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The dielectric virial expansion is developed for composite systems with embedded interacting dielectric dipolar spheres. Introducing a multiple-scattering expansion for the polarization energy in the presence of an external field enables the derivation of a virial expansion for the polarizability. Substituting the polarizability into the Clausius-Mossotti relation yields the virial series for the effective medium permittivity. When the dipole moment of the particles or inclusions vanishes, the leading-order term in the series reduces to the Maxwell-Garnett mixing rule, whereas the higher-order terms provide corrections that become important at higher densities. The dielectric virial coefficients are readily evaluated by replacing the surface charge contributions with image lines. Numerical data are presented for the second virial coefficients to illustrate the effects of polarization. [ABSTRACT FROM AUTHOR]

The wave dispersion characteristics for loop array-based metamaterials were analyzed, based on the general transmission line model of a one-dimensional host medium interacting with a chain of coupled loops. By relating the wave propagation constant and the effective parameters of the coupled host medium, we showed that an active medium embedded with non-Foster loaded loop array can be designed to exhibit broadband negative material parameters with positive gain. Accounting for all interactions, the stability of the active medium was investigated, further yielding necessary design specifications for the non-Foster loads. Subsequently, an experimental demonstration was provided to verify the theoretical analysis, showing that stable reconfigurable broadband gain metamaterials at microwave frequencies can be obtained with proper negative impedance converter design. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO)-doped dimethyl sulfate (DMS)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) superconductive alignment layer, aligning liquid crystals (LCs) with super switching and non-residual direct current (non-residual DC) performance, is presented in this manuscript. Doping of GO increased the pristine polar energy of a thin composite layer as well as the corresponding anchoring energy of the LCs sandwiched between these thin layers but only slightly affected the thin layers' morphology. When rubbed GO/DMS/PEDOT:PSS composite layers were used as alignment layers, a homogeneous alignment of nematic LCs was observed with competitive optoelectrical switching properties and non-residual DC performance because of the enhanced field effect and charge transport induced by the doped GO. [ABSTRACT FROM AUTHOR]

In this paper, the multilayered structure composed of periodic arrays of graphene ribbons separated by the dielectric slabs is investigated for both the transverse electric (TE) and transverse magnetic (TM) polarizations. The transmission spectra show a stopband region between the low-THz frequency passband region and the higher-frequency one for TM polarization due to dual capacitive-inductive nature of the surface impedance corresponding to arrays of graphene ribbons. For TE polarization, the surface impedance is pure inductive; therefore, a passband region can be seen after the low-THz frequency stopband region. The in-plane permittivities are calculated based on the scattering parameters retrieval method. The negative permittivities are obtained in stopband regions corresponding to Bloch evanescent modes. This structure allows the propagation of backward waves in negative permittivity regime for TM polarization. [ABSTRACT FROM AUTHOR]

The properties of disordered metamaterial absorbers are analyzed on the basis of numerical simulations and experimental characterizations. A broadening of the absorption spectrum is clearly evidenced. This effect is the consequence of both the coupling between nearby resonators leading to the occurrence of extended magnetic resonance modes and the interconnection of elementary particles yielding the definition of resonating clusters. The angular robustness of the absorbing structure under oblique incidence is also demonstrated for a wide domain of angles. [ABSTRACT FROM AUTHOR]

Metal-insulator-metal metamaterial thermal emitters or absorbers have been widely investigated, and the fundamental and higher-order modes are generally excited in these metamaterial resonators. In this paper, we propose a methodology to widen the frequency interval between the fundamental and the second-order modes by enhancing coupling between resonators in close-proximity. At the second-order mode, antiparallel magnetic fields are excited in the insulating layer of rectangular resonators. A diagonal arrangement of rectangles allows destructive interaction between neighboring resonators, resulting in higher second-order frequency. The maximum frequency interval between the two modes is achieved when resonators are shifted by half a period. Furthermore, we suggest a possibility to split the second-order mode by adjusting the arrangement of rectangles. Measured reflection spectra of fabricated metamaterial absorbers agree well with numerical simulations. [ABSTRACT FROM AUTHOR]

Second harmonic generation in a transversely isotropic plate and a symmetric composite laminate is analyzed from a theoretical perspective. The strain energy function for a nonlinear elastic transversely isotropic material is expressed in terms of the five invariants of the Green-Lagrange strain tensor. Internal resonance conditions for the generation of cumulative second harmonics indicate that a cumulative second harmonic exists when the primary-secondary mode pair satisfies the phase matching and non-zero power flux criteria. In particular, for transversely isotropic plates, when the primary mode propagates along the material principal direction, only symmetric second harmonic Lamb-like wave modes can be cumulative. Also, when the primary wave propagates along other directions, only symmetric second harmonic modes can be generated. Additionally, for the case of symmetric composite laminates, only symmetric modes can be generated as cumulative second harmonics regardless of the propagation direction of the primary mode. To validate the above theoretical predictions, finite element simulations were conducted for mode pairs that are: (i) phase matched but have zero power flux, (ii) not phase matched but have non-zero power flux, and (iii) internally resonant i.e., satisfying both phase matching and non-zero power flux criterion. The results obtained from the simulations corroborate the theoretical findings for both transversely isotropic plates and symmetric composite laminates. [ABSTRACT FROM AUTHOR]

