John Shearer and his company, Powercast, is trying to solve an interesting problem: how do you send power wirelessly? He points out that wireless power isn’t a new phenomenon – solar power is wireless, as is water power. But sending electicity through the air from one point to another would be pretty cool. Even better would be harnessing radio frequency energy that’s already in the air to serve useful purposes.
This idea of reclaiming power comes from his father’s work on television transmitters. He watched his father build transmitters which used huge amounts of energy to send a signal over a few miles. He wondered, “You’re putting all this power into the air – couldn’t we harvest it for other purposes?”
It is, in fact, possible to do this. But you need to consider low levels of power, in the milliwatt ranges. There are useful things you can do with milliwatts of power – you can trickle charge a battery, can power a mobile phone in sleep mode, can power medical devices. Because battery technology is so poor, electronics have had to get very power efficient, and there are thousands of possible applications for milliwatt power. You could power higher power devices, “but sending 90 watts across your desk with a radio transmitter is not safe, unless you want to keep your coffee hot at the same time.”
It’s also possible to harvest existing RF energy, but taking baby steps, it makes sense to work with a wire-powered transmitter and wireless receivers that can harvest energy and convert it to power. The first example Shearer offers of this is a project for a zoo where sensors needed to monitor the temperature of water in a penguin tank. Those sensors ripped through AA batteries very quickly, because batteries perform poorly under cold conditions. By powering these sensors remotely from a powered antenna and power-harvesting antennas, Powercast was able to demonstrate the utility of its technology.
A much sillier demo is now commercially available – it’s a very geeky Christmas tree, where the trunk is an antenna, and each bulb is a receiver that uses RF energy to power itself. If you’ve got $400 to spare, you can buy one for yourself.
While wireless Christmas trees may not change the world, the idea of free-space power transmission might well be, and it’s exciting to see an early manifestation of it.
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