Disruptive Feature Platforms
In developing ideas for possible technologies for anticounterfeiting features, there will always be technologies that can be applied in the near term as well as those that require a longer-term approach. This chapter addresses what the committee refers to as feature platforms, which require a longer time scale, more than 7 years, for implementation in currency. These feature platforms will require additional evaluation, research, and development in order to mature salient portions of the technology so as to allow the identification of specific counterfeit-deterrent features that could be effectively implemented into banknotes. Specific details of these feature platforms are described in detail in Appendix D, “Long-Term Feature and Feature Platform Descriptions.” Box 5-1 outlines the information presented in this appendix for each feature platform.
DEVELOPING THE IDEA OF FEATURE PLATFORMS
Currency is now produced almost exclusively by conceptually old printing techniques (for example, offset, intaglio, and so on) that have traditionally dominated the conventional printed-paper industry. Also, most if not virtually all of the banknote anticounterfeiting features have been optical. The nature of emerging threats and the even more capable digital technologies that are becoming available to the counterfeiter suggest that this basic approach to counterfeit deterrence will likely not continue to provide a path to secure currency indefinitely into the future. Intrinsic limits in resolution, registration, pattern layouts, and inks associated with these printing methods may make it necessary to consider radically different materials and manufacturing concepts.
The Structure of Appendix D, “Long-Term Feature and Feature Platform Descriptions”
The in-depth feature descriptions of the longer-term features and feature platforms—that is, features that can be implemented in a time frame of more than 7 years—are presented in Appendix D, “Long-Term Feature and Feature Platform Descriptions.”
The revolutionary, longer-term approaches suggested in this chapter exploit a wide range of technologies. Certainly, features based on the optical properties of materials will remain highly utilized since currency is for the most part a visual medium. But the committee concluded during the study’s feature brainstorming and
evaluation process that advances in currency features will progress from a reliance on printed optical features to a reliance on features based on advanced materials and processes that would be far above the simulation capability of opportunist counterfeiters. Indeed, many of these advanced features could only be plausibly attempted by state-sponsored counterfeiters with great effort.
The feature platforms presented in this chapter require the use of special materials and/or special manufacturing technologies, such as microfabrication. These new production platforms can produce highly recognizable features that would be very challenging for a counterfeiter to replicate both in terms of the feature’s response mechanism and the feature’s perceptible output. In this regard, these feature platforms are disruptive in nature and could be characterized as “game changing” with respect to counterfeit deterrence. They will demand that prospective counterfeiters greatly increase their expertise and investment far beyond that required to replicate optical images. In most cases, the effort to produce features based on these platforms will provide a significant deterrence to all counterfeiting classes. Those counterfeiters with virtually unlimited resources, such as state-sponsored organizations, may have the facilities to replicate such features, but the time required to replicate a specific active response should be considerable. The one caveat to this assessment is that information sharing via the Internet is an emerging game-changing technology that is benefiting the counterfeiter, and this may reduce the advantage offered by these new feature platforms.
Many enhanced security features highlighted in this report are technically sophisticated enough to require instrumentation or, at a minimum, some type of “gadget” or device to aid authentication. These devices could be as simple as a penlight or as readily available as a cellular telephone screen, or more complex, involving machine readers with built-in sensors and logic. This trend toward increased feature complexity is a direct reaction to the reality that, given the advancement in digital and reprographic technology, it is probably not possible to construct a human-perceptible currency feature that cannot be readily counterfeited or simulated.
For anticounterfeiting, future technology appears to be driven by two potentially divergent trends:
The desirability of features that are easily and rapidly evaluated via human senses. A desirable feature is one for which the assessment is simple and the outcome is Boolean, that is, it may be completely described by a simple “yes” or “no.” Features such as “feel” of the substrate and security strips are popular because they can be rapidly sensed and a “yes” or “no” authenticity decision made within the time it takes for the currency note to change hands in a normal transaction.
The increasing ability of counterfeiters to simulate or replicate the desirable features. This trend motivates the exploitation of specific emerging areas of science and technology for the creation of new features that cannot be readily attempted by counterfeiters. The technology of interest would probably not otherwise be considered for a feature. Indeed, these platforms would only be considered in the context of a proactive strategy of counterfeit deterrence—that is, searching for features that are well beyond the current and projected capability of the most common counterfeiters.
