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In this study, porous carbon has been prepared through potassium hydroxide (KOH) activation of coconut fiber (CF) and subsequent carbonization in the presence of an inert gas. The activated carbons (AC) were prepared via carbonization of the precursor at different temperatures. Subsequently, their electromagnetic wave absorption (EMWA) performance was investigated at X-band frequency. The phase crystallinity, porous features, and degree of graphitization of the activated carbons were studied using XRD, nitrogen adsorption/desorption isotherm, and Raman spectroscopy, respectively. Using the BET method, the activated carbon prepared at 750 °C displayed a high specific surface area of 602.9 m2 g−1 and an average pore size of 6 nm, which confirms the extant of mesopores. The EMWA was studied using COMSOL Multiphysics software based on the finite element method. Results show that the activated carbon prepared at 750 °C attained an optimal reflection loss of −45.6 dB at 10.96 GHz with a corresponding effective bandwidth of 3.5 GHz at a thickness of 3.0 mm. In conclusion, this study interestingly shows that porous carbon obtained from coconut fiber has great potential for attenuating electromagnetic waves.

The evolution of nanomaterials has significantly contributed to the advancement of smart and lightweight electromagnetic (EM) wave absorbing materials. In this study, Ni0.5Zn0.5Fe2O4 nanoclusters were synthesized by a facile co-precipitation route. The morphology, structure, phase, and chemical composition of the sample was investigated. Results show that the sample is composed of clustered Ni0.5Zn0.5Fe2O4 nanoparticles, wherein the nanoparticles clusters are composed of tiny individual particles with spherical morphology. Investigation of the EM wave absorption reveals that a composite of paraffin containing 20 wt% of the Ni0.5Zn0.5Fe2O4 nanoclusters absorbs a large percentage of the incident EM wave at a thin absorber thickness. The sample attains − 48.8 dB reflection loss at 14.42 GHz with a 3.0 mm thickness. The enhanced EM absorption performance can be ascribed to interface polarization resulting from the many active atoms on the surface of the Ni0.5Zn0.5Fe2O4 nanoclusters. These results show that the Ni0.5Zn0.5Fe2O4 nanoclusters can be used to effectively attenuate microwaves.

Chromium (Cr) substituted nickel ferrite nanoparticle was fabricated via a facile coprecipitation route and the microwave absorption performance was investigated within 8.2–18 GHz range. Several characterization approaches have been employed to investigate the morphology, phase composition, chemical composition, and structure of the Ni0·5Cr0·5Fe2O4 nanoparticles. We observed that the nanoparticles are spherical, having compact arrangement and traces of inter-particle porosity. This suggests that the morphology would favor multiple transmission routes for the absorption of EM wave. Analysis of the sample's microwave absorption performance reveals that 20 wt percent loading of Ni0·5Cr0·5Fe2O4 nanoparticles in paraffin can effectively attenuate a large portion of EM wave within 8.2–18 GHz frequency range. The sample achieved an optimum reflection loss value −47.3 dB at 16.0 GHz at 2.5 mm thickness. The EM wave absorption observed can be credited to impedance match, interfacial polarization, and good dielectric/magnetic loss coupling. The absorption bandwidth of the sample covers the X-band and P-band frequency via tuning of the absorber thickness between 2.5 and 4.5 mm. These results show that the Cr-substituted nickel ferrite has good EM properties and can be considered as a possible EM wave absorbing filler.

Electromagnetic pollution has become a serious concern with the immense utilization of wireless information technologies and this has aroused huge interest in the area of microwave absorption. To solve this issue, fabrication of advanced, novel and superior microwave absorbing materials (MAM) with high electromagnetic wave absorption, wide absorption bandwidth, lightweight and cost-efficient are highly required. To date, magnetite (Fe3O4) is being thoroughly investigated as MAM, due to its exceptional dual electromagnetic properties (permittivity and permeability), proper saturation magnetization and high Curie temperature. However, large density and impedance mismatch are some of the limiting factors that hinder its microwave absorption performance (MAP). To circumvent these challenges, reduction of size to the nanoscale, fabrication of hierarchical nanostructures and/or conjugation with other lossy materials have been extensively explored as viable solutions to optimize the MAP of Fe3O4. In this review, the progressive research in the fabrication of Fe3O4 based nanocomposites as MAM is discussed. The factors influencing the MAP of these absorptive materials are likewise discussed in detail. Conclusively, some challenges, limitations, and future prospects in the development of Fe3O4 based MAM are put forth.

Electromagnetic wave is a viable means of introducing energy into reservoirs for the recovery of residual oil. However, previous studies have not considered the precise frequency of the electromagnetic (EM) wave. These studies focused on EM heating, not considering the efficiency dependence of EM transmitter and EM propagation on the EM properties of the medium. Thus, sandstone effective permittivity was experimentally measured, and electrical conductivity calculated for different saturation stages encountered in the nanofluid enhanced oil recovery process. The effective permittivity at the resonant frequency of the sandstone increased from 10.94 to 19.1 with a simultaneous frequency shift from 1.2 to 0.6 GHz due to the inclusion of magnetite nanofluid. This implies that the maximum transfer of EM energy for stimulation and activation of injected nanofluid can be achieved by irradiating the EM wave of this frequency within the reservoir for mobilization of the residual oil.

