Dielectric Loss Mechanisms Research Articles

Dielectric properties and negative permittivity performance modulated by dual fillers in CNTs/TiN/CaCu3Ti4O12 ternary composites

Ceramic composites with negative permittivity have attracted widespread attention during the development of novel electromagnetic metamaterials. Herein, carbon nanotubes/TiN/CaCu3Ti4O12 (CNTs/TiN/CaCu3Ti4O12) ternary composites were prepared, and the effects of dual fillers on the dielectric properties of the ternary composites are discussed. The electrical conductivity increased markedly, and the conduction mechanism changed owing to the percolation of the dual conductor fillers. The switching of the reactance, from negative to positive, suggests that the ternary composites underwent a capacitive-inductive transition. The dielectric permittivity was negative owing to the plasmonic state of the free electrons in the percolating conductor fillers. Regulating the electron concentration by changing the filler content or adjusting the microstructure by changing the relative content of the dual fillers proved to be an effective way to tailor the negative permittivity performance of ternary composites. In addition, conduction loss dominated the dielectric loss mechanism of the negative permittivity composites. The realization and regulation mechanism of the negative permittivity of ternary composites are clarified, shedding light on the preparation and development of negative permittivity materials for various electromagnetic applications.

Epoxy composites filled with graphite nanoplatelets modified by FeNi nanoparticles: Structure and microwave properties

This paper is concerned with investigation of the structure and microwave properties of epoxy resin composites with graphite nanoplatelets (GNPs) decorated by FeNi nanoparticles prepared by the salt impregnation. It was confirmed by SEM and XRD that the method gives nanopowder where the metal componentFe20Ni80 is in the form of nanoparticles (20–40 nm in diameter) which are distributed over the surface and edges of the GNPs. The graphite phase in the investigated nanopowder is predominant, and Fe20Ni80 component mainly contains fcc FeNi3. Measurements of magnetic properties confirmed that Fe20Ni80 are small, randomly oriented assembly of spherical (or close to spherical) particles on the GNPs surface. The saturation magnetization of GNP-Fe20Ni80 particles is 25 emu/g and it weakly depends on temperature. Electrical resistivity measurements have shown that decoration of GNPs leads to essential increase of conductivities well as improvements EMR absorption properties in high frequency range (26–60 GHz) in (GNP-Fe20Ni80)/with in compression GNP/epoxy under the same volume content of 1.45 vol.%(GNP-Fe20Ni80)/L285 composites demonstrated superior broadband absorption properties with microwave absorption efficiency higher than 97% in the whole investigated frequency region.The effective absorption bandwidths are as high as 12.2 GHz were observed at the frequency range 41.9 and 53.2 GHz and 13.3 GHz at the frequency range 51.1 GHz–64.4 for this composite. It is assumed that decoration of GNPs surface by nanoscale Fe20Ni80 particles leads to a formation of the multiple dielectric and magnetic loss mechanisms, such as interfacial polarization, dipole polarization, space-charge polarization, eddy current loss, Debye dipolar relaxation, natural resonance and exchange resonance, which improve the microwave absorption properties of the investigated composites.

Facile fabrication of Fe/Fe5C2@N-doped porous carbon as an efficient microwave absorbent with strong and broadband absorption properties at an ultralow filler loading

The challenge of realizing low filler loading and high-performance microwave absorbing (MA) materials is still an urgent issue to be solved. Herein, porous N-doped carbon wrapped Fe/Fe5C2 (Fe/Fe5C2@NC) nanocomposite is successfully synthesized by a facile one-step calcination of carbon nitride and ferrocene precursors. The magnetic Fe/Fe5C2 nanoparticles are tightly and uniformly anchored on the wrinkled carbon nanosheets. Abundant of voids exist between the three-dimensional conductive carbon network, which can result in a low density and a strong interfacial polarization relaxation with effect. Based on the double attenuation mechanisms of dielectric loss and magnetic loss, the optimized Fe/Fe5C2@NC-800 possesses a minimum reflection loss value reaching −63.1 dB and an effective absorption bandwidth (EAB) as broad as 7.3 GHz with an extremely low filler loading of 4 wt%. The Fe/Fe5C2@NC-800 can even achieve a broad EAB within 4.5–18.0 GHz by tuning the absorber thickness in the range of 2.5–5.0 mm, covering nearly 85% of the whole measured frequency band. This work provides new insights for the development of advanced lightweight MA materials, which has wide effective absorption frequency range and strong absorption intensity at low filling levels.

Multi-interfacial magnetic carbon nanotubes encapsulated hydrangea-like NiMo/MoC/N-doped carbon composites for efficient microwave absorption

Developing high-performance microwave absorbing materials is still a challenge to address the electromagnetic pollution. Interfacial engineering to heighten interfacial polarization plays a key role in microwave absorption. In this work, Multiple interfacial magnetic carbon nanotubes encapsulated hydrangea-like NiMo/MoC/N-doped carbon were prepared via carbothermic reduction. The phase structure and electromagnetic properties can be regulated by thermal treatment temperature. Dielectric loss mechanisms were analyzed deeply by Debye relaxation theory. The results indicated the composites exhibit excellent microwave absorption properties. Reflection loss (RL) less than −20 dB can be achieved in the frequency range of 3.76–17.52 GHz with the absorber thickness varied from 1.3 mm to 5.0 mm when the thermal treatment temperature was 700 °C. The strongest RL value reach to −70.1 dB at 14.2 GHz with the absorber thickness of only 1.52 mm when the thermal treatment temperature is 800 °C. The radar cross section (RCS) reduction calculated through computer simulation technology is used to analyze the microwave absorption capability in the actual far field. The RCS reduction is 17.05 dBm2 when the scattering angle is 0°. This work provided a novel approach for realizing the multi-interface absorbers for high-performance microwave absorption.

Impact of reduced graphene oxide on microstructure evolution in m-caproamine/imidazole toughened epoxy composites – Synergia of viscoelastic and microwave absorption properties

The present study investigates the effect of reduced graphene oxide (r-GO) on the microstructure evolution, damping, and microwave absorption performance of the caproamine (CA) toughened epoxy /imidazole (m-CA/ER/MI/r-GO) system. The X-ray diffraction analysis revealed good dispersion levels of r-GO featuring intercalation of r-GO into galleries of polymer chains. The effective role of r-GO in tuning the microstructure was confirmed from SEM, AFM and TEM analysis and the consequence of this is reflected in the dynamic mechanical characteristics. The m-CA/ER/3 wt% r-GO composites achieved an outstanding microwave absorption performance with a reflection loss of −51.6 dB (99.999% microwave absorption) at 9.51 GHz and an effective absorption bandwidth of 2.48 GHz when compared to m-CA/ER composite. The microwave performances are justified with the attenuation constant, impedance matching ratio, and the dielectric loss mechanisms operating in the composites. Hence, the developed m-CA/ER/r-GO will serve as a potential multifunctional composite with synergetic thermomechanical properties and excellent microwave absorption performance.

Introducing graphite nanosheets to change the microscopic morphology of CoS nanoparticles to obtain ultra-thin and excellent electromagnetic wave absorption performance

The composite material of metal sulfide and dielectric material has always been regarded as a research hotspot in the field of electromagnetic wave absorption. In this work, the cobalt sulfide (CoS) particles were successfully grown on the modified graphite nanosheets (GNs) by the two-step hydrothermal method to obtain excellent CoS/GNs EM wave absorption materials. SEM images show that after adding GNs, the morphology of CoS particles will change from micron-scale regular spheres to irregular nano-fragments which attached to the surface of GNs. The reason is that the binding sites on the surface of GNs will limit the growth of CoS particles. Fortunately, the introduction of GNs not only adjusted the impedance matching performance of CoS, but also perfectly combined the dielectric loss and magnetic loss mechanisms. EM analysis showed that the minimum reflection loss (RLmin) of CoS/GNs materials is −52 dB at an ultra-thin thickness of 1.1 mm, and the effective absorption bandwidth (EAB) is 3.7 GHz (14.3 GHz–18 GHz). Therefore, this ultra-thin nanocomposite material is expected to have broad market application prospects.

Dielectric loss mechanism of powdered infant formula milk

Dipole loss of main compositions of powdered infant formula milk (PIFM), including whey protein (WP), fat and lactose and the ionic loss of PIFM were analyzed over frequency range of 10 to 3000 MHz at temperature range of 20–80 °C. Dielectric loss factor of PIFM decreased with increasing fat content, while increased with increasing WP content and lactose content at investigated frequencies in our study. The dipole loss of WP, fat and lactose followed Debye equation which increased with increasing frequency till around 1.2,1 and 1 GHz, respectively, and then decreased. Ionic loss of PIFM was constant with increasing frequency at investigated frequencies and increased with increasing temperature. A general formula to calculate ionic loss for both solid and liquid materials was obtained. Validation experiments based on the dielectric loss factor of different compositions indicated that increasing WP proportion in PIFM can increase heating rate in radio frequency field and also result in lower lipid oxidation of treated PIFM. This provides a solution to adjust RF heating performance and product quality based on loss mechanisms of different ingredients.

