Man­u­fac­tur­ing Fo­cus

Shield­ing elec­tronic de­vices from elec­tro­mag­netic ra­di­a­tion

Electronics Bazaar - - Contents - By Baishakhi Dutta

To­day’s prod­uct de­sign­ers face a num­ber of chal­lenges when it comes to de­sign­ing elec­tronic de­vices for con­sumers as well as for the busi­ness-to-busi­ness (B2B) mar­kets. As these de­vices be­come in­creas­ingly smaller and more com­plex in na­ture, shield­ing them against elec­tro­mag­netic in­ter­fer­ence gets more dif­fi­cult.

High-fre­quency ra­di­a­tion, par­tic­u­larly ra­dio waves, em­a­nat­ing from gad­gets like cell phones, not only pro­duces cross-talk be­tween de­vices, but also has a neg­a­tive im­pact on the health of people. In an ef­fort to min­imise such in­ter­fer­ence, en­gi­neers de­sign the printed cir­cuit boards (PCBs) of the de­vices in a way that the com­po­nents re­main iso­lated from one an­other.

All re­puted brands in the in­dus­try fo­cus on the care­ful se­lec­tion and use of proper EMI shield­ing ma­te­ri­als, as this is not only cru­cial for ef­fec­tive shield­ing, but also im­por­tant in or­der to meet a wide range of ap­pli­ca­tion chal­lenges that to­day’s de­sign­ers face.

Types of EMI shield­ing

De­vice fail­ure caused by in­ter­fer­ence or ‘noise’ from elec­tro­mag­netic en­ergy is in­creas­ing due to the grow­ing num­ber of prod­ucts that con­tain sen­si­tive elec­tronic com­po­nents.

• Re­flec­tion: The pri­mary mech­a­nism of elec­tro­mag­netic shield­ing in­volves re­flec­tion. In or­der to be able to re­flect the ra­di­a­tion, the shield needs to be elec­tri­cally con­duc­tive. Since met­als have this prop­erty, they are good shield­ing ma­te­ri­als; how­ever, they are bulky. In or­der to over­come this short­com­ing, sheets with metal coat­ings that are cre­ated by elec­tro­plat­ing, elec­tro­less plat­ing or vac­uum de­po­si­tion, are gen­er­ally used. Ab­sorp­tion: The sec­ondary as­pect of shield­ing in­volves the ab­sorp­tion of ra­di­ated en­ergy. In or­der to fa­cil­i­tate ab­sorp­tion, the ma­te­rial should have elec­tric and/or mag­netic dipoles – the sep­a­ra­tion of pos­i­tive and neg­a­tive charges. Mag­netic dipoles can be pro­vided by ma­te­ri­als with high lev­els of mag­netic per­me­abil­ity. Su­per permal­loy, mumetal and iron ox­ide are some of the ma­te­ri­als that are ex­cel­lent for ab­sorp­tion.

Mul­ti­ple re­flec­tions: This process in­volves the re­flec­tion off var­i­ous sur­faces and in­ter­faces. To be ef­fec­tive, this mech­a­nism re­quires a large sur­face area. Shields made of foam or por­ous ma­te­ri­als are good for mul­ti­ple re­flec­tions. Com­pos­ite ma­te­ri­als

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