I have an older house (1950s) and I'd really like to see behind my walls without physically excavating so I can try to run some wires without encountering surprise obstructions. There are tools which use WifI to do detect humans[1] (<a href="https://www.tomshardware.com/news/wi-fi-routers-used-to-detect-human-locations-poses-within-a-room" rel="nofollow">https://www.tomshardware.com/news/wi-fi-routers-used-to-dete...</a>) [2](<a href="https://news.ycombinator.com/item?id=40897828">https://news.ycombinator.com/item?id=40897828</a>) but I'm looking for a way to use Wifi for more general imaging. There's a paper from 2017 ("Holography of WiFi Radiation)[<a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.183901" rel="nofollow">https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.11...</a>] and many other scholarly papers about object detection via WiFi, but I haven't been able to find any off-the-shelf products/projects that would just build a 3D environmental density map without any object detection. The resolution doesn't have to be great - not looking for millimeter scale features e.g. structural weakness. Is there anything out there that comes close? Given recent archaeological uses of drone LIDAR and satellite tomography, I figure the software for interpreting this kind of data should be pretty robust by now, just maybe it hasn't filtered down to the consumer market.
Did you look into stud finders? They’re devices specifically made to detect pipes and electrical wiring in walls.<p>I love that you immediately went to WiFi for this though. Gotta love us tech people over complicating things haha!
5 GHz WiFi has a wavelength around 6cm so it can’t “see” anything smaller than approximately that. The things you want to see in your walls are below the diffraction limit for WiFi.
Get an infrared thermometer camera. I have a FLIR add-on for iPhone that lets me see studs, gaps in insulation, leaks... it's amazing what shows up.<p>It won't show cables, unless they're hot. You can use an AC stud finder for that.<p>You can flip the photo between the actual and IR image, and it overlays an outline over the image.<p>I make a video in and out of the house on the hottest and coldest days.
2.4ghz isn't great at detecting small obstacles like wires. There's a smartphone mounted device that can do this with 60ghz: <a href="https://walabot.com/" rel="nofollow">https://walabot.com/</a>
I would like to ask about what cool hacky attachments can I buy for a smartphone? Such as the thermal sensor mentioned in this thread <a href="https://news.ycombinator.com/item?id=40947011">https://news.ycombinator.com/item?id=40947011</a>.<p>Amazon (in India) turned up nothing when I searched for cool attachments etc.
Walabot sounds interesting... but here's an article about similar tools:
<a href="https://www.doityourself.com/stry/4-tools-that-can-see-through-walls" rel="nofollow">https://www.doityourself.com/stry/4-tools-that-can-see-throu...</a>
For anyone trying to find and map electrical wires in their walls I recommend an inductive electromagnetic listening device like the FarField on Tindie. Plug a device into an outlet and you'll be able to hear the electromagnetic field of the wire in your wall via the FarField's stereo inductors. Soma Ether is also a good one but pricey.
An educated guess, but I'd think wifi signal object detection works on recording a baseline (empty room signals) and then doing a diff to the baseline when some object moves. If that's the case, you cound not use the wifi signal to map the static room itself.
The "cheap and foolproof" way to do it is to cut a hole in your wall using a drywall cutter, and then feel with your hand. When you're done, you put the drywall back and patch it.<p>A drywall cutter is like a cast cutter; it works by vibrating and won't cut through wires, pipes, skin, ect.<p>If you don't want to use a stud finder, look for electrical boxes and remove the plate. That will tell you where a studs is. The rest of the studs are typically (US) 16" apart, but vary near corners and windows. You can often make an educated guess by knocking on the wall, the sound changes depending on if you knock on the stud.
