http://www.newscientist.com/article/dn27633-gadgets-powered-wirelessly-at-home-with-a-simple-wifi-router.html
Small devices could use this as part of an internet of things, says Ben Potter at the University of Reading, UK.
Key to this is that the router needs modifying to transmit almost continuously at full power on multiple channels at times when the channels are not utilised for real traffic.
Key to this is that the router needs modifying to transmit almost continuously at full power on multiple channels at times when the channels are not utilised for real traffic.That is a pretty good definition of the bad old days practices of the Communist-era jammers.
A 2.4 GHz users that does anything resembling that will be VERY unpopular with their neigibors who are trying to use WiFi (or Bluetooth, etc.)
Wishing something would work is not a viable alternative to understanding the laws of physics as we know them on this planet.
We seem to be losing our grip on reality here, folks.
Seriously, I strongly suggest you read it before jumping to conclusions as I indeed did.
Before we all write the idea off as cranky, take a look at this POWIFI paper http://arxiv.org/pdf/1505.06815v1.pdf
It seems to have been covered in a number of popular news outlets, including several mainstream ones, over the past two or three days. I was on the tube this morning and noticed it in the Metro's pop sci section overlooking someone's shoulders. Brain said "bollocks", but I thought I'd look at the underlying details, from both what they're claiming it can do, and how they apparently achieve it.
Once you get beyond the media hyperbole, the actual claims are rather more sensible. Furthermore, I spent half an hour or so with the back of an envelope and, against my gut feel, it does seem workable.
Key to this is that the router needs modifying to transmit almost continuously at full power on multiple channels at times when the channels are not utilised for real traffic. The harvester end itself is actually quite simple but there have been some rather careful parts.
Seriously, I strongly suggest you read it before jumping to conclusions as I indeed did.It wasn't my conclusion. It was yours.
Before we all write the idea off as cranky, take a look at this POWIFI paper http://arxiv.org/pdf/1505.06815v1.pdf
It seems to have been covered in a number of popular news outlets, including several mainstream ones, over the past two or three days. I was on the tube this morning and noticed it in the Metro's pop sci section overlooking someone's shoulders. Brain said "bollocks", but I thought I'd look at the underlying details, from both what they're claiming it can do, and how they apparently achieve it.
Once you get beyond the media hyperbole, the actual claims are rather more sensible. Furthermore, I spent half an hour or so with the back of an envelope and, against my gut feel, it does seem workable.
Key to this is that the router needs modifying to transmit almost continuously at full power on multiple channels at times when the channels are not utilised for real traffic. The harvester end itself is actually quite simple but there have been some rather careful parts.
I've not yet read the paper, but surely you are always going to be limited by the max legally allowed ERP of the Tx, and the old bastard of the inverse square law...?
Before we all write the idea off as cranky, take a look at this POWIFI paper http://arxiv.org/pdf/1505.06815v1.pdf
It seems to have been covered in a number of popular news outlets, including several mainstream ones, over the past two or three days. I was on the tube this morning and noticed it in the Metro's pop sci section overlooking someone's shoulders. Brain said "bollocks", but I thought I'd look at the underlying details, from both what they're claiming it can do, and how they apparently achieve it.
Once you get beyond the media hyperbole, the actual claims are rather more sensible. Furthermore, I spent half an hour or so with the back of an envelope and, against my gut feel, it does seem workable.
Key to this is that the router needs modifying to transmit almost continuously at full power on multiple channels at times when the channels are not utilised for real traffic. The harvester end itself is actually quite simple but there have been some rather careful parts.
I've not yet read the paper, but surely you are always going to be limited by the max legally allowed ERP of the Tx, and the old bastard of the inverse square law...?
All of this is dealt with in the paper if you read it, it is a good read, and, as I said I was most sceptical until I'd read it and done a few back of envelope calculations.
The only thing glossed over in the paper as far as I can see is the energy harvesting matching network, although it appears to match reasonably well from their graphs. I can't see how it achieves this considering the rectifier after the matching network and the matching network itself.
