ChingSeong Tan

Model of gated imaging in turbid media

Range-gated imaging can improve the signal to backscattering noise ratio (SBR) in turbid media. This is achieved by synchronizing a short duration, high intensity pulse with precise camera gating. It is well known that shorter pulse length and shorter camera gate duration can enhance the SBR. However, there is no analytical model of the backscattering noise (as a function of the pulse length and gate timing) that can be used to minimize backscattering noise within the camera-captured signal. We propose a formulation (a modification of Falks lidar equation) that models the backscattering noise as a convolution with a fixed upper limit. This formulation predicts a variation of backscattering noise within the returning signal. In particular, the model predicts higher SBR toward the tail region of the target-reflected irradiance. It confirms the experimental results reported by other authors. Additionally, the model explains experimentally observed SBR improvement for shorter pulses and shorter gating intervals (if adequately positioned within the returning pulse).

Performance evaluation of hybrid VLC using device cost and power over data throughput criteria

Visible light communication (VLC) technology has attained its attention in both academic and industry lately. It is determined by the development of light emitting diode (LED) technology for solid-state lighting (SSL).It has great potential to gradually replace radio frequency (RF) wireless technology because it offers unregulated and unlicensed bandwidth to withstand future demand of indoor wireless access to real–time bandwidth-demanding applications. However, it was found to provide intrusive uplink channel that give rise to unpleasant irradiance from the user device which could interfere with the downlink channel of VLC and hence limit mobility to users as a result of small coverage (field of view of VLC).To address this potential problem, a Hybrid VLC system which integrates VLC (for downlink) and RF (for uplink) technology is proposed. It offers a non-intrusive RF back channel that provides high throughput VLC and maintains durability with conventional RF devices. To deploy Hybrid VLC system in the market, it must be energy and cost saving to attain its equivalent economical advantage by comparing to existing architecture that employs fluorescent or LED lights with RF technology. In this paper, performance evaluation on the proposed hybrid system was carried out in terms of device cost and power consumption against data throughput. Based on our simulation, Hybrid VLC system was found to reduce device cost by 3% and power consumption by 68% when compares to fluorescent lights with RF technology. Nevertheless, when it is compared to LED lights with RF technology, our proposed hybrid system is found to achieve device cost saving as high as 47% and reduced power consumption by 49%. Such promising results have demonstrated that Hybrid VLC system is a feasible solution and has paved the way for greater cost saving and energy efficient compares with the current RF architecture even with the increasing requirement of indoor area coverage.

Performance Optimization of Organic Solar Cells

Organic solar cells (OSCs) have been gaining great popularity in recent years due to their potentials to be low cost, lightweight, and flexible. The performance of OSCs is growing steadily, and they have achieved a power conversion efficiency close to 10% (for single-junction polymer-fullerene OSC). Although there are still limitations and challenges faced by the development of OSCs, in view of the potentials, recent studies have been focusing on the design optimization of OSC layer structure through material engineering, interfacial layer insertion, layer thickness optimization, and morphological control. In this paper, we provide a comprehensive review and detailed discussion on the optimization works and development on OSCs, with particular focus on the bulk-heterojunction (BHJ) polymer-fullerene OSCs. We also provide a summary of the performance, in a chronological order, and the future outlook of OSC.

Automated Crack Detection for Digital Radiography Aircraft Wing Inspection

Radiography testing is one of the most important nondestructive testing (NDT) techniques for aircraft wing inspection. Traditionally, radiography inspection is time and manpower consuming work. In addition, human inspection of cracks and damage based on film radiography is very subjective, inconsistent, and sometimes biased. Digital radiography allows all the benefits of producing significant increases in magnification and image clarity, as well as efficient management of digital images. Therefore, it is desirable to develop a computer aided system to assist interpretation of radiographic images to increase the objectivity, accuracy, and efficiency of radiographic inspection. In this article, an automated crack detection algorithm using region of interest (ROI) minimization and improved Canny edge detection techniques is developed for aircraft wing inspection. Cracks of up to 2 mm long on the aircraft wing around the fastener holes are detected automatically.

