Lightweight porous materials for electromagnetic interference (EMI) shielding applications are reviewed. EMI shielding refers to the capability of a material to protect from electromagnetic fields (EMFs) generated by electronic devices. Traditionally conducting metals are used in EMI shielding applications, which are slowly being replaced by conducting polymer based shields. This review is narrowly focused on understanding the approaches related to porous high EMI shielding composite materials that have very low density values. While metallic fillers can increase the EMI shielding capabilities of polymers, they also increase the weight, which can be offset by inducing the porosity in the matrix. Porosity is found to be effective in providing higher shielding effectiveness at low filler volume fraction due to concentrating the filler in the solid polymers. However, use of gas porosity results in composites with low mechanical properties. This problem can be alleviated to some extent by reinforcing polymer foams with lightweight conductivefillers such as carbon nanofibers (CNFs), carbon nanotubes (CNTs) and graphene. But the properties of pores such aspore size and distribution cannot be effectively controlled in such cases. Syntactic foams containing hollow particle fillers seem to be the best combination of EMI shielding capabilities and mechanical properties. These composites can be either filled with a second phase conducting filler, or hollow particles can be coated with a conducting layer, or hollow particles made of conducting materials can be used as fillers. The hollow particle wall thickness and volume fractions can be optimized to obtain the desired combination of properties in syntactic foams to enable their multifunctional applications.

A review of porous lightweight composite materials for electromagnetic interference shielding

Fabrication and characterisation of Al–7Si–0.35Mg/fly ash metal matrix composites processed by different stir casting routes

Tribological behaviour of powder metallurgy-processed aluminium hybrid composites with the addition of graphite solid lubricant

In this contribution, authors present a review on the state-of-the-art in the utilization of industrial and agricultural waste materials for the development of metal–matrix composites (MMCs), providing, through the judicious analysis of an ample and varied references source – from the oldest to the newest ones – an insight into the challenges and opportunities for the exploitation to their full potential. In addition to its topicality, the novelty of this contribution lies in the presentation of key statistical, technical, and property-related information of a comprehensive variety of waste materials classed into two main groups, namely, fly ash reinforced MMCs and MMCs derived from other waste materials. Although fly ash has been exploited in a broad range of applications, the attention paid for its use in the development of MMCs seems to be insufficient. A purposely designed chart helped to pinpoint the more demanding and profitable applications of fly ash, and establish strategic opportunity ar...

Development of metal-matrix composites from industrial/agricultural waste materials and their derivatives

The demand for new materials in the field of electromagnetic interference shielding has increased dramatically in the last few decades due to the advancements in the electronics industry. To meet these growing demands, many new materials are being investigated to replace traditionally used metal sheets. Some of the promising materials being researched are polymer-based composites due to their low specific weight, ease of fabrication, and low cost. Some researchers have also looked into the modification and synthetization of new metal-based shielding materials. One of the significant disadvantages of modifying metallic materials is the reduction of their electrical conductivity that adversely affects the shielding effectiveness. Hence, the modifications carried out should be able to maintain the shielding effectiveness at high values while eliminating the shortcomings of metal sheets. In this review article, novel metal-based materials are analyzed for their shielding effectiveness. While some of the materials reviewed in this paper are merely metal-based composites, others consist of more complex additives including metal oxides and carbides. Apart from the shielding effectiveness, this article analyses the variation of other important properties such as electrical conductivity and mechanical properties for a few of these materials.

A review on recent advancement of electromagnetic interference shielding novel metallic materials and processes

The cenosphere and precipitator fly ash particulates were used to produce two kinds of aluminum matrix composites with the density of 1.4–1.6 g cm −3 and 2.2–2.4 g cm −3 separately. The electromagnetic interference shielding effectiveness (EMSE) properties of the composites were measured in the frequency range of 30.0 kHz–1.5 GHz. The results indicated the EMSE properties of the two types of composites were nearly the same. By using the fly ash particles, the shielding effectiveness properties of the matrix aluminum have been improved in the frequency ranges 30.0 kHz–600.0 MHz and the increment varied with increasing frequency. The EMSE properties of 2024Al are in the range −36.1 ± 0.2 to −46.3 ± 0.3 dB while the composites are in the range −40.0 ± 0.8 to −102.5 ± 0.1 dB in the frequency range 1.0–600.0 MHz. At higher frequency, the EMSE properties of the composites are similar to that of the matrix. The tensile strength of the matrix aluminum has been decreased by addition of the fly ash particulate and the tensile strength of the composites were 110.2 MPa and 180.6 MPa separately. The fractography showed that one composite fractured brittly and the other fractured in a microductile manner.

Electromagnetic shielding effectiveness of aluminum alloy–fly ash composites

Mechanical properties of SiC/Gr/Al composites fabricated by squeeze casting technology

Fly-ash cenosphere particles were used as mixture in aluminum matrix composite by squeeze casting method [1]. The electromagnetic interfering shielding effectiveness (EMISE) was investigated in the frequency range from 0.03 MHz to 1.5 GHz. It showed the SE value of Al2024/cenospheres composite (ACC) is higher than that of aluminum alloy, and comparative to traditional material 1J50. Unlike 1J50, the mechanism of EMI shielding for ACC is reflection and multiple reflections. Analyzed by XRD and SEM, chemical reactions may occur between the matrix and cenosphere particles during the casting procedure, but it affects the shielding effectiveness little.

Electromagnetic interfering shielding of aluminum alloy–cenospheres composite

A structure factor k was used to investigate the relations between aspect ratio of ligaments and yield strength of open-cell Fe–Ni foams. The results indicated yield strength of Fe–Ni open-cell foam increased with the decreasing aspect ratio of ligaments, and varying cross-section of ligaments had distinct effect on compressive properties of Fe–Ni open-cell foams. The yield strength predicted by the uniform cross-section ligament model ( k  = 1) agreed well with experimental values within the relative density of 2.5–5%, while the varying cross-section of ligaments with k  = 0.85 was suitable for the foams with relative density lower than 2.5%.

Xiaoli Huang

Papers

Electromagnetic shielding effectiveness of aluminum alloy–fly ash composites

Mechanical properties of SiC/Gr/Al composites fabricated by squeeze casting technology

Electromagnetic interfering shielding of aluminum alloy–cenospheres composite

Compressive properties of open-cell Fe–Ni foams