Low Frequency Magnetic Shielding - Interference Technology

© Integran Technologies Inc. 2equilibrium state grain size of around 1‐10µm,the large grain structure must be achievedthrough annealing the metal at hightemperatures, often in a tightly controlledatmosphere to control impurities.Other foils have an amorphous (i.e. nocrystalline grains) or nanocrystalline structurewhich is normally achieved through complexmanufacturing techniques including rapidsolidification and high frequency annealingprocesses.2.2 Existing Shielding SolutionsAlthough specialty foils are very effective EMIshields, they are best suited to shielding simplyshaped parts. There are currently a fewmethods for creating parts with relativelycomplex geometries, described in Figure 2 andFigure 3.Figure 2 ‐ Existing Shielding Solutions (Part 1).Figure 3 ‐ Existing Shielding Solutions (Part 2).2.3 Foil Lay‐up and Formed FoilsSince sheet metal or foils are manufactured flat,materials that resist forming operations, likeglassy amorphous alloys, must be cut to shapeand laid onto flat surfaces in order to achievethe necessary part shielding. Although thesematerials have excellent shielding performance,this lay‐up approach is a cumbersome methodfor shielding parts with any contour or shape.Other less brittle shielding materials can also becut and formed to the shape required. Forexample, a sensitive transducer measuring afaint analog current might require a “can” ofmaterial to be formed to integrate into theenclosure or circuit board for the device. Thisshape would need to be cut and stamped fromthe original sheet metal or foil supply. Althoughthis process adds cost to the shield, it is not, initself, a particularly challenging operation.Unfortunately, the forming operation reducesthe effectiveness of the shield by introducingdeformation into the material – destroying thekey material characteristic that generates thehigh permeability. To restore the defect‐freestructure, the material must be annealed oncemore in the high temperature controlledenvironment to restore shielding effectiveness.