7 ms·

Visualising Electromagnetic Fields

108 points by lelf 9y ago

deleted 9y ago
[deleted]
ttoinou 9y ago
Hard to believe. What's the secret to see them ?
- sqquuiiiddd 9y ago
  A simple coil of wire could act as a receiver. And attached to a light emitter, the strength of the signal would translate to a brighter light. Just a guess though.
- piptastic 9y ago
  They have a video you can watch
  - saeranv 9y ago
    The video doesn't really explain what they're doing though. Can anyone explain how they're visualizing the EM fields here?
    - mmcconnell1618 9y ago
      It looks like they have a metering device that glows different colors based on the strength of the field detected. They then appear to be systematically moving the meter across a grid with time lapse photography. The lights photographed from different positions are blended together to create a voxel-like view of the field.
      - saeranv 9y ago
        Thanks for explaining that makes sense. What kind of metering device will glow based on these kinds of EM fields?
- kbaker 9y ago
  Similar to this project: https://hackaday.io/project/4329-wifi-power-mapping https://hackaday.io/project/4329-wifi-power-mapping Also see this video which goes over the concept: https://www.youtube.com/watch?v=aqqEYz38ens https://www.youtube.com/watch?v=aqqEYz38ens
mpolichette 9y ago
I've always wondered about this... if an EM field is composed of photons which have higher energy than light, how come I've never seen image/video captured where the device is 'glowing' or something as a photon source? Is there something I'm missing that prevents us from detecting them similar to the way we detect visible light?
- doctoboggan 9y ago
  Nope, it is definetly possible to capture images in the non-visible spectrum. We simply need to convert them into the visible spectrum using some transform (usually just translation) so we can see them. You probably have seen images like this, you just might not have realized. Many of the most beautiful astronomy photographs are actually captured in different spectrums. If you've ever seen a "thermal image" that is also non-visible photons. Some examples: https://asd.gsfc.nasa.gov/blueshift/wp-content/uploads/2013/08/9511009080_0095e8c8b3_h.jpg https://asd.gsfc.nasa.gov/blueshift/wp-content/uploads/2013/... https://smd-prod.s3.amazonaws.com/science-red/s3fs-public/thumbnails/image/ultraviolet-2.jpg https://smd-prod.s3.amazonaws.com/science-red/s3fs-public/th... http://www.greenbuildingadvisor.com/sites/default/files/Thermal%20Image%20UK%20-%203%20-%20Tom%20Barbour.jpg http://www.greenbuildingadvisor.com/sites/default/files/Ther...
- Koshkin 9y ago
  > how come I've never seen image Of course you have, it's called an x-ray.
- whatshisface 9y ago
  > if an EM field is composed of photons which have higher energy than light That's not right - visible light is sort of a "midrange" photon energy that's exceeded by ultraviolet, x-rays and gamma rays and preceded by infrared, microwaves and radio waves. Everyday devices emit at low frequencies, with energies significantly below that of visible light. The higher energies (ultraviolet, xray, gamma) absolutely do have images: - Ultraviolet [https://en.wikipedia.org/wiki/Ultraviolet_photography#/media/File:UV_Portrait.jpg https://en.wikipedia.org/wiki/Ultraviolet_photography#/media...] - Xray https://en.wikipedia.org/wiki/X-ray#/media/File:Radiograf%C3%ADa_pulmones_Francisca_Lorca.cropped.jpg https://en.wikipedia.org/wiki/X-ray#/media/File:Radiograf%C3... - Gamma https://en.wikipedia.org/wiki/Gamma_ray#/media/File:VACIS_Gamma-ray_Image_with_stowaways.GIF https://en.wikipedia.org/wiki/Gamma_ray#/media/File:VACIS_Ga... Now, the photons with lower energies than visible light form an interesting case. First off there's infrared, which is fairly familiar: - Infrared https://en.wikipedia.org/wiki/Infrared_photography#/media/File:Tree_example_IR.jpg https://en.wikipedia.org/wiki/Infrared_photography#/media/Fi... Now, as the photon energies get lower the wavelengths get longer. This introduces a problem for lower-energy images: when the wavelength is around the size of the aperture, wave-like things will happen involving the aperture. This tends to blur the images, meaning that for longer and longer wavelengths larger and larger cameras are required to achieve the same level of detail. However, these images still exist - but they are rarely taken of everyday things. Note that the imaging you are talking about (to capture the glowing of everyday electronic devices in low frequencies) would have to happen in the microwave and radio bands - because that's around the frequency at which electronics operate. The result is that a reasonably-sized camera would not be able to take a meaningfully sharp image of a router's "glow." - Microwave https://en.wikipedia.org/wiki/Microwave_imaging#/media/File:3D_image_of_rebars_with_corrosion_produced_using_microwave_imaging..JPG https://en.wikipedia.org/wiki/Microwave_imaging#/media/File:... - Radio Waves http://www.gb.nrao.edu/epo/PageMill_Resources/galaxy.jpg http://www.gb.nrao.edu/epo/PageMill_Resources/galaxy.jpg The radio wave picture depicts a galaxy. Radio imaging setups are usually very large, like this one: http://mstecker.com/pages/astroVLAa15vlad-2c1.htm http://mstecker.com/pages/astroVLAa15vlad-2c1.htm
ghaff 9y ago
