Core-Multishell Heterostructure with Excellent Heat Dissipation for Electromagnetic Interference Shielding

Recent achievements and performance of nanomaterials in microwave absorption and electromagnetic shielding

Due to the swift advancement of the electronic industry and information technology, electromagnetic wave absorption materials are gaining significance in the field of intelligent equipment and weaponry. Nanomaterials were developed to investigate wave absorbing materials that can achieve both impedance matching and attenuation balance. Nanomaterials possess the properties of being thin, lightweight, and capable of absorbing microwave radiation across a wide range of frequencies. This work aims to present a systematic overview of the recent advancements in core-shell materials, specifically carbon, oxide, and sulfide nanomaterials, with regards to their applications in electromagnetic absorption and electromagnetic shielding. This review intends to emphasize the core principles of electromagnetic interference (EMI) shielding and microwave absorption in different systems documented in the literature, along with diverse methods of synthesis and fabrication for creating effective wideband electromagnetic absorbers/shields. Lastly, we also endeavor to offer a comprehensive view and insight into the areas where future research will thrive. This study provides a comprehensive assessment of the current advancements in the field of microwave absorption and electromagnetic shielding of nanomaterials.

A review on recent progress in polymer composites for effective electromagnetic interference shielding properties - structures, process, and sustainability approaches

The rapid proliferation and extensive use of electronic devices have resulted in a meteoric increase in electromagnetic interference (EMI), which causes electronic devices to malfunction. The quest for the best shielding material to overcome EMI is boundless. This pursuit has taken different directions, right from materials to structures to process, up to the concept of sustainable materials. The emergence of polymer composites has substituted metal and metal alloy-based EMI shielding materials due to their unique features such as light weight, excellent corrosion resistance, and superior electrical, dielectric, thermal, mechanical, and magnetic properties that are beneficial for suppressing the EMI. Therefore, polymer nanocomposites are an extensively explored EMI shielding materials strategy. This review focuses on recent research developments with a major emphasis on structural aspects and processing for enhancing the EMI shielding effectiveness of polymer nanocomposites with their underlying mechanisms and some glimpses of the sustainability approaches taken in this field.

3D-Networks Based Polymer Composites for Multifunctional Thermal Management and Electromagnetic Protection: A Mini Review

The rapid development of miniaturized, high-frequency, and highly integrated microelectronic devices has brought about critical issues in electromagnetic compatibility and thermal management. In recent years, there has been significant interest in lightweight polymer-based composites that offer both electromagnetic interference (EMI) shielding and thermal conductivity. One promising approach involves constructing three-dimensional (3D) interconnection networks using functional fillers in the polymer matrix. These networks have been proven effective in enhancing the thermal and electrical conductivity of the composites. This mini-review focuses on the preparation and properties of 3D network-reinforced polymer composites, specifically those incorporating metal, carbon, ceramic, and hybrid networks. By comparing the effects of different filler types and distribution on the composite materials, the advantages of 3D interconnected conductive networks in polymer composites are highlighted. Additionally, this review addresses the challenges faced in the field of multifunctional thermal management and electromagnetic protection materials and provides insights into future development trends and application prospects of 3D structured composites.

The Effect of Porosity on the Thermal Conductivity of Highly Thermally Conductive Adhesives for Advanced Semiconductor Packages

This study suggests promising candidates as highly thermally conductive adhesives for advanced semiconductor packaging processes such as flip chip ball grid array (fcBGA), flip chip chip scale package (fcCSP), and package on package (PoP). To achieve an extremely high thermal conductivity (TC) of thermally conductive adhesives of around 10 Wm^-1K^-1, several technical methods have been tried. However, there are few ways to achieve such a high TC value except by using spherical aluminum nitride (AlN) and 99.99% purified aluminum oxide (Al₂O₃) fillers. Herein, by adapting highly sophisticated blending and dispersion techniques with spherical AlN fillers, the highest TC of 9.83 Wm^-1K^-1 was achieved. However, there were big differences between theoretically calculated TCs that were based on the conventional Bruggeman asymmetric model and experimentally measured TCs due to the presence of voids or pores in the composites. To narrow the gaps between these two TC values, this study also suggests a new experimental model that contains the porosity effect on the effective TC of composites in high filler loading ranges over 80 vol%, which modifies the conventional Bruggeman asymmetric model.

