Squid-ink inspired screen displays images without electronics

Engineers at the University of Michigan have developed a flexible screen that can store and display encrypted images like a computer, without using electronics. Instead, inspired by squid ink, it uses magnetic fields.

"It's one of the first times where mechanical materials use magnetic fields for system-level encryption, information processing and computing. And unlike some earlier mechanical computers, this device can wrap around your wrist," said Joerg Lahann, the Wolfgang Pauli Collegiate Professor of Chemical Engineering and co-corresponding author of the study.

The screen could be used for clothing, ID badges or e-book readers, the researchers say. A single screen can be used to reveal an image when placed near a standard magnet, or, if privacy is required, a complex array of magnets can act like an encryption key. "This device can be programmed to show specific information only when the right keys are provided. And there is no code or electronics to be hacked," said Abdon Pena-Francesch, U-M assistant professor of materials science and engineering and co-corresponding author. "This could also be used for colour-changing surfaces, for example, on camouflaged robots."

To erase the screen, users simply need to shake it—like an Etch-A-Sketch, but the image will return when the beads inside are exposed to a magnetic field again. The beads act like pixels, flicking between orange and white. The orange halves are magnetic and rotate up or down when exposed to a magnetic field. 

Some pixels are made with iron oxide magnetic particles, and their polarization can be changed with relatively weak magnetic fields. But the polarization of pixels that also include neodymium particles is harder to change—a strong magnetic pulse is required.

Holding the screen over a grid of magnets with different strengths and orientations can selectively change the polarization in some parts of the screen, causing some pixels to flip white and others to flip orange under the same magnetic field orientation. This is how an image is encoded.

The team decided on the resolution of the screen by studying squid and octopi, which change colour using pigment sacs in their skin. "If you make the beads too small, the changes in colour become too small to see," said Zane Zhang, U-M doctoral student in materials science and engineering and the study's first author. "The squid's pigment sacs have optimised size and distribution to give high contrast, so we adapted our device's pixels to match their size."

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