Novel optical fingerprint sensor utilizing optical characteristics of skin tissue under fingerprints

Abstract

We have developed an optical fingerprint sensor for personal identification. Conventional sensors detect contact between the convex parts of fingerprints and the input surface of the sensor, however, we have devised a novel sensor that utilizes the optical characteristics of the skin tissue under fingerprints. We obtained tomographic images from under fingerprints by optical coherence tomography (OCT), and discovered that the reflected and scattered light from the skin tissue under the concave parts of fingerprints was lower than the convex parts. In other words, the concave parts had a higher light transmittance than the convex parts. Moreover, even when there were wrinkles in a fingerprint, the same optical characteristics were present. Based on this, we made an experimental sensor that detected fingerprint patterns using light transmittance dispersion in the skin tissue. This sensor consists of light emitting diodes (LED) that irradiate red light from the side of a fingernail and an image formation system that forms an image onto an imaging device, by using the light that penetrated the finger. Using this sensor, we obtained fingerprint pattern images in which the concave parts were brighter than the convex parts. These results showed good agreement with the transmittance dispersion described above. Consequently, it has been demonstrated that a fingerprint sensor utilizing the optical can efficiently increase the recognition of fingerprint patterns of wrinkled or wet fingers, which conventional sensors have difficulty recognizing.