PANI-wrapped BaFe12O19 and SrFe12O19 with rGO composite materials for electromagnetic interference shielding applications

We report electromagnetic interference (EMI) shielding efficiency in the PANI-wrapped BaFe₁₂O₁₉ and SrFe₁₂O₁₉ with rGO composites. Barium and strontium hexaferrites were synthesized using the nitrate citrate gel combustion method. These hexaferrites were polymerized in situ with aniline. The PANI-coated ferrite-based composite materials were developed along with reduced graphene oxide (rGO) in acrylonitrile butadiene styrene (ABS) polymer, and their shielding effectiveness was assessed in X-band frequency range (8.2-12.4 GHz). The reflection (SE_R) and absorption (SE_A) mechanism of shielding effectiveness was discussed with the different rGO concentrations. The results reveal that 5 wt% of rGO with PANI-coated barium and strontium hexaferrite polymer composites exhibit shielding efficiency of 21.5 dB and 19.5 dB, respectively, for 1 mm thickness composite. These hexaferrite polymer-based composite materials can be used as an attractive candidate for EM shielding materials in various technological applications.

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

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 (g_s) 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, g_s, and heat dissipation ability. Interestingly, maximum total shielding effectiveness (SE_T) of -52 dB (88% absorption @8.2 GHz) and specific shielding effectiveness/thickness (SSE_t) of -373 dB/cm²g were achieved for a symmetric construct whereas, for the asymmetric construct, the SE_T and SSE_t were -37 dB and -280 dB/cm²g, respectively, with an exceptionally high g_s of 8.6, the highest reported so far. The asymmetricity in the construct led to directional dependence of the absorption component (% SE_A, 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.

Effect of Multilayered Structure on the Static and Dynamic Properties of Magnetic Nanospheres

The development of flexible and lightweight electromagnetic interference (EMI)-shielding materials and microwave absorbers requires precise control and optimization of core-shell constituents within composite materials. Here, a theoretical model is proposed to predict the static and dynamic properties of multilayered core-shell particles comprised of exchange-coupled layers, as in the case of a spherical iron core coupled to an oxide shell across a spacer layer. The theory of exchange resonance in homogeneous spheres is shown to be a limiting special case of this more general theory. Nucleation of magnetization reversal occurs through either quasi-uniform or curling magnetization processes in core-shell particles, where a purely homogeneous magnetization configuration is forbidden by the multilayered morphology. The energy is minimized through mixing of modes for specific interface conditions, leading to many inhomogeneous solutions, which grow as 2ⁿ with increasing layers, where n represents the number of magnetic layers. The analytical predictions are confirmed using numerical simulations.

High-Efficiency Electromagnetic Interference Shielding of rGO@FeNi/Epoxy Composites with Regular Honeycomb Structures

With the rapid development of fifth-generation mobile communication technology and wearable electronic devices, electromagnetic interference and radiation pollution caused by electromagnetic waves have attracted worldwide attention. Therefore, the design and development of highly efficient EMI shielding materials are of great importance. In this work, the three-dimensional graphene oxide (GO) with regular honeycomb structure (GH) is firstly constructed by sacrificial template and freeze-drying methods. Then, the amino functionalized FeNi alloy particles (f-FeNi) are loaded on the GH skeleton followed by in-situ reduction to prepare rGH@FeNi aerogel. Finally, the rGH@FeNi/epoxy EMI shielding composites with regular honeycomb structure is obtained by vacuum-assisted impregnation of epoxy resin. Benefitting from the construction of regular honeycomb structure and electromagnetic synergistic effect, the rGH@FeNi/epoxy composites with a low rGH@FeNi mass fraction of 2.1 wt% (rGH and f-FeNi are 1.2 and 0.9 wt%, respectively) exhibit a high EMI shielding effectiveness (EMI SE) of 46 dB, which is 5.8 times of that (8 dB) for rGO/FeNi/epoxy composites with the same rGO/FeNi mass fraction. At the same time, the rGH@FeNi/epoxy composites also possess excellent thermal stability (heat-resistance index and temperature at the maximum decomposition rate are 179.1 and 389.0 °C respectively) and mechanical properties (storage modulus is 8296.2 MPa).