Reconfigurable metamaterials have great potential to alleviate complications involved in using passive metamaterials to realize emerging electromagnetic functions, such as dynamical filtering, sensing, and cloaking. This paper presents a new type of tunable meta-atoms in the X-band frequency range (8-12 GHz) toward reconfigurable metamaterials. The meta-atom is made of all flexible materials compliant to the surface of an interaction object. It uses a liquid metal-based split-ring resonator as its core constituent embedded in a highly flexible elastomer. We demonstrate that simple mechanical stretching of the meta-atom can lead to the great flexibility in reconfiguring its resonance frequency continuously over more than 70% of the X-band frequency range. The presented meta-atom technique provides a simple approach to dynamically tune response characteristics of metamaterials over a broad frequency range. [ABSTRACT FROM AUTHOR]

The newly introduced metamaterial-based optical circuit, an analogue of electronic circuit, is becoming a forefront topic in the fields of electronics, optics, plasmonics, and metamaterials. However, metals, as the commonly used plasmonic elements in an optical circuit, suffer from large losses at the visible and infrared wavelengths. We propose here a low-loss, all-semiconductor metamaterial-based optical circuit board at the microscale by using interleaved intrinsic GaAs and doped GaAs, and present the detailed design process for various lumped optical circuit elements, including lumped optical inductors, optical capacitors, optical conductors, and optical insulators. By properly combining these optical circuit elements and arranging anisotropic optical connectors, we obtain a subwavelength optical filter, which can always hold band-stop filtering function for various polarization states of the incident electromagnetic wave. All-semiconductor optical circuits may provide a new opportunity in developing low-power and ultrafast components and devices for optical information processing. [ABSTRACT FROM AUTHOR]

For the tri-layer symmetric magnetoelectric (ME) laminated composites made of giant magnetostrictive materials and piezoelectric materials, we chose the nonlinear magnetostrictive constitutive with variable coefficients and the linear piezoelectric constitutive to obtain the vibration equation for the laminated composites. The surface force and displacement speed were equivalent to the circuit voltage and current in the equivalent circuit for the laminated composites. According to the equivalent circuit, a model of the static magnetoelectric field coefficient for the strong nonlinear thermo-magneto-electro-mechanical coupling was obtained. Without considering the pre-stress, the comparisons of the static ME coefficient versus temperature curves for the experimental and theoretical results were in good agreement both qualitatively and quantitatively for low and moderate magnetic fields. The theoretical results were smaller than the experimental results under high magnetic fields. This model was adopted to predict variations in the ME coefficients in the laminated composites under different bias magnetic fields, temperatures, and stresses. This showed that the laminated composites had the strongest magnetoelectric effect at 0 °C; a large compressive stress effectively suppressed the magnetoelectric effect attenuation caused by high temperatures; an appropriate tensile stress improved the maximum magnetoelectric coefficient and lowered its bias magnetic field near room temperature. These results provide a theoretical basis for the design and application of high-performance and miniaturized magnetoelectric devices, operating under extreme temperature conditions. [ABSTRACT FROM AUTHOR]

The indentation problem of a flat circular punch with uniform heat flux distributed at its base, pressed into a semi-infinite transversely isotropic magneto-electro-thermo-elastic space is investigated. The closed-form solution in the full space is obtained by potential theory method. In addition, the factors of indentation stiffness that relates mechanical force, electric charge, magnetic induction with the heat flux are presented. The obtained solution can be degenerated for the corresponding problems of thermopiezoelectric, thermomagnetoelastic, and thermoelastic materials and can also be superposed to construct the solution to the corresponding indentation problems with coupled thermal, electric, magnetic, mechanical effects. In addition, the solution presented in this article can not only help to investigate mechanisms of the image formation in the area of nanoscience and nanotechnology, but also can serve as benchmarks for future numerical studies of multiphase composites. [ABSTRACT FROM AUTHOR]

Hydrogels have found many practical uses in drug release, wound dressing, and tissue engineering. However, their applications are restricted due to their weak mechanical properties. The role of graphene oxide nanosheets (GONS) as reinforcement agent in poly (acrylic acid) (PAA)/Gelatin (Gel) composite hydrogels is investigated. Composite hydrogels are synthesized by thermal initiated redox polymerization method. Samples are then prepared with 20 and 40 wt. % of PAA, an increasing amount of GONS (0.1, 0.2, and 0.3 wt. %), and a constant amount of Gel. Subsequently, cylindrical hydrogel samples are subjected to a series of compression tests in order to measure their elastic modulus, maximum stress and strain. The results exhibit that the addition of GONS increases the Young's modulus and maximum stress of hydrogels significantly as compared with control (0.0 wt. % GONS). The highest Young's modulus is observed for hydrogel with GO (0.2 wt. %)/PAA (20 wt. %), whereas the highest maximum stress is detected for GO (0.2 wt. %)/PAA (40 wt. %) specimen. The addition of higher amounts of GONS leads to a decrease in the maximum stress of the hydrogel GO (0.3 wt. %)/PAA (40 wt. %). No significant differences are detected for the maximum strain among the hydrogel samples, as the amount of GONS increased. These results suggest that the application of GONS could be used to improve mechanical properties of hydrogel materials. This study may provide an alternative for the fabrication of low-cost graphene/polymer composites with enhanced mechanical properties beneficial for tissue engineering applications. [ABSTRACT FROM AUTHOR]

