High efficient dye sensitized solar cells typically apply expensive materials. To reduce the costs natural dyes, carbon nanotubes and an additional contact layer were introduced. UV-irradiation substitutes typical sintering processes for the TiO₂ nanoparticle film. Replacing the ITO coated glass electrodes by a metal grid structure reduces the integration costs further more. Best results were achieved using a grid structure with openings in the dimension of the diffusion length of the charge carriers.

Variable laser power and temperature dependent photoluminescence (PL) measurements were used to identify some of the optical transitions and impurity-related emissions for chemically treated (Br-methanol, (NH₄)₂S + S or [(NH₄)₂S/ (NH₄)₂SO₄] + S solutions) or oxidised (annealed in oxygen) bulk n-InAs (111)A. A combination of PL and X-ray photoelectron spectroscopy (XPS) measurements before and after various treatments was used to identify the chemical nature of the impurities giving rise to bound exciton recombination in InAs (111). Band–to-band transitions have been observed at 0.4185 eV. In addition, two shallow neutral donor bound excitons ascribed to atomic oxygen (at 0.412 eV) and to sulphur (at 0.414 eV), have been detected after treatment.

This work aims to provide an analysis on the material properties, layer geometries, design, and fabrication of a singleelement, direct band gap indium gallium arsenide (In_xGa_1-xAs) infrared photo-detector on a lattice matched indium phosphide (InP) substrate with cut-off wavelength of 1700 nm. A theoretical study on the mechanisms present during device operation allows accurate modelling and simulation on the intrinsic behaviour and transport physics to provide reasoning behind material type, carrier concentrations and doping profiles, and the proposed physical dimensions. The estimated device performance based on the responsivity and quantum efficiency, dark current, bandwidth, and intrinsic junction capacitance is also presented. Device optimization through silicon nitride (SiN_x) anti-reflection and silicon dioxide (SiO₂) passivation layer combinations is investigated based on light reflection and diffraction minimization. Finally, an equivalent electrical circuit representation of the dominant noise sources in light and dark conditions aims to provide additional insight into device optimization.

The National Metrology Institute of South Africa (NMISA) is developing a new optical frequency standard based on the Rubidium two-photon transition in collaboration with the National Institute of Standards (NIS, Egypt) that will use both bulk and fiber optics in the system. This is system is called A-POD; an acronym for a portable photonic oscillator device. Rubidium two-photon standards can yield relatively simple and precise standards that are compatible with standard Ti:Sapphire optical frequency combs, as well as the need for a precise frequency standard in the optical telecommunication domain and for measurement of length with a visible beam. The robustness and transportability of the standard are important considerations for the optical frequency standard. This projects implements a framework for better two-photon standards that can be highly accurate, and possibly compete with much more complex clocks in the metrology environment, and especially so in the smaller national metrology institutes found in the developing world. This paper discusses the design constraints and the development considerations towards the optical setup. The robustness and transportability was greatly improved via the usage of optical fiber in the light source of the system, or even in atom-light interaction region. Of particular importance are the beam parameters inside the atomic interaction area. The extent of Doppler broadening and the intensity dependent line shift have to be optimized within practical extents, where both these aspects are affected by the beam shape and optical geometry. A way to fully treat the optical beam effects together with atomic movement is proposed. Furthermore a method is proposed to do real time compensation of intensity dependent light shift, which could have major applicability to frequency standards in general - the complexity is shifted from physical setups to digital signal processing, which is easily adaptable and stable.

The beam from a laser resonator is determined by the optical elements it contains. Most commonly, these consist of two spherical mirrors, but phase- and amplitude-modulating elements can also be included to produce custom beams. For every custom beam new optics are required, and the resonator must be realigned, a process which can take several hours to days. The digital laser [1] is an innovation which allows the laser beam produced by a laser to be dynamically controlled by a computer. Essentially, one of the resonator mirrors is replaced by a spatial light modulator (SLM), which is a computercontrolled, pixellated, liquid-crystal device. While the concept is the device is simple, the implementation revealed subtle properties of spatial light modulators and the liquid crystals contained in them. These properties had to be well understood before their undesirable characteristics could be overcome, allowing the laser to function as conceived in the design.

