2. Introduction
Computerized fingerprint
scanners have been a
mainstay of spy thrillers for
decades, but up until
recently, they were pretty
exotic technology in the real
world. In the past few years,
however, scanners have Photo courtesy Siemens
A computer mouse with a built-in fingerprint scanner
started popping up all over
the place -- in police stations,
high-security buildings and
even on PC keyboards.
3. Finger Print Basics
Fingerprints are one of those People have tiny ridges of
bizarre twists of nature. Human skin on their fingers because
beings happen to have built-in, this particular adaptation was
easily accessible identity cards.
extremely advantageous to
You have a unique design,
which represents you alone,
the ancestors of the human
literally at your fingertips. species. The pattern of ridges
and "valleys" on fingers make
it easier for the hands to grip
things, in the same way a
rubber tread pattern helps a
tire grip the road.
4. Optical Scanner
A fingerprint scanner system has two
basic jobs -- it needs to get an image
of your finger, and it needs to
determine whether the pattern of
ridges and valleys in this image
matches the pattern of ridges and
valleys in pre-scanned images.
There are a number of different ways
to get an image of somebody's The heart of an optical scanner is a
finger. The most common methods charge coupled device (CCD), the
today are optical scanning and same light sensor system used in
capacitance scanning. Both types digital cameras and camcorders. A
come up with the same sort of CCD is simply an array of light-
image, but they go about it in sensitive diodes called photosites,
completely different ways. which generate an electrical signal in
response to light photons.
5. Capacitance Scanner
Like optical scanners, capacitive
fingerprint scanners generate an
image of the ridges and valleys that
make up a fingerprint. But instead of
sensing the print using light, the
capacitors use electrical current.
The diagram below shows a simple The sensor is connected to an
capacitive sensor. The sensor is integrator, an electrical circuit built
made up of one or more around an inverting operational
semiconductor chips containing an amplifier. The inverting amplifier is a
array of tiny cells. Each cell includes complex semiconductor device,
two conductor plates, covered with made up of a number of transistors,
an insulating layer. The cells are tiny resistors and capacitors. The details
-- smaller than the width of one ridge of its operation would fill an entire
on a finger. article by itself, but here we can get a
general sense of what it does in a
capacitance scanner.
6. Analysis
In movies and TV shows, automated fingerprint analyzers
typically overlay various fingerprint images to find a match. In
actuality, this isn't a particularly practical way to compare
fingerprints. Smudging can make two images of the same print
look pretty different, so you're rarely going to get a perfect
image overlay. Additionally, using the entire fingerprint image in
comparative analysis uses a lot of processing power, and it
also makes it easier for somebody to steal the print data.
Instead, most fingerprint scanner systems compare specific
features of the fingerprint, generally known as minutiae.
Typically, human and computer investigators concentrate on
points where ridge lines end or where one ridge splits into two
(bifurcations). Collectively, these and other distinctive features
are sometimes called typica.
