Development of Low frequency, Flexible EMI Shielding Materials

The electromagnetic interference (EMI) shielding effectiveness of a material of fixed thickness is a function of the incident wave frequency and the conductivity/permeability product of the shielding material. Effective low frequency shielding requires either a high conductivity/permeability product or a relatively thich piece of material. Current low frequency shielding materials compensate for limited conductivity/permeability values by increasing the thickness of the shielding material, which generally limits their application. This proposal is for the development of a low frequency, flexible EMI shield. To maintain flexibility the shielding material must be quite thin, typically below 20 um, therefore the conductivity/permeability product must be high. We propose to use an amorphous, non-magnetostrictive ferromagnetic alloy in a multilayer structure, with a metallic interlayer, to achieve high permeability and high conductivity. A moderate value coercive force is required to avoid saturation of the shielding material. The design of the multilayer structure will be guided by analytic models developed for modelling shielding effectiveness. Other design issues include selection of substrate and shielding material combinations for superior adhesion, durability, and low cost as well as shielding effectiveness. Promising candidates will be fabricated to demonstrate the feasibility of such products.