Dielectric Loss Mechanism in Electromagnetic Wave Absorbing Materials.

Electromagnetic (EM) wave absorbing materials play an increasingly important role in modern society for their multi‐functional in military stealth and incoming 5G smart era. Dielectric loss EM wave absorbers and underlying loss mechanism investigation are of great significance to unveil EM wave attenuation behaviors of materials and guide novel dielectric loss materials design. However, current researches focus more on materials synthesis rather than in‐depth mechanism study. Herein, comprehensive views toward dielectric loss mechanisms including interfacial polarization, dipolar polarization, conductive loss, and defect‐induced polarization are provided. Particularly, some misunderstandings and ambiguous concepts for each mechanism are highlighted. Besides, in‐depth dielectric loss study and novel dielectric loss mechanisms are emphasized. Moreover, new dielectric loss mechanism regulation strategies instead of regular components compositing are summarized to provide inspiring thoughts toward simple and effective EM wave attenuation behavior modulation.

Combustion synthesis of porous Fe3-xZnxO4 powders for high-performance microwave absorbers

Fe3-xZnxO4 (x = 0.1, 0.2, and 0.3) powders were synthesized by facile combustion method using metal nitrates as oxidants and glycine as fuel. The structural, microstructural, magnetic, and microwave absorption properties are characterized as a function of Zn2+ substitution. With the increase of Zn2+ contents, some hematite (α-Fe2O3) phases appeared together with the magnetite (Fe3O4) phase. The transmission and scanning electron microscopy observations showed that the particle size was decreased from 120 to 70 nm, while the amount and size of pores increased with adding Zn2+ cations. The as-synthesized Fe2.9Zn0.1O4 powders had the highest saturation magnetization of 92 emu/g, which decreased to 72 emu/g for the Fe2.7Zn0.3O4 sample. The Fe2.8Zn0.2O4 sample exhibited an intense reflection loss of −53 dB in the Ku band at the matching thickness of 2 mm. Despite the reduction of reflection loss, the effective bandwidth increased up to 5.5 GHz with the Zn content, which is attributed to the better impedance matching and higher contribution of magnetic and dielectric loss mechanisms.

PVDF/CFO-anchored CNTs ternary composite system with enhanced EMI shielding and EMW absorption properties

Lightweight, flexible electromagnetic interference (EMI) shields and electromagnetic wave (EMW) absorbers with low filler and improved impedance matching is the subject of intense global research. In this work, CoFe2O4@CNTs hybrids are synthesized in situ by solvothermal method and then the flexible PVDF/CoFe2O4@CNTs composites are prepared by solution casting. The content of CNT’s in the CoFe2O4@CNTs hybrids was varied between 1 and 5 wt% of the CFO. These nano-inclusions (CoFe2O4 (CFO) decorated CNTs) were dispersed in polyvinylidene fluoride (PVDF) with 7 wt%, 10 wt% and 15 wt%. The prepared systems were characterized using X-ray diffractometry, FTIR spectroscopy, transmission electron microscopy, vibrating samples magnetometry and vector network analyzer. TEM results show well dispersed CFO nanoparticles uniformly attached to the walls of CNTs, thus confirming their functionalization. Good impedance matching, which is a prerequisite for EMW absorption was observed for 7 wt% CFO@CNTs hybrid in PVDF which resulted in shielding effectiveness of 12.68 dB corresponding to 94.65% attenuation at a thickness of 1.88 mm. Moreover, EMW absorption properties of PVDF/CFO@CNTs composites were also studied by backing with metallic conductor where the same sample also showed the best minimum reflection loss (RLmin) of −26.09 dB at 11.26 GHz (bandwidth is 0.48 GHz). Excellent absorption properties are attributed to good impedance matching, effective dielectric and magnetic loss mechanisms and formation of 3D conductive networks which facilitates multiple reflection and scattering mechanism.

