Showing papers on "Relative permittivity published in 2014"
TL;DR: In this article, a low-gain 20 dBi Luneburg lens antenna using a rapid prototyping machine as a proof-of-concept demonstrator was designed, built, and tested.
Abstract: In this work, we designed, built, and tested a low-gain 20 dBi Luneburg Lens antenna using a rapid prototyping machine as a proof of concept demonstrator. The required continuously varying relative permittivity profile was implemented by changing the size of plastic blocks centered on the junctions of a plastic rod space frame. A 12-cm ( 4λ0 at 10 GHz) diameter lens is designed to work at X-band. The effective permittivity of the unit cell is calculated by effective medium theory and simulated by full-wave finite-element simulations. The fabrication is implemented by a polymer jetting rapid prototyping method. In the measurement, the lens antenna is fed by an X-band waveguide. The measured gain of the antenna at X-band is from 17.3 to 20.3 dB. The measured half-power beam width is from 19° to 12.7° while the side lobes are about 25 dB below the main peak. Good agreement between simulation and experimental results is obtained.
239 citations
TL;DR: In this paper, the authors measured dielectric constant, mid-gap defect density, Urbach energy of tail states in CH3NH3PbIxCl1−x perovskite solar cells.
Abstract: We report on measurement of dielectric constant, mid-gap defect density, Urbach energy of tail states in CH3NH3PbIxCl1−x perovskite solar cells. Midgap defect densities were estimated by measuring capacitance vs. frequency at different temperatures and show two peaks, one at 0.66 eV below the conduction band and one at 0.24 eV below the conduction band. The attempt to escape frequency is in the range of 2 × 1011/s. Quantum efficiency data indicate a bandgap of 1.58 eV. Urbach energies of valence and conduction band are estimated to be ∼16 and ∼18 meV. Measurement of saturation capacitance indicates that the relative dielectric constant is ∼18.
229 citations
TL;DR: In this paper, a planar complementary split-ring resonator (CSRR) was used to measure the dielectric constants and loss tangents of material under test (MUT) using the equivalent RLC resonator circuit model.
Abstract: A noninvasive planar complementary split-ring resonator (CSRR) for measuring the dielectric constants and loss tangents of material is presented in this letter. Measurements were developed to extract the complex permittivity of the material under test (MUT) using the equivalent RLC resonator circuit model. This technique enables a single-step measurement of the MUT without the need for machining or reshaping. The method requires calculating only two parameters, the resonant frequency (fr) and the magnitude (dB) response, thus achieving a substantial reduction in cost and computation time. A CSRR sensor operating in the 1.8 to 2.8 GHz band is fabricated and tested for verification. The measurement errors in the dielectric constant were less than 7.6%. An efficient technique of CSRR measuring complex permittivity is experimentally verified.
187 citations
TL;DR: In this article, the effects of annealing temperature on the microstructure evolution, direct-current electrical conductivity, dielectric properties, and microwave absorption properties of SiCN in the frequency range 8.2-12.4 GHz (X-band) were investigated.
Abstract: Porous SiCN ceramics were successfully fabricated by pyrolysis of a kind of polysilazane. The effects of annealing temperature on the microstructure evolution, direct-current electrical conductivity, dielectric properties, and microwave absorption properties of SiCN in the frequency range 8.2–12.4 GHz (X-band) were investigated. With the increase of annealing temperature, SiC, Si3N4 and free carbon nanodomains are gradually formed in the SiCN. Both the SiC and free carbon nanodomains lead to the increases of the complex relative permittivity and loss tangent of SiCN. With the increase of the annealing temperature, the average real permittivity, imaginary permittivity and loss tangent increase from 4.4, 0.2 and 0.05 to 13.8, 6.3 and 0.46, respectively. The minimum reflection coefficient and the frequency bandwidth below −10 dB for SiCN annealed at 1500 °C are −53 dB and 3.02 GHz, indicating good microwave absorption properties.
149 citations
TL;DR: In this paper, a square-shaped complementary split-ring resonator (CSRR) was used to measure the thickness and permittivity of multilayer dielectric structures.
