# How to isolate a strong magnet from things it could damage in a small backpack?

I have a pretty strong magnet for magnet fishing. The problem that I am running into when taking it places is that I need a way to isolate it from my wallet/phone/compass inside my backpack as otherwise they could be damaged by the magnetic field.

My current solution is to roll it up inside several socks, is there a better way of doing this?

• Contain it within some type of magnetic material (e.g., steel). Stronger the field the thicker the material needs to be. Dec 6, 2018 at 22:01
• @topshot Next question, how do I get my powerful magnet out of its steel container? Dec 6, 2018 at 22:03
• My solution would be to keep my phone and wallet in my pocket. Or maybe hold the magnet in my hand. Dec 7, 2018 at 6:37
• Pry bar? :P Perhaps pad the container with foam so it's not in direct contact. I'm not so sure about the answer saying there's nothing to worry about. It would certainly wipe out the card strips if close enough and interfere with the reception of the phone. I've not studied (I'm an EE but from long ago) how such a strong magnetic field would (if at all) interfere with flash memory or RFID since those didn't exist at the time and I've been in software dev since school. Dec 7, 2018 at 12:25
• flash memory: superuser.com/a/338656 Dec 7, 2018 at 13:08

To keep this answer focused, let's set the discussion aside, whether a permanent magnet can be strong enough to damage electronics.

Physically speaking, you cannot shield magnetic fields -- you can just "dilute" them. To prevent magnetic field strength from being too high at the place of magnet sensible stuff you have two possibilities:

1. Put distance between the magnet and the things to be protected. Your approach with packing the magnet into some socks is exactly that. Since the field strength decreases roughly proportional to the square of the distance to the magnet, even a small increase in distance has quite some effect.
2. According to this page you can reduce the magnetic field strength by putting it behind an iron plate or into an iron container to separate it from the sensible stuff. This will dilute the magnetic field lines more effectively than just putting spatial separation between them. However, at least with the iron container, you will of course have the problem of getting the magnet out of the container. If you take the iron plate approach, you might put the magnet close to your backpack's outer wall and use the plate as a separator towards the rest of the pack's content.

Is a mu-metal box outside your price range?

https://en.wikipedia.org/wiki/Mu-metal

If you can't afford mu-metal, the answer will vary depending on how strong your magnets are. Generally speaking you want a plastic box just large enough to fit your magnet, set inside a larger plastic or wood box with spacers to maintain a consistent air gap between the two boxes.

If steel nuts and bolts stick to the outer box, it isn't big enough, keep trying bigger ones until you find the right size.

As a direct answer to your question: Yes, there are better ways of protecting your gear from damage caused by a magnet. However, they might not be worth the effort.

My suggestions are:

• Go magnet fishing with someone else. That way, one of you can carry your valuables and the other can carry kit you need for magnet fishing (rope and the like). This not only helps protect your belongings but helps you stay safe when on adventures.

• Avoid taking valuables with you. Any card with a magnetic strip can easily be damaged by even a small magnet. As for technology, certain electrics can very easily be damaged (such as hard drives) but most modern smartphones won't be greatly affected. (We use magnetic phone holders all the time nowadays and LCD screens aren't really affected by magnets anyway).

It is correct that increasing distance from the magnet dramatically decreases its power, so wrapping it in socks or tying it to the outside of your bag may help. Putting it in an iron container would definitely help (as others have stated) but probably isn't worth the extra weight. If your bag has a 'top' pocket could you put your phone and wallet in that and put your magnet in the bottom of your bag?

Basically, you can happily take your phone along without much worry, but be careful with credit/ debit cards or anything that uses magnetic storage/ with delicate moving parts. Maybe leave them in your car/ at home - you are cutting down on weight after all (which is always helpful when hiking/ walking).

Note: I am not accountable for any damage that occurs to your belongings. I can only provide advice according to my experience. You should always check product manuals/ manufacturer info first. Why not google which things damage specific items in your kit how to avoid such damage.

There is no magnet you can lift that is strong enough to damage a cell phone, so don't worry about your phone, apart from physicial damage e.g. dropping it on your phone. You may need to be careful the phone doesn't violently thrash into the magnet, but other than that, electrically phones are virtually unaffected by magnetism.

As for your wallet, chip cards are also not affected, so just rely on those and a little cash.

In other words, you really don't need to do anything.

• Sources for your claims? Dec 7, 2018 at 12:25
• This might NOT be true. Small Neodymium magnet can totally destroy some monitors. "Someone" placed a half-dollar sized Neodymium magnet on the outside of my closed laptop computer. When I opened the thing up I found that the screen was messed up - parts were unresponsive, other parts had white or black bands, and then there were mixes of colors. I eventually had to replace the screen because the device was unusable. Dec 7, 2018 at 13:43
• @topshot - there are several cell phone holders (for car dashes, etc.) that use a fairly strong magnet mounted on the phone case to hold the phone onto a ball or flat support. So it isn’t totally out of the question. Still, a wooden box might be a reasonable answer to the OP... Jan 6, 2019 at 17:51
• This is arguably false for cell phones, but it is demonstrably false for thins such as credit cards etc. that come with magnet strips. Just try it out and swipe any of your magnet strip cards with a small fridge magnet... (actually, don't do that!) Jan 7, 2019 at 9:31
• Also available portable neodymium magnets have reached ridiculous strengths, with some of the strongest ones being able to hold several hundreds of kilograms if attached to a suitable metal surface. The sheer force is likely enough to mess up whatever you attach to such a magnet... Jan 7, 2019 at 9:32