Direct current (DC) electro-optical (EO) control of transmitted laser beam intensity based on EO controlled coherent light scattering and diffraction by stationary longitudinal texture pattern (LTP) is achieved in planar-oriented cells with a composite mixture of polymer-coated gold spherical nanoparticles (Au-NPs) with a mean diameter of about 12 nm and the room-temperature nematic pentylcyanobiphenyl (5CB). At relatively low DC voltage of about 5 V, the effective scattering/diffraction by Au-NPs/5CB composites leads to a spatial spreading of transmitted coherent light from a low-power continuous wave laser beam, resulting in a drastic reduction of its local intensity. The effect is polarization dependent and is strongest when the polarization of the input laser beam is along the LTP. The EO response of Au-NPs/5CB mixtures is studied under DC and alternating current (AC) joint action with the aim of the potential use of these composite materials as EO controlled diffusers. The specific V-shaped sharp dip in the DC voltage-dependent coherent light transmittance of Au-NPs/5CB planar films, as well as the possibility for erasing the scattering/diffractive LTP in the films by joint low AC voltage, can be useful for EO applications in the field of process control and for detection of weak dynamic electric fields. [ABSTRACT FROM AUTHOR]

In Pb-free β-Zn4Sb3 based composites incorporated with (Bi2Te3) 0.2 (Sb2Te3)0.8, we concurrently realize ~30% increase in thermoelectric power factor through an energy filtering effect caused by carrier scattering at interface barriers, and ~15% reduction in thermal conductivity due to interface scattering, allowing the figure of merit to reach 1.1 at 648K in the composite system with 1 vol. % of (Bi2Te3) 0.2 (Sb2Te3)0.8. [ABSTRACT FROM AUTHOR]

Phthalocyanines in combination with C60 are benchmark materials for organic solar cells. Here, we have studied the morphology and electronic properties of co-deposited mixtures (blends) of these materials forming a bulk heterojunction as a function of the concentration of the two constituents. For a concentration of 1:1 of Cu-Phthalocyanine (CuPc):C60, a phase separation into about 100 nm size domains is observed, which results in electronic properties similar to layered systems. For low C60 concentrations (10:1 CuPc:C60), the morphology, as indicated by Low-Energy Electron Microscopy images, suggests a growth mode characterized by (amorphous) domains of CuPC, whereby the domain boundaries are decorated with C60. Despite of these markedly different growth modes, the electronic properties of the heterojunction films are essentially unchanged. [ABSTRACT FROM AUTHOR]

Compositional, frequency, and temperature studies of impedance and electrical conductivity in (Ag3AsS3)x(As2S3)1-x superionic glasses and composites were performed. Frequency range from 10 Hz to 3 x 109 Hz and temperature interval 300-400K were used for the measurements. Compositional dependences of electrical conductivity and activation energy are analyzed; the most substantial changes are observed with the transition from (Ag3AsS3)0.4(As2S3)0.6 glass to (Ag3AsS3)0.5(As2S3)0.5 composite. With increase of Ag3AsS3 content, the investigated materials are found to have crystalline inclusions and show the two-phase composite nature. Addition of (Ag3AsS3) leads to the increase of electrical conductivity whereas the activation energy decreases. [ABSTRACT FROM AUTHOR]

Laser driven experiments were used to investigate the shock compression behavior of powder processed Bismuth/Tungsten (Bi/W) composite samples. The constituents provide different functionality to the composite behavior as Bi could be shock melted at the pressures attained in this work, while the W could not. Samples were prepared by uniaxial pressing, and the relative density was measured as a function of particle size, applied pressure, and composition for both hot and cold pressing conditions. This resulted in sample densities between 73% and 99% of the theoretical maximum density, and also noticeable differences in microstructure in the hot and cold pressed samples. The compression waves were generated with a 1.3 x 1.3 mm square spot directly onto the surface of the sample, using irradiances between 1012 and 1013 W/cm², which resulted in calculated peak pressures between 50 and 150 GPa within a few micrometers. Sample recovery and post-mortem analysis revealed the formation of a crater on the laser drive surface, and the depth of this crater corresponded to the depth to which the Bi had been melted. The melt depth was found to be primarily a function of residual porosity and composition, and ranged from 167 to 528 µm. In general, a higher porosity led to a larger melt depth. Direct numerical simulations were performed, and indicated that the observed increase in melt depth for low-porosity samples could be largely attributed to increased heating associated with work done for pore collapse. However, the relative scaling was sensitive to composition, with low volume fraction Bi samples exhibiting a much stronger dependence on porosity than high Bi content samples. Select samples were repeated using an Al foil ablator, but there were no noticeable differences ensuring that the observed melting was indeed pressure-driven and was not a result of direct laser heating. The resultant microstructures and damage near the spall surface were also investigated qualitatively. [ABSTRACT FROM AUTHOR]

Novel analytical models have been proposed in this study which extends current available fluid-structure interaction (FSI) theories for explosion induced shock loading on monolithic and laminated composite plates to sandwich composite panels, featuring core compression. The proposed models have been asymptotically validated against other FSI existing theories in low pressure range. A qualitative comparative analysis of the proposed models has been made with other existing FSI theories from the viewpoint of energy conservation. Core compression as predicted by the proposed models can be utilized for more economical, robust design of blast resistant sandwich composite structures. [ABSTRACT FROM AUTHOR]

