Dielectric Loss Mechanisms Research Articles

Hierarchical Engineering on Built‐In Electric Field of Bimetallic Zeolitic Imidazolate Derivatives Towards Amplified Dielectric Loss

AbstractConstruction of built‐in electric field (BIEF) in nanohybrids has been demonstrated as an efficacious strategy to boost the dielectric loss by facilitating oriented transfer and transition of charges, thus optimizing the electromagnetic wave absorption property. However, the specific influence of BIEF on interface polarization needs to explore thoroughly and the BIEF strength should be further augmented. Herein, several dielectric systems incorporated Mott–Schottky heterojunctions and hollow structures are designed and constructed, where bimetallic zeolitic imidazolate framework are employed to derive Cu‐ZnO Mott–Schottky heterojunctions, and hierarchical structures and BIEF are further enriched by introducing hollow structure and reduced graphene oxide. The well‐established “double” BIEF verified by theoretical calculation and hollow engineering can regulate the conductivity, and enhance the polarization relaxation effectively. Especially, there always coexisted both enhanced charge separation and reversed charge distribution in this “double” BIEF, boosting the interface polarization. Attributing to the synergy of well‐matched impedance and amplified dielectric loss, the obtained hybrids exhibited superior absorption (reflection loss of −46.29 dB and an ultra‐wide effective absorption bandwidth of 7.6 GHz at only 1.6 mm). This work proves an innovative model for dissecting dielectric loss mechanisms and pioneers a novel strategy to explore advanced absorbers through enhancing BIEF.

Preparation of M-type barium ferrite submicron absorbing powder by one-step high-temperature ball milling and its particle structure regulation

This study investigates a simple and rapid process for directly preparing M-type barium ferrite using high-temperature ball milling. By adjusting the rotation speed of the high-temperature ball milling, the morphology and size of the powder can be altered to regulate its electromagnetic properties, aiming for an overall good absorbing effect. The powder’s morphology, agglomeration properties, elemental valence states, and electromagnetic parameters were characterized using SEM, BET, XPS, EDS, and VNA. The results show that as the milling speed increases, the particle size of the M-type barium ferrite decreases, transitioning from the typical hexagonal flake particles to spherical block particles, forming a porous loose structure with richer dielectric loss mechanisms and enhanced electromagnetic wave loss capacity. Electromagnetic loss performance analysis indicates that at a milling speed of 50 rpm, the powder achieves the best electromagnetic loss of −61.16 dB at a matching thickness of 8.77 mm and a microwave absorption bandwidth of 4.1 GHz.

Zn-Al Ferrite/Polypyrrole Nanocomposites: Structure and Dielectric and Magnetic Properties for Microwave Applications.

In this study, Zn-Al ferrite/polypyrrole (PPy) nanocomposites were synthesized and thoroughly characterized to explore their potential for microwave applications. X-ray diffraction analysis confirmed the presence of ZnO, AlFeO3, and Fe2O3 phases, with the crystal size decreasing from 31 nm to 19.6 nm as aluminum content increased. High-resolution transmission electron microscopy (HR-TEM) revealed a distinctive core-shell morphology, where the polypyrrole encapsulates the ZnAlxFe2-xO4 particles. Magnetic measurements showed that decreasing aluminum concentration led to a reduction in both saturation magnetization (Ms) from 75 emu/g to 36 emu/g and remanent magnetization (Mr) from 2.26 emu/g to 2.00 emu/g. Dielectric analysis indicated that both the real (ε') and imaginary (ε″) components of dielectric permittivity decreased with increasing frequency, particularly between 10 and 14 GHz. Furthermore, electrical modulus analysis highlighted the significant impact of aluminum doping on relaxation time (τIP), indicating the presence of interface polarization. Impedance spectroscopy results underscored the dominance of interface polarization at lower frequencies and the presence of strong conduction paths at higher frequencies. These combined magnetic and dielectric loss mechanisms suggest that the Zn-Al ferrite/polypyrrole nanocomposite is a promising candidate for advanced microwave absorption applications.

