What is Fingerprint scanner?
[[File:Fingerprint scanner in Tel Aviv.jpg|thumb|A stand-alone fingerprint scanner, such as one used at the [[wikt:Entrance|entrance]] to a [[building]]]] '''Fingerprint scanners''' are security systems of [[biometrics]]. They are used to unlock doors and in other security applications. During the 2010s fingerprint scanners became commonplace on [[mobile phone]]<nowiki/>s. People have a pattern of ridges on their fingers. This [[fingerprint]] cannot be removed or changed. Every fingerprint is different from any other in the world. Because there are countless combinations, fingerprints are much used for identification. == Various Types == === Optical reflexive === They are based on the oldest technique, that consists of placing your finger on a glass surface or a prism that is illuminated by a led diode. When the ridges of fingerprints touch the surface, the light is absorbed, while between these crests a total reflection occurs. The resulting light and dark areas are recorded in an [[image sensor]]. In practice there are some difficulties with this technique: wet and dry fingers make very different images, and the system is sensitive to dust and dirt on the surface. The unit is large and expensive. This system is also easy to cheat and if the skin is damaged, the fingerprint is not recognized correctly. The recognition of the fingerprint of older people is also difficult to do because their skin may not be elastic enough. In some circumstances this may result in false recognition. If the stored fingerprint was taken with less pressure, false acceptances may occur. === Capacitive === The sensor is a silicon [[integrated circuit]] with a surface that is covered by a large number of transducer elements (or pixels), with a typical resolution of 500 dpi. Each element contains two adjacent metal electrodes. The [[capacitance]] between the electrodes, which forms a feedback path for an inverting amplifier, is reduced when the finger is applied to said surface: it is further reduced when it detects ridges and