scholarly journals Methods of decreasing losses in optical metamaterials

2018 ◽  
Vol 31 (4) ◽  
pp. 501-518 ◽  
Author(s):  
Zoran Jaksic ◽  
Marko Obradov ◽  
Olga Jaksic ◽  
Goran Isic ◽  
Slobodan Vukovic ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Integrated Circuits ◽  
Noble Metals ◽  
Volume Fraction ◽  
Practical Interest ◽  
Frequency Dispersion ◽  
High Refractive Index ◽  
Optical Metamaterials ◽  
Strong Localization ◽  
Metal Volume

In this work we review methods to decrease the optical absorption losses in metamaterials. The practical interest for metamaterials is huge, but the possible applications are severely limited by their high inherent optical absorption in the metal parts. We consider the possibilities to fabricate metamaterial with a decreased metal volume fraction, the application of alternative lower-loss plasmonic materials instead of the customary utilized noble metals, the use of all-dielectric, high refractive index contrast subwavelength nanocomposites. Finally, we dedicate our attention to various methods to optimize the frequency dispersion in metamaterials by changing their geometry and composition in order to reach lower absorption, which includes the use of the hypercrystals. The final goal is to widen the range of different metamaterialbased devices and structures, including those belonging to transformation optics. Maybe the most important among them is the fabrication of a novel generation of alloptical or hybrid optical/electronic integrated circuits that would operate at optical frequencies and at the same time would offer a packaging density and complexity of the contemporary integrated circuits, owing to the strong localization of electromagnetic fields enabled by plasmonics.

Scaling of Complex Conductivity for A Percolating Metal-Insulator Composite with Inter granular Tunneling Above and Below the Superconducting Transition

1995 ◽  
Vol 411 ◽  
Author(s):  
D. S. Mclachlan ◽  
A. B. Pakhomov ◽  
I. I. Oblachova ◽  
F. Brouers ◽  
A. Sarychev
Keyword(s):  
Volume Fraction ◽  
Frequency Dispersion ◽  
Scaling Theory ◽  
Complex Conductivity ◽  
Superconducting Transition ◽  
Percolation Transition ◽  
Metal Insulator ◽  
Metal Volume ◽  
Metal Volume Fraction ◽  
Composite Samples

ABSTRACTThe complex conductivity was measured on 3d granular NbC-KCI composite samples at varying metal volume fraction p, frequency ω and temperature above and below the superconductivity critical Tc. The observed frequency dispersion is anomalous in that it is not in accord with the scaling theory of percolation transition. The results are compared with a recently developed scaling theory, which takes both intercluster tunneling and intercluster capacitance into account. The experimental estimates for the new critical exponents are in reasonable agreement with the theory. The very low value of the crossover frequency can also be understood. We also present the data showing the dispersion of the complex conductivity well below the superconducting transition Tc of NbC.

scholarly journals Constitutive relations for compressible granular flow in the inertial regime

2019 ◽  
Vol 874 ◽  
pp. 926-951 ◽  
Author(s):  
D. G. Schaeffer ◽  
T. Barker ◽  
D. Tsuji ◽  
P. Gremaud ◽  
M. Shearer ◽  
...  
Keyword(s):  
Steady State ◽  
Granular Flow ◽  
Numerical Solutions ◽  
Volume Fraction ◽  
Constitutive Relations ◽  
Practical Interest ◽  
Time Dependent ◽  
Direct Result ◽  
Wide Range ◽  
Inertial Regime

