No doubt someone will find a use for wireless sensors that could be scattered around the kitchen which are powered using this.
Radiation snatched from leaky microwave ovens to power gadgets
A collaboration between universities in Tokyo and Atlanta has spawned a device for harvesting power leaked from domestic microwave ovens – turning wasted waves into free energy. Microwaves pump out energy in the 2.4GHz band: the industrial, scientific and medical (ISM) radio space popularised by Wi-Fi and Bluetooth. The casing …
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Tuesday 24th September 2013 08:58 GMT frank ly
How about .....
... an outside thermometer/display in the form of a 2 inch square sheet that is stuck to the outside surface of the window and uses e-ink display that is updated every 15 minutes (or whatever). If the internal battery runs low then it can put up a 'please use the microwave' symbol.
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Tuesday 24th September 2013 09:35 GMT Allan George Dyer
Re: How about .....
And if someone obeys that instruction once a year, they'll wipe out any energy saving.
It's a neat use of leaked power, but if someone switches on the microwave because the parasitic device needs recharging it just becomes a 99.9997% inefficient recharger (assuming a 300W microwave).
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Tuesday 24th September 2013 18:06 GMT Acme Fixer
Re: How about .....
I find it amusing that so much trouble is go to just to harvest a fraction of a milliwatt. I have an inside/outside thermometer with LCD that has been running for much more than a decade on a single AAA cell. With an LR44 button cell, it should run for much more than a year. So it seems a waste to try to get energy from an unpredictable source when a button cell at a cost of a few cents does a much better job. Or take the design from the calculator industry. Just use a small solar cell and get a lot more energy than from a very intermittent microwave source.
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Wednesday 25th September 2013 04:24 GMT Yet Another Anonymous coward
Re: How about .....
Batteries are large and in a limited range of shapes
They need mechanical contacts cause pollution, are difficult to recycle and mean you get hit with all sorts of extra packaging/labelling/shipping/disposal requirements.
If you wanted to print a disposable sensor with electronic polymers and only need a tiny bit of juice this could be useful
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Tuesday 24th September 2013 09:19 GMT Vladimir Plouzhnikov
Possible uses
Boiling tea/coffee water for radar station crews or airport tower controllers - just stick the rectenna up the antenna and enjoy a cuppa. "Golf Lima Charlie to Heathrow Arrivals - please repeat your last, you are breaking up..." - "No, we're not, our kettle is boiling, mate, is all..."
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Tuesday 24th September 2013 13:21 GMT Irongut
Re: Question
A sneaky way to search for WiFi? WTF are you talking about?
Walk about with any WiFi enabled device (phone, laptop, whatever) and you can detect WiFi. With the right app you can even make a pretty good guess where it is coming from, know what the SSID is, tell what security is has, etc. And, no one knows unless you try to connect (and probably not even then). With this technique all you know is there is radiation in the 2.4GHz band. It could be WiFi, a Microwave, Bluetooth, DECT phones or dozens of other possible sources.
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Tuesday 24th September 2013 09:17 GMT Caesarius
Re: It worries me
And worry you should, at short distances. Whereas microwave ovens may well be better shielded now than when they first became popular, I remember in the past we could get an LED and bend its legs so as to make a suitable sized dipole, and the LED would light when placed near a uW oven. I never let anyone put their face to the glass: you don't really need to, and why risk it?!
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Tuesday 24th September 2013 12:44 GMT Don Jefe
Re: It worries me
No. Modern microwaves have far less power with a much narrower output than the big old school mechanical timer driven microwaves. That's why the old ones did weird things to phones and LED's but modern units don't, they were simply grossly overpowerd. That's also why food from them tasted even worse than it does now.
A microwave has zero shielding other than that provided by the 1/16" sheet metal casing. The only reason they are that thick is because thinner sheetmetal wouldnt survive (prettily) in your kitchen long. They work because the microwaves are trapped inside the heating chamber and bounce around, heating your food along the way; not because they are super powerful omnidirectional emitters; the magic is the heating chamber. The shielding provided by the case is fairly minimal because there's no reason in a consumer wattage oven to provide it.
Minimal radiation escapes even with really, really long cooking times. Which you'd think would be obvious since all microwaves are vented with open holes/slots and in some you can look through the vents and see the magnetron and power supply. Just sitting there, in the wide open, held in by one screw and a metal tab.
Pop the case off your microwave and have a look. They are depressingly simple devices but there's still a mystique around them that there's some sort of sorcery and/or fissile material inside. The turntable mechanism is the most complicated part in one and 99.8% of the electronics and are just for 'timing options' (the 'popcorn' button).
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Tuesday 24th September 2013 14:11 GMT Caesarius
Re: It worries me
I have just checked a "modern" microwave with a bent LED, and the LED did not light that I could see. Perhaps I am worrying too much. Like people who worry about being 50 yards from a mobile phone base station but will happily put a mobile to their head, and I should hate to be quite so squeamish. I still refuse to put my face up to the microwave, because that's a rotten way to test for leaks. Reminds me of "do not look into laser with remaining good eye".
