Layered polymer composite foams for broadband ultra-low reflectance EMI shielding: a computationally guided fabrication approach

Magnetic-electric module design and fabrication of high performance electromagnetic interference shielding sandwich structure melamine foam composites with ultra-low reflection

The development of an efficient electromagnetic interference (EMI) shielding material that balances the paradoxical relationship between low thickness and ultra-low reflectivity is highly significant for mitigating secondary electromagnetic wave pollution. In this work, a sandwich structure consisting of thermoplastic composite, porous foam, and conductive film was meticulously designed, employing a modular assembly strategy. This design aims to tackle the challenge by optimally leveraging the inherent advantages of each individual layer, thereby enhancing the overall performance and functionality of the structure. The core design features a melamine foam framework impregnated with discontinuous copper/silver nanoparticles and carbonyl iron magnetic nanosheets serving as the middle layer which offers abundant pores and interfaces, contributing to dielectric and magnetic losses for electromagnetic waves. The synergistic effect between the top layer (thermoplastic polyurethane/carbonyl iron), the middle layer and the bottom layer (a conductive polyester fiber@copper@nickel) was investigated in terms of impedance matching and magnetic loss as well as reflective shielding. The composite exhibited a shielding effectiveness of 78.01 dB across the X-band (8.2-12.4 GHz) with a thickness of only 2.26 mm. A low-reflection bandwidth (R < 0.1) of 2.69 GHz was obtained which constitutes 64.04 % of the X-band. Importantly, the composite achieved a remarkably low reflectivity of 0.818 %, corresponding to a reflecting shielding effectiveness (SER) of merely 0.035 dB. A finite element analysis was conducted to elucidate the wave shielding mechanism. This research provides a dependable and straightforward approach for creating EMI composites with low thickness, ultra-low reflection, and robust shielding efficiency.

MAX phase coatings: synthesis, protective performance, and functional characteristics

Mn+1AXn (MAX) phases are a novel class of materials with a closely packed hexagonal structure that bridge the gap between metals and ceramics, garnering tremendous research interest worldwide in recent years. Benefiting from their unique layered structure and mixed covalent-ionic-metallic bonding characteristics, MAX phase coatings possess excellent oxidation resistance, and exceptional electrical and thermal conductivities, making them highly promising for applications in advanced nuclear materials, battery plate protection materials, and aero-engine functional materials. This review aims to provide a comprehensive understanding of MAX phase coatings. It presents an overview of their compositions and microstructure, highlighting well-established structures like 211, 312, and 413. Furthermore, it delves into the various synthesis methods employed in fabricating MAX phase coatings, including physical vapor deposition, chemical vapor deposition, spraying methods, and laser cladding, among others. The potential applications of MAX phase coatings, high-temperature oxidation resistance, mechanical protection, salt spray corrosion resistance, etc., are also investigated. Finally, this review discusses the future potential of MAX phase coatings and proposes areas for further research and improvement. The primary goal is to offer theoretical guidance and innovative ideas for the synthesis and development of superior MAX phase coatings for commercial applications.

MXene Nanoribbon Aerogel-Based Gradient Conductivity Electromagnetic Interference Shields with Unprecedented Combination of High Green Index and Shielding Effectiveness

The desire to reduce secondary pollution from shielded electronics devices demands electromagnetic interference (EMI) shields with high green index (GI), which is the ratio of absorbance over reflectance. Achieving high GI values simultaneously with high shielding effectiveness (SE) over 50 dB is a serious unresolved challenge. Reducing the impedance mismatch between the shield and free space is the key to reducing the reflection of incoming radiation and enabling more penetration into the body of the shield for absorption. Here a sandwich structure with gradient conductivity is introduced that achieves a combination of high GI (≈2) and SE (70 dB). The top layer deliberately uses an aerogel of low conductivity MXene nanoribbon in PEDOT:PSS polymer to boost the GI. The aerogel also reduces the permittivity of the shield, as another way to reduce the impedance mismatch for a nonmagnetic material. The bottom layer consists of a MXene nanosheet-polymer with its high metal-like conductivity to provide high SE. This successful demonstration is expected to lead to other novel ways to create conductivity gradient EMI shields.

