# US 11,442,074 B1 · Offset-reduced zero-gauss-magnet with polepiece for differential, twist-insensitive magnetic speed sensors

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- Number: US 11,442,074 B1
- Document ID: US11442074B1
- Status: Granted
- Kind: B1
- Application number: 17/235,434
- Filed: 2021-04-20
- Granted: 2022-09-13
- Earliest claimed: 2021-04-20
- Assignees: Infineon Technologies AG
- Applicants: Infineon Technologies AG
- Inventors: Gernot Binder
- Web page: https://patentgrep.com/patent/US11442074B1

## CPC

- G01P 3/481: of pulse signals
- G01P 3/487: delivered by rotating magnets
- G01P 3/488: delivered by variable reluctance detectors
- G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G})

## Abstract

A magnetic sensor module includes an axially polarized back-bias magnet having a body that radially extends from a magnet center axis and a bore extending along the magnet center axis. The magnet generates a radial bias magnetic in-plane field about a magnetization axis in a sensor plane. The magnetic 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. The magnetic sensor module includes a shim polepiece mechanically coupled to an end of the axially polarized back-bias magnet. The shim polepiece includes a second bore centered on a polepiece center axis that is aligned with the magnet center axis. The second bore extends through the shim polepiece along the polepiece center axis and is congruent with the first bore.

## Claims

### Claim 1

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.

### Claim 2 (depends on 1)

The magnetic sensor module of claim 1, wherein the axially polarized back-bias magnet, in combination with the shim polepiece, generates the zero-field closed loop in the sensor plane.

### Claim 3 (depends on 2)

The magnetic sensor module of claim 2, wherein the shim polepiece is configured to rectify the radial bias magnetic in-plane field such that the perimeter of the zero-field closed loop vertically overlaps with the magnet body in a plan view.

### Claim 4 (depends on 3)

The magnetic sensor module of claim 3, wherein the magnetization axis is tilted away from the magnet center axis and the shim polepiece is configured to shift the magnetization axis towards the center axis of the axially polarized back-bias magnet.

### Claim 5 (depends on 1)

The magnetic sensor module of claim 1, wherein the magnetization axis is tilted away from the magnet center axis and the shim polepiece is configured to shift the magnetization axis towards the center axis of the axially polarized back-bias magnet.

### Claim 6 (depends on 5)

The magnetic sensor module of claim 5, wherein the shim polepiece is configured to rectify the radial bias magnetic in-plane field such that the perimeter of the zero-field closed loop vertically overlaps with the magnet body in a plan view.

### Claim 7 (depends on 1)

The magnetic sensor module of claim 1, wherein the shim polepiece is configured to rectify the radial bias magnetic in-plane field such that magnetization axis is maintained at the magnet center axis.

### Claim 8 (depends on 1)

The magnetic sensor module of claim 1, wherein the shim polepiece is configured to homogenize a first in-plane magnetic field component and a second in-plane magnetic field component of the radial bias magnetic in-plane field.

### Claim 9 (depends on 1)

The magnetic sensor module of claim 1, wherein the shim polepiece is configured to reduce a gradient of the radial bias magnetic in-plane field at the magnetization axis and at the perimeter of the zero-field closed loop.

### Claim 10 (depends on 1)

The magnetic sensor module of claim 1, wherein the radial bias magnetic in-plane field comprises a first in-plane magnetic field component and a second in-plane magnetic field component, and the shim polepiece is configured to reduce a gradient of the first in-plane magnetic field component and the second in-plane magnetic field component at the magnetization axis and at the perimeter of the zero-field closed loop.

### Claim 11 (depends on 1)

The magnetic sensor module of claim 1, wherein a shape profile of the shim polepiece is substantially the same as a shape profile of the axially polarized back-bias magnet in a plan view.

