a dipole it is known that where c is the velocity of light according to the present invention an electric field sensor is provided for coupling via a capacitive mechanism to a sample in order to acquire the nmr signal the electric field vector e is perpendicular to the magnetic field component b and rotating at the larmor precession frequency formally the two components are related by a maxwell equation this provides the information needed to position an electrode arrangement for the sensor in order to pick up the electric field component as described below the electrode arrangement is placed perpendicular to the axis of the coil providing the rf input the electrode arrangement may comprise a single electrode arranged to measure the potential with respect to the signal ground or it may comprise a pair of electrodes in the following description it will be assumed that each sensor only includes a single electrode it is advantageous to use two electrometers or sensors in a differential arrangement to enhance the signal to noise ratio by noise subtraction for this to operate effectively the to electrodes of the two sensors must be at two unequal radial distances from the centre of the coil axis in order to provide a differential signal for amplification fig6 illustrates the implementation of this principle in an electric field sensor arrangement 20 which is applicable to both continuous wave and pulse nmr applications the apparatus of fig6 is similar to that of fig2 except in that two electric field sensors e 1 and e 2 have been added similar reference numerals designate the same elements.