The coupling of electromagnetic (EM) wave to nanoflooding experiments, termed EM-assisted nanoflooding has gained enormous attention in recent years. This brings about the consideration of transmitter efficiency and the propagation pattern of the ensuing EM wave, both of which depend on reservoir electromagnetic properties. However, this has not been considered in previous works, despite its potential to improve the efficiency of the process through energy maximization. Hence, this study considers the effects of reservoir EM properties on the operation of a transmitter. The EM properties of saturated reservoir rock samples were measured. Afterward, a half-wave dipole antenna was modeled in a cylindrical reservoir based on the measured EM properties. The EM propagation pattern of the antenna was simulated in a frequency range of 100 MHz&mdash, 2.0 GHz using the finite element method. The antenna was found to display dual resonance (at 800 MHz and 1.3 GHz) for sandstone saturated with oil, brine and nanofluid. Application of the EM wave at resonance frequency can help increase the efficiency of EM-assisted nanoflooding.

Magnetite (Fe3O4) have been thoroughly investigated as microwave absorbing material due to its excellent electromagnetic properties (permittivity and permeability) and favorable saturation magnetization. However, large density and impedance mismatch are some of the limiting factors that hinder its microwave absorption performance (MAP). Herein, Fe3O4 nanoparticles prepared by facile co-precipitation method have been coated with citric acid and embedded in a polyvinylidene fluoride (PVDF) matrix. The coated Fe3O4 nanoparticles were characterized by X-ray diffraction spectrometer (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). COMSOL Multiphysics based on the finite element method was used to simulate the rectangular waveguide at X-band and Ku-band frequency range in three-dimensional geometry. The citric acid coated Fe3O4/PVDF composite with 40 wt.% filler loading displayed good microwave absorption ability over the studied frequency range (8.2&ndash, 18 GHz). A minimum reflection loss of &minus, 47.3 dB occurs at 17.9 GHz with 2.5 mm absorber thickness. The composite of citric acid coated Fe3O4 and PVDF was thus verified as a potential absorptive material with improved MAP. These enhanced absorption coefficients can be ascribed to favorable impedance match and moderate attenuation.

Fabrication of smart materials for electromagnetic (EM) wave absorption has been propounded as efficient EM interference and pollution mitigation method. Herein, a porous lightweight graphene@Ni0.5Co0.5Fe2O4 composite was prepared via a coprecipitation method. The results show that Ni0.5Co0.5Fe2O4 nanoparticles are homogeneously dispersed and anchored on the graphene flakes. Investigation of the EM waves absorption properties of the material at different filling in paraffin reveals that at 15 wt% loading, the composite absorbs large percent of the EM waves at minimal thickness. The composite attains optimum reflection loss peak −44.7 dB at 17.45 GHz, with 1.5 mm thickness. This enhanced EM wave absorption performance (at lesser thickness than Ni0.5Co0.5Fe2O4 in literature) could be ascribed to interfacial polarization and a good impedance match arising from unique pore configuration of the dielectric (graphene) and magnetic (Ni0.5Co0.5Fe2O4) composite. These results indicate that the lightweight G@Ni0.5Co0.5Fe2O4 composites with strong absorption at reduced thickness is an efficient absorber for high-frequency EM wave attenuation.

Interfacial tension (IFT) reduction is widely acknowledged as one of the prominent oil recovery mechanism during nanofluid flooding enhanced oil recovery (EOR). Hence, in this work, an investigation of IFT at the crude oil-nanofluids interfaces was carried out using the Wilhelmy plate method in the presence of electromagnetic (EM) field. EM wave propagation within sandstone saturated with oil and nanofluids were simulated using COMSOL Multiphysics solver. A dielectric (ZnO) and magnetic (Fe2O3) nanoparticles were synthesized, and their EM properties as well as IFT reduction ability were measured. The superior EM properties of Fe2O3 nanoparticle contribute to its maximum IFT reduction of 6.13% of the crude oil-nanofluid interface under EM wave. The presence of Fe2O3 nanoparticles in sandstone saturated with oil and Fe2O3 nanofluid increases the sandstone response to EM wave. This is shown by reflection loss peak of −19.9 dB, equivalent to approximately 99% absorption of the EM wave at 1 GHz, with a matched impedance of 46.5 Ω. Hence, EM-assisted nanofluid flooding experiment conducted with bespoke core flooding system shows that oil recovery increased by 13.6% over the case without EM propagation during Fe2O3 nanoflooding. This could be attributed to increased fluid mobility in the sandstone due to IFT alteration and high EM response of the sandstone core. This result shows the potential application of magnetic nanofluid coupled with EM wave for enhanced oil recovery.

Due to the unremitting emission of electromagnetic (EM) wave pollution from electronic and electrical devices, the fabrication of materials with EM waves absorption capacity is an active research domain. Ferrite nanoparticles are one of the widely studied materials in the area of EM wave absorption. Hence in this work, Ni0.5Cu0.5Fe2O4 nanoparticles were synthesized using four different coprecipitating agents (NaOH, KOH, NH4OH, and Na2CO3). The structure, composition, morphology, magnetic and thermal properties of all the samples were characterized and compared using XRD, FT-IR, XPS, FESEM, VSM and TGA analysis, respectively. The effect of coprecipitating agents on the EM properties of all the samples for optimum EM wave absorption was investigated and presented within the X-band frequency range. The Ni0.5Cu0.5Fe2O4 nanoparticles prepared with NH4OH was identified as the optimal material due to its superior physiochemical and EM properties. An enhanced EM wave absorption with optimum RL of −42.1 dB was achieved with the optimal material at 11.7 GHz, with 3.5 mm thickness. The material has an absorption bandwidth of 1.51 GHz. Thus, the use of NH4OH amongst other coprecipitants for Ni0.5Cu0.5Fe2O4 synthesis is more favorable for EM wave absorption application.