But I disagree with several things you said. Perhaps I shouldn't bite, but my pride is injured ;-)
Modern microwaves have similar or more power than the ones I was reporting, i.e. typically 800W rather than 500W.
Microwaves heat food the same way now as then, so the things making food taste better will be a) better controlled cooking times and b) recipes formulated to withstand microwave cooking.
A narrower output would have just as much effect on a LED.
Modern microwaves have a similarly crude generator, with mains-plus-harmonics going through a step-up transformer and then to the magnetron. So I see no reason for a narrower output. (Then again, it is possible for very simple snubbers to limit the frequencies of the magnetron drive: we should measure it sometime.) Besides, if they are better shielded, there is less worry about the spectrum of the output.
The sheet steel case is not the only shielding. There is also the mesh in the glass window and springy bits of metal round the door to help close up gaps.
The shielding is not minimal, and is definitely needed. I know what 50W feels like (hand in front of TWT+horn), so 10dB shielding is not enough.
But I agree with other points. E.g. the sheet steel need not be so thick for shielding, but rather for mechanical strength. Compare with the mesh in the glass window.
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Tuesday 24th September 2013 09:23 GMT Caesarius
Energy saving probably not as applicable as hoped
The idea that you can use energy that would otherwise be wasted must be tempered with concepts like "near field", "waveguide below cutoff", "evanescent", etc. Basically, if there is no way for some of the electromagnetic field to transfer energy, it won't; not tapping into an energy source does not always mean it is going to leak away.
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Tuesday 24th September 2013 10:00 GMT Mine's a pint
Parasitic radio power
I recall a magazine project from around the late sixties which was to build a medium wave radio which was powered from a long wave receiver (Radio 4). Due to the small power harvested it could only drive an earphone. Such a step up from a crystal set using the received radio power directly?
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Tuesday 24th September 2013 13:21 GMT Don Jefe
Re: Parasitic radio power
The core idea is as old as Tesla (really). So is the idea that the setups you describe are considered theft by the courts. It's pretty depressing to realize that the courts have been utilized by private parties to reduce 'theft and piracy' of intangible things for so long. The RIAA/MPAA just added a new level of dickishness to the whole thing, they didn't invent it.
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Tuesday 24th September 2013 14:22 GMT Caesarius
Re: Parasitic radio power
Yes. Another depressing fact is that when BT did not allow their customers to connect anything unapproved to the phone line, the charge would be "stealing electrical power". Clearly, there is no information transferred without power transfer, so I would be prosecuted for stealing microwatts.
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Tuesday 24th September 2013 16:26 GMT John Smith 19
So it's basically the way an RFID tag is powered.
Incidentally rectenna is a contraction of "rectifying antenna," as it rectifies the incoming (power) signal so it's all oscillating 0-X volts instead of +/1 y volts.
I'll also note the shielding maybe better than people realize. 2.4GHz is roughly a wavelength of 12.5cm, so any opening below that is (roughly) opaque if conductive.
So that grill you can see the food cooking through is actually an EM shield, as is the grill between the cooking chamber and the magnetron.
Take them off and start it up and you won't like what happens to you.
What's it good for? Time signal powered clock? Outside air temp display? Humidity detector for stuff boiling over?
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Tuesday 24th September 2013 20:35 GMT cyberdemon
This is about as daft..
as putting solar panels on your ceiling to collect the 'wasted energy' from your energy-saving lightbulb!
As for "1.8V, enough for most gadgets", this reporter clearly hasn't heard of electric current. In particular, that old relation P=IV!
Wait, forget I said anything - I hear another clueless mug, er I mean EPSRC executive on his way!
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Thursday 26th September 2013 21:08 GMT wdmot
Re: This is about as daft..
It really depends on the device you're trying to power with it, and how long you need it to run. For example, with the optimistic best (measured) case of 9.98mJ stored in the capacitor over 120s from 5cm in front of the microwave, if your device requires 1mA at 1.8V, you can run it for about 5.5s. Note that this best case is when the microwave is empty -- the energy harvested is 10x LESS when there's 200ml water in it!
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Wednesday 25th September 2013 00:24 GMT Bloakey1
Errr Crystal Radio
Hmmm.
When I was 13 I knocked up one of these using a few nails, a bit of wood, a thermionic diode and a variable capacitor. The speaker came from a vandalised B.T. phone. The engineers said I could have it when I asked and it was as good a microphone as it was a low impedance speaker. My father thought I was the bees knees when he heard radio four coming through it.
Old hat and available to any of us geeks from mags such as Popular Wireless or a simple O'Level Physics book..
Those were the days. When one was given a visit to the school computer room and the gubbins consisted of a pallet and a half and the modem was a handset and an acoustic coupler.
"Yoof" of today know nothing. I later graduated to PRC319s, AN PRC 10s etc but life was good then.Who needed multi frequency skipping and burst transmission as we use now? Our gear worked and we knew how to the fix it when under pressure.
I am sure our grandchildren of the correct geeky mien will consider us as mere novices.
Ferrous alert.
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