Transparent and Flexible Electromagnetic Interference Shielding Film Using ITO Nanobranches by Internal Scattering

A transparent and flexible film capable of shielding electromagnetic waves over a wide range of frequencies (X and K_u bands, 8-18 GHz) is prepared. The electromagnetic wave shielding film is fabricated using the excellent transmittance, electrical conductivity, and thermal stability of indium tin oxide (ITO), a representative transparent conductive oxide. The inherent mechanical brittleness of oxide ceramics is overcome by adopting a nanobranched structure. In addition, mechanical stability is maintained even after repeated bending experiments (200 000 times). The produced transparent and flexible shielding film is applied to practical GHz devices (Wi-Fi and LTE devices), and signal sensitivity is confirmed to decrease. Therefore, it can be widely applied to various transparent and flexible electronic devices.

Magnetic Energy Morphing, Capacitive Concept for Ni0.3Zn0.4Ca0.3Fe2O4 Nanoparticles Embedded in Graphene Oxide Matrix, and Studies of Wideband Tunable Microwave Absorption

Nanoparticles of Ni_0.3Zn_0.4Ca_0.3Fe₂O₄ (NZCF) were successfully prepared by the facile wet chemical method coupled with the sonochemical method. These nanoparticles were embedded in a graphene oxide (GO) matrix (NZCFG). Rietveld analyses of X-ray diffraction, transmission electron microscope, scanning electron microscope, and X-ray photoelectron spectroscopy were carried out to extract different relevant information regarding the structure, morphology, and ionic state. A major improvement in saturation magnetization is achieved due to substitution of Ca²⁺ in the ferrite lattice. Interestingly, the observed value of electromagnetic absorption for a sample thickness of 1.5 mm is ∼-67.7 dB at 13.3 GHz, and the corresponding bandwidth is 5.73 GHz. The Cole-Cole plot, the Jonscher power-law fitting, and the Nyquist plot confirm the probability of improved hopping conductance and attractive capacitive behavior in NZCFG. The presence of magnetic energy morphing in combination with a higher attenuation constant, lower skin depth, and various forms of resonance and relaxation makes NZCFG the most suitable for microwave absorption.

Polymer-Derived Lightweight SiBCN Ceramic Nanofibers with High Microwave Absorption Performance

Lightweight SiBCN ceramic nanofibers were prepared by a combination of electrostatic spinning and high-temperature annealing techniques, showing tunable electromagnetic wave absorption. By controlling the annealing temperature, the nanoscale architectures and atomic bonding structures of as-prepared nanofibers could be well regulated. The resulting SiBCN nanofibers ∼300 nm in diameter, which were composed of an amorphous matrix, β-SiC, and free carbon nanocrystals, were defect-free after annealing at 1600 °C. SiBCN nanofibers annealed at 1600 °C exhibited good microwave absorption, obtaining a minimum reflection coefficient of -56.9 dB at 10.56 GHz, a sample thickness of 2.6 mm with a maximum effective absorption bandwidth of 3.45 GHz, and a maximum dielectric constant of 0.44. Owing to the optimized A + B + C microstructure, SiBCN ceramic nanofibers with satisfying microwave absorption properties endowed the nanofibers with the potential to be used as lightweight, ultrastrong radar wave absorbers applied in military and the commercial market.

