Engineers create ultra-high resolution images in anti-counterfeiting breakthrough

Engineers from the University of Glasgow have uncovered a new form of high-resolution image printing that could be used for data storage and digital imaging, in particular for anti-counterfeiting measures in banknotes.

A new form of high-resolution "printing" that could be developed for anti-counterfeiting measures in banknotes has been discovered by scientists from the University of Glasgow, Scotland.

The team of engineers developed nanoscale plasmonic colour filters that display different colours depending on the orientation of the light that hits it.

According to the university, the nanoscale printing breakthrough could also have implications for data storage and digital imaging as the new technique allows the "printing" of two entirely different, but exceptionally detailed, full-colour images within the same surface area.

The team demonstrated their technique with several examples, including a nanoscale image that shows the university's crest when the light reaches it in one orientation, and an image of the university tower when the orientation of the light is reversed.

"We've discovered that if we make colour pixels from tiny cross-shaped indents on a strip of aluminium film, the colour they display becomes polarisation-dependent, allowing us to encode two colours into a single pixel, and then select which colour is displayed by shining different polarisations of light at the surface," said biomedical engineering lecturer Dr Alasdair Clark, lead author of the research paper.

"By changing the size and shape of the nanoscale indent, we can create a wide range of different colours at very high resolutions."

Instead of relying on dyes and pigments as in traditional printing, structural colour uses specially structured nanomaterials to render colours, which the university said allows for much higher-resolution prints that do not fade over time.

Plasmonic colour filtering has provided a range of new techniques for "printing" images at resolutions beyond the diffraction-limit, significantly improving upon what can be achieved using the traditional, dye-based filtering methods.

While a typical printed image in a magazine might consist of around 300 coloured dots per inch of page, or 300 DPI, a page printed with structural colour techniques could reach a resolution of 100,000 DPI or more, the engineers explained.

As the field of plasmonic colour generation advances, Clark and his team said there is a tremendous scope for devices based on these principles to be one of the few nanoplasmonic technologies that make the jump from research curiosity to commercial deployment.

"We have demonstrated a means of using dual-colour nanopixels to encode two full-colour information sets, whether they are images or codes, into the same unit area," the paper, published in Advanced Functional Materials, explains. "As a result, this technology is positioned as a promising candidate for microimage encoding, particularly if the design principles were transferred to nanoimprinting technologies.

"Furthermore, with a PPI [pixels per inch] value exceeding 100,000, each able to encode two colour states, this technology may prove useful for high-resolution printing applications and counterfeit-prevention measures."

On Wednesday, the Reserve Bank of Australia (RBA) sent Australia's new AU$10 banknote into circulation, with the new note boasting a number of security features aimed at keeping them secure from counterfeiting.

Also in Australia, a team of physicists from the Australian National University (ANU) earlier this year invented a tiny device using infrared that creates the highest-quality holographic images ever achieved.

Lead researcher and PhD student at the ANU Research School of Physics and Engineering Lei Wang touted the complex holographic image advancement as opening the door to imaging technologies such as those seen in science fiction movies.

According to the university, holograms perform the most complex manipulations of light and enable the storing and reproduction of all information carried by light in 3D; standard photographs and computer monitors, however, capture and display only a portion of 2D information.

"While research in holography plays an important role in the development of futuristic displays and augmented reality devices, today we are working on many other applications such as ultra-thin and light-weight optical devices for cameras and satellites," Wang said previously, noting that the device could replace bulky components to miniaturise cameras and save costs in astronomical missions by reducing the size and weight of optical systems on spacecraft.

With AAP

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