A sensor device for performing measurements on an at least partially conductive surface includes a number of conductive structures at or directly below the sensor surface. The conductive structures consist of at least one stimulation or current sink electrode and a number of sensor elements coupled to interrogation electrodes in an electronic circuit for measuring impedance between the electrodes and the stimulation electrode. The sensor device also includes at least one additional clamping electrode positioned in the vicinity of the sensor elements and coupled to a chosen voltage.