For a basic magnet, there was an old science fair type of experiment where you laid the magnet on a piece of photo paper, sprinkled iron filings, flashed the paper and developed. Of course, these days you can just basically shoot a digital photo of the magnets and filings. Lots of examples online.
- FreeFull 9y ago
  The one misleading thing about iron fillings is that they tend to arrange themselves into lines, but the actual magnetic field is continuous rather than made out of discrete lines.
  - msla 9y ago
    That is, in a sense, just calculus: Building a curve out of a huge number of straight segments is immediately comparable to the method of Riemann sums. https://en.wikipedia.org/wiki/Riemann_sum https://en.wikipedia.org/wiki/Riemann_sum I think it forms a nice bridge from univariate calculus to visualizing the vector fields.
    - tlarkworthy 9y ago
      It's not that though. The iron filing change the magnetic field making it denser where the filing are. So they self organize into reenforcing channels of flux. So it's not a true visualization of the field, because the field is changed by the measurements.
      - noobermin 9y ago
        Useless pedantic then, it is not a "true visualization" of the B field in free space absent the filings. It is however, an approximate visualization of it.
kyleblarson 9y ago
This is cool and reminds me of avalanche rescue training as you have to learn to follow flux lines during searches: http://beaconreviews.com/transceivers/rescue_searching_coarse.asp http://beaconreviews.com/transceivers/rescue_searching_coars... edit: better link
hansjorg 9y ago
Another take on this (Light painting WiFi by Timo): https://vimeo.com/20412632 https://vimeo.com/20412632
balnaphone 9y ago
An explanation of this kind of visualization given in a stanford lecture by Steve Mann, see 35-45 min into video. Stanford Seminar: 42 years of Phenomenological AR for Natural/Reality/Direct User-Interfaces https://www.youtube.com/watch?v=6IpBVC-p3iU https://www.youtube.com/watch?v=6IpBVC-p3iU Example in video https://youtu.be/6IpBVC-p3iU?t=2436 https://youtu.be/6IpBVC-p3iU?t=2436
timthorn 9y ago
Some years ago, an artist-in-residence at Bristol's Physics dept planted fluorescent tubes under overhead power lines, which then glowed due to the field and could be played with by visitors like a plasma ball: http://www.bris.ac.uk/changingperspectives/projects/field/ http://www.bris.ac.uk/changingperspectives/projects/field/
- ChuckMcM 9y ago
  In high school it was a fun geeky thing to do and drive out into the desert where the power lines from Hoover Dam headed over to LA and light up fluorescent bulbs. There is a story, possibly apocryphal, that was told by one of the professors at USC of a guy who lived out there and used a few hundred feet of 12ga wire to build what would essentially be a secondary coil of an air gap transformer to power his shack. I found it interesting but not interesting enough to pursue a career in power engineering :-).
- westbywest 9y ago
  This installation gives a better intuitive sense of field strength, e.g. emissions still strong enough to cause fluorescence dozens of meters away. I'm curious how Sturgeon's visualizations would appear around household appliances with (relatively) high-amperage induction motors like vacuum cleaners.
- userbinator 9y ago
  Depending on the field strength, it can be sufficient to do more than light fluorescent tubes: https://www.youtube.com/watch?v=SD2dfMfgkTw https://www.youtube.com/watch?v=SD2dfMfgkTw
- im3w1l 9y ago
  That must be pulling a lot of energy out of the power lines huh? I wonder at what point people start complaining...
lovemenot 9y ago
Excuse my question. I'm curious about a basic formula to calculate magnetic flux at a given distance from an AC conductor at a given power level?
- tensor_rank_0 9y ago
  http://www.softschools.com/formulas/physics/magnetic_field_formula/343/ http://www.softschools.com/formulas/physics/magnetic_field_f... the strength of the magnetic field is equal to the (current times the permeability of the medium) divided by (the distance times 2 pi). magnetic flux is the dot product of the magnetic field and the area vector representing the area through which you want the flux. theres another way to express flux as a ?derivative of voltage? but I can't find a reference and the exact relationship escapes me at the moment.
  - lovemenot 9y ago
    thanks
zestyping 9y ago
These are pretty, and I can appreciate them as art. As a visualization, though, it doesn't seem very satisfying because most of these images are pictures of the path traced by the person waving the screen, not pictures of the electromagnetic field. The shape we see is mainly a visualization of whatever way the person decided to move the screen through space, that only incidentally happens to be slightly affected by the field.
- saeranv 9y ago
  Not sure why you're being downvoted, it's a good point. There's a couple of links here that time-lapse the meter across a consistent 2D or 3D voxel space which gives a better idea of the radiation field, but some are clearly just driven by an arbitrary path chosen by the photographer.
stats111 9y ago
Someone needs to do a same visualisation for wireless pollution in public and private spaces. With bluetooth, smart meters, wifi, emf, mobile phones etc. there is a hidden world that most people are unaware of.

