Frequently Asked Questions - EMI Shielding
Glossary of Shielding Terms
Annealing: The treatment of a metal, alloy, or other material by heating to a predetermined temperature, holding for a certain time, and then cooling to room temperature.
Attenuation: A ratio used to measure the effectiveness of a given shield. The ratio is expressed as the field strength at a given point vs. the resulting field strength at the same point with a magnetic shield in place. A shield which provides a reduction of 100 times has an attenuation of 100:1.
Coercive Force: The magnetic force necessary to demagnetize a substance. Also called coercivity.
Curie Point: Temperature at which magnetism changes; the temperature at which in some substances, such as iron, there is a change in the magnetic characteristics, from ferromagnetic to paramagnetic behavior.
D/C Field: A magnetic field that is non-varying, or perhaps slowly changing. DC fields might be from the Earth, a permanent magnet, or a coil carrying direct current.
Electromagnetic Field (EMF): A field of force associated with a moving electric charge and consisting of electric and magnetic fields that are generated at right angles to each other.
Electromagnetic Interference (EMI): Interference caused by the radiation of an electric or magnetic field.
ELF: Stands for Extremely Low Frequency usually referring to magnetic fields at 0.5 to 100 Hertz.
Ferromagnetism: strong magnetization induced by weak field: a property of some substances, including iron and some alloys, in which application of a weak magnetic field within a certain temperature range induces high magnetism.
Ferromagnetic: With the property of ferromagnetism. Iron, cobalt, and nickel are ferromagnetic metals.
Flux: The strength of a magnetic field represented by lines of force. Symbol f
Frequency: The frequency of a magnetic field, measured in cycles per second (Hz), is usually the same as the operating frequency of the field's source.
Gauss: The number of magnetic lines of force (flux) emitted per square centimeter.
Induction: Refers to magnetic lines of force….see Magnetic Flux Density.
Magnetic Field Strength: Describes the intensity of a magnetic field in free space*. (*at some distance from its source)
Magnetic Flux Density: Describes the concentration of magnetic lines of force in a material.
MuMETAL®: A registered trade name for a high-permeability alloy used for magnetic shielding. It is made up of 80% nickel, 15% iron, and a balance of other metals depending upon the particular formula.
Paramagnetic: Used to describe a substance that is weakly magnetized so that it will lie parallel to a magnetic field.
Permeability: Refers to a materials ability to attract and conduct magnetic lines of flux. The more conductive a material is to magnetic fields, the higher its permeability.
Oersted: A unit (symbol Oe) of magnetic field strength. It is equal to a force of one dyne acting upon a unit magnetic pole in a vacuum.
Saturation: The limiting point of a material to conduct additional lines of flux. The saturation and permeability characteristics of most ferromagnetic materials are inversely related, therefore the higher a material's permeability, the lower its saturation point.
Shield: Something that serves as protection or acts as a defense.