Neither the title of this item (currently "A cell phone powered by ambient light") nor the article's ("This Cell Phone Can Make Calls Even Without a Battery") is really accurate.
Because the phone relies on those signals for its energy harvesting, it has a range of just 15 meters from the basestation.
This is neither a cellphone nor solar-powered. It's an RF-powered cordless phone. Interesting nonetheless.
To normal folks, maybe, but in technical language it can refer to the entire EM spectrum (as there's no meaningful difference between "visible" and "invisible" EM radiation for anything other than human eyes).
EDIT:
I looked up the spectrum PV cells tend to respond to and some sources on the usual meaning of the word "light", and I admit my original comment was me being pedantic about the more obscure usage of the word. Sorry :(.
FWIW, this isn't universal usage. When I took physics in college we used "visible light" to refer to the visible spectrum, and "light" to refer to EM radiation generally. I know that others have had an experience similar to yours, though; this seems to depend a great deal on the preferences of the people who taught you.
"The prototype basestation uses an unlicensed frequency, limited to low-power transmissions. ... Real cell towers have a hundred times as much power, and would increase the range to perhaps a kilometer,"
Real cell towers may use more power than unlicensed is allowed to in some cases, but not significantly much and definitely not hundreds of times. I worked at Clearwire (Clear wimax) and even on the spectrum we owned we generally used less than 1W of power per sector. Very small ones would only use a couple of hundred mW and our longest range sites in rural Texas were either 2W or 5W (memory is fuzzy).
To be fair, we used more sites closer together instead of a few larger ones, but the point stands. Cell sites biggest advantage is elevation and line of site, not massive transmit power.
I work at Ericsson (one of the largest radio companies in the world) and we have towers that crank out 80w for 4g/5g. Mind you, I'm a software guy, not a hardware guy.
Elevation and line of sight are important but power is too!
Ctrl-f "watts" on this page to see what I'm talking about:
You are confusing peak power with average power. The law of reciprocity says that nothing is to be gained if the base transmitter is more powerful than the mobile TX.
However because the base has multiple (hundreds) of low-power transmitters, it must cater for a very large instantaneous peak power when they momentarily add up.
And more importantly, excess Transmit power reduces the re-use ability of that frequency in nearby cells.
The what? The only thing I can find about reciprocity is that antennas have the same characteristics in either direction. That doesn't mean your noise levels are the same, and you very often have different bandwidth requirements in each direction.
> The law of reciprocity says that nothing is to be gained if the base transmitter is more powerful than the mobile TX.
Late response, but that assumes that the mobile RX is as good as the tower's RX, and I can assure you that's not the case.
The gear up on a tower has a way better low noise amplifier than a mobile phone, so it's able to "hear" the phone at a greater distance than you'd expect. That's why it's a-okay to have a base transmitter with a quite a bit more power than a mobile TX.
That would be with an isotropic radiator, right? I'd assume a cell tower antenna would send very little energy straight up or down, which would mean it was somewhat focused.
It assumes the cell tower is just a scaled up version of the small antenna. If a cell tower has better technology that allows it to focus its signal better then obviously it is going to perform better.
Although, if you are interested in powering things by ambient light, there are a few options besides 'traditional' solar panels.
Like non-traditional solar panels; a company called Ixys has some interesting small "solar bits"[1] which are what they sound like. Or old-school amorphous solar cells, like the kind that used to power calculators. They're not very efficient, but they perform okay in indoor lighting and they're cheap.
Also, PIN photodiodes[2] are intended for detecting whether an object is in light or not, but they can actually deliver around 25 microAmps @ 5V in less than 5 sq. mm. Not much, but it could charge something ambiently for short bursts of usage. (Edit: and I'd be remiss if I didn't point to the project that made me aware of this: https://hackaday.io/project/21342-bpw34-solar-powered-led-wa...)
An IPhone battery has a capacity of roughly 10Wh. The energy density of the sun is approx. 1kW/m2 on earth. Let's assume a solar cell with 20% efficiency, so 200W/m2. To charge the iPhone battery in 4h you would need a solar panel with an area of 11cmx11cm.
