Design and application of a novel contactless sensor

The paper presents a novel design of the contactless sensor by the giant magnetoresistance (GMR) effect, instead of the traditional Hall effect or optical technology. The contactless sensing device comprises a magnetic stripe fixed on a tested object, a GMR detector and a processor. The magnetic stripe has arranged plurality of N-pole and S-pole blocks. While the object is moving to make the magnetic stripe pass through the GMR detector, the magnetic direction of the free magnetic layer is influenced by the N-pole and S-pole blocks, such that the magnetic direction of the free magnetic layer is parallel or antiparallel to the fixed magnetic layer. The induced change of the magnetoresistance results in the obvious change of the output signal to the processor, and then the information of the tested object is calculated. The advantages of the contactless sensor are demonstrated in the paper, such as: (1)GMR effect is firstly applied to the sensor design, with the advantages of simple structure, easy installation, low power consumption, low cost, portability, and flexible installing function. (2)The output signal, with high sensitivity, noise immunity and bandwidth, is synchronous with external magnetic field change. (3)Compared with traditional contactless sensor, e.g. optical tachometers, which is only applicable to measure RPM, the sensor is multifunctional to detect not only the position, but also RPM, translational speed and abnormal information.