Abstract: This paper presents a non-invasive microwave method based on a square-shaped complementary split-ring resonator (CSRR) to measure the thickness and permittivity of multilayer dielectric structures. The CSRR sensor is etched on the ground plane of a microstrip line. The change of resonance frequency depends on the thickness and permittivity of the multilayer dielectric sample below the ground plane. For resolution analysis, the resonance frequency shifts caused by a variation of permittivity (Δe = 0.01) and thickness (Δd=0.01 mm) in the detection layer were compared across various design dimensions. Sensor size optimization improved the resolution in permittivity and thickness measurement by 66% and 37%, respectively. Subsequently, the permittivity and thickness resolution was improved by 28% and 16%, respectively, by optimizing the separation of the etched CSRRs. The analysis results show that a CSRR sensor can be designed with excellent resolution in core layer permittivity changes and thickness resolution in multilayered dielectric structures.
143 citations
TL;DR: Complex electric modulus, defined as the inverse of complex relative permittivity, can be a significantly powerful tool for analyzing dielectric behavior of polymeric insulating material, especially at relatively high temperatures, where complex permittivities usually becomes very high due to electrode polarization and carrier transport as mentioned in this paper.
Abstract: Complex electric modulus, defined as the inverse of complex relative permittivity, can be a significantly powerful tool for analyzing dielectric behavior of a polymeric insulating material, especially at relatively high temperatures, where complex permittivity usually becomes very high due to electrode polarization and carrier transport. In this paper, a typical example of the above is clearly shown by referring to an experimental result obtained for epoxy resin.
139 citations
TL;DR: The phase change from rhombohedral in BiFeO3-rich compositions to pseudocubic at a BaTiO3 content of x=033 was observed in this article.
111 citations
TL;DR: In this article, Li2MoO4 disks were fabricated by moistening water-soluble Li 2 MoO4 powder with deionized water and compressing it under a pressure of 130 MPa.
Abstract: Lithium molybdate disks were fabricated by moistening water-soluble Li2MoO4 powder with deionized water and compressing it under a pressure of 130 MPa. Disks were postprocessed at room temperature, at 120°C, and at 540°C, which is a common sintering temperature for Li2MoO4. Regardless of the postprocessing temperature, densities as high as 87%–93% of the theoretical value were achieved. The X-ray diffraction patterns of processed disks were all the same with no signs of hydrates or constitutional water. The samples also exhibited very similar microstructures and microwave dielectric properties with a relative permittivity of 4.6–5.2 and a Q × f value of 10 200–18 500 at 9.6 GHz, depending on the postprocessing temperature.
110 citations
TL;DR: A novel cavity-based unified approach to measure the complex permittivity of dielectric samples placed in the E-plane of a rectangular cavity is presented, which is validated by designing two rectangular cavities having different slot sizes operating in the TE107 mode.
Abstract: A novel cavity-based unified approach to measure the complex permittivity of dielectric samples placed in the E-plane of a rectangular cavity is presented. The proposed generalized cavity method is not limited to test specimens of smaller electrical dimensions, and requires two basic steps. The first step modifies the conventional cavity perturbation technique, where the effects of possible air gap between the cavity slot and the test specimen are also considered. The second step of the proposed approach employs a numerical optimization scheme, where the actual 3-D geometry of the fabricated cavity is simulated using the numerical field simulator, the Computer Simulation Technology (CST) Microwave Studio. The dielectric properties of the test specimen in this case are determined with the help of a MATLAB-based optimization routine, which calls the CST modules over the component object model interface and minimizes the error between the measured and the simulated scattering coefficients. The permittivity of the test specimen determined using the first step is provided as the initial guess to improve the convergence of the numerical optimization scheme. The proposed unified approach is validated by designing two rectangular cavities having different slot sizes operating in the TE107 mode. A number of standard dielectric samples are measured with the help of a vector network analyzer, and a very good agreement is observed between the measured permittivity values and the published data available in the literature having a typical error of less than 2% for samples of even larger dimensions.
105 citations
TL;DR: The dielectric properties of SrTiO 3 ceramics sintered in nitrogen (N 2 ) exhibit a weak temperature and frequency-dependent giant permittivity (>10 4 ) as well as a very low dielectron loss as mentioned in this paper.
Abstract: The dielectric properties of SrTiO 3 ceramics sintered in nitrogen (N 2 ) exhibit a weak temperature- and frequency-dependent giant permittivity (>10 4 ) as well as a very low dielectric loss (mostly
104 citations
TL;DR: In this article, a silicone elastomer system with high dielectric permittivity was prepared through the synthesis of siloxane copolymers, thereby allowing for the attachment of high DE molecules through copper-catalysed azide-alkyne 1,3-dipolar cycloaddition (CuAAC).
