This system is much faster than conventional manual analysis and offers the additional benefit of reduced risk of contaminating the tapes with magnetic powder. Top end shielded rooms use alternating layers of mu-metal and copper, with air gaps.The National Institute of Standards and Technology (NIST) has developed an improved version of a real-time magnetic microscopy system that converts evidence of tampering on magnetic audio and video tapes-erasing, overdubbing and other alterations-into images with four times the resolution previously available. The soft iron works well at low frequencies, and the copper sheet at high frequencies. A few Hz can be treated as above, hundreds of Hz will be more complicated.ĭynamic fields can be shielded by a combination of the magnetically soft iron described above and highly conductive metal sheets. If you give a rough guide to field strength and frequencies, I might be able to add more. Broadly speaking, they are rather worse than static fields of the same strength, and may cause all sorts of problems with any electronics. These are very complicated, so I'm not going to give a complete answer here. In the unlikely event you have a cryogenic system, superconductors also make excellent shields - wrap things in lead foil. The most effective shielding is a series of concentric tubes aligned along the field direction, with the delicate electronics inside. Mu-metal is a more expensive but also much more compact and effective option. The cheap way is to use iron plates or tubes. You can shield against static fields with magnetically soft materials and careful geometry. 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. are very suceptable, but also usually well shielded (particularly modern hard disks). Magnetic recording media such as hard disks, tape, floppy disks.They tend to have half decent shielding, so you may be pleasantly surprised. Motors almost always use magnetic fields internally and may or may not work.LVDT position sensors probably won't be remotely accurate in an external field.Watch out for them in motors and in some sensors. Hall sensors obviously measure magnetic field, and will measure the external field.It may also introduce harmonic content in transformers. This reduces the inductance of inductors and ferrites, and reduces the efficiency of transformers. The field they create adds with the external field, so the external field can cause early saturation. 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. Inductors and transformers have magnetically soft cores, which couple magnetic flux much better than air. Strong fields may open them, close them, or get them stuck in whatever position they are in.
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