The longer-term features and feature platforms are outlined below. They are grouped into substrate features, composite additions, and electronic platforms. These brief explanations prove a quick look at the new features considered, with additional detail available in Appendix D.
There is a tremendous potential to develop new features by adding elements to the banknote substrate. The committee suggests two feature platforms that will modify the substrate to significantly improve counterfeit deterrence. One route is to engineer the cotton fiber, or dope the cotton fibers, to impart special properties that would be proprietary to U.S. banknotes. Another approach is to add optical fibers to the substrate in such a way as to form a unique random pattern. Both methods rely on devices for authentication, but they would be highly resistant to counterfeiting attempts.
Digitally Encrypted Substrate
With a digitally encrypted substrate, random patterns can be included in each banknote, and information about that specific pattern can be encoded directly on the banknote for digital authentication. For example, the fiber-infused substrate feature described in Chapter 4 and Appendix C employs optical fibers randomly distributed throughout the substrate. The location of each fiber face could be measured at the point of manufacture, and statistics about that location distribution could be encoded in a bar code printed onto the banknote. In order to authenticate the note, a machine reader would measure the distribution and compare it to the information stored in the encrypted bar code. The potential effectiveness of this feature platform resides in the difficulty of embedding the random pattern throughout the note and requires an unimpeachable algorithm linking the pattern to the bar code.
This feature is based on the idea of adding small-diameter optical-fiber segments to the currency substrate during its manufacture. This process creates a
random mixing of the fiber in the paper batch before the paper is dried. The fiber segments, when illuminated by laser light or narrow-spectrum illumination, create a unique optical signature that can be tagged to the specific note. When the finished substrate is illuminated with light, especially laser light, the pattern lights up as the incident light emanates from the ends of the fibers. After the manufacturing cycle of the banknote was nearly completed, a selected region of the note would be scanned or digitally photographed. This image would then be converted to a secure, two-dimensional bar code that would then be printed on the banknote. In order to authenticate the note, a machine reader would compare the image of the selected region to that stored in the encrypted bar code.
In the committee’s evaluation, this feature platform has a high rating for counterfeit deterrence owing to the extreme difficulty of exactly duplicating the optical pattern and to the utility of the highly robust image analysis of the fiber placement. Re-creating the exact fiber placement would be virtually impossible. Furthermore, this feature would not be reproducible using electronic printing and scanning techniques, and hence it would frustrate nearly all counterfeiters. It is expected that only a few very persistent counterfeiters would attempt to generate their own substrate with fibers in it. If they did, they still could not duplicate the exact fiber structure in authentic currency substrate materials.
Engineered Cotton Fibers
The cotton fiber is a complex biological structure engineered by both natural selection and intensive human plant breeding. Engineered cotton fibers are not a feature but rather set of tools that may be employed to generate a wide array of potential features. There are a number of ways to engineer a cotton fiber, including the addition of new materials to the fiber lumer, the modification of the cellulosic material that forms 90 percent of the fiber itself, the modification of the proteins associated with the fiber, or the combining of these methods. Engineered cotton fibers offer the opportunity to retain that unique, highly distinctive “feel” of the U.S. dollar, while simultaneously providing a feature that would be extremely challenging to simulate.
Examples of the new capabilities that would be possible range from features that could be detected without any assistance to those that would require a simple device for authentication:
A highly visible color-shift of the substrate,
Complex fluorescence patterns incorporated directly in the substrate,
The filling of the normally hollow cotton fiber with a material in order to tailor the properties of the substrate, and
A unique spectroscopic signature that the substrate would possess.
The committee suggests two feature platforms that incorporate advanced materials within the substrate to produce a desired response, tactile or visual, based on the characteristics of the advanced material. One approach, the anomalous currency space (ACS), provides a region or regions within the substrate composed of materials that differ entirely from the banknote substrate itself. The second approach is to incorporate shape memory materials, such as NiTi, in the substrate to exploit its superelastic effect.
