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.

Simulation of Stiffness and Thermal Conductivity of Ordered Metal Microstructure Reinforced Polymer Composite Interposer

2013 ◽  
Vol 663 ◽  
pp. 326-330 ◽  
Author(s):  
Ming Wang ◽  
Ping Cheng ◽  
Yan Wang ◽  
Hong Wang ◽  
Gui Fu Ding
Keyword(s):  
Thermal Conductivity ◽  
Polymer Composite ◽  
Volume Fraction ◽  
Pure Polymer ◽  
Reinforced Polymer ◽  
Metal Volume ◽  
The One ◽  
Metal Microstructure ◽  
Triangular Model ◽  
Metal Volume Fraction

An interposer model based on ordered metal microstructure reinforced polymer composite was established using ANSYS software. The shape of metal microstructure includes quadrilateral, hexagon and triangle. The stiffness and thermal conductivity of composite interposer was calculated and discussed. Simulation results show that the stiffness of the metal microstructure-reinforced polymer composite interposer increases with augmenting the volume fraction of metal compared with the pure polymer. For the composite with metal volume fraction of 65%, the stiffness of the triangular composite interposer is 3.12 times that of the pure polymer interposer. The thermal conductivity of the hexagonal model is the best, while the one of quadrilateral and triangular model is similar. For the composite with the metal volume fraction of 65%, the thermal conductivity of the triangular composite interposer is 3.42 times that of the pure polymer interposer. Therefore, metal microstructure can effectively improve the performance of the pure polymer interposer.

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.

Effective Thermal Conductivity of Phase Change Material-Based Composites for High Heat Flux Electronic Cooling

2020 ◽  
Author(s):  
Ayushman Singh ◽  
Srikanth Rangarajan ◽  
Leila Choobineh ◽  
Bahgat Sammakia
Keyword(s):  
Thermal Conductivity ◽  
Phase Change ◽  
Effective Thermal Conductivity ◽  
Phase Change Material ◽  
Heat Sink ◽  
Volume Fraction ◽  
Electronic Cooling ◽  
Metal Volume ◽  
Metal Volume Fraction ◽  
Change Material

Abstract This work presents a simplified approach to optimally designing a heat sink with metallic thermal conductivity enhancers infiltrated with phase change material for electronic cooling. In present study, thermal conductivity enhancers are in the form of a honeycomb structure. A benchmarked two-dimensional computational fluid dynamics model was employed to investigate the thermal performance of the phase change material-metallic thermal conductivity enhancer composite heat sinks. Metallic thermal conductivity enhancers are often used in conjunction with phase change material to enhance the conductivity of the composite heat sink. Under constrained heat sink volume, the higher volume fraction of thermal conductivity enhancers improves the effective thermal conductivity of the composite, while it reduces the amount of latent heat storage simultaneously. The present work arrives at the optimal design of heat sink for electronic cooling by resolving the stated tradeoff. In this study, the total volume of the heat sink and the interfacial heat transfer area between the phase change material and thermal conductivity enhancers are constrained for all design points. Furthermore, assuming conduction-dominated heat transfer, an effective numerical model that solves the single energy equation with the effective properties of the phase change material- metallic thermal conductivity enhancer composite has been developed. The temperature gradient-time history is compared and matched for both the models to arrive at the accurate effective thermal conductivity value. The relationship of effective thermal conductivity as a function of metal volume fraction and thermal conductivity of metallic thermal conductivity enhancer is obtained. The figure of merit (FOM) is used to define the balance between effective thermal conductivity and energy storage capacity. The FOM is maximized to find the optimal volume fraction for the present design. The results from the study reveals that there exists an optimal metal volume fraction that maximizes the thermal performance of the composite.

Nanoidentation Study of the Mechanical Properties of Granular Metal Thin Films

1993 ◽  
Vol 308 ◽  
Author(s):  
M. R. Scanlon ◽  
M. K. Ferber ◽  
R. C. Cammarata
Keyword(s):  
Mechanical Properties ◽  
Volume Fraction ◽  
Metal Films ◽  
Rate Of Change ◽  
Metal Thin Films ◽  
Interfacial Sliding ◽  
Metal Ceramic ◽  
Metal Volume ◽  
Large Peak ◽  
Metal Volume Fraction

ABSTRACTNanoindenter techniques have been used to investigate the mechanical properties of Ag-Al2O3 and Fe-SiO2 granular metal films. A discontinuity in the rate of change of hardness as a function of metal volume fraction p was observed. The discontinuity occurs at the percolation threshold pc of the metal, and appears to result from a change in the deformation mechanism at pc. A large peak in compliance (inverse modulus) as measured during indentation unloading was observed in the Ag-Al2O3 films near pc, but was not observed for the Fe-SiO2 films. The compliance peak displayed by Ag-Al2O3 is believed to result from debonding at the metal-ceramic interface and subsequent interfacial sliding, and is not an intrinsic materials property.

scholarly journals Tuning the Optical Properties of Hyperbolic Metamaterials by Controlling the Volume Fraction of Metallic Nanorods

Nanomaterials ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 739 ◽  
Author(s):  
Alexey P. Leontiev ◽  
Olga Yu. Volkova ◽  
Irina A. Kolmychek ◽  
Anastasia V. Venets ◽  
Alexander R. Pomozov ◽  
...  
Keyword(s):  
Aluminum Oxide ◽  
Functional Properties ◽  
Anodic Aluminum Oxide ◽  
Volume Fraction ◽  
Electrochemical Preparation ◽  
Hyperbolic Metamaterials ◽  
Anodic Aluminum ◽  
Wide Range ◽  
Metal Volume ◽  
Metal Volume Fraction

Porous films of anodic aluminum oxide are widely used as templates for the electrochemical preparation of functional nanocomposites containing ordered arrays of anisotropic nanostructures. In these structures, the volume fraction of the inclusion phase, which strongly determines the functional properties of the nanocomposite, is equal to the porosity of the initial template. For the range of systems, the most pronounced effects and the best functional properties are expected when the volume fraction of metal is less than 10%, whereas the porosity of anodic aluminum oxide typically exceeds this value. In the present work, the possibility of the application of anodic aluminum oxide for obtaining hyperbolic metamaterials in the form of nanocomposites with the metal volume fraction smaller than the template porosity is demonstrated for the first time. A decrease in the fraction of the pores accessible for electrodeposition is achieved by controlled blocking of the portion of pores during anodization when the template is formed. The effectiveness of the proposed approach has been shown in the example of obtaining nanocomposites containing Au nanorods arrays. The possibility for the control over the position of the resonance absorption band corresponding to the excitation of collective longitudinal oscillations of the electron gas in the nanorods in a wide range of wavelengths by controlled decreasing of the metal volume fraction, is shown.

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