<title>Polymeric self-authenticating banknotes</title>

Abstract

ABSTRACT This paper discusses a new concept in overt security called the self-authenticating banknote. The self-authenticating banknote concept is built around the transparent window feature of the polymer banknote. This feature allows the incorporation of transmission based optical devices on a banknote so that the user, by folding the note over on itself andlooking through an optical device which is a part ofthe note itself, can visually inspect and verify certain security features onthe banknote. This paper presents a number of examples of optical devices which are presently being developed for thispurpose. 1. INTRODUCTION Banknotes have been printed on paper since they first started being used as a form of currency. After hundreds of years andmuch development banknote paper technology has certainly matured due to the continual research and development effortsof paper suppliers and suppliers of ancillary technologies. The various elements of the technology have advanced throughthe years to a stage where they are now, necessarily, very sophisticated in their implementation. Watermarks and threads,probably the mainstays of banknote paper security, are classic examples of how the technology has matured. The quality,tonal range and defmition of the modem cylinder mould made watermarks available today are truly remarkable and stillpresent a serious challenge to the counterfeiters' efforts if the banknote user inspects it carefully enough. Threads have alsoadvanced significantly since their inception, and now offer a multitude of visible and machine readable features includingwindowing, micro-text, holographic-based optical variability, magnetic readability, etc.It is clear however that the inherent properties of paper and associated features have by now become exploited almost asmuch as possible. As with advancements in most technological fields, the law of diminishing returns dictates that newdevelopments tend to become only incremental in nature once a field has matured sufficiently. This trend is noticeable in thefield ofbanknote paper, and is particularly the case for features which are designed to be overt rather than machine readableand perhaps explains why more and more new developments tend to be for machine readable features. It is therefore difficultto foresee in the near future many new developments, using traditional banknote materials, which can truly be considered tobe breakthroughs or quantum leaps.This begs the question: what do alternative materials have to offer and what opportunities do they present? Materialproperties can dictate the approach we take to arrive at a particular solution because they provide us with the building blockswith which we have to work. For example, we might consider what would be possible if we were offered only a single newmaterial property. How would this dictate our approach to a particular problem? Let's consider the property of lightpropagation since most overt security features tend to be visual. What would be possible if we were to adopt a new materialwhich could be completely transparent in specified areas rather than opaque or at best translucent? We know that withtraditional banknote substrates we are not afforded this property. The substrate is normally either opaque or in some areastranslucent at best. This fact has governed or directed the development efforts relating to visually-based security features forbanknotes for many years, and these features tend to work in one of three ways. Surface printed or applied features workentirely in reflected light (eg. optically variable inks, DOVDs, micro-printed text, latent images, etc). Integral or buriedfeatures (eg. Watermarks, threads) require the user to either differentiate the appearance of the feature when viewed with abacking light in comparison to reflected light, or to be able to discern the contrast in opacity within and around the featurewhen viewed with a backing light. It is clear that paper-based features have not been designed to process or transform extrainformation or detail which exists beyond the back surface of the material; the user is not supposed to look through such adevice at some other feature behind it. The furthest the user is expected to see, in the case of a printed see-through registerdevice, is the back surface of the material.