# How to create a strong magnetic field using permanent magnets

I would like to build a strong magnet using 100 6"x4"x1" permanent magnet blocks. What is the best way to place them so I get the strongest magnetic field? (Should I stack 2 row of 50 blocks and put them side by side? Should I place them like halbach array?...) I use this magnet to attract metal particles that are on a conveyor. The field must attract the medium sized particles(2"x3"x2" approx.) upon a fairly good distance. Thank You!

• You answered your own question writing about Hallbach array, aren't you? – HolgerFiedler Jun 17 '16 at 17:34
• You are going at this the exact wrong way. In engineering we don't start with "I have six brick, now how do I build a house?" but with "I want to build a house, how many bricks do I need?". The correct procedure here is experimental. Use one or a few of your magnets to measure the area in which they attract exactly the kinds of parts that you want, then scale it up. Using magnets alone, without a proper magnetic return path is not going to get you a good magnet, anyway, though. – CuriousOne Jun 17 '16 at 18:31
• If you tie these magnets parallel to each other such that all the north are facing one direction you would likely to have a strong attracting force. It is just my gut feeling, in any case field very close to magnet pole remain same as of one magnet. – hsinghal Jun 17 '16 at 19:20
• Ok thank you I'll make some your tests monday and I will come back with the results! – Jean-Gabriel Deshaies Morin Jun 17 '16 at 20:23

The permanent magnets are magnetic dipoles which means that their field goes down like $B\sim 1/r^3$ with the distance from the dipole. The number of such magnets in a volume goes like $r^3$, so regardless of the value of $r$, the magnetic field will have basically the same magnitude.