Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It only takes a minute to sign up.
Sign up to join this community
Considering that there are cameras for infrared, X-ray and ultraviolet, I wonder if there are also cameras that can picture the WLAN or mobile phone parts of the electromagnetic spectrum.
Considering that everything is flooded with mobile phone radiation, and you have Wi-Fi in almost every household, I imagine this would give some interesting pictures, maybe overlaid on a real photo.
In order to get an image, both the subject and the "camera" must be much larger than the wavelength of the light that you use for imaging. The wavelength of visible light is between approximately 400 and 800 nm, i.e. smaller than a µm.
Radio frequencies go up to several GHz, which corresponds to wavelengths of many centimeters. For example, the 2.4 GHz WIFI band has a wavelength of about 12.5 cm. Thus your camera would have to be several meters large, and you would only be able to image similarly large subjects. There are no radio-frequency cameras for our everyday world.
However, scientists have actually built "cameras" that are several meters wide, and use them to image very large objects such as stars and galaxies. These cameras are called radio telescopes.
I disagree with the answer with many upvotes. Physical lengths can be "swindled" in a number of ways and theoretically it would be possible to build a portable camera that snaps images of a very tiny portion of the electromagnetic spectrum. Plus, you are not considering that there are not only high-band signals, but also ultra-high-band signals that could be a LOT easier to detect. The question which I'd find interesting would be: How would you color the spectrum?
Here is an example of EM photography by an University of Copenhagen.
Here is a home-made experiment involving the use of an antenna and some post-processing software to actually create an image.
Probably the "lens" of such camera would look like this.
Sort of. Not a "camera", but a computational imaging technique.
We explore the feasibility of achieving computational imaging using Wi-Fi signals. To achieve this, we leverage multi-path propagation that results in wireless signals bouncing off of objects before arriving at the receiver. These reflections effectively light up the objects, which we use to perform imaging. Our algorithms separate the multi-path reflections from different objects into an image. They can also extract depth information where objects in the same direction, but at different distances to the receiver, can be identified. We implement a prototype wireless receiver using USRPN210s at 2.4 GHz and demonstrate that it can image objects such as leather couches and metallic shapes in line-of-sight and non-line-of-sight scenarios. We also demonstrate proof-of- concept applications including localization of static humans and objects, without the need for tagging them with RF devices. Our results show that we can localize static human subjects and metallic objects with a median accuracy of 26 and 15 cm respectively. Finally, we discuss the limits of our Wi-Fi based approach to imaging
The paper contains a number of fuzzy blobs overlaid on photos. It's a lot closer to a Kinect sensor in that it gives depth information as well but has poor spatial resolution, limited to one wavelength of WiFi.
Because of the much lower frequency of radio compared to light, it's possible to do signal processing based on arrival time. Using this technique gives useful information from reflected and diffracted signals, whereas in optical systems they would just be noise.
Another 'sort of' answer:
One possibility, more analogous to a traditional camera, is to use a stationary receiver and a strongly directional antenna. If the antenna is directed in the same way that an electron beam moves across a CRT screen, a render of signal strength can be created that can then be overlaid with a photo taken from the same point. While the parts are readily available (see wikipedia/cantenna), I haven't come across a project or commercial solution that uses the cantenna as a camera in the way described above.
As @Michael noted, this probably wouldn't give you a 'good' image: radiation at these wavelengths behaves differently to visible and near-visible light. Rather than simply behaving differently depending on the relevant surfaces, radiation at these wavelengths is more measurable as amplitudes per point in a 3d space. The question uses a key word: the room or space is truly flooded.
Youtuber CNLohr provided an explanatory video showing how to measure transmitter power from a single WiFi source using relatively low-cost components.
This isn't a "camera" as such, even though a camera is used to translate the signal from point measurements to a 3d image, one vertical layer at a time. However, it does give a (3d) image that can be flattened and overlaid onto a normal photograph. On the downside, it relies on moving the sensor through every point in the space to be imaged; not exactly a 'snapshot' measurement.
It's conceivable that this design could be adapted: the sensor could store position information based on an indoor GPS and record its own data, rather than needing a camera. The software can also be adapted to measure the total signal per point instead of simply the signal from a single transmitter. When selecting a wireless signal, a list of identifiable signals and strengths is presented.
I believe this would give an aesthetically better image than directional measurement; however, like the directional antenna camera, it's not available as a commercial product.
As there is currently no such camera known to me, it would be possible to build a quite effective one using an array of patch antennas to form a phased array. As such, a large flat antenna, say 1 by 1m, could be made from printed circuit board. However, a large amount of expensive HF components would be needed to integrate all individual antenna elements into an phased array.
Such an array is capable of sweeping and focussing its aperture by electronic means. While it can not overcome the wavelength resolution limit, it can take live pictures by rapid scanning, especially for visualizing active transmitters like nearby mobile phones, giving a large radiation power output.
The phased array technique is extensively used for radar scanning, see Wikipedia: https://en.wikipedia.org/wiki/Phased_array
Some engeneers expect the use of phased arrays in future mobile phones or wifi routers, as it would enable a more directed transmission between the peers which would require much less energy and allows for higher bandwith as one peer's connection would not interfere with another directed connection unless in the same line.
Simple answer is no, at least not yet.
I say this because if this was possible then equipment would exist in the test & measurement world. and instead we have equipment that can only use calibrated antennas to compute relative strength and frequency. You move a detector around and observe results. I think this is the kind of measurement system out there currently: http://www.emscan.com/rfxpert/
It would be a major breakthrough in technology to be able to image the radiation via photography.
