Electromagnetic Shielding
“Electromagnetic shielding is the process of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive and/or magnetic materials. Shielding is typically applied (1) to enclosures to isolate electrical devices from the 'outside world' and (2) to cables to isolate wires from the environment through which the cable runs. Electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as RF shielding.”
“The shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields, though not static or low-frequency magnetic fields (a conductive enclosure used to block electrostatic fields is also known as a Faraday cage). The amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic field.”
Recent US Patents
2/25/2011
Dispersions of carbon nanotubes/polyhedral oligomeric silsesquioxanes hybrids in polymer: the mechanical, electrical and EMI shielding properties
(2324-2330) Journal of Materials Science 46 #7 (2011)
Li et al, China and South Korea synthesized a hybrid by grafting polyhedral oligomeric silsesquioxane (POSS) to multiwalled carbon nanotubes (MWCNTs). The MWCNT/polymer composites produced using silsesquioxane grafted MWCNTs as a filler had a high electromagnetic interference shielding effectiveness. Homogeneous dispersion of silsesquioxane grafted MWCNTs occurred throughout the polymer without any aggregation. A high electromagnetic interference shielding effectiveness (15–16 dB) was obtained in the 36–50 GHz range at a relatively low filler loading (4 wt%) in the PLLA/silsesquioxane grafted MWCNT composite. (RDC 2/22/2011)
Recent Journal Articles
Functionalized Graphene–PVDF Foam Composites for EMI Shielding
(894–898)Macromolecular Materials and Engineering 296 #10 (2011)
Eswaraiah, Sankaranarayanan and Ramaprabhu of the Indian Institute of Technology, India, prepared foam composites consisting functionalized graphene (f-G) and polyvinylidene fluoride (PVDF). The electrical conductivity increases with the increase in concentration of f-G in insulating PVDF matrix. A dramatic change in the conductivity is observed from 10−16 S · m−1 for insulating PVDF to 10−4 S · m−1 for 0.5 wt.% f-G reinforced PVDF composite, which can be attributed to high-aspect-ratio and highly conducting nature of f-G nanofiller, which forms a conductive network in the polymer. An EMI shielding effectiveness of ≈20 dB is obtained in X-band (8–12 GHz) region and 18 dB in broadband (1–8 GHz) region for 5 wt.% of f-G in foam composite. The application of conductive graphene foam composites as lightweight EMI shielding materials for X-band and broadband shielding has been demonstrated. (RDC 10/13/2011)