Over the past three decades, the digital world we access via smartphones and computers has become so rich and detailed that much of our physical world has a corresponding life in this digital reality. Today, physical and digital realities are on the path to merging, as robots, augmented reality (AR), and wearable digital devices enter our physical world, and physical objects obtain their twin computer representations. digital in the digital world.
These digital twins can be uniquely identified and protected against manipulation using cryptographic technologies such as blockchains. The trust these technologies provide is extremely powerful, helping to fight counterfeiting, increase supply chain transparency and enable the circular economy. However, a weak point is that there is no general purpose and generally applicable identifier of physical items as reliable as a blockchain. This breaks the link between physical and digital twins and therefore limits the potential for technical solutions.
In a new article published in Light: science and applicationsan interdisciplinary team of scientists led by Professors Jan Lagerwall (physics) and Holger Voos (robotics) from the University of Luxembourg, Luxembourg, and Professor Mathew Schwartz (architecture, construction of the built environment) from the New Jersey Institute of Technology , US, propose an innovative solution to this problem where physical objects are given unique, non-clonable fingerprints made using cholesteric spherical reflectors, or CSRs for short.
Lagerwall explains: “The unique characteristic of CSRs is that they are selective retroreflectors, returning light to a source in any direction, but only in a narrow wavelength band and only with a specific circular polarization. The narrow wavelength band allows us to make the CSRs undetectable to humans by localizing the reflections in the near-infrared or near-ultraviolet regions, easily readable by robots and AR devices but invisible to the eye human.”
“Circular polarization allows us to separate only CSR signals from any complex background, making any message written using CSR stand out with extraordinary contrast.”
It is by coating surfaces with CSR arranged in a particular pattern that the team gives physical objects their “fingerprints”. Since robots and AR devices can read fingerprints with exceptional clarity and reliability, their operation becomes much more reliable if CSR fingerprints encode information about objects, giving the devices in question a much better understanding of their environment.
The ideal pattern in which CSRs are arranged in fingerprints is one of the so-called fiducial markers, as Voos explains: “Fiducial markers are square-shaped binary patterns, quite similar to QR codes in their appearance. The particular arrangement of the black and white pixels encode an identity, for example, telling a machine reading the pattern that it is a door, a car or a wall.And measuring the size of the pattern and how it is distorted due to the viewing angle from the original square shape, the machine can, with very little computational effort, establish how far away the object bearing the pattern is and how it is oriented relative to the machine.
Conventional black-and-white marker markers are common in robotics and AR research, but their large size and high-contrast physical appearance make them impractical to deploy in most human-populated spaces. They must also be illuminated by visible light to be useful. For these reasons, they are now relegated to research laboratories or confined spaces.
By making markers using CSRs optimized for near-infrared or near-UV operation, their assistive power to robots and AR devices becomes accessible anywhere, including spaces where people work, play, or rest, because these CSR markers are invisible to humans and do not disturb the environment as we experience it.
At the same time, the circular polarization of CSR reflections highlights CSR markers against any background for machines that need to detect them, eliminating false positive issues and detection difficulties.
Omnidirectional retroreflectivity is key to their usefulness, and Schwartz points out that “retroreflectors are common in motion capture work, whether tracking humans or robots, because it doesn’t matter how the subject under study moves , the retroreflector reflects the light back to the camera which also sends the light signal.But ordinary retroreflectors reflect all the light, so they are very visible, that’s why they are also used in traffic signs and high visibility clothing .
“By making fiducial markers using CSR, a robot or AR device can track objects in its environment that carry the markers from any angle, day or night, by illuminating the scene with a light near-infrared or near-UV that is harmless and invisible to humans,” continues Schwartz.
A final key advantage of markers made using CSRs is that the exact local arrangement of individual CSRs is unpredictable and so difficult to replicate that each CSR marker is effectively unclonable. Moreover, when studying a CSR marker at close range, the appearance depends on how one illuminates and observes it, which means that a certain marker does not give a pattern when viewed. close inspection, but actually an endless series of dynamic patterns, unique to each marker still well defined.
This turns CSR markers into so-called Physical Unclonable Functions, or PUFs, which are very powerful in authenticating physical objects.
This is the last key advantage of CSR markers, says Lagerwall, summarizing: “CSR markers operate at multiple scales: at a distance, they reproducibly and reliably give a model we have chosen, in particular the fiducial marker model which identifies which category of object But when a robot or AR device manipulates an object, it can study the marker up close, revealing the locations of individual CSRs and checking how they reflect light that is sent in different directions or over different areas , for example by switching on and off the individual LEDs in a standard lighting ring.”
“Unlike the far-field fiducial marker model, the resulting near-field models are unique to that particular object, thus also giving it its identity. This is how CSR markers allow robots and AR devices to link safely the physical world to the digital twins, because they tell the machine not only what kind of object they are dealing with, but even what specific item it is.And since the optics are outside of the visible spectrum, we humans won’t notice that anything has changed.
Help robots analyze their environment
Hakam Agha et al, Non-clonable human-invisible machine vision markers leveraging omnidirectional chiral Bragg diffraction of cholesteric spherical reflectors, Light: science and applications (2022). DOI: 10.1038/s41377-022-01002-4
Provided by Chinese Academy of Sciences
Quote: Research team proposes invisible, unclonable machine vision markers using cholesteric spherical reflectors (2022, October 27) Retrieved October 28, 2022 from https://techxplore.com/news/2022-10-team-unclonable- invisible-machine-vision.html
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