Granular flows occur in a wide range of situations of practical interest to industry, in our natural environment and in our everyday lives. This paper focuses on granular flow in the so-called inertial regime, when the rheology is independent of the very large particle stiffness. Such flows have been modelled with the $\unicode[STIX]{x1D707}(I),\unicode[STIX]{x1D6F7}(I)$-rheology, which postulates that the bulk friction coefficient $\unicode[STIX]{x1D707}$ (i.e. the ratio of the shear stress to the pressure) and the solids volume fraction $\unicode[STIX]{x1D719}$ are functions of the inertial number $I$ only. Although the $\unicode[STIX]{x1D707}(I),\unicode[STIX]{x1D6F7}(I)$-rheology has been validated in steady state against both experiments and discrete particle simulations in several different geometries, it has recently been shown that this theory is mathematically ill-posed in time-dependent problems. As a direct result, computations using this rheology may blow up exponentially, with a growth rate that tends to infinity as the discretization length tends to zero, as explicitly demonstrated in this paper for the first time. Such catastrophic instability due to ill-posedness is a common issue when developing new mathematical models and implies that either some important physics is missing or the model has not been properly formulated. In this paper an alternative to the $\unicode[STIX]{x1D707}(I),\unicode[STIX]{x1D6F7}(I)$-rheology that does not suffer from such defects is proposed. In the framework of compressible $I$-dependent rheology (CIDR), new constitutive laws for the inertial regime are introduced; these match the well-established $\unicode[STIX]{x1D707}(I)$ and $\unicode[STIX]{x1D6F7}(I)$ relations in the steady-state limit and at the same time are well-posed for all deformations and all packing densities. Time-dependent numerical solutions of the resultant equations are performed to demonstrate that the new inertial CIDR model leads to numerical convergence towards physically realistic solutions that are supported by discrete element method simulations.

BRITTLE/DUCTILE ASSESSMENT OF HYBRID REINFORCED CONCRETE BEAMS CONTAINING STEEL REBAR AND FIBERS

2017 ◽  
Vol 4 (1) ◽  
Author(s):  
Alessandro P. Fantilli ◽  
Andrea Gorino ◽  
Bernardino Chiaia
Keyword(s):  
Reinforced Concrete ◽  
Volume Fraction ◽  
Practical Interest ◽  
Design Procedure ◽  
Fiber Reinforced Concrete ◽  
Reinforced Concrete Beams ◽  
Minimum Reinforcement ◽  
Steel Rebar ◽  
Definition Of ◽  
Hybrid Reinforcement

Many structures, such as precast and cast-in-situ tunnel linings, are nowadays realized with Hybrid Reinforced Concrete (HRC), where a combination of continuous steel rebar and discrete fibers is used to reinforce the cementitious matrix. Hence, the definition of a minimum amount of hybrid reinforcement (i.e., rebar and fibers), which prevents the brittle failure, is of practical interest. For predicting the brittle/ductile response of HRC beams in bending, a theoretical model is introduced and presented in this paper. It is based on the flexural response of both Lightly Reinforced Concrete (LRC) and Fiber-Reinforced Concrete (FRC) beams, separately analyzed. The numerical results of the model, and some experimental data as well, show that the minimum reinforcement of HRC beams can be determined with a new design procedure. It requires the definition of the ductility index (DI), which is proportional to the difference between ultimate and effective cracking load. As DI linearly increases with the amount of rebar and fibers, the minimum reinforcement in HRC members can be found when DI is equal to zero. In addition, the minimum hybrid reinforcement can be defined with a suitable linear combination of the minimum area of rebar and the minimum fiber volume fraction, related to LRC and FRC beams, respectively.

scholarly journals All-dielectric meta-optics and non-linear nanophotonics

2018 ◽  
Vol 5 (2) ◽  
pp. 144-158 ◽  
Author(s):  
Yuri Kivshar
Keyword(s):  
Refractive Index ◽  
High Refractive Index ◽  
Magnetic Response ◽  
New Approach ◽  
New Era ◽  
Optical Metamaterials ◽  
Flexible Control ◽  
Non Linear ◽  
Recent Developments ◽  
Research Frontiers

Abstract Most optical metamaterials fabricated and studied to date employ metallic components resulting in significant losses, heat and overall low efficiencies. A new era of metamaterial physics is associated with all-dielectric meta-optics, which employs electric and magnetic Mie resonances of subwavelength particles with high refractive index for an optically induced magnetic response, thus underpinning a new approach to design and fabricate functional and practical metadevices. Here we review the recent developments in meta-optics and subwavelength dielectric photonics and demonstrate that the Mie resonances can play a crucial role in the realization of the unique functionalities of meta-atoms, also driving novel effects in the fields of metamaterials and nanophotonics. We discuss the recent research frontiers in all-dielectric meta-optics and uncover how Mie resonances can be employed for a flexible control of light with full phase and amplitude engineering, including unidirectional metadevices, highly transparent metasurfaces, non-linear nanophotonics and topological photonics.

