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Image credit: Chelsea Turner, MIT

MIT engineers give RFID tags chemical-sensing capabilities

It turns out chip-centric designs are more reliable than antennae.
Chelsea Turner, MIT

Engineering specialists from MIT have devised a way to make RFID (radio-frequency identification) tags more reliable and pick up on chemicals in the surrounding environment -- without needing the typical battery.

The 'plug-and-play' nature of the new designs is very promising for facilities that need to monitor pipes or gas containers over larger networks. It also offers an increased communication range (up to 10 meters) which can help minimize the amount of required readers and thereby lower overall costs.

RFID tags are already ubiquitous in retail, libraries and hospitals. They're cheap, wireless, not too power hungry, and are very useful for keeping track of inventory. However, it's their design that subjects them to inefficiency; most RFID tags have tiny, in-built antennae, which deflect a radio signal and transmit code that's then stored in the tag's chip. The problem is when the radio waves reflect against walls (or other objects) and interfere with sensing. Sai Nithin Reddy Kantareddy, a graduate student, explained that antennae-based sensors increase the chances of getting false positives or negatives which makes them unreliable.

To deal with that complication, MIT's Auto-ID lab has a design which turns ordinary RFID tags into sensors. Some RFID tags are battery-assisted, while others are more passive (meaning they get their energy from a remote reader), but both types use antennae. Aware of the shortcomings associated with antennae, the researchers came up with an UHF (ultra-high frequency) tag sensor configuration which is less prone to interference, and was able to sense glucose in the environment. The glucose-sensing chip produces an electric charge whenever it identifies glucose, and that acts as the battery.

Their approach involved memory chips that could switch between a 'passive' energy-based mode and a local, energy-assisted mode (where an external battery is normally required) into an RFID tag with standard radio-frequency antennae. A circuit wrapped around the chip allowed it to activate the energy-assisted mode only when it sensed particular stimuli.

In the future, the researchers hope to develop RFID tag sensors that can identify environmental carbon monoxide -- and the good news is their chip-centric design is much more scalable and than the specificity demanded by antennae designs.

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