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 less reduced when it detects the space between them.