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Article
Publication date: 10 October 2016

Hongyan Tian, Jianbing Sang, Rihan Ao and Shujun Hou

As a good absorbing material candidate, a functionally graded wave absorber can be tailored to satisfy the impedance match principle by gradually changing material property

Abstract

Purpose

As a good absorbing material candidate, a functionally graded wave absorber can be tailored to satisfy the impedance match principle by gradually changing material property. The paper aims to discuss these issues.

Design/methodology/approach

The electromagnetic wave absorption properties are discussed. An analysis model is proposed to provide an insight into its mechanical characteristics during wave absorption. Considering the energy-converting and thermal deformation properties, the thermoelastic behaviors of an absorber are analyzed by numerical method. The effects of material and geometrical properties are discussed in detail.

Findings

The results demonstrate that absorbing effect of graded composite is enhanced. Good performance of low reflectance and high absorption with gentle thermal stress distribution can be obtained by proper designing of the gradient absorber.

Originality/value

Functionally graded materials exhibit a progressive compositional gradient change along certain dimension of structures, which can be used as absorbing materials for the gradual change of material property tailored to satisfy the principle of impedance match. The design of functionally graded absorbing materials usually should consider not only the electromagnetic performance, but also the mechanical properties simultaneously. Therefore, few investigations have addressed the mechanical characteristics of absorbers. This paper presents some studies on the electromagnetic, especially mechanical behaviors during electromagnetic wave absorption. It is helpful to provide mechanical reference for designing an absorber.

Details

Multidiscipline Modeling in Materials and Structures, vol. 12 no. 3
Type: Research Article
ISSN: 1573-6105

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Article
Publication date: 2 April 2019

Wan Yusmawati Wan Yusoff, Norliza Ismail, Nur Shafiqa Safee, Ariffin Ismail, Azman Jalar and Maria Abu Bakar

The purpose of this paper is to discuss the effect of a blast wave on the microstructure, intermetallic layers and hardness properties of Sn0.3Ag0.7Cu (SAC0307) lead-free solder.

Abstract

Purpose

The purpose of this paper is to discuss the effect of a blast wave on the microstructure, intermetallic layers and hardness properties of Sn0.3Ag0.7Cu (SAC0307) lead-free solder.

Design/methodology/approach

Soldered samples were exposed to the blast wave by using trinitrotoluene (TNT) explosive. Microstructure and intermetallic layer thickness were identified using Alicona ® Infinite Focus Measurement software. Hardness properties of investigated solders were determined using a nanoindentation approach.

Findings

Microstructure and intermetallic layers changed under blast wave condition. Hardness properties of exposed solders decreased with an increase in the TNT explosive weight.

Originality/value

Microstructural evolution and mechanical properties of the exposed solder to the blast wave provide a fundamental understanding on how blast waves can affect the reliability of a solder joint, especially for military applications.

Details

Soldering & Surface Mount Technology, vol. 31 no. 2
Type: Research Article
ISSN: 0954-0911

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Article
Publication date: 12 October 2015

Rajneesh Kakar

– The purpose of this paper is to investigate the existence of SH-waves in fiber-reinforced layer placed over a heterogeneous elastic half-space.

Abstract

Purpose

The purpose of this paper is to investigate the existence of SH-waves in fiber-reinforced layer placed over a heterogeneous elastic half-space.

Design/methodology/approach

The heterogeneity of the elastic half-space is caused by the exponential variations of density and rigidity. As a special case when both the layers are homogeneous, the derived equation is in agreement with the general equation of Love wave.

Findings

Numerically, it is observed that the velocity of SH-waves decreases with the increase of heterogeneity and reinforced parameters. The dimensionless phase velocity of SH-waves increases with the decreases of dimensionless wave number and shown through figures.

Originality/value

In this work, SH-wave in a fiber-reinforced anisotropic medium overlying a heterogeneous gravitational half-space has been investigated analytically and numerically. The dispersion equation for the propagation of SH-waves has been observed in terms of Whittaker function and its derivative of second degree order. It has been observed that on the removal of heterogeneity of half-space, and reinforced parameters of the layer, the derived dispersion equation reduces to Love wave dispersion equation thereby validates the solution of the problem. The equation of propagation of Love wave in fiber-reinforced medium over a heterogeneous half-space given by relevant authors is also reduced from the obtained dispersion relation under the considered geometry.