Robust Multifunctional Films with Excellent EMI Shielding, Anti-Peeling, and Joule Heating Performances Enabled by an Encapsulated Highly Conductive Fabric Strategy

Recently, the issue of electromagnetic pollution has become increasingly prominent. Flexible polymer films with various conductive fillers are preferred to address this problem due to their highly efficient and durable electromagnetic interference (EMI) shielding performance. However, their applications are restricted by the unbalanced and insufficient electromagnetic wave absorption and shielding capabilities, as well as the weak interlayer bonding force. In this work, robust flexible multifunctional AgNW/MXene/NiCo-C (AMN) films are fabricated by hierarchical casting assembly and an encapsulated conductive fabric strategy. The synergistic effect of the conductive-absorption integrated sandwich core fabric and the conductive encapsulation layer collaborate to provide excellent absorption-dominated EMI shielding (EMI SEmax = 89.12 dB with an ultralow reflectivity value of 0.19) and Joule heating (a high temperature of 103.5 °C at 4.5 V) performances. Besides, AMN films with embedded fabrics as a reinforcement structure achieved enhanced peel (1.97 N mm-1) and tensile (7.85 MPa) strengths through an interface enhancement process (plasma and pre-immersion treatments). In conclusion, this paper proposes a feasible paradigm to prepare flexible multifunctional conductive films, which demonstrate tremendous potential for applications in the wearable electronics and aerospace fields.

Succulent inspired grown g-C3N4@lithium sodium niobate for supercapacitors and piezo-tuned electrochemical potential controlled smart electromagnetic shielding management

A synchronous way of energy generation and storage in a single portable device is in high demand for the development of high-end electromagnetic interference (EMI) free modern electronics. Thus, this study highlights the devising of a piezoelectrically self-chargeable symmetric supercapacitor (PSCS) device using a polyvinyl alcohol (PVA)/succulent inspired grown g-C3N4@lithium sodium niobate (GNLNN)/potassium hydroxide (KOH) based piezo separator with GNLNN electrode. The GNLNN electrode exhibits a surface capacitive controlled specific capacitance of 503 F g-1. The PSCS device exhibits an energy density of 15.3 W h kg-1 and a power density of 4.2 kW kg-1 with an impressive capacitive retention capability of 93.2% after 6000 cycles of charging-discharging. The PSCS device can be charged up to 393 mV within 180 s under 14.2 N of cyclic pressing by human finger imparting. The fabricated PSCS device was also investigated for self-charging potential regulated smart EMI shielding applications. The smart PSCS device achieves an 88.3 dB increment from 40.9 dB of EMI shielding under charging from 0 mV to 300 mV. The increased charging potential of the PSCS device enhances the destructive interference and leads to boosted absorption and decreased reflection of incident EM radiation.

Synergistic Layered Design of Aerogel Nanocomposite of Graphene Nanoribbon/MXene with Tunable Absorption Dominated Electromagnetic Interference Shielding

Electromagnetic pollution presents growing challenges due to the rapid expansion of portable electronic and communication systems, necessitating lightweight materials with superior shielding capabilities. While prior studies focused on enhancing electromagnetic interference (EMI) shielding effectiveness (SE), less attention is given to absorption-dominant shielding mechanisms, which mitigate secondary pollution. By leveraging material science and engineering design, a layered structure is developed comprising rGOnR/MXene-PDMS nanocomposite and a MXene film, demonstrating exceptional EMI shielding and ultra-high electromagnetic wave absorption. The 3D interconnected network of the nanocomposite, with lower conductivity (10-3-10-2 S/cm), facilitates a tuned impedance matching layer with effective dielectric permittivity, and high attenuation capability through conduction loss, polarization loss at heterogeneous interfaces, and multiple scattering and reflections. Additionally, the higher conductivity MXene layer exhibits superior SE, reflecting passed electromagnetic waves back to the nanocomposite for further attenuation due to a π/2 phase shift between incident and back-surface reflected electromagnetic waves. The synergistic effect of the layered structures markedly enhances total SE to 54.1 dB over the Ku-band at a 2.5 mm thickness. Furthermore, the study investigates the impact of hybridized layered structure on reducing the minimum required thickness to achieve a peak absorption (A) power of 0.88 at a 2.5 mm thickness.

