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TMAG5170: Magnetic Field Behavior Near Magnet Surfaces in Precision Sensing Applications

Part Number: TMAG5170


I am currently working on a precision angle sensing application involving the use of a 3-axis hall sensor in close proximity to a diametrically magnetized ring magnet (NdFeB). This is for a medical device which we aim to commercialize in early 2025.

In our application, the hall sensor is aligned coaxially to the magnet, and is calibrated using an external magnetometer which is placed in-plane, off-axis to the magnet.

I understand that sintered magnets have a magnetization direction tolerance resulting from individual grain magnetization. My uncertainty is whether the magnetic field near a magnet's surface will behave somewhat randomly due to grain structure behavior. If true, the theoretical relationship between magnetometer angle reading and hall sensor angle reading, which are in different places, could be inaccurate.

Do you have any insights into these concerns? We are trying to better understand magnetic field shape repeatability across a manufacturing lot, and whether near-field shape deviates from theoretical models due to grain magnetization. Ultimately, we'd like to find a combination of magnet selection and sensor design that results in the most accurate solution.

Best regards,

  • Lucas,

    If the sensor is aligned axially to the magnet like this

    Then the sensor will be detecting a purely rotating field vector which will be constant with respect to the magnet itself.  So measurements of angle change should be very linear.  It is possible that the grain structure could cause the field vector at the sensor location to have a slight offset, but with calibration the 0 degree position should be identifiable.

    Sometimes with larger ring magnets, it is possible to observe that the field is not perfectly sinusoidal.  I would recommend using our simulator tool (TIMSS) to look for this type of behavior.  If there is distortion in the measured sine/cosine of the field, this will create non-linearities of the angle measurement.