BIOMETRICS



Part 1. How biometrics works
Please see the image below. The image is originally published at the website of Jean-Fransois Mainguet

 

The first step in any biometric system is called enrollment. This is where one or several biometric samples are captured, and processed. Some specific features are extracted and stored in a template. This template is linked to a person and can be used for comparison.
Comparison of fresh biometric sample to one or few templates is called authentication. Comparison of sample to many templates is called identification.
It is important to note that biometric identification works on the principle of a threshold. That is, it is nearly impossible to capture the biometric the same way every time it is used for access. Therefore, the system cannot expect a 100% match. Instead, a thresholds system is used and it can be modified depending on the application. For very secure applications, where we can allow false rejections due to the level of security, the threshold would be set very high, so that only those live biometrics which matched, say, 99% of the template would be allowed in. In low security applications, though, we may be able to deal with a few false acceptances because whatever is being protected is of low value or may be protected by other means as well. In this case, the threshold may be set to 70%.

Part 2. Fingerprint sensors.

Optical – a simplest way to scan fingerprint. Finger is illuminated by light source, a reflected through a glass prism image is captured by CCD matrix

Capacitive – the difference of capacity between ridges and valleys of finger is captured and amplified by a matrix of tiny sensing units.

 

RF – almost the same as capacitive, but another range of frequencies is used

Thermal – the difference of temperatures is measured.

Ultrasound – captures the reflected wave. Bulky and expensive

Pressure – a matrix of MEMS switches register a binary image

 

 

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