### Author Topic: WAVE: A cell phone that charges battery with wifi signal.  (Read 21618 times)

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#### edy

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #50 on: June 03, 2015, 02:22:45 am »
I think we should use a hand-crank to charge the phone.... Like this idea....(photo3.jpg).  Or maybe just a very big antenna to capture the WiFi radio waves...(photo4.jpg). Or even better a repurposed satellite dish to concentrate a larger reception field for radio waves to be captured by the phone which as you can see is held at the focal-point in this rig (photo5.jpg).
« Last Edit: June 03, 2015, 03:07:15 am by edy »
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#### mikerj

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #51 on: June 03, 2015, 09:32:09 pm »

Small devices could use this as part of an internet of things, says Ben Potter at the University of Reading, UK.

The University of Reading; that makes sense.  I suspect they have some kind of cloning device for their academic staff which has been seeded with DNA from Kevin Warwick.

#### edy

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #52 on: June 03, 2015, 11:09:41 pm »
The surface area of a sphere is 4 x pi x radius^2. So even 1 meter out from a WiFi source the output would be spread across a sphere of 4pi.... 100 W source spread over an area of 12.57 meter squared. 1 meter Sq. Is 10,000 cm Sq. So the surface of a sphere 1 meter radius is 125700 cm squared. The 100 W is now 1/1257 or 0.8 mW per cm square.

Let's round it to 1 mW per sq cm. Imagine a phone or let's be generous a tablet of 10 x 20 cm size. That is 200 cm sq so at 1 meter it will have 200 mW falling on it from the 100 W source.

If we are 2 meters out we will have 1/4 the power per unit area than at 1 meter out (inverse square law). So at 2 meters the power capture is 50 mW on our huge phablet. At 3 meter it is 12.5 mW.... and so on.

What is the FCC limit and what is the typical power of WiFi? Are these crude calculations valid? My understanding is WiFi cannot be over 1 W so we can already reduce the power by a factor of 100x.

In the scenario above, 1 W source would provide a 10x20 cm area about 2 mW at 1 meter away. Phones are smaller than that. Nobody sits 1 meter from the WiFi. You may as well put it on an inductive charging pad. At 2 meters it is 0.5 mW. This is a factor of 1000x less than what is needed just to keep up with standby power consumption.

Maybe these WiFi power sources need to be massively scaled up in power and used for very energy efficient sensor modules (not phones). To call it WiFi even is a joke because by the time it is implemented they aren't even using it for data transmission. They need it on full power all the time and maybe just in the WiFi spectrum. It is just a bad idea all around and trying to solve a problem that is not really a problem, only risking more of our health.
« Last Edit: June 03, 2015, 11:36:42 pm by edy »
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#### Howardlong

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #53 on: June 05, 2015, 10:17:45 am »
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 selections.

But no, charging a mobile phone over WiFI, it's not going to happen unless you're prepared to wait an awfully long time and it's switched off while you do it.

#### Richard Crowley

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #54 on: June 05, 2015, 01:15:36 pm »
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.

#### Howardlong

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #55 on: June 05, 2015, 03:22:34 pm »
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.

Did you read the paper? That, and many other possible problems are specifically addressed in there, including its effects on channel bandwidth.

Seriously, I strongly suggest you read it before jumping to conclusions as I indeed did.

http://arxiv.org/pdf/1505.06815v1.pdf

#### Richard Crowley

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #56 on: June 05, 2015, 03:27:56 pm »
Seriously, I strongly suggest you read it before jumping to conclusions as I indeed did.
It wasn't my conclusion. It was yours.

#### Delta

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #57 on: June 05, 2015, 09:16:26 pm »
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...?

#### Howardlong

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #58 on: June 05, 2015, 09:51:42 pm »
Seriously, I strongly suggest you read it before jumping to conclusions as I indeed did.
It wasn't my conclusion. It was yours.

Correct, but I don't understand how you would have come to all of your conclusions had you read it in toto?

#### Howardlong

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #59 on: June 05, 2015, 10:27:25 pm »
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.

« Last Edit: June 06, 2015, 01:38:57 am by Howardlong »

#### Delta

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #60 on: June 07, 2015, 07:27:48 am »
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.

#### Richard Crowley

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #61 on: June 07, 2015, 09:43:55 am »
Bollocks. Gain antennas on a bog standard wifi router? 3 Routers blasting illegal power? Zero losses in the whole system?

Bollocks.

Agree 1000%.  You don't have to read the document to know that it is pure fiction.
But apparently written well enough to fool many people who ought to know better.