Visualization of Mixed Convective Rolls of a Slot Jet in a Fluid-Superposed Metallic Porous Foam Heated from below

Flow visualization and numerical study of a slot jet in a horizontal channel partially filled with FeCrAlY foam is carried out to observe the flow structure under buoyancy effect. The flow patterns in the fluid region for different jet velocity (0 ≤ Pe ≤ 548.9) are captured using particle imaging velocimetry. The flow patterns obtained from simulations are similar to the experimental results. The flow patterns for 219.5 ≤ Pe ≤ 548.9 with buoyancy strength of Ra = 1.024 × 106 and Ra = 1.048 × 106 for dimensionless height of 0.6 and 0.8, respectively, demonstrated mixed convective flows. Buoyancy driven roll is observed near the edge of the metal foam, and jet driven roll is observed above the metal foam.

Range compensation for accurate 3D imaging system.

Range determination has crucial dependency of intensity over distance due to the fact that output of a range gated system is the reflectivity and range information expressed in term of intensity. From our experimental study, the analyzed trend line of reflected intensity versus range agrees with the theoretical model where it underlies an inverse range-squared dependency. Considering the energy attenuation factor for a better three-dimensional (3D) solution, a range compensation model is derived based on time slicing technique to compensate the effect imposed by distance beyond an optimum range. A range gated imaging system with pulse profile feedback is proposed in order to apply the range compensation model. Experimental results show noticeable improvement as compared to the conventional weighted average method for reflected laser pulse data across different ranges and 3D surface reconstruction using the proposed range compensation model.

Scattering noise estimation of range-gated imaging system in turbid condition

The range-gated imaging systems are reliable underwater imaging system with the capability to minimize backscattering effect from turbid media. The tail-gating technique has been developed to fine tune the signal to backscattering ratio and hence improve the gated image quality. However, the tail-gating technique has limited image quality enhancement in high turbidity levels. In this paper, we developed a numerical model of range-gated underwater imaging system for near target in turbid medium. The simulation results matched the experimental work favorably. Further investigation using this numerical model shows that the multiple scattering components of the backscattering noise dominate for propagation length larger than 4.2 Attenuation Length (AL). This has limited the enhancement of tail-gating technique in high turbidity conditions.

Ground plane detection for autonomous vehicle in rainforest terrain

This paper presents the determination of the ground plane method for navigation in rainforest terrain using stereo vision. Ground plane detection plays an important role for obstacle detection task as it act as the reference plane of the scene. V-disparity image is widely used to detect the ground plane for on-road and off-road navigation. However, it relies on distinct road features such as lines and edges which may not exist in rainforest terrain. In this work, we attempted to use colour clustering method to extract possible ground profile even without using distinct road features.

Improved Range Estimation Model for Three-Dimensional (3D) Range Gated Reconstruction

Accuracy is an important measure of system performance and remains a challenge in 3D range gated reconstruction despite the advancement in laser and sensor technology. The weighted average model that is commonly used for range estimation is heavily influenced by the intensity variation due to various factors. Accuracy improvement in term of range estimation is therefore important to fully optimise the system performance. In this paper, a 3D range gated reconstruction model is derived based on the operating principles of range gated imaging and time slicing reconstruction, fundamental of radiant energy, Laser Detection And Ranging (LADAR), and Bidirectional Reflection Distribution Function (BRDF). Accordingly, a new range estimation model is proposed to alleviate the effects induced by distance, target reflection, and range distortion. From the experimental results, the proposed model outperforms the conventional weighted average model to improve the range estimation for better 3D reconstruction. The outcome demonstrated is of interest to various laser ranging applications and can be a reference for future works.

Feasibility study of long period grating as an optical biosensor for dengue virus detection - an alternative approach to dengue virus screening

Dengue being one of the current global epidemic diseases currently is mainly found in tropical and large swamp areas. A fast diagnostic method is required to give an accurate result of a suspected dengue patient in order to save lives. Long period grating -LPG (or sometimes known as long period fibre grating-LPFG) has a fast detection method almost to real time gives an immediate result and it is highly sensitive towards its ambient refractive index. Long period grating is a modified fibre optic with grating at a specific portion of the optical fibre; the fibre optics signal transmission does not decay easily and remains almost ideal for all application. This paper aims to study an alternative approach to screen patient who are suspected with dengue and results obtained will be used as a future guideline for subsequent research.