Anomalous Currency Space
The anomalous currency space is a materials-based approach that serves as a platform for a wide range of anticounterfeiting strategies by providing a region or regions that differ entirely in materials composition from the banknote substrate. The primary objective is to provide an eye-catching visual feature that would also possess tactile properties. The simplest implementation of this feature platform is a clear plastic window. However, the space does not have to be shaped like a typical window. For example, the shape could be a strip that runs the full length or width of the banknote, or a strip that runs along any or all of the edges of the note, or a series of dispersed regions throughout the currency note. Also, the materials composition of this region does not necessarily need to be a polymer.
Examples of how the ACS provides for the incorporation of heterogeneous materials into the Federal Reserve note (FRN) include the following:
A strip along the banknote’s outer edge: A strip of ultratough materials around the outer edge of the bill could be easily detected by its distinct look and feel, such as being resistant to tearing or perforation.
Distribution of small ACS features throughout the banknote: Such patterns could exhibit dynamic as well as passive behavior if, for example, memory metals or polymers were employed.
Memory polymers: A simple case would involve reversible surface “stippling” that would manifest as a change in roughness that could be detected qualitatively by touch and quantified by instrumentation.
NiTi Shape Memory and Superelastic Responsive Materials
Shape memory materials, most commonly based on the intermetallic alloy NiTi, offer various phenomena that can produce active responses which would be useful for developing human-perceptible features. These phenomena are based on the reversible austenite-to-martensite phase transformation. Probably the most
exploitable phenomenon is transformation superelasticity, in which structures can be deformed owing to large strains but recover shape when the stress is released. These structures could be wires or thin-foil-based patterns (dots, eagles, numbers, buildings, and so on) that could be easily deformed but would spring back to shape. The NiTi features would provide the public with a dramatic feature that should be robust and easy to identify. Such features would also be very useful for the blind.
The active nature of these features would be a strong deterrent to currency counterfeiting for all but the most sophisticated counterfeiters. The professional criminal counterfeiter would have difficulty duplicating the chemistry (stoichiometry) and processing to achieve a suitable response.
The committee suggests four feature platforms that represent radically new active platforms that produce a sensible response to some form of user input. Described below, they are chemical sensors, e-substrate, smart nanomaterials, and tactilely active piezoelectric features.
Chemical sensors are sensors are embedded in a banknote that detect chemicals generated either by direct human interaction or from a dedicated “pen” and produce a human-perceptible signal. Passive sensors change their appearance directly; active sensors require power that can be either self-generated on the banknote or obtained from a battery at the point-of-sale. Active sensors can trigger visual, audible, or tactile responses (see the subsection below “e-Substrate”). This feature class can enable features for unassisted use or use with devices and features for the blind. The sensed chemical could even be an exhalation gas, activated by breathing on the sensor.
The effectiveness of chemical sensors for banknote authentication depends entirely on how sensitive and robust the sensors are and on the specific implementation of the human-perceptible response. In general, active features (those that change in response to a stimulus) should be easily noticed by the general public. Chemical sensors would be difficult to reproduce by opportunist counterfeiters and petty criminals.
Two distinct classes of feature platform can be collectively described as electronic (e)-substrates. Both involve a fundamentally new approach that adapts, for the production of currency or currency features, tools and fabrication facilities
principally designed for electronics that are used in large-area applications, such as liquid-crystal televisions and computer monitors. The basic approaches used in these proven applications are sufficiently adaptable that they can be implemented with a wide range of substrates (for example, plastics and, in some cases, textiles), materials (for example, polymers) and designs (for example, passive patterns as well as active electronics) that could provide outstanding innovative deterrent features for currency.
The first type of e-substrate feature, referred to here as a passive e-substrate feature, employs the manufacturing techniques used to form patterns, images, and/or multilayer structures on polymer sheets for large-area electronic systems with feature sizes, material types, and overlay registration that lie well outside the capabilities of any existing (or likely future) printing technology. When this type of feature is integrated in a security strip in a banknote paper substrate or, ultimately, when a passive e-substrate is employed as the currency substrate itself, it can provide excellent security. In the second and much more technically challenging type of e-substrate feature, the active e-substrate feature, the patterns that compose the feature are active devices that can respond to a cash handler or a machine reader. Active e-substrate features require three primary elements: power generation, circuitry, and a human-perceptible response. Features such as chemical sensors and tactilely active piezoelectric features described elsewhere in this chapter would use active e-substrate technology.