### Claim 12 (depends on 1)

The magnetic sensor module of claim 1, wherein:
the axially polarized back-bias magnet comprises a magnet inner perimeter defined by the first bore and a magnet outer perimeter, and
the shim polepiece comprises a polepiece inner perimeter congruent with the magnet inner perimeter and a polepiece outer perimeter congruent with the magnet outer perimeter.

### Claim 13 (depends on 1)

The magnetic sensor module of claim 1, further comprising:
a magnetic sensor including a plurality of sensor elements arranged in the sensor plane of the magnetic sensor at locations where the radial bias magnetic in-plane field has a magnetic flux density of substantially zero, wherein the plurality of sensor elements are configured to generate measurement values in response to sensing the radially symmetric bias magnetic in-plane field,
wherein at least two of the plurality of sensor elements are arranged on the perimeter of the zero-field closed loop at substantially equidistant angles about the magnet center axis of the axially polarized back-bias magnet.

### Claim 14 (depends on 13)

The magnetic sensor module of claim 13, wherein one sensor element of the plurality of sensor elements is arranged on the extension of the magnet center axis.

### Claim 15 (depends on 13)

The magnetic sensor module of claim 13, wherein one sensor element of the plurality of sensor elements is arranged on the magnetization axis.

### Claim 16 (depends on 15)

The magnetic sensor module of claim 15, wherein three sensor elements of the plurality of sensor elements are linearly arranged along an in-plane axis of the sensor plane, wherein the in-plane axis is orthogonal to the magnet center axis.

### Claim 17 (depends on 13)

The magnetic sensor module of claim 13, wherein the magnetic flux density of substantially zero means less than 15 milliteslas (mT).

### Claim 18 (depends on 17)

The magnetic sensor module of claim 17, wherein the plurality of sensor elements are arranged in the sensor plane of the magnetic sensor at locations where the radial bias magnetic in-plane field has a magnetic flux density of substantially zero.

### Claim 19 (depends on 1)

The magnetic sensor module of claim 1, wherein the perimeter of the zero-field closed loop is defined as an area in the sensor plane where the magnetic flux density of the radially symmetric bias magnetic in-plane field is less than 15 milliteslas (mT).

### Claim 20 (depends on 1)

The magnetic sensor module of claim 1, wherein the perimeter of the zero-field closed loop is defined as an area in the sensor plane where the magnetic flux density of the radially symmetric bias magnetic in-plane field is zero.

### Claim 21 (depends on 1)

The magnetic sensor module of claim 1, wherein the axially polarized back-bias magnet, in combination with the shim polepiece, generates the radial bias magnetic in-plane field that is zero at the magnetization axis and the extension thereof, increases in the radial direction in the sensor plane from the magnetization axis to a first radial distance, decreases in the radial direction in the sensor plane from the first radial distance to a second radial distance that defines a portion of the permitter of the zero-field closed loop, and increases in the radial direction in the sensor plane from the second radial distance to a third radial distance that defines the outer sidewall.

### Claim 22 (depends on 21)

The magnetic sensor module of claim 21, wherein the second radial distance is located between the inner sidewall and the outer sidewall.

### Claim 23 (depends on 1)

The magnetic sensor module of claim 1, wherein the bore extends from the first end to the second end.

### Claim 24 (depends on 1)

The magnetic sensor module of claim 1, wherein the bore extends from the first end partially towards the second end.

### Claim 25 (depends on 1)

The magnetic sensor module of claim 1, wherein the bore extends partially between the first closed end and the second closed end.

### Claim 26 (depends on 13)

The magnetic sensor module of claim 13, wherein the magnetic sensor further comprises a sensor circuit configured to receive the measurement values from the plurality of sensor elements, and generate a measurement signal using at least one differential calculation configured to cancel out stray-fields present along at least one sensitivity-axis of the magnetic sensor based on the received measurement values.

### Claim 27 (depends on 13)

The magnetic sensor module of claim 13, wherein the magnetic sensor module is twist-insensitive about the magnet center axis of the axially polarized back-bias magnet.