N. Khalid

Directional and wideband antenna for ground penetrating radar (GPR) applications

This paper presents a directional and wideband antenna for ground penetrating radar (GPR) applications. The antenna is designed by introducing slots on bowtie patch. The design is implemented on FR4 board with dielectric constant of 4.7 and thickness of 0.8 mm. As a result of having thinner substrate, the design is compact and light weight. The bowtie antenna performance is investigated across 0.5 GHz to 3 GHz. The parametric study of the length and location of slot are also demonstrated in this paper to obtaining the best return loss across widest operational bandwidth. The both simulated and fabricated antenna bandwidth are more than 50% (fractional bandwidth). The additional reflector is included at the back of bowtie antenna in the simulation for obtaining directional radiation pattern and high gain. The comparison between simulated and measured reflection coefficient is also presented.

Solid State Lighting Stress and Junction Temperature Evaluation on Operating Power

LEDs are being utilized as lighting source due to its superior advantages over incandescent lamps in terms of higher efficiency, brighter light emission and longer lifetime. However, the reliability and efficiency of the LED is dependent on the junction temperature of the LED chip. Hence, the heat dissipation of single chip LED package with aluminum heat slug was investigated through simulation in this study .The heat dissipation was evaluated in terms of junction temperature. The single chip LED was powered with input power of 0.1W and 1W. The Von Mises stress of the LED chip at both input power was evaluated. The maximum junction temperature of the LED at steady state is 119.43°C at input power of 1W.

Stress and Temperature Simulation Using Copper-Diamond Composite Slug

A revolution to illumination industry, the high power light emitting diodes, LEDs have significant dominance in terms of optical performance, low power consumption and superior reliability over conventional lights. In spite of that the junction temperature of the LED is an imperative aspect which manipulates the consistency of the LED. This study discusses the thermal and stress analysis of single chip LED package with copper diamond heat slug. The simulation was carried out using Ansys version 11. In this simulation, input power of 0.1W and 1W were applied to the LED chip. The key findings of this study exhibited that the max junction temperature of 113.13 °C and stress of 116.36 MPa were gained.

Remazol orange dye sensitized solar cell

Water based Remazol Orange was utilized as the dye sensitizer for dye sensitized solar cell. The annealing temperature of TiO2 working electrode was set at 450 °C. The performance of the device was investigated between dye concentrations of 0.25 mM and 2.5 mM at three different immersion times (3, 12 and 24 hours). The adsorption peak of the dye sensitizer was evaluated using UV-Vis-Nir and the device performance was tested using solar cell simulator. The results show that the performance was increased at higher dye concentration and longer immersion time. The best device performance was obtained at 0.2% for dye concentration of 2.5 mM immersed at 24 hours.

Natural Heat Convection Analysis on Cylindrical Al Slug of LED

This paper presents the characterization of a single chip high power LED package through simulation. Ansys version 11 was used for the simulation. The characterization of the LED package with aluminum cylindrical heat slug was carried out under natural convection condition at ambient temperature of 25°C. The junction temperature and the stress of the LED chip was assesed. The LED chip was powered with input power of 0.1 W and 1 W and the heat dissipation was assesed. Results showed that that the junction temperature and the Von Mises Stress of the single chip LED package increases with the increased input power.

Few-layers graphene oxide for NO2 gas sensor on plastic

Vacuum filtration method was used in order to fabricate a homogeneous and uniform thin film of multi-layer graphene oxide on plastic substrate. This self-regulating technique allows the number of graphene oxide layer to be controlled thus controlling the film thickness by simply varying either the concentration of the graphene oxide in the suspension or the filtration volume. Measurement of the sheet resistance as a function of graphene oxide concentration in solution shows the percolation behavior of multi-layer films. The device was then exposed in nitrogen dioxide (NO2) environment at room temperature and 200 °C, under atmospheric pressure. Results demonstrate that the graphene oxide film shows good sensitivity and excellent recovery time using plastic substrate.

Fundamental study of reduction graphene oxide by sodium borohydride for gas sensor application

The efficient reduction of graphene oxide (rGO) was performed using Sodium Borohydride (NaBH4). These reduction approaches remove the majority of the oxygen-containing functional groups at the basal plane and surface of graphene oxide sheets. Structural and physiochemical properties of the GO were investigated with help of Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and Ultraviolet-Visible-Near infrared (UV-Vis-NIR). The effects of the chemical reduction on a GO surface were analyzed using a Semiconductor Parameter Analyzer (SPA) in order to obtain the electrical resistance measurement. It was found that the resistance of reduced graphene oxide was greatly reduced when compared to the condition of before reduction process. Then, the formation of uniform thin film of rGO sheets was produced using vacuum filtration method in order to fabricate a gas sensor. In this project, plastic was used as a substrate. The sensor was then being e...

Multi-walled carbon nanotubes plastic NH3 gas sensor

Multi-walled Carbon Nanotubes (MWCNTs) functionalized -COOH was used as the sensing material. The MWCNTs suspension was then deposited on the plastic substrate using vacuum filtration method, hence created uniform thin film carbon nanotubes network. Plastic membrane was chosen as the substrate in order to produce flexible, lightweight, wearable and low cost sensor. This device was exposed to ammonia gas (NH3) at two different concentrations; 19.2 and 231.4 ppm. The device shows high sensitivity at 23.4 % when exposed to 231.4 ppm NH3 and less sensitivity at 4.39 % for 19.2 ppm NH3 exposure.

The enhancement of high speed pHEMT device for IoT applications

We report the enhancements on pHEMT epilayers to suite the high speed applications for IoT. Presented here are the DC and RF comparisons between XMBE #109 as the baseline of high speed pHEMT and VMBE #2100 as the enhanced epitaxial layer. The Hall data from Van der Pauw measurement shows higher sheet carrier concentration is observed on the improved epitaxial layer devices. The DC comparisons between the devices from both epilayers verified that the enhanced epitaxial layer demonstrates low leakage-high breakdown characteristics. Improvement of transconductance and output current density also been observed from the VMBE #2100 epitaxial layer. The RF characteristics, however, show comparable fT of 25 GHz. In short, this will facilitates the implementation of high speed circuits, including high speed broadband systems for IoT applications.

Comprehensive study on gate recess step for the fabrication of high-speed InGaAs/InAlAs/InP pHEMT

We report a comprehensive etching study on the gate recess step for the fabrication of the novel high speed pHEMT devices. The experiments focused on the elimination of “hump” structure as a result of an incomplete etching process at the InGaAs cap layer. In this work, two types of test samples were used, namely bulk InGaAs and epitaxial structure together with an etch stop layer. The result showed that the etch rate of bulk InGaAs is about 360 A/min and the percentage of dome height is consistent at approximately 25%. Meanwhile, the study on pHEMT epitaxial layer showed that the etching time of 3 minutes is sufficient in order to completely remove the cap layer. Gate leakage current of magnitude more than 10 times lower is observed on the devices that engaging Succinic Acid as the gate recess etching agent. The optimized processing steps will tailor for highly reproducible pHEMT fabrication process for high speed applications.