Effective Medium Theory Model Research Articles

Non-destructive characterization of silicon nanowires and nanowire coatings using mid-infrared spectroscopy

Silicon nanowires (SiNWs) have attracted much attention owing to their potential applications in electronics and photonics, while remaining as a cost-effective material platform. Key material properties in engineering SiNWs for different applications include their length, density, and presence of oxides or other chemicals on the surface. However, monitoring these properties is challenging, as scanning electron microscopy and atomic force microscopy (AFM), which directly image the wires, require destructive cleaving of the sample. This paper uses polarized, variable-angle Fourier Transform IR reflectance spectroscopy as a nondestructive technique to characterize the areal density and length of metal-assisted chemically etched SiNW arrays. In addition to the ability to characterize “as-etched” wires, we show that IR spectroscopy can also measure few-nanometer thick layers of aluminum oxide (AlOx) grown radially around the length of the SiNWs utilizing atomic layer deposition. Despite sample inhomogeneities, an effective medium theory (EMT) model can determine the length and density of the NWs for a range of lengths between 3 and 14 μm. The EMT can also reproduce the experimentally measured vibrational bands for coated NWs, demonstrating that IR spectroscopy can also evaluate the presence of molecular contaminants on the wires.

Fused Deposition Modeling of Isotactic Polypropylene/Graphene Nanoplatelets Composites: Achieving Enhanced Thermal Conductivity through Filler Orientation.

High-performance thermally conductive composites are increasingly vital due to the accelerated advancements in communication and electronics, driving the demand for efficient thermal management in electronic packaging, light-emitting diodes (LEDs), and energy storage applications. Controlling the orderly arrangement of fillers within a polymer matrix is acknowledged as an essential strategy for developing thermal conductive composites. In this study, isotactic polypropylene/GNP (iPP/GNP) composite filament tailored for fused deposition modeling (FDM) was achieved by combining ball milling with melt extrusion processing. The rheological properties of the composites were thoroughly studied. The shear field and pressure field distributions during the FDM extrusion process were simulated and examined using Polyflow, focusing on the influence of the 3D printing processing flow field on the orientation of GNP within the iPP matrix. Exploiting the unique capabilities of FDM and through strategic printing path design, thermally conductive composites with GNPs oriented in the through-plane direction were 3D printed. At a GNP content of 5 wt%, the as-printed sample demonstrated a thermal conductivity of 0.64 W/m · K, which was 1.5 times the in-plane thermal conductivity for 0.42 W/m · K and triple pure iPP for 0.22 W/m · K. Effective medium theory (EMT) model fitting results indicated a significantly reduced interface thermal resistance in the through-plane direction compared to the in-plane direction. This work shed brilliant light on developing PP-based thermal conductive composites with arbitrarily-customized structures.

An alternative general model for the effective longitudinal diffusion in chromatographic beds filled with ordered porous particles

The two-zone moment-analysis method for the determination of the dispersion tensor in hierarchical retentive porous media has been adopted to compute and model the effective longitudinal diffusion Deff, or equivalently the B-term band broadening, in chromatographic beds filled with ordered porous particles. On the one hand, this approach offers accurate numerical results for Deff while keeping computational expenses low. On the other hand, it also gives direct insight for the analytical modelling, readily revealings the two main essential quantities (resp. referred to as the mobile-zone and stationary-zone effective diffusion factors γm and γs) that contribute to Deff. Modelling these two main parameters provided us with two new analytical models for Deff: a general one, valid for diluted and concentrated packings and accurate in the whole range of relevant intra-particle diffusion coefficient Dpz, and an approximate one, reliable for diluted packings and accurate also for concentrated packings with low to intermediate values of Dpz. The large advantage of both models is that they do not need any fitting parameter because all the required information is incorporated into the experimentally accessible geometric obstruction factor in the mobile phase originating from the tortuosity of the through-pore space (limiting case of fully solid particles without any retention). These models hence serve as an alternative to the Effective Medium Theory (EMT) models used so far in the literature. To validate the theory, five ordered geometries have been investigated. The accuracy of the general model proposed has been quantified and found to be comparable with that of the 3rd order approximate Torquato model for four geometries, even for macro-porosities close to the close-packing limit. The case of a 2-d triangular array of ellipsoidal particles with different elongations is also investigated to show the general validity and applicability of the models.

