Scientists from Pennsylvania State University and Carnegie Mellon University have created the tiniest QR code ever, as a demonstration of a new type of technology. The objective is to enhance visual security, prevent counterfeiting, and enhance infrared monitoring.
The resulting QR code is less than 2% of an inch and cannot be seen with the naked eye. An infrared camera is required to read it.
What's particularly interesting is that this technology imitates minuscule structures on the surface of leafhoppers, specifically the Graphocephala coccinea. These remarkable structures interact with light in unique ways, making the insects almost invisible, especially in the ultraviolet range, to predators.Graphocephala coccinea) are particularly effective at staying out of sight.
The lead author stated, “Our collaborators brought us brochosomes—a 'magic' structure leafhoppers create to hide from predators.” Sheng ShenThis was said by a professor of mechanical engineering at Carnegie Mellon University.
“We wanted to understand brochosomes’ optical limitations to see what more we could do with them.”
The world’s smallest soccer balls to world’s smallest QR code
Tiny leafhoppers, often smaller than a grain of rice, are experts at staying dry thanks to their brochosomes. Other insects typically rely on chemical properties or microscopic surface textures for water resistance. In contrast, leafhoppers produce unique nanoparticles to cover their bodies, making them hydrophobic.
The brochosomes have a complex structure, resembling hollow soccer balls made of proteins and lipids. Their size ranges from about 200 to 1,000 nanometers wide. To put it in perspective, an average human hair is roughly 200 times wider than a brochosome.
Brochosomes are produced inside the leafhopper’s body in structures known as Malpighian tubules, similar to human kidneys. The insects release these brochosomes through liquid droplets and then spread them over their bodies with comb-like structures on their hind legs.
These remarkable qualities have piqued the interest of many researchers, who use these nanostructures as a guide to craft new materials with hydrophobic and antireflective properties. However, it was not the hydrophobic properties that sparked the new research. Design and development of novel materials with hydrophobic and antireflective qualities have been influenced by the nanostructures found in leafhoppers.
Brochosome physics in action
Brochosomes absorb light instead of reflecting it, allowing leafhoppers to blend seamlessly into their surroundings.
“According to a fundamental law of physics, if a structure absorbs energy effectively, it can also emit an equal amount of energy,” explained Zhuo Li, a Ph.D. candidate at Carnegie Mellon.
“We soon realized that if we put both structures together, one would give off more energy than the other. This would cause one to appear brighter to an infrared camera than the other.”
The scientists used a unique 3D printing method that can control how a material absorbs or gives off energy on a tiny scale. In this case, they printed a very small structure with or without gaps, which is how they created this tiny QR code — so small it can only be detected through a microscope.
From blending in to securing information
The practical uses would not involve something very small. The aim is to enlarge its scale so that the combination of visible disguise and infrared display could lead to some intriguing opportunities.
“With this technology, we are ultimately altering an object’s heat signature,” said Li. “We have the ability to disguise how objects are displayed on an infrared camera. In theory, if we arranged the tiny structures accordingly, we could make a police car look like a delivery van to infrared security.”
“This is just the beginning of a new research area my team can explore,” said Sheng. “We’ve taken infrared light and transformed it from an energy carrier to an information carrier.”
Earlier, in 2017, the Penn State scientists investigated how the leafhopper’s nanoparticles could enable them to create an invisibility cloak. One of their experimental devices that imitated these properties was able to absorb up to 99% of incoming light, from ultraviolet to visible and near infrared. With the ability to generate invisible QR codes, objects can carry coded data visible only to specific infrared cameras. This could provide a new layer of security.
The results were reported in the journal Science Advances.
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