Offset-reduced zero-gauss-magnet with polepiece for differential, twist-insensitive magnetic speed sensors

A magnetic sensor module configured to detect a rotation of an object, comprising:

• an axially polarized back-bias magnet comprising a magnet body that extends in a radial direction from an inner sidewall to an outer sidewall and a first bore that defines the inner sidewall, wherein the axially polarized back-bias magnet generates a radial bias magnetic in-plane field about a magnetization axis of the axially polarized back-bias magnet in a sensor plane that is orthogonal to an extension of a magnet center axis of the axially polarized back-bias, wherein the first bore is centered on the magnet center axis and extends along the magnet center axis in an axial direction of the axially polarized back-bias magnet, wherein the radial bias magnetic in-plane field has a magnetic flux density of substantially zero along the extension of the magnetization axis and at a perimeter of a zero-field closed loop located in the sensor plane, wherein the perimeter of the zero-field closed loop encircles the extension of the magnet center axis, wherein the axially polarized back-bias magnet comprises a first end and a second end arranged opposite to the first end in the axial direction;
• and
• a shim polepiece mechanically coupled to the first end of the axially polarized back-bias magnet, wherein the shim polepiece comprises a second bore centered on a polepiece center axis that is aligned with the magnet center axis, wherein the second bore extends through the shim polepiece along the polepiece center axis and is congruent with the first bore.