Improving thermal insulation and fire resistance of ceramifiable EVA/ceramic hybrid composites via low temperature sintering and foaming strategy

Energy efficient buildings, propulsion components and thermal protection systems require materials with high thermal protective properties. Traditional polymer composites or ceramic materials have limited comprehensive applications because of their poor thermal protective properties or poor processability. Herein, a novel fire resistant and thermally insulating polymer/ceramic hybrid ceramifiable composite was developed based on low temperature sintering principle and foaming on fire strategy. Specifically, the influences of raw materials of low temperature ceramics, such as glass frit, phosphate, etc, on the properties of ceramifiable ethylene-vinyl acetate (EVA) composites were investigated. Its fire resistance and thermal insulation properties were evaluated by simulating different sintering environments. The results show that the ceramifiable composite exhibits the highest improvement in fire resistance because a crystalline phase was formed at high temperatures. Gas evolution from the thermal decomposition of ammonium polyphosphate (APP) and EVA contributes to the formation of the porous structure in ceramic residues. The optimal system can resist above 1000 °C flame for 30 min without disintegration, and the temperature of the unfired side was maintained around 200 °C. The reliability of the strategy was verified by the effective medium theory model.

Improved compressive and flexural performances of functionally graded graphene nanoplatelet reinforced cement composites: Experiments and modelling

Graphene reinforced cement composites (GRCCs) have demonstrated competitive mechanical and physical properties. Instead of uniform distribution, functionally graded distribution of the graphene fillers can effectively utilize the advantages of each constituents with improved performances and reduced cost. This paper conducts experiments and modelling on mechanical properties of functionally graded graphene nanoplatelet reinforced cement composites (FG-GNPRCCs). Samples with three functionally graded distributions (X, A and O types) together with uniform distribution (H-type) are prepared and tested. Compared to uniform distribution, the flexural strength and maximum compressive load of functionally graded distributions are significantly increased. For example, the flexural strength of X-5 pattern is increased by 24.36% and the maximum compressive load of O-3 pattern is increased by 13.42%. Based on effective medium theory (EMT) and Mori-Tanaka (MT) model, a parallel triple-inclusion model is developed to predict the Young’s modulus of GNPRCCs. The effects of GNP dispersion, agglomeration and pores on the mechanical properties of the composites are comprehensively studied. Moreover, the cracking load for FG-GNPRCCs is evaluated by combining experiments and modelling, which can provide reference for the design and optimization of high-performance of cement composites and structures.

Microstructure and thermal-physical properties of hypereutectic Al-Ni alloys

The microstructure and thermal-physical properties of Al-xNi (x = 6–25 wt.%) alloys were investigated by experiments first. With the increase of Ni content, the volume fraction and size of the Al3Ni increase significantly, while the morphology has no change. The thermal expansion coefficient (CTE) and the thermal conductivity (TC) decrease at the same time. The CTE of Al-6 wt.%Ni alloy is 20.2 × 10−6/K at 100 °C, decreasing to 15.4 × 10−6/K for Al-25 wt.%Ni, which demonstrates favorable thermal expansion performance. The TC changes from 202.8 W/(m·K) to 103.9 W/(m·K). Besides, the structure and thermal properties of Al3Ni were studied by the first-principles calculation to provide relevant thermodynamic data. The expansion performance was analyzed at the same time, the linear CTE of Al3Ni is 13.82 × 10−6/K at 100 °C. Based on the experiments and first-principles calculations, the modified Turner and general Effective Medium Theory (GEMT) models were used to explain the relationships between microstructure and thermal expansion coefficient, thermal conductivity of Al-xNi alloys.