Uncooled infrared (IR) microbolometer cameras are gaining popularity in a variety of military and commercial applications due to their simplicity, compactness and reduced cost when compared to photon detectors. Three commercially available IR microbolometer cameras have been investigated for use in a system. The cameras have been characterized in terms of camera response and noise as function of camera temperature with the aim of modelling the cameras for use in simulation. Ideally, the camera systems, consisting of a detector, electronics, and optics, should be modelled from a low-level physical point of view and measurements should be performed for verification. However, the detector and electronic design parameters are not available for the commercially acquired cameras, and a black-box approach of the systems was adopted for modelling and characterization. The black-box approach entails empirical mathematical modelling of the camera response and noise through measurements and subsequent data analysis. A 3D noise model was employed to characterize camera noise in terms of orthogonal noise components, and an empirical temperature-dependent model was deduced for each component. The method of modelling through measurement is discussed, and the accuracy of specifically the empirical noise models is shown. The cameras are also compared in terms of measured noise performance.

The technology for the measurement of colour rendering and colour quality is not new, but many parameters related to this issue are currently changing. A number of standard methods were developed and are used by different specialty areas of the lighting industry. CIE 13.3 has been the accepted standard implemented by many users and used for many years. Light-emitting Diode (LED) technology moves at a rapid pace and, as this lighting source finds wider acceptance, it appears that traditional colour-rendering measurement methods produce inconsistent results. Practical application of various types of LEDs yielded results that challenged conventional thinking regarding colour measurement of light sources. Recent studies have shown that the anatomy and physiology of the human eye is more complex than formerly accepted. Therefore, the development of updated measurement methodology also forces a fresh look at functioning and colour perception of the human eye, especially with regard to LEDs. This paper includes a short description of the history and need for the measurement of colour rendering. Some of the traditional measurement methods are presented and inadequacies are discussed. The latest discoveries regarding the functioning of the human eye and the perception of colour, especially when LEDs are used as light sources, are discussed. The unique properties of LEDs when used in practical applications such as luminaires are highlighted.

The technology for the measurement of colour rendering and colour quality is not new, but many parameters related to this issue are currently changing. A number of standard methods were developed and are used by different specialty areas of the lighting industry. CIE 13.3 has been the accepted standard implemented by many users and used for many years. Light-emitting Diode (LED) technology moves at a rapid pace and, as this lighting source finds wider acceptance, it appears that traditional colour-rendering measurement methods produce inconsistent results. Practical application of various types of LEDs yielded results that challenged conventional thinking regarding colour measurement of light sources. Recent studies have shown that the anatomy and physiology of the human eye is more complex than formerly accepted. Therefore, the development of updated measurement methodology also forces a fresh look at functioning and colour perception of the human eye, especially with regard to LEDs. This paper includes a short description of the history and need for the measurement of colour rendering. Some of the traditional measurement methods are presented and inadequacies are discussed. The latest discoveries regarding the functioning of the human eye and the perception of colour, especially when LEDs are used as light sources, are discussed. The unique properties of LEDs when used in practical applications such as luminaires are highlighted.

With the application for wafer level packages, which could be Complementary Metal–Oxide–Semiconductor (CMOS) based, and which requires a reduced atmosphere, a copper tube connection to a vacuum pump and the package is proposed. The method evaluated uses laser assisted brazing of a solder, to join the copper tube to a silicon wafer. The method was applied to a silicon wafer coated with a metallic interface to bond to the solder. The hermeticity of the joint was tested with a helium leak rate tester and the bonding energy thermal extent was verified with a thin layer of indium that melted wherever the substrate temperature rose above its melting temperature.

