Magnetic Shield

A magnetic shield is a device that can be used to protect an area from a magnetic field. It is usually made of a material that is magnetically permeable, such as iron or steel. The shield can be placed around an object to protect it from the effects of a magnetic field, or it can be used to create a space where there is no magnetic field.

Magnetic shields are used in many different applications. They are used to protect electronic equipment from damage caused by electromagnetic fields, and they are also used in medical MRI scanners to keep the strong magnetic fields from harming patients. Magnetic shields can also be used to block out unwanted magnetic fields, such as those produced by power lines.

There are two main types of magnetic shields: active and passive. Active shields use energy to create a counteracting field that cancels out the unwanted field. Passive shields simply block the unwanted field using their physical presence. Both types of shields have their advantages and disadvantages, and the type that is best for a particular application depends on the specific needs of that application.

Active Shields

Active shielding uses electric current flowing through coils of wire to generate its ownmagneticfield which opposes and cancels outthe externalfield. Thiscanbemade with either alternatingcurrent(ac)or directcurrent(dc). When using ac power,theactive shield musthaveitsownpower source;it cannotbe pluggedinto an outletand leftonindefinitely becausethe currentwill alternately flow one wayand thenreverse direction periodically,and this will not producea steadystate Shieldingeffect.The advantageof usingan activeshieldisthatit doesnotrequireany contactwiththe shieldedobject;thus itcanbesetupin advanceand turnedon when neededto provideimmediateprotectionfroman externalmagneticfield.Italsoworksregardlessofwhetherornotthe externalfieldis staticor changingover time, so longas themagneticfieldproducedbytheshieldremains strongerthanthe externaloneatthe pointswherethey meet—at least temporarilyuntiltherate at whichenergyismovingintotheexternal environmentfromtheshieldedregionexceedstherateatwhichitisbeingdissipatedorexpelledbyothermeans (suchas being conductedawaybymovingconductors).However,activeshielding generallyrequiresmore electricitythanpassiveshielding,whichmaynotbepracticalfor someapplicationswhere low-poweredevicesmustbecontrolledin high-magneticeld environments.- Anotherdrawbackisthatifthemagneticsourceispowereddownorturnedoffbeforetheactive Shieldingdeviceisdeactivatedordecoupledfromitssubject,”remanenceeffects”mayallow partofthe protectedarea’sinternalfieldto “leak”outwardsfortimeperiodsonther orderofsecondsor minutesuntilallofthemagnetization inthesubjecthasdecayedaway completely—unlikethecaseforpassive shieldingtechniqueswhichblockoutexternal eldscompletelyimmediatelyuponbeing removedfromtheir surroundingenvironments.- Finallybecauseactivedevicessuchastheses typicallyusecoils wiredin serieswithone anothertoproducetheircounteractingfields,:p37–38 any breakinthewiringduetoaccidentaldamageorcrappingduringoperationwillrenderthesystem powerlessanduselessunlessrepairedalmost immediatelyafterwardstopreventtotal systemfailureandalsopossiblyundesirable consequencesduetothecollapseofthestrong internalcounteractingeldnowthat nothingismaintainingitanylongeragainstthe muchweakerexternal eldstillpresentoutside (i