They say you shouldn't judge a book by its cover, but a new imaging system from MIT can see right through the cover and read the book while it's still closed.
That's thanks primarily to terahertz radiation, the band of electromagnetic radiation between microwaves and infrared light, and the tiny gaps of air between the pages of any closed book.
Terahertz radiation can distinguish between ink and blank paper in a way that X-rays can’t, and it also offers much better depth resolution than ultrasound does. The prototype new system developed by researchers from MIT and Georgia Tech uses a standard terahertz camera to emit ultrashort bursts of radiation and then measure how long it takes for that radiation to be reflected back. An algorithm then gauges the distance to each of the book's individual pages.
Equipped with that data, the system uses two different measures of the reflections’ energy to extract information about the chemical properties of the reflecting surfaces, all the while doing its best to filter out the irrelevant "noise" produced along the way. In that way, it distinguishes paper with ink from blank paper, using a separate algorithm to interpret the often distorted or incomplete images as individual letters.
The researchers tested their prototype on a stack of papers, each with one letter printed on it, and found that it could correctly identify the letters on the top nine sheets.
The Metropolitan Museum in New York has expressed interest in the system as a way to examine antique books without touching them, said Barmak Heshmat, a research scientist at the MIT Media Lab. The technology could be used to analyze any materials organized in thin layers, he added, such as coatings on machine parts or pharmaceuticals.
A paper describing the work was published Friday in Nature Communications.