Chapter Three Magnetic Sensors: Principles and Applications

Abstract

In this chapter, we cover the advances in the field of magnetic sensors: both, sensors of magnetic field and sensors that use magnetic materials or principles for measuring nonmagnetic quantities. The overview of materials used for magnetic sensors comprises semiconductor materials and the soft and hard magnetic materials in thin film, bulk, and tape form in detail. We discuss the properties and effects most critical for the decisive parameters of magnetic sensors, for example, remanence, crossfield sensitivity, and temperature stability of the offset. By far, most of the produced magnetic sensors are devices based on the Hall effect. These semiconductor sensors are cheap and can be made small, but their resolution and stability is rather limited. The fast development of ferromagnetic magnetoresistors (AMR, GMR, and SDT) for magnetic reading heads also brought these devices into the sensor scope. In the chapter devoted to fluxgate sensors, we concentrate on miniaturization of these traditional devices and compare them to GMI sensors. We describe the status of resonant sensors, induction coils, and SQUIDs, and briefly mention other more exotic methods of magnetic field measurements. An overview of magnetic sensors for mechanical quantities, such as position and force, is also given with special focus on torque sensors. One section is devoted to the sensing of electric current based on magnetic principles. In conclusion various applications of magnetic sensors are listed and discussed.