A new technology developed by researchers from The Langevin Institute (Paris, France) enables subsurface imaging of the finger. The “internal fingerprint,” according to the device’s creators, could provide cheaper, more secure authentication than traditional scanners.
The technology is based on optical coherence tomography (OCT), a technique already used in medicine to view the retina, esophagus, and cardiovascular structures. With the OCT process, a light source, such as a laser, provides three-dimensional interior images.
Langevin’s “full-field” tomography method, invented in the early 2000s by the ESPCI ParisTech academic institution, does not require sophisticated data processing, acquisition of 3D data, or the laser scanning needed in standard OCT techniques. The Langevin-developed device images a whole field of view and provides direct imaging of the more-or-less two-dimensional flat fingerprints.
“With our method, we need only to acquire one image,” said Egidijus Auksorius, postdoctoral researcher at The Langevin Institute. Auksorius worked with Claude Boccara, a professor who specializes in scientific instruments at the Paris facility, to develop the fingerprint sensor.
What is an Internal Fingerprint?
Also known as the dermis epidermis junction, the internal fingerprint, about a half a millimeter below the skin’s surface, has a pattern identical to its external print. Because the body feature is deeper, it is less susceptible to tampering or fooling traditional authentication systems that scan the fingerprint’s surface.
Although users can try to modify their external fingerprint — an individual could scuff his or her fingers against a hard surface to flatten the skin pattern, for example, to prevent scanners from forming a correct image — the majority of minor damages would not reach the depth of the internal authenticator.
Because the Langevin technology does not require the sophisticated laser system of a traditional OCT device, the internal fingerprint sensor could be considered a cheaper security option.
“Since we don’t need a laser, we can use, in principle, any simple light source,” said Auksorius.
The most expensive part of the technology, however, is the specialized camera that acquires large amounts of photons from a specified depth, thanks to interferometric detection cap - abilities; similar to high-speed cameras used to image slow-motion or explosive recordings, the camera must acquire large quantities of light in a short amount of time.
The ‘Dark’ Side of Imaging
The lab has partnered with TUBITAK - The Scientific & Technological Research Council of Turkey, scanning the fingerprints — and closer-to-the-surface sweat ducts — of more than 100 users. The implementation is one of three biometric technologies being tested as part of Europe’s INGRESS project — an initiative designed to research, develop, and validate fingerprint imaging tools for border control and law enforcement applications.
The researchers are also currently preparing to add a new feature to the instrument: the ability to reject the specular reflections coming from the glass-sample interfaces. With the so-called “dark field” implementation of OCT, an opaque disk blocks the reflections and, therefore, brings more light to a given sample.
The camera thus detects more photons, effectively helping to increase the depth of imaging in tissue like a finger. The dark-field imaging capability exists in the lab and will be added to the next data acquisition session in Turkey, which takes place in February of 2016.
The market for this kind of technology is wide, according to Auksorius, but the most obvious applications areas would be border control, law enforcement, or other sectors where large numbers of passersby need to be identified.
Auksorius does not see the technology being used on mobile phones or other handheld devices because of the price and the size of the system. Although the device could be considered expensive, he expects manfacturers to eventually be able to create the cameras at a more affordable price.
“Even though this is still not that cheap compared to standard fingerprint scanners, of course, its price can be either driven down with time or this can be used for special applications where security is very important,” said Auksorius.