The initiation of chemical reaction in cold-rolled Ni/Al multilayered composites by shock compression is investigated numerically. A simplified approach is adopted that exploits the disparity between the reaction and shock loading timescales. The impact of shock compression is modeled using CTH simulations that yield pressure, strain, and temperature distributions within the composites due to the shock propagation. The resulting temperature distribution is then used as initial condition to simulate the evolution of the subsequent shock-induced mixing and chemical reaction. To this end, a reduced reaction model is used that expresses the local atomic mixing and heat release rates in terms of an evolution equation for a dimensionless time scale reflecting the age of the mixed layer. The computations are used to assess the effect of bilayer thickness on the reaction, as well as the impact of shock velocity and orientation with respect to the layering. Computed results indicate that initiation and evolution of the reaction are substantially affected by both the shock velocity and the bilayer thickness. In particular, at low impact velocity, Ni/Al multilayered composites with thick bilayers react completely in 100ms while at high impact velocity and thin bilayers, reaction time was less than 100 µs. Quantitative trends for the dependence of the reaction time on the shock velocity are also determined, for different bilayer C thickness and shock orientation. [ABSTRACT FROM AUTHOR]

Ferromagnetic BiFeO3 nanocrystals of average size 11 nm were used to form nanocomposites (x)BiFeO3/(100 - x)NiO, x = 0, 20, 40, 50, 60, 80, and 100 by simple solvothermal process. The ferromagnetic BiFeO3 nanocrystals embedded in antiferromagnetic NiO nanostructures were confirmed from X-ray diffraction and transmission electron microscope studies. The modification of cycloidal spin structure of bulk BiFeO3 owing to reduction in particle size compared to its spin spiral wavelength (62 nm) results in ferromagnetic ordering in pure BiFeO3 nanocrystals. High Neel temperature (TN) of NiO leads to significant exchange bias effect across the BiFeO3/NiO interface at room temperature. A maximum exchange bias field of 123.5 Oe at 300K for x = 50 after field cooling at 7 kOe has been observed. The exchange bias coupling causes an enhancement of coercivity up to 235 Oe at 300 K. The observed exchange bias effect originates from the exchange coupling between the surface uncompensated spins of BiFeO3 nanocrystals and NiO nanostructures. [ABSTRACT FROM AUTHOR]

The commonly used coordinate transformation for cylindrical cloaks is generalized. This transformation is utilized to determine an anisotropic inhomogeneous diagonal material tensors of a shell type cloak for various material types, i.e., double-positive (DPS: [variant_greek_epsilon], μ > 0), double-negative (DNG: [variant_greek_epsilon], μ < 0), [variant_greek_epsilon]-negative (ENG), and μ-negative (MNG). To obtain conditions of perfect cloaking for various material types, a rigorous analysis is performed. It is shown that perfect cloaking will be achieved for same type material for the cloak and its surrounding medium. Moreover, material losses are included in the analysis to demonstrate that perfect cloaking for lossy materials can be achieved for identical loss tangent of the cloak and its surrounding material. Sensitivity of the cloaking performance to losses for different material types is also investigated. The obtained analytical results are verified using a Finite-Element computational analysis. [ABSTRACT FROM AUTHOR]

Half-metallic (CrO2)1-x-(SnO2)x composites were prepared under high temperature and high pressure conditions. The composites are composed of large rod-like CrO2 grains and small SnO2 nanoparticles. The CrO2 in the composites is very pure and its saturation magnetization is very close to the theoretical value. The composition dependence of magnetic and magnetotransport properties of the composites was studied. The coercive force (Hc) and remanence ratio (Mr/Ms) of the composites increase dramatically with increasing SnO2 content x for x > 0.6. This should be due to that the CrO2 grains have been well separated by SnO2 nanoparticles and the magnetic interactions among CrO2 grains become weak when x > 0.6. The resistivity and magnetoresistance at 5 K of the composites increase with increasing x, and the increase quickens up at x = 0.5. When x ≥ 0.5, the (CrO2)1-x-(SnO2)x composites show insulator behavior, and the temperature dependence of the resistivity can be well described by fluctuation-induced tunneling model. But when x ≤ 0.4, the (CrO2)1-x-(SnO2)x composites show insulator-metal transitions, and the transition temperature increases with increasing SnO2 concentration. Below the transition temperature, their resistivity can also be explained by fluctuation-induced tunneling model. The (CrO2)1-x-(SnO2)x composites show greater magnetoresistance than pure CrO2 at low temperature, which is attributed to enhancement of tunneling magnetoresistance by adding of SnO2. [ABSTRACT FROM AUTHOR]

Unidirectional carbon fiber reinforced epoxy composite samples were tested to determine their response to one dimensional shock loading with the ultimate goal of developing a micromechanics based numerical model of the dynamic response. The material tested had high fiber content (62-68% by volume) and low porosity. Wave speeds for shocks traveling along the carbon fibers are significantly higher than for those traveling transverse to the fibers or through the bulk epoxy. As a result, the dynamic material response is dependent on the relative shock-fiber orientation; a complication that must be captured in the numerical models. Shocks traveling transverse to the fibers show an inelastic response consistent with the material constituent parts. Shocks traveling along the fiber direction travel faster and exhibit both elastic and plastic characteristics over the stress range tested; up to 15 GPa. Results presented detail the anisotropic material response, which is governed by different mechanisms along each of the two principle directions in the composite. Finally, numerical modeling of this response is described in detail and validated against the experimental data. [ABSTRACT FROM AUTHOR]

A model is presented that integrates the critical path approximation with percolation theory to describe the dependence of electrical conductivity upon volume fraction in nanofiber-based composites. The theory accounts for clustering and correlation effects that reflect non-randomness in the spatial distribution of the particles. Results from this formalism are compared to experimental measurements performed upon carbon nanotube-based conductive nanocomposites. [ABSTRACT FROM AUTHOR]