So the phone is probably not very powerful. Certainly it's power draw is nowhere near current smartphones. (It's mentioned in TFA, 800mW when calling, tens of microwatts when on standby)
That... sounds too good to be true. 11x11cm panel is basically a pocket one; hell, my S7 has surface area (one side) of ~80% of that. And 4h for charging a smartphone is a typical time.
So it sounds like not only this should be very useful according to those numbers, but would also imply that solar chargers for smartphones are not complete bullshit fake non-product I always assumed they were?
They're definitely a real product. Popular with campers; someone was selling a backpack with integrated solar panels.
Achieving those numbers does require the panel to be aimed at the sun and the sky to be clear, though; cloud or off-axis aiming drops the efficiency dramatically.
They aren't worth the money or the weight. You are almost always better off bringing the equivalent in spare rechargeable batteries. I've written an article on it:
While that is extremely light, it still weighs as much as 3x18650. Breakeven point would be after four days of perfect 100% utilization of solar power.
Is it practical even then? I'd gladly carry a few extra batteries so that I don't have to sit around camp and keep adjusting the panel every hour.
My phone has a battery of around 12 Wh and lasting maybe 30 h on a full charge, that's a power consumption of 0.4 W on average. With a surface area of about 70 cm², we get about 60 W/m².
Phone eats 60 W/m².
Sun provides 1000 W/m².
Okay, let's cut that into a fourth because, you know, clouds and nights and stuff. Retake.
Phone eats 60 W/m².
Sun provides 250 W/m².
Essentially, if you find a solar panel with 25% efficiency and the right size, you can slap that on the back of your phone for a very tiny size increase, and you now have a phone that powers itself as long as you put it down in the sun instead of in your pockets when you don't use it!
250 W/m2 is still rather optimistic -- though not absurdly so!
Obviously it varies a lot depending on where you are. For example, in Germany the total sunshine you have to work with is approximately 1000 kWh/year[1], or 115W/m2 on average. I think that still assumes you find a way to perfectly align your phone to be perpendicular to the sun's rays; otherwise you get less energy still.
Likely I don't know enough about the components involved, but I've wondered for years about the viability of a solar cell as the bottom layer for AMOLED screens since those don't need a white/reflective back layer for lighting behind an LCD panel. Even if the diode electronics blocked a big chunk of the light I suspect there are plenty of places where a low usage always charged phone might be desirable.
1. This sounds very useful both as a backup capacity to make calls when your battery died; a smartphone could run in a restricted, super-power-saving mode off that. Could be handy in cities, where there's lots of RF background.
2. Energy that can be harvested this way from human-made RF is energy wasted. I expect less and less of such background RF to be enabled as time goes on and people figure out more tricks to do hyper advanced magic with beamforming.
>1. This sounds very useful both as a backup capacity to make calls when your battery died; a smartphone could run in a restricted, super-power-saving mode off that. Could be handy in cities, where there's lots of RF background.
Just make 5% battery the new 0% and whatever super-power-saving mode magic you have to run off that 5%. I think that might make more sense in terms of power envelope than to bother with all this stuff.
regarding (2), I would say while energy use gets smarter, that will be offset by the greater number of electronic devices. I would also wouldn't be suprised once a large number devices start depending on ambient RF, then cities might deliberately dump ambient RF energy around their cities to power the potentially millions of legacy devices that might rely on ambient back-scatter.
It looks like the power limitations of running from radio waves are limiting. What about a battery or phone that charges from radio waves? It would give the phone a lot more power to operate, because the phone itself doesn't run 24/7.
from the article, harvesting RF generates tens of microwatts at best, which probably isn't enough to even operate the charging circuitry much less actually charge anything.
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[ 4.0 ms ] story [ 75.3 ms ] threadBecause the phone relies on those signals for its energy harvesting, it has a range of just 15 meters from the basestation.
This is neither a cellphone nor solar-powered. It's an RF-powered cordless phone. Interesting nonetheless.
EDIT:
I looked up the spectrum PV cells tend to respond to and some sources on the usual meaning of the word "light", and I admit my original comment was me being pedantic about the more obscure usage of the word. Sorry :(.
Also consider what of the sun's radiation makes it to the surface of the Earth.
