Electromagnetic Shielding Materials

Electromagnetic (EM) radiation pollution is becoming more and more serious with increasing use of electrical and electronic devices in our daily lives. Mutual interference among devices such as TVs, computers, mobile phones, and radios can degrade device performance. One technique to meet EM compatibility (EMC) requirements is to shield or block the EM interfering (EMI) signals from being emitted and/or penetrating into a defined space. One example depicted below is the EMI shielding film attached to the filter of a plasma television display panel.

Plasma display panel (PDP) requires an EMI shielding film layer to function reliably.

In modern automobiles, the growing quantity of onboard electronics and microprocessor-controlled systems requires that the electronic sub-assemblies (ESA) in the vehicle meet EMC requirements. If airbag, cruise control, anti-lock braking, or other electronically controlled assemblies are adversely affected by EMI, operation of the vehicle or its critical safety systems could be compromised. As mandated by safety and reliability requirements, the automotive onboard ESAs must not emit EMI signals, and must be immune to external EMI signals.

Metal, in the form of thin sheets or sheathing, is an effective EMI shielding material common in automotive applications. However, metal is expensive, heavy, and prone to corrosion, while adding to the complexity and cost of manufacturing processes. Conductive polymer composites offer a potentially cost-effective and process-friendly alternative to metal. Conventional conductive fillers such as metal flakes, stainless steel fibers, or carbon fibers are dispersed in a polymer matrix creating an electrically conductive network that acts like a Faraday cage. EM radiation is either reflected or absorbed by the shielding composite materials.

Recently, conductive polymer nano-composites have attracted a great deal of academic and industrial interest due to their potential applications in many areas including EMI shielding. In contrast to larger conventional composite fillers, nano-composite fillers have at least one dimension in the nanometer range, including materials such as carbon nanotubes (CNT) and graphite nanoplatelets (GNP). These high-aspect ratio nano-scale fillers form conductive networks much more readily than conventional conductive fillers. Due to larger filler-matrix interface, mechanical and thermal properties may also be enhanced or improved. Furthermore, conductive polymer nano-composites are lighter and more easily processed.

YTCA is currently engaged in research and development of EMI shielding materials for automotive and other applications. One research focus is to optimize dispersion of conductive nano-fillers in the matrix of polymers such as polypropylene (PP). Because of the strong tendency of nanoparticles to agglomerate, uniform dispersion of conductive nano-fillers in the polymer matrix is a considerable challenge. Yet, this is essential to the formation of an effective conductive network at low filler loading. Advancements have been achieved in this area through the use of a proprietary compounding technique.

YTCA is also studying the use of large-scale polymer processing techniques, for producing practical EMI shielding products from conductive polymer nanocomposites. Unlike the research work on filler dispersion optimization, few organizations have addressed the mass-production issue. Promising composite formulation and process techniques are being identified and will then be tested on pre-pilot-production scale.

© 2008 YTC America Inc.