How MIT Media Lab researchers are using terahertz imaging to read closed books

MIT Media Lab researchers have prototyped a machine that can scan through the first 20 pages of a closed book , the first 9 with high accuracy. The technology uses terahertz imaging for obtaining the information. The aim of the initiative is to allow museum workers and researchers to read rare, dilapidated or old books that can be damaged if handled. A system to completely read a closed book is being designed. [caption id=“attachment_334919” align=“aligncenter” width=“640”]  Image: Barmak Heshmat/ MIT[/caption] Terrahertz imaging uses a lower frequency than visible light. Infrared frequencies are used in night vision goggles, also known as thermal imaging, and remote controls. Millimeter wave frequencies are used in car detection radars, such as the one used by Autopilot in Tesla vehicles . Terrahertz imaging uses the frequencies between the infrared and millimeter wave. Terrahertz imaging uses non ionising radiation for scanning, as compared to say, x-rays. Terrahertz imaging is used in security scanners to identify concealed contraband or weapons. Similar techniques are also used to identify cracks or damage between layers in the aerospace industry, most notably to identify defects in NASA’s Space Shuttles. [caption id=“attachment_334905” align=“aligncenter” width=“640”]  Image: National Institute of Standards and Technologies, US[/caption] The technology did exist to scan the contents of a closed envelope with terrahertz imaging. Terrahertz radiation interacts with chemicals in different ways to yield a unique frequency signature. This signature can be used to distinguish between ink and paper, something that x-ray imaging does not allow for. Terrahertz radiation can be used in extremely short bursts, which lets researchers accurately measure the time it takes for bounced of radiation to return to the sensor, something not possible on ultrasound. The terrahertz radiation gives a depth perception to the information, using which the page number of a book can be measured. The natural air gaps between pages in a book reflect the radiation back to the detector.

Once the information is obtained, image recognition algorithms kick in to make sense of the detected text. There are shadows formed in the images where text from the adjoining pages overlap, but the image recognition can still detect the right letters. These algorithms work so well, that they can bypass the captchas used to differentiate bots from humans in web pages. The constraints for the technology right now is the amount of power used by the radiation sources, and the accuracy of the detectors. [caption id=“attachment_334918” align=“aligncenter” width=“640”]  Image: MIT[/caption] With developments in these two areas, it should be possible to use the same technology to completely image a book from cover to cover. Laura Waller, an associate professor of Electrical Engineering and Computer Science at the University of California at Berkeley, said “This work is one of the first to use these new tools along with advances in computational imaging to get at pictures of things we could never see with optical technologies. Now we can judge a book through its cover!” [caption id=“attachment_334914” align=“aligncenter” width=“640”]  Image: TeraSense[/caption] Terahertz imaging cameras are available from TeraSense, in a variety of resolutions and sizes. Some of the cameras are meant to be embedded for security applications, such as beneath converyer belts at airports. Some cameras though, are available with a standard USB interface.