A two-step homogenization micromechanical model for strain-sensing of graphene reinforced porous cement composites

The incorporation of graphene and its derivatives into cement for electrically conductive composites is currently under extensive investigations due to their potential applications as smart materials for large-scale self-sensing structures. It is of great importance to develop theoretical models to predict the response of the electrical conductivity of the cement composites when subjected to mechanical deformation. Experimental studies have demonstrated that pores and rippled graphene fillers exist in the cement composites. However, currently there are limited theoretical models to predict the electrical conductivity and piezoresistive properties of the cement composites with incorporating the effects of pores and graphene ripples. To address the research gap, this paper develops a two-step micromechanical modelling to predict the effective electrical conductivity and the response of conductivity to compression strain of graphene nanoplatelet (GNP) reinforced cement composites (GNPRCCs) with considering the effects of pores and graphene ripple for the first time. The effective medium theory and Mori-Tanaka model are employed to homogenize the GNP and pores as inclusions with considering several influencing mechanisms. Parametric study is carried out to identify the effects of the attributes of GNPs, pores and electron tunnelling on the electrical and piezoresistive properties of the GNPRCCs. It is found that the piezoresistive response is proportional to porosity when the conductive behavior of GNPRCC is dominated by the tunnelling effect. Increasing porosity has a negative impact on the strain-sensing performance of the GNPRCCs once the conductive network is formed.

Enabling high dielectric constant and low loss tangent in BaTiO3–epoxy composites through a 3D interconnected network structure of ceramic phase

Constructing ceramic–polymer composites with a 3–3 connectivity is an effective strategy to achieve a notable increase in the dielectric constant at low ceramic contents. However, the dielectric data of the 3–3 composites with a low ceramic content (<10 vol. %) are still limited, and further investigation is thus required. Herein, composites with a 3–3 connectivity, in which BaTiO3 (BTO) and epoxy are self-connected in three dimensions, were developed and constructed at low BTO contents (2.0–8.3 vol. %). A three-dimensional network structure of the BTO ceramic (3D-BTO) was constructed via the sacrificial template method using polyurethane foam as the template. The dielectric constant and loss tangent of the composites increased with increasing BTO content. At a BTO content of 8.3 vol. %, the dielectric constant of the composite considerably increased to 33.4 at 1 kHz, which was ∼10-fold higher than that of neat epoxy (3.5). The loss tangent had a low value of< 0.030. By comparing with several theoretical models, the dielectric constants of the composites were well fitted with the effective medium theory model at low fitting factors (n = 0.008–0.013). The considerable increase in the dielectric constant of the composites with a low loss tangent at a low BTO content was attributed to the strong interfacial polarization and continuous polarization pathways through the interconnected 3D-BTO network structure in the composites. This study fills the gap in the literature by providing missing data on the dielectric properties of 3–3 composites at low ceramic contents (<10 vol. %), as well as a theoretical prediction.

Temperature dependence of the dielectric function of dehydrated biological samples in the THz band.

Terahertz technology has demonstrated enormous potential for the analysis of biological systems and the diagnosis of some medical conditions, given its high sensitivity to detect water content. In previously published papers, effective medium theories are used to extract the water content from the terahertz measurements. When the dielectric functions of water and dehydrated bio-material are well known, the volumetric fraction of water can be left as the only free parameter in those effective medium theory models. While water complex permittivity is very well known, the dielectric functions of dehydrated tissues are normally measured for each individual application. In previous studies, it has been traditionally assumed that, unlike water, the dielectric function of the dehydrated tissues is temperature independent, measuring it only at room temperature. Yet, this is an aspect that has not been discussed and that is relevant in order to get THz technology closer to clinical and in-the-field applications. In this work, we present the characterization of the complex permittivity of dehydrated tissues; each studied at temperatures ranging from 20°C to 36.5°C. We studied samples of different organism classifications to have a wider confirmation of the results. We find that, in each case, the dielectric function changes of dehydrated tissues caused by temperature are smaller than for water across the same temperature interval. Yet, the changes in the dielectric function of the dehydrated tissue are not negligible and should, in many cases, be taken into account for the processing of terahertz signals that interact with biological tissues. While this study gives a first introduction into the probable relevancy of temperature-dependent optical behavior of biological samples, this work only focuses on the experimental proof for this relationship and will, therefore, not give a deeper analysis of how the underlying models have to be modified.

