Sensor module for measuring surfaces

This invention relates to a sensor module for measuring structures in a surface, in particular a finger surface, which moves over the sensor module, comprising a number of sensor elements and an outer electrode placed next to the sensor elements, the sensor elements being connected to at least one AC driver circuit applying a varying current or voltage, thereby connecting a signal through the sensor elements to the outer electrode. The sensor elements are also connected to an electronic circuit located on a substrate, which substrate comprises a conductor which connects the sensor elements to the electronic circuit, and where the electronic circuit is arranged to measure the magnitude of the capacitance or AC impedance between each sensor element and the outer electrode. The sensor elements constitute a substantially linear array, where the array is arranged to measure the capacitance or impedance between each sensor element and the outer electrode at selected times, and that the measured values ​​are combined to form a representation of the surface pattern.