108 points by lelf 9y ago

deleted 9y ago

[deleted]

ttoinou 9y ago

Hard to believe. What's the secret to see them ?

sqquuiiiddd 9y ago
A simple coil of wire could act as a receiver. And attached to a light emitter, the strength of the signal would translate to a brighter light. Just a guess though.
piptastic 9y ago
They have a video you can watch
- saeranv 9y ago
  The video doesn't really explain what they're doing though. Can anyone explain how they're visualizing the EM fields here?
  - mmcconnell1618 9y ago
    It looks like they have a metering device that glows different colors based on the strength of the field detected. They then appear to be systematically moving the meter across a grid with time lapse photography. The lights photographed from different positions are blended together to create a voxel-like view of the field.
    - saeranv 9y ago
      Thanks for explaining that makes sense. What kind of metering device will glow based on these kinds of EM fields?
kbaker 9y ago
Similar to this project: https://hackaday.io/project/4329-wifi-power-mapping https://hackaday.io/project/4329-wifi-power-mapping Also see this video which goes over the concept: https://www.youtube.com/watch?v=aqqEYz38ens https://www.youtube.com/watch?v=aqqEYz38ens

mpolichette 9y ago

I've always wondered about this... if an EM field is composed of photons which have higher energy than light, how come I've never seen image/video captured where the device is 'glowing' or something as a photon source? Is there something I'm missing that prevents us from detecting them similar to the way we detect visible light?

