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1 – 10 of 16Chemseddine Zara, Zinelabiddine Mezache and Fatiha Benabdelaziz
The purpose of this paper is to demonstrate a novel chiral photonic crystal with thin thickness and small unit cells via numerical calculations. The multi-band circular dichroism…
Abstract
Purpose
The purpose of this paper is to demonstrate a novel chiral photonic crystal with thin thickness and small unit cells via numerical calculations. The multi-band circular dichroism is found in a wide frequency range from 400 to 600 THz by studying the transmission properties.
Design/methodology/approach
To investigate this chiral photonic structure, refection coefficients are analytically computed using finite element method. Numerical results are given, and physical properties are discussed, including the optical rotation, the circular dichroism and the absorption.
Findings
The results of this modeling and simulation under COMSOL multiphysics environment have led the authors to study the scattered parameters such as the coefficient of transmission (S21) and the coefficient of reflection (S11) for a 2D CPC nanostructure. The authors have also developed script under the Matlab environment which studies absorption and circular dichroism and ensure the existence of optical activity. According to the obtained results, the coefficient of transmission is proportional to the parameter of chirality.
Originality/value
The authors have designed a novel chiral photonic structure that exhibits larger circular dichroism. The CD spectrum has typically both positive and negative bands. The design principles defined in this work, which combine the concepts of the photonic crystal with the chiral structure (optical activity, circular dichroism and absorption), represent a model for simulation of the properties of a more complex chiral photonic structure. These results led to realization of novel circularly polarized devices in nanotechnologies.
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Luke Mizzi, Arrigo Simonetti and Andrea Spaggiari
The “chiralisation” of Euclidean polygonal tessellations is a novel, recent method which has been used to design new auxetic metamaterials with complex topologies and improved…
Abstract
Purpose
The “chiralisation” of Euclidean polygonal tessellations is a novel, recent method which has been used to design new auxetic metamaterials with complex topologies and improved geometric versatility over traditional chiral honeycombs. This paper aims to design and manufacture chiral honeycombs representative of four distinct classes of 2D Euclidean tessellations with hexagonal rotational symmetry using fused-deposition additive manufacturing and experimentally analysed the mechanical properties and failure modes of these metamaterials.
Design/methodology/approach
Finite Element simulations were also used to study the high-strain compressive performance of these systems under both periodic boundary conditions and realistic, finite conditions. Experimental uniaxial compressive loading tests were applied to additively manufactured prototypes and digital image correlation was used to measure the Poisson’s ratio and analyse the deformation behaviour of these systems.
Findings
The results obtained demonstrate that these systems have the ability to exhibit a wide range of Poisson’s ratios (positive, quasi-zero and negative values) and stiffnesses as well as unusual failure modes characterised by a sequential layer-by-layer collapse of specific, non-adjacent ligaments. These findings provide useful insights on the mechanical properties and deformation behaviours of this new class of metamaterials and indicate that these chiral honeycombs could potentially possess anomalous characteristics which are not commonly found in traditional chiral metamaterials based on regular monohedral tilings.
Originality/value
To the best of the authors’ knowledge, the authors have analysed for the first time the high strain behaviour and failure modes of chiral metamaterials based on Euclidean multi-polygonal tessellations.
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Quan-Quan Wang, Hong-Bo Zhu, Ru-Shan Chen and Yun-Qin Hu
Analysis of the frequency selective surface (FSS) is of great significance. In the method of moments, when the electric size of the FSS increases, huge in-core memory and CPU time…
Abstract
Purpose
Analysis of the frequency selective surface (FSS) is of great significance. In the method of moments, when the electric size of the FSS increases, huge in-core memory and CPU time are required. The purpose of this paper is to efficiently analyze the finite FSS backed by dielectric substrate utilizing sub-entire-domain (SED) basis function method.
Design/methodology/approach
Different types of SED basis functions are generated according to the locations of the cells in the entire structure, and a reduced system is constructed and solved. The couplings of all cells of the FSS are taken into account by using Green’s function and Galerkin’s test procedure. The spatial Green’s function is obtained with the discrete complex image method. The reflection and transmission coefficients of the FSS are calculated using the far field of the FSS and the metallic plate with the same size.
