ELECTROMAGNETIC INTERFERENCE occurs when electronic equipment and devices are subjected to ELECTROMAGNETIC radiation from unwanted sources at high intensity in the working frequency ranges of these devices. INTERFERENCE interrupts and degrades the effective performance of these equipments. ELECTROMAGNETIC INTERFERENCE shielding is the process of reaching sufficient attenuation level of the waveseither by reflection or absorption respectively at the surface and in the body of the shielding materials. In this study, the shielding effectiveness of epoxy-graphene nanoeomposites was. investigated. Graphene was first synthesized and charaeterized and graphene-epoxy nanocomposite samples upto 3wt% grapheme were fabricated by casting method. Then shielding effectiveness of samples in the 8 to 12GHz (X band) was investigated. Results showed the ELECTROMAGNETIC INTERFERENCE shielding ability of these nanocomposites such that shielding effectiveness of 22.3 and 17.6dB at 12 and 8GHz was attained respectively for 3wt% graphene sample. The dominant mechanism of shielding in the range of graphene composition and test frequencieswas absorption so that the 3wt% graphene sample showed 89.7 and 81.8 percent at 12 and 8GHz respectively. This result indicated that these nanocomposites were appropriate candidates for absorbing ELECTROMAGNETIC waves.

Measurements of the high frequency ELECTROMAGNETIC INTERFERENCE (EMI) of a pulse tube cryocooler are made in a typical laboratory environment using laboratory-made current transformers. The inverter makes high frequency EMI which could cause severe INTERFERENCE with SQUID operation inside the Pulse Tube cryocooler. By covering the power lines, which include a neutral line, of the valve motor with a copper mesh cover, as a ground line, one order decrease in the magnitude of the EMI noise is successfully obtained. This paper describes one example to show how to observe and reduce conducted high frequency noise currents in a precision experimental system.

Measurements of the high frequency ELECTROMAGNETIC INTERFERENCE (EMI) of a pulse tube cryocooler are made in a typical laboratory environment using laboratory-made current transformers. The inverter makes high frequency EMI which could cause severe INTERFERENCE with SQUID operation inside the pulse tube cryocooler. By covering the power lines, including a neutral line, of the valve motor with a copper mesh cover, as a ground line, one order decrease in the magnitude of the EMI noise is successfully obtained. This paper describes an example to show how to observe and reduce conducted high frequency noise currents in a precision experimental system.

Conducting polymers represent a class of materials that possess unique combination of electrical conductivity, processability, and mechanical properties. One of the most important applications of these materials is ELECTROMAGNETIC INTERFERENCE shielding which are receiving increasing attention by progress of technology and increment in the amount of ELECTROMAGNETIC waves sources. In the present study, attempts have been made to prepare improved ELECTROMAGNETIC INTERFERENCE shielding (EMI-SE) material of flexible composite films based on thermoplastic urethane (TPU) and graphene nanosheets. For this purpose, the prepared graphene oxide using Hummer’ s method has been thermally reduced. Then the surface of the graphene was grafted with polar and long molecules of 2-aminoethyl methacrylate (AEMA) and denoted as functionalized graphene nanosheets (FGN). Then the nanocomposites with various loadings of FGN were fabricated by solution mixing. The increased compatibility between TPU segments and FGN due to graphene modification leads to increase in electrical conductivity. Moreover, the intensified interactions and improved dispersion state of the FGN increase viscous motions and energy dissipation which leads to higher EMI SE. Results showed that the TPU based nanocomposite containing only 5 vol. % of FGN attenuate ELECTROMAGNETIC wave energy up to 99. 8%.

Hypothesis: Nowadays, lightening of polymer composites for specific applications and engineering purposes, especially ELECTROMAGNETIC wave absorber materials, has attracted research studies. In this work, polypropylene nanocomposite and hybrid foams incorporated with carbon nanotubes and glass fibers were produced through solid-state microcellular foaming using supercritical carbon dioxide. Methods: First, the microstructure of nanocomposites, hybrids, and produced foams were examined by scanning electron microscopy. The electrical properties and ELECTROMAGNETIC INTERFERENCE shielding performance of the solid and foamed nanocomposites were investigated using a four-point probe method and a vector analyzer, respectively. The effect of glass fiber and CNT incorporation on tensile, compressive, and impact mechanical properties was also investigated. Findings: Nanotubes were finely dispersed in the polypropylene matrix through melt compounding. By incorporation of CNTs, the average cell size reduced (from 49 to 22. 5 μ, m), and cell density increased. Also, the SEM micrographs of the hybrid foams revealed that, in general, cell size increased by incorporating fiber due to nearby heterogeneous nucleation, and the size of cells that were not adjacent to the fiber decreased. As a result, a bimodal microstructure with two different cell sizes was obtained. With the incorporation of CNTs, electrical conductivity increased from ~10-16 to ~10-4 and ~10-5 for unfoamed and foamed PP/CNT3 samples, respectively, and EMI shielding effectiveness increased to 11 dB and 9. 5 dB for unfoamed and foamed PP/CNT3 samples, respectively. The mechanical test results showed that the addition of nanoparticles help to improve mechanical properties, including tensile, compression and impact. In solid samples, the addition of glass fiber improves the modulus and tensile strength, but due to poor interaction with polypropylene, it reduces the tensile properties of the foams. The results of both compression and impact resistance tests of foams showed that these properties are enhanced with the addition of fibers and nanoparticles.

The application of conductive particles with segregated distribution in the polymeric matrices is one of the most effective ways to reduce percolation threshold, increase conductivity, and improve ELECTROMAGNETIC INTERFERENCE (EMI) shielding properties. In this study, mechanical mixing and hot compression molding were used to fabricate polyethylene/carbon black composite with segregate structure and random distributions. Scanning electron microscope images showed that during the mechanical mixing process, the polymeric granules were well coated with carbon black. besides, there is good relation between conductivity and well dispersed of carbon black on the surface of HDPE granules. The electrical conductivity of segregated structure composite ( 2 wt% carbon black) increased about 3000 times compared to the random structure(2%wt carbon black). Using the vector network analyzer, it was revealed that by increasing the black carbon content from 2 to 5 wt%, the maximum EMI shielding effectiveness of the composite increased from 6 dB to 16 dB, respectively.