doctoboggan 9y ago
Nope, it is definetly possible to capture images in the non-visible spectrum. We simply need to convert them into the visible spectrum using some transform (usually just translation) so we can see them. You probably have seen images like this, you just might not have realized. Many of the most beautiful astronomy photographs are actually captured in different spectrums. If you've ever seen a "thermal image" that is also non-visible photons. Some examples: https://asd.gsfc.nasa.gov/blueshift/wp-content/uploads/2013/08/9511009080_0095e8c8b3_h.jpg https://asd.gsfc.nasa.gov/blueshift/wp-content/uploads/2013/... https://smd-prod.s3.amazonaws.com/science-red/s3fs-public/thumbnails/image/ultraviolet-2.jpg https://smd-prod.s3.amazonaws.com/science-red/s3fs-public/th... http://www.greenbuildingadvisor.com/sites/default/files/Thermal%20Image%20UK%20-%203%20-%20Tom%20Barbour.jpg http://www.greenbuildingadvisor.com/sites/default/files/Ther...
Koshkin 9y ago
> how come I've never seen image Of course you have, it's called an x-ray.
whatshisface 9y ago
> if an EM field is composed of photons which have higher energy than light That's not right - visible light is sort of a "midrange" photon energy that's exceeded by ultraviolet, x-rays and gamma rays and preceded by infrared, microwaves and radio waves. Everyday devices emit at low frequencies, with energies significantly below that of visible light. The higher energies (ultraviolet, xray, gamma) absolutely do have images: - Ultraviolet [https://en.wikipedia.org/wiki/Ultraviolet_photography#/media/File:UV_Portrait.jpg https://en.wikipedia.org/wiki/Ultraviolet_photography#/media...] - Xray https://en.wikipedia.org/wiki/X-ray#/media/File:Radiograf%C3%ADa_pulmones_Francisca_Lorca.cropped.jpg https://en.wikipedia.org/wiki/X-ray#/media/File:Radiograf%C3... - Gamma https://en.wikipedia.org/wiki/Gamma_ray#/media/File:VACIS_Gamma-ray_Image_with_stowaways.GIF https://en.wikipedia.org/wiki/Gamma_ray#/media/File:VACIS_Ga... Now, the photons with lower energies than visible light form an interesting case. First off there's infrared, which is fairly familiar: - Infrared https://en.wikipedia.org/wiki/Infrared_photography#/media/File:Tree_example_IR.jpg https://en.wikipedia.org/wiki/Infrared_photography#/media/Fi... Now, as the photon energies get lower the wavelengths get longer. This introduces a problem for lower-energy images: when the wavelength is around the size of the aperture, wave-like things will happen involving the aperture. This tends to blur the images, meaning that for longer and longer wavelengths larger and larger cameras are required to achieve the same level of detail. However, these images still exist - but they are rarely taken of everyday things. Note that the imaging you are talking about (to capture the glowing of everyday electronic devices in low frequencies) would have to happen in the microwave and radio bands - because that's around the frequency at which electronics operate. The result is that a reasonably-sized camera would not be able to take a meaningfully sharp image of a router's "glow." - Microwave https://en.wikipedia.org/wiki/Microwave_imaging#/media/File:3D_image_of_rebars_with_corrosion_produced_using_microwave_imaging..JPG https://en.wikipedia.org/wiki/Microwave_imaging#/media/File:... - Radio Waves http://www.gb.nrao.edu/epo/PageMill_Resources/galaxy.jpg http://www.gb.nrao.edu/epo/PageMill_Resources/galaxy.jpg The radio wave picture depicts a galaxy. Radio imaging setups are usually very large, like this one: http://mstecker.com/pages/astroVLAa15vlad-2c1.htm http://mstecker.com/pages/astroVLAa15vlad-2c1.htm

ghaff 9y ago

For a basic magnet, there was an old science fair type of experiment where you laid the magnet on a piece of photo paper, sprinkled iron filings, flashed the paper and developed. Of course, these days you can just basically shoot a digital photo of the magnets and filings. Lots of examples online.