Heterointerface-engineered SnO2@SnO nanoparticle@foamed C composites for prominent microwave absorption and thermal conduction performance

The development of multifunctional materials with wide-band microwave absorption properties (MWAPs), high thermal conductivity (TC), and excellent electrical isolation is rather challenging due to the performance incompatibility. To resolve this challenge, SnO2@SnO nanoparticle(NP)@foamed C composites are synthesized as an electrically insulated filler with low loads, excellent MWAPs, and high TC via a facile salt-template-assisted freeze-drying-annealing route. By controlling the annealing temperature (Ta) and the amount of SnCl2·2H2O (n), their heterointerfaces, textures, and defects were finely modulated. Our results show that the SnO2@SnO NP@foamed C composites have a large TC (3.48 W/(m·K); 1.5 wt% load), a minimal reflection loss (RLmin) of −40.75 dB, and an effective absorption bandwidth (EAB) of 6.88 GHz at a low load of 25 wt%. The composites exhibit an 8.0 % increase in TC, a 9.4 % increase in EAB, and an 11.0 % increase in RLmin compared with pure foamed C. Besides, the mechanism of dielectric loss and thermal transfer at the atomic level was revealed by the calculations of the density of states (DOS) and the phonon density of states (PDOS). The boosted MWAPs could be ascribed to the breakdown of local microstructural symmetry and the formation of extra electric dipoles at the interfaces of SnO/C, SnO/SnO2, and SnO2/C. The improved TC mainly results from the combined effect of the low-energy phonons from SnOx and the high-energy phonons from C. This study provides theoretical guidance for designing integrated materials with effective microwave absorption and thermal conduction in the electronic industry.

Effect of Etching Methods on Dielectric Losses in Transmons

Superconducting qubits are considered as a promising platform for implementing a fault tolerant quantum computing. However, surface defects of superconductors and the substrate leading to qubit state decoherence and fluctuations in qubit parameters constitute a significant problem. The amount and type of defects depend both on the chip materials and fabrication procedure. In this work, transmons produced by two different methods of aluminum etching: wet etching in a solution of weak acids and dry etching using a chlorine-based plasma are experimentally studied. The relaxation and coherence times for dry-etched qubits are more than twice as long as those for wet-etched ones. Additionally, the analysis of time fluctuations of qubit frequencies and relaxation times, which is an effective method to identify the dominant dielectric loss mechanisms, i-ndicates a significantly lower impact of two-level systems in the dry-etched qubits compared to the wet-etched ones.

Fluorine atom substituted aromatic polyimides: Unlocking extraordinary dielectric performance and comprehensive advantages

Low-dielectric polymers face prominent development challenges at high frequency. Particularly, the relationship between the high-frequency dielectric loss and polymer structures remains not clear enough. Besides, the strategies for achieving low dielectric loss usually have to scarify other important materials properties, e.g., heat resistance or dimensional stability. Herein, fluorine-containing aromatic polyimides were systematically investigated. Among them, simple fluorine atom (-F) substituted polyimides exhibit remarkable low dielectric loss at high frequency (10 GHz) as well as comprehensive advantages, including near-zero thermal expansion coefficient, extremely high thermal decomposition stability, high optical transmittance and excellent mechanical properties. The fundamental mechanisms of low dielectric loss are fully discussed. Benefiting from the unique electric effect and compact size of -F group, -F substituted polyimides display low dipolar density and strongly restricted dipolar motion, contributing to a reduced permanent dipolar polarization loss. Moreover, the concept of induced dipolar polarization was introduced to illustrate the nontrivial impact of F-substituted effect on conjugated electron cloud polarization loss in aromatic polymer system. This work not only provides valuable insights for understanding the mechanism of dielectric loss at high frequency for aromatic polymers, but also opens up broader application possibilities of polyimides in microelectronic and wireless communications industries.

