rare earth magnets

I'm looking at new knife storage and the one I picked has rare earth magnets. I know they're stronger and heard we need to be careful around them but didn't know much more about them so went on a hunt to learn more. This article is the easiest to understand that's from a reputable source (NIH) so thought I'd share. It's from 2008, didn't see anything newer. A rare earth magnet can put a pacer in magnet mode up to 24 cm (9") so slightly longer average distance than a regular magnet (6").

https://pubmed.ncbi.nlm.nih.gov/18334784/#:~:text=Abstract,cardioverter%2Ddefibrillators%20(ICDs).&text=NdFeB%20magnets%20for%20home%20and%20office%20use%20may%20cause%20interference,distances%20up%20to%2024%20centimeters.

I thought this was interesting also, has a chart with magnet size vs distance at which it affected a pacer

https://www.kjmagnetics.com/blog.asp?p=pacemaker-safety

Bottom line, looks like they only slightly more likely to affect us than a regular magnet so I'm going to order myself a pretty new knife storage rack.


4 Comments

Rare-earth magnets

by AgentX86 - 2020-06-28 17:09:37

The point about rare-earth magnets (AKA "super magnets") is that they can be very small, yet powerful.  This size/weight advantage allows manufacturers to make reasonably good ear buds.  Without these magnets, they would be impossible.  Given their size, it's easier to get them close to your PM and much easier to do it without thinking about it.  As the device tech told me, when I was being discharged, don't let anyone lie on my chest with headphones and don't keep my cell phone in a left shirt pocket.  Both probably contain rare-earth magnets.

That said, magnetic feilds drop off as the cube of the distance, so double the separation and the field strength falls by a factor of eight.  Yeah, your knife holder is just fine on the wall but don't sleep on it.

I've seen glasses holders that are held to the shirt by a pair of these magnets.  This isn't a good idea either, though probably wouldn't be a problem if worn only on the opposite side.

magnets

by Tracey_E - 2020-06-28 19:56:16

The biggest reason I'm blase about magnets is I've taken things that are questionable- magnetic case for my ipad, magnetic name tag- to appointments with me and the tech and I tried to get it to interefere and were not able to. Any time I've done anything questionable, I've asked at my next appointment if anything showed up ( a mode switch will be on the report), and it never has, not even the day I toured the generator room at the power plant. This will be the first time getting something that I know has a rare earth magnet. Sounds like I've been around them before and didn't know it. If my running pants don't have pockets, my phone gets tucked in my bra right over the pacer.  If it switched mode, I would not be able to run so I'm 99.9% sure either it doesn't cause problems or my iphone doesn't have strong magnets.

I'll try not to fall asleep hugging my pretty new knife holder ;o)

Super magnets

by AgentX86 - 2020-06-28 20:31:51

Every time you fall down, you don't break a leg, either.

I've said this before but generator rooms, and such, are a whole different kettle of fish than a magnet on the PM.  A magnet may switch the PM to its default mode but won't cause and huge problems.  Large moving magnetic feilds, like a welder, car alternator, or yes, like you could find in a generator room, may cause a current to be induced in the leads (a permanent magnet sitting anywhere can't do this), mimicing a heartbeat causing the PM to inhibit.  This is known as "over-sensing" and is very different and far more serious, particularly for the dependent, than a simple mode switch.

Magnetmeter App

by CyborgMike - 2020-06-28 22:48:16

There is a free app for the iPhone (probably for Android too) called MagnetMeter - in the app store.  Every phone has a very sensitive magnometer built into the hardware for navigation and other useful daily functions. The app is sensitive enough to show you 50 uT and the direction of travel for the flux lines from earth's magnetic field. The safe limit for PMs is about 10gauss. As you move the phone/app closer to a magnet you will see the field strength increase. When it gets to 10g (1000 uT "microTesla" on the app) that is your "safe distance" (in theory). I have a lot of very powerful magnets in the garage from "pre-PM" that were used in coil motors. Some are so strong they need to be in special boxes with a 1 foot clearance. Even with these very high power magnets I'm only seeing 10g about 8" away, although it hits 80g at about 4" so climbs fast. Note to self: I do need to get rid of these...

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