Hall probes: physics and application to magnetometry

Abstract

This lecture aims to present an overview of the properties of Hall effect devices. Descriptions of the Hall phenomenon, a review of the Hall effect device characteristics and of the various types of probes are presented. Particular attention is paid to the recent development of three-axis sensors and the related techniques to cancel the offsets and the planar Hall effect. The lecture introduces the delicate problem of the calibration of a threedimensional sensor and ends with a section devoted to magnetic measurements in conventional beam line magnets and undulators. The measurement of magnetic fields plays a key role in various areas. The mastering of the magnetic field intensity allows the construction of alternators and of electrical motors, the storage of information on magnetic tapes or hard disks, and the study of phenomena in condensed matter physics like the flux distribution in superconductors. Magnetic fields of very strong intensity are used in particle accelerators or in Tokomaks to guide and focus beams with high energy and make them collide. Field measurements are also omnipresent in the domain of medicine to detect heart and brain activity. The Hall effect is an ideal magnetic field sensing technology. Discovered in 1879 by a professor of the Johns Hopkins University in the USA, E. H. Hall [1], its application remained confined to laboratory experiments until the 1950s as a tool for measuring the magnetic field or exploring the basic electronic properties of a solid. With the mass production of semiconductors and the development of the associated electronics, it became progressively feasible to combine a Hall effect sensing element with electronics in a single integrated circuit. This changed the end objective of the Hall effect devices. From the simple measurement of the magnetic field, they became a key element in the sensing of pressure, current, position or temperature via magnetic field detection. Hall sensors can be found nowadays in many products ranging from computers to automobiles, aircraft and medical equipment. An overview of the Hall effect devices used as magnetic sensors can be found, for example, in the bibliographic items [B1]–[B6].