When vending machines began accepting paper bills in the 1960s, they relied on magnetism to determine the bill’s denomination. US dollar bills used iron-based ink and the magnetic detectors could read the bill’s quantity of ink. Unfortunately, counterfeiters quickly caught up with the technology. Fast forward to today and advanced infrared imaging techniques using inks, dyes and taggants are used to identify everything from fake currency to drugs & medicines, non-authentic electronic components, and counterfeit consumer goods.
Today’s currency is printed on paper with a specific thickness and weight. US bills have both a 3D band and security strips embedded in them. While many inks are still iron-based, today’s currencies are printed with different ink technology. Subtle watermarks are hidden until held up to the light. Color-shifting inks change color depending on the viewed angle. Printing techniques create unique textured patterns. Infrared and ultraviolet sensitive inks make certain features visible only when exposed to specific light wavelengths or through an image converter.
Modern ATMs, vending machines, and counterfeit detectors utilize advanced optical technology not only to determine a bill’s value but also to determine whether it is fake. They can detect the presence and location of the 3D band and security strip. Ultraviolet, infrared, magnetic and spectrometry detectors can examine the unique features and properties of the bill’s printing and paper.
Using Near-Infrared (NIR) light for counterfeit detection goes far beyond currency examination. Infrared inspection has long been used in forensics for comparing inks to detect document forgeries. It is used not only for art restoration but also forgery detection. Infrared-sensitive inks may be incorporated into a product’s design or its tags for fast detection and sorting. Infrared inspection can be employed to inspect electronic components, medicines, and other consumer products even without special ink.
The US 100-dollar bill is the most widely used piece of currency in the world, and also the world’s most counterfeited bill. So, it should come as no surprise that it is also the most technologically complex currency piece in the US. A single $100 bill has a security strip, 3D band, watermark, holographic image, color-shifting ink, ultraviolet sensitive ink and infrared-sensitive ink.
Infrared currency inspection devices range from simple IR light sources for visible inspection to devices that measure the bill’s thickness. Visual inspection is inexpensive but depends on a person recognizing patterns that may include minute differences from the real thing.
Machine scanners have an infrared light source (commonly an LED array), optical lenses and filters, an infrared camera, and an image processor. These are common in ATMs, vending machines, and store scanners used to detect infrared-sensitive ink. The device examines features of a bill for electronic comparison to known images. Some high-end and expensive scanners can precisely measure a bill’s thickness, a unique feature for each currency denomination. The amount of infrared light transmitted through the bill gets attenuated is related to its thickness.
Figure 1 shows a simplified block diagram of a counterfeit detector. The infrared optical filter filters stray light before the image reaches the infrared camera.
Drugs and Medicines
The production of counterfeit medicines is a growing threat to public health. Some counterfeits contain lower doses of drugs, while others are poor facsimiles of authentic drug formulas. Counterfeiters aim to duplicate the physical appearance of the drug as well as the chemicals in the product. The chemical composition of the drug is proprietary to the manufacturer and nearly impossible to duplicate precisely. Minute differences in physical appearance and the chemical signature can be detected using Near Infrared (NIR) spectrometry.
To detect counterfeit drugs, a database of chemical signatures for known medicines is required. Since each manufacturer’s signature is different and many authentic generics are available, these libraries can be vast. However, since NIR spectrometry is nondestructive, it is a desirable inspection technique. Product libraries combined with handheld spectrometers allow for large quantities of drugs to be quickly inspected on-site and through packaging.
Manufacturing and Electronics
Modern life is dependent on digital devices, which has made electronic goods some of the most counterfeited products in the world. While entire devices might be counterfeited, non-authentic individual components make it into supply chains for everything from consumer electronics to military equipment.
Fourier Transform Infrared (FTIR) spectroscopy is one technology used to inspect electronic components. Fake components are often coated with a polymer that can help cloak a forgery. FTIR spectroscopy is used to determine the materials used in the component to detect these coatings.
Inks, Dyes, and Taggants
Thousands of shipments of counterfeit goods are seized and shipped to the United States each year. This includes electronic devices and luxury products—watches, jewelry and handbags/wallets—clothing and shoes, automotive parts, and copyrighted material. Unlike pharmaceuticals, many of these items do not have a specific chemical signature that can be cataloged for detection.
Instead, manufactures are taking a cue from currency design. Some companies use various security taggants (inks and dyes) to mark their products for authenticity. They can be blended into injection molds, painted or stamped onto surfaces, added to a product label or tag, or used for security packaging. Infrared taggants (IR-wavelength absorbing or reflecting inks and dyes) are considered the most effective taggants. Accompanying IR readers can be tuned to detect proprietary patterns for authentication.
As counterfeits become increasingly sophisticated, the technology to detect them is also advancing. Infrared systems are one of the most promising methods for detecting counterfeits. Infrared sensitive inks and taggants are one method for combatting counterfeits. Advanced counterfeiters are able to create fakes that duplicate authentic ink and taggant patterns. However, it is nearly impossible to duplicate the inherent spectral signature of authentic products. Near infrared spectrometry is promising for the future of counterfeit detection.