Thermal Transport Properties of Sulfur-Loaded Carbon-Based Nanotubes and Composite Sulfur Cathodes in Lithium-Sulfur Batteries.

The thermal management of lithium-sulfur batteries with high specific energy has become one of the critical issues for their applications. Carbon-based nanotubes are widely used to construct composite sulfur cathodes. This paper focuses on the thermal transport properties of sulfur-coated and sulfur-embedded boron carbide nanotubes (BCNTs) and carbon nanotubes (CNTs) and their composites using molecular dynamics. It is found that phonon softening and localization play a role in making BCNT exhibit a lower thermal conductivity (TC) than CNT. Furthermore, it is discovered that the sulfur embedded inside the carbon-based nanotube has a greater negative impact on carbon-based nanotube phonon transport. Moreover, the effective medium theory model is not suitable for predicting the effective thermal conductivity of coated sulfur composites, in contrast to its good applicability to embedded sulfur composites. These findings provide an in-depth understanding of the thermal transport properties of composite sulfur cathodes in lithium-sulfur batteries.

Numerical simulation of pore structure and heat transfer behavior in aerated concrete

The pore structure of porous concrete is randomly formed, which brings thorny obstacle to accurately predict its thermal performance. In this study, a numerical approach was proposed for the simulation of pore structure and heat transfer behavior in aerated concrete. According to the porosity (ε) and log-normal pore size distribution parameters (μ, σ), an idea of “random distribution” was developed to reconstruct the pore structure via computer modeling, and also an overlap ratio (δ) was defined and adopted to generate a structure closer to reality. In parallel with this, a Finite Volume Model (FVM) was established to solve the energy control equation, and thus the effective thermal conductivities (ETCs) were numerically calculated. The calibrated and validated FVM model was also used to systematically study the effects of air-void content, air-void distribution and structural parameters, including pore size and porosity on the heat transfer behavior of aerated concrete. The numerical results show that the ETCs tend to slightly decrease with the increase of overlap ratio (δ), pore size (μ) and distribution (σ) due to an increased degree of consolidation between pores, which leads to the solid phase easily blocked by the connected pores so that the optimal heat transfer path through the solid phase conduction is blocked. Further, the comparisons of predictions of ETCs with the experimental data and other existing models indicate that the numerical predictions agree well with the experimental data, and the experimental and simulated values of the ETCs are intermediate between the Maxwell-Eucken 1 and Effective Medium Percolation Theory (EMPT) models.

Estimation of the gas hydrate saturation from multichannel seismic data on the western continental margin of the Chukchi Rise in the Arctic Ocean

A multichannel seismic survey was conducted to investigate the geophysical characteristics of gas hydrates along the western continental margin of the Chukchi Rise around an ARAON mound cluster, which was first recovered in 2016. In the seismic data, gas hydrate-related bottom simulating reflection was widely distributed along the western continental margin of the Chukchi Rise. High-precision seismic P-wave velocity was obtained to investigate the geophysical characteristics of the gas hydrate structures in the BSR areas. Iterative migration velocity analysis was used to construct a detailed P-wave velocity model from the acquired seismic data. The gas hydrate and free gas layers have abnormally high- and low-seismic P-wave velocities; the precise velocity model allows us to understand the detailed spatial distribution of gas hydrate and free gas structures. The effective medium theory model enables estimations of the gas hydrate saturation from constructed seismic P-wave velocity model. We propose the P-wave velocity and gas hydrate saturation models from acquired multichannel seismic data in the western continental margin of the Chukchi Rise for the first time.

