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Supercapacitor performance with activated carbon and graphene aerogel composite electrodes
Get PDFLink to publisher's homepage at http://ijneam.unimap.edu.myThus far, activated carbon (AC) has been the material of choice as practical supercapacitor electrode material. However, graphene can be a better alternative material. This work presents a comprehensive ratio study of AC and Graphene Aerogel (GA) as the sole and composite electrodes. The material and facile-fabricated electrodes were characterized, and the electrochemical performances of the prototypes were correlated and discussed in terms of specific capacitance, internal resistances, cyclic performance, and self-discharge. It was found that 20% GA addition on the AC electrode (GA20 specimen) recorded the highest charge-discharge specific capacitance at 78.9 F/g, which was 4% higher than AC at 75.8 F/g, even though the estimated surface area for the electrode was 20% lower than the pure AC electrode. Further addition of GA wt% decreased the capacitance due to the lack of electrode surface area. The equivalent series resistance (ESR) increased with an increase in GA wt% due to the higher electronic resistance of GA material. AC electrode had the lowest self-discharge among all specimens, which was caused by the deeper ion storage inside the electrode’s pores
Fabrication of MEMS piezoresistive accelerometer for human gait analysis using laser micromachining
No full textMaster of Science in Microelectronic EngineeringGait analysis measurement is a method to access and identify gait events and the
measurements of motion parameters involving the lower part of body. This significant
method is widely used in rehabilitation, sports, as well as health diagnostic towards
improving the quality of life. However, it is not a routine practice due to the costs
involved in producing the mechanism and using gait labs. Alternatively, inertial sensors
such as microcantilever accelerometer can be used in the development of cheap and
wearable gait analysis systems. Human stride segmentation measurement based on
micro-accelerometer cantilever is used in the study of the lower limb movement
patterns that include walk, jump and run; and the measurements of the motion
parameters. A complete system consists of a fabricated sensor, a Wheatstone bridge
circuit and a signal amplifier tailored for real-time stride analysis measurement is
proposed. As such, this thesis reporting the requirement of research studies, design,
fabrication development and analysis of a MEMS acceleration sensor for gait movement
measurement. Current conventional method requires high combination of dry and wet
process in structuring sensor formations. A novel method for accelerometer sensor
fabrication is by using laser micromachining in order to develop a simple way in
realizing the sensor formation. Polysilicon doped boron material is uses as sensing
material for sensor. Experimental work clearly reveals that a linearity measurement of
acceleration is achievable using the fabricated sensors. The sensors also demonstrated
good signal magnitudes for efficient diagnosing of movement given. This study allows
us to optimize the requirements of hard-mask and fabrication process steps by reduction
of 30% and 25% steps respectively. In the general framework, the research activities is
focused towards development of piezoresistive cantilever formation by using laser
micromachining for fast fabrication development for real life gait and stride
segmentation measurement applications
The optimization of P-i-N power switching diode in term of reverse breakdown voltage and electrostatic disharge performance
No full textMaster of Science in Nanoelectronic EngineeringThe Power switching diode (P-i-N diode) is one of the widely used diode in high power
semiconductor devices as circuit protection. This popularity comes from excellent
reverse voltage blocking and better electrostatic discharge (ESD) performance. As a
result, the exploration on the P-i-N power switching diode to make the device more
robust and competitive in the market is boundless, which aims for continuous
improvement on the electrical characteristics. In this thesis, the design structure of P-i-N
power switching diode consist of a circular shape anode junction, an n-type bulk
substrate and the epitaxial layer of silicon substrate that represent the intrinsic region is
used. Two different type of reverse breakdown voltage range P-i-N power switching
diode are discussed in this thesis which is 250 V and 300 V. Independently, the
optimization of reverse breakdown voltage and ESD respectively is conducted using
250 V and 300 V respectively as both diode have different good and poor electrical
performance. The improvement of both diodes are performed by process simulation and
as well as the confirmation by the design of experiment (DOE) of physical wafers
fabrication process. For the ESD analysis, the devices are then subjected to nondestructive
and destructive test of the fabricated diodes. Initially, this thesis describes
the research work to widen the operating range of the 250 V P-i-N power switching
avalanche diodes that can be operated more than 300 V by exploring the effects of the
thickness and resistivity of epitaxial layer during forward and reverse biasing. Purpose
of widen the operating range is to be used in power distribution application instead of
telecommunication application. The result shows that, the changes on a P-i-N type
structure of the power switching avalanche diode can increase the reverse breakdown
voltage performance to ~500 V, which is beyond 300 V during reverse bias. The
improvement of reverse breakdown voltage is more than 65% from 250 V. In addition
to the electrical characteristics operating range improvement in the thesis, the study of
ESD improvement of 300 V reverse breakdown voltage P-i-N diode is demonstrated. A
better ESD performance of the P-i-N diode is also achieved by changing the
characteristic profile of the P+ anode junction of P-i-N diode. The characteristics
profiles are altered by lightening the dopant concentration and increasing the depth of
the P-i-N diode junction. It is found that, the 300V P-i-N power switching diode can
