Superior Shielding Effectiveness Research Articles

Thin and flexible multi-walled carbon nanotube/waterborne polyurethane composites with high-performance electromagnetic interference shielding

A type of lightweight and flexible multi-walled carbon nanotube (MWCNT)/waterborne polyurethane (WPU) composites is fabricated, which show superior shielding effectiveness (SE) of electromagnetic interference in the X-band even under the thin thickness of samples. The thickness values 0.05, 0.32 and 0.8 mm correspond to SE of 24, 49 and 80 dB, respectively. This attributes to the extremely high MWCNT loading up to 76 wt%. Moreover, the composites show much higher specific SE (up to 3408 dB cm2/g) than other carbon-based polymer composites with similar filler amount. Shielding mechanisms of the composites with wide ranges of MWCNT loadings are discussed based on the concentration, thickness and conductivity. High concentration of MWCNT/WPU composites at low thicknesses indicates higher capability of shielding by absorption compared to reflection, which is adverse to composites with relatively low MWCNT mass ratios. A comparison between experimental and theoretical SE results is made in detail based on observed microstructures by scanning electron microscopy. The MWCNT/WPU composite films fabricated on large-area polyimide and cloth substrates are also demonstrated.

Enhanced Electromagnetic Interference Shielding of Mg–Zn–Zr Alloy by Ce Addition

The effects of Ce addition on microstructure and electromagnetic interference (EMI) shielding response of Mg–6Zn–0.5Zr (ZK60) alloy have been investigated. Ce addition resulted in grain refinement and higher density of Mg–Zn–Ce and MgZn2 intermetallic particles in the alloy. In particular, this was substantially remarkable as the addition of Ce was up to 1.0 wt%. It is interesting to note that as-extruded ZK60 alloy with 1.0 wt% Ce addition exhibited an EMI shielding effectiveness (SE) exceeding 70 dB at the frequency range of 30–1,500 MHz, which was significantly higher than that of ZK60 alloy without Ce addition and reached the requirement of high protection. The superior SE was probably related to the increased reflection and multiple reflection of electromagnetic radiation induced by Ce addition. Direct artificial aging at 150 °C for 25 or 50 h led to a further increase of 7–10 dB in the SE of the alloy with 1.0 wt% Ce addition. The advantages of excellent shielding capacity and favorable mechanical strength make the Mg–Zn–Zr–Ce alloy an attractive shielding candidate material for a variety of technological applications.

Structured Reduced Graphene Oxide/Polymer Composites for Ultra‐Efficient Electromagnetic Interference Shielding

A high‐performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high‐pressure solid‐phase compression molding. Superior shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO loading owning to multi‐facet segregated architecture with rGO selectively located on the boundaries among PS multi‐facets. This special architecture not only provides many interfaces to absorb the electromagnetic waves, but also dramatically reduces the loading of rGO by confining the rGO at the interfaces. Moreover, the mechanical strength of the segregated composite is dramatically enhanced using high pressure at 350 MPa, overcoming the major disadvantage of the composite made by conventional‐pressure (5 MPa). The composite prepared by the higher pressure shows 94% and 40% increment in compressive strength and compressive modulus, respectively. These results demonstrate a promising method to fabricate an economical, robust, and highly efficient EMI shielding material.

Temperature Dependencies of the Permittivities and Microwave Shielding Effectiveness of a Carbon-containing Electrically Conductive Concrete

AbstractConductive concrete is a construction material that can be utilized for a number of applications: in particular, electromagnetic shielding. In this research, the microwave shielding effectiveness of a carbon containing electrically conductive concrete was determined from both the real and the imaginary permittivities. Also, the permittivities and the shielding effectiveness of a normal concrete were determined for comparison purposes. It was shown that the permittivities of the conductive concrete were significantly higher than those of the normal concrete. The shielding abilities of both of the concretes were determined as a function of concrete thickness and temperature, and the conductive concrete had a superior shielding effectiveness. For the normal concrete, at room temperature and a frequency of 912 MHz, a shielding effectiveness of 30 dB was achieved for a thickness of about 400 cm. For the conductive concrete, under the same conditions, a thickness of only about 3 cm was required to achieve the same shielding effectiveness.

Enhanced electromagnetic interference shielding in ZK60 magnesium alloy by aging precipitation

Electromagnetic interference shielding, hardness, and electrical conductivity measurements were employed to evaluate the effect of aging precipitation on shielding characteristics of ZK60 magnesium alloy. During artificial aging MgZn2 phase precipitates occurred and the age hardening peak happened at 150°C for 15h. Aging precipitation induced enhanced shielding effectiveness as well as tensile strength in the alloy. It is interesting to note that the shielding effectiveness exhibited a rapid increase with increase in aging time until 15h, but for longer aging time it tended to remain largely unchanged. Artificial aging at 150°C for 15h can thus be considered as the optimum heat treatment condition. In this condition, the good combination of superior shielding effectiveness greater than 70dB and high mechanical properties was achieved. The origin of the attractive electromagnetic interference shielding properties is discussed based on second phase precipitation in the alloy.