Scott G. McMeekin

Asymmetric split ring resonators for optical sensing of organic materials

Asymmetric Split Ring Resonators are known to exhibit resonant modes where the optical electric field is strongest near the ends of the arms, thereby increasing the sensitivity of spectral techniques such as surface enhanced Raman scattering (SERS). By producing asymmetry in the structures, the two arms of the ring produce distinct plasmonic resonances related to their lengths - but are also affected by the presence of the other arm. This combination leads to a steepening of the slope of the reflection spectrum between the resonances that increases the sensitivity of the resonant behavior to the addition of different molecular species. We describe experimental results, supported by simulation, on the resonances of a series of circular split ring resonators with different gap and section lengths--at wavelengths in the mid-infra red regions of the spectrum--and their utilization for highly sensitive detection of organic compounds. We have used thin films of PMMA with different thicknesses, resulting in characteristic shifts from the original resonance. We also demonstrate matching of asymmetric split ring resonators to a molecular resonance of PMMA.

A Comprehensive Performance Study of OPNET Modeler for ZigBee Wireless Sensor Networks

OPNET has been widely used as a network simulator, but not much emphasis has been given on the performance of this simulator for ZigBee wireless sensor networks (WSN). Simulation of WSNs is a challenging task due to the nature of hardware design, energy limitations, and deployment of a vast number of nodes. An inclusive study and analysis of the QoS performance evaluation of the ZigBee protocol within the OPNET simulator for different WSN topologies and routing schemes is presented here. Based on simulation and analysis of results this paper can be considered as a guide for researchers in evaluating OPNET Modeler as a WSN simulator for Zigbee networks. Some enhancements needed in OPNET Modeler to be more suitable for the simulation of ZigBee WSNs are discussed.

Magnetic response of split ring resonators (SRRs) at visible frequencies

In this paper, we report on a substantial shift in the response of arrays of similarly sized Split Ring Resonators (SRRs), having a rectangular U-shaped form--and made respectively of aluminium and of gold. We also demonstrate that it is possible to obtain the polarization dependent LC peak in the visible spectrum--by using SRRs based on aluminium, rather than gold. The response of metallic SRRs scales linearly with size. At optical frequencies, metals stop behaving like nearly perfect conductors and begin displaying characteristically different behaviour, in accord with the Drude model. The response at higher frequencies, such as those in the visible and near infra-red, depends both on their size and on the individual properties of the metals used. A higher frequency limit has been observed in the polarization dependent response (in particular the LC resonance peak) of gold based SRRs in the near infrared region. By using aluminium based SRRs instead of gold, the higher frequency limit of the LC resonance can be further shifted into the visible spectrum.

Enhanced Fano resonance of organic material films deposited on arrays of asymmetric split-ring resonators (A-SRRs)

Depositing very thin organic films on the surface of arrays of asymmetric split-ring resonators (A-SRRs) produces a shift in their resonance spectra that can be utilized for sensitive analyte detection. Here we show that when poly-methyl-methacrylate (PMMA) is used as an organic probe (analyte) on top of the A-SRR array, the phase and amplitude of a characteristic molecular Fano resonance associated with a carbonyl bond changes according to the spectral positions of the trapped mode resonance of the A-SRRs and their plasmonic reflection peaks. Furthermore, we localize blocks of PMMA at different locations on the A-SRR array to determine the effectiveness of detection of very small amounts of non-uniformly distributed analyte.

Resonance hybridization in nanoantenna arrays based on asymmetric split-ring resonators

Asymmetric split ring resonators (A-SRRs) are composed of two separate metallic arcs of asymmetric lengths that share the same center-of-curvature. The two arcs interact to produce a very steep slope in the reflection spectrum. We utilize the plasmon resonance hybridization model to understand and describe the working of an A-SRR and produce experimental and simulation results to show that the A-SRR resonances are a “modified linear superposition” of the individual plasmon resonances coming from each of the arcs.