Findings
Moderate problems of the finite FSS backed by dielectric substrate are solved with the SED basis function method. The original problem can be simplified to two smaller problems. It enables a significant reduction to the matrix size and storage, and efficient analysis of FSS can be performed. The band-stop type of FSS can be composed of periodic conductive patch cells on the dielectric substrate, and shows total reflection property at the resonant frequency.
Originality/value
The SED basis function method is mostly used to analyze periodic PEC structures in free space. The layered medium Green’s function is successfully employed and several dielectric substrate backed finite FSSs are discussed in this paper. The calculation of reflection and transmission coefficients, which are more effective rather than far field scattering of the FSS, are described.
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Mark Blome, Kevin McPeak, Sven Burger, Frank Schmidt and David Norris
The purpose of this paper is to find an optimized thin-film amorphous silicon solar cell design by numerically optimizing the light trapping efficiency of a pyramid-structured…
Abstract
Purpose
The purpose of this paper is to find an optimized thin-film amorphous silicon solar cell design by numerically optimizing the light trapping efficiency of a pyramid-structured back-reflector using a frequency-domain finite element Maxwell solver. For this purpose short circuit current densities and absorption spectra within the investigated solar cell model are systematically analyzed. Furthermore, the authors employ a topology simulation method to accurately predict the material layer interfaces within the investigated solar cell model. The method simulates the chemical vapor deposition (CVD) process that is typically used to fabricate thin-film solar cells by combining a ballistic transport and reaction model (BTRM) with a level-set method in an iterative approach. Predicted solar cell models are far more realistic compared to solar cell models created assuming conformal material growth. The purpose of the topology simulation method is to increase the accuracy of thin-film solar cell models in order to facilitate highly accurate simulation results in solar cell design optimizations.
Design/methodology/approach
The authors perform numeric optimizations using a frequency domain finite element Maxwell solver. Topology simulations are carried out using a BTRM combined with a level-set method in an iterative fashion.
Findings
The simulation results reveal that the employed pyramid structured back-reflectors effectively increase the light path in the absorber mainly by exciting photonic waveguide modes. In using the optimization approach, the authors have identified solar cell models with cell periodicities around 480 nm and pyramid base widths around 450 nm to yield the highest short circuit current densities. Compared to equivalent solar cell models with flat back-reflectors, computed short circuit current densities are significantly increased. Furthermore, the paper finds that the solar cell models computed using the topology simulation approach represent a far more realistic approximation to a real solar cell stack compared to solar cell models computed by a conformal material growth assumption.
Research limitations/implications
So far in the topology simulation approach the authors assume CVD as the material deposition process for all material layers. However, during the fabrication process sputtering (i.e. physical vapor deposition) will be employed for the Al:ZnO and ITO layers. In the framework of this ongoing research project the authors will extend the topology simulation approach to take the different material deposition processes into account. The differences in predicted material interfaces will presumably be only minor compared to the results shown here and certainly be insignificant relative to the differences the authors observe for solar cell models computed assuming conformal material growth.
Originality/value
The authors systematically investigate and optimize the light trapping efficiency of a pyramid nano-structured back-reflector using rigorous electromagnetic field computations with a 3D finite element Maxwell solver. To the authors’ knowledge such an investigation has not been carried out yet in the solar cell research literature. The topology simulation approach (to the best of the authors’ knowledge) has previously not been applied to the modelling of solar cells. Typically a conformal layer growth assumption is used instead.
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Andrea G. Chiariello, Carlo Forestiere, Giovanni Miano and Antonio Maffucci
Nowadays, nano-antennas or nanoscale absorbers made by innovative materials such as carbon nanotubes are gaining more and more interest, because of their outstanding features. The…
Abstract
Purpose
Nowadays, nano-antennas or nanoscale absorbers made by innovative materials such as carbon nanotubes are gaining more and more interest, because of their outstanding features. The purpose of this paper is to investigate the scattering properties of carbon nanotubes, either isolated or arranged in arrays. The peculiar behaviour of such innovative materials is studied, taking also into account the finite length of the structure and the dependence of the scattering field from the operating temperature.