Details

Multidiscipline Modeling in Materials and Structures, vol. 11 no. 3
Type: Research Article
ISSN: 1573-6105

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Article
Publication date: 4 September 2017

Athanasios N. Papadimopoulos, Stamatios A. Amanatiadis, Nikolaos V. Kantartzis, Theodoros T. Zygiridis and Theodoros D. Tsiboukis

Important statistical variations are likely to appear in the propagation of surface plasmon polariton waves atop the surface of graphene sheets, degrading the expected…

Abstract

Purpose

Important statistical variations are likely to appear in the propagation of surface plasmon polariton waves atop the surface of graphene sheets, degrading the expected performance of real-life THz applications. This paper aims to introduce an efficient numerical algorithm that is able to accurately and rapidly predict the influence of material-based uncertainties for diverse graphene configurations.

Design/methodology/approach

Initially, the surface conductivity of graphene is described at the far infrared spectrum and the uncertainties of its main parameters, namely, the chemical potential and the relaxation time, on the propagation properties of the surface waves are investigated, unveiling a considerable impact. Furthermore, the demanding two-dimensional material is numerically modeled as a surface boundary through a frequency-dependent finite-difference time-domain scheme, while a robust stochastic realization is accordingly developed.

Findings

The mean value and standard deviation of the propagating surface waves are extracted through a single-pass simulation in contrast to the laborious Monte Carlo technique, proving the accomplished high efficiency. Moreover, numerical results, including graphene’s surface current density and electric field distribution, indicate the notable precision, stability and convergence of the new graphene-based stochastic time-domain method in terms of the mean value and the order of magnitude of the standard deviation.

Originality/value

The combined uncertainties of the main parameters in graphene layers are modeled through a high-performance stochastic numerical algorithm, based on the finite-difference time-domain method. The significant accuracy of the numerical results, compared to the cumbersome Monte Carlo analysis, renders the featured technique a flexible computational tool that is able to enhance the design of graphene THz devices due to the uncertainty prediction.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 36 no. 5
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 10 May 2011

Dejan V. Tošić and Marija F. Hribšek

The purpose of this paper is to model multilayer structure surface acoustic wave (SAW) sensors, incorporated in CMOS or micro‐electro‐mechanical system integrated…

Abstract

Purpose

The purpose of this paper is to model multilayer structure surface acoustic wave (SAW) sensors, incorporated in CMOS or micro‐electro‐mechanical system integrated circuits, and to derive the corresponding wave velocity as an analytic expression in terms of the layers‘ thickness and density, which is suitable for analysis and design.

Design/methodology/approach

The method is based on an electro‐mechanical equivalent model of multilayer structure SAW sensors. A multilayered SAW device is represented by a two‐port electrical equivalent circuit consisting of three parts: input transducer, output transducer, and between them the delay line, which is the sensing part. The sensing part is modelled as a mechanical two‐port network. The wave velocity is calculated using analogy between the mechanical and electrical quantities and the fact that the wave motion of the SAW extends below the surface to a depth of about one wavelength.

Findings

The presented model predicts very efficiently and accurately the velocity of SAW sensors with multilayer substrates in the case where the thicknesses of upper layers are much smaller than the signal wavelength. The velocity can be calculated from the formula, so that elaborate numerical computations involving partial differential equations are avoided.

Research limitations/implications

The model and the velocity calculation can be applied only to acoustically thin upper and middle layers where acoustically thin means that a layer is sufficiently thin and rigid (large shear modulus). The presented results provide a starting‐point for further research in the analysis and design of sensors fabricated using AlGaN, GaN, AlN/diamond.

Practical implications

Since the majority of SAW sensors is designed with acoustically thin layers, the proposed model and calculation can be of interest for many practical material combinations. The presented model and calculation can be used in most cases of the optimal sensor design with respect to the sensor sensitivity or required area on the sensor chip.