SU-8/Clay nanocomposite is considered as a candidate material for microcantilever sensor fabrication. Organically modified montmorillonite clay nanoparticles are dispersed in the universally used negative photoresist polymer SU-8, for a low cost material, which is also biocompatible. If varying the clay loading of the composite material yields a variation of the Young's modulus, the tailored material stiffness presents an opportunity for fabrication of microcantilevers with tunable sensor sensitivity. With this microcantilever application perspective, mechanical and thermal properties of the material were investigated. SU-8/Clay nanocomposite samples were prepared with clay loadings from 1wt% - 10wt%. Tensile test results show a general trend of increase in composite modulus with an increase in the clay loading up to 7wt%, followed by a small drop at 10wt%. The composite material indeed yields moderate variation of the Young's modulus. It was also found that the thermal degradation peak of the material occurred at 300°C, which is beyond the operating temperature of typical microcantilever sensor applications. The fabrication of a custom designed microcantilever array chip with the SU-8/Clay nanocomposite material was achieved in a class 100 cleanroom, using spin-coating and photolithography microfabrication techniques. The optimization of the process for fabricating microcantilever with the SU-8/Clay nanocomposite material is discussed in this paper. The results of this research are promising for cheaper mass production of low cost disposable, yet sensitive, microcantilever sensor elements, including biosensor applications.

Some key electro-optical measurements required to characterize an aircraft plume for automated recognition are shown, as well as some aspects of the processing and use of these measurements. Plume measurements with Short Wavelength Infrared (1.1 – 2.5 um), Mid-Wavelength Infrared (2.5 – 7 um) and Long Wavelength Infrared (7 – 15 um) cameras are presented, as well as spectroradiometer measurements covering the whole Mid-Wavelength, Long Wavelength and upper part of the Short Wavelength Infrared bands. The two limiting factors for the detection of the plume, i.e. the atmospheric transmission bands and the plume emission bands, are discussed, and it is shown how a micro turbine engine can assist in aircraft plume studies. One such a study, regarding the differentiation between an aircraft plume and a blackbody emitter using subbands in the Mid-Wavelength Infrared, is presented. The factors influencing aircraft plume emission are discussed, and the measurements required to characterize an aircraft plume for the purpose of constructing a mathematical plume model are indicated. Since the required measurements are prescribed by the plume model requirements, a brief overview of the plume model, that can be used to simulate the results of the plume’s emission under different conditions and observation configurations, is given. Such a model can be used to test the robustness of algorithms, like the mentioned subband method, for identifying aircraft plumes. Such a model furthermore enables the simulation of measurements that would be obtained by an electro-optical system, like an infrared seekerhead of a missile, of a plume for the purpose of algorithm training under various simulated environmental conditions.

Road distresses, such as potholes and edge cracks, are not only a source of frustration to drivers but also negatively impact the economy due to damage to motor vehicles and costly ro6ad repairs. Regular and rapid pavement inspection and maintenance is vital to preventing pothole formation and growth. To improve the efficiency of maintenance and reduce the cost thereof, the Visual Surveying Platform (VSP) is being developed that will automatically detect and analyse road distresses. The VSP consists of a vehicle mounted sensor system, consisting of a high speed camera and a Global Positioning System (GPS) receiver, and an analysis and visualization software suite. The system extracts both a visual image and the coordinates of a detected road defect from recorded video and presents it in an interactive interface for use by technical experts and maintenance schedulers. The VSP automatically detects and classifies road distresses using a two-stage artificial neural network framework. Video frames first undergo hue, saturation and value (HSV) colour space conversion as well as a spatial frequency transformation before being used as inputs to the neural networks. A road detector neural network first classifies which section of the image contains the road, after which a distress detector neural network identifies those road regions containing defects. Although the VSP can be adapted to detect any type of road distress it has been trained to specifically detect potholes. An initial prototype of the VSP was designed and constructed. The prototype was also trained and tested on real-world data collected from provincial roads.

A new resolution refinement method is introduced for template-matching. Fine-correlation uses sample replication to re ne match-accuracy to discrete inter-sample positions. Fine-correlation can be done in both the time and frequency domain. The achievable resolution-re finement is a function of signal-to-noise ratio; signal bandwidth; template-length and template information content. Templates can easily be described to a 10 times or higher time-resolution than the incoming signal. Fine-correlation provides a method of matching in such scenarios. Possible implementations are discussed. The preferred method is chosen. A noise-level- and templatelength analysis is done illustrating achievable resolution improvement. Two implementations of Fine-correlation conclude this paper. An appendix is devoted to the derivation of the resampling DFT and resampling DHT.

A brief overview of the properties of the Gauss-Laguerre circular harmonic functions and the associated transform is given. Based on these properties, an efficient algorithm is developed for computing a normalized cross-correlation, in the full space of translation and rotation, between an image and template. The resulting algorithm is compared to standard spatial and frequency domain normalized cross-correlation in terms of computational complexity. The capabilities of the algorithm are illustrated in a complex scene.

