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Tim Kannegieter

IOT without batteries

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Hello all,

A news item in the media caught my eye " An IOT battery to last a billion years"...

Apart from the unlikely nature of anything man-made lasting a billion years, the article linked some interesting research from the University of Cambridge in the UK. The research apparently has developed an ultra low power transistor that can operate soley through power scavenging without the need for a battery, by exploiting Schottky barrier power leakage. See the paper at http://science.sciencemag.org/content/354/6310/302

Is this realistic in the near future or just pie in the sky?

Please share any other such research initiatives.

 

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Another day, another radical new battery claim.

Unfortunately this one too seems to be in the realm of make-believe and misrepresentation. The ultra low power transistor itself seems feasible enough, but single transistors do not typically represent a significant proportion of the current draw in an IoT device.

So sure, if all you want to do is power the transistor, then the power draw is low. In fact, the self-discharge of any battery will be many orders of magnitude higher, so the battery will run flat just as quickly if it was powering the transistor or not. But any useful IoT device will need to be doing a lot more - powering sensors, radios, analog circuitry, power and signal conditioning, etc.

This probably has applications in devices that are already low power enough to be harvesting energy, where every microwatt counts. Maybe it would mean you could add some extra simple functionality without having to add a battery. But if you already require a battery then ultra low power transistors are unlikely to make any difference.

I can just imagine the conversation with the researcher:

Quote

 

Journalist: "These nanowatts, can you put them in units we can appreciate?"

Researcher: "It's an extremely small amount of power - the amount you can feasibly harvest from the environment through vibration, heat, etc."

Journalist: "Great. But when I'm writing about new jigawatt solar farms I need to put it in number of houses powered. So how many batteries is this transistor?"

Researcher: "Haha, well it's not really in the realm of batteries - in fact in theory even a AA has enough energy to power one of these transistors for billions of years, but of course no battery would last that long, so it's a silly comparison."

Journalist: "An IoT battery to last a billion years... nice, I like it. Thank you."

 

 

Edited by Heath
Formatting

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On 05/11/2016 at 9:10 AM, Geoff Sizer said:

Maybe they are talking about the big yellow battery in the sky ....

Or maybe they just don't know what they are talking about?

This sort of misrepresentation is distressingly common, and rarely the fault of the original researcher.

The publicity machines of many large institutions often trumpet early stage inventions way before practical issues are resolved.

Such hype is more than simply fatuous, it is dangerous. Public cynicism is its natural by-product.

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'Plant-based' IoT

One of the most interesting ideas that I've seen for powering tiny IoT sensor-radio nodes in forests and crops involves 'plant-based' energy sources.

Essentially, a potential difference exists between the plant tissue in the stem and the soil, because of the different pH values within the plant compared to the soil. This potential is generated across the root membranes. [I might add here 'sometimes'. The actually potential difference depends upon the match between the soil pH - which varies with locality - and the plant's own internal chemistry. Sometimes the pH values of soil and plant simply match up due to coincidence, and there is no available energy]

When I read about some University chaps messing about with this technology, I got pretty excited, because the very latest energy-harvesting technology can scrape up a working voltage of about 3V from just a few hundred millivolts of thermoelectric energy.

So I made some measurements between grapevines and soil and connected up a low-voltage boost converter, only to have Mother Nature remind me that you can't beat the physics, no matter how exciting the potential application.

TEGs (thermo-electric generators) have a very low source impedance, measured in ohms, while the plant pH generator has a source impedance that I measured to be in kilohms. The TEG-boost technology just flattened the potential without extracting any energy. Some other technology will be needed to make this work.

Shame about that - it's the most perfect 'renewable energy', while the plant still lives. It would mean the IoT could run on a living 'bio-fuel'.

Now if only I had time to work on such interesting electronic circuits...

 

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