Ultralow-content Co decoration on Ti3C2Tx MXene induced electromagnetic characteristic modulation for efficient microwave absorption

Ti3C2Tx MXene has been regarded as a promising candidate for advanced microwave absorption materials. However, the microwave absorbing performance of Ti3C2Tx MXene is suppressed by the single dielectric loss mechanism and impedance mismatch because of the high conductivity. To effectuate a good absorption capability of Ti3C2Tx MXene, this paper constructs a heterostructured Co/Ti3C2Tx hybrid by atomic layer deposition of magnetic Co nanoparticles on Ti3C2Tx nanosheets. The microstructures, magnetism, and microwave absorption behaviors of the Co/Ti3C2Tx hybrids are investigated systematically. The results show that the frequency-dependent electromagnetic parameters of the Ti3C2Tx MXene become tunable by controlling the content of Co decorations, which are conducive to both magnetic loss and impedance matching. The Co/Ti3C2Tx hybrid with ultralow Co decoration content (only 1.52 wt%) achieves the minimum reflect loss of −54.32 dB at a thin matched thickness of 1.29 mm, and the corresponding effective absorption bandwidth with reflection loss below −10 dB reaches 4.29 GHz. The atomic layer deposited magnetic metal nanostructures provides an effective strategy for preparing MXene-based hybrids which not only have high absorption efficiency but also significantly reduce the use of magnetic metals.

Microwave dielectric characterization and loss mechanism of biowaste during pyrolysis

The effectiveness of microwave heating of biomass depends on the changes in dielectric properties. This study systematically investigated the microwave dielectric properties and loss mechanism of biowaste at different frequencies (915 and 2,450 MHz) and temperatures (25–800 °C) using the cavity perturbation method. The gas emissions and properties of the biochar produced during pyrolysis were characterised by SEM, XRD, and TG-FTIR. The findings revealed that the dielectric properties and penetration depth of the biomass and biochar changed significantly during microwave pyrolysis. The dielectric constant and dielectric loss coefficient first increased and then decreased during the drying stage, and they decreased continuously with the volatile’s generation in the pyrolysis stage, while the formation and high conductivity of biochar promoted a sharp increase in dielectric properties during the carbonisation stage. The loss tangent angle is 0.01–0.05 in the first two stages, while it increased to 0.10–0.25 in the carbonization stage, demonstrated that the biowaste is a low-loss material. However, the microwave absorption capacity was enhanced for pyrolyzed biochar. The loss mechanism revealed that dipole polarisation primarily contributes to the dielectric loss during the drying and pyrolysis stages, whereas interfacial polarisation plays an important role during the carbonisation stage. The data provided in this paper contribute to the evaluation of microwave penetration depth in biomass and the design of large-scale microwave-based heating systems. Furthermore, this study offers a theoretical basis for modelling and simulating the microwave heating of biomass and achieving efficient energy conversion.

Dielectric Property, AC Conductivity, and Electric Modulus Studies of Pristine and Green‐Synthesized ZnO Nanoparticles

Frequency‐dependent dielectric constant and dielectric loss of pristine and green‐synthesized (using Tabernaemontana divaricata flower extract) ZnO nanoparticles (NPs) are studied at different temperatures. Below 1 kHz frequency and at temperatures above 100 °C, ZnO NPs have giant dielectric constant values (≈3 × 104). At lower frequencies and at/below 100 °C, the nature of temperature dependence of dielectric constant for pristine and green‐synthesized ZnO NPs are reversed, and this anomalous temperature dependence is correlated with the in‐plane and out‐of‐plane thermal expansions of ZnO. A temperature‐dependent poly‐dispersive relaxation mechanism in ZnO has been observed. The electrical conduction mechanism is found to be significantly modulated by the use of flower extract. The electric modulus study suggests similar mechanism of electrical conduction and dielectric polarization followed in these materials. A plausible growth mechanism of the ZnO NPs in presence of the flower extract is explored. Variations in the dielectric constant, dielectric loss, conductivity, and polarization mechanisms of the ZnO NPs are understood as signatures of the capping effect of the phytochemicals present in the flower extract on the crystal growth and formation of grain boundaries.