The van der Waals interaction between a lipid membrane and a substrate covered by a graphene sheet is investigated using the Lifshitz theory. The reflection coefficients are obtained for a layered planar system submerged in water. The dielectric response properties of the involved materials are also specified and discussed. Our calculations show that a graphene covered substrate can repel the biological membrane in water. This is attributed to the significant changes in the response properties of the system due to the monolayer graphene. It is also found that the van der Waals interaction is mostly dominated by the presence of graphene, while the role of the particular substrate is secondary. [ABSTRACT FROM AUTHOR]

Metals are known to have unique thermal, mechanical, electrical, and catalytic properties. On the other hand, metallic nanowires are promising materials for variety of applications such as transparent conductive film for photovoltaic devices, electrodes for batteries, as well as nano-reinforcement for composite materials. Whereas varieties of methods have been explored to synthesize metal nanowires with different characteristics, electrospinning has also been found to be successful for that purpose. Even though electrospinning of polymeric nanofibers is a well-established field, there are several challenges that need to be overcome to use the electrospinning technique for the fabrication of metallic nanowires. These challenges are mainly related to the multi-steps fabrication process and its relation to the structure evolution of the nanowires. In addition to reviewing the literature, this article identifies promising avenues for further research in this area with particular emphasis on the applications that nonwoven metal wires confined in a nano-scale can open. [ABSTRACT FROM AUTHOR]

The local piezoelectric properties of ferroelectric composites consisting of P(VDF-TrFE) copolymer matrix with barium lead zirconate titanate ceramic inclusions were addressed both experimentally using piezoresponse force microscopy technique and theoretically applying the Landau-Ginzburg-Devonshire formalism. A transient region with a width of approximately 40 nm has been found at the interface between the two constituents. It is shown that the piezoresponse in the vicinity of the interface is strongly affected by inhomogeneous stresses originating from an incompatibility of thermal expansion coefficients of PVDF and lead zirconate titanate. [ABSTRACT FROM AUTHOR]

We have studied magnetic and structural properties of the composite microwires consisted of the metallic core and the outer glass shell. Nominal chemical composition of the core was Ni49.5Mn25.4Ga25.1, its diameter was 13.2 μm, and the total diameter of the glass-covered microwires was 26.4 μm. We have found out that at room temperature the core of the as-cast microwires was composed by two phases with tetragonal I4/mmm and cubic Fm3m crystal structures, but annealing rendered it single phase. Measurements of the magnetic properties have demonstrated substantial growth of the magnetic anisotropy with cooling, which we have attributed to the phase transition from the room-temperature austenitic to the low-temperature martensitic state. Magnetic easy axis was found to be perpendicular to the axis of the microwires at low temperatures. We believe that it is a result of the crystallographic texture induced in the martensite by high internal stress characteristic of the glass-covered magnetic microwires. Though rearrangement of the martensitic microstructure under external pressure was previously observed in the single crystal Ni2MnGa samples, in composite materials this effect is new and can be potentially useful for the applications. [ABSTRACT FROM AUTHOR]

Two different formalisms for the homogenization of composite materials containing ellipsoidal inclusions based on Bruggeman's original formula for spherical inclusions can be found in the literature. Both approximations determine the effective macroscopic permittivity of such an idealized composite assuming randomly distributed dielectric particles of equal shape and differ only in the definition of the depolarization factors. The two approaches are applied to analyze ellipsometric Mueller matrix spectra acquired in the visible and near-infrared spectral region from metal and semiconductor slanted columnar thin films. Furthermore, the effective dielectric function tensor generated by the two Bruggeman formalisms is compared to effective major axes dielectric functions individually determined with a homogeneous biaxial layer approach. Best-match model parameters of all three model approaches are discussed and compared to estimates from scanning electron microscope images. The structural parameters obtained from all three optical modeling approaches agree well with the electron microscopy technique. A comparative discussion is given for the validity and applicability of the three model approaches for analysis of future devices structures that may require optical readout using generalized ellipsometry methods. [ABSTRACT FROM AUTHOR]

The effective thermal conductivity models for particulate composites are usually restricted to the dilute limit, with volumetric concentrations of particles typically less than 15%. By considering the particle interactions through a crowding factor, in this work, a new formula is developed to describe the thermal conductivity of composites with a dielectric matrix, for volume fractions of particles up to their maximum packing fraction. The crowding factor model is then applied to analyze two particulate composites with dielectric or metallic particles, where the effects of both interfacial thermal resistance and the electron-phonon coupling are taken into account. It is shown that the predictions of the proposed crowding factor model are larger than the ones predicted by the dilute-limit models, for composites with high volume fractions of particles, due to the particle interactions. The proposed crowding factor model extends the applicability of various thermal conductivity models for composites reported in the literature and its predictions are in good agreement with published experimental data. [ABSTRACT FROM AUTHOR]

An alternative to obtain multiferroic materials is the production of composite materials that combine ferroelectric and magnetic materials. In particular, the use of magnetostrictive materials as ferromagnetic phase in composites is very important because the mechanical stress applied in ferroelectric phase induces the appearance of magnetoelectric effect. In this work, we have proposed a generalized model for the magnetostriction dependence with the magnetization of the 0-3 type composite magnetoelectric materials. Including both piezomagnetic and stress dependence in the magnetostriction, a relevant improvement was reached as compared to the ordinary square magnetization model. Based on the Gibbs free energy expansion, the magnetostriction behavior of the composite (1-x)Pb(Mg1/3Nb2/3)-xPbTiO3/CoFe2O4 at 300 K and 5 K is described. Furthermore, using the piezomagnetic correction, the magnetostriction data for the pure CoFe2O4 is fitted showing that this ferrite presents a relevant piezomagnetic effect. [ABSTRACT FROM AUTHOR]