Enhanced thermoelectric properties of Ca3Co4O9 by adding nano MoSi2

Adding nanoparticles is a method to regulate the performance of thermoelectric materials. Ca3Co4O9/x MoSi2 (x = 0, 0.05, 0.10, 0.13, and 0.16) was synthesized by a wet chemical method combined with atmospheric pressure sintering. The XRD and SEM results reveal that there are no other reaction in the samples. The grain size of all samples decrease with increasing MoSi2 content, and all presented a similar flake morphology. The influence of MoSi2 on the thermoelectric performance of Ca3Co4O9 is systematically analysed. The appropriate addition of nano-MoSi2 particles can increase the carrier concentration and enhance conductivity of Ca3Co4O9. The electrical conductivity of Ca3Co4O9/0.05 MoSi2 is 83.16 Scm−1, which is 49.2% higher than that of Ca3Co4O9 at 1080 K. The Seebeck coefficient of the Ca3Co4O9/0.16 MoSi2 sample reaches 197.56 μVK−1 at 980 K, which is significantly better than that of previously reported samples prepared by the same method. Moreover, combined with the experimental results and the analysis of the effective medium theory model, the addition of MoSi2 can effectively debase the thermal conductivity of Ca3Co4O9. The thermal conductivity of Ca3Co4O9/0.16 MoSi2 (∼1.26 Wm−1K−1, 1080 K) samples decrease greatly, which is attributed to the influence of interfacial thermal resistance and pores in the Ca3Co4O9/MoSi2. The ZT value of the Ca3Co4O9/0.05 MoSi2 sample increases by 44.4% compare with that of Ca3Co4O9 and reaches 0.26 at 1080 K. These results demonstrate that adding an appropriate amount of MoSi2 particles is one of the methods to enhance the thermoelectric performance of Ca3Co4O9 ceramic samples.

Dielectric spectroscopy of nanofluids in deionized water: Method of removing electrode polarization effect

HypothesisThe electrode polarization observed in the measured complex dielectric frequency responses of the nanosuspensions could be isolated by using time-domain analysis. ExperimentsComplex impedance and dielectric frequency responses of various ferroelectric and magnetic nanofluids were ultrasonically dispersed in deionized water and measured within 20 Hz to 6 GHz range for the first time. A general Kramer-Krönig continuous relaxation model was fitted to the dielectric spectra in the least-squares sense using the Tikhonov’s regularization. The independent ζ-potential measurements of the BTO-C2 and Fe3O4 nanosuspensions were performed. FindingsThree distinct peaks were observed in the time-domain responses. Zero padding of the two slowest peaks, followed by the inversion of the corrected time domain responses, resulted in the flattening of the lower frequency portion of the dielectric constant. The effective medium theory model coupled with the pattern search optimization routine, were used to match these flattened responses. The surface charge on the nanoparticles was estimated from the measured ζ-potential using the Gouy-Chapman-Stern-Grahame model. The resulting values were comparable with the ones obtained from the effective medium theory fitting procedure, which proves effectiveness of the proposed approach at removing the electrode polarization effects. The proposed method has the advantage over the existing ones, because it is carried out in time domain and requires no prior knowledge about the underlying relaxation time amplitude distributions or specific equivalent circuits.

Thermally conductive silicone rubber composites with vertically oriented carbon fibers: A new perspective on the heat conduction mechanism

