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Skin Spectroscopy
Skin is a layered tissue structure and has complex interaction with light. Light undergoes scattering and absorption in skin. Scattering is caused by the structural characteristics such as the arrangement of the collagen fibers. Absorption is caused by the chromophores present in the layers. The depth of light penetration depends on the wavelength of light and the level of pigmentation. Furthermore, the reflectance spectrum of skin provides information regarding the distribution and concentration of various chromophores present in the skin and is highly person dependant. Thus spectroscopic measurements can be successfully used as a biometric. Some preliminary studies have already been done in our lab demonstrate the inter-user variability of signals.
It has also been widely published in popular technical press that commercial biometrics systems have been defeated by use of fake fingers based on gelatin. The interaction of live skin with light differs sufficiently from other skin like materials like gelatin. We are developing fingerprint sensors that integrate skin spectroscopy devices to prevent such spoof attacks. Furthermore, this multi-modal arrangement will also improve the accuracy of the biometric system in addition to providing liveness detection. Similar efforts were proposed earlier, but have not yet been operational.
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 Sensor arrays exist for the simultaneous detection of multiple chemicals.
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