Effect of magnetic field on electronic components

Question

Are electronic components like diodes,transistors, micro-controllers, microprocessors, wireless transceivers etc are damaged by strong static or dynamic magnetic fields? If yes, at what strength the field becomes dangerous? Also, what are the ways to protect the components against such fields?

Answer 1

Static field effects on devices

Strong static magnetic fields will have little effect on most electronics, including most of the ones on your list. We routinely placed basic electronics in 1-2T fields, and never had any real problems. There are some exceptions though (this is probably not a complete list):

• Relays work by using a magnet to move a piece of ferrous material to close a switch. Strong fields may open them, close them, or get them stuck in whatever position they are in.
• Inductors and transformers have magnetically soft cores, which couple magnetic flux much better than air. They are designed for a certain flux density based on the properties of the coils in them, and beyond that they saturate, becoming less effective. The field they create adds with the external field, so the external field can cause early saturation. This reduces the inductance of inductors and ferrites, and reduces the efficiency of transformers. It may also introduce harmonic content in transformers.
• Hall sensors obviously measure magnetic field, and will measure the external field. Watch out for them in motors and in some sensors.
• LVDT position sensors probably won't be remotely accurate in an external field.
• Motors almost always use magnetic fields internally and may or may not work. They tend to have half decent shielding, so you may be pleasantly surprised.
• Magnetic recording media such as hard disks, tape, floppy disks... are very suceptable, but also usually well shielded (particularly modern hard disks). So will usually be OK.

If you have any items in the above list, it would probably be wise to check with the manufacturer with your specific field strength and field gradient. Or look for alternatives.

Shielding static fields

You can shield against static fields with magnetically soft materials and careful geometry. The cheap way is to use iron plates or tubes. Mu-metal is a more expensive but also much more compact and effective option. The most effective shielding is a series of concentric tubes aligned along the field direction, with the delicate electronics inside. In the unlikely event you have a cryogenic system, superconductors also make excellent shields - wrap things in lead foil.

Dynamic fields

These are very complicated, so I'm not going to give a complete answer here. Broadly speaking, they are rather worse than static fields of the same strength, and may cause all sorts of problems with any electronics. If you give a rough guide to field strength and frequencies, I might be able to add more. A few Hz can be treated as above, hundreds of Hz will be more complicated.

Dynamic fields can be shielded by a combination of the magnetically soft iron described above and highly conductive metal sheets. The soft iron works well at low frequencies, and the copper sheet at high frequencies. Top end shielded rooms use alternating layers of mu-metal and copper, with air gaps.

Answer 2

For protection : a Faraday cage.

Answer 3

Electronic components such as the list you provided will normally not be damaged by any magnetic field, static or dynamic.

Let still note:

• A magnetic field can influence the electrical property of your devices, it is difficult to really define strength, (depends on a lot of parameters) but you could consider some impacts already at 50KG (~field of a fridge magnet, ~100 times earth magnetic field). This means the devices may not behave as you would expect but still will not be damaged and will work again once the field is removed.

• If that is a concern, most devices are already protected against charge accumulations (due to antenna effects)

• other electronic devices magnetic based (for instance hard disks) are nowadays not very sensible to static magnetic fields, you can have a look at this question/answer
• If the field is really too strong you may have some physical damages, but it will not happen at device level but rather on the connections/packaging