Mithali Chengappa

Bio: Mithali Chengappa is an academic researcher. The author has contributed to research in topics: Buckypaper & Electromagnetic shielding. The author has an hindex of 1, co-authored 1 publications receiving 9 citations.

Lightweight, flexible and thin Fe3O4-loaded, functionalized multi walled carbon nanotube buckypapers for enhanced X-band electromagnetic interference shielding

Abstract: Electromagnetic interference (EMI) is undesirable and uncontrolled interference with the signal of intelligence. This is controlled by using either novel materials, or appropriate electronic design or a combination of both. In this context, functionalized multiwalled carbon nanotubes (FMWCNTs) have been proposed to use as EM shielding materials because of their promising electromagnetic properties, high flexibility, and high electrical conductivity. The non-functionalised MWCNTs does not demonstrate high shielding of electromagnetic waves but with acid functionalisation and further loading with optimized nanoparticles of Fe3O4, enhanced absorption (15.85 dB), enhanced reflection (9.43 dB), resulted in high total specific shielding effectiveness of around 49.56 dB (g cm−3)−1. All samples were light weight, flexible, thin and self-standing in the form of a buckypaper of thickness of 50 µm and density of 0.51 g cm−3. These buckypapers could be promising materials for electromagnetic shielding via both absorption and reflection. A fine amalgamated system of MWCNTs with half metallic Fe3O4, resulting in enhanced conductivity, in an extremely thin and flexible matrix, is considered to be the main contribution to these high shielding effectiveness values.

Enhanced thermomechanical and electrical properties of multiwalled carbon nanotube paper reinforced epoxy laminar composites

Abstract: Thermomechanical and electrical properties of multiwalled carbon nanotubes (MWCNTs) bucky paper reinforced epoxy laminar composites have been studied. Incorporation of bucky paper in epoxy matrix led to improvement in thermomechanical properties but it reduced through-plane electrical conductivity. Therefore, 0.05 wt.% of MWCNTs is incorporated as secondary network in epoxy matrix to improve the electrical conductivity. The storage modulus for a 0.05 wt.% dispersed MWCNTs in epoxy resin impregnated 20 plies of bucky paper based composites (20Ply.05) was 4.84 GPa as compared to 2.24 GPa of pure epoxy. The glass transition temperature of 20Ply.05 laminar composite reaches to 191.6 °C as compared to pure epoxy (168.5 °C). The increment in electrical conductivity (792%) is reflected in improved electromagnetic shielding effectiveness (SE) over a wide frequency range of X & Ku band. The SE of more than 50 dB for 20Ply.05 laminar composite in both the bands was obtained.

Role of spin disorder in magnetic and EMI shielding properties of Fe3O4/C/PPy core/shell composites

Abstract: Novel core/shell Fe3O4/C/polypyrrole (PPy) composites were prepared via facile hydrothermal and chemical oxidative polymerization method. The obtained Fe3O4/C/PPy exhibits a dual core–shell structure in which an intermediate carbon layer provides excellent electrical connectivity between Fe3O4 nanoparticles and PPy polymer. Further, these trilaminar core/shell composites were investigated for EMI shielding material to prevent EMI pollution. The excellent EMI shielding efficiency (> 28) dB was attained for Fe3O4/C:PPy (2:8 wt/wt) at thickness 0.8 mm which is mainly governed by absorption. Additional evidence of superior EMI absorption performance is the magnetic property of Fe3O4/C:PPy composites. It was observed that magnetic properties of Fe3O4/C:PPy composites highly depend on the content and thickness of the shell which influences the spin motion of Fe3O4 nanoparticles. Thus, it is anticipated that spin motion plays a decisive role in EMI shielding performance of Fe3O4/C/PPy composites.

