

WiFi light painting - KhalilK
http://www.nearfield.org/2011/02/wifi-light-painting

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darsham
I've always wondered if it's possible to build a video camera that films on
the microwave spectrum instead of the visible light spectrum. Would such a
tool would allow you to "see" wi-fi access points ? I guess they would look
like bright, pulsating sources of light, and they would be visible through
walls.

I did a bit of research on the subject, and they don't seem to really exist.
It's possible that the longer wavelength poses technical difficulties. The
individual receptors are too big and you can't cram them together at a
sufficient density. Also, the lensing and shielding needs to be completely re-
thought.

There's a 2012 paper called "Portable Real-Time Microwave Camera at 24 GHz"
but i couldn't access it (not in academia).

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derefr
There are two ways to capture an EM signal. The static-array method, where you
have something like a CCD (a matrix of antennas that sample a signal in
parallel), is basically only useful around the visible-light part of the EM
spectrum.

What you do for the _rest_ of the spectrum is to take one antenna and move it
around. As long as the signal is relatively static with respect to time, this
has the same effect (and is much cheaper to implement.)

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csense
> The static-array method, where you have something like a CCD...is basically
> only useful around the visible-light part of the EM spectrum

Why is this the case? Is it just that technology is further along for visible
light because there's more economic incentive for a digital camera that
replicates the human eye?

Is it a materials problem, where we haven't discovered arrangements of matter
with the right properties (e.g. CCD's respond to visible wavelengths and are
adaptable to semiconductor manufacturing techniques)?

Or is it something to do with fundamental physics like the wavelengths are a
lot longer which requires detectors that are too large to be practical? Or
maybe diffraction is a problem?

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DougWebb
I wonder how much of the variation is temporal instead of spatial. There are a
few shots in there that were done twice with different results, showing that
the signal strength in a single spot varies over time. You can't use light
painting to capture that usefully; you can only make pretty artistic
impressions.

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TrainedMonkey
I think pretty artistic impression was the point. Project tried to reconcile
art with technology that humans can't perceive. By appealing to our aesthetics
this drives home the point that we are living surrounded by information fields
that we can't perceive and give little thought to.

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femto
This reminds me of a project, that a group of us talked about, but never did.

I used to work on a radio system with a very large and powerful phased array
transmitter, the ground mat being hundreds of metres on each side. We though
it would be fun to stick a bunch of fluorescent tubes into the ground. In
theory we should have been able to see the antenna beam sweeping across the
ground mat, as it was steered in difference directions and the tubes lit up.
It would have been a very cool demonstration, but like so many other projects
we only talked about it.

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MasterScrat
Great idea!

I'd love to see that in 3D... maybe with drones flying around instead of a
single human doing the measurements?

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cordite
I remember seeing this, though I still think that it wouldn't be so helpful,
since I almost never have any luck with public wifi.

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lnanek2
Same, much better off tethering to my phone here in the US. Maybe they could
do it for carriers with cell signal and the carriers could improve any gaps,
though. Same for private WiFi at a building or company.

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lucb1e
Ever since seeing this in 2011 I wanted to use it to find signal shadow in the
house. I have yet to build it...

