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UW scientists create the first battery-free mobile phone

by Mark Tyson on 7 July 2017, 14:01

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A mobile phone that requires no batteries is an interesting proposition. While not a smartphone, this device could prove to be extremely useful for some, and mark the origin of a battery-less mobile tech industry. Researchers at the University of Washington (UW) have created a battery-free cellphone which operates using energy harvested from ambient radio signals and light. The device only requires 3.5 microwatts for continuous operation and was demonstrated making Skype calls.

The prototype mobile phone from the UW is said to use off the shelf parts. Its unique capabilities stem more from how the hardware is used than the particular component choices. "To achieve the really, really low power consumption that you need to run a phone by harvesting energy from the environment, we had to fundamentally rethink how these devices are designed," explained UW associate professor Shyam Gollakota.

An example of the lateral thinking applied is that the converting of analogue signals, that convey sound into digital data and vice-versa, is simply bypassed. No A/D conversion takes place in the 'phone' as the tiny vibrations in a phone's microphone or speaker that occur when a person is talking into a phone or listening to a call are communicated as-is via analogue radio antenna to a base station.

The tiny battery-less mobile phone was tested in transmitting voice, data, and button presses. Using Skype the phone could make and receive voice calls and even put callers on hold. Calls need a constant connection to the base station, unlike some IoT devices might, so keeping power flow for the call duration was a particular challenge.

Currently this mobile phone requires a custom base station to transmit and receive the radio signals. However, the tech could be integrated into standard cellular network infrastructure, or into home Wi-Fi routers that are so ubiquitous. In tests the researchers found their mobile phone was functional within 31ft of the base station relying only on energy harvesting ambient radio signals. If the phone design included a tiny solar cell, roughly the size of a grain of rice, the device was able to communicate with a base station that was up to 50ft away.

Work on this project continues as the UW researchers are looking into adding an e-Ink screen to the device, and even implementing streaming video capbilities.



HEXUS Forums :: 6 Comments

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I think it's a bit of a stretch to call this a mobile phone to be fair; it's a very simple analogue radio transmitter with any sort of processing done on the base side, not unlike the sort of thing you make from Maplin project kits. And I remember making ‘battery-free’ crystal radio circuits in primary school, so the reception side is hardly groundbreaking. They might have improved the quiescent current over some existing products, but it's probably because it's not an area anyone was really focussing on, and there are solid limits of how much power you need to transmit a given distance.

Solar roadways, that ultra-cheap BeSang 3D NAND we were supposed to have seen by now, and that solar-powered water harvesting device all spring to mind for examples of things which kinda make sense at the first stage, but fall apart in one way or another when it comes to actually making the things do what they're supposed to. Exceptional claims demand exceptional proof, especially when something claims to somehow outdo the huge companies with billions in R+D at their own game…
Yeah… as soon as they said it has a “base station” it becomes fairly apparent that all they've done (whilst still clever) is simply shift the majority of the power consumption away from the device to somewhere else, rather than actually reducing all power required for the entire process. Not really a huge leap forward in technological efficiency.. more of a side-step.
It's also far away from being practical for a whole host of reasons, not least because of things like encryption, authentication, multiplexing, signalling, etc. It's a fun little project, but we've had solar powered calculators for decades - this is much of the same thing - it doesn't need much power simply because of what it actually is.
Well, its a mobile phone in the same sense as a cordless landline phone. Useful round the house (perhaps) but as it stands, thats about it. whether it can be scaled up is another matter!
peterb
its a mobile phone in the same sense as a cordless landline phone
I'd say it has much more in common with a walkie talkie, the push-to-transmit button and all. At least a cordless landline handset does digital signal processing, bi-directional transmission, and encrypts what it's transmitting. But yeah.

peterb
whether it can be scaled up is another matter!
Naw, it can't transmit a powerful enough signal. The nearby base station is going to be a hard requirement. Maybe with more power gathering components you could push out the range a bit. But it'll never be able to power all the other components that makes up a smartphone.

It looks like a fun lab experiment in electrical engineering, but that's about it.