Enhanced electromagnetic interference shielding properties of carbon fiber veil/Fe3O4 nanoparticles/epoxy multiscale composites

Abstract: The multiscale approach has been adapted to enhance the electromagnetic interference shielding properties of carbon fiber (CF) veil epoxy-based composites. The Fe3O4 nanoparticles (NPs) were homogeneously dispersed in the epoxy matrix after surface modification by using silane coupling agent. The CF veil/Fe3O4 NPs/epoxy multiscale composites were manufactured by impregnating the CF veils with Fe3O4 NPs/epoxy mixture to prepare prepreg followed by vacuum bagging process. The electromagnetic interference shielding properties combined with the complex permittivity and complex permeability of the composites were investigated in the X-band (8.2–12.4 GHz) range. The total shielding effectiveness (SET) increases with increasing Fe3O4 NPs loadings and the maximum SET is 51.5 dB at low thickness of 1 mm. The incorporation of Fe3O4 NPs into the composites enhances the complex permittivity and complex permeability thus enhancing the electromagnetic wave absorption capability. The increased SET dominated by absorption loss SEA is attributed to the enhanced magnetic loss and dielectric loss generated by Fe3O4 NPs and multilayer construction of the composites. The microwave conductivity increases and the skin depth decreases with increasing Fe3O4 NPs loadings.

Carbon coated paramagnetic Fe 3 O 4 nanoparticles decorated MWCNTs-GNS composites: synthesis, characterization and their excellent electromagnetic absorption properties

Abstract: Carbon coated paramagnetic Fe3O4 nanoparticles decorated multi-wall carbon nanotubes (MWCNTs)—graphene (GNS) composites were synthesized. In addition, we studied the influence of the magnetic nanoparticle content on the absorbing properties. The results showed that the frequency corresponding to the maximum absorption shifted toward the lower frequency with the increase content of the magnetic nanoparticles. The results indicated that combination of graphene-MWCNTs with carbon coating and Fe3O4 nanoparticles can improve the impedance matching. In the composites, Fe3O4 nanoparticles improved the magnetic loss, and the graphene as well as the MWCNTs improved the dielectric loss. In addition, the presence of carbon coating enhanced the Debye dipole and dipole polarization, which enhanced the dielectric loss. The carbon coated paramagnetic Fe3O4 nanoparticles decorated MWCNTs-GNS composites that were composed of approximately 60% Fe3O4 nanoparticles showed the best electromagnetic absorption properties. The maximum reflection loss was − 57.13 dB at 6.1 GHz with a thickness of 3.4 mm.

Absorption Dominated Directional Electromagnetic Interference Shielding through Asymmetry in a Multilayered Construct with an Exceptionally High Green Index.

Abstract: Fabricating green electromagnetic interference (EMI) shields is the need of the hour because strong secondary reflections in the vicinity of the shield adversely affect the environment and the reliability of the neighboring devices. To this end, the present work aims to maximize the absorption-based EMI shielding through a multilayered construct comprising a porous structure (pore size less than λ/5), a highly conducting entity, and a layer to match the impedance. The elements of this construct were positioned so that the incoming electromagnetic (EM) radiation interacts with the other layers of the construct before the conducting entity. This positioning of the layers in the construct offers a high green shielding index (gs) and low reflection coefficient (R ∼ 0.1) with an exceptionally high percent absorption (up to 99%). Polyurethane (PU) foams were fabricated using the salt-leaching technique and strategically positioned with carbon nanotube (CNT) papers and polycarbonate (PC)-based films to obtain symmetric and asymmetric constructs. These structures were then employed to gain mechanistic insight into the directional dependency of shielding performance, gs, and heat dissipation ability. Interestingly, maximum total shielding effectiveness (SET) of -52 dB (88% absorption @8.2 GHz) and specific shielding effectiveness/thickness (SSEt) of -373 dB/cm2g were achieved for a symmetric construct whereas, for the asymmetric construct, the SET and SSEt were -37 dB and -280 dB/cm2g, respectively, with an exceptionally high gs of 8.6, the highest reported so far. The asymmetricity in the construct led to directional dependence of the absorption component (% SEA, shielding effectiveness due to absorption) and heat dissipation, primarily governed by the electrical and thermal conductivity gradient, respectively. This study opens new avenues in this field and reports constructs with an exceptionally high green index.