Magnetic system for counting rotations having increased stability against magnetic interference fields
View Patent ↗A magnetic system for counting revolutions is provided having increased immunity to magnetic interference fields and which can be used in a magnetic field range (B-field range) that is considerably above that customarily used according to the prior art, with the width of the magnetic window ΔB, which is to say the difference between the lower and upper B-values permissible during use, being as large as possible, an angle sensor for determining the field direction of a magnetic field of a permanent magnet which jointly captures the angle sensor and a revolution counter with the revolution counter being formed by a GMR or TMR revolution counter having a known design being used, and the angle sensor and the revolution counter being disposed next to one another in a shared enclosure and/or on a shared printed circuit board.
1. A magnetic system for counting revolutions having increased magnetic interference field immunity, comprising an angle sensor configured to determine a field direction of a magnetic field of a permanent magnet which jointly captures the angle sensor and a revolution counter, the revolution counter being formed by a GMR or TMR revolution counter, and the angle sensor and the revolution counter being disposed next to one another in a shared enclosure and/or on a shared printed circuit board, wherein a magnetic damping structure not made of a homogeneous soft magnetic material and configured to adapt magnetic action thereof is assigned to the revolution counter, the damping structure having no, or only a negligibly small, magnetic field of its own at an external magnetic field of zero, and wherein the damping structure comprises a plurality of regions oriented in a magnetically anti-parallel configuration or in a magnetically disordered configuration.
2. The magnetic system according to claim 1 , wherein the damping structure comprises a damping layer which does not laterally protrude beyond the soft magnetic GMR or TMR structures of the revolution counter by more than 30%.
3. The magnetic system according to claim 2 , wherein the damping layer comprises ferromagnetic sub-layers, which are stacked on top of one another, magnetized in a plane thereof, and in each case oriented anti-parallel, the respective thickness of which being selected such that these compensate for one another magnetically, the sub-layers being separated by non-ferromagnetic thin films.
4. The magnetic system according to claim 2 , wherein the damping layer is formed of a layer stack comprising at least one ferromagnetic layer which is captured on each side by a respective non-ferromagnetic layer, the ferromagnetic layer having a perpendicular magnetization parallel to a normal of the ferromagnetic layer, and neighboring magnetic field regions taking on an anti-parallel direction.
5. The magnetic system according to claim 2 , wherein the damping layer is formed of a layer system comprising an accumulation of small superparamagnetic particles each having a superparamagnetic moment and being oriented in a disordered manner and embedded in a non-magnetic matrix.
6. The magnetic system according to claim 2 , wherein the damping layer is provided above or below the soft magnetic GMR or TMR structures of the revolution counter.
7. The magnetic system according to claim 2 , wherein, depending on characteristics of the revolution counter with the damping layer, a geometry deviating from a circular shape, in a top view, is selected so as to take an effect of shape anisotropy into consideration.
8. The magnetic system according to claim 1 , wherein a distance between the angle sensor and the revolution counter is less than 500 μm, and at least these two components are enclosed in a hermetically sealed manner by the shared enclosure.
9. The magnetic system according to claim 1 , wherein a distance between the angle sensor and the revolution counter is less than 500 μm, and at least these two components, together with evaluation electronics, are enclosed in a hermetically sealed manner by the shared enclosure.