Originality/value

The paper presents a new original model of multilayer structure SAW sensors and a new method of SAW velocity calculation. The method gives good results, with much simpler calculations than in the wave equation method, in cases where certain layers are acoustically thin.

Details

Microelectronics International, vol. 28 no. 2
Type: Research Article
ISSN: 1356-5362

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Article
Publication date: 1 September 1995

G. Shabha and K. Kuhwald

Aims to investigate the problems of subsidence and theirimplications for domestic buildings by addressing a number of questions.What are the main causes of land…

Abstract

Aims to investigate the problems of subsidence and their implications for domestic buildings by addressing a number of questions. What are the main causes of land subsidence? What is the potential damage of subsidence, and how can this be prevented and reduced? What are the financial and legal implications for all those involved? Looks critically at the effect of subsidence due to coal mining on residential properties and the particular problems encountered by valuation surveyors. Briefly examines the history and past operation of the compensation system to assess its effectiveness. Finally, considers the fears inherent following privatization, along with future proposals.

Details

Structural Survey, vol. 13 no. 3
Type: Research Article
ISSN: 0263-080X

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Article
Publication date: 27 March 2009

Moe Alramahi

The purpose of this paper is to clarify the legal status of domain names from both a contractual and a property right perspective, and to consider whether domain names are…

Abstract

Purpose

The purpose of this paper is to clarify the legal status of domain names from both a contractual and a property right perspective, and to consider whether domain names are to be considered as a new form of property, in particular as virtual property.

Design/methodology/approach

The paper approaches the topic from contractual perspective. It then examines the concept and various property law theories. This is followed by an analysis to the intangibility of domain names and the appropriate category of protection.

Findings

Domain names are creatures of contract and contract law will provide some form of protection. According to the bundle of rights theory, domain names are intangible property with limitations. Some names are very valuable but nevertheless attract no protection beyond contractual rights. These names should be clothed with property rights protection. The relevant form of property rights is still contentious issue.

Originality/value

The nature of rights over domain names is a key emerging issue in the area of information technology law, with little to guide lawyers and judges. There is currently no consensus on what the legal status of a domain name is and opinions vary about the nature of these rights. The paper offers an insight to the nature of rights in an attempt to further the protection and recognition of rights over domain names.

Details

Journal of International Trade Law and Policy, vol. 8 no. 1
Type: Research Article
ISSN: 1477-0024

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Article
Publication date: 1 February 2016

Omokolade Akinsomi, Katlego Kola, Thembelihle Ndlovu and Millicent Motloung

The purpose of this paper is to examine the impact of Broad-Based Black Economic Empowerment (BBBEE) on the risk and returns of listed and delisted property firms on the…

Abstract

Purpose

The purpose of this paper is to examine the impact of Broad-Based Black Economic Empowerment (BBBEE) on the risk and returns of listed and delisted property firms on the Johannesburg Stock Exchange (JSE). The study was investigated to understand the impact of Black Economic Empowerment (BEE) property sector charter and effect of government intervention on property listed markets.

Design/methodology/approach

The study examines the performance trends of the listed and delisted property firms on the JSE from January 2006 to January 2012. The data were obtained from McGregor BFA database to compute the risk and return measures of the listed and delisted property firms. The study employs a capital asset pricing model (CAPM) to derive the alpha (outperformance) and beta (risk) to examine the trend amongst the BEE and non-BEE firms, Sharpe ratio was also employed as a measurement of performance. A comparative study is employed to analyse the risks and returns between listed property firms that are BEE compliant and BEE non-compliant.

Findings

Results show that there exists differences in returns and risk between BEE-compliant firms and non-BEE-compliant firms. The study shows that BEE-compliant firms have higher returns than non-BEE firms and are less risky than non-BEE firms. By establishing this relationship, this possibly affects the investor’s decision to invest in BEE firms rather than non-BBBEE firms. This study can also assist the government in strategically adjusting the policy.

