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Seeing New Security in Invisible Codes

Thursday, September 13, 2012

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You won’t see it, but South Dakota researchers have created an invisible Quick Response (QR) code that could help reduce counterfeiting and increase security on printed documents.

The new code also could be used to authenticate other solid objects, report researchers from the University of South Dakota and South Dakota School of Mines and Technology.

 Invisible codes, revealed by near-infrared light, could enhance security on checks, documents and products.
Invisible codes, revealed by near-infrared light, could enhance security on checks, documents and products.

Created from nanoparticles combined with blue and green fluorescent ink, the code absorbs photons at a nonvisible wavelength but emits them at a visible wavelength. The code is created using computer-aided design, and then printed onto a surface using an aerosol jet printer.

The research was published Wednesday (Sept. 12) in the Institute of Physics’ journal Nanotechnology and is explained in a new video.

Billion-Dollar Problem

“Counterfeiting costs governments and private industries billions of dollars annually, due to loss of value in currency and other printed items,” the researchers report.

The research “demonstrates that QR codes, which have been used primarily for information sharing applications, can also be used for security purposes,” the team wrote.

QR Codes are a type of two-dimensional barcode designed originally for the automotive industry to track vehicles in production. Capable of storing a hundred times more information than conventional barcodes, the square black-and-white codes are now in widespread use on documents, in advertising, and on product and equipment labeling.

How it Works

The new QR code is made of tiny nanoparticles that have been combined with blue and green fluorescent ink. The code can be printed onto paper, glass or other materials and is invisible to the naked eye, but readable using a near-IR laser—a process known as upconversion. The new codes, like conventional codes, can be scanned using a smart phone.

Video: QR codes

Researchers believe the new codes can help protect documents from counterfeiting, since the complexity of the code creation process is quite difficult to replicate.

Combining the blue and green inks also enables researchers to experiment with embedding characters and symbols of different colors and sizes, from microscopic to macroscopic, further increasing security.

Growing Applications

Nanoparticles used to print the QR code are chemically and mechanically stable, meaning they could withstand the stresses of being put on paper, with potential for greater security of checks, currency and other documents, the researchers say.

As a test, researchers printed the invisible code onto a piece of paper and randomly folded it 50 times; afterward, the code was still readable.

The new codes have also been printed on glass and a flexible plastic film, giving them potential for use with many commercial goods. The code’s invisibility has the added benefit of not interfering with the appearance of the product. The ink can also be optimized for line width, thickness and stability on different substrates.

Cracking the Code

Creating the code, from the CAD process to printing and scanning, took 90 minutes. Researchers believe that once the QR file has been created, printing en masse for commercial use would take about 10-15 minutes.

Jeevan Meruga, the study’s lead author, said the code was tough to counterfeit. “We can also change our parameters to make it even more difficult to counterfeit, such as controlling the intensity of the upconverting light or using inks with a higher weight percentage of nanoparticles,” Meruga said.

Or, for true encryption connoisseurs, he offers: “We can take the level of security from covert to forensic, simply by adding a microscopic message in the QR code, in a different colored upconverting ink, which then requires a microscope to read the upconverted QR code.”


Tagged categories: Coatings technology; Nanotechnology; QR codes; Research

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