In the literature on composite materials with extreme or unusual electromagnetic properties (so-called metamaterials), it is common to retrieve the effective material parameters from the scattering parameters (complex reflection and transmission coefficients) of the metamaterial layer. Most often, this retrieval is done by using the well-known Nicolson-Ross-Weir method or its modifications. It is commonly known that one of the two effective parameters of many metamaterials retrieved in this way (either effective permittivity or permeability) exhibits the so-called anti-resonance, which is a nonphysical feature. This effect has been understood as a manifestation of spatial dispersion in the sample. Many previous works have either claimed or assumed that the anti-resonance is an effect caused by the periodicity of the composite material. To our knowledge, this claim was never supported by comparisons of periodical and random samples. In some other works, it has been theoretically shown that the anti-resonance of the retrieved material parameters can be avoided, e.g., by the introduction of additional surface parameters into the retrieval procedure. If it is so, the anti-resonance has nothing to do with the internal periodicity of the bulk medium. In the present work, we numerically and experimentally investigate the question if the internal periodicity of metamaterial layers is essential for the appearance of anti-resonances in extracted material parameters. We show that it is not so. Therefore, our result is in favor of the theory which treats the anti-resonance as a deficiency of the Nicolson-Ross-Weir retrieval procedure applied to spatially dispersive media. [ABSTRACT FROM AUTHOR]

The work reported in this paper aims at studying the magneto-electric field variation accounting for a thin interphase layer with different materials. Thin interphase within a solid can significantly affect the overall response of the composite material. In order to obtain this phenomenon, we replace the interphase by an imperfect interface with appropriately devised interface conditions. To get the interface conditions, a Taylor expansion of the relevant physical fields in the thin region is introduced. Those conditions do not involve the fields within the interphase, which just have relation to the material properties and the fields of the adjacent media. Finally, the influence of the thin interphase on the performance of fibrous multiferroic composites is analyzed in detail by using our method and some useful conclusions are summarized. [ABSTRACT FROM AUTHOR]

Nanomaterials composed of a population of particles dispersed in a matrix represent the building block for the next generation of several technologies: energy storage and conversion, thermal management, electronics, and photovoltaics. When interfaces between particles and matrix are imperfect, the size of the particles may strongly influence the effective linear and nonlinear response of the whole system. Here, we study these scale effects mainly focussing on the nonlinear transport behavior of composite structures. The theory is developed, in the framework of the electrical conductivity, for an arbitrary nonlinearity of the constituents; however, explicit results are discussed for Kerr-like nonlinear responses. Two kinds of imperfect interfaces are considered: the T-model and the Π-model, which represent a generalization of the classical schemes largely employed in literature, namely the low and the high conducting interface models. The dependence of the nonlinear effective properties on the size of the dispersed particles is explained through intrinsic length scales governing some universal scaling laws. [ABSTRACT FROM AUTHOR]

Here, we report the magnetic, ferroelectric, dielectric properties, and Raman spectroscopic studies of multiferroic [(1-x)Pb(Fe0.5Nb0.5)O3-xNi0.65Zn0.35Fe2O4] composites at room temperature. The phase formation of composites was confirmed independently from the X-ray diffraction and Raman studies. The room temperature magnetic studies reveal ferromagnetic like behavior of these composites in contrast to the paramagnetic nature of Pb(Fe0.5Nb0.5)O3. Furthermore, with increasing x, the saturation magnetization, remnant magnetization, and coercive fields are found to increase. The electrical characterizations of these composites reveal a decrease in remnant polarization and dielectric constant with increasing x. More importantly, the x = 0.2 composite is found to be a very good multiferroic material at room temperature among the composites and could be a potential candidate for future potential applications. [ABSTRACT FROM AUTHOR]

Nitrogen-doped and pure carbon nanotube (CNT) based composites were fabricated for investigating their dielectric properties in static regime as well as electromagnetic response properties in microwave frequency range (Ka-band). Two classes of host matrix-polystyrene and phosphate unfired ceramics-have been used for composites fabrication. The study reveals miscellaneous effect of nitrogen doping on the dielectric permittivity, dc conductivity and electromagnetic interference shielding efficiency of CNT-based composites, produced with both polymer and ceramic matrices. The high-frequency polarizability, estimated for different-length CNTs, and static polarizability, calculated for nitrogen-containing CNT models using a quantum-chemical approach, show that this effect results from a decrease of the nanotube defect-free-length and deterioration of the polarizability with incorporation of nitrogen in pyridinic form. [ABSTRACT FROM AUTHOR]

Large amplitude steady waves in materials have been observed to display certain scaling relationships between the strain rate and the stress amplitude. In many homogeneous materials, strain rate scales with stress to the fourth power. However, scaling of strain rate with stress to the first, second, and fourth power has been found for different classes of heterogeneous materials. We examine wave structures for three classes of heterogeneous materials through mesoscale simulations that resolve the scale of heterogeneity explicitly. We utilize these simulations to gain insight into the scaling phenomena observed and to identify the critical non-dimensional parameters for the phenomena. These parameters are then applied to the available experimental data for the three classes. The same set of non-dimensional groups is found to be appropriate for layered and particulate composite materials, while somewhat different groups are found for granular materials. Two different types of simulations lead to different conclusions on the need for the inclusion of strength in the non-dimensionalization for granular materials. The groups formed are found to collapse the experimental data quite well when the strength parameter is not included. Finally, a simple model for granular materials demonstrates that the crucial aspect of their behavior that controls the scaling of waves is the need for mass transfer to close voids in the material. [ABSTRACT FROM AUTHOR]

