Oooh, this is interesting (low-power radio tech)

[Eight Bit]

https://www.sciencedaily.com/releases/2017/07/170705164453.htm

A battery free cell phone. I so see something like this transform into a small wearable over time... I guess some hurdles are to overcome for a battery free Pyra

I love initiatives for an environment- and energy saving economy, so I'd like to share this too
http://gravitylight.org/

 

[Binky]

Interesting, yes - but overhyped, I suspect - and hardly new.

If I'm reading the article right, this thing is powered by radio emissions of a base station (misleadingly called 'ambient'), which should be ringing alarm bells with anyone who's heard of the inverse square law. It may work in the tens-of-metres range of a typical home or office - but GSM works over tens-of-kilometres. If you want to increase the range by a factor of a thousand, you need increase the transmit power by a factor of a million.

They say their prototype has a total power of 3.5µW and a range of 10m. Now, suppose they can get that down to 1µW through further research, and want to increase the range to 10km (reasonable outside big cities).

That's 1,000 times the range, so 1,000,000 times the power is needed. 1W, say. This is about the same as the power used by a normal mobile phone.

Now, if that 1W were provided from a local power supply, a battery, fuel cell, PV panel, or similar, that wouldn't be a problem. The problem is that you're now trying to collect 1W from a transmitter 10km away. Assuming the transmitter is clever enough not to spray radio signals up or down, there's still a cylindrical space around the mast that needs power. Say, 100m high. At 10km, that cylinder has a curved area of pi*2*10,000*100 ~= six million square metres. The phone might occupy a 10cm square or so. So thats 600,000,000 phone-sized spaces around the mast. Each needing up to 1W. So 600MW. That's the entire output of a medium-sized power station, and too absurd to contemplate.

This might be an interesting system for "smart home" or PAN applications - where you can already buy self-powered wireless light-switches and BLE devices working in the mW range - but a passive transmitter like this isn't (and cannot possibly be) a replacement for existing cell-phone tech.

If they could transmit the power to the handset in tightly focused beams tracking the user, that would be neat - but it wouldn't work well inside buildings.

If this thing ever comes to market, it will be in something like a wireless earpiece, with a base station in your pocket, not a standalone device.

[head --> desk]

Edit: Added clarification to clickbaity thread title

 

[PCXT]

This is rather like ambient power converters, not only with GSM, but it converts, with different efficiencies, lower frequency radio or even power interference. I've built a few ambient power units myself for experimenting. The best ones (which are made around Ge diodes, not Si), allowed me to power up an LCD watch from ca. 10 meters of old network cable stretched over the attic. About powering it up everything sticks with physics, especially in urban environment where electromagnetic pollution is large. However, I don't think that it may power anything which has to respond in high frequency and high power. Watts are watts, you cannot get more watts from transmitter than transmitter takes as its power supply (not including transmitter efficiency), OK, there are a few irregularities, but they're on the second end of frequency range.
To solve it, we may have to go into messy and unofficially banned domains like low-power urban mesh networks or similar things.

 

[levi]

If I'm reading the article right, this thing is powered by radio emissions of a base station (misleadingly called 'ambient'), which should be ringing alarm bells with anyone who's heard of the inverse square law.

It strikes me as a rather unclear article. It talks for some paragraphs about harvesting the sound waves, but then also talks about harvesting wifi signals which I understand are generally more powerful due to their closeness, and harvesting photons. I'm not sure what's actually in the prototype they've built and what isn't.

 

[Binky]

urban environment where electromagnetic pollution is large.

EM pollution works both ways though. If your super-low-power transmitter wants to make itself heard in a big city, you need a very tightly controlled slice of spectrum for it to do so on.

 

[PCXT]

...and we need to get through all interferences in this spectrum. But we don't need big power all time, maybe super/capacitors are extensively used in such moments?

//EDIT
Looking into paper, they don't use DAC at all, base station sends analog audio and this receives. Something like an old detector radio receiver (this one in which it was needed to knock the crystal with pin until reception was good), used in some countries until 1950s as it needed no power. Alternatively when it sends analog audio, it's using power from circuit which looks like ambient power converter.

 

[levi]

I remember the electronics kit I got in the 1980s had a design for a no-battery AM radio. It worked, but you needed really sensitive earphones to hear anything with it. And in these days of software-defined radios, I wouldn't especially want to be broadcasting my chats in the clear.

 

[rygD]

Sexting?