An RF-powered cordless phone

https://www.wired.com/story/this-cell-phone-can-make-calls-even-without-a-battery

by jonbaer • 9 years ago

74 39 9 years ago

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.

TeMPOraL6• 9 years ago

Well, technically RF-harvesting phone is powered by "ambient light". The title says nothing about solar, or visible light.

maxxxxx• 9 years ago

Nice marketing talk!

occamrazor• 9 years ago

The word "light" denotes EM radiation in the visible spectrum or in the near IR/UV only, not generic EM radiation.

Timshel• 9 years ago

They use a custom low power basestation. Cf :

"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,"

mostlyskeptical• 9 years ago

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.

contravariant2• 9 years ago

Unless I'm mistaken about how these things work, 100 times as much power would only increase the range 10 fold to about 150 meters.

leggomylibro• 9 years ago

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...)

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

dang• 9 years ago

Ok, we've put your phrase above.

donquichotte• 9 years ago

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)

TeMPOraL6• 9 years ago

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?

pjc50• 9 years ago

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.

kqr• 9 years ago

Huh, I guess you're right.

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!

TeMPOraL6• 9 years ago

Two observations:

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.

jimmies• 9 years ago

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.

em3rgent0rdr• 9 years ago

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.

gwbas1c• 9 years ago

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.

TheAdamist• 9 years ago

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.

relyks• 9 years ago

Here's a link to the research paper for those who are interested: "Ambient Backscatter: Wireless Communication Out of Thin Air" (http://abc.cs.washington.edu/files/comm153-liu.pdf)

An RF-powered cordless phone

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