MIT researchers and associates are currently developing an imaging system that can read closed books.

The latest issue of Nature Communications features an article describing a prototype which they tested on a stack of papers, each with one letter printed on it. The system correctly identified the letters on the top nine sheets.

According to Barmak Heshmat—one of the research scientists at MIT Media Lab—the project is drawing interest from the Metropolitan Museum in New York.  This system could potentially allow them to look into delicate antique books without having to physically touch them.

The system utilizes terahertz radiation, the band of electromagnetic radiation between microwaves and infrared light.  This has advantages over others such as X-rays and sound waves.  Terahertz frequency can distinguish between ink and blank paper in ways that X-rays can’t.  And by being emitted in short bursts, it gives much better depth resolution than ultrasound.

The key to the system’s success lies in the fact that there are tiny air pockets about 20 micrometers deep between book pages.  “The difference in refractive index — the degree to which they bend light — between the air and the paper means that the boundary between the two will reflect terahertz radiation back to a detector.”

Terahertz imaging is a fairly young technology, but scientists are investing a lot of time and energy into improving the accuracy of detectors and the power of radiation sources.  They believe that in time, deep penetration will be possible.

Hardesty, Larry (September 9, 2016).  “Judging a book through its cover.” Retrieved September 13, 2016 from MIT News: