In this paper a review is presented of light emission from forward-biased silicon diodes. After a treatment of the carrier recombination physics governing in this indirect-bandgap material, the article describes important works in this field. Then, routes are proposed for further improvement of the internal quantum efficiency for light emission. A good choice of carrier injection level will limit the impact of both Shockley-Read-Hall recombination and Auger recombination. However, the structural design of the diode has a strong influence on the overall quantum efficiency, as both surface recombination must be dealt with, and contact recombination avoided. New attributes of CMOS such as embedded SiGe offer additional opportunities for silicon LED architectures and their application.

Optical emission probabilities from silicon were analyzed by appropriate modelling, taking the silicon energy band structure, available carrier energy spread, and available carrier momentum spreads that can be realized with typical device design and operating conditions as available in current silicon technologies. The analyses showed that creation of micron-dimensioned conduction channels as made possible by using a RF bipolar fabrication process, appropriate doping and variations in the channel utilizing Boron, Phosphorous and Germanium doping, and using reversed biased junctions to energize specifically electrons, appropriately controlling carrier energy and carrier density, and control over carrier momentum through appropriate impurity scattering technology; particularly, 280nm, 650nm and 850nm emissions can be stimulated. Particularly, using p+nn and p+np+ device designs with appropriate control over carrier energy, carrier type balancing and implementing enhanced impurity scattering in some device regions, show the greatest potential to enhance these emissions. First iteration empirically conducted device realizations results show interesting peaking features and nonuniform high intensity behaviors. Particularly, it was succeeded to increase the emissions at 650nm with about two orders of magnitude. Internal electrical- to- optical conversion efficiencies of up to 10^-4 and intensity emissions of up to 200 nW μm² are derived, with further prospects to increase emissions further. The attained results compare extremely favorable, and in some cases exceeds, results as published by Venter et al, Kuindersma et al and Du Plessis et al using related technologies.

Si Av LEDs are easily integrated in on-chip integrated circuitry. They have high modulation frequencies into the GHz range and can be fabricated to sub-micron dimensions. Due to subsurface light generation in the silicon device itself, and the high refractive index differences between silicon and the device environment, the exiting light radiation has interesting dispersion characteristics. Three junction micro p+-np+ Silicon Avalanche based Light Emitting Devices (Si Av LEDs) have been analyzed in terms of dispersion characteristics, generally resulting in different wavelengths of light (colors) being emitted at different angles and solid angles from the surfaces of these devices. The emission wavelength is in the 450 - 850 nm range. The devices are of micron dimension and operate at 8 - 10V, 1μA - 2mA. The emission spot sizes are about 1 micron square. Emission intensities are up to 500 nW.μm-2. The observed dispersion characteristics range from 0.05 degrees per nm per degree at emission angle of 5 degrees, to 0.15 degrees per nm at emission angles of 30 degrees. It is believed that the dispersion characteristics can find interesting and futuristic on-chip electro-optic applications involving particularly a ranging from on chip micro optical wavelength dispersers, communication de-multiplexers, and novel bio-sensor applications. All of these could penetrate into the nanoscale dimensions.

This paper investigates the avalanche electroluminescence characteristics of pn junctions formed in silicon nanowires fabricated in a silicon-on-insula*tor (SOI) technology. Since carriers are confined to the nanowires, it is possible to study the effect of electric field strength on device performance while the current density and carrier concentrations are kept constant. This is achieved by varying the nanowire length while keeping the bias current constant, eventually driving the pn junction into the reach-through bias condition. It is observed that photon emission for photon energies higher than 1.2 eV increases when the nanowire length is reduced, while photon emission with energies less than 1.2 eV decreases. The higher electric field in the nanowire at shorter nanowire lengths enhances the high-energy photon emission and attenuates the low energy photon emission.

Nanostructured semiconducting carbon system, described by as a superlattice-like structure demonstrated its potential in switching device applications based on the quantum tunneling through the insulating carbon layer. This switching property can be enhanced further with the association of Josephson’s tunneling between two superconducting carbon (diamond) grains separated by a very thin layer of carbon which holds the structure of the film firmly. The superconducting nanodiamond heterostructures form qubits which can lead to the development of quantum computers provided the effect of disorder present in these structure can be firmly understood. Presently we concentrate on electrical transport properties of heavily boron–doped nanocrystalline diamond films around the superconducting transition temperature measured as a function of magnetic fields and the applied bias current. Microstructure of these films is described by a two dimensional superlattice system which can also contain paramagnetic impurities. We report observation of anomalous negative Hall resistance in these films close to the superconductor-insulator-normal phase transition in the resistance versus temperature plots at low bias currents at zero and low magnetic field. The negative Hall effect is found to be suppressed as the bias current increase. Magnetoresistance study shows a distinct peak at zero field when measured in the low current regimes which suggest a superconductor-insulator-superconductor structure of films. Current vs. voltage characteristics show signature of π-Josephson like behaviour which can give rise to a characteristic frequency of several hundred of gigahertz. Signature of spin flipping also shows novel spintronic device applications.

