Seeing Through Walls

Images of the X-ray security center in the movie "Total Recall"(Source:i-mockery.com)

Researchers at the MIT Lincoln Laboratory have developed a new radio technology that can allow them to "see" through solid walls. The system is an array of antennas in two rows; eight antenna are used to recieve signals, and thirteen are used to send signal, a total of twenty-one antennas. The researchers designed the antenna array to be mobile and as small as possible, in order for the military to be able to make full use of it in a combat situation. So far the technology can only work against walls that are eight inches thick or less, and cannot detect inanimate objects behind the wall, but they do work well in detecting people through the wall, and can be used at a distance of about 60 feet (from the wall). As well, the machine can provide a real-time view of whoever is behind the wall at a rate of about 11 frames per second. However, the images of the "people" behind the wall are displayed as blobbed areas on the screen.

Image of the Radar System (Source: img.mit.edu)

This radar system works very similar to the way human vision works. Our eyes can detect light reflected from an object and recieve it, allowing us to interpret what it is, just like radio waves can be recieved to an antenna. The only difference is that light cannot pass through solid objects, such as walls, and therefore we cannot see the other side. Even if light does pass through the solid object, we do not recieve enough of it back to be able to interpret what is on the other side. Radio waves have an easier time passing through solid objects, the problem is getting them to come back, as most of the signal strength is lost while passing through the wall. Signal amplifiers can be used to give the signal additional strength so it can be dectected.  Larger wavelengths have an easier time passing through solid objects, however the MIT Lincoln team decided to use S-band radio waves, which have smaller wavelengths, but allow the equiptment to be smaller, allowing the system to be mobile.

From there, the system uses a function from the wave recieved to interpret how far something is behind the wall. A certain distance will produce a certain type of wave in reception, according to Gregory Charvat. research leader at MIT: "So if the wall is 20 feet away, let's say, it shows up as a 20-kilohertz sine wave, ... If you, behind the wall, are 30 feet away, maybe you'll show up as a 30-kilohertz sine wave." The team is still working on making the real-time image clearer, as the wall itself does come up as the brightest object on the screen.


Read original article about the Radar System at dailytech.com