Top 3 visual authentication features for enhanced banknote security
Banknotes use multiple visual authentication indicators. Among them, high resolution single colour shapes are the easiest to recognize but are also the easiest for counterfeiters to copy. Colours and shapes used for a security feature on a banknote does make the note more secure but also requires tilting or turning by the user to gain the benefit of the specific effect. This user interaction adds time and education for a user to initiate an authentication check. For these reasons, multicolour and movement combined with 3D depth is potentially the most formidable visual effect that can be used for a security feature, however it is very difficult to achieve, particularly on a banknote surface. Nano-optic technology like Nanotech’s KolourOptik platform can create Optically Variable Device security features that are capable of multicolour, 3D depth and float, and movement effects. Through a combination of micro and nanostructures, many of the limitations of conventional grating and lens-based optics can be overcome, to create a new security feature paradigm with wide-viewing angles and multi-colour animated imagery.
The current state-of-the-art overt security features found on high-end security documents, banknotes, passports etc. rely on diffraction based OVDs, which are largely holographic in nature – they are monochromatic or have a limited palette of colours. Nanotech has demonstrated that sub-wavelength periodic nanohole arrays can produce high efficiency diffractive colours, extraordinary optical transmission, and surface plasmonic resonance for absorption and reflection of specific wavelengths of light.
At the most fundamental level, the sub-wavelength dimension of nano-scale structures leads to high-intensity diffractive colours that can be complemented and enhanced. The nano-scale structures result in a pattern resolution of 127,000 dpi or higher, while yielding potential perceivable image resolutions as high as 6350 ppi (1 pixel per micron). Collections of tailored nano-structure arrays, each exhibiting an independently unique structural colour, are adjacently placed to form striking effects. In such manner, a single thin layer of arrays can be arranged to produce multiple visual authentication feelings like fluid motion, colour transitions, high definition artwork, as well as covert, forensic, and machine-readable features.
Movement within a banknote security feature is important, and Nanotech has the capability to produce full parallax multi-axis 3D images and animations for currency authentication. It is also intuitive for the public and does not require any auxiliary tools. The movement features in KolourOptik threads, patches and stripes are carefully designed keeping in mind key human senses in authentication. They are designed to be like a puzzle, where the public receives a visual reward when the banknote is tilted the right way. Moreover, these movement features are extremely difficult to replicate or simulate using any other technology.
Three-dimensional depth gives the public an impression of floating images below and above the surface of the banknote, has the power to delight and surprise, and give life to icons, symbols, and objects. Nanotech’s proprietary optics engine maps 2D perspectives onto the surface of a 3D faceted micro-structure. Each group of surfaces that point to the same spatial direction display content of one of the 2D perspectives.
In addition to depth and parallax-based optical effects, the security features demonstrated here are shown to have many other applications and advantages, including thin application formats of <5um, flexible design parameters, multiple substrate application options, multi-colour imagery, true omni-directionality, ease of viewing in low lighting environments, and tilt-based movement effects for further authentication checking. Fabrication of these devices is discussed from EBL grey-scale origination through manufacturing considerations for to roll- to -roll production foil formats.
Combing the power of nano-scale plasmonic coloration and macro-scale light diffusion or angular viewing of micro-structures opens pathways to a variety of effects. Effects from static full colour imagery, to simple colour shifting films, to complex 3D images and movement can be realized from a single layer of embossed aluminum-coated structures. In conclusion, multicolour, movement, 3D depth or a combination of all three are the top visual authentication features for enhanced banknote security.
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