The continual increase in power density and consumption of modern electronic devices calls for high-performance thermal interface materials (TIMs). In this work, silicone rubber composites with vertically oriented magnetic carbon fibers (o-MCF/SR) were successfully prepared via the cast molding and filler orientation upon uniform magnetic field in a vacuum environment. The through-plane thermal conductivity of o-MCF/SR composites showed an unusual power-law growth with increasing MCF loading. At a 9 vol% MCF loading, the o-MCF/SR composite exhibited a maximum through-plane thermal conductivity of 4.72 W/(m·K) with 2045.5 % TCE, about 3.55 W/(m·K) higher than that of SR composites with randomly dispersed MCF (λ = 1.17 W/(m·K), TCE = 431.8 %). To reveal the underlying through-plane heat conduction mechanism of o-MCF/SR composites, finite element simulation combined with classical effective medium theory model and machine learning method was used. A homogeneous unit fiber-filled composite (HUFC) was modelled, and a new parameter influencing the through-plane thermal conductivity, i.e., shape factor (b/a), was introduced here for the first time. Theoretically, this shape factor was dependent on the filler content and indirectly reflected the assembly of matrix and 1D filler in HUFC fit to a parallel-series hybrid model. Furthermore, a decrease of b/a was practically found with increasing MCF loading, and the dominant series-type assembly gradually transformed to parallel-type assembly of the o-MCF/SR composites. This work not only developed a method to fabricate desirable TIMs that hold great promise for advanced thermal management, but also introduced a new parameter to reveal the underlying mechanism for heat conduction capacity of polymer composites.

Thermal Conduction: Computational Model and Engineering Applications

MATLAB was used to compute the effective thermal conduction of different samples of hard isotropic low porosity composites. The computational algorithms intended to use the Effective Medium Theory (EMT) Model to estimate the effective thermal conductivity (keff) of homogeneous composites. It estimates keff of a homogeneous mixture of components with known volume fractions and components’ conductivities. Starting with preliminary indicators to check the homogeneity conditions, we follow two approaches one for the measured samples and the other for a hypothetical sample with a certain specific desired property. One approach is to use preliminary indicators of surface homogeneity of the measured samples either via electron and/or via optical transmission microfilm scanning. The other approach is used for both measured and hypothetical samples by assuming a layered structure of parallel and series of slabs to compute upper and lower bounds of conduction. We used MATLAB to implement a fine precision computing algorithm to investigate the composite samples. The results predicted by the EMT model were examined for validation. The deviation of keff from the experiment for the homogenous samples is between 3 to 28% depending on the uniformity of distribution of phases within the composite matrix.

Facile Method for Preparing Hierarchical Al2O3-Glass Foam Ceramics with Superior Thermal Insulating Property.

Porous ceramics are good candidates for thermal-insulating materials. Glass is a low-cost material that possesses low intrinsic thermal conductivity of less than 10 W·m-1·K-1. However, the mechanical strength of a homogeneous glass material is fairly low. We, in this work, have fabricated Al2O3-hollow glass sphere (HGS) foam ceramics with a facile particle-stabilized foaming method. The obtained foam ceramic presents a hierarchical microstructure that is rare to be seen elsewhere using this foaming technique. The foaming system contains two types of particles having opposite charges, and the particle-stabilized foaming mechanism is hence discussed. The optimal sample possesses a porosity above 94% with a thermal conductivity as low as 0.0244 W/m·K, which reaches the level of superinsulating materials. The compressive strengths of the foam ceramics range from 0.07 to 0.83 MPa. The effective medium theory model is used to calculate the thermal conductivities as reference. The deviation of the theoretical values from the experimental ones are derived from the effect of the hierarchical microstructure of the foams. The results of this work may deepen one's understanding and pave new ways for the particle-stabilized foaming technique. The unique microstructure of the ceramic may also shed some light on fabricating superior thermal-insulating ceramic materials.