Design/methodology/approach
First a model is presented for the electrical transport along the carbon nanotubes, based on Boltzmann quasi-classical transport theory. The model includes quantistic and inertial phenomena observed in the carbon nanotube electrodynamics. The model also includes the effects of temperature. Using this electrodynamical model, the electromagnetic formulation of the scattering problem is cast in terms of a Pocklington-like equation. The numerical solution is obtained by means of the Galerkin method, with special care in handling the logarithmic singularity of the kernel. Case studies are carried out, either referred to isolated single-wall carbon nanotubes (SWCNTs) and array of SWCNTs.
Findings
The scattering properties of SWCNT are strongly influenced by the temperature and by the distance between the tubes. As temperature increases, the amplitude of the resonance peaks decreases, at a rate which is double the rate of changes of temperature. The resonance frequencies are insensitive to temperature. As for the distance between the tubes in an array, it influence the scattering resonance introducing a shift in the resonance frequencies which is appreciable for distances lower than the semi-length of the CNT. For higher distances the CNT scattered field may be regarded as the sum of the fields emitted by each CNT, as if they were isolated.
Research limitations/implications
As far as now only SWCNTs have been studied. The multi-wall carbon nanotubes would show a richer behaviour with temperature, due to the joint effect of reduction of the mean free path and increase of the number of conducting channels, as temperature increases.
Practical implications
Possible use of carbon nanotubes as absorbing material or scatterers.
Originality/value
The model presented here is based on a self-consistent and physically meaningful description of the CNT electrodynamics, which takes rigorously into account the effect of temperature, size and chirality of each CNT.
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Afreen Khursheed and Kavita Khare
This paper is an unprecedented effort to resolve the performance issue of very large scale integrated circuits (VLSI) interconnects encountered because of the scaling of device…
Abstract
Purpose
This paper is an unprecedented effort to resolve the performance issue of very large scale integrated circuits (VLSI) interconnects encountered because of the scaling of device dimensions. Repeater interpolation technique is an effective approach for enhancing speed of interconnect network. Proposed buffers as repeater are modeled by using dual chirality multi-Vt technology to reduce delay besides mitigating average power consumption. Interconnects modeled with carbon nanotube (CNT) technology are compared with copper interconnect for various lengths. Buffer circuits are designed with both CNT and metal oxide semiconductor technology for comparison by using various combination of (CMOSFET repeater-Cu interconnect) and (CNTFET repeater-CNT interconnect). Compared to conventional buffer, ProposedBuffer1 saves dynamic power by 84.86%, leakage power by 88% and offers reduction in delay by 72%. ProposedBuffer2 brings about dynamic power saving of 99.94%, leakage power saving of 93%, but causes delay penalty. Simulation using Stanford SPICE model for CNT and silicon-field effective transistor berkeley short-channel IGFET Model4 (BSIM4) predictive technology model (PTM) for MOS is done in H simulation program with integrated circuit emphasis for 32 nm.
Design/methodology/approach
Usually, the dynamic power consumption dominates the total power, while the leakage power has a negligible effect. But with the scaling of device technology, leakage power has become one of the important factors of consideration in low power design techniques. Various strategies are explored to suppress the leakage power in standby mode. The adoption of a multi-threshold design strategy is an effective approach to improve the performance of buffer circuits without compromising on the delay and area overhead. Unlike MOS technology, to implement multi-Vt transistors in case of CNT technology is quite easy. It can be achieved by varying diameter of carbon nanotubes using chirality control.
Findings
An unprecedented approach is taken for optimizing the delay and power dissipation and hence drastically reducing energy consumption by keeping proper harmony between wire technology and repeater-buffer technology. This paper proposes two novel ultra-low power buffers (PB1 and PB2) as repeaters for high-speed interconnect applications in portable devices. PB1 buffer implemented with high-speed CML technique nested with multi-threshold (Vt) technology sleep transistor so as to improve the speed along with a reduction in standby power consumption. PB2 is judicially implemented by inserting separable sized, dual chirality P type carbon nanotube field effective transistors. The HSpice simulation results justify the correctness of schemes.
