Sensor magnets create a controlled magnetic field that a nearby sensing element converts into an electrical signal. For Hall-effect, TMR, AMR and rotary position sensing, the magnet should be selected around the required magnetic flux density at the sensor location, field direction, air gap, polarity, operating temperature and tolerance stack—not simply the highest magnet grade or catalog pull force.

The magnet does not measure position, speed or proximity by itself; the measurement comes from the interaction between the magnet’s field, the sensor technology, the working gap and the motion of the target. If you already know the geometry you need, browse stocked Sensor Magnets. For a custom field, pole pattern or package, use the Magnet RFQ Builder.

For broader engineering reference on magnetic materials, grades, coatings, field behavior, temperature and sourcing, use the Magnet Knowledge Base.

Sensor Magnet Selection: Start With the Field at the Sensor

The most useful first question is not “How strong is the magnet?” but “What magnetic field does the sensor require at its actual operating location?” Start with the sensor manufacturer’s recommended B-field window and sensitive-axis direction, then evaluate the magnet at the minimum, nominal and maximum expected air gap.

1. Define the sensor requirement: switching threshold, linear operating range or recommended B-field magnitude and polarity.
2. Define the geometry: magnet envelope, sensor location, nominal gap and worst-case tolerance stack.
3. Select magnetization direction: axial, diametric, radial or multipole based on the sensing architecture.
4. Check field versus distance: use the Magnet Field Distance Calculator for preliminary screening.
5. Check temperature and grade margin: confirm Br and HcJ remain appropriate across the operating range using the Neodymium Magnet Grade Chart.
6. Define production verification: if gauss is an acceptance criterion, specify probe orientation, measurement point, air gap and temperature. See the Gauss Measurement Guide.

How a Sensor Magnet System Works

A typical magnetic sensing system has three parts:

Permanent magnet: provides a stable magnetic field.
Magnetic sensor: detects field magnitude, direction or changes in the field.
Electronics: converts the sensor output into position, speed, angle, proximity or another useful measurement.

Common Sensor Technologies

Hall-effect sensors: detect magnetic flux density and are widely used for proximity, speed, current and position sensing.
AMR sensors: anisotropic magnetoresistive devices are useful when magnetic-field direction is part of the measurement, including position and angle sensing.
TMR sensors: tunnel magnetoresistance sensors offer high sensitivity and are widely used in precision position, angle and current-sensing systems.
Reed switches: use a magnetic field to mechanically open or close electrical contacts.

Which Magnet Arrangement Fits Each Sensor Type?

Sensor application	Common magnet arrangement	Key design variable
Hall proximity / presence sensing	Axially magnetized disk, cylinder or block approaching the sensor face	Field magnitude and polarity at the Hall sensing axis
Hall speed sensing	Alternating poles, rotating magnet, or magnetized target passing the sensor	Field transition at the required speed and air gap
Rotary angle sensing	Diametrically magnetized disk or ring centered over the sensor	Field direction, concentricity, axial gap and angular error
TMR / AMR position sensing	Axial, diametric or multipole magnet depending on sensor architecture	Field direction and magnitude across the full travel range
Reed switch activation	Axial disk, cylinder or block moving toward or past the switch	Operate and release field at the switch location

The sensor manufacturer’s recommended field range and sensitive-axis orientation should drive the magnetic design. A magnet that produces a strong surface-gauss reading can still perform poorly if the field component reaching the sensing axis is too low, too high, or oriented incorrectly.

How Strong Should a Sensor Magnet Be?

For most sensor applications, specify the required magnetic field at the sensor—not the magnet’s pull force. Hall, TMR and AMR devices respond to magnetic flux density at a defined location and orientation. A pull-force rating instead describes a mechanical attraction test and can vary with steel thickness, contact area, air gap and test setup.

Start with the sensor datasheet’s operating field, switching threshold or recommended magnetic field range. Then verify that the magnet produces an acceptable field at the minimum and maximum expected working gap, including dimensional tolerances and temperature effects.

A stronger magnet is not automatically better. Excess field can saturate some sensing systems or reduce useful measurement range, while insufficient field can cause missed switching, poor signal-to-noise ratio or loss of accuracy.

Use the Magnet Field Distance Calculator for preliminary field-versus-gap screening and the Gauss Measurement Guide when defining a production measurement method.

Polarity, Sensor Axis and Switching Direction

Magnetic polarity matters because many magnetic sensors are designed to respond to a particular field direction or polarity. A unipolar Hall switch may respond primarily to one pole orientation, while bipolar or latching Hall devices can use opposite polarities for switching and release behavior.

The drawing should therefore define not only magnetization direction but also which pole faces the sensor in the assembled condition. For analog position and angle sensing, the sensor’s sensitive axes should be aligned with the intended field components throughout the full travel range.

Why Magnetization Direction Matters

The magnetization pattern is often just as important as magnet grade or size. An axially magnetized disc creates a very different field at the sensor than a diametrically magnetized disc or ring.

For rotary sensing, a diametrically magnetized magnet is often useful because the north and south poles are on opposite sides of the curved surface. As the magnet rotates on a shaft, the field direction rotates relative to the sensor, allowing the electronics to calculate angular position.

See Diametrically Magnetized vs. Radially Magnetized Magnets for the field-orientation differences.