TL;DR: The results demonstrate the suitability of the investigated OCs for the determination of high resolution soil dielectric spectra with a broadband relaxation model, as well as a novel, coupled hydraulic-dielectric mixture approach.
Abstract: Open-ended coaxial line probes (OCs) are systematically analyzed by means of numerical 3-D finite element calculations in combination with experimental investigations for microwave dielectric spectroscopy on fine grained soils. The probes, based on conventional coaxial lines and connectors (N, SMA), are broadband characterized in the frequency range from 1 MHz to 10 GHz. The sensitive region for dielectric measurements is ±7-mm lateral and 7-mm perpendicular to the midpoint of the sensor aperture. The spatial spreading of the sensitive zone is stable for the investigated low-loss and high-loss strongly dispersive standard liquids, as well as the saturated and unsaturated soils. Dielectric spectra are determined based on a bilinear relationship between effective permittivity and complex reflection coefficient of the probe after probe-calibration with known standards. The mean relative error of the real part of the complex permittivity from 100 MHz to 10 GHz is smaller than 3.5% and is less than 10% for the imaginary part. A lower limit of the measurement range of 50 MHz with the used procedure and materials is suggested. Complex effective permittivity of saturated fine-grained soils is determined with the developed probes and procedure. The soil dielectric spectra were analyzed with a broadband relaxation model, as well as a novel, coupled hydraulic-dielectric mixture approach. The results demonstrate the suitability of the investigated OCs for the determination of high resolution soil dielectric spectra.
TL;DR: The static dielectric permittivity of Ionic solvents is defined in this article as the zero-frequency limit of the real part of the frequency-dependent complex dielectrics.
TL;DR: In this paper, the structural and electrical properties of thin films with compositions (1−−x)(0.94Bi1/2Na 1/2TiO3, 0.06BaTiOO3) and 0.5Na0.5NbO3 have been investigated.
Abstract: Thick films with compositions (1 − x)(0.94Bi1/2Na1/2TiO3–0.06BaTiO3)–x(K0.5Na0.5NbO3) (x = 0, 0.03, 0.09 and 0.18) have been prepared and their structural and electrical properties have been investigated. Dielectric properties show that these films are well suited for high-temperature applications due to their low variance in permittivity (<15%) over large temperature ranges. The thick film with x = 0.18 offers an operational temperature range from room temperature to 350 °C. Films with x = 0.03 and 0.09 also possess a stabile permittivity up to 400 °C. The improvement in the thermal stability of the permittivity is attributed to the addition of K0.5Na0.5NbO3 which leads to breaking of the long-range order in the materials. However, the polarizability of the materials was found to decrease possibly due to the clamping effect of the substrate. The characteristics of each film are discussed based on dielectric and electrical properties.
TL;DR: In this article, the massive permittivity of fast-firing barium titanate ceramics was investigated using a dielectric spectroscopy analysis. And the authors showed that the bulk conduction in fast-fired barium- titanate is the result of variable-range hopping with relatively short hopping distance (∼0.5 nm).
Abstract: Fast-fired barium titanate ceramics have been shown to exhibit room temperature colossal permittivity (er′ ≈ 105, tan δ ≈ 0.05 at 1 kHz) when synthesized via the spark plasma sintering technique. Broadband dielectric spectroscopy analysis is here utilized to identify the active conduction mechanisms in the compound. Analysis of the temperature-dependent bulk dc conductivity reveals that the bulk conduction in fast-fired barium titanate is the result of variable-range hopping with relatively short hopping distance (∼0.5 nm) compared to other colossal permittivity materials. A common equivalent circuit that can model the contributions of the different polarization mechanisms to both the dc conductivity and colossal permittivity is established.
TL;DR: In this paper, a bandpass frequency selective surface (FSS) with miniaturized periodic element is presented, which is printed on one face of a single-layer substrate with a relative permittivity of 2.65.
Abstract: In this letter, a novel bandpass frequency selective surface (FSS) with miniaturized periodic element is presented. The proposed FSS is printed on one face of a single-layer substrate with a relative permittivity of 2.65. The novel FSS has promising miniaturization characteristics with the unit-cell dimension 0.058λ×0.058λ, where λ represents the free-space wavelength corresponding to the resonant frequency. The FSS exhibits excellent stability under different polarizations and incident angles. Both the simulation and measurement results validate the stable performance of this FSS.
