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"We've seen terahertz cameras that can look through walls and X-ray scanners that fit in the palm of your hand. Now, scientists at MIT have developed a way to track movement through walls using Wi-Fi signals.\nThe idea is pretty simple: take two transmitters and one receiver. Each transmitter sends out a signal that is precisely 180 degrees out of phase with the other, so the two cancel each other out, and the receiving antenna \u201Chears\u201D nothing.\nBut put any moving object in the area, and it reflects the signals. The signals don\u2019t cancel out, and where once there was no radio \u201Cnoise\u201D at all, now radio energy is emanating off the moving object or person. A still object also reflects radio waves, but the time it takes for a wave to bounce back to the receiver stays the same, and the reflections will still cancel out.\nSEE ALSO: PHOTOS: I Am Iron Man: Top 5 Exoskeleton Robots\nThe invention \u2014 which Dina Katabi, an electrical engineering professor, and her graduate student Fadel Adib are developing \u2014 is called Wi-Vi. The two will present it at the Sigcomm conference in Hong Kong this August.\nThere are several uses for this technology. A small handheld detector could find people buried under tons of rubble, showing rescue workers where to look, or police could use it to see if there is someone inside a room.\nWi-Vi differs from traditional X-ray or terahertz wave systems. In that case a beam of radio waves is sent to an object that reflects them back. This kind of detection is just like what your eyes do \u2013 seeing reflected light. (Radio waves just happen to be in a different part of the spectrum).\nIt\u2019s also a twist on a previous attempt at using Wi-Fi routers to see through walls by taking advantage of the signals they emit. Wi-Vi doesn\u2019t require that a router be in place.\nSEE ALSO: Could We Probe E.T. With Interstellar Radar?\nThe advantage here is that this works with radio frequencies that penetrate walls relatively easily, at least for short distances. The wavelengths are also short, so the antenna doesn\u2019t need to be very large. It also needs just one receiving antenna, so it can be fit onto a hand-held device.\nAnd the reason it uses Wi-Fi type signals is that they aren\u2019t reserved for the military, and are open to use by any device with less need to get approvals from regulators.\nvia MIT News\nPhoto via iStockphoto, saffetucuncu"^^<http://www.w3.org/2001/XMLSchema#string>
<http://mashable.com/2013/06/28/wi-fi-tech-through-walls/>