Design of porous FeNi-carbon nanosheets by a double-effect synergistic strategy for electromagnetic wave absorption

The electromagnetic pollution problem caused by the wide application of electromagnetic waves has seriously affected human life and prompted people to research efficient electromagnetic absorption materials. In this work, a porous FeNi-carbon nanosheet was designed and synthesized by a double-effect synergistic strategy. The three raw materials achieved perfect structural synergy, organically combining the magnetic medium with carbon materials. FeNi nanoparticles are evenly distributed on hierarchical pore carbon nanosheets. This unique structure dramatically reduces the materials’ density and improves impedance matching. The minimum density of porous FeNi-carbon nanosheets (FeNi-CNSs) is 36.3 mg cm3, comparable to that of carbon aerogels. More importantly, the synergistic attenuation mechanism of dielectric loss and magnetic loss promotes the efficient attenuation of FeNi-CNSs to electromagnetic waves. The minimum reflection loss (RLmin) of FeNi-CNSs is −47.27 dB at 3.0 mm, and the effective absorption bandwidth (EAB) is as high as 7.1 GHz at 2.5 mm. More surprisingly, when the thickness is in the range of 1.8–3.0 mm, the average EAB reaches 6.22 GHz, which expands the operational range of practical applications and provides the possibility for the application and promotion of lightweight magnetic carbon nanosheet microwave absorbing materials.

Enhancing breakdown strength and lifetime of multilayer dielectric films by using high temperature polycarbonate skin layers

Polymer multilayer films (MLFs) hold a potential to achieve high energy density, high temperature rating, and high breakdown strength simultaneously for next-generation film capacitors. Under extreme conditions such as high AC electric fields and high temperatures, an important dielectric loss mechanism is the homocharge injection from metal electrodes and subsequent charge recombination (i.e., AC electronic conduction) at the electrode/dielectric interfaces. In this work, the mechanism of the AC electronic conduction loss is studied for high-temperature polycarbonate (HTPC)/poly(vinylidene fluoride) (PVDF) MLFs with either HTPC (MLF@HTPC) or PVDF skin layers (MLF@PVDF). Based on the DC/AC breakdown strength and lifetime measurements, it is observed that homocharge injection was more significant for MLF@PVDF than MLF@HTPC. Using the electric displacement-electric field loop analysis, dielectric losses from both AC electronic conduction and ferroelectric switching (PVDF) are quantified. A dipolar electric double layer model at the electrode/PVDF interfaces is proposed to explain the more significant ferroelectric switching and charge injection in MLF@PVDF. From these experimental results, it is concluded that enhanced breakdown strength and lifetime can be achieved for MLF@HTPC because of the reduced homocharge injection and AC electronic conduction at high electric fields and high temperatures.

Effects of (Mg1/3Nb2/3)4+ substitution on the temperature-stable and low-loss (Mg1/3Nb2/3)x(Zr0.5Ti0.5)1-xO2 microwave dielectric ceramics

(Mg1/3Nb2/3)x(Zr0.5Ti0.5)1-xO2 (x = 0.00, 0.05, 0.10, 0.13, 0.15, and 0.20) systems without additives are fabricated by facile solid-state reaction method in the air atmosphere. The influence of (Mg1/3Nb2/3)4+ substitution on microwave dielectric properties of (Mg1/3Nb2/3)x(Zr0.5Ti0.5)1-xO2 ceramics is investigated systematically. The XRD results convey that the doping ion ((Mg1/3Nb2/3)4+) should occupy (Zr0.5Ti0.5)4+ site throughout the composition. An appropriate amount of (Mg1/3Nb2/3)4+ tremendously increases the temperature stability and reduces the microwave dielectric loss of the ZrTiO4 ceramic. In addition, to further investigate the dielectric loss mechanism, high-resolution Raman mapping is used to characterize residual stresses at the grain level. The result justifies that there is non-uniform residual stress in the ceramic, which is closely related to the anharmonic vibrations of the crystal lattice and the intrinsic loss of (Mg1/3Nb2/3)x(Zr0.5Ti0.5)1-xO2 ceramics. Meanwhile, the annealing approach is applied for reducing the intrinsic loss and further improving the Q × f value. Ultimately, the optimum microwave dielectric properties with τf ∼0.8 ppm/°C, high ϵr ∼40.9 and Q × f ∼40,217 GHz are obtained in annealed (Mg1/3Nb2/3)0.13(Zr0.5Ti0.5)0.87O2 ceramic, which suggests that it can be as one of the candidates exploiting for microwave devices in 5G wireless communication technology.

