B.V. Bhaskara Rao

Bio: B.V. Bhaskara Rao is an academic researcher from Defence Institute of Advanced Technology. The author has contributed to research in topics: Dielectric & Electromagnetic shielding. The author has an hindex of 6, co-authored 8 publications receiving 133 citations.

Single-layer graphene-assembled 3D porous carbon composites with PVA and Fe3O4 nano-fillers: an interface-mediated superior dielectric and EMI shielding performance

Abstract: In this study, a novel composite of Fe3O4 nanofiller-decorated single-layer graphene-assembled porous carbon (SLGAPC) with polyvinyl alcohol (PVA) having flexibility and a density of 0.75 g cm−3 is explored for its dielectric and electromagnetic interference (EMI) response properties. The composite is prepared by the solution casting method and its constituents are optimized as 15 wt% SLGAPC and 20 wt% Fe3O4 through a novel solvent relaxation nuclear magnetic resonance experiment. The PVA–SLGAPC–Fe3O4 composite shows high dielectric permittivity in the range of 1 Hz–10 MHz, enhanced by a factor of 4 as compared to that of the PVA–SLGAPC composite, with a reduced loss by a factor of 2. The temperature dependent dielectric properties reveal the activation energy behaviour with reference to the glass transition temperature (80 °C) of PVA. The dielectric hysteresis with the temperature cycle reveals a remnant polarization. The enhanced dielectric properties are suggested to be the result of improvement in the localized polarization of the integrated interface system (Maxwell–Wagner–Sillars (MWS) polarization) formed by the uniform adsorption of Fe3O4 on the surface of SLGAPC conjugated with PVA. The EMI shielding property of the composite with a low thickness of 0.3 mm in the X-band (8.2–12.4 GHz) shows a very impressive shielding efficiency of ∼15 dB and a specific shielding effectiveness of 20 dB (g cm−3)−1, indicating the promising character of this material for flexible EMI shielding applications.

Comparative evaluation of MAX, MXene, NanoMAX, and NanoMAX-derived-MXene for microwave absorption and Li ion battery anode applications.

Abstract: MAX and MXene phases possess unique physical properties, encompassing the realms of both ceramics and metals. Their nanolaminated layered configuration, high anisotropic electrical conductivity, and ability to scatter electromagnetic radiation are beneficial in multiple applications. Herein, detailed applications of MAX and MXene are studied in the fields of microwave absorption and Li ion batteries (LIB). In particular, coatings based on MAX, MXene, ball-milled NanoMAX, and NanoMAX-derived-MXene (MXene-N) and their composites are examined in terms of their comparative efficacy for the aforesaid applications. NanoMAX and MXene-N based composites with graphite exhibit superior performance with specific reflection loss values (representing absorbance when measured with metal-backing) of -21.4 and -19 dB cm3 g-1, respectively, as compared to their bulk counterparts, that too with a low density (0.63 g cm-3) and very small thickness (0.03 mm). These performance improvements in absorbance in only 30 μm coatings can be attributed to reflective losses compounded with multiple internal reflections within the nanocomposite intensified by dielectric losses, arising from high interface density. The pristine samples were also studied for their performance as Li ion battery anodes. Herein, MXene-N exhibits the best performance with a specific capacity of 330 mA h g-1 at 100 mA g-1 and excellent cycling stability tested up to 1000 cycles.

Fe3O4-decorated graphene assembled porous carbon nanocomposite for ammonia sensing: study using an optical fiber Fabry-Perot interferometer.

Abstract: A porous graphene-coated optical fiber Fabry-Perot interferometer (G-FPI) and Fe3O4-graphene nanocomposite coated Fabry-Perot interferometer (FG-FPI) have been investigated and compared for the detection of ammonia gas at room temperature. The sensor probes were subjected to ammonia concentrations varying from 1.5 ppm to 150 ppm. An increased sensitivity was observed for FG-FPI (36 pm ppm-1) when compared with that of G-FPI (25 pm ppm-1). The observed sensor detection limits for FG-FPI and G-FPI were around 7 and 10 ppb, respectively. The sensing mechanism was based on the change in refractive index/dielectric constant of the material; which changed the conductivity of coated material in presence of NH3. It was observed that the modified refractive index induced a wavelength shift in the FPI. The highly porous structure of graphene and the uniform dispersion of Fe3O4 nanoparticles into this framework effectively facilitated the target gas diffusion and hence improved the sensing performance. The sensing was correlated to the oxygen vacancies on the Fe3O4 surfaces and the depletion region manipulations with the ammonia interactions along with Schottky-type electron conductivity via the conducting graphene assembled porous carbon framework. The mathematical evaluation of the phenomenon also justified the excellent repeatability and reversibility of this sensitive, room temperature sensor.

Electromagnetic interference shielding with 2D transition metal carbides (MXenes)

Abstract: Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti3C2Tx film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti3C2Tx films (4600 Siemens per centimeter) and multiple internal reflections from Ti3C2Tx flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.

Review of electromagnetic interference shielding materials fabricated by iron ingredients

Abstract: Iron (Fe) and its counterparts, such as Fe2O3, Fe3O4, carbonyl iron and FeO, have attracted the attention of researchers during the past few years due to their bio-compatibility, bio-degradability and diverse applications in the field of medicines, electronics and energy; including water treatment, catalysis and electromagnetic wave interference shielding etc. In this review paper, we aimed to explore iron based materials for the prevention of electromagnetic interference (EMI) by means of both reflection and absorption processes, including the standard methods of synthesis of Fe-based materials along with the determination of EMI performance. It is customary that a proper combination of two dielectric-losses, i.e. electrical and magnetic losses, give excellent microwave absorption properties. Therefore, we focused on the different strategies of preparation of these iron based composites with dielectric carbon materials, polymers etc. Additionally, we explained their positive and negative aspects.

High-strength scalable MXene films through bridging-induced densification

Abstract: MXenes are a growing family of two-dimensional transition metal carbides and/or nitrides that are densely stacked into macroscopically layered films and have been considered for applications such a...