The ferroelectric properties and strain behaviors of 0-3-type-ceramic composites were investigated. (100-x)Bi0.5(Na0.75K0.25)TiO3-xBiAlO3 (x = 5, 6, and 7: abbreviated as 95BNKT-5BA, 94BNKT-6BA, and 93BNKT-7BA, respectively, and the three compositions are altogether designated as BNKT-BA) were chosen as a matrix materials, and ferroelectric Bi0.5Na0.5TiO3 (f-BNT), Bi0.5(Na0.8K0.2)0.5TiO3 (f-BNKT), and 98.5Bi0.5(Na0.8K0.2)0.5TiO3-1.5BiAlO3 (f-BNKTBA) grains as inclusions. Large f-BNT, f-BNKT, and f-BNKTBA grains strongly affect the ferroelectric properties and strain behaviors of the BNKT-BA matrix in the composite. In 95BNKT-5BA with f-BNT and f-BNKT, negative strain was observed, indicating that the ferroelectric phase is formed and stabilized. 93BNKT-7BA with f-BNT, f-BNKT and f-BNKTBA showed an increase in positive strain, which is associated with low field-induced phase transition. It was found from the strain curve that two contributions, ferroelectric phase stabilization and phase transition activation, were involved in the strain behaviors of the ceramic composites. [ABSTRACT FROM AUTHOR]

The effect of microstructure on electromagnetic properties was investigated in Al18B4O33w/Co and Al18B4O33w/FeCo composite particles. Resistivity (ρ) and saturation magnetization (Ms) were introduced to determine the relationship between microstructure and electromagnetic properties indirectly. The ρ of Co coatings decreased by nine orders of magnitude when annealed in H2, which substantially affected permittivity and permeability. Intense dielectric relaxation occurred in 2 GHz to 18 GHz band, particularly when the ρ was lower than 1.16 × 10-3 Ω·cm, and a strong eddy current effect began to emerge when the ρ decreased to 5 × 10-4 Ω·cm. An unusual increase in the permeability of the Co coatings was identified, and enhanced exchange-coupling interaction was correspondingly revealed, which was assumed to be related to microstructure evolution. The influence of microstructure observed in Al18B4O33w/Co was further found in the Al18B4O33w/CoFe composite particles. This study suggested that the introduction of ρ and Ms was helpful in demonstrating the relationships between microstructure and electromagnetic properties. However, the quantitative characterization of microstructures and the identification of intrinsic electromagnetic parameters should be studied further. [ABSTRACT FROM AUTHOR]

Active acoustic metamaterials (AAMM) have been developed to overcome the limited frequency bandwidth characteristics of passive acoustic metamaterials. The AAMM rely in their operation on using piezoelectric active ingredients in a fluid-solid composite structure forming the basic building block of a larger metamaterial periodic arrangement. A prototype of AAMM composite cell is manufactured and active control strategies are implemented on the piezoelectric elements to vary its stiffness in order to control the effective dynamic density of the cell. Acoustic characterization of the developed AAMM cell is carried out by measuring its acoustic impedance and transmission loss and comparing the results with the predictions of a finite element model. The obtained experimental measurements and the predictions of the finite element model are in very good agreement for the considered frequency range. The transfer functions between the reference microphone in the impedance tube and the piezoelectric elements demonstrate the coupling nature inside the cell rendering it to a system of single acoustic properties acting as a single degree of freedom system. The proposed AAMM can be useful in manufacturing the next generation of acoustic cloaks and metamaterials with controllable directivity and dispersion characteristics. [ABSTRACT FROM AUTHOR]

We have presented a theoretical model to describe the magnetoelectric coupling in Tb0.3Dy0.7Fe2/PZT laminate composite material. In this model, the stresses introduced by the magnetic field or electric field in the composite material are assumed to be the axial force. The magnetization of magnetostrictive phase can indirectly couple with the electrical polarization of piezoelectric phase through the stresses. The numerical results have shown that both the magnetic field and electric field can cause significant changes in the magnetization and electric polarization in the composite material. [ABSTRACT FROM AUTHOR]

In this work, we present field emission characteristics of multi-wall carbon nanotube (MWCNT)-polystyrene composites at various weight fractions along the cross-section of sample. Scanning electron microscope images in cross-sectional view reveal that MWCNTs are homogeneously distributed across the thickness and the density of protruding tubes can be scaled with weight fraction of the composite film. Field emission from composites has been observed to vary considerably with density of MWCNTs in the polymer matrix. High current density of 100 mA/cm2 was achieved at a field of 2.2 V/μm for 0.15 weight fraction. The field emission is observed to follow the Fowler-Nordheim tunneling mechanism, however, electrostatic screening is observed to play a role in limiting the current density at higher weight fractions. [ABSTRACT FROM AUTHOR]

Nanostructured composites and nanowire arrays of traditional thermoelectrics, like Bi, Bi1-xSbx, and Bi2Te3, have metallic Rashba surface spin-orbit bands featuring high mobilities rivaling that of the bulk for which topological insulator behavior has been proposed. Nearly pure surface electronic transport has been observed at low temperatures in Bi nanowires, with diameter around the critical diameter, 50 nm, for the semimetal-to-semiconductor transition. The surface contributes strongly to the thermopower, actually dominating for temperatures T < 100 K in these nanowires. The surface thermopower was found to be -1 T μV/K2, a value that is consistent with theory. We show that surface electronic transport together with boundary phonon scattering leads to enhanced thermoelectric performance at low temperatures of Bi nanowire arrays. We compare with bulk n-BiSb alloys, optimized CsBi4Te6, and optimized Bi2Te3. Surface dominated electronic transport can be expected in nanomaterials of the other traditional thermoelectrics. [ABSTRACT FROM AUTHOR]