FreeFull 9y ago
The one misleading thing about iron fillings is that they tend to arrange themselves into lines, but the actual magnetic field is continuous rather than made out of discrete lines.
- msla 9y ago
  That is, in a sense, just calculus: Building a curve out of a huge number of straight segments is immediately comparable to the method of Riemann sums. https://en.wikipedia.org/wiki/Riemann_sum https://en.wikipedia.org/wiki/Riemann_sum I think it forms a nice bridge from univariate calculus to visualizing the vector fields.
  - tlarkworthy 9y ago
    It's not that though. The iron filing change the magnetic field making it denser where the filing are. So they self organize into reenforcing channels of flux. So it's not a true visualization of the field, because the field is changed by the measurements.
    - noobermin 9y ago
      Useless pedantic then, it is not a "true visualization" of the B field in free space absent the filings. It is however, an approximate visualization of it.

kyleblarson 9y ago

This is cool and reminds me of avalanche rescue training as you have to learn to follow flux lines during searches: http://beaconreviews.com/transceivers/rescue_searching_coarse.asp http://beaconreviews.com/transceivers/rescue_searching_coars... edit: better link

hansjorg 9y ago

Another take on this (Light painting WiFi by Timo): https://vimeo.com/20412632 https://vimeo.com/20412632

balnaphone 9y ago

An explanation of this kind of visualization given in a stanford lecture by Steve Mann, see 35-45 min into video. Stanford Seminar: 42 years of Phenomenological AR for Natural/Reality/Direct User-Interfaces https://www.youtube.com/watch?v=6IpBVC-p3iU https://www.youtube.com/watch?v=6IpBVC-p3iU Example in video https://youtu.be/6IpBVC-p3iU?t=2436 https://youtu.be/6IpBVC-p3iU?t=2436

timthorn 9y ago

Some years ago, an artist-in-residence at Bristol's Physics dept planted fluorescent tubes under overhead power lines, which then glowed due to the field and could be played with by visitors like a plasma ball: http://www.bris.ac.uk/changingperspectives/projects/field/ http://www.bris.ac.uk/changingperspectives/projects/field/

ChuckMcM 9y ago
In high school it was a fun geeky thing to do and drive out into the desert where the power lines from Hoover Dam headed over to LA and light up fluorescent bulbs. There is a story, possibly apocryphal, that was told by one of the professors at USC of a guy who lived out there and used a few hundred feet of 12ga wire to build what would essentially be a secondary coil of an air gap transformer to power his shack. I found it interesting but not interesting enough to pursue a career in power engineering :-).
westbywest 9y ago
This installation gives a better intuitive sense of field strength, e.g. emissions still strong enough to cause fluorescence dozens of meters away. I'm curious how Sturgeon's visualizations would appear around household appliances with (relatively) high-amperage induction motors like vacuum cleaners.
userbinator 9y ago
Depending on the field strength, it can be sufficient to do more than light fluorescent tubes: https://www.youtube.com/watch?v=SD2dfMfgkTw https://www.youtube.com/watch?v=SD2dfMfgkTw
im3w1l 9y ago
That must be pulling a lot of energy out of the power lines huh? I wonder at what point people start complaining...

lovemenot 9y ago

Excuse my question. I'm curious about a basic formula to calculate magnetic flux at a given distance from an AC conductor at a given power level?

tensor_rank_0 9y ago
http://www.softschools.com/formulas/physics/magnetic_field_formula/343/ http://www.softschools.com/formulas/physics/magnetic_field_f... the strength of the magnetic field is equal to the (current times the permeability of the medium) divided by (the distance times 2 pi). magnetic flux is the dot product of the magnetic field and the area vector representing the area through which you want the flux. theres another way to express flux as a ?derivative of voltage? but I can't find a reference and the exact relationship escapes me at the moment.
- lovemenot 9y ago
  thanks

zestyping 9y ago

These are pretty, and I can appreciate them as art. As a visualization, though, it doesn't seem very satisfying because most of these images are pictures of the path traced by the person waving the screen, not pictures of the electromagnetic field. The shape we see is mainly a visualization of whatever way the person decided to move the screen through space, that only incidentally happens to be slightly affected by the field.

saeranv 9y ago
Not sure why you're being downvoted, it's a good point. There's a couple of links here that time-lapse the meter across a consistent 2D or 3D voxel space which gives a better idea of the radiation field, but some are clearly just driven by an arbitrary path chosen by the photographer.

stats111 9y ago

Someone needs to do a same visualisation for wireless pollution in public and private spaces. With bluetooth, smart meters, wifi, emf, mobile phones etc. there is a hidden world that most people are unaware of.