Sensor device for performing measurements on an at least partially conductive surface, the sensor comprising a number of conductive structures at or directly below the sensor surface, said conductive structures consisting of at least one stimulation or current sink electrode 1 and a number of sensor elements 3 coupled to interrogation electrodes in an electronic circuit for measuring impedance between the electrodes 3 and said at least one stimulus electrode 1, the sensor device also comprising at least one additional clamping electrode being positioned in the vicinity of said sensor elements and being coupled to a chosen voltage.