Polyvinylidene Fluoride Core-Shell Nanofiber Membranes with Highly Conductive Shells for Electromagnetic Interference Shielding

As the demand for wireless sensors and equipment is unprecedentedly increasing, the interest in electromagnetic interference (EMI)-shielding materials that can effectively block accompanying electromagnetic interference is also constantly increasing. In particular, flexible and lightweight EMI-shielding materials that exhibit high EMI-shielding effectiveness (SE) have been more actively investigated as they are applicable to various applications. In this work, we reported the fabrication and performance of conducting polymer nanofiber EMI-shielding material, which was realized using electrospun polyvinylidene fluoride (PVDF) core-shell nanofiber membranes with highly conductive shells. Using the chemical polymerization method, core-shell nanofibers with highly conductive shells were employed without compositing with conductive fillers, resulting in shell-conductive lightweight EMI-shielding material without impairing the original properties of the nanofiber. In particular, thanks to the nanofiber structure, the EMI-shielding material exhibits superb flexibility, and the EMI SE was also improved through the enhanced absorption of EM waves and multireflections by the porous nanofiber film structure. Specifically, the developed EMI-shielding material in this work exhibited a SE of ∼40 dB in the X-band, which corresponds to an absolute shielding effectiveness (SSE_t) of 16,230 dB·cm²/g at a thickness of 14 μm. Moreover, the high durability and hydrophobicity of the PVDF nanofibers with poly (3,4-ethylenedioxythiophene) (PEDOT)-polymerized shell can also be useful in practical applications.

Thermal Conductivity and Electromagnetic Interference (EMI) Absorbing Properties of Composite Sheets Composed of Dry Processed Core-Shell Structured Fillers and Silicone Polymers

This paper proposes dual-functional sheets (DFSs) that simultaneously have high thermal conductivity (TC) and electromagnetic interference (EMI) absorbing properties, making them suitable for use in mobile electronics. By adopting a simple but highly efficient dry process for manufacturing core–shell structured fillers (CSSFs) and formulating a close-packed filler composition, the DFSs show high performance, TC of 5.1 W m⁻¹ K⁻¹, and a −4 dB inter-decoupling ratio (IDR) at a 1 GHz frequency. Especially, the DFSs show a high dielectric breakdown voltage (BDV) of 3 kV mm⁻¹, which is beneficial for application in most electronic devices. The DFSs consist of two kinds of CSSFs that are blended in accordance with the close-packing rule, Horsfield’s packing model, and with polydimethylsiloxane (PDMS) polymers. The core materials are soft magnetic Fe-12.5%Cr and Fe-6.5%Si alloy powders of different sizes, and Al₂O₃ ceramic powders of a 1-μm diameter are used as the shell material. The high performance of the DFS is supposed to originate from the thick and stable shell layer and the maximized filler loading capability owing to the close-packed structure.

Mechanically robust, UV screener core-double-shell nanostructures provide enhanced shielding for EM radiations over wide angle of incidence

Herein, we have designed and synthesized first of its kind core-double shell nano heterostructured materials in which primitive ferrite (Fe3O4) acts as a diffused shell around an amorphous conducting core (carbon nanosphere, CNS), separated by a dielectric spacer (SiO2). This material when composited with polyvinylidene difluoride (PVDF) showed an excellent electromagnetic interference (EMI) shielding effectiveness of -42 dB (>99.99% attenuation) having a 600 μm thick film and interestingly, shielding effectiveness remained unaltered even after repeated heat cycles at various service temperatures. Moreover, far-field testing revealed that over the 10-18 GHz range the antenna radiated ca. 85% of electromagnetic power even if it was shielded with the composite film containing the heterostructure, which indicated low-performance degradation of the antenna due to the presence of the shield. Intriguingly, these composites also showed excellent UV blocking (>99.996% blocking) performance. These core-double shell heterostructure nanocomposites showed enhanced Young's modulus (344%) and proof strength (173.6%) as compared to neat PVDF. Besides, these films are fairly durable as the shielding performance was not affected after being subjected to heating (up to high service temperature of 90 degrees), bending (10 000 cycles), and stretching cycles (200 cycles).

