Papers by Keyword: Shielding Effectiveness

Abstract: Electric and electronic devices are mainly emitting electromagnetic radiation, and shielding from radiation is essential. Electrically conductive materials are suitable for radiation shielding applications. The designing of the textile material for the radiation shielding is challenging because of its open area and design. In general, more open area has transmit the radiations tend to lesser in shielding. Another factor is the laying angle of the textile material also plays important role beyond open area. In this study, the effect of laying angle and open area was analysed for effective utilization of conductive materials. The conductive nonwoven fabric was used to form as strips to simulate the various textile structures for shielding application. The Cu/Ni coated ultrathin polyester nonwoven fabric sample is taken to form two-layers strips and test for electromagnetic shielding effectiveness. In experimental design, three factors of strips which are strips laid angle, strip thickness, and gap between the strips are taken at three levels. The strip cover area and aperture area were calculated geomentrically for each design and significant difference on shielding effectiveness was noticed.

Abstract: Electromagnetic shielding materials are widely used in engineering. Shielding effectiveness is an important index to measure the shielding effect of electromagnetic shielding materials. A method for calculating the shielding effectiveness of electromagnetic shielding materials is discussed in this paper. This method applies the small reflection theory in transmission line theory. Two kinds of materials are selected as samples. Firstly, the shielding performance is calculated by calculation. Then, shielding performance was measured using a network analyzer and coaxial devices. By comparing the above two results, the feasibility of this method is verified. By using this method, the shielding performance with acceptable accuracy can be obtained when the electromagnetic parameters of the material are known. Thus, the limitation for the application of electromagnetic shielding materials is reduced.

Abstract: The nickel fiber was added into the cement-based composite materials as a shielding medium. Influences of the three different types and amount of dispersants and weight fraction of nickel fiber on the electrical conductivity and electromagnetic shielding effectiveness of the cement matrix composite were discussed. The conductivity of cement based composite materials and the uniformity distribution of shielding medium were characterized by four-point probe meter and scanning electron microscopy, respectively. Electromagnetic interference shielding effectiveness in the frequency range of 1 MHz to 1500 MHz was characterized by coaxial cable method. The results indicated that the improved dispersion of nickel by incorporation of dispersants might yield the enhancement of the electrical properties of nickel fiber-reinforced cement composites. When the dosage of methyl cellulose reaches 0.4 wt.%, the pre-dispersing nickel fiber enhances the electrical conductivity of the cement-based composite materials significantly. With the increase of fiber volume fraction, the shielding effectiveness and trend of frequency change of the corresponding fiber-reinforced concrete were enhanced. When the content of nickel fiber powder was 9.0 vol.%, the conductivity was 2.65×10^-3 s·cm^-1, and the average shielding effectiveness of the specimen in 1MHz-1500 MHz was about 21.78 dB, with the maximum shielding effectiveness of 24.48 dB and the minimum shielding effectiveness 19.85 dB.

Abstract: An amorphous Ni-Fe-P alloy coated shielding fabric with dense uniform coating was prepared by conducting electrical deposition of amorphous Ni-Fe-P alloy on copper-coated polyethylene terephthalate (PET) fabric. This research investigated the preparation process by using orthogonal test with 8 factors and 3 levels. It analyzed the influences of components of the plating solution on the ohms per square, weight gain rate, and shielding effectiveness of coating. Besides, the morphology, composition, and structure of the coating were analyzed by using Scanning Electron Microscope (SEM), Energy Dispersive Spectrdmeter (EDS), and X-ray Diffraction (XRD). The shielding effectiveness of the alloy fabric was also tested. The results indicated that the processing conditions of the amorphous Ni-Fe-P alloy coated fabric using electrical deposition consisted of 135 g/L of NiSO₄•6H₂O, 105 g/L of FeSO₄•7H₂O, 8 g/L of NaH₂PO₂•H₂O, 24 g/L of C₆H₈O₆, 36 g/L of C₆H₈O₇, 22 g/L of H₃PO₃, 65°C, pH=1.5, and current density =13 A/dm². The fabric obtained in the paper presented compact, smooth, and uniform coating with fine crystal. The coating was the amorphous Ni-Fe-P alloy with 18.67% of P (mass fraction). The shielding effectiveness of this coated fabric reached to 60.82 dB-73.63 dB in a broad frequency range of 300 kHz-1.5 GHz.

Abstract: In this study lightweight carbon fiber and multiwalled carbon nanotubes filled hybrid nanocomposite was fabricated for electromagnetic interference (EMI) shielding in spacecraft. Electrical conductivity was conducted to assess the affect of MWCNT addition on composite. EMI shielding effectiveness (SE) was tested in the frequency range of 1-18 GHz. Comparison of SE was also made with AA6061-T6 sheet. Dispersion of nanotubes in the matrix was examined through microscopy. Results indicated that the conductivity was increased with increasing MWCNTs up to 0.25 wt%. Higher loading level of MWCNTs has resulted in decrease in conductivity due to agglomeration in cured samples. Hybrid nanocomposite exhibited improved SE than AA6061-T6 in 1-8 GHz frequency range. Best SE and electrical conductivity was witnessed in 0.25 wt% MWCNT sample. EMI SE in range of-20 dB to-40 dB can be easily achieved in our developed material.

Abstract: With quasi-static field approximation, an analytic formula is derived for shielding effectiveness analysis of a spherical shield made of medium conductivity material (10 S/m-1000 S/m) against low-frequency electric field. The effects of frequency, material conductivity, and shield dimensions on shielding effectiveness are investigated. It is shown that the shielding effectiveness decreases at first and then increases with the frequency increasing from DC to MHz if the thickness of the shield is large. However, the shielding effectiveness decreases versus the increase of frequency continuously if the thickness is small. The shielding effectiveness can be enhanced by increasing either the material conductivity or the shield thickness. This research is helpful for the evaluation of composite conductive material for electromagnetic shielding applications.

Abstract: The carbon coils (d-CCs) having the diverse geometries were deposited on Al₂O₃ substrate by continuous injection of SF₆ in C₂H₂ source gas under the thermal chemical vapor deposition system. d-CCs with polyurethane (PU) composites (d-CCs@PU) were fabricated by dispersing d-CCs in PU solvent with dimethylformamide (DMF) additive. The electromagnetic wave shielding properties of d-CCs@PU composites were investigated in the frequency range of 0.25-1.5 GHz. The shielding effectiveness (SE) of d-CCs@PU composites were measured and discussed according to the weight percent of d-CCs in CCs@PU composites and the thickness of d-CCs@PU composites layers. Based on these results, we discussed the shielding properties of d-CCs@PU composites and the main mechanism of the SE in this work.

Abstract: Anechoic chambers are widely used in performing EMC measurements according to the established EMC standards. In space area, the elements of EMC measurements such as emission, immunity and susceptibility are critically important to ascertain that all of electrical and electronic components in the satellite body will function correctly without fail, thus ensures the smoothness of satellite operation upon launching into space. Realising this, level of anechoic chamber performance should always be in the optimum state as possible. This paper presents the specific tests that were carried out in the anechoic chamber as to determine the accuracy of its performance. All four types of tests were run in main chamber, control and amplifier room within frequencies range of 10 kHz to 20GHz. The tests will characterize the shielding effectiveness of RF shielded enclosure, the Field Uniformity Area (FUA), Site VSWR and Normalised Site Attenuation (NSA) of anechoic chamber. The basis of the measurement techniques is described and typical test results are discussed. Based on the results, it is concluded that the anechoic chamber is in good condition, ready for testing and capable to produce reliable output.

Abstract: The coupling effect under HEMP calculation model of the shielding control box is established with the CST software. The shielding effectiveness of the shielding control box with different incidence directions of HEMP were studied on, and the field distribution of the shielding control box was analyzed. The results show that incidence direction of HEMP in the depth direction of the gap and perpendicular to the long side of the gap can provide the worst electromagnetic pulse protection of shielding control box. The coupling field of the complex system box has resonant characters. The gap filled with conductive rubber can effectively reduce the coupling of electromagnetic energy pulse.

Abstract: Electromagnetic interference easily appears in the propulsive wheel - a key component of the mobile robots, because internal space of propulsive wheel is very small, there are numerous electronic devices, and signal communication is complex. So electromagnetic shielding is very important for the propulsive wheel. In this paper, a wheel model and an equivalent source model of electromagnetic interference of the wheel were developed based on considerations of the internal electromagnetic properties. At the same time, a secondary source of electromagnetic interference is formed by heat sink. Hence, shielding effectiveness is taken as one of the evaluation criteria for the Electro-Magnetic Compatibility (EMC) problem, and the Genetic Algorithm (GA) in the software Ansoft HFSS platform was used to optimize the first resonance frequency of heat sink.