The field of “smart” nanomaterials may provide the foundation for security features that are simultaneously extremely complex to fabricate and easy to use. Smart nanomaterials are currently being developed for a wide range of applications. Many of the smart nanomaterials projected to come out of the nanotechnology revolution will be created by some variation of molecular manufacturing (MM). These materials are expected to exhibit a wide range of dynamic behaviors that may be applicable to anticounterfeiting features. Many research programs in smart nanomaterials have targeted the use of extremely high technology manufacturing systems to create materials capable of independent dynamic responses. The final output of these responses may be both human-perceptible and Boolean, that is, their state represented by a simple “yes” or “no” answer regarding authenticity. These features could also be readily interrogated by sensors. If such a smart nanomaterial can be designed in a manner that fits within the physical and fiscal constraints required for currency, the result would be an anticounterfeiting feature almost impossible to counterfeit or simulate yet as simple to use as color-shifting ink or a watermark.
Smart materials whose macroscopic structure depends on the molecular self-
assembly of engineered molecular structures may offer a unique combination of “ultrahigh technology” fabrication that produces simple yet uncounterfeitable Boolean behavior. Molecular self-assembly (MSA) is being explored as a manufacturing base for the large-scale industrial processing of consumer items such as computer chips and scaffolds for bioengineering applications. Large-scale industrial demand for MSA/MM-based facilities may bring the cost of security features using the same technology into line with the economic constraints of FRN production the near future. In a sense, these security features could be considered as a spin-off of the National Nanotechnology Initiative.
Tactilely Active Piezoelectric Features
A piezoelectric crystal develops a voltage when strained. Conversely, if a voltage is applied to a piezoelectric crystal, it responds with a strain resulting in a shape change or deflection. This effect may be used in currency applications to generate a detectable change in the tactile feel at a specific location on a note. In the simplest sense, one can envision bumps that would raise or lower on the note when a voltage is applied. Patterns of fine bumps could possibly be produced to provide each denomination with a unique, readily identifiable pattern. Ideally, the voltage would be supplied by an internal power source embedded within the substrate (see discussion in the subsection above, “e-Substrate”), but the feature could also be powered by a battery that would be attached at point-of-sale locations.
Such features would have a number of advantages for use by the general public. The novel nature of the features would attract attention from the public, leading to the users’ taking advantage of the features. Currency users could readily detect changes in the tactile nature of the features. Tactilely active piezoelectric features would be quite effective in deterring counterfeiting by all but the most sophisticated counterfeiter.
SUMMARY AND CONCLUSIONS
This chapter introduces disruptive features that could radically change the currency platform, that is, the banknote. These advancements, if applied to currency features, will hasten the expected shift from printed, static features to advanced substrates and composites with active features. Smart materials and substrates can be used to develop features that require advanced printing methods or other physical processes to create the currency substrate. The e-substrate feature platform and the anomalous currency space are essentially a collection of technologies that can be assembled to produce the desired security capability. The great benefit of these approaches is that they should be highly extensible, with new developments in power sources, printed circuitry, and miniaturized readout devices. These active
features create ongoing opportunities for the design and implementation of new currency beyond what is imagined in this report.
A number of these features could be used by the blind through the improved tactile response of banknote currency. For example, the piezoelectric effect used to modify the surface profile of the currency can be used to create surface “bumps” or patterns through some external power source. Currency tactility would be altered with and without electrical power. Also, nearly all of the features can be designed to be readily machine-readable.
Importantly, the features that result from these technologies would present a huge barrier to opportunist counterfeiters, effectively negating the advantages that the counterfeiters have enjoyed from rapidly advanced digital printing technology. In summary, the committee makes the following conclusions:
The manufacturing processes for features derived from disruptive technologies require special materials or microfabrication techniques, such as nanotechnology, biomaterials, electronics, and advanced materials manufacturing.
These disruptive feature platforms can provide the basis for a large supply of highly effective features, enabling a proactive strategy of staying well ahead of counterfeiter capability, especially the opportunist counterfeiters who would be ill-equipped to invest in complex, high-technology techniques not dependent on printing.
Many of the advanced feature platforms require simple tools or devices for authentication. The committee expects that authenticating devices will become pervasive and inexpensive.
A proactive research, development, and evaluation program would facilitate the identification of highly capable deterrence features. Since these technologies are not mature for security applications, a long-term research and development program would be necessary.