Superconducting Quantum Interference Devices (SQUIDs) have made the detection of low-field (LF) and ultra-low field nuclear magnetic resonance (ULF-NMR) a reality. The latter has been proven to be a potential tool for non-destructive quality testing of horticultural products, amongst many other applications. High-Temperature Superconductor (HTS) dc SQUIDS are likely to allow for the development of not only low-cost NMR systems but also prototypes that are mobile and easily maintainable. A HTS dc SQUID was manufactured on an YBCO thin film, using a novel laser based lithography method. The lithography was implemented by a new laser system developed in-house, as a model of low-cost lithography systems. The junctions of the dc SQUID were tested and displayed normal I-V characteristics in the acceptable range for the application. In order to determine the viability of low-field NMR for non-destructive quality measurement of horticultural products, a commercial HTS dc SQUID-NMR system was used to measure quality parameters of banana during ripening. The trend of color change and sugar increase of the banana during ripening were the most highly correlated attributes to the SQUID-NMR measured parameter, average T1 (spin-lattice relaxation time). Further studies were done, that involved processing of the NMR signal into relaxation time resolved spectra. A spectral signature of banana was obtained, where each peak is a T₁ value corresponding to a proton pool, and is reported here. These results will potentially lead to deeper understanding of the quality of the samples under study.

A new electrically insensitive optical fibre link was installed between two buildings using commercially available equipment. The aim of the link was to transfer the frequency accuracy from the South African National Measure- ment Standard for Time and Frequency (derived from caesium atomic clocks) to an optical frequency comb. This enables direct traceability of optical frequency measurements to internationally verified time standards (UTC), via the timing links at the National Metrology Institute of South Africa (NMISA). A clean-up oscillator is used to improve any degrading of the stability caused by the laser link. Highly precise loop-back experiments were done to verify the accuracy and stability of the fibre link and clean-up oscillator combination. The nature and results of such experiments are presented here, in order to demonstrate the traceability of the fibre link, and therefore the traceable link between the optical frequency comb and the National Measurement Standards for Time and Frequency of South Africa.

Si Avalanche based LEDs technology has been developed in the 650 -850nm wavelength regime [1, 2]. Correspondingly, small micro-dimensioned detectors with pW/μm² sensitivity have been developed for the same wavelength range utilizing Si-Ge detector technology with detection efficiencies of up to 0.85, and with a transition frequencies of up to 80 GHz [3] A series of on-chip optical links of 50 micron length, utilizing 650 – 850 nm propagation wavelength have been designed and realized, utilizing a Si Ge radio frequency bipolar process. Micron dimensioned optical sources, waveguides and detectors were all integrated on the same chip to form a complete optical link on-chip. Avalanche based Si LEDs (Si Av LEDs), Schottky contacting, TEOS densification strategies, silicon nitride based waveguides, and state of the art Si-Ge bipolar detector technologies were used as key design strategies. Best performances show optical coupling from source to detector of up to 10GHz and - 40dBm total optical link budget loss with a potential transition frequency coupling of up to 40GHz utilizing Si Ge based LEDs. The technology is particularly suitable for application as on-chip optical links, optical MEMS and MOEMS, as well as for optical interconnects utilizing low loss, side surface, waveguide- to-optical fiber coupling. Most particularly is one of our designed waveguide which have a good core axis alignment with the optical source and yield 10GHz -30dB on-chip micro-optical links as shown in Fig 9 (c). The technology as developed has been appropriately IP protected.

