How do fingerprint sensors work?

All fingerprint sensors try to generate a digital picture of the finger surface. This picture normally has a pixel resolution of 500 dpi. The picture generation can be different for every type of sensor.

Static Capacitive Sensor Type 1 Here, one electrode is responsible for each pixel and measures the capacity compared to the neighbor electrode/ pixel (inter pixel measurement). The capacity, in turn, is dependent on the dielectric. If a pixel is on a groove (i.e.

Air), the capacity is substantially smaller than on a finger line (ridge). In this case, the dielectric is water, which is distinguished by a very high dielectric constant. The measurement of capacity is static in the sense that charging happens with fixed charge units and then voltage is measured.

Practical systems are always a mix of type 1 and type 2. Static Capacitive Sensor Type 2 Also here one electrode per pixel is used, but the capacity is measured between pixel and ground, whereby the conductivity of the fingers ... more.

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