TL;DR: In this article, the Langevin-Poisson-Boltzmann (LPB) and Langevin -Bikerman (LBP) models were used to model the electrolyte-charged surface interface and the space dependence of relative permittivity.
TL;DR: In this article, an analytical formulation for relative dielectric con- stant retrieval is reconstructed to establish a relationship between the response of a spiral microstrip resonator and the effective relative Dielectric constant of a lossy superstrate, such as biological tissue.
Abstract: An analytical formulation for relative dielectric con- stant retrieval is reconstructed to establish a relationship between the response of a spiral microstrip resonator and effective relative dielectric constant of a lossy superstrate, such as biological tissue. To do so, an analytical equation is modified by constructing functions for the two unknowns, filling factor A and the effective length leff of the resonator. This is done by simulating the resonator with digital phantoms of varying permittivity .T he values of A and leff are determined for each phantom from the resulting S-parameter response, using Particle Swarm Op- timization. Multiple non-linear regression is applied to produce equations for A and leff, expressed as a function of frequency and the phantom's relative dielectric constant. These equations are combined to form a new non-linear analytical equation, which is then solved using the Newton-Raphson iterative method, for both simulations and measurements of physical phantoms. To verify the reconstructed dielectric constant, the dielectric properties of the physical phantoms are determined with a commercial high temperature open-ended coaxial probe. The dielectric properties are reconstructed by the described method, with less than 3.67% error with respect to the measurements.
TL;DR: In this paper, a novel microstrip transmission line method for broadband relative permittivity measurement of planar dielectric substrate materials is presented, which requires three sets of S-parameter measurements of the microstrip line together with an obstacle in three equidistant positions over the line.
Abstract: This paper presents a novel microstrip transmission line method for broadband relative permittivity measurement of planar dielectric substrate materials. The method requires three sets of S-parameter measurements of the microstrip line together with an obstacle in three equidistant positions over the line. The measurement and simulation results for the broadband relative permittivity of high-frequency substrates, TLX-8, RF60A, CER10, and the widely used FR4 are presented. The errors are calculated based on the manufacturers' data sheet value. Both the simulation and measurement results are found to be within 16% of the data sheet values for CER10 and 10% for all other substrates. The proposed method can minimize errors due to the nonreproducibility of connectors and impedance mismatch problems, prevalent in transmission line methods. However, the method is highly sensitive to the positioning of the obstacle, which can be overcome through the use of high accuracy obstacle positioning methods.
TL;DR: In this article, BaTiO3-supporting Ag hybrid particles (BT-Ag) with varied fraction of Ag were synthesized by reducing silver nitrate in the glycol solution containing BT suspensions, and dielectric performance of the composites containing the BT-Ag as fillers in the matrix of polyvinylidene fluoride (PVDF) was investigated.
Abstract: BaTiO3-supporting Ag hybrid particles (BT-Ag) with varied fraction of Ag were synthesized by reducing silver nitrate in the glycol solution containing BaTiO3 (BT) suspensions. The Ag nano particles with a size of about 20 nm were discretely grown on the surface of the BT. The dielectric performance of the composites containing the BT-Ag as fillers in the matrix of polyvinylidene fluoride (PVDF) was investigated. The relative permittivity (er) of the BT-Ag/PVDF composites increased prominently with the increase of BT-Ag loading amount, and the typical conductive path of the conductor/polymer system was not observed even with a high loading of BT-Ag. The er at 100 Hz for the three BT-(0.31, 0.49, 0.61)Ag/PVDF composites at room temperature were 283, 350, and 783, respectively. The er of the composites was enhanced by more than 3 times compared with that of the composite containing untreated BT nanoparticles at frequencies over 1 kHz and the loss tangent (tan δ) was less than 0.1 which should be attributed to the low conductivity of the composites. Theoretical calculations based on the effective medium percolation theory model and series-parallel model suggested that the enhanced permittivity of BT-Ag/PVDF composites should arise from the ultrahigh permittivity of BT-Ag fillers, which was over 104 and associated with the content of Ag deposited on the surface of BT.
