips backscatter 10-15% of the energy they receive and, therefore, can usually be read from only a few feet away.
- Battery-assisted passive (BAP) RFID tags contain an embedded power source – a thin film battery or other energy storage device. When receiving a signal from a reader, the power source enables the tag to backscatter much more of the energy it receives (some claim as much as 90%). BAP Tags have been shown to be read from dozens of feet to over 100 feet away.
- Active RFID tags utilize a power source (usually a stronger battery than BAP tags), are typically 'always on', and emit the energy from the battery rather than through backscatter. This means essentially that they are always broadcasting a signal and therefore do not reflect back the signal from a reader. They are needed in electromagnetically unfriendly environments and some can be read from readers over 100 feet away; and, with additional power, some can be read from over 300 feet away.
There have been three major issues with the energy storage components of BAP and active RFID tags: cost, reliability and maintenance. Up until recently, active and BAP technologies added significant bulk and therefore cost to RFID tags. With recent thin film battery technologies bulk is less of an issue, however the thin film batteries can be less reliable and more costly. In addition, detection ranges can drop significantly with the age of the tag and battery, with some dropping from dozens of feet to a range comparable to a passive tag.
There are a wide variety of uses for RFID however, and they make use of all the different RFID characteristics. We will discuss more on RFID applications in later postings, but small, inexpensive and simple Passive RFID tags can be printed out in large quantities and used to help track large volume, but relatively low cost items such as garments for Wal-Mart. Their low-read range is not a problem when used for things like contactless payment cards, or automobile toll station passes. BAP or Active tags, while more expensive, provide options for tracking large items in large fields like containers in a dockyard, automobiles in a parking lot, or pallets in a warehouse.
At some city libraries you can now use a self-checkout where you place your stack of library books on an RFID pad (the reader), scan your library card, and within seconds the books are identified and checked out on your account. One day soon, we expect to use a “smart shopping cart” where you put the items you want in a cart, they are logged and payment is done automatically when you exit the store. Companies should see the ability to easily and cost-effectively track assets or track inventory throughout their supply chains, and food and pharmaceutical supply chains should be able to more effectively control the quality of their products making them safer for consumers.
RFID has the potential to impact all of our lives. Using the unique characteristics of different types of tags and systems RFID should see a wide variety of uses and is sure to have tremendous implications for our future.
[1] Roberti, Mark “The History of RFID Technology” RFID Journal http://www.rfidjournal.com/article/view/1338
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