2. Capacitive Scanners.
Themost commonly used fingerprint scanner is a capacitivescanner. Nowadays, most
smartphones use this type of scanner because it isvery secure. As the name suggests, it uses
capacitors, and instead of taking images, it collectsdetails of the finger with the help of arrays of
tiny capacitors circuits. There are conducting plateson the surface of the scanner connected to
the capacitors and as a capacitor stores electriccharge. When a finger is placed on the scanner
there are changes in electric charge on conductingplates, the charge will reduce in the place
where the finger touches the scanner, and the chargewill retain where there are air gaps. This
difference in electrical charges is tracked with thehelp of op-amp integrator circuit, and stored in
digital form with the help of analog to digital converter.
The digital data captured is used to differentiatebetween unique fingerprints. This technique is
very secure as it can’t easily be fooled with imageand it's really tough to use prosthetic as
different material changes electrical charges differentlyat the capacitor. The only drawback is
that software can be hacked.
The number of capacitors used is directly proportionalto the security, as more the capacitor
more detailed image of fingerprints increasing security.
Due to many components in the circuit and a largenumber of capacitors used, the capacitive
scanner has been a little pricey. So to cut the price,developers reduced the number of
capacitors, which resulted in decreased speed andincreasing attempts to detect fingerprints.