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Ant-size radios for the Internet of Things

Ant-size radios for the Internet of Things

The day is not far off when a patient admitted to a hospital will be wearing a tiny sensor affixed to a Band-Aid that continuously transmits body temperature to a computer that monitors readings 24-hours a day for signs of infection.

That’s just one of the applications in the Internet of Things (IoT) that Amin Arbabian, assistant professor of electrical engineering at Stanford University, foresees will result from new ant-size radios being developed by researchers at Stanford and the University of California at Berkeley.

These ultra-low power smart radios that can provide unique IP addresses and their locations are a key ingredient in the connected world of the IoT.

According to Arbabian, the radio sensors – currently measuring only 3.7 millimeters by 1.2 millimeters – could also be used to ensure that no instruments get left inside patients in the operating room.  “You can put one of these radios on every single item in the operating room,” said Arbabian. Once that is done, transmissions from sensors on the radio can be monitored to be sure that every item is in its proper place.

Arbabian adds that the potential applications of the technology are not just for medicine.  “Attaching radios to $100 bills is the scenario we started out with,” said Arbabian. Specifically, researchers tested attaching a radio chip to each bill.  The unique identifier on the chip was transmitted continuously and, as it came within range of a base station, it was identified. 

The trick to engineering a device small enough to work in such environments was development of new techniques for miniaturizing devices on silicon chips.   

In fact, the Stanford device carries everything on board a single piece of silicon – processors, sensors, oscillators and antennae.  And since everything is on a single chip, the device’s power requirements are very small.

“Our chip is consuming an average of 1.5 microwatts of standby power,” said Arbabian.  “If you compare that to the wireless standards today, it is orders of magnitude lower.”

The low power requirement also allowed the team to dispose of batteries.  Instead, the device is powered by extremely high-frequency millimeter waves, which is also the medium for transmitting data to base stations.

The main tradeoff of using millimeter waves is a very restricted range. The device as currently designed has a range of only 1 meter, though Arbabian said the team has plans to extend the range to up to three meters. 

Using millimeter waves also meant the team had to create its own transmission protocol.  “We could not follow any specific standards because none of them are efficient enough,” said Arbabian. 

While that means any actual deployment of the devices would also require base stations that support the Stanford team’s protocol, Arbabian pointed out that support for millimeter wave communications is growing rapidly.

“Already some in the mobile industry are integrating millimeter wave receivers on mobile devices,” said Arbabian.  “So we can leverage the fact that cell phones in the near future will have millimeter wave capability and can act as a gateway to these radios.”

Arbabian is quick to note that the Stanford-Berkeley device is only a limited piece of the IoT puzzle.  “The solution is not going to be the be-all and end-all for all IoT applications,” said Arbabian.  “This is a solution for applications where you need a very dense network and also very small size.”

While the devices have so far been tested without sensors, Arbabian said the team is looking to put a variety of sensors right on the chips.  “We know ways of designing temperature sensors on the chip,” he said. “We have some ideas on how to put more sophisticated sensors on the chip. Can you measure humidity based on conductivity? Can you measure other biochemical markers?”

When sensors can be put right on the silicon chip, Arbabian noted, the price doesn't increase.  That’s especially important in an IoT environment, where people are looking to deploy many, many devices.  

Posted by Patrick Marshall on Sep 30, 2014 at 12:50 PM


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