The goal of this research is the design and implementation of an
integrated system for personal identification which uses fingerprint
recognition. The system is made of a sensor, a classification and a
validation systems. Some important issues to be addressed are:
compactness, low-cost and reliability. For the above reasons we have
faced the problem by studying and implementing a non-optical
fingerprint imager which uses a capacitive sensor cell array. A 390
dpi (dot per inch) prototype has been successfully implemented in a
general purpose CMOS technology.
The sensor senses the distance of the skin surface by means of
capacitive sensing made by cell arrays arranged in $200$ rows by $200$
columns. The primary goal is to get two dimensional images whose gray
level function is linear with respect to the distance of the skin
surface to the sensor array. To achieve this goal, several circuit
techniques have been proposed, simulated and implemented. The measured
result has confirmed the models and several further applications can
be found for this kind of sensor: from pressure to acceleration
sensors from micro-machinery to integrated microphones.
The classification system enhances the sensor image and identifies the
fingerprint image, comparing it to a previously stored one. The result
of the classification consists in accepting the two images as those
belonging to the same person, or rejecting such a statement. The
fingerprint identification is based on the comparison of feature points in
both the images and on the matching of the regions surrounding these
areas. The feature points are the standard ending/bifurcation points
of the skin ridges.