Effects of Zr4+ and Hf4+ substitution on the structure and dielectric response of Ba4Sm9.33Ti18O54 ceramics

Microwave dielectric ceramics with high relative permittivity (εr) are commonly used for the miniaturation of microwave devices. The dielectric loss mechanism of microwave dielectric ceramics, as well as the property modification, has been a concerned topic among scholars. Herein, the lattice structure, defects, and broadband dielectric response of Zr4+ and Hf4+ substituted Ba4Sm9.33Ti18O54 (BST) ceramics are systematically examined. The negative temperature coefficient of resonant frequency (τf) of BST ceramics can be tuned to near zero via ion substitution, owing to the Sm2Ti2O7 second phase with a large positive τf. Optimal microwave dielectric properties of εr = 81.3, Q × f = 10,800 GHz, and τf = −4.6 ppm/°C are achieved. The lattice vibration behavior and defect concentration are analyzed by Raman spectra and thermally stimulated depolarization currents (TSDC), respectively. The increasing volume of the unit cell and TiO6 octahedra, which is because of the large-radius substitution ions, leads to an increase in lattice vibration damping factor and the generation of more oxygen vacancies (VO∙∙). Therefore, the dielectric losses in the microwave and terahertz (THz) bands increase after substitution. Meanwhile, the low-frequency dielectric losses at high temperatures also increase due to the weak restraint of carriers by the lattice. The broadband loss mechanism of Zr4+ and Hf4+ substituted BST ceramics related to lattice vibration and defects might be referenced for developing low-loss dielectric ceramics.

Enhanced microwave absorption performance of Fe3Al flakes by optimizing the carbon nanotube coatings.

Fe3Al is a good magnetic loss absorber for microwave absorption. However, due to the relatively high density and poor impedance matching ratio, the potential of Fe3Al cannot be fully released. Herein, a dielectric loss absorber of carbon nanotubes (CNTs) is coupled with Fe3Al to form Fe3Al/CNTs composite absorbers. CNTs are randomly tangled and coated on the surface of the Fe3Al flakes, forming a connecting conductive network. By carefully tuning the content of CNTs, the optimized Fe3Al/CNTs composite absorber with 1.5% of CNTs can combine both magnetic loss and dielectric loss mechanisms, thus achieving an impedance matching ratio close to 1 while keeping strong attenuation for enhanced microwave absorption. As a result, an effective absorption bandwidth (RL ≤ -10 dB) of 4.73 GHz at a thickness of 2 mm is achieved.

Effect of carbon allotropes and thickness variation on the EMI shielding properties of PANI/NFO@CNTs and PANI/NFO@RGO ternary composite systems.

The innovative design of thin, multiphase flexible composite systems with good mechanical properties, low density and improved EMI shielding properties at low filler content has become a key area of research. In this work, we report the low temperature synthesis of three-dimensional ternary composites (PANI/NFO@CNTs and PANI/NFO@RGO) by oxidative chemical polymerization of aniline in the presence of two different binary composites, viz. NFO@CNTs and NFO@RGO. Enhanced impedance matching is achieved by varying the ratio of the carbon allotropes (CNTs and RGO) to the ferrite component. The synthesis of NFO, PANI/NFO@CNTs and PANI/NFO@RGO is validated by XRD and FTIR spectroscopy. Field emission scanning electron microscopy (FE-SEM) confirmed the synthesis of core-shell structures of PANI/NFO@CNTs and PANI/NFO@RGO, where the binary composites (NFO@CNTs and NFO@RGO) serve as a core onto which a tubular PANI layer was coated. Shielding effectiveness of 22.36 dB (99.41% attenuation) is exhibited by the ternary composite PANI/NFO@CNTs (8 : 1), while for PANI/NFO@RGO (20 : 1) a total shielding effectiveness of 31 dB equivalent to 99.92% attenuation was observed at a thickness of 2 mm. The ternary composite PANI/NFO@RGO (20 : 1) 4 mm showed a maximum SET of 43 dB corresponding to 99.996% attenuation of incident EM waves. The enhanced EMI shielding properties of the synthesized ternary composite systems are accredited to good impedance matching, effective dielectric and magnetic loss mechanisms and good conductivity, which facilitate multiple reflections and scattering of incident radiation.