Equivalent Circuit Modeling and Experimental Analysis of Low Frequency Metamaterial for Efficient Wireless Power Transfer

This study proposes a low-frequency metamaterial(MM) coupled with an equivalent circuit model to emulate the behavior of an MM-based Wireless Power Transfer (WPT) system. For this purpose, the electromagnetic simulation and Finite Element Analysis (FEA) of the proposed MM-based WPT system are performed in ANSYS three-dimensional (3D) High-Frequency Structured Simulator (HFSS). In addition, numerical analysis of the circuit design of the proposed structure is performed in a MATLAB simulation environment to evaluate its transfer characteristics. While some methods, including effective medium theory and transmission line circuit model, have been exploited to explain the physical mechanism of MM-based WPT systems, some of the reactive parameters and the fundamental physical interpretation have not been clearly expounded. In contrast to existing theoretical models, the proposed approach focuses on the effect of system parameters of the MM and transfer coils on transfer characteristics, coupled with its effectiveness in analyzing complex circuits. A design prototype is fabricated for experimental measurement of power transfer efficiency and medium parameters using the KeySight ENA 5061 vector network analyzer (VNA), confirming the validity of the proposed design. The excellent efficiency enhancement and mutual coupling make the design an attractive solution for WPT applications. A close agreement of the experimental results and numerical simulation validates the accuracy of the analytical model.

Theoretical prediction of elastic modulus at different states and squirt-flow-related attenuation: extension of Cracks-Pores Effective Medium model

SUMMARYSquirt flow plays an essential role in elastic modulus dispersion and attenuation for fluid-saturated cracked porous rocks. The Mavko–Jizba model and relevant modified models can describe the squirt flow well based on the related elastic moduli, such as dry/drained bulk modulus. However, when these elastic moduli are challenging to attain, it is impossible to model the squirt-flow-related elastic moduli and attenuations with the models. On the other hand, the effective medium theory (EMT) model can estimate these elastic moduli, but cannot predict the undrained/relaxed and partially relaxed saturated elastic moduli and the squirt-flow-related attenuations. This paper extended an EMT model—Cracks–Pores Effective Medium (CPEM) model—to cover the undrained/relaxed and partially relaxed states following the elastic–viscoelastic correspondence principle. The proposed model [i.e. frequency-dependent CPEM (CPEMF) model] can thus estimate the elastic moduli over the different states (dry/drained, undrained/relaxed, partially relaxed and unrelaxed) and associated attenuations. It agrees well with the prediction of the modified Mavko–Jizba–Gurevich model (MJGZ-HF) at unrelaxed state and is precisely consistent with the prediction of Gassmann at undrained/relaxed state. Also, it analytically shows good consistency with the modified Mavko–Jizba–Gurevich model (MJGZ-MF) at partially relaxed state. The numerical simulations of CPEM/CPEMF models and MJGZ-HF/MJGZ-MF models show good agreement at the different states. Furthermore, we interpreted the experimental data on a basaltic sample and a sandstone sample with the CPEM/CPEMF models. The CPEMF model's predictions of elastic modulus at different states and associated modulus dispersion/attenuation are in good agreement with the corresponding measured ones, suggesting that the proposed CPEMF model can efficiently predict the elastic moduli at different states (dry/drained, undrained/relaxed, partially relaxed and unrelaxed) and quantify the squirt-flow-related elastic modulus dispersion and attenuation among different states well.

Low-loss NiZnCo ferrite composites with tunable magneto-dielectric performances for high-frequency applications

A series of Ni0.5Zn0.3Co0.2Fe2O4/epoxy magnetodielectric composites were synthesized through solvent-assisted method and demonstrate tunable permeability and permittivity, ultralow losses and high refractive index over a broad frequency region of the VHF and UHF bands. Experimental results reveal that the permeability μ' decreases from ~4.2 to ~3.5 while the permittivity ε' was improved from ~5.0 to ~6.1 with an increase in epoxy weight fraction from 1 to 20 wt%. These variations are shown to be intimately related to the microstructures in accordance with effective medium theory and magnetic circuit model. Correspondingly, the characteristic impedance of the magnetodielectric composite medium is varied from ~0.75 to ~0.90 while maintaining a refractive index around 4.5. Typical magnetic loss as tan δμ and dielectric loss as tan δε at 0.5 GHz are as low as in the order of 10−2 and 10−3, respectively. These magnetodielectric materials provide excellent radio frequency results that allowing for the realization of the high-performance miniaturized electronic devices, systems, and platforms.