Researchers at Stanford University and UC Berkley have designed and built a radio wave energy-harvesting radio and computer SoC, which combines all the required computing power, antennas, radio and communication software stack onto a device the size of an ant – only 3.7mm x 1.2mm. The all-silicon construction of the unit means that it could be mass produced using existing techniques, giving it a cost of “pennies per device.”
The device uses RF waves in the 24GHz band to generate power, and transmits in the 60GHz range – a process that requires two separate antennas. This harvested power then lets the chip run the required computation and send a signal back to the origin of the request, before powering down again into sleep mode. STMicroelectronics manufactured a hundred of the modules as proof of concept, in 65nm CMOS, which required only standard wafer printing equipment.
“The next exponential growth in connectivity will be connecting objects together and giving us remote control through the web,” said Amin Arbabian, the assistant professor who demonstrated the chip at the VLSI Technology and Circuits Symposium. “By putting all the essential elements of a radio on a single chip that costs pennies to make, you put a bi-directional wireless control system in every light bulb,” or any other device he added.
Arbabian’s work on the unit began as a PhD project in 2011, where he focused on miniaturizing radios to reduce power consumption. If powered by an AAA battery, Arbabian says it could power the chip for a century. But miniaturizing the chip meant reworking the antenna to 10% the size of a WiFi antenna and ensuring it could operate at 24 billion cycles per second – a rate at which standard transistors wouldn’t function, according to Arbabian. The benefit of moving to the higher frequencies was found in the ability to shrink the antenna to a much smaller size than radios using conventional lower frequency RF would require.
In addition, the technical description states “a modified 60GHz transmitter (6-bits per slot) is used to communicate data sequence as well as the local timing reference. Pulse signaling enables real-time localization through time-of-flight. The chip operates with a standby power of less than 1.5uW coming from the reader.”
The chips have yet to be deployed in a product, but Arbabian envisions an embedded mesh network comprised of dozens of chips per home, deployed every 50cm so that the high-attenuation transmissions can be conveyed from one end of a building to another. This architecture would require a hub, as the chips themselves lack the required processing power to self-orchestrate a network.
But this type of connectivity is what is required if we are going to see a world with trillions of connected objects. IPv6 can certainly handle that amount of unique IP address, by several orders of magnitude, but currently it is the cost per device that holds back the trillion-forecast. There isn’t enough lithium in the world to provide batteries for that many devices, but when you apply energy harvesting technology to a device with such a low power consumption, you can begin to see where the trillions of devices might go – and your imagination is your only limit when it comes to deploying a device like this. That, and the physical constraints of optimal temperatures, durability ratings and communication ranges.