Interfacial engineering of hybrid MXene-Ni-CF tri-core–shell composites for electromagnetic interference shielding and E-heating applications

In response to the the needs for multifunctional carbon fiber reinforced polymer (CFRP) composites, we present a novel, tri-core–shell CFRP consisting of MXene, nickel (Ni), and CF synthesized throughlayer-by-layer assembly. The hybridcomposites demonstrate remarkable electrical conductivity and electromagnetic interference (EMI) shielding, alongside efficient electrical (E-) heating properties. Additionally, the MXene-Ni-CF/EP hybrid composite displayed improved flexural strength and ILSS compared to Ni-CF/EP composite. Outstanding enhancements were observed in both the through-thickness and in-plane electrical conductivities, with a 116-fold and 14-fold improvement, respectively, attributed to the complex MXene-Ni-CF conductive paths. The hierarchical compositessignificantly outperformed the state of the art and demonstrated a superior EMI shielding efficiency of 72.4 dB by virtue of the dielectric and magnetic loss mechanisms. Thelow-voltage-driven E-heating capacity could be utilized for de-icing applications due to the thermally conductive networks. The producedcomposites offer a highly promising solution to tackle challenges associated with lightning strikes and icy weather conditions, while also aligning with the goal of cost-effective industrial production.

Microwave absorption behaviour of novel rib cage structured piper betel leaves: Effect of drying and sintering processes

This paper focuses on a simple and cost−effective technique to explore the impact of the drying and sintering process on the microwave absorption behavior of piper betel leaves. The microwave absorption behavior of dried leaves and leaves sintered at 800 ℃ for 3 h was examined. X − Ray Diffraction (XRD) study confirms the presence of elemental composites such as sucrose, cellulose, hemicellulose, and lignin in the dried sample, while sintered betel powder exhibited crystalline phases of CaSiO5, SiO2, Mg2P2O7, CaO, KPO3, Na2K(P3O9) K2CO3, and CaCO3. Microstructure study showed a unique rib cage and nanorod strand structure in the dried leaves and a porous structure in the sintered leaves. Spectroscopy analysis confirmed the occurrence of chemical composites in both dried and sintered betel leaves. The optical band gap of the sintered and dried leaves was 2.7 and 2 eV, respectively. Dielectric loss and loss mechanism in the betel leaf were studied using the DAK 3.5 kit. Results of the microwave absorption studies revealed that dried betel leaves with a thickness of 9 mm exhibited a high Reflection Loss (RLmax) of − 22.69 dB at 11.37 GHz. Also, the same thickness has an effective absorption bandwidth (EAB) of 3.69 GHz, 87.8% of the X band frequency. On the other hand, sintered betel leaves with a thickness of 9 mm have a reflection loss (RLmax) of − 48.57 dB at 10.52 GHz, with an effective absorption bandwidth (EAB) of 2.88 GHz, covering 68.5% of the X band frequency.

