Abstract
Nanocomposite foam with a large expansion ratio and thin cell walls is promising for electromagnetic interference (EMI) shielding materials, due to the low electromagnetic (EM) reflection and high EM absorption. To overcome the dimensional limitation from two-dimension (2D) thin walls on the construction of conductive network, a strategy combining hybrid conductive nanofillers in semi-crystalline matrix together with supercritical CO2 (scCO2) foaming was applied: (1) one-dimension (1D) CNTs with moderate aspect ratio was used to minimize the dimensional confinement from 2D thin walls while constructing the main EM absorbing network; (2) zero-dimension (0D) carbon black (CB) with no dimensional confinement was used to connect the separated CNTs in thin walls and to expand the EM absorbing network; (3) scCO2 foaming was applied to obtain a cellular structure with multi-layer thin walls and a large amount of air cells to reduce the reflected EM; (4) semi-crystalline polymer was selected so that the rheological behavior could be adjusted by optimizing crystallization and filler content to regulate the cellular structure. Consequently, an advanced material featured as lightweight, high EM absorption and low EM reflection was obtained at 0.48 vol.% hybrid nanofillers and a density of 0.067 g/cm3, whose specific EMI shielding performance was 183 dB cm3/g.
Highlights
Nowadays, with the increasing demand of high-performance communication equipment in industry, medical treatment, military and many other aspects, the transmission of electromagnetic (EM) waves especially at high frequency become important [1]
The way that electromagnetic interference (EMI) shielding material works is to reflect and absorb EM repeatedly to block the transmission of a redundant signal [5]
Along with increasing bandwidth in mobile communication equipment, a high frequency signal requires less reflective. This means the advanced EMI shielding materials absorb the incident redundant signal in very high efficiency but reflect the incident redundant signal in an extremely low efficiency. Due to this the redundant signal could be fully absorbed by the EMI shielding material and be blocked from both transmission and reflection [6,7,8]
Summary
With the increasing demand of high-performance communication equipment in industry, medical treatment, military and many other aspects, the transmission of electromagnetic (EM) waves especially at high frequency become important [1]. EMI shielding materials are an important issue to guarantee the high performance and signal integrity in communications equipment [4]. The way that EMI shielding material works is to reflect and absorb EM repeatedly to block the transmission of a redundant signal [5]. Along with increasing bandwidth in mobile communication equipment, a high frequency signal requires less reflective. This means the advanced EMI shielding materials absorb the incident redundant signal in very high efficiency but reflect the incident redundant signal in an extremely low efficiency. The high-end mobile communication equipment of signal integrity, accuracy and reliability is calling for advanced lightweight
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