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Physics/Rare Earth Magnetic Repulsion Field Strength



I have a three part question regarding repulsive fields and strength (Gauss).

SCENARIO: If you have 2 opposing RE Neodymium(N50) magnets shaped 1" X 2" X 0.5" (W X H X D)moving towards each other at a constant rate of speed.  Each magnet has a plastic protective layer of 0.2" th. in the air gap and you are trying to reduce the impact("G"force) via repulsion/deflection.  
1. Is there a negative shielding effect of the repulsive field for the 0.4" cumulative plastic, and can that be quantified? And would the repulsive strength increase if you could remove a substantial cross sectional area of the plastic layer and expose say 75% of the magnets 1" X 2" surface area?
2. If we were to increase the magnet mass, which dimension would offer best repulsive results in this scenario; increase cross sectional area (WXH), or thickness(D)?
3. Lastly, Is there any benefit to clustering smaller magnets(like Hallbach Array) to get a higher net effect repulsion compared to one solid mass?

Thanks for your help and expertise.  I am a civil/structural engineer by schooling and field, but electromagnetic fields are much more complicated.....

Look forward to your response....


1)  The plastic will have very little effect on the magnetic field itself, almost zero.  The contact distance (0.4") may or may not be significant, depending on how fast you move them.  Direct exposure to air and/or modification of protective coatings is not recommended.
2)  The cross sectional area you mention is relatively large.  This will have the single biggest effect on the range of the magnetic field.
3)  A Hallbach array is designed to create a field parallel to the surface of the magnets.  While ganging more magnets together to make a single larger magnet will help, a Hallbach array is not a good configuration for your purposes if all you want it simple repulsion.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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