Electric potential sensor

The present invention provides an electric potential sensor (28) for the measurement of potentials non-invasively. The sensor comprises at least one detection electrode (12) arranged for capacitive coupling with a sample under test and for generating a measurement signal, and a sensor amplifier (14) adapted to receive the measurement signal as input and to supply an amplified detection signal as output. Input impedance enhancing means (12a, 32, 36, 38, 44) are included for providing a high input impedance to the sensor amplifier for increasing the sensitivity of the electrode to reduced electric potentials, and a discrete pre-amplifier stage (30) is arranged to co-operate with the sensor amplifier to reduce the input capacitance of the amplifier