CleanSpace CO Sensor Runs On Freevolt RF Harvesting

mspohr writes: A few years ago, a Kickstarter was set up to develop a locator tag powered by free radio frequency (RF) energy harvested from the environment. This was called a scam here on Slashdot and was shut down before it was funded on Kickstarter. However, it now appears that the concept is not as far-fetched as some predicted. A UK company CleanSpace has developed a carbon monoxide (CO) sensor which is powered by free RF. A review of the product has been posted on YouTube. It uses Freevolt technology to keep a battery charged and the CO sensor running. Since they have several thousand of these devices collecting data, they do appear to work and it seems to be in the 'not a scam' department.

Comments

I worked on this

[Anonymous Coward]

I've worked on this project and it doesn't work.

Basically all it is is an antenna with a half bridge diode rectifier. This is pretty straightforward however the problem is that despite using 'zero drop' diodes the ambient RF energy does not produce a sufficient voltage (power out of the antenna with the line impedance at the diode) to switch the diode properly which causes a rapid drop off in efficiency. Basically the diode is still in the sloped part of the IV curve (zoom in on an IV curve at the knee). This combined with the fairly low amounts of power available means that the power output of these things is in the 10s of uW, which is less power than is consumed by the charge pump needed to top the battery up! So how does it work then? Check the tear down photos and you'll see a massive battery...

The other interesting thing about this 'technology' is that you can calculate the energy density of a harvester, it's simply the mean time till failure x power output / volume of device. When you do this calculation you quickly realise that due to the size of the antenna needed to see any appreciable power the device would have to last for 10-20 years to begin to approach the energy density of even coin cells (including the casing)!

Warning: Part 15 broadband unintentional radiator

[Bruce Perens]

One of the side-effects of this device, implicit in its design, is that it will re-radiate mixing products of all received signals. This tends to interfere with nearby radio reception.