Magnetic field shaping for improved 1-D linear position measurement

Abstract

Linear position measurement is currently present in diverse formats in industrial and automotive applications, sometimes as a direct way of measuring distance or detecting position and sometimes as a way of indirectly detecting other observables such as temperature, force, stress and others. Both in industrial and automotive applications, it is not uncommon to face environments with rough physical characteristics, such as extreme temperatures, physical stresses, changes in humidity and dirt. While many sensing systems cannot operate in such harsh environments, magnetic systems present themselves as a robust solution in the presence of water, dirt and at high temperature with life-times up to decades. In addition, permanent magnets as the source of the magnetic reference field do not require a power supply. With such beneficial features it is easy to understand the increased use of magnetic systems for industrial applications. On the other hand, the fast decay of the magnetic field of a permanent magnet is a known characteristic and normally a limiting factor regarding the distance between magnet and sensor, raising the requirement for stronger and more expensive magnetic materials. Another point to be taken in consideration is the fact that state of the art systems require costly 2D magnetic sensors that provide extended measurement ranges and a more stable handling of the constructive tolerances involved in the system. Especially when dealing with industrial mass production the application costly components is a critical and often limiting factor. To overcome these issues, a proposal for shaping the magnetic fields is presented. The idea is to shape the magnetic field using magnetic compound systems such that a 1D sensor will see a linear field as a function of the magnet displacement. The ability to shape the magnetic field allows for an optimal use of the magnetic material, so that developers can use smaller magnets and cheaper magnetic sensors, which decrease production costs.