October 2019

– When Micro is Nano  

The subject of the Banknote of the Month in the September issue of Currency News was the new Aruban Florin series, the first circulating notes to feature Crane Currency’s MOTION SURFACE® technology. 

It was 15 years ago that MOTION® first burst onto the scene, at the Optical Document Security conference in 2004, prompting the development of a whole new range of authentication features based on micro-optics. To mark this milestone, we take a closer look at this latest incarnation of the technology.

When MOTION was first released in a circulating banknote, the Swedish 1000 kroner in 2006, its unique three dimensional, motion effects both surprised and fascinated central bankers, banknote designers and the public at large. It also attracted the attention of physicists, not least because while the scientifc principle (Moiré magnification) was not new, the application, material science and engineering most certainly were.

Today there are a number of banknote security features that use micro-optics, but in different ways from the MOTION technology. And MOTION itself has not remained a one effect, one product technology – we had the MOTION RAPID® thread in 2014. And now MOTION SURFACE®, a stripe.

An important visual effect of MOTION SURFACE is Topo, which produces a very strong three dimensional effect. The name Topo derives from the word topography, ie. the practice of describing relative position, elevation and contour of surface features. Producing its visual effects on a security feature thin enough to be applied to the surface of a banknote requires very specialized materials, equipment and know-how.

On a typical 10mm wide MOTION SURFACE stripe, an array of over 3 million lenses is aligned horizontally over 3 million icons, each of them subtly and uniquely altered to achieve the desired effect. The changes in the position of each icon are so small as to be unmeasurable by conventional means, but the three dimensional effect of Topo could not be produced without this tightly-managed array of iconography.

Creating this unique artwork takes hours of computation using state-of-the-art computer processing, which represents a major improvement over Crane’s production of the first MOTION features.

The addition of skilled software engineers to Crane’s micro-optic technical design team has produced proprietary software that has speeded up the process by well over 100,000 times, allowing for more intricate designs and effects and accurate renderings of the final product. Were Crane to use the same computational software now to render MOTION SURFACE designs, the computer processing time would be measured in months.

Today, by virtue of these advancements in algorithms and computing power, the process is so controlled that it allows the creator to fine tune every characteristic of an effect. It is possible to revise specific dimensions, shape, and magnification of the moving images. The strong 3D effect and the curved images one sees in the final feature is a result of the combination of expertise and equipment which enables every icon to be unique in its size and shape from those around it, and to position each precisely under each lens.

Once the design of micro-optic icons are created and arrayed into position, this master artwork must be delivered to production. In a similar way that digital print files are delivered through the modern process of pre-press in security printing, the artwork for the MOTION icon and lens array is created using proprietary technology that ensures no distortions or inaccuracies are introduced into the process.

At such a scale, the production tolerance between the lens and icon are critical; the smallest misalignment will destroy the effect and distortions must be limited to within nanometers.

In fact, the only technology currently capable of accurately measuring distortion is the micro-optics themselves. Inside the Crane facility, measurement schemes using micro-optics have been developed that allow artifacts smaller than 25 nanometers and distortions less than 10 nanometers to be visible to the naked eye.

These tight tolerances drove Crane to develop customised production equipment capable of producing multiple layers of millions of individual micro-optic structures, while keeping everything precisely aligned and in specification to the original digital rendering. This equipment is required to keep the angular alignment between the lens and icon layers extremely tight (to one sixtieth of a degree) while producing hundreds of thousands of kilometres of material, and billions of precise optical microstructures per second.

The results justify the investment because it enables visual effects that are bold and very easy to use despite their invisible complexity.