back to article 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 …

COMMENTS

This topic is closed for new posts.
Silver badge

No doubt someone will find a use for wireless sensors that could be scattered around the kitchen which are powered using this.

0
0
Silver badge

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.

1
0
Silver badge
Holmes

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).

6
0

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.

3
0
Silver badge

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

0
0
Nym

I wanna write here...

And make idiotic comments on my OWN stories rather than everyone else's.

True comment: I was absolutely sure that microwave ovens did not constitute Faraday cages. I saw some military specs back in the early 70s indicating some real and consistent problems with the idea.

0
0

Very interesting

But less use in the 'average' household, I suspect, than a chocolate teapot. At least you could eat the teapot, presuming you're not allergic to any of the ingredients.

Sometimes the question "why?" should indeed be the first one to be asked.

4
0

Re: Very interesting

I Imagine they could find more use in a commercial setting where the microwaves are in more regular use; Perhaps to power the Canteen clock or similar? it's free (well - utilised waste) power at the end of the day - why not use it?

2
1
Silver badge

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..."

1
0
Silver badge

Re: Very interesting

Not really. Pretty boring and mundane if you ask me. I could have told you this was possible decades ago, as could anyone that has studied radio or electronics even at a basic level.

2
0
Bronze badge
Coffee/keyboard

Rectenna?

The mind boggles at the images.

3
0
Silver badge

Re: Rectenna?

Wrecked it? Damn near killed it! >Badum-tish<

2
0
Silver badge

Question

If it's using energy in the same range as wifi, wouldn't it also be tapping wifi for energy as well?

Might be useful as a sneaky way to snoop for wifi's presence.

2
1
Silver badge

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.

0
0
Anonymous Coward

It worries me

That my Microwave may be leaking

0
0
Bronze badge
Boffin

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?!

1
0
Silver badge
Boffin

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).

2
1
Bronze badge
Facepalm

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.

2
0
Bronze badge

Free energy

The ideal time for this tool would presumably be while grabbing an after-work pint in a local Wetherspoons - if they're preparing food, the microwaves will be going crazy.

1
0

Re: Free energy

Wetherspoons microwave their food? Oh nooooe....

0
0
TRT
Silver badge

Re: Free energy

Food used in its broadest context...

0
0
Bronze badge
Boffin

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.

2
0
Silver badge

I'd be concerned if my microwave was leaking enough energy that it was worth collecting it.

I guess in the colder months you could cut out the middleman and stand next to it to keep warm...

1
0
Silver badge

235 years

is about how long it would take to recoup the energy needed to make the equipment to capture all this free power!

3
0

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?

1
0
Silver badge
Unhappy

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.

0
0
Bronze badge
Unhappy

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.

0
0
Bronze badge

"Free energy"

There is the same potential flaw in using "free energy" as driving ten miles to save a penny on the shopping.

The energy may otherwise be going to waste but one needs to take into account the hidden costs of harvesting it.

1
0

Is it really wasted energy?

"all from energy that would otherwise be wasted"

Genuine question. For example, does the leaked energy have no effect in heating the house, or curing acne, or whatever?

2
0
Silver badge
Trollface

Proof for you unbeleivers!

At last, they admit that microwaves leak radiation.

That's the same stuff that kills people.

We knew all along it was a conspiracy of silence but now they've gone and admitted it.

Wontsomebodythinkofthechildrenandlittlekittens.com

2
1
Devil

Feeling mischievous?

I wonder if you could convince people they can charge their phone by putting it inside a microwave oven?

1
0
Anonymous Coward

Re: Feeling mischievous?

Well they persuaded at least one person that updating to IOS7 made his iPhone waterproof...

3
0
Silver badge

Re: Feeling mischievous?

In case anyone else wants to point and laugh:

http://metro.co.uk/2013/09/23/ios-7-doesnt-make-your-phone-waterproof-but-that-doesnt-stop-people-from-trying-4088922/

0
0
Bronze badge

Well baked.

Tesla patented the basic concept in 1901- http://www.google.co.uk/patents/US685957

0
0
Joke

This is news? Langley has been using this stuff for years. Where do you think the term "bugger all" came from?

0
0
Gold badge
Meh

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?

1
0
Facepalm

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!

0
0

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!

0
0
Silver badge

Quick - someone turn on the microwave oven, I need to check the time on my microwave-parastic-power-wristwatch.

0
0
Bronze badge
Happy

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.

.

2
0
Silver badge

prescient or what?

http://vps.templar.co.uk/Cartoons%20and%20Politics/117322.strip.gif

1
0
Anonymous Coward

self fulfilling

Sounds like they invented a very effective microwave detector, powered by the very thing it is designed to detect! Next, a solar powered light detector. Well done, boffins!

0
0
This topic is closed for new posts.

Forums