Multifunctional MXene-Based Fireproof Electromagnetic Shielding Films with Exceptional Anisotropic Heat Dissipation Capability and Joule Heating Performance

The burgeoning development of wearable electronic devices has resulted in urgent demands for electromagnetic interference (EMI) shielding films that feature excellent fireproof and heat dissipation capability. Herein, multifunctional fireproof EMI shielding films with excellent anisotropic thermal conductivity are constructed based on MXene and montmorillonite (MMT) via a simple vacuum-assisted filtration technique. The presence of MMT can protect the MXene from oxidation and endow the composite films with exceptional fire-resistant ability. The impressive thermal conductivity performance, high in-plane thermal conductivity (28.8 W m^-1 K^-1) and low cross-plane thermal conductivity (0.27 W m^-1 K^-1), ingeniously enables highly efficient in-plane heat dissipation and cross-plane heat insulation in the MXene-based films simultaneously. The high electrical conductivity (4420 S m^-1) of the composite film enables an excellent EMI shielding effectiveness of over 65 dB in the entire X-band and a high specific shielding effectiveness of over 10 000 dB cm² g^-1 at a thickness of only 25 μm. Importantly, the EMI shielding effectiveness is maintained at above 60 dB even after burning for 30 s. Besides, the composite films show outstanding Joule heating performance with a fast thermal response (<10 s) and a low driving voltage (<5 V). These multifunctional films are highly promising for applications concerning fire protection, de-icing, heat dissipation/insulation, and EMI shielding devices.

Tuning of Shells in Trilaminar Core@Shell Nanocomposites in Controlling Electromagnetic Interference through Switching of the Shielding Mechanism

Fe₃O₄@SiO₂@PPy core-shell nanocomposites were fabricated by the coating of SiO₂ on Fe₃O₄ through base catalyzed hydrolysis of tetraethyl orthosilicate followed by encapsulation of polypyrrole (PPy). Subsequently, these trilaminar composites have been characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller, superconducting quantum interference devices, and measurement of the total shielding efficiency in the frequency range of 2-8 GHz. Our findings showed the highest total shielding efficiency (∼32 dB) of Fe₃O₄@SiO₂@PPy (Fe₃O₄@SiO₂/pyrrole wt/wt = 1:9) and followed reflection as the dominant shielding mechanism. Such performance was attributed to poor impedance matching between the PPy (conducting)/SiO₂ (insulating) and high electrical conductivity of Fe₃O₄@SiO₂@PPy. Alternatively, electromagnetic (EM) waves incident on the SiO₂@PPy interface could also account for enhancing the total shielding efficiency of Fe₃O₄@SiO₂@PPy because of multireflection/refraction. Our earlier work also showed excellent total shielding efficiency of Fe₃O₄@C@PANI nanocomposites, through absorption as the dominant shielding mechanism. These findings clearly suggest that EM interference shielding in Fe₃O₄@SiO₂@PPy and Fe₃O₄@C@PANI trilaminar core@shell nanocomposites is controlled by tuning of the shells through switching of the mechanism.

Magnetized MXene Microspheres with Multiscale Magnetic Coupling and Enhanced Polarized Interfaces for Distinct Microwave Absorption via a Spray-Drying Method

As a typical 2D (two dimensional) material, Ti₃C₂T_x, has been used as a promising microwave absorber (MA) because of its massive interface architecture, abundant natural defects, and chemical surface functional groups. However, its single dielectric-type loss and excessive high conductivity seriously restrict the further enhancement of MA performance. Herein, we first describe a simple spray-drying routine to reshape the 2D MXene into a confined and magnetized microsphere with tightly embedded Fe₃O₄ nanospheres (designated as M/F), contributing to the enhanced specific interfaces and strong dielectric polarization. These Fe₃O₄ magnetic units are highly dispersed into the dielectric Mxene framework, leading to the optimized impedance balance and electromagnetic coordination capability. This composite way effectively exceeds the conventionally physical mixing, simple loading, and local phase separation method. Meanwhile, strong magnetic loss capability with significantly improved magnetic flux line density is achieved from microscale MXene and nanoscale Fe₃O₄, confirming our 3D multiscale magnetic coupling network. Accordingly, the M/F composites hold distinct microwave absorption property with the strong reflection loss (-50.6 dB) and effective absorption bandwidth (4.67 GHz) at the thickness as thin as only 2 mm. Our encouraging strategy provides important designable implications for MXene-based functional materials and high-performance absorbers.

