MIT Media Lab 弄出個好玩的東西，可以不打開書直接掃描書的內容：「Can computers read through a book page by page without opening it?」，主標題是「Terahertz time-gated spectral imaging for content extraction through layered structures」。
用 100Ghz 到 3Thz 的電磁波掃描：
In our new study we explore a range of frequencies from 100 Gigahertz to 3 Terahertz (THz) which can penetrate through paper and many other materials.
先前也有類似的方法，用 X-ray 或是超音波，但效果都不好：
Can’t X-ray or ultrasound do this? It may seem that X-ray or ultrasound can also image through a book; however, such techniques lack the contrast of our THz approach for submicron pen or pencil layers compared next to blank paper. These methods have additional drawbacks like cost and ionizing radiation. So while you might be able to hardly detect pages of a closed book if you use a CT scan, you will not be able to see the text. Ultrasound does not have the resolution to detect 20 micron gaps in between the pages of a closed book -distinguishing the ink layers from the blank paper is out of the question for ultrasound. Based on the paper absorption spectrum, we believe that far infrared time resolved systems and THz time domain systems might be the only suitable candidates for investigating paper stacks page by page.