Abstract
Biometrics is described as the science of identifying people based on physical characteristics such as their
fingerprints, facial features, hand geometry, iris patterns, palm prints, or speech recognition. Notably, all of these
physical characteristics are visible or detectable from the exterior of the body. These external characteristics can be
lifted, photographed, copied or recorded for unauthorized access to a biometric system. Individual humans are unique
internally, however, just as they are unique externally.
New biometric modalities have been developed which identify people based on their unique internal
characteristics. For example, "BoneprintsTM" use acoustic fields to scan the unique bone density pattern of a thumb
pressed on a small acoustic sensor. Thanks to advances in piezoelectric materials the acoustic sensor can be placed in
virtually any device such as a steering wheel, door handle, or keyboard. Similarly, "Imp-PrintsTM" measure the electrical
impedance patterns of a hand to identify or verify a person's identity. Small impedance sensors can be easily embedded
in devices such as smart cards, handles, or wall mounts.
These internal biometric modalities rely on physical characteristics which are not visible or photographable,
providing an added level of security. In addition, both the acoustic and impedance methods can be combined with
physiologic measurements such as acoustic Doppler or impedance plethysmography, respectively. Added verification
that the biometric pattern came from a living person can be obtained. These new biometric modalities have the potential
to allay user concerns over protection of privacy, while providing a higher level of security.*
