Inspired by squid and octopus, new display stores and displays encrypted images without electronics

A flexible display inspired in part by squid can store and display encrypted images like a computer, using magnetic fields rather than electronics. The research is reported in Advanced materials by engineers at the University of Michigan.

“This is one of the first times that mechanical materials have used magnetic fields for encryption, information processing and system-level computation. And unlike some previous mechanical computers, this device can wrap around your wrist,” said Joerg Lahann, professor of chemical engineering at Wolfgang Pauli Collegiate and co-corresponding author of the study.

The researchers’ display could be used anywhere light and power sources are cumbersome or undesirable, including on clothing, stickers, ID badges, barcodes and e-book readers. A single display could reveal a publicly viewable image when placed near a standard magnet or a private encrypted image when placed on top of a complex array of magnets that acts as an encryption key.

“This device can be programmed to display specific information only when the right keys are pressed. And there’s no code or electronics to hack,” said Abdon Pena-Francesch, assistant professor of materials science and engineering at UM and co-corresponding author. “It could also be used to change the color of surfaces, for example on camouflaged robots.”

Shaking the screen causes the image to fade (like in an Etch-A-Sketch), except the image is encoded in the magnetic properties of the beads inside the screen. It reappears when the screen is exposed to the magnetic field again.

The balls act like pixels by alternating between orange and white hemispheres. The orange halves of the balls contain microscopic magnetic particles that allow them to rotate up or down when exposed to a magnetic field, providing the color contrast needed to display an image.

Exposing the pixels to a magnet will program them to display white or orange in a pulling or pushing magnetic field, a state called polarization. For some pixels made with magnetic iron oxide particles, the polarization can be changed with relatively weak magnetic fields. But the polarization of pixels that also include neodymium particles is harder to change: a powerful magnetic pulse is required.

By holding the screen over a grid of magnets of different strengths and orientations, the polarization in certain parts of the screen can be selectively changed, causing some pixels to turn white and others to turn orange under the same magnetic field orientation. This is how an image is encoded.

The image can then be displayed under any weak magnetic field, including a regular magnet. But because the iron oxide particles can be reprogrammed with relatively weaker fields, the private images can be displayed with a second magnetic grid that selectively rewrites how certain areas of the screen flip. When they are returned to the standard magnet, the iron oxide pixels return to their original polarization to display the public image.

Multiple private images can be displayed from a single public image, each with a unique key. Decoding keys can also be programmed to only work with specific encryption keys for added security.

The team determined the screen resolution by studying squid and octopus, which change color by expanding and contracting pigment sacs in their skin.

“If the beads are too small, the color changes become too small to see,” said Zane Zhang, a doctoral student in materials science and engineering at UM and first author of the study. “The squid’s pigment sacs are optimized in size and distribution to provide high contrast, so we adapted the pixels in our device to match their size.”