There is an inherent trade-off between cost and operational integrity of microfluidic components, especially when intended for use in point-of-care devices. We present an analysis system developed to characterise microfluidic components for performing blood cell counting, enabling the balance between function and cost to be established quantitatively. Microfluidic components for sample and reagent introduction, mixing and dispensing of fluids were investigated. A simple inlet port plugging mechanism is used to introduce and dispense a sample of blood, while a reagent is released into the microfluidic system through compression and bursting of a blister pack. Mixing and dispensing of the sample and reagent are facilitated via air actuation. For these microfluidic components to be implemented successfully, a number of aspects need to be characterised for development of an integrated point-of-care device design. The functional components were measured using a microfluidic component analysis system established in-house. Experiments were carried out to determine: 1. the force and speed requirements for sample inlet port plugging and blister pack compression and release using two linear actuators and load cells for plugging the inlet port, compressing the blister pack, and subsequently measuring the resulting forces exerted, 2. the accuracy and repeatability of total volumes of sample and reagent dispensed, and 3. the degree of mixing and dispensing uniformity of the sample and reagent for cell counting analysis. A programmable syringe pump was used for air actuation to facilitate mixing and dispensing of the sample and reagent. Two high speed cameras formed part of the analysis system and allowed for visualisation of the fluidic operations within the microfluidic device. Additional quantitative measures such as microscopy were also used to assess mixing and dilution accuracy, as well as uniformity of fluid dispensing - all of which are important requirements towards the successful implementation of a blood cell counting system.

Uncooled microbolometers have become extremely popular as low cost thermal detectors used in FPAs for thermal imaging cameras. Most of the emphasis of researchers have gone towards the design and optimisation of device structures, materials, processes and readout electronics with this application in mind. However, microbolometers have the potential to be utilised towards the development of alternate applications. It is well known that the thermal conduction of microbolometers depend on the pressure surrounding the device, as this governs the dominating conduction method. This work investigates the possibility of employing a Ti thinfilm microbolometer as a low pressure sensor. A well known multi-physics simulation environment is utilised to simulate the microbolometer thermoelectric response over varied atmospheric pressure conditions. These simulation results are compared with a much simpler air pressure model than previous works using microbolometers, as well as experimental data, where the fabricated prototype showed a measured device TCR of about 0.085% K^-1 and a sensitivity of about 0:701 – 10^-9 W K^-1 Pa^-1.

The infrared band is widely used in many applications to solve problems stretching over very diverse fields, ranging from medical applications like inflammation detection to military, security and safety applications employing thermal imaging in low light conditions. At the heart of these optoelectrical systems lies a sensor used to detect incident infrared radiation, and in the case of this work our focus is on uncooled microbolometers as thermal detectors. Microbolometer based thermal detectors are limited in sensitivity by various parameters, including the detector layout and design, operating temperature, air pressure and biasing that causes self heating. Traditional microbolometers use the entire membrane surface for a single detector material. This work presents the design of a readout circuit amplifier where a dual detector element microbolometer is used, rather than the traditional single element. The concept to be investigated is based on the principle that both elements will be stimulated with a similar incoming IR signal and experience the same resistive change, thus creating a common mode signal. However, such a common mode signal will be rejected by a differential amplifier, thus one element is placed within a negative resistance converter to create a differential mode signal that is twice the magnitude of the comparable single mode signal of traditional detector designs. An instrumentation amplifier is used for the final stage of the readout amplifier circuit, as it allows for very high common mode rejection with proper trimming of the Wheatstone bridge to compensate for manufacturing tolerance. It was found that by implementing the above, improved sensitivity can be achieved.

Multiplexed or parallelised droplet microfluidic systems allow for increased throughput in the production of emulsions and microparticles, while maintaining a small footprint and utilising minimal ancillary equipment. The current paper demonstrates the design and fabrication of a multiplexed microfluidic system for producing biocatalytic microspheres. The microfluidic system consists of an array of 10 parallel microfluidic circuits, for simultaneous operation to demonstrate increased production throughput. The flow distribution was achieved using a principle of reservoirs supplying individual microfluidic circuits. The microfluidic devices were fabricated in poly (dimethylsiloxane) (PDMS) using soft lithography techniques. The consistency of the flow distribution was determined by measuring the size variations of the microspheres produced. The coefficient of variation of the particles was determined to be 9%, an indication of consistent particle formation and good flow distribution between the 10 microfluidic circuits.

Light emission from silicon is possible in CMOS through hot carrier electroluminescence. Low conversion and low extraction efficiency remains a challenge. By using existing back-end-of-line interconnect structures it is possible to improve the extraction efficiency. Such light directing structures were analysed with the use of a focused ion beam and scanning electron microscope. It was found that it is possible to improve light extraction efficiency and directionality of the light sources through a combination of back-end-of-line structures and field oxide manipulation resulting in an improved optical path for emitted photon radiation. However, further analysis indicates that total internal reflections, scattering and electromagnetic absorption from the via plugs and metal interconnects in the back-end-of-line stack are some of the key contributors to the inefficient light extraction efficiency.

