Magnetic proximity sensor based on colossal magnetoresistance effect

Magnetic proximity sensors are widely used to determine the distance to ferromagnetic or highly conductive materials and to investigate their shape or to detect their motion. In this study, a magnetic proximity sensor incorporating a cylindrical permanent magnet and a scalar magnetic field sensor (measuring the magnitude of the field independently from its orientation) based on the phenomenon of colossal magnetoresistance in manganite films is presented. Two versions of the sensor, one with a solid cylindrical magnet and one with a hollow cylindrical magnet, were constructed and tested. A steel plate and a superconducting YBaCuO disk were used to investigate the static response. The measurements of the dynamic behavior were carried out with rotating steel and duralumin plates. The results of the static experiments and modelling showed that the output response (change of the magnetic field) of the sensor had a hyperbolic relationship with the distance between the sensor and the measured object. This change was positive for solid cylindrical magnet design and negative for hollow cylindrical magnet design when the target was steel. In contrast, the solid magnet-based sensor produced a negative signal for the superconducting material, while the hollow cylindrical magnet sensor showed a positive signal. It was found that the main features of the dynamic response of the proximity sensors can be explained by the magnetization of steel and the induction of eddy currents in duralumin. The present study demonstrates that the proposed magnetic proximity sensor can be successfully used to search for ferromagnetic objects, investigate the properties of superconductors and detect the motion of non-ferromagnetic conductive materials and can have advantages over conventional magnetic proximity sensors.