A kind of Fe3N alloy powders prepared by high-temperature chemical nitriding treatment with excellent wave-absorbing properties in C band

Firstly, the flake Fe95Si1B2P0.5Cu1.5 alloy powders were prepared by the combined technology of “medium frequency melting + 3D printing + high energy ball milling”, and then the flake single phase ε-Fe3(SiBPCu)-N powders were prepared by the chemical high temperature nitriding reaction using the flake alloy powders prepared as the precursors. The samples were characterized by Field Emission Scanning Electron Microscope (FESEM), X-ray Diffractometer(XRD) and Vector Network Analyzer, and the electromagnetic parameters and electromagnetic loss mechanism of the alloy powders prepared by different nitriding processes in 0.3–8.5 GHz band were focused, and wave-absorbing properties were optimized according to the transmission line theory finally. FESEM showed that holes were formed on the surface of the powders after nitriding, which was easy for electromagnetic waves to be absorbed. XRD confirmed that the physical phase structure of the alloy powder prepared after salt bath nitriding was ε-Fe3N, and average crystallite size of ε-Fe3N increased with the complete nitriding reaction. The generation of ε-Fe3N phase lead to an increase in the real part of the complex permittivity of the alloy powder, and the real part of the permeability decreases slightly, however, larger average crystallite size of ε-Fe3N is beneficial for the improvement of the permeability. After the nitriding reaction at 580 °C *1h, the loss mechanism of alloy powders is changed from magnetic loss dominated to a dual loss mechanism of dielectric loss dominated and magnetic loss supplemented, and the loss angle tangent value increased from 0.6 to 0.7 to 2.3–1.0, and the thickness values of interference absorption decreased significantly, which is conducive to the realization of the effect of strong absorption of thin material. Taking a multilayer laminate thickness of 5.0 mm as the design index, the optimized GF/FeSiBPCu-N powders (thickness of 1 mm)/GF composite plate has excellent wave absorption in the C-band with reflectivity R < −10 dB in the frequency band of 5.52 ∼ 8.5 GHz and a bandwidth of nearly 3 GHz, which has achieved a breakthrough.

Porous Carbonaceous Aerogels Composed of Multiscale Carbon-Based Units for High-Performance Microwave Absorption.

Structural engineering is definitely a promising and effective approach to develop excellent microwave absorbing materials with quantities of advantages. Especially, when carbon materials act as the constituents, the fabricated absorbers are available to gain more prominent absorption performance. However, extra high conductivities and the widespread aggregations and stacking of low-dimensional carbon materials always detrimentally affect the impedance matching and weaken the attenuation capacity, inevitably confining their further absorption applications. Herein, by introducing the amorphous chiral carbon nanocoils to overcome the challenges and achieve the strategies of structure optimization and multicomponent recombination, the reduced graphene oxide/carbon nanocoil/carbon nanotube aerogels were successfully synthesized by a successive hydrothermal method and freeze-drying strategy. The as-obtained aerogels possess a porous architecture that contribute to the extraordinary impedance matching and multiple reflections, which integrate the multifarious dielectric loss mechanisms of diverse carbon materials simultaneously. Benefiting from the tricomponent synergistic effect, the ultralight aerogels reach an outstanding microwave absorption property with an extremely low filler content of only 6 wt %. This work provides a helpful approach to design hierarchical absorbers consisted by multidimensional carbon materials for fantastic microwave absorption.

Confined In-Situ Encapsulation of Co/C Composites with Increased Heterogeneous Interface Polarization for Enhanced Electromagnetic Performance.

It is an urgent problem to realize reliable microwave absorption materials (MAMs) with low density. To address this issue, a series of controlled experiments w ere carried out, which indicated that the tubular structure enables excellent microwave absorption properties with a lower powder filling rate. This performance is attributable to the combined dielectric and magnetic loss mechanisms provided by Co/C and the interface polarization facilitated by multiple heterogeneous interfaces. Particularly, Co@C nanotubes, benefiting from the enhanced heterointerface polarization due to their abundant specific surface area and the reduced electron migration barrier induced by their 1D stacked structure, effectively achieved a dual enhancement of dielectric loss and polarization loss at lower powder filling ratios. Furthermore, the magnetic coupling effect of magnetic nanoparticle arrays in tubular structures is demonstrated by micromagnetic simulation, which have been few reported elsewhere. These propertied enable Co@C nanotubes to achieve minimum reflection lossand maximum effective absorption broadband values of 61.0dB and 5.5GHz, respectively, with a powder filling ratio of 20wt% and a thickness of 1.94mm. This study reveals the significance of designing 1D structures in reducing powder filling ratio and matching thickness, providing valuable insights for developing MAMs with different microstructures.

