Posts Tagged‘energy harvesting’

Recycling Electromagnetic Energy? iFind, Surely You Jest.

If you’re reading this article, which is only available through the Internet, then you’re basking in a tsunami of electromagnetic radiation. Don’t worry though, the vast majority of these waves are so low power that they don’t make it through the first layer of your skin before dissipating harmlessly. Still they do carry power, enough so that this article can worm its way from the server all the way to the device that you’re reading it on. Considering just how pervasive wireless signals are in our modern lives it then follows that there’s a potential source of energy there, one that’s essentially free and nigh on omnipresent. Whilst this is true, to some extent, actually harvesting a useful amount of it is a best impractical but that hasn’t stopped people from trying.

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If you’re a longtime fan of Mythbusters like myself you’ll likely remember the episode they did on Free Energy back in 2004. In that episode they tested a myriad of devices to generate electricity, one of them being a radio wave extractor that managed to power half of a wristwatch. In an unaired segment they even rigged up a large coil of wire and placed it next to a high voltage power line and were able to generate a whopping 8mV. The result of all this testing was to show that, whilst there is some power available for harvesting, it’s not a usable quantity by any stretch of the imagination.

So you can imagine my surprise when a product like iFind makes claims like “battery free” and “never needs recharging” based around the concept of harvesting energy from the air.

The fundamental functionality of the iFind isn’t anything new, it’s just yet another Bluetooth tag system so you don’t lose whatever you attach the tag to. It’s claim to fame, and one that’s earned it a rather ridiculous half a million dollars, is that it doesn’t have a battery (which it does, unless you want to get into a semantic argument about what “battery” actually means) and that it charges off the electromagnetic waves around you. They’ve even gone as far to provide some technical documentation that shows the power generated from various signals. Suffice to say I think their idea is unworkable at best and, at worst, outright fraud.

The graphs they show in this comment would seem to indicate that it’s capable of charging even under very weak signal conditions, all the way down to -6dBm. That sounds great in principle until you take in account what a typical charging scenario for a device like this would be, like the “ideal” one that they talk about in some of their literature: a strong wifi signal. The graph shown above is the signal strength of my home wifi connection (an ASUS RT-N66U for reference) with the peak readings being from when I had my phone right next to the antennas. That gives a peak power output of some -22dBM, which sounds fine right? Well since those power ratings are logarithmic in nature the amount of power output is about 200 times weaker which puts the actual charge time at about 1000 days. If you had a focused RF source you could probably provide it with enough power to charge quickly but I doubt anyone has them in their house.

There’s also the issue of what kind of power source they have as the size precludes it from being anything hefty and they’re just referring to it as a “power bank”. Non-rechargeable batteries that fit within that form factor are usually on the order of a couple hundred milliamps with rechargeable variants having a much smaller capacity. Similar devices like Tile, which includes a non-rechargeable non-replaceable battery, lasts about a year before it dies which suggests a minimum power drain of at least a couple mAh per day. Considering iFind is smaller and rechargeable I wouldn’t expect it to last more than a couple weeks before giving it up, Of course since there’s no specifications on either of them it’s hard to judge but the laws of physics don’t differ between products.

However I will stop short of calling iFind a scam, more I think it’s a completely misguided exercise that will never deliver on its promises. They’ve probably designed something that does work under their lab circumstances but the performance will just not hold up in the real world. There’s a lot of questions that have been asked of them that are still unanswered which would go a long way to assuring people that what they’re making isn’t vaporware. Until they’re forthcoming with more information however I’d steer clear of giving them your money as it’s highly unlikely that the final product will perform as advertised.