In this paper we report on the fabrication of a spintronic device based on multiwalled carbon nanotubes functionalized/coupled with a rare earth element complex. The spin valve behavior is verified by magneto-resistance fluctuations at low temperatures. We report the magneto-transport features of spin valve devices based on multiwalled carbon nanotube covalently functionalized with a gadolinium complex. The switching is encoded in the composite from which devices are fabricated by di-electrophoresis. The magnetic field dependent electronic transport characteristics are investigated through the Cryogenic high field measurement system at 300 mK. Structural characterization of the material through transmission and scanning electron microscopy and Raman spectroscopy of the pristine and composite is done. The electronic transport shows a magnetic field dependence which is characteristic of spin valve at 300 mK and furthermore this spin valve feature is temperature dependent.

We utilize nano-manipulting probes for the fabrication of a range of devices including multilayered graphene coplanar waveguides, suspended multilayered graphene hall bars and air-gap single crystal organic field effect transistors. We find that devices fabricated using this technique are of high quality and can be used to probe not only application based phenomena (such as transistor behaviour), but also fundamental quantum transport properties. Magnetoresistance measurements show that the multilayered graphene devices exhibit either quantum linear magnetoresistance (QLMR) or Shubnikov de-Haas oscillations depending on the topology (i.e. either wrinkled or smooth) of the graphene sheet. From this data we calculate the carrier density (ns) in the wrinkled graphene to be in the range 5.2 × 10⁹ cm^-2 (at B~0) to 3.5 × 10¹³ cm^-2 (at B=12 T) with effective masses of 0.001m_e and 0.121m_e, respectively. The smooth multilayer graphene devices have a carrier density 1.39 - 2.85 × 10¹² cm^-2 and effective mass (0.022m_e ≤ m*≤ 0.032m_e) as calculated from the analysis of the Shubnokov de-Haas oscillations. The high frequecny coplanar waveguide devices fabricated using this technique demonstrated high transmission up to 50 GHz, highlighting the potential for HF application. Organic field effect transistors were also fabricated using the manipulation technique, the transfere characteristics were measured, it was found that the devcies with channel length of 1 μm have non-linear transfere characterisitcs and pass a maximum current of between 0.1 and 10 nA. These OFET devices showed pronounced switching behaviour with mobilities of up to 3 cm²V^-1s^-1 in the best devices.

A multi-sensor application specific integrated circuit has been developed with a number of sensors: capacitive, inductive, magnetic, ambient light, infrared and acceleration. The capacitive sensing is implemented using a unique, patented, charge transfer technique allowing the measurement of very small capacitances while at the same time eliminating the effects of unwanted parasitic capacitances in the measurement circuit. For cost effective implementation the charge transfer measurement circuit has been has been modified, augmented and expanded to not only measure capacitance but also to act as the measurement circuit for all the sensors. Enabling the multi-sensor chip to measure acceleration on a range of MEMs accelerometer chips including a single axis accelerometer, a dual axis xy accelerometer and a z-axis accelerometer, innovative and patent pending techniques have been developed and implemented on standard CMOS. The CMOS ASIC and a MEMs chip will be double bonded in a plastic package offering multi-sensor capability in a small low cost package.

Nowadays, thin-film transistors (TFTs) are being actively researched not only by the scientific community but also by the industry. They are the crucial elements for the driving currents in flexible displays, radio frequency identification tags and wearable electronic skins. In this study, we present a low-cost integration process of ZnO nanoparticle TFTs on flexible substrates with a maximum process temperature limited to 115 °C. As gate dielectric a high-k resin filled with TiO₂ nanoparticle was used. This nanocomposite combines the mechanical flexibility of organic compounds with the high dielectric permittivity of inorganic materials. For the stabilization of the nanoparticulated ZnO film, a high humidity treatment was performed subsequent to an ultra-violet irradiation step in order to prevent the adsorption of oxygen molecules by the nanoparticles. