dB Of Shielding Effectiveness Research Articles

Effect of secondary phase on the electromagnetic shielding effectiveness of magnesium alloy

The microstructure, electrical conductivity, and electromagnetic interference (EMI) shielding effectiveness (SE) of Mg-xZn and Mg-xSn (x = 3,5) alloys prepared under different rolling and heat treatment conditions were systematically investigated to understand the effect of secondary-phase orientation on the electromagnetic-shielding property of magnesium alloys. Alloys were rolled to form basal textures and then subjected to different durations of solid-solution treatment and aging to induce the precipitation of secondary-phase particles along a specific direction. Experimental results indicated that in Mg-Zn and Mg-Sn alloys, secondary phases precipitated along directions perpendicular and parallel to the basal plane, respectively. When the direction of the incident electromagnetic wave is perpendicular to the basal plane, precipitates in Mg-Sn alloy parallel to the basal plane improve SE. The increment in SE is mainly attributed to the improvement in the reflection and multiple reflection losses of incident electromagnetic waves, which are caused by increasing the amounts of precipitates with specific orientations. Mg-5Sn alloy subjected to 16 h of solution treatment at 480 °C and 60 h of artificial aging at 170 °C for 60 h exhibited the maximum value of 107–89 dB and maximum increment in SE of 13 dB at 1200 MHz.

Graphite oxide/Polyvinyl alcohol nanocomposites with excellent dielectric and AC conductivity properties for efficient electromagnetic interference shielding

Graphite Oxide (GO) was prepared from graphite powder by Hummer’s method. GO was characterized by X-ray diffraction analysis and Scanning electron microscopy. Frequency dependence of dielectric constant (ε′), dielectric loss tangent (tanδ), a.c. conductivity (σac) and Electromagnetic Interference (EMI) shielding effectiveness (SE) studies have been undertaken on GO blended with polyvinyl alcohol (PVA) in the frequency region 50Hz-5MHz at room temperature. Dielectric properties such as ε′ and tanδ are found to decrease with increase in the frequency. GO/PVA nanocomposites are found to possess exceptionally high dielectric constants of over 10000 below 100Hz. The a.c. conductivity of GO/PVA nanocomposites was found to increase with an increase in the frequency. The SE is found to decrease with an increase in the frequency, exhibiting maximum value 38.87 dB of SE at 50Hz. The highly dielectric GO/PVA nanocomposites were demonstrated a favorable efficient lightweight material for the absorbing of electromagnetic waves at low frequencies.

Structural, dielectric, magnetic and electromagnetic interference shielding investigations of polyaniline decorated Co0.5Ni0.5Fe2O4 nanoferrites

In the present work, we have investigated structural, dielectric, ac conductivity, magnetic and electromagnetic interference (EMI) shielding effectiveness (SE) performance of Co0.5Ni0.5Fe2O4 nanoparticles and Polyaniline (PANI)/Co0.5Ni0.5Fe2O4 nanocomposites for EMI shielding applications. The Co0.5Ni0.5Fe2O4 nanoparticles were synthesized by solution combustion method. PANI/Co0.5Ni0.5Fe2O4 nanocomposites were prepared by in-situ polymerization method. As-prepared samples were examined by using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The microstructural and composition studies have been performed using Field emission scanning electron microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) analysis. Thermal stability of the composite was analyzed using thermo gravimetric analysis (TGA). Frequency dependence of dielectric and ac conductivity (σac) studies have been undertaken on the Co0.5Ni0.5Fe2O4 nanoparticles and PANI/Co0.5Ni0.5Fe2O4 nanocomposites in the frequency range 50 Hz–5 MHz. The electrical conduction mechanism in the synthesized samples found to be in accordance with the electron hopping model. Present Co0.5Ni0.5Fe2O4 nanoparticles and PANI/Co0.5Ni0.5Fe2O4 nanocomposites exhibited hysteretic behavior under the applied magnetic field at room temperature. The maximum values 39.9 and 58.22 dB of SE at 50 Hz were obtained at room temperature for Co0.5Ni0.5Fe2O4 nanoparticles and PANI/Co0.5Ni0.5Fe2O4 nanocomposites respectively. Present Co0.5Ni0.5Fe2O4 nanoparticles decorated with PANI can be recognized as a promising functional material for the absorbing of electromagnetic (EM) waves due to large amount of dipole polarizations in the polymer backbone and at the interfaces of the Co–Ni ferrite nanoparticles and PANI matrix.

Structural, dielectric, ac conductivity and electromagnetic shielding properties of polyaniline/Ni0.5Zn0.5Fe2O4 composites

A conducting polymer, polyaniline (PANI)/Ni0.5Zn0.5Fe2O4 composites with high dielectric absorbing properties and electromagnetic shielding effectiveness at low frequencies were successfully synthesized through a simple in situ emulsion polymerization. PANI was doped with hydrochloric acid to improve its electrical properties and interactions with ferrite particles. PANI/Ni0.5Zn0.5Fe2O4 composites were characterized by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and thermal gravimetric analysis. Frequency dependence of dielectric and ac conductivity (σac) studies have been undertaken on the PANI/Ni0.5Zn0.5Fe2O4 composites in the frequency range 50 Hz–5 MHz. The electrical conduction mechanism in the PANI/Ni0.5Zn0.5Fe2O4 is found to be in accordance with the electron hopping model. Further, frequency dependence of electromagnetic interference (EMI) shielding effectiveness (SE) is studied. The EMI shielding effectiveness is found to decrease with an increase in the frequency. The maximum value 55.14 dB of SE at 50 Hz was obtained at room temperature for PANI/Ni0.5Zn0.5Fe2O4 composites in the 50 Hz–5 MHz frequency range. PANI/Ni0.5Zn0.5Fe2O4 composites were demonstrated as a promising functional material for the absorbing of electromagnetic waves at low frequencies because of a large amount of dipole polarizations in the polymer backbone and at the interfaces of the Ni–Zn ferrite particles and PANI matrix.

An Innovative Package EMC Solution Using a Highly Cost-Effective Sputtered Conformal Shield

High-speed digital and wireless devices radiate undesired electromagnetic noises that affect the normal operation of other devices causing electromagnetic interference (EMI) problems. Printed circuit board (PCB) and system-level shielding may alleviate inter-system EMI between the PCB board and the outside environment, but does not prevent intra-system EMI within the shielding enclosure. Package and System in Package (SiP) level shielding is often used to minimize intra-system EMI issues. An external metal lid is traditionally employed to prevent noise emission from a device, but the cost and size of this technique makes it unattractive for modern electronics. Conformal shielding is gaining momentum due to its size and height advantages. However, high cost and complexity of the sprayed coating shield prevents it from being used for a wide range of low cost commercial applications. In this paper, an innovative shielding technology with sputtered metal conformal shield is investigated using a specially designed test vehicle. By sputtering a conductive material onto a package, a very thin (typically a few μm) metal layer is constructed on the top and around four sides of the package. This thin sputtered metal layer adds virtually zero penalty to the package size. The cost and complexity of the sputtering process is significantly lower compared to a spraying process. Several types of shielded and unshielded modules were built and extensively tested for both far-field and near-field shielding effectiveness (SE) in a semi-anechoic chamber. The performance of the sputtered conformal shield is compared to that of an unshielded module and the sprayed shield. The measured results show that the sputtered shield performs equally well to a sprayed shield, in far field test, with most measurements better than 40 dB of SE. In near field testing, sputtered shields mostly outperform the sprayed shield, especially when compared in the entire scanned region. A well-designed sputtered conformal shield can, therefore, be a very cost-effective EMI solution for a wide range of packages, such as SiP. Also in the paper, a full wave 3D HFSS model is presented and simulated results for both far and near field are compared with measured data.

Study on the graphite nanosheets/resin shielding coatings

Shielding coatings based on graphite nanosheets were prepared by compounding method. The surface morphology of the graphite nanosheets and conductive coatings was examined by scanning electron microscopy. The surface resistivity of the coatings was greatly declined by incorporating the graphite nanosheets. The electromagnetic interference shielding effectiveness (SE) from 0.3 MHz to 1.5 GHz was also studied, and found that the SE of the coatings was consistent with its conductivity. The best sample was shown to exhibit up to 38 dB of SE at 1.5 GHz (with a thickness of 400 μm). The main shielding mechanism of the system was reflection and multiple reflections.

Electromagnetic interference shielding effectiveness of carbon nanofiber/LCP composites

Abstract Vapor grown carbon nanofiber reinforced liquid crystal polymer (LCP) composites were studied. The surface resistivity of LCP was lowered more than 11 orders of magnitude by incorporating 5 wt% of nanofibers. The electromagnetic interference shielding effectiveness (SE) at different frequencies was also studied. The composites were shown to exhibit up to 41 dB of SE. The shielding mechanism of the system was mainly reflection and multiple reflections. The thermal conductivity of the composites showed no significant enhancement with the inclusion of nanofibers.

A novel structure of woven continuous-carbon fiber composites with high electromagnetic shielding

A novel structure employing the woven continuous-carbon fiber (CCF) epoxy composite with high electromagnetic (EM) shielding is presented experimentally and theoretically. The influences of weave type, number, and angle of overlapped plates upon the shielding effectiveness (SE) of the woven CCF-epoxy composite are investigated. The minimum SE of the single, double, and triple-plain or balanced-twill woven CCF-composite plates was measured to be as high as 50 dB, 60 dB, and 70 dB, respectively. More than 100 dB in SE was obtained for the triple-overlapped, plain-weave CCF composite at a frequency of 0.9 GHz. The weight percentage of the single CCF-composite plate required for electronic application is 4.8% only, which is less than one quarter of the CF content, and the performance in SE is 10 dB higher in comparison with long, CF-filled, liquid-crystal polymer (LCP) composites. The SE calculated theoretically is consistent with that measured by the experiment.