Altering Magnetic Field Strength at a Radius

USMechE6 · Mar 10, 2023

Hello,

Please forgive my lack of knowledge on magnetism. I have an application in which I need a ring magnet of fixed strength on a piston to trip a sensor (reed switch) a certain radius away from the axis of travel (greater than the OD of the magnet). The sensor requires a field strength of a certain range. If I need to keep the sensor location fixed, can I tweak the Gauss it sees by placing another ring of steel (or aluminum or stainless) around the magnet? Will this redirect the field lines more through the outer ring and less through free space where the sensor is? The magnet is described as being axially magnetized, N42.

IRstuff · Mar 10, 2023

A drawing would clarify any misconceptions that arise from a verbal description.

Nevertheless, there's not much you can do to concentrate the field as you describe. Putting something at the sensor end might possibly improve things.

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EdStainless · Mar 10, 2023

You may be able to create steel pole pieces for the magnet and focus the field more.
A sketch would help a lot.

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MagBen · Mar 13, 2023

possible. the effective way is to increase your ring magnet thickness. Attaching a steel ring to the magnet at the reed switch side could also work, however attaching to the other side could weaken field strength depending on their relative locations.
Aluminum or austenitic stainless won't have an effect, while martensitc or ferrite stainless are ferromagnetic.

USMechE6 · Mar 13, 2023

My main concern is having too great of a magnetic field, since the sensor has an upper limit as well as lower limit on Gauss. Experimenting with different sized magnets is less practical for us. I know there isn't really such thing as magnetic shielding, hence my question around redirecting the field. Here is a sketch.

MagBen · Mar 13, 2023

i thought your reed switch was located along the axial of the magnet, such that adding a steel ring would increase the flux strength. With the sensor located on top of the radius of the magnet, adding a steel ring could weaken the flux the sensor "sees", guiding some flux away from senor.

Yes magnetic shielding does exist. you can have a design to even shield all magnetic flux, with zero Guess going through the sensor.

USMechE6 · Mar 13, 2023

Thank you for all of your responses so far.
Yes, the sensor is located some radius away from the magnet's axis of travel so that when the piston reaches a certain linear position, the sensor is tripped.
Since there is a piston cap above the magnet (not seen in the sketch), I am thinking of stacking ferritic rings as needed around the magnet (thinner than or equal to the magnet thickness itself) to redirect some of the flux and lessen the field the sensor sees. Am I understanding correctly?
I did not know about the shielding, sources I read said otherwise but then that's why I also came back to this website.

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Altering Magnetic Field Strength at a Radius

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