Sensor Magnet Design Variables

Material and grade: NdFeB is common when high field is required from a small package; ferrite can be attractive where more space is available and cost or corrosion resistance matters.
Shape and size: discs, cylinders, blocks and rings are common; geometry changes the field distribution.
Air gap: magnetic field decreases with distance, so the sensor-to-magnet gap must be controlled.
Magnetization direction: axial, diametric or multipole patterns should match the sensing geometry.
Temperature: both the magnet and sensor must remain within their operating limits.
Mechanical alignment: eccentricity, tilt and axial displacement can create measurement error.
Nearby steel: ferromagnetic hardware can redirect flux and change the field seen by the sensor.
Coating and adhesive thickness: even small added gaps can matter in compact sensing assemblies.

Use the Neodymium Magnet Grade Chart when comparing Br, HcJ and temperature-capable grades.

Air Gap and Tolerance Stack: Design for Worst Case

A sensor that works on the prototype bench can fail in production if the magnetic window is too narrow. The effective sensor-to-magnet spacing can change because of magnet thickness tolerance, sensor package placement, PCB position, adhesive bond line, coating thickness, housing dimensions, shaft runout, radial offset and assembly tilt.

Evaluate the magnetic field at both the minimum and maximum possible gap, then include temperature and magnet-property variation where the application requires tight switching or accuracy limits. For rotary systems, also evaluate eccentricity and axial offset because both can create angle error even when the nominal air gap is correct.

Common Sensor Magnet Applications

Motor shaft angle and speed sensing
Robotic joint and actuator position feedback
Automotive pedal, throttle, steering and position sensing
Industrial proximity and end-of-travel detection
Flow meters and rotating equipment
Appliance and consumer-product position sensing
Medical-device mechanisms requiring non-contact position feedback
Encoders, knobs and human-machine interface controls

Choosing a Magnet for a Rotary Sensor

Start with the sensor manufacturer’s recommended field range and geometry. Then define the shaft size, available magnet envelope, sensor location, air gap, operating temperature and required angular accuracy.

Diametric disc and ring magnets are common for on-axis rotary sensing. Other applications may use axial, multipole or custom magnetization patterns. If the application involves an annular motor or specialized radial field rather than a sensing magnet, review What Is a True Radial Magnet?.

Stock Sensor Magnet or Custom Sensor Magnet?

Use a stocked magnet when	Consider custom when
A standard disk, rod or ring fits the available envelope	The sensor requires a nonstandard geometry or very tight package
Axial or standard diametric magnetization meets the sensing geometry	A specific multipole, indexed or custom magnetization pattern is required
The required field can be reached by adjusting gap or magnet size	The field window must be achieved at a tightly controlled working distance
Standard temperature and coating options are acceptable	Elevated temperature, corrosion exposure or special coating requirements drive the design

For stocked options, shop Sensor Magnets. For OEM designs, provide the sensor type, required field range, measurement location, air gap, magnet envelope, temperature, magnetization direction and annual volume through the Magnet RFQ Builder.

What to Put on a Sensor Magnet Drawing or RFQ

Magnet material and grade
Dimensions and tolerances
Magnetization direction or pole pattern
Required north/south pole orientation in the assembly
Required magnetic field range at a defined sensor location
Nominal, minimum and maximum sensor air gap
Operating and excursion temperature
Coating or surface finish
Magnetic test method and probe location if field is an acceptance criterion
Annual volume, traceability and quality-documentation requirements

Frequently Asked Questions

What magnet should I use with a Hall-effect sensor?

Choose the magnet from the Hall sensor’s required field range, sensitive-axis direction, available air gap and package size. Axially magnetized disks or cylinders are common for proximity sensing, while diametrically magnetized disks or rings are common for rotary angle sensing.

What magnet should I use with a TMR or AMR sensor?

Start with the sensor manufacturer’s specified field magnitude and sensitive-axis orientation. TMR and AMR systems may use axial, diametric or multipole magnetization depending on whether the design measures linear position, angle, speed or proximity. The magnet should be validated across the full travel range and worst-case air gap.

Is N52 always better for a magnetic sensor?

No. The correct magnet should produce the required field window at the sensor across tolerance and temperature. A lower grade or smaller magnet may be preferable if N52 produces more field than the sensing system needs.

Does pull force matter for Hall, TMR or AMR sensors?

Usually not as the primary specification. These sensors respond to magnetic field at the sensing element, so field magnitude, direction, air gap and tolerance are normally more important than a catalog magnet-to-steel pull-force rating.

What magnetization is used for a rotary angle sensor?

A diametrically magnetized disk or ring is common for on-axis rotary angle sensing because the field direction rotates as the magnet turns. The exact magnet and gap should follow the sensor manufacturer’s recommended magnetic geometry.

How does air gap affect a magnetic sensor?

Increasing the sensor-to-magnet distance generally reduces the magnetic field at the sensor. Because compact magnets can have steep field gradients, small gap changes from tolerances, coatings or assembly position can materially change switching or measurement performance.

Sensor Magnet Sourcing

Radial Magnets stocks sensor-oriented disk, rod and ring geometries for prototyping and production sourcing. When comparing parts, do not rely on diameter and grade alone: verify thickness, magnetization direction, field at the working gap, coating, temperature margin and dimensional tolerance.

Browse Sensor Magnets for stock options. For a custom size, grade, coating or magnetization pattern, submit the drawing and sensor requirements through the Magnet RFQ Builder.