
Converting Wi-Fi signals to electricity with new 2-D materials - beautifulfreak
http://news.mit.edu/2019/converting-wi-fi-signals-electricity-0128
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joezydeco
There's a whole generation of kids that haven't built a razor blade diode /
foxhole radio. That's a fun thing to do.

[https://en.wikipedia.org/wiki/Foxhole_radio](https://en.wikipedia.org/wiki/Foxhole_radio)

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netrap
Thanks for the link. I knew about crystal radios but didn't know about the
razor blade technique.

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mmagin
There's a remarkable array of ways you can get a crude semiconductor junction.
See also
[https://en.wikipedia.org/wiki/Rusty_bolt_effect](https://en.wikipedia.org/wiki/Rusty_bolt_effect)

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janekm
This press release is quite misleading... the only novel aspect here is
"flexible". It's less efficient than the existing rectenna solutions. And it's
just as useless unless it's placed directly next to a WiFi router that is
experiencing unusually high load. A single AA battery can deliver 40uW for
about 4 years, continuously.

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ecpottinger
And if you forget the battery in those four years (which is often) when it
finally fails you find the inside is full of chemical garbage.

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simcop2387
Use a carbon zinc dry cell for things like that, they won't leak like other
alkaline battery types. Bit lower capacity so you'll have to replace them more
often but they'll not lead to destruction of the device either.

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Hello71
or if you really need higher capacity, a lithium battery.

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HashHishBang
Correct me if I'm wrong here but wouldn't tech like this also sap signal
strength like nothing else?

This seems like it would be a potentially nice to have first layer in a
secured room/building. Recoup some energy then actually go about blocking
unwanted signal leakage.

From a wild speculation side: if a tour bus of the elderly with pacemakers
powered by this goes by are they just a traveling dead zone?

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Wowfunhappy
Can't you just do this with tinfoil?

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HashHishBang
You can make a Faraday cage out of a lot of stuff but I doubt you could get
much in the way of power out of it. Granted you can't get much out of this
either but it's measurable.

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ransford
FWIW, Wi-Fi is generally considered a poor source of harvestable RF for little
doodads you might want to power passively. Among other issues, there's a lot
of "quiet time" as radios on the same Wi-Fi network negotiate who gets to use
the channel at a given moment.

If you are interested in the challenges of harvesting energy from Wi-Fi and
some ways to address those challenges, here's a nice paper (originally in
CoNEXT 2015) from a team I was fortunate to be on:
[https://cacm.acm.org/magazines/2017/3/213830-powering-the-
ne...](https://cacm.acm.org/magazines/2017/3/213830-powering-the-next-billion-
devices-with-wi-fi/fulltext)

[Edit: the relevance here is that, even with an awesome antenna like the one
in the news, the Wi-Fi protocol kinda works against you, which raises a bunch
of interesting questions.]

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Junk_Collector
You really just have to assume that the writer of the article is completely
ignorant in this case. I hardly think that MIT is claiming to have invented
the worlds first antenna connected to a diode but that's the claim that seems
to be made in the article. The state of technical reporting is rather sad.

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Junk_Collector
I guess to be fair to the authors. The actual technical achievement is
mentioned, albeit briefly, "To build their rectifier, the researchers used a
novel 2-D material called molybdenum disulfide (MoS2)" It's a novel material
that can be used to make planar shoctkey diodes via an unusual process.

The entire rest of the article is just pointless misleading fluff.

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matthewmacleod
_The entire rest of the article is just pointless misleading fluff._

No, it's not. It's a press release, which while being pretty technically basic
is broadly accurate. It includes some comparisons with existing technology,
reasons that this development is different, and possible applications. The
point is to make this development known to other people outside the field who
have less knowledge about the underlying technology. That's a totally
reasonable goal; not every article has to be an in-depth technical review.

This article does commit one unforgivable crime, which is failing to link to
the research itself. I absolutely cannot understand why media outlets and
press offices are so reticent to do this simple thing.

~~~
Junk_Collector
Let's break it down then. The first paragraph opens with, "the first fully
flexible device that can convert energy from Wi-Fi signals into electricity
that could power electronics." This is blatantly false.

The second paragraph is sort of true. They are using their novel diode in an
otherwise standard antenna structure.

Third paragraph repeats the second. Mentions that it can be manufactured in
sheets?

Fourth paragraph sort of repeats the previous but this time as a quote from
someone. The Quote, " have come up with a new way to power the electronics
systems of the future — by harvesting Wi-Fi energy in a way that’s easily
integrated in large areas — to bring intelligence to every object around us."
It's pure marketing speak. We need more funding, let's throw ai onto this for
some reason.

The next 3 paragrpahs are repeats of, This device that provides power can be
used to provide power to things. It at least mentions a broad figure of merit,
40 uWatts when exposed to 150 uWatts.

We are now half way through the article when the next paragraph finally
mentions rectifiers, giving a brief but not great definition of what they are
and their current state of the art. It mentions some problems with modern
rectifiers, which are not actually true.

The next paragraph is actually only a single sentence and contains the
entirety of the new development that the whole article is supposed to be
about!

The next paragraph tries to explain the shortcomings of current Schottky
diodes with bad physics.

Another quote about the device but lacking in broader context.

The second to last paragraph gives a better version of the efficiency figure
of merit from earlier. Lacks details.

Last paragraph is a list of funders who are paying for the research.

That is a pretty crappy fluff to meat ratio in my book.

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cyberfart
> Let's break it down then. The first paragraph...

Can we have this as a service? Fluff-to-meat-ratio feature is a requirement
though.

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beautifulfreak
Here's the source article in Nature:
[https://www.nature.com/articles/s41586-019-0892-1](https://www.nature.com/articles/s41586-019-0892-1)

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akrasuski1
40 microwatts of power, to be precise. Compared to, say, 5V*1A=5W of typical
phone charger, this is impractical by a large margin.

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DeRock
Why is “enough power to charge your phone” your line of practicality? Phones
contain an enormous amount of power hungry electronics, bright screens,
speakers, multiple GHZ CPUs and radios for transmitting across different
spectrum. With 40uW, you’d have to strip most of that away, but you could do
something like: power up, take a temperature/CO2/RH/etc reading, transmit to a
base station, sleep and repeat every 5 minutes. Sensor networks like these are
extremely practical, especially in an industrial setting. Being able to
accumulate some power, eg. with an integrated capacitor could also increase
your max power draw for when your device is doing work.

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Junk_Collector
Because the first line of the article alludes to using this to power your
phone.

It also states. "Promising early applications for the proposed rectenna
include powering flexible and wearable electronics, medical devices, and
sensors for the “internet of things.” Flexible smartphones, for instance, are
a hot new market for major tech firms."

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lostgame
Oh, wow. I had to do a double-take when I read '2-D', because the initial
shock of 'converting wi-fi signals to electricity' was already too much for my
mortal mind to comprehend.

If this ends up being practical, this is really, really, cool - and that's an
understatement.

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CyberDildonics
Antennas already convert wifi signals to electricity, so it isn't that much of
a stretch.

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SHAKEDECADE
I foresee the Amazon/Google slogan ‘Always Charged. Always Connected.’

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tictoctec
We're not even going to need to have electrical wiring in homes anymore.
802.11ad 60GHz wifi mesh routers with a lot of coherence and a directional
mechanism could power the whole home.

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gnicholas
> _Devices that convert AC electromagnetic waves into DC electricity are known
> as “rectennas.”_

This is apparently a portmanteau of "rectifying" and "antenna".

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aaaaaaaaaaab
So, like an antenna?