Originality/value
Result analysis points out that compared to conventional Cu interconnect, the CNT interconnects paired with Proposed CNTFET buffer designs are more energy efficient. PB1 saves dynamic power by 84.86%, reduces propagation delay by 72% and leakage power consumption by 88%. PB2 brings about dynamic power saving of 99.4%, leakage power saving of 93%, with improvement in speed by 52%. This is mainly because of the fact that CNT interconnect offers low resistance and CNTFET drivers have high mobility and ballistic mode of operation.
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Yingli Li, Chenwei Wu, Yong Peng and Xudong Jiang
In order to investigate the vibration reduction properties of a three-dimensional elastic metastructure with spherical cavities at low frequencies.
Abstract
Purpose
In order to investigate the vibration reduction properties of a three-dimensional elastic metastructure with spherical cavities at low frequencies.
Design/methodology/approach
The bandgap characteristics of a three-dimensional elastic metastructure with spherical cavities are studied based on analytical and numerical approaches.
Findings
The results of both method revealed that the vibration of the vertexes masses is important for opening bandgaps. The fact that the big sphere cavity radius or short side length of the cube unit leads to a wider bandgap, is noteworthy.
Originality/value
This research provides theoretical guidance for realizing the vibration attenuation application of EMs in practical engineering.
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Chunlan Liu, Yang Gao, YaChen Gao, Yong Wei, Ping Wu and Yudong Su
This paper aims to clarify the relationship between the performance of the metal nanoparticles and the sensitivity of the fiber surface plasma resonance (SPR) sensor. It proposes…
Abstract
Purpose
This paper aims to clarify the relationship between the performance of the metal nanoparticles and the sensitivity of the fiber surface plasma resonance (SPR) sensor. It proposes modeling the sensing effects of a single-mode fiber SPR sensor with a cone angle structure decorated with metal nanoparticles. This study uses the metal nanoparticles to the realize enhanced sensitivity of refractive index sensing.
Design/methodology/approach
This paper opted for an exploratory study using a simulation approach of finite-difference time-domain (FDTD). Specifically, the effect of size, the material and the shape of the metal nanoparticle on sensing performance are investigated theoretically.
Findings
In conclusion, it is evident that the localized SPR (LSPR) effect weakens as the diameter of the gold nanosphere increases, the SPR effect enhances and the SPR sensitivity increases first and then decreases. The metal nanoparticle with the different materials and different shapes also have different LSPR and SPR sensitivity and wavelength length dynamic range. The investigation shows that, by changing parameters, the reflection spectra of the fiber SPR sensor exhibit an obvious transition from LSPR to SPR characteristics, and enhanced sensitivity of the refractive index is realized.
Originality/value
This paper fulfills an identified need to study how the sensitivity of the fiber SPR sensor can be enhanced by the metal nanoparticle. After the optimization of parameters, the sensitivity of 5,140 nm/RIU is achieved, which provides a new research direction for sensitivity enhancement of fiber SPR sensor.
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Olga Ivanova, Christopher Williams and Thomas Campbell
This paper aims to provide a review of available published literature in which nanostructures are incorporated into AM printing media as an attempt to improve the properties of…
Abstract
Purpose
This paper aims to provide a review of available published literature in which nanostructures are incorporated into AM printing media as an attempt to improve the properties of the final printed part. The purpose of this article is to summarize the research done to date, to highlight successes in the field, and to identify opportunities that the union of AM and nanotechnology could bring to science and technology.
Design/methodology/approach
Research in which metal, ceramic, and carbon nanomaterials have been incorporated into AM technologies such as stereolithography, laser sintering, fused filament fabrication, and three‐dimensional printing is presented. The results of the addition of nanomaterials into these AM processes are reviewed.
Findings
The addition of nanostructured materials into the printing media for additive manufacturing affects significantly the properties of the final parts. Challenges in the application of nanomaterials to additive manufacturing are nevertheless numerous.
Research limitations/implications
Each of the AM methods described in this review has its own inherent limitations when nanoparticles are applied with the respective printing media. Overcoming these design boundaries may require the development of new instrumentation for successful AM with nanomaterials.
Originality/value
This review shows that there are many opportunities in the marriage of AM and nanotechnology. Promising results have been published in the application of nanomaterials and AM, yet significant work remains to fully harness their inherent potential. This paper serves the purpose to researchers to explore new nanomaterials‐based composites for additive manufacturing.
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