To reiterate, I smelt bullshit, tons of it, but there's little I can question having read it and run the numbers.
Assume 3W* output (34.7dBm) aggregate across three non-overlapping channels and a 4dBi tx antenna and 0dBi receive antenna. Path loss over 17' is 54.5dB giving net -15.8dBm or 26.3uW at the receiver.
At 50 ohm that is 0.036V rms or 0.10Vpp, the rectifier doubler gets that to 0.20V at 131uA peak so you're now well within the territory for energy harvesting capabilities of the BQ25570 (100mV min, operating quiescent current <500nA).
So, in 30 minutes you can accumulate 26.3 x 60 x 30 = 47mJ.
Alternatively, that's 47mW for 1 second, that's quite a lot of MCU processing these days.
While my calculations assume 100% efficiency, they are there to show that this doesn't appear to be complete baloney.
* edit: I would question the legality of running 3W from a single unit as a use case under FCC regs which specify 1W max. That does not stop the end user from deploying three 1W units themselves.
Edit 2: To put this into perspective, this means it takes 10.6 hours to generate 1J. A typical phone battery is 5Wh, or 18kJ. It will take about 21 years to charge that battery assuming 100% efficiency and no self-discharge at a distance of 17'.
On the other hand, if we place the energy harvester 2" away, the path loss is only 14dB, giving a power of 290mW. This would take 17.2 hours to charge a 5Wh battery assuming 100% efficiency.
But then unlike other "products" the POWIFI is not claiming to be a phone charger.
Bollocks. Gain antennas on a bog standard wifi router? 3 Routers blasting illegal power? Zero losses in the whole system?
Bollocks.
Even "optimized" wireless charging with specially-made charging antennas on the devices, and placed INSIDE a "charging bowl" where a high-power signal is blasted into the bowl using an OUT-OF-BAND frequency (to not interfere with the primary communication channels) are having a hard time getting started. And even with massive funding by the big names in technology and consumer electronics. This IN-BAND "charging" scheme just fails on so many levels it is a waste of time to even discuss it.
I gotta hand it to U-dub. If they are training their students in modern hand-waving they are doing an excellent job.
A 24-hour "test" in their private homes is hardly a "real world" evaluation of the technique's impact on WiFi traffic. Lets see them install it for a couple months in six Starbucks coffee shops or some other high-traffic WiFi environment. The 2.4GHz ISM band is already becoming overloaded with users and adding communication-blocking wireless charging to the load just seems to me wildly abusive to a scarce resource.
I admit that they could have a scheme for reducing the impacting blocking legitimate use of the bandwidth, but I can't see how they could ever make it transparent and zero-impact. And they could implement the scheme with only a change to the WiFi protocol and re-writing the firmware on the routers.
But the biggest barrier to the scheme IMHO is the minuscule efficiency. Their examples show very low power, intermittently-operating devices or offline applications like trickle-charging batteries, etc. And in an age when the EC is demanding that even wall-wart chargers have near-zero power consumption when not in use, I can't see how this PoWiFi scheme could ever be practical for real-world high-power gadgets like cell phones.
Why do you suppose that Tesla's wireless power schemes never got anywhere? There are reports that the Russians are trying to revive the scheme. Lets see how far they get.
I agree with Mr Crowley.
Unless a radical new technology is brought to the table, these RF charging systems are not going anywhere.
In military applications, using AESA antennas, it is possible to focus emission on another antenna to jam it.
So, why not do one to charge our Iphones, golly gee!?
But we are talking about systems that cost in the millions , use kWs of power, active cooling and would fry your brain if you were to step in front at close range...
I'm pretty sure that if you manage to build an AESAish system in your shed, for a few thousand Euros, that manages to follow AND charge your Iphone in real time...
While not burning you leg or dimming your neighbourhoods lights - of course.
Then you won't need no kickstarter! THales, Hugues or BAE will shovel money at you and make you a job offer that you will simply not be able to refuse.
edit:
Looks rather more complex than a Wifi base station.