The camera, from the Camera Culture Group at MIT, uses microwaves. Thanks to their longer wavelength compared to visible light, microwaves can penetrate objects that shorter waves just bounce off from. Microwave imagers already exist, but they are huge and expensive, and they also have to deal with one big problem: because the microwaves are pretty big, they can encounter objects that are of a similar size. When this happens, the resulting image is specular. That is, it acts like a mirror.
The MIT camera, from a team led by the Media Lab’s Gregory Charvat, uses microwave “flashes” to illuminate the scene. These flashes are 100,000 times weaker than the microwaves from your oven, says the Boston Globe, and 100 times weaker than the radio in your cellphone. By firing off multiple flashes from different spots, and taking a photo each time, the camera’s brain can piece together an image.
The camera itself is also unusual in that the image sensor faces away from the scene, and into a large reflecting dish. This dish gathers the returning microwaves and focuses them on the sensor.
The camera, says Charvat in his paper, is “capable of producing images that recover 2-D brightness, depth, and multi-spectral response of objects.” To demonstrate the camera, the team shot photos of a mannequin, first in the open, then behind drywall, and then behind plywood. In all cases, the camera achieved a similar resolution. The mannequin was wrapped in aluminum foil to make it opaque to the microwaves, although a regular water-filled human would do the same job.
To our eyes, the results look rather blobby, but to the eyes of rescue workers, or to the trained brain of Indiana Jones as he peeks through the wall of a buried tomb, they are much more useful. The camera can also build 3-D images by processing photos from multiple angles, allowing the operator to identify objects inside boxes. Or, in the case or adventuresome archeologists, mummies inside sarcophagi.
Right now, even though it is small and cheap (around $1,000) compared to existing options, the camera is a big piece of laboratory equipment, and each “exposure” takes an hour to capture. By using shorter wavelengths, the camera too could be shrunk, and as component process decrease, a cheap, portable device could become possible, so the next time you’re searching for something in the attic, you won’t have open and reseal all those boxes yet again.