In the past, high resolution thermal sensors required expensive cooling techniques making the early thermal imagers expensive to operate and cumbersome to transport, limiting them mainly to military applications. However, the introduction of uncooled microbolometers has overcome many of earlier problems and now shows great potential for commercial optoelectric applications. The structure of uncooled microbolometer sensors, especially their smaller size, makes them attractive in low cost commercial applications requiring high production numbers with relatively low performance requirements. However, the biasing requirements of these microbolometers cause these sensors to generate a substantial amount of noise on the output measurements due to self-heating. Different techniques to reduce this noise component have been attempted, such as pulsed biasing currents and the use of blind bolometers as common mode reference. These techniques proved to either limit the performance of the microbolometer or increase the cost of their implementation. The development of a low cost lock-in amplifier provides a readout technique to potentially overcome these challenges. High performance commercial lock-in amplifiers are very expensive. Using this as a readout circuit for a microbolometer will take away from the low manufacturing cost of the detector array. Thus, the purpose of this work was to develop a low cost readout circuit using the technique of phase sensitive detection and customizing this as a readout circuit for microbolometers. The hardware and software of the readout circuit was designed and tested for improvement of the signal-to-noise ratio (SNR) of the microbolometer signal. An optical modulation system was also developed in order to effectively identify the desired signal from the noise with the use of the readout circuit. A data acquisition and graphical user interface sub system was added in order to display the signal recovered by the readout circuit. The readout circuit was able to enhance the SNR of the microbolometer signal significantly. It was shown that the quality of the phase sensitive detector plays a significant role in the effectiveness of the readout circuit to improve the SNR.

Microsensing is a leading field in technology due to its wide application potential, not only in bio-engineering, but in other fields as well. Microsensors have potentially low-cost manufacturing processes, while a single device type can have various uses, and this consequently helps with the ever-growing need to provide better health conditions in rural parts of the world. Capacitive biosensors detect a change in permittivity (or dielectric constant) of a biological material, usually within a parallel plate capacitor structure which is often implemented with integrated electrodes of an inert metal such as gold or platinum on a microfluidic substrate typically with high dielectric constant. There exist parasitic capacitance components in these capacitive sensors, which have large influence on the capacitive measurement. Therefore, they should be considered for the development of sensitive and accurate sensing devices. An analytical model of a capacitive sensor device is discussed, which accounts for these parasitic factors. The model is validated with a laboratory device of fixed geometry, consisting of two parallel gold electrodes on an alumina (Al₂O₃) substrate mounted on a glass microscope slide, and with a windowed cover layer of poly-dimethyl-siloxane (PDMS). The thickness of the gold layer is 1μm and the electrode spacing is 300μm. The alumina substrate has a thickness of 200μm, and the high relative permittivity of 11.5 is expected to be a significantly contributing factor to the total device capacitance. The 155μm thick PDMS layer is also expected to contribute substantially to the total device capacitance since the relative permittivity for PDMS is 2.7. The wideband impedance analyser evaluation of the laboratory device gives a measurement result of 2pF, which coincides with the model results; while the handheld RLC meter readout of 4pF at a frequency of 10kHz is acceptable within the measurement accuracy of the instrument. This validated model will now be used for the geometric design and simulation of efficient capacitive sensors in specific biological detection applications.

Integrated circuit (IC) technology has emerged as a suitable platform for infrared (IR) detector development. This technology is however susceptible to on-chip intrinsic noise. By using double-gate MOSFETs for detectors in the near-IR band, noise performance in the readout circuitry is improved, thereby enhancing the overall performance of these detectors. A 1 dB reduction in low-frequency noise is achieved, which is verified through simulations. It is shown that by using short-channel devices that noise improvement is furthermore obtained due to reduction in threshold voltage variation. The double-gate concept is applied in simulation to the three-transistor pixel topology and can also be implemented in other detector topologies such as the four-transistor pixel topology, since readout noise is not limited to specific IR detector topologies. The overall performance of near-IR detectors and the fill factor are significantly improved.