The composites of In nanoparticles embedded in Al-based amorphous matrix were synthesized. As the content of In increases, the average size of In nanoparticles increases. The melting behaviors of embedded In nanoparticles were investigated, indicating that the melting temperature is suppressed, and the smaller the size is, the lower the melting temperature is. It is confirmed by comparing the differential scanning calorimetry curves with those of the size distribution. The size dependent melting behaviors of nanoparticles were discussed with the thermodynamic model. [ABSTRACT FROM AUTHOR]

The effective thermal conductivity of particulate composites with oriented spheroidal metallic particles embedded in a dielectric matrix is analyzed under the framework of the two-temperature model of heat conduction. The obtained analytical results show that the effective thermal conductivity depends strongly on (1) the relative size of the particle inclusions with respect to the electron-phonon coupling length and (2) the ratio between the electron and phonon thermal conductivities. The effect of the electron-phonon coupling inside metallic particles is expressed by the reduction of the composite thermal conductivity with respect to its corresponding values obtained for an infinite electron-phonon coupling factor, where the analysis could be established based on the Fourier law of heat conduction. It is shown that the composite thermal conductivity has upper and lower bounds, which are determined by the particle size in comparison with the electron-phonon coupling length. The generalized model for spheroidal particles is then used to analyze the thermal conductivity for limiting cases on the particle shape including spheres, cylinders, and flat plates. For perfect electron-phonon coupling, the proposed model reduces to various previously-reported results. This study shows that the particle size dependence of the thermal conductivity of metal-nonmetal composites appears not only through the interfacial thermal resistance but also by means of the electron-phonon coupling. The results of this work could be useful for guiding the design of particulate composites with spheroidal metallic inclusions from macro/micro- to nanoscales. [ABSTRACT FROM AUTHOR]

A magnetoelectric laminate composite was proposed by combing a piezoelectric transformer and a Terfenol-D plate. Converse magnetoelectric effect was researched by using an induction method with frequency, bias magnetic field, ac voltage, and Terfenol-D thickness. A giant converse magnetoelectric coefficient of 35.7 G/V was obtained at half-wavelength vibration mode in the composite with the Terfenol-D thickness of 0.7 mm, which is a great improvement in comparison with the previous reports. The magnetoelectric distribution exhibited that the converse magnetoelectric effect was dominated by the stress in the composite. [ABSTRACT FROM AUTHOR]

In this work, we have proposed a general 3D analytical model for giant magnetostrictive composites based on the Mori-Tanaka theory. Taking into consideration both the interface effect and thermal residual stress (TRS) in the curing process, we have studied the relationship between the effective magnetostriction of giant magnetostrictive composites and different magnetic fields, and investigated the influence of TRS, inclusion shape, and direction of the magnetic field on the effective magnetostriction. The results show that TRS has significant influence on the effective magnetostrictive normal strains but little effect on the effective magnetostrictive shear strains. Both the magnetic field direction and the inclusion shape significantly affect the effective magnetostriction. Moreover, the Wiedemann effect is expected to occur on the giant magnetostrictive composites according to our theoretical calculations. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) behavior for PZT/Ni composites with PZT embedded in Ni is investigated. The embedded composites show a four-state phenomenon of ME coupling. Upon applied magnetic fields, polarization reversal occurs when the applied static magnetic field exceeds a certain value. Based on the experimental data, a geometric factor k is proposed which captures the size effect on the ME behavior. To quantify the ME behavior of the embedded composites, finite element analysis is performed, which fits well with the experimental data. The calculation enables us to deduce that the four-state ME coupling is related to the change of the compressive force on the contact surfaces between PZT and Ni upon the applied magnetic field. The results are of importance for both the basic understanding of the ME coupling in the embedded PZT/Ni composites and the potential device applications, such as four-state memory devices, magnetic field switches, etc. [ABSTRACT FROM AUTHOR]

Beam steering has found wide applications in many areas such as wireless communications, satellite communications, and intelligent transportation systems.Different approaches have been presented to achieve the beam steering, most of which, however, are complicated and expensive. In this paper, we propose a simple and efficient principle to realize this goal based on a partial Luneburg lens. In the experiment, a traditional Vivaldi antenna is used as the platform to test the principle, in which the partial Luneburg lens is constructed by drilled-holes dielectric composite material. The measurement results show that good beam-steering performance from -20 to 20° in a broad bandwidth (8-11 GHz) has been achieved using the proposed method, and the antenna's gain and directivity have been significantly improved in the same bandwidth after using the special lens. [ABSTRACT FROM AUTHOR]

In this paper, we illustrate new functionalities for nonlinear optical applications of bio-molecular systems. This study presents DNA complex with new ionic surfactants. These surfactants enabled DNA solubility in solvents other than alcohols, like aromatic and chlorinated ones. Composites with two nonlinear optical (NLO) active dyes are subjects of the second and third harmonic generation experiments. The found effective nonlinear susceptibilities values are much higher than that for standard fused silica. We also demonstrate any influence of the surfactant on NLO properties. [ABSTRACT FROM AUTHOR]