Least Squares Interpolation Methods for LTE System Channel Estimation over Extended ITU Channels

Abstract — Performance of pilot-aided channel estimation techniques such as the Least Squares (LS) method depends on not only on the signal-to-noise ratio (SNR), channel conditions and pilot ratio, but also on the choice of interpolation method for deriving channel estimates at non-pilot subcarriers. This paper investigates the bit-error-rate (BER) performance of linear, spline and Piecewise Cubic Hermite Interpolating Polynomial (PCHIP) interpolation methods in LS channel estimation over the three extended ITU channel profiles defined for Long Term Evolution (LTE) testing. Simulation results show that applying the linear interpolation method produces the best BER performance over the fading channel with the smallest multipath delay spread. It is also shown that the choice of best interpolation method actually depends on the SNR in some of the fading channel profiles. Index Terms—ITU, LS, LTE, PCHIP, spline. I. INTRODUCTION Orthogonal frequency division multiplexing (OFDM) technology has been adopted in many of the next generation communication systems such as Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX) [1]. OFDM is preferred not only because it offers high data rate transmission but also because of its flexibility and robustness against multipath fading [1]. Multipath channel fading exists when multiple delayed copies of a transmitted signal are received at the receiver, thereby resulting in the distortion of the transmitted signal. These distortions are collectively termed „channel fading‟, causing reception errors and hence increased bit-error-rate (BER). Channel fading can be broadly classified as time-selective and/or frequency selective, depending on the relationship between the fading channel and the transmitted signal parameters [2]. To combat multipath fading and improve BER, some form of channel estimation method is required in order to estimate the channel distortion effect for each of the active subcarriers within an OFDM symbol [3].

Feed-In Tariff for solar PV in Malaysia: Financial analysis and public perspective

Malaysia is joining the global race for solar photovoltaics (PVs), where the Feed-In Tariff (FIT) mechanism has been introduced recently. This paper presents, first, a chronological overview of solar PV in Malaysia until the present time. Next, a general concept of the FIT Malaysia is explained and a financial analysis is carried out, comparing the return on investment of installing solar PV in different locations in Malaysia, as well as in other countries. The paper also shows a preliminary survey conducted to Malaysians to see their awareness on the national initiatives related to green technologies and their likelihood to invest in the FIT scheme. The financial analysis indicates that installation of PV in Malaysia could potentially generate good investment return during the duration of a contract. The survey on the other hand suggests that Malaysians are not aware of the national initiatives and are not willing to invest in solar PV installation.

Optimised dielectric totally internally reflecting concentrator for the solar photonic optoelectronic transformer system: maximum concentration method

Renewable energies have become a matter of global attention during the last few years, with solar energy being a major focus. Building Integrated Photovoltaic (BIPV) system is an example of solar energy applications. This paper describes the Solar Photonic Optoelectronic Transformer (SPOT) system, one of the components in the SolarBrane, a BIPV system developed by SolarEmpower Ltd. The general design of a dielectric totally internally reflecting concentrator (DTIRC) is described. The process of designing an optimized solar concentrator using the maximum concentration method (MCM) for the SPOT system is also outlined with detailed steps on the simulation setup presented. The paper then compares the performance of the new concentrator with the current concentrator design. The results from the MATLAB simulation shows that the MCM offers a higher geometrical concentration gain, with a slight increase in the concentrator size.

Effect of dry band location on electric field distribution along a polymeric insulator under contaminated conditions

To study the effect of dry band location on electric field distribution of polymeric insulators, simulations were carried out using Comsol Multiphysics. The effect of dry band along a polymeric insulator at shed, core and junction of core and shed regions on the electric field distribution was investigated. Pollution was modelled as a 2-mm uniform conductive water layer on the insulator surface. Conductivity of pollution layer was set at 500μS/cm to simulate medium pollution conditions. Simulation was carried out by considering a 2-cm dry band at the shed, core and junction of shed and core regions respectively. The highest electric field strength was observed when the dry band was considered at the junction of shed and core region while the electric field strength was minimum along the dry band at the shed regions. The result of this study will help scientists and engineers to improve the design of weather sheds for high voltage insulators so that the possibility of dry band formation at the junction of shed and core is minimized.

Effect of pollution severity on electric field distribution along a polymeric insulator

To study the effect of pollution level on electric field distribution of polymeric insulators, simulations were carried out using Comsol Multiphysics. The effect of light, medium, heavy and very heavy pollution on the electric field and potential distribution was investigated. Pollution was modelled as a uniform conductive water layer on the insulator surface. Electric field analysis was carried out by changing the conductivity of the pollution layer. Simulation results show that electric field strength is high at the junction of the sheath and shed and minimum at the top of the shed. It was also observed from simulations that electric field stress increases with increasing pollution level. The result of this study will help scientists and engineers in the design and selection of outdoor insulators for different polluted environments.