A flexible screen engineered by University of Michigan researchers, inspired by squid skin, can store and display encrypted images using magnetic fields instead of electronics. This innovation allows mechanical materials to use magnetic fields for encryption, information processing, and computing. “Unlike some earlier mechanical computers, this device can wrap around your wrist,” said Joerg Lahann, co-author of the study.
The study appears in Advanced Materials.
The screen can be used in settings where light and power sources are impractical, such as clothing, stickers, ID badges, barcodes, and e-book readers. A single screen can reveal a public image when near a standard magnet or a private encrypted image when over a complex array of magnets acting as 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, assistant professor and co-author. “This could also be used for color-changing surfaces, for example, on camouflaged robots.”
Erasing the display is like using an Etch-A-Sketch; shaking the screen erases the image, but it returns when exposed to a magnetic field again. The beads within the screen act like pixels, flipping between orange and white hemispheres. The orange halves contain magnetic particles that rotate up or down when exposed to a magnetic field, providing color contrast.
The pixels’ colors are determined by their polarization, which can be easily changed with weak magnetic fields for iron oxide pixels. Neodymium particles, however, require a strong magnetic pulse to alter their polarization.
Holding the screen over an array of magnets with different strengths can rewrite the magnetic properties of pixels, encoding the image. This image can be displayed under any weak magnetic field, including a standard magnet. Iron oxide pixels can be reprogrammed with a second magnetic grid to show private images, which revert back to the public image when exposed to the standard magnet.
Multiple private images can be displayed from a single public image, each needing a unique key. Encoding keys can be made to work only with specific decoding keys for added security.
The screen’s resolution was inspired by squids and octopi, which change color by expanding and contracting pigment sacs in their skin. “If you make the beads too small, the changes in color become too small to see,” said Zane Zhang, the study’s first author. “The squid’s pigment sacs have optimized size and distribution to give high contrast, so we adapted our device’s pixels to match their size.”
This research was funded by the American Chemical Society Petroleum Research Fund and the National Science Foundation. An invention disclosure was submitted with the help of Innovation Partnerships.
Lahann is also a professor of materials science and engineering, biomedical engineering, and macromolecular science and engineering, and directs U-M’s Biointerfaces Institute. Pena-Francesch is also an assistant professor of macromolecular science and engineering, chemical engineering, and in the Robotics Institute.
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