Optical Absorption in Noble Metals

1965 ◽  
Vol 20 (9) ◽  
pp. 1610-1619 ◽  
Author(s):  
Eijiro Haga ◽  
Hiroaki Okamoto
Keyword(s):  
Optical Absorption ◽  
Noble Metals

Modeling and Measurement of Pressure-Dependent Junction-Spreader Thermal Resistance for Integrated Circuits

2001 ◽  
Author(s):  
Peng Zhou ◽  
Kenneth E. Goodson
Keyword(s):  
Integrated Circuits ◽  
Thermal Resistance ◽  
Volume Fraction ◽  
Past Research ◽  
Theoretical Models ◽  
Thermal Interface Material ◽  
Simple Relationship ◽  
Reliability Engineering ◽  
Transient Model ◽  
Filler Volume Fraction

Abstract The junction-spreader thermal resistance is an important part of the overall junction-ambient thermal resistance in electronic packages. Past research has provided theoretical models for contact thermal resistance between the thermal interface material (TIM) and the contacting rough solid surface. However, these models are based on steady-state assumptions and do not describe the evolution of the junction-spreader thermal resistance during the lifetime of an electronic package. This chapter presents a transient model for the junction-spreader thermal resistance based on classical theories for lubrication and surface wettability. This transient model provides a simple relationship for pressure-dependent junction-spreader thermal resistance and yields an optimum filler volume fraction for particle filled TIMs. An experimental approach developed in this chapter measures the pressure-dependence, as well as the spatial distribution of junction-spreader thermal resistance. The data agree reasonably well with the model predicting for the pressure-dependent junction-spreader thermal resistance. The theoretical and experimental approaches developed in this study are promising tools for thermal management and reliability engineering of electronic packaging.

Effect of Carbon Black on Hysteresis of Rubber Vulcanizates: Equivalence of Surface Area and Loading

1976 ◽  
Vol 49 (4) ◽  
pp. 1076-1094 ◽  
Author(s):  
J. M. Caruthers ◽  
R. E. Cohen ◽  
A. I. Medalia
Keyword(s):  
Carbon Black ◽  
Surface Area ◽  
Functional Form ◽  
Volume Fraction ◽  
Dynamic Properties ◽  
Dynamic Test ◽  
Practical Interest ◽  
Interfacial Area ◽  
Experimental Conditions ◽  
Tan Δ

Abstract We have developed an empirical correlation between the loss tangent (tan δ) and the product of the volume fraction (ϕ) of carbon black in the composite and the total filler-polymer interfacial area per unit volume of composite (ψ). This correlation was applied to vulcanizates based on SBR-1500, SBR-1712, and NR with various compounding procedures and under different deformation conditions, including forced vibration nonresonant dynamic test machines, and the Goodyear-Healey pendulum rebound. The functional form of the correlation was qualitatively similar in all instances ; however, quantitative aspects of the correlation are dependent upon the particular experimental conditions. Tan δ is a weak function of the deformation amplitude over the region of practical interest. This is in contrast to hysteretic energy loss, which is proportional to the square of the amplitude. The validity of the correlation over wide ranges of amplitude, temperature, and frequency indicates that the viscoelastic relaxation or loss processes are similar over the range of conditions studied. Since the combined parameter, ϕψ, is proportional to ϕ2 multiplied by the specific surface area of the carbon black, this relation implies an equivalence between surface area and loading, with regard to tan 5. It has previously been shown that the elastic modulus depends on structure and loading. Thus, the dynamic properties, including hysteresis under various conditions, can be predicted from the carbon black properties, and compounds can be designed for desired dynamic properties by independent adjustment of loading, structure and surface area.

Sign in / Sign up

Export Citation Format

Share Document