Facile One-Pot Solvothermal Synthesis of the RGO/MWCNT/Fe3O4 Hybrids for Microwave Absorption

How to effectively regulate the electromagnetic parameters of magnetic composites to achieve better microwave absorption (MA) performances is still a serious challenge. Herein, we constructed nanocomposites composed of magnetic constituents and carbon materials to obtain high-efficiency electromagnetic wave absorbers. Self-assembled, multi-interfacial, and porous RGO/MWCNT/Fe₃O₄ hybrids (GMFs) were synthesized via in situ one-pot solvothermal method. The growth mechanism of the GMFs would be that the defects on reduced graphene oxide (RGO) provide sites for the crystallization of Fe₃O₄. Also, the RGO and Fe₃O₄ were further linked by the cross-connection of multiwalled carbon nanotubes (MWCNTs), which acted as a bridge. The MA mechanism of GMFs was studied while considering the synergistic effects between the three components (RGO, MWCNT, and raspberry-shaped Fe₃O₄) and their multi-interfacial and porous structure. Also, the MA performance of the GMFs was conducted. The GMFs exhibited a maximum reflection loss (RL) value of -61.29 dB at 10.48 GHz with a thickness of 2.6 mm when the contents of RGO and MWCNT were 6.3 and 1.3 wt %, respectively. The RL values (≤-10 dB) were observed to be in the range of 8.96-12.32 GHz, and the effective microwave absorption bandwidth was tunable from 3.52 to 18 GHz by changing the sample thickness. The results revealed that the multi-interfacial and porous structure of the GMFs is beneficial to MA performance by inducing multiscatterings. Since no toxic solvents were used, this method is environmentally friendly and has potential for large-scale production. The prepared GMFs may have a wide range of applications in MA materials against electromagnetic interference pollution.

Mechanically Durable, Highly Conductive, and Anticorrosive Composite Fabrics with Excellent Self-Cleaning Performance for High-Efficiency Electromagnetic Interference Shielding

Metal-based materials have been widely used for the electromagnetic interference (EMI) shielding due to their excellent intrinsic conductivity. However, their high density, poor corrosion resistance, and poor flexibility limit their further application in aerospace and flexible electronics. Here, we reported a facile means to prepare lightweight, mechanically durable, superhydrophobic and conductive polymer fabric composites (CPFCs) with excellent electromagnetic shielding performance. The CPFC could be fabricated by three steps: (1) the polypropylene (PP) fabric was coated by a polydopamine (PDA) layer; (2) PP/PDA adsorbed the Ag precursor that was then chemically reduced to Ag nanoparticles (AgNPs); (3) PP/PDA/AgNPs fabrics were modified by one layer of polydimethylsiloxane (PDMS). The contact angle (CA) of the CPFCs could reach ∼152.3° while the sliding angle (SA) was as low as ∼1.5°, endowing the materials with excellent self-cleaning performance. Thanks to the extremely high conductivity of 81.2 S/cm and the unique porous structure of the fabric, the CPFC possessed outstanding EMI shielding performance with the maximum shielding effectiveness (SE) of 71.2 dB and the specific shielding effectiveness (SSE) of 270.7 dB cm³ g^-1 in the X band. The interfacial adhesion is remarkably improved owing to the PDMS layer, and the superhydrophobicity, conductivity and EMI SE of CPFCs are almost maintained after cyclic abrasion and winding test. Also, the CPFCs can be used in a harsh environment, due to their excellent water proof property.

Nitrogen doping as a fundamental way to enhance the EMI shielding behavior of cobalt particle-embedded carbonaceous nanostructures

The influence of nitrogen doping in pyrolysis-derived carbonaceous nanostructures with embedded Co-nanoparticles (Co@C) for electromagnetic (EM) absorption at microwave frequencies is explored.