Co, Ni-coordinated ZIF derived nitrogen doped carbon network with encapsulated alloy for microwave absorption

Carbon-based composites have been widely used to prepare microwave absorption materials, but it still remains hard to achieve full X band (8.2–12.4 GHz) absorption at a thin thickness. Herein, NiCo alloy and N co-doped carbon with spontaneous three-dimensional network was obtained by preparing precursors using Ni2+ and Co2+ to be designed into zeolitic imidazolate frameworks (ZIF). The morphology of composites is able to be controlled by regulating Ni/Co ratios in crystallization. During pyrolysis, 3D network structure with N-doped carbon and NiCo alloy can be catalyzed to form under a specific Ni/Co ratio. Excellent microwave absorption performance, the minimum reflection loss is −41.9 dB at 1.5 mm and entire X band absorption at 2.6 mm, is achieved. The 3D network structure containing N-doped carbon and NiCo alloy not only provide favorable dielectric and magnetic loss, but also have a crucial impact on reflection and scattering of incident microwave. The mechanism of dielectric loss including polarization relaxation, conductive loss and magnetic loss derived from resonance also is investigated. The chemical components and network structure controlled by ZIF-derived strategy have practical research value to improve microwave absorption performance.

Progress on Polymer Composites With Low Dielectric Constant and Low Dielectric Loss for High-Frequency Signal Transmission

The development of information transmission technology towards high-frequency microwaves and highly integrated and multi-functional electronic devices has been the mainstream direction of the current communication technology. During signal transmission, resistance-capacitance time delay, crosstalk, energy consumption increase and impedance mismatch restrict the high density and miniaturization of Printed circuit board (PCB). In order to achieve high fidelity and low delay characteristics of high-frequency signal transmission, the development of interlayer dielectric materials with low dielectric constant (Dk) and low dielectric loss factor (Df) has become the focus of researchers. This review introduces the dielectric loss mechanism of polymer composites and the resin matrix commonly used in several high-frequency copper-clad laminates, and mainly describes how to reduce the dielectric constant and dielectric loss of materials from the level of molecular structure design, as well as the effect of fillers on the dielectric properties of polymer substrates. As a kind of potential functional fillers for dielectric polymeric composites, the carbon nanofillers are used to tailor the dielectric properties of their composites via different dimensions and loadings, as well as their proper preparation methods. This review finally summarizes the interface bonding failure mechanism and a feasible idea to optimize the dielectric properties of polymer matrix composites is also proposed.

Electromagnetic microwave absorption properties of high entropy spinel ferrite ((MnNiCuZn)1−xCoxFe2O4)/graphene nanocomposites

High entropy spinel ferrite (HEF) nanoparticles were synthesized by solution combustion method as high-performance microwave absorbers. The structural, microstructural, magnetic and microwave absorption properties of (MnNiCuZn) 1−x Co x Fe 2 O 4 powders (x = 0.05, 0.1, 0.2, and 0.3) were studied as a function of Co contents by modern characterization methods including X-ray diffractometry, Raman spectroscopy, electron microscopy, vibrating sample magnetometry, and vector network analyzer. The as-combusted powders were single phase with the space group of F d 3 ¯ m . The cation distributions showed that the fraction of Fe 3+ cations in (A) sites decreased with the substitution of Co cations. The (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 nanoparticles (~30–70 nm) were dispersed on the graphene sheets. The coercivity increased from 94 to 225 Oe with the Co contents, while the saturation magnetization slightly changed in the range of 67–71 emu/g. The saturation magnetization and coercivity of the (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 /graphene composite powders were lower than those of (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 powders due to their smaller particle size. The (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 /paraffin composite sample at the mass fraction of 70 wt.% showed the maximum reflection loss of −27 dB at the matching thickness of 5.3 mm in Ku band. The interfacial relaxation and ferromagnetic resonance were determined as main dielectric and magnetic loss mechanisms, respectively. By compositing the (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 powders with graphene, the maximum reflection loss of −16 dB at the matching thickness of 4.5 mm in Ku band was obtained at the lower mass fraction of 30 wt.% because of the higher dielectric loss of graphene.