TL;DR: In this article, the authors present the approaches and developments of magneto-dielectric materials of three types: spinel-based, hexagonal-based and composite magnetodirelectric material, and show that when the application frequency is low (less than 30 MHz), adopting composites of spinel ferrite and high-diesel material is the best choice to improve the refractive index.
Abstract: Magneto-dielectric materials with matching permeability and permittivity have significant advantages for miniaturization and efficiency improvement of antennas. The main requirements for this kind of magneto-dielectric material include a high refractive index, matched permeability and permittivity, and low magnetic and dielectric losses at the application frequency. However, it is very difficult to meet these requirements simultaneously. This review presents the approaches and developments of magneto-dielectric materials of three types: spinel-based, hexagonal-based, and composite magneto-dielectric materials. It is proved that choosing the proper type of magneto-dielectric material is very important to obtain a higher refractive index and matched permeability and permittivity in the application frequency band. When the application frequency is low (less than 30 MHz), adopting composites of spinel ferrite and high-dielectric material is the best choice to improve the refractive index. When the application frequency is between 30 MHz and 100 MHz, it is better to choose spinel-based magneto-dielectric materials in consideration of both their relatively high refractive index and low losses. When the application frequency increases to 100 MHz to 500 MHz, hexagonal-based magneto-dielectric materials offer better performance. Finally, when the application frequency is beyond 500 MHz, to obtain matched permeability and permittivity, choosing composites of hexaferrite and an organic medium is recommended. Solutions for how to decrease magnetic and dielectric losses and expand the application frequency range are also discussed.
TL;DR: In this article, the dielectric and ferroelectric properties of (1−−x)Ba0.8Ca0.2TiO3-Bi(Zn0.5Ti0.4)O3 were investigated for compositions 0.
Abstract: The dielectric and ferroelectric properties of the ceramic system, (1 − x)Ba0.8Ca0.2TiO3–xBi(Zn0.5Ti0.5)O3, were investigated for compositions 0 ≤ x ≤ 0.4. X-ray powder diffraction patterns indicated tetragonal symmetry at x ≤ 0.05, switching to pseudocubic at x ≥ 0.1, with a single-phase solid solution limit at 0.2
TL;DR: In this article, temperature-stable relaxor dielectrics have been developed in the solid solution system: 0.45Ba0.8Ca0.2TiO3-(0.55-x) Bi(Mg0.5)O3-xNaNbO3.
Abstract: Temperature-stable relaxor dielectrics have been developed in the solid solution system: 0.45Ba0.8Ca0.2TiO3-(0.55-x) Bi(Mg0.5Ti0.5)O3-xNaNbO3. Ceramics of composition x = 0 have a relative permittivity ?r = 950 ± 15% over a wide temperature range from +70°C to 600°C. Modification with NaNbO3 at x = 0.2 decreases the lower limiting temperature to -70°C, but also decreases relative permittivity such that ?r ∼ 600 ± 15% over the temperature range -70°C to 500°C. For composition x = 0.3, the low-temperature dispersion in loss tangent, tan δ, (at 1 kHz) shifts to lower temperature, giving tan δ values ≤0.02 across the temperature range -60°C to 300°C in combination with ?r ∼ 550 ± 15%. Values of dc resistivity for all samples are of the order of 1010 Ω m at 250°C and 107 Ω m at 400°C.
TL;DR: In this article, a flexible three-phase composite material with enhanced dielectric permittivity was prepared with both graphene and BaTiO3 nanoparticles as fillers and polyimide (PI) as matrix.
TL;DR: In this article, Ba3Co2+xIrxFe24−2xO41 composites of nominal composition were studied in order to achieve low magnetic and dielectric losses and equivalent permittivity and permeability over a frequency range of 0.3-1 GHz.
Abstract: Ferrite composites of nominal composition Ba3Co2+xIrxFe24−2xO41 were studied in order to achieve low magnetic and dielectric losses and equivalent permittivity and permeability over a frequency range of 0.3–1 GHz. Crystallographic structure was characterized by X-ray diffraction, which revealed a Z-type phase accompanied by increasing amounts of Y-type phase as the iridium amount was increased. The measured microwave dielectric and magnetic properties showed that the loss tan δe and loss tan δμ decreased by 80% and 90% at 0.8 GHz with the addition of iridium of x = 0.12 and 0.15, respectively. An effective medium approximation was adopted to analyze the composite ferrites having mixed phase structures. Moreover, adding Bi2O3 enabled equivalent values of real permittivity and real permeability over the studied frequency range. The resultant data give rise to low loss factors, i.e., tan δe/e′ = 0.008 and tan δμ/μ′ = 0.037 at 0.8 GHz, while characteristic impedance was the same as that of free space.