There's a youtube channel called "Thought Emporium" which earned my sub many years ago with this video series on building a wifi camera.<p>Part 1: <a href="https://www.youtube.com/watch?v=o6WHhqDHSQ4" rel="nofollow">https://www.youtube.com/watch?v=o6WHhqDHSQ4</a>
Part 2: <a href="https://www.youtube.com/watch?v=VABeN4uv03s" rel="nofollow">https://www.youtube.com/watch?v=VABeN4uv03s</a>
You would likely have an exceedingly hard time getting that sort of output using WiFi. The real issue is resolution (your ability to isolate your target from nearby reflectors) which, in range, is determined by your usable bandwidth. In the best case, with the 1.2 GHz (ish) supplied by WiFI-6, your resolution would be c/(2B) = 12.5 cm (with c being the celerity of light). Then, you would have to measure from at least three different locations to get a 3D image with sufficient resolution.<p>An alternative approach would be to use holographic principles, but these require you to measure very accurately the position of your transmitters, whether you use a multiplicity of them placed in different locations or employ Synthetic Aperture Radar methods with a single one (by moving your transmitter).<p>That is why using 60 Ghz radars (with 4 GHz of bandwidth and Angle of Arrival capabilities) at short ranges would probably be the most promising direction. You can get a dev kit for one of these from Texas Instruments or some other supplier for not too much money.
You're most likely overthinking it.<p>For your use case, you are primarily concerned with fireblocks. They are unlikely to exist in an older home. They can be detected with a simple stud finder, which range from $30 for the simple (good enough) kind, to $1000 for the radar kind. Simply knocking on the wall is also good for this purpose.<p>You likely have pretty fixed locations where you want the wires to exit into the room, so you can run a borescope through those places. These are also pretty inexpensive.
Instead of imaging with RF I'm wondering if acoustic devices (like the piezo transducers they use for echocardiography or prenatal imaging?) are available for homeowners. I've never heard of any and assume they'd be stooopid expensive.
I have remodeled a dozen houses of and haven't hit anything of importance. How:<p>Study the building code to determine with >95% accuracy what is behind the wall based upon surrounding fixtures.
Wi-Fi is nowhere near the <i>effective</i> resolution (forget the 6cm wavelength) you need and it's subject to all sorts of electro-magnetic artefacts. Stud finders.
Not using Wifi, but radar (so it needs at least a little movement) :<p>Pixel 4 have SOLI 60Ghz radar chips that allows various object categorization (eventually through walls applications).<p>Unfortunately the radar API was never released. It's unfortunate because a smartphone already has various sensors that ideally you'd like to use to do some sensor fusion using the camera and accelerometers to determine the position of the sensor and fuse the radar information in the map, like in those 3D photogrammetry room scanning applications.<p>Various object categorization :<p><a href="https://www.youtube.com/watch?v=B6sn2vRJXJ4" rel="nofollow">https://www.youtube.com/watch?v=B6sn2vRJXJ4</a><p><a href="https://www.theverge.com/2019/1/4/18168083/google-project-soli-radar-hardware-applications-radarcat-solinteraction-university-of-st-andrews" rel="nofollow">https://www.theverge.com/2019/1/4/18168083/google-project-so...</a><p>Reverse-engineered attempt have been successful (but are locked behind paywalls (since it's a 2021 paper and sci-hub doesn't download recent (>=2021) articles during its trial in india) :
"Reverse Engineering the Soli Radar API for Military Applications" : <a href="https://ieeexplore.ieee.org/document/9455321/" rel="nofollow">https://ieeexplore.ieee.org/document/9455321/</a><p>SOLI chips are based on infineon chips
<a href="https://www.infineon.com/cms/en/product/promopages/60GHz/" rel="nofollow">https://www.infineon.com/cms/en/product/promopages/60GHz/</a><p>You can find some demo board using the chip :<p><a href="https://www.digikey.fr/fr/videos/i/infineon-technologies/getting-started-with-xensiv-60ghz-bgt60utr11aip-radar-demo-board" rel="nofollow">https://www.digikey.fr/fr/videos/i/infineon-technologies/get...</a><p>The walabot referenced in other comments is an example. Based on a different chip from
<a href="https://vayyar.com/technology/" rel="nofollow">https://vayyar.com/technology/</a> <a href="https://cdn.sparkfun.com/assets/learn_tutorials/7/2/4/walabot-tech-brief-416.pdf" rel="nofollow">https://cdn.sparkfun.com/assets/learn_tutorials/7/2/4/walabo...</a>
To me, WiFi is the X in an XY problem. An endoscope can be had for <$50 and will let you actually see what is going on.<p><a href="https://www.google.com/search?q=endoscope" rel="nofollow">https://www.google.com/search?q=endoscope</a><p>Good luck.