"The prototype basestation uses an unlicensed frequency, limited to low-power transmissions. ... Real cell towers have a hundred times as much power, and would increase the range to perhaps a kilometer,"
To be fair, we used more sites closer together instead of a few larger ones, but the point stands. Cell sites biggest advantage is elevation and line of site, not massive transmit power.
Elevation and line of sight are important but power is too!
Ctrl-f "watts" on this page to see what I'm talking about:
https://www.ericsson.com/en/networks/offerings/connecting-th...
However because the base has multiple (hundreds) of low-power transmitters, it must cater for a very large instantaneous peak power when they momentarily add up.
And more importantly, excess Transmit power reduces the re-use ability of that frequency in nearby cells.
The what? The only thing I can find about reciprocity is that antennas have the same characteristics in either direction. That doesn't mean your noise levels are the same, and you very often have different bandwidth requirements in each direction.
Late response, but that assumes that the mobile RX is as good as the tower's RX, and I can assure you that's not the case.
The gear up on a tower has a way better low noise amplifier than a mobile phone, so it's able to "hear" the phone at a greater distance than you'd expect. That's why it's a-okay to have a base transmitter with a quite a bit more power than a mobile TX.
Any excess power prevents re-use of the frequency in adjacent cells.
Like non-traditional solar panels; a company called Ixys has some interesting small "solar bits"[1] which are what they sound like. Or old-school amorphous solar cells, like the kind that used to power calculators. They're not very efficient, but they perform okay in indoor lighting and they're cheap.
Also, PIN photodiodes[2] are intended for detecting whether an object is in light or not, but they can actually deliver around 25 microAmps @ 5V in less than 5 sq. mm. Not much, but it could charge something ambiently for short bursts of usage. (Edit: and I'd be remiss if I didn't point to the project that made me aware of this: https://hackaday.io/project/21342-bpw34-solar-powered-led-wa...)
So, you know. Hop to, everyone.
[1]: http://ixapps.ixys.com/DataSheet/KXOB22-04X3F_Nov16.pdf
[2]: https://www.fairchildsemi.com/datasheets/QS/QSB34.pdf
So it sounds like not only this should be very useful according to those numbers, but would also imply that solar chargers for smartphones are not complete bullshit fake non-product I always assumed they were?
Achieving those numbers does require the panel to be aimed at the sun and the sky to be clear, though; cloud or off-axis aiming drops the efficiency dramatically.
https://www.reddit.com/r/flashlight/wiki/solarcharging
Works well on sunny days if you adjust it to point directly at the sun, and it charges in 6-8 hours.
Is it practical even then? I'd gladly carry a few extra batteries so that I don't have to sit around camp and keep adjusting the panel every hour.
$100 isn't practical for most people either.
My phone has a battery of around 12 Wh and lasting maybe 30 h on a full charge, that's a power consumption of 0.4 W on average. With a surface area of about 70 cm², we get about 60 W/m².
Phone eats 60 W/m².
Sun provides 1000 W/m².
Okay, let's cut that into a fourth because, you know, clouds and nights and stuff. Retake.
Phone eats 60 W/m².
Sun provides 250 W/m².
Essentially, if you find a solar panel with 25% efficiency and the right size, you can slap that on the back of your phone for a very tiny size increase, and you now have a phone that powers itself as long as you put it down in the sun instead of in your pockets when you don't use it!
Obviously it varies a lot depending on where you are. For example, in Germany the total sunshine you have to work with is approximately 1000 kWh/year[1], or 115W/m2 on average. I think that still assumes you find a way to perfectly align your phone to be perpendicular to the sun's rays; otherwise you get less energy still.
[1] http://www.solar.lucycity.de/index.php/sonnenenergie/9-sonne... I think the technical term may be solar irradiance, here's a global map: https://en.wikipedia.org/wiki/Solar_irradiance#/media/File:S...
1. This sounds very useful both as a backup capacity to make calls when your battery died; a smartphone could run in a restricted, super-power-saving mode off that. Could be handy in cities, where there's lots of RF background.
2. Energy that can be harvested this way from human-made RF is energy wasted. I expect less and less of such background RF to be enabled as time goes on and people figure out more tricks to do hyper advanced magic with beamforming.
Just make 5% battery the new 0% and whatever super-power-saving mode magic you have to run off that 5%. I think that might make more sense in terms of power envelope than to bother with all this stuff.