Exploring the efficacy and future potential of polypyrrole/metal oxide nanocomposites for electromagnetic interference shielding: a review

With recent advancements in technology, the emission of electromagnetic radiation has emerged as a significant issue due to electromagnetic interferences. These interferences include various undesirable emissions that can degrade the performance of equipment and structures. If left unresolved, these complications can create extra damage to the security operations and communication systems of numerous electronic devices. Various studies have been conducted to address these issues. In recent years, electrically conductive polypyrrole has gained a unique position because of its many advantageous properties. The absorption of microwaves and the electromagnetic interference (EMI) shielding characteristics of electrically conductive polypyrrole can be described in relation to its great electrical conductivity with strong relaxation and polarization effects due to the existence of strong bonds or localized charges. In the present review, advancements in electromagnetic interference shielding with conjugated polypyrrole and its nanocomposites with metal oxides are discussed and correlated with various properties such as dielectric properties, magnetic properties, electrical conductivity, and microwave adsorption properties. This review also focuses on identifying the most suitable polypyrrole-based metal oxide nanocomposites for electromagnetic interference shielding applications.

Enhanced polarization via Joule heating in wood-derived carbon materials for absorption-dominated EMI shielding

To cope with sophisticated application scenarios, carbon materials can provide opportunities for integrating multi-functionalities into superior electromagnetic interference (EMI) shielding properties. Nevertheless, carbon materials usually possess high electrical conductivity, which allows them to counteract electromagnetic waves by reflection. Moreover, the identification of factors that dominate the shielding mechanisms has typically been result-oriented, leading to a reliance on a trial-and-error approach for the development of shielding materials. Thus, it is crucial to identify the dominant factors for EMI shielding and elucidate the mechanism underlying the coordination of the balance between reflection and absorption in carbon materials. In this study, we developed a promising and viable approach to create Co@CNTs embedded in carbonized wood (CW) via chemical vapor deposition, producing Co@CNTs/CW foams. The CNTs, densely grown on the CW surface, tightly encapsulated the Co nanoparticles within them. By manipulating the Co content, the defect density and CNT length varied within the Co@CNTs. Through first-principles calculations, these variations substantially influenced the work function, charge density, and dipole moment of the Co@CNTs. Thus, defect-induced and interfacial polarizations were improved, inducing a transformation of the shielding mechanism from reflection to absorption. Regarding the Co@CNTs/CW foams, while high conductivity was essential for achieving satisfactory shielding performance, the enhanced polarization loss dominated the contribution of absorption to the overall shielding effectiveness. Taking advantage of the enhanced polarizations, the Co@CNTs/CW foams exhibited an impressive shielding effectiveness of 42.0 dB, along with an absorptivity of 0.64, which were instrumental in effectively minimizing secondary reflections. Remarkably, these as-prepared foams possessed outstanding hydrophobicity and Joule heating features with a water contact angle of 138° and a saturation temperature of 85.5 °C (2.5 V). Through the stimulation of voltage-driven Joule heating, the absorptivity of Co@CNTs/CW foams can be significantly enhanced to a range of 0.61 to 0.73, irrespective of the Co content. This research would provide a new avenue for designing carbon materials with an absorption-dominated mechanism integrated into EMI shielding performance.

Recent Trends in Polymeric Foams and Porous Structures for Electromagnetic Interference Shielding Applications

Polymer-based (nano)composite foams containing conductive (nano)fillers limit electromagnetic interference (EMI) pollution, and have been shown to act as good shielding materials in electronic devices. However, due to their high (micro)structural complexity, there is still a great deal to learn about the shielding mechanisms in these materials; understanding this is necessary to study the relationship between the properties of the microstructure and the porous structure, especially their EMI shielding efficiency (EMI SE). Targeting and controlling the electrical conductivity through a controlled distribution of conductive nanofillers are two of the main objectives when combining foaming with the addition of nanofillers; to achieve this, both single or combined nanofillers (nanohybrids) are used (as there is a direct relationship between electrical conductivity and EMI SE), as are the main shielding mechanisms working on the foams (which are expected to be absorption-dominated). The present review considers the most significant developments over the last three years concerning polymer-based foams containing conductive nanofillers, especially carbon-based nanofillers, as well as other porous structures created using new technologies such as 3D printing for EMI shielding applications. It starts by detailing the microcellular foaming strategy, which develops polymer foams with enhanced EMI shielding, and it particularly focuses on technologies using supercritical CO2 (sCO2). It also notes the use of polymer foams as templates to prepare carbon foams with high EMI shielding performances for high temperature applications, as well as a recent strategy which combines different functional (nano)fillers to create nanohybrids. This review also explains the control and selective distribution of the nanofillers, which favor an effective conductive network formation, which thus promotes the enhancement of the EMI SE. The recent use of computational approaches to tailor the EMI shielding properties are given, as are new possibilities for creating components with varied porous structures using the abovementioned materials and 3D printing. Finally, future perspectives are discussed.