Biomass-derived ferrous magnetic carbon-based nanocomposites from loofah collaterals for excellent electromagnetic wave-absorbing materials

High-performance wave-absorbing materials are always pursuing the goals of thin, lightweight, wide and strong absorption. Hitherto carbonaceous materials are still one kind of the most popular wave-absorbing materials. This work proposed a facile biomass-derivation route to prepare carbonaceous wave-absorbing materials. Loofah collaterals were impregnated with Fe(NO3)3 solution, and a process of iron-catalyzed carbonization for the dried precursors ensued, leading to the formation of Fe@Fe3C/C ternary nanocomposites. It’s found that the Fe@Fe3C/C nanocomposites possessed the absorption abilities from 13.0 to 18.0 GHz with the effective absorbing bandwidth almost covered the Ku band. The superior wave-absorbing properties were mainly ascribed to the synergism of dielectric and magnetic loss mechanisms. Meanwhile, the improved impedance matching and the elevated attenuation ability also favored the strong absorption at specific thickness. This work paved the way for the green synthesis and mass production of high-efficient wave-absorbing materials, and further inspired the regeneration of biomass waste for electromagnetic applications.

B‐site internal‐strain regulation engineering of tungsten bronze structural dielectric ceramics

AbstractInternal strain is considered to be related to the dielectric loss of tungsten bronze structural ceramics, while its effects often cannot be effectively distinguished from non‐intrinsic factors. To quantitatively determine the influential mechanism of dielectric loss by internal strain, B‐site controllable co‐substituted (Al3+, Ga3+, and Sc3+) Ba4Nd9.33Ti18O54 ceramics with single phase were designed and synthesized, and the ratio is designed with the equivalent radius of substituted ions is equal to Ti4+. Through calibrating the global instability index, the relatively straightforward relationship between internal strain and Q×f value is established. As a result, a loss gradient (Q×f value from 8468 to 14311 GHz) and an almost stable real part of permittivity (εr ∼ 68 with near‐zero τf) can be obtained. Not only does it provide direct evidence for the effectiveness of internal strain control on dielectric loss, but also decouples three key parameters of microwave dielectric ceramics, which may be of great significance in future device physics, especially for all‐ceramic non‐Hermitian devices.

Novel preparation of FeCo alloy/graphene foam composites for efficient microwave absorption

Five groups of FeCo alloy/graphene foam (FeCo/GF) composites with different GF contents (1%, 2%, 3%, 4%, and 5% of the mass of the FeCo alloy) were prepared in this work. The results show that the morphology, saturation magnetization, and electromagnetic parameters of the composites were greatly affected by the GF amount. The reticular porous structure of GF significantly increases the multiple scattering events and loss paths of electromagnetic waves and provides an excellent electric loss. Being a typical soft magnetic material, FeCo exhibits a high saturation magnetization and an excellent magnetic loss. The FeCo/GF composite has excellent microwave absorption properties, which are attributed to its superior dielectric loss, conductive loss, natural resonance, and exchange resonance loss mechanisms. In particular, when the content of GF is 3% of the mass of FeCo alloy, it exhibits the best effective absorption bandwidth. With a matching thickness of only 1.85 mm, this composite achieves a maximum effective absorption bandwidth of 7.2 GHz (10.8–18 GHz). Additionally, when the content of GF is 4% of the mass of FeCo alloy, the sample exhibits the lowest reflection loss, which reaches −61.68 dB at a frequency of 3.44 GHz.