ACTIVE SHIELDING OF EDDY-CURRENT SENSORS - A METHOD TO FOCUS THE MAGNETIC-FIELD IN ORDER TO IMPROVE LATERAL RESOLUTION AND COUPLING COEFFICIENT

We present an original method called 'active shielding', which provide s improved eddy current sensor performance, mainly in terms of the cou pling coefficient with the target, distance range and spatial resoluti on, The method is derived from the theory of electrical images. Initia lly, the basic principles of such sensor are highlighted. Then we pres ent the method applied to the design of a cup sensor. We finally discu ss the effects of active shielding based on the use of active elements to modify the distribution of the magnetic field in the sensing regio n of the sensor. The advantages of this method are demonstrated with e xamples: the coupling coefficient and the spatial resolution are impro ved whereas the distance range is not modified.