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Invisible QR Codes Tackle Counterfeit Bank Notes and Other Security Applications

September 21, 2012
An invisible quick response (QR) code has been created by researchers in an attempt to increase security on printed documents and reduce the possibility of counterfeiting, a problem that costs governments and private industries billions of pounds each year.

Publishing their research today in IOP Publishing’s journal Nanotechnology, the researchers from the University of South Dakota and South Dakota School of Mines and Technology believe the new style of QR code could also be used to authenticate virtually any solid object.

The QR code is made of tiny nanoparticles that have been combined with blue and green fluorescence ink, which is invisible until illuminated with laser light. It is generated using computer-aided design (CAD) and printed onto a surface using an aerosol jet printer.



According to the researchers, the QR code will add an increased level of security over existing counterfeiting methods as the complexity of the production process makes it very difficult to replicate.

The combination of the blue and green inks also enabled the researchers to experiment with a variety of characters and symbols in different colors and sizes, varying from microscopic to macroscopic. Embedding these into the QR code further increases the level of security.

Under normal lighting conditions the QR code is invisible, but becomes visible when near infra-red light is passed over it. This process, known as upconversion, involves the absorption of photons by the nanoparticles at a certain wavelength and the subsequent emission of photons at a shorter wavelength.

Once illuminated by the near infra-red light, the QR code can be read by a smartphone in the conventional manner.

QR codes can hold one hundred times more information than conventional barcodes and have traditionally been used in advertising and marketing. For example, simply scanning a QR code on a commercial product with a smartphone will take the user to a company’s website, giving them more information about the product they are scanning.

The nanoparticles that were used to print the QR code are both chemically and mechanically stable meaning they could withstand the stresses and strains of being placed on paper. To prove this, the researchers printed the QR code onto a piece of paper and then randomly folded it fifty times; the code was still readable.
 

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