#### Howardlong

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #62 on: June 08, 2015, 12:46:27 am »
I am not saying there are zero losses in a real system.

What I am stating is that the POWIFI thing is not complete baloney, they are in the ball park, well within an order of magnitude.

Again, unlike other systems that are several orders of magnitude out, the POWIFI lot are not claiming they can charge a phone from 17'. They are claiming something very different. I hope that was clear.

Where do you think the losses are, and of what magnitude do you think those losses are? RF magnitude losses are easily calculated, but I doubt that's the main source of loss* once path loss (54.5dB) is already accounted for: I would suggest that the rectifier and energy harvesting process will provide the largest losses in the system. Remember too that in real RF situations once in the ether there is both constructive and destructive interference particularly from reflections.

I am a little surprised at the response considering I've done the figures in an open and objective manner. The reason I did it was because my gut feel said "bollocks" too. If you want to debunk it, please give it objective due consideration with reasonable and representative calculations.

Regarding the gain antenna on the router, 4dBi is not at all unreasonable. Why do you think otherwise? Antenna theory and practice are well understood, and this is easily achievable, even a lambda/2 dipole gives you 2.15 dBi. All you're doing is taking a spherical radiation pattern and squashing it in the horizontal plane into a doughnut with the same volume, thus giving gain horizontally. In fact if anything, I'd say 4dBi is on the low side, 6dBi is the maximum legally allowed assuming 30dBm transmit power at the feedpoint giving an EIRP of 36dBm.

So please, let's have your reasonable and representative figures debunking this! Without numbers, it's just a subjective opinion, and one that I shared originally too. It's not like I have a history of supporting these kinds of claims, quite the opposite in fact, I'm often the one debunking them myself, which is why I spent time looking at it in the first place!

« Last Edit: June 08, 2015, 05:15:00 am by Howardlong »

#### Richard Crowley

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #63 on: June 08, 2015, 12:50:36 am »
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.

#### Howardlong

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #64 on: June 08, 2015, 01:24:52 am »
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.

Look, I have a lot of respect for you, you have a proven career, but in this regard I really don't understand your blinkered stance. The figures are there. I am not sure whether it's because you are misunderstanding what the POWIFI folks are claiming, or if it's something else, but to just reject the claims, and not give an objective basis for that rejection doesn't stand up to scrutiny.

I have no agenda to support their claims, in fact the whole point of me running the numbers to begin with was to discount them!

Refusing to discuss it because "it fails on so many levels" and then not identifying what those failing levels are is no proof of failure. So far, the few objections raised have already been covered in the paper cited. For example, the DoS of the channels that was raised is a very valid concern, and it is very heavily addressed in the paper in terms of detailing the mitigation algorithms that are subsequently shown to work both quantitatively and qualitatively in empirical testing. No laws of physics have been broken, either. The math(s) is there, but please, if you think I've made a fundamental mistake in my calculations, let me know where that is and I'll re-run them and prove myself wrong.

#### Richard Crowley

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #65 on: June 08, 2015, 02:23:51 am »
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.

#### gildasd

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #66 on: June 08, 2015, 02:51:18 am »
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.
« Last Edit: June 08, 2015, 04:38:18 am by gildasd »
I'm electronically illiterate

#### Howardlong

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #67 on: June 08, 2015, 04:11:09 am »
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.

Well, I don't think there's anything there I would disagree with. It is a wildly inefficient way of powering anything, the loss budget alone is already 50.5dB, or 0.0009% efficient, you are already better off with solar panel derived power and battery charging, using room lighting is going to generate more power than that from ISM 2.4GHz unless you leave your microwave oven's door open, and that technology has been successfully powering ultra low power devices like LCD calculators and watches for decades now.

The key difference I've been reiterating which seems to have been lost is that unlike so many other schemes POWIFI were not claiming to be charging phones or breaking the laws of physics, they were just powering small ultra low power devices.

But precisely as you say it's difficult to see where this technology would apply where, for example, something solar wouldn't be better, even indoors.

#### Howardlong

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##### Re: WAVE: A cell phone that charges battery with wifi signal.
« Reply #68 on: June 08, 2015, 05:19:13 am »
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.

I saw one of those radar phased arrays in action at Lockheed Martin in Fort Worth, they had a permanent installation that pointed to DFW and used the commercial air transports as their test chickens a few miles away. There was a perimeter zone to avoid wondering into about 100' radius from the antenna. Serious hardware indeed.

Smf