Research limitations/implications

This study employs a CAPM which is a single-factor model. Further study could employ a multi-factor model.

Practical implications

The results of this investigation, with the effects of BEE on returns, using annualized returns, the Sharpe ratio and alpha (outperformance), results show that BEE firms perform better than non-BEE firms. These results pose several implications for investors particularly when structuring their portfolios, further study would need to examine the role of BEE on stock returns in line with other factors that affect stock returns. The results in this study have several implications for government agencies, there may be the need to monitor the effect of the BEE policies on firm returns and re-calibrate policies accordingly.

Originality/value

This study investigates the performance of listed property firms on the JSE which are BEE compliant. This is the first study to investigate listed property firms which are BEE compliant.

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Article
Publication date: 31 January 2020

Subhendu Bikash Santra and Subodh Kumar Mohanty

The purpose of this study is to present a new methodology of selective harmonics elimination (SHE) technique suitable for single-phase photovoltaic (PV) tied pulse width…

Abstract

Purpose

The purpose of this study is to present a new methodology of selective harmonics elimination (SHE) technique suitable for single-phase photovoltaic (PV) tied pulse width modulated (PWM) inverter.

Design/methodology/approach

In the proposed SHE, switching angles for inverter control are determined offline through numerical techniques and stored in a microcontroller memory as a function of modulation index (md). The methodology uses the solution that leads to a lower change of switching angles from the previous modulation index (md) for storing in the processor memory for multiple solutions. This leads to a smaller number of sections when a piecewise mixed model is considered for storing the entire switching angle curve for the online inverter control. The proposed idea is simulated and experimentally validated on a laboratory prototype of PV (500 W) grid-tied PWM inverter. The control environment is then realized in NI c-RIO 9082.

Findings

This proposed technique is suitable for limiting voltage total harmonics distortion (THD) in single-phase PV tied grid connected voltage source inverter (VSI). Moreover, it is found that filter (L-C) size requirement is less.

Originality/value

The proposed SHE with piecewise mixed model technique effectively reduces voltage THD with less filter size (L-C) in a single-phase PV-tied system.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 39 no. 2
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 8 July 2020

Norliza Ismail, Azman Jalar, Maria Abu Bakar, Nur Shafiqa Safee, Wan Yusmawati Wan Yusoff and Ariffin Ismail

The purpose of this paper is to investigate the effect of carbon nanotube (CNT) addition on microstructure, interfacial intermetallic compound (IMC) layer and…

Abstract

Purpose

The purpose of this paper is to investigate the effect of carbon nanotube (CNT) addition on microstructure, interfacial intermetallic compound (IMC) layer and micromechanical properties of Sn-3.0Ag-0.5Cu (SAC305)/CNT/Cu solder joint under blast wave condition. This work is an extension from the previous study of microstructural evolution and hardness properties of Sn-Ag-Cu (SAC) solder under blast wave condition.

Design/methodology/approach

SAC/CNT solder pastes were manufactured by mixing of SAC solder powder, fluxes and CNT with 0.02 and 0.04 by weight percentage (Wt.%) separately. This solder paste then printed on the printed circuit board (PCB) with the copper surface finish. Printed samples underwent reflow soldering to form the solder joint. Soldered samples then exposed to the open field air blast test with different weight charges of explosives. Microstructure, interfacial IMC layer and micromechanical behavior of SAC/CNT solder joints after blast test were observed and analyzed via optical microscope, field emission scanning microscope and nanoindentation.

Findings

Exposure to the blast wave induced the microstructure instability of SAC305/Cu and SAC/CNT/Cu solder joint. Interfacial IMC layer thickness and hardness properties increases with increase in explosive weight. The existence of CNT in the SAC305 solder system is increasing the resistance of solder joint to the blast wave.

Originality/value

Response of micromechanical properties of SAC305/CNT/Cu solder joint has been identified and provided a fundamental understanding of reliability solder joint, especially in extreme conditions such as for military applications.

Details

Soldering & Surface Mount Technology, vol. 33 no. 1
Type: Research Article
ISSN: 0954-0911

Keywords

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