sustain more than 1 kV during ESD Human Body Modal (HBM) surge test (400%
higher from initial surge) and more than 400 V during ESD Machine Modal (MM)
surge test (100% higher from initial surge)
Purata harga bahan binaan terpilih, Malaysia September 2022
No full textLink to publisher homepage at https://www.dosm.gov.m
Synthesis and characterisation of ternary system LiCoPO₄-LiNiPO₄-LiMnPO₄ cathode materials for Li-ION batteries
No full textDoctor of Philosophy in Materials EngineeringElectrochemical energy storage devices with high energy density are important in modern society. In order to obtain high energy density Li ion batteries, cathode materials with high discharge voltage and discharge capacity are required. Hence, high voltage cathode materials such as olivine LiMPO₄ (M = Mn, Co, and Ni) and spinel Li₂CoMn₃O₈ have been extensively studied by researchers. In this study, three analogous series with the formula of LiCo₁-x[Ni₀.₅Mn₀.₅]xPO₄, LiNi₁-x[Co₀.₅Mn₀.₅]xPO₄ and
LiMn₁-x[Co₀.₅Ni₀.₅]xPO₄ (0 ≤ x ≤ 1) within the phase triangle of LiCoPO₄ – LiNiPO₄ –LiMnPO₄ were systematically studied as potential candidates for high voltage rechargeable lithium ion batteries. The samples were synthesized by conventional solid
state route at temperature 750–1000 °C in air for 12 hours with two different cooling conditions (i.e. slow cooling and quenching). These compositions were characterised by using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Impedance
Spectroscopy Analyser. Initially, LiCoPO₄, LiNiPO₄ and LiMnPO₄ were prepared as end members and were used as standard references. The prepared samples were single phase and structurally stable up to 1000 °C. All the XRD patterns could be indexed with the olivine structure and the space group of Pnma. Structural analysis using Rietveld refinement of conventional XRD data revealed that the estimated anti-site defects was comparably low which is less than ~5 %. The changes in lattice parameters across the series Mn, Co and Ni were in accordance with Vegard’s law. The structure and electrical properties of the slow-cooled and quenched samples were compared. The results showed that the anti-site defects in both the quench and slow-cooled samples have quite similar values. Nevertheless, all the samples exhibits low intrinsic electrical conductivities of
about ~10-8 S cm-1 that were measured using a LCR meter at 300 °C. Hence, further modification were performed on complex olivine LiNi₁/₃n₁/₃Co₁/₃PO₄ in order to improve the conductivity. LiNi₁/₃Mn₁/₃Co₁/₃PO₄ was ball milled to reduce the particle size followed by ball milling with three different carbon sources: graphene nano-platelets (GNP), carbon nanotube (CNT) and carbon black (CB) to form composites. The results showed that these composites have exhibited relatively higher coin cell conductivity compare to the bare sample. Hence, it was believed that this processing route can probably be applied to improve the conductivity of the three analogous series. On the other hand, a small research was also carried out to study the effect of Zn doped into spinel Li₂CoMn₃O8, however, the result was not quite promising because the doped samples exhibited low discharge capacity
Symmetric wideband five port reflectometer for microwave-imaging based brain injury diagnosis
No full textMaster of Science in Communication EngineeringBrain injury is considered as one of the vital reasons for death worldwide with more than
15 million people suffer from brain stroke attack each year, according to World Health
Organization (WHO). The limitations of conventional head imaging techniques such as
MRI and CT-scan have been pointed out in the thesis where a portable and prompt
diagnosis features are not made possible. Radar-based imaging (RBI) is addressed as a
potential solution due to its effectiveness and aptness for a primary diagnosis of brain
injury. However, the bulky structure and high-cost of vector network analyzer (VNA)
limit the RBI potential. Five port reflectometer (FPR) has potential to substitute VNA.
Two prototypes of FPR have been proposed in this thesis. First prototype involves a
single negative (SNG) metamaterial array located at the ground of single ring FPR,
whereas the second one involves double tier compensating network in additional to the
first central ring. In the first prototype, the single ring FPR is designed based on the
theoretical parameters integrated with SNG metamaterial array at the ground plane which
has been optimized to obtain a larger bandwidth. It is observed that the effective
permittivity of the substrate is changed due to the influence of SNG metamaterial which
eventually changed the characteristic impedance of the transmission lines of the FPR at
the front side of the substrate. The metamaterial array enhances the overall performance
of single ring FPR with an increment of 65.62% fractional bandwidth (BW-10 dB) in the
first band and 76.23% in the second band as compared to the design without metamaterial
array. The first prototype has a dual-band operating zone extending from 0.93 GHz to
2.19 GHz and from 3.27 GHz to 4.49 GHz. The second prototype consists of double tier
networks with inter-tier transmission lines and multi-section matching at each of arms.
In the evolution of the second prototype, inter-tier transmission lines are shifted by 36˚
(which is half factorized value of inter-port angular distance of 72˚) in several optimizing
steps, namely, a) non-shifted b) partially shifted and c) fully shifted design. Fully shifted
design which has 36˚ shifted inter-tier and another 36˚ shifted arms has created additional
electrical length traversed by inter-port transmission signals to enhance the bandwidth up
to 88.04% (from 1.004 GHz to 2.583 GHz). In addition of bandwidth achievement, such
compactness of proposed FPR is contributed by the curved lines at the outer matching
sections which enable a reduction of 43.09% in length and 43.12% in width compared to
the non-compact design. Both prototypes have been fabricated and measured.
Discrepancies between simulated and measured results are assessed using mean absolute
deviation. The 88.04% bandwidth of the proposed fully shifted FPR is the highest
bandwidth among literatures which potentially leads to a higher accuracy of microwave
imaging-based brain injury diagnosis