TL;DR: In this paper, the properties of holmium substituted nickel ferrites (NiHoxFe2−xO4) with x ranging from 0.0 to 0.15 have been prepared by the sol-gel auto-combustion method.
TL;DR: In this article, two models that can predict the voltage-dependent scattering from liquid crystal (LC)-based reflectarray cells are presented, and the validity of both numerical techniques is demonstrated using measured results in the frequency range 94-110 GHz.
Abstract: Two models that can predict the voltage-dependent scattering from liquid crystal (LC)-based reflectarray cells are presented. The validity of both numerical techniques is demonstrated using measured results in the frequency range 94–110 GHz. The most rigorous approach models, for each voltage, the inhomogeneous and anisotropic permittivity of the LC as a stratified media in the direction of the biasing field. This accounts for the different tilt angles of the LC molecules inside the cell calculated from the solution of the elastic problem. The other model is based on an effective homogeneous permittivity tensor that corresponds to the average tilt angle along the longitudinal direction for each biasing voltage. In this model, convergence problems associated with the longitudinal inhomogeneity are avoided, and the computation efficiency is improved. Both models provide a correspondence between the reflection coefficient (losses and phase-shift) of the LC-based reflectarray cell and the value of biasing voltage, which can be used to design beam scanning reflectarrays. The accuracy and the efficiency of both models are also analyzed and discussed.
TL;DR: In this paper, the complex permittivity of materials required to achieve a single-layer electromagnetic absorber with a high absorption coefficient in the 60-GHz band was calculated and the results indicated that an absorption coefficient of 0.95 can be achieved for a 5-mm sheet when the real part of the relative permittivities is close to that of the free space and the conductivity σ is around 3.
TL;DR: In this paper, the morphology and structure of solvent cast and compression-molded films, and their thermal, viscoelastic, and dielectric properties were investigated, and surface modified BaTiO3 particles were incorporated in poly(vinylidene fluoride-trifluoroethylene) to fabricate composites with up to 60 vol% of ceramic phase.
Abstract: Micron- and submicron-sized barium titanate (BaTiO3) particles, untreated and surface modified with aminopropyl triethoxy silane, were incorporated in poly(vinylidene fluoride–trifluoroethylene) to fabricate composites with up to 60 vol% of ceramic phase. The morphology and structure of solvent cast and compression-molded films, and their thermal, viscoelastic, and dielectric properties were investigated. When surface-modified BaTiO3 was used, it was possible to decrease both the viscoelastic and the dielectric losses of highly filled solvent cast films, while their storage modulus and relative permittivity either increased or remained equal, owing to reduced porosity and improved matrix-filler compatibility. The effect of BaTiO3 surface modification on the morphology of compression-molded films was less marked, leading to unchanged viscoelastic properties, and lower permittivity and dielectric losses. For all composites the frequency dependency of the dielectric properties at low frequencies was suppressed with modified BaTiO3.
TL;DR: In this article, a percolation phenomenon appears, and expected radio-frequency negative permittivity is obtained, and the dependences of negative perceptivity on the composites' compositions and microstructures are investigated in detail.
Abstract: “Natural” metamaterials with intrinsic negative permittivity and permeability have attracted significant attention because of their wide promising applications and facile preparation processes. In order to match the negative permeability band which is usually located in the radio-frequency range, radio-frequency negative permittivity is desired. Moreover, the negative permittivity should be tunable to satisfy different application circumstances. Herein, nickel/alumina composites consisting of nickel particles homogeneously dispersed in alumina were prepared using a facile wet chemical process. A percolation phenomenon appears, and expected radio-frequency negative permittivity is obtained. Furthermore, the dependences of negative permittivity on the composites' compositions and microstructures are investigated in detail. It is shown that higher nickel content results in higher negative permittivity magnitude and lower negative permittivity frequency. Besides, the addition of alumina particles leads to decreasing negative permittivity magnitude and higher negative permittivity frequency band owing to the deteriorated interconnectivity between nickel particles. The present work will greatly facilitate the fabrication and application of “natural” metamaterials with tailored properties.