“Radio frequency energy harvesting” might sound like snake oil — Free energy, pulled out of thin air? Yeah, right! — but the idea of using radio waves to transmit power has been around for more than a century and is finally coming into its own with the Internet of Things. Between Wi-Fi, Bluetooth, cell phones and myriad other wireless signals, there are plenty of ambient RF sources to draw from. And even though only small amounts of energy can be reclaimed this way, it doesn’t take much to keep a simple sensor or actuator running.
Freevolt, developed by Drayson Technologies, is an RF energy harvester designed with the IoT in mind. It’s essentially a broad-spectrum antenna that picks up all kinds of wireless signals and, instead of reading them for data, converts a bit of their energy into usable electricity.
According to the company’s promotional materials, an antenna about the size of a credit card can collect 100 microwatts of power in a typical home or office. That’s several orders of magnitude less than you’d need to run your smartphone, but it’s enough for low-power devices like embedded sensors that can subsist on a trickle of energy. As long as there are enough wireless signals available, a Freevolt device would never need to be plugged in or have its batteries changed.
In a presentation last year at the Royal Institute, CEO Paul Drayson said the technology could be scaled up, with larger antennas embedded in billboards or walls to provide energy for e-ink displays or building infrastructure. But as a first step, the company is marketing an air pollution sensor, the CleanSpace Tag, to demonstrate Freevolt’s immediate applications in the IoT market. The gadget is about the size of a smartphone, connects over Bluetooth Low Energy to share sensor data, and uses Freevolt to maintain the charge of an internal battery with a usable lifespan of five years.