Defect engineering for reduced large AC signal dielectric loss of PZT‐based hard piezoelectric ceramics

AbstractA low dielectric loss value under large AC electric fields is highly desired for piezoelectric ceramics in high‐power applications. However, only a few reports have focused on studying or revealing the dielectric loss behavior and mechanism of piezoelectric ceramics under an AC electric field. In this work, x (Ca, Fe) co‐doped Pb0.96Sr0.04Zr0.53Ti0.47O3 (x = 0.0, 0.25, 0.5, 1.0, 1.5 mol.%) hard piezoelectric ceramics (PSZT‐xCF) were selected for investigation. The lowest dielectric loss (@ E = 500 V mm−1) was 0.8% at x = 1.5 mol.% after aging for 30 days, which was a decrease by an order of magnitude compared with the counterpart pure PSZT. The origin of ultra‐low dielectric loss was thoroughly analyzed. Combined with Rayleigh's law, we investigated the reason behind the changes in dielectric permittivity under AC electric fields with aging time. The significant reduction in the contribution of extrinsic effect of domain wall motion dominated the reduction in dielectric loss because of the introduction of defect dipoles. This work provides a fundamental understanding of low dielectric loss piezoelectric ceramics under AC electric fields for high‐power applications.

Carbonized fibers with multi-elemental doping and hollow architecture derived from natural cotton for tunable microwave absorption properties

The exploration of bio-derived materials for various applications has attracted considerable attention due to the global challenges of elemental sustainability. Herein, we report the synthesis of hollow-structure carbon fibers by carbonizing natural cotton at different temperatures. The microwave absorption properties are investigated, and the dielectric loss mechanism is studied furtherly. During the pyrolysis process, multi-elements such as oxygen, sulfur, and nitrogen existing in natural cotton can remain and in-situ doped into the carbonized fibers. And a high-concentration atomic-scale substitute is realized, which becomes the dielectric polarization site for microwave attenuation due to the symmetry breaking of localized charge. Moreover, the pyrolysis process results in forming a hollow structure of carbonized fibers, implying an ultra-low density of the resultant fibers. In the present study, it is found that the sample carbonized at 700 °C for 120 min (denoted as S700-120) exhibits the minimum reflection loss (RLmin) of − 51.9 dB at 12.1 GHz with the absorption bandwidth (fb) of 5.5 GHz when the thickness is 1.96 mm. The RLmin and fb for S700-80, S800-40, S800-80, and S800-120 are − 47.0 dB and 3.9 GHz, − 57.3 dB and 3.1 GHz, − 42.7 dB and 2.1 GHz, − 44.2 dB and 1.8 GHz, respectively, demonstrating a significant tunability of microwave absorption performances. Our work provides an alternative for the development of high-performance microwave absorbents from bio-sources.

Structural, magnetic, and gigahertz-range electromagnetic wave absorption properties of bulk Ni\u2013Zn ferrite

Nickel–zinc ferrite (Ni0.5Zn0.5Fe2O4) powders were prepared by the conventional solid-state route and sintered at 1100 and 1300 °C for utilization as a tile electromagnetic wave absorber. Structural, magnetic, and microwave absorption properties were investigated by characterization techniques of X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, electron microscopy, vibrating sample magnetometry, and vector network analyzer. The samples sintered at 1300 °C showed high magnetic saturation of 87 emu/g and low coercivity of 4 Oe. Electromagnetic investigations exhibit high reflection losses up to − 48.1 dB at certain high and low gigahertz frequencies, as clearly depicted in the 3D contour plot. The optimized condition between reflection loss, thickness, and bandwidth revealed a reflection loss of about − 36.1 dB at the matching thickness of 3.7 mm for the X-band. Furthermore, the effective working bandwidth at − 10 dB was up to ~ 7.1 GHz for the minimum thickness of 4.3 mm, which thoroughly covered the C-band. The microwave absorption performance of the well-sintered Ni–Zn ferrite was attributed to the incorporation of dielectric and magnetic loss mechanisms in which the magnetic part prevails.

RCS Frequency Response Analysis of Luneberg Lens Reflector Based on Dielectric Loss

This paper presents an analysis method of RCS frequency response characteristics based on dielectric loss, and explains the cause of the difference between theoretical formula and measured data of Loneberg lens reflector. Based on the design principle of the thickness of the shell and the dielectric constant of the Luneberg lens reflector, the expression of the electric path of the electromagnetic wave propagating inside the reflector is derived. At the same time, based on the dielectric loss mechanism, the RCS theoretical formula of Loneberg lens reflector is improved, and the rationality is verified through the analysis of measured data in microwave anechoic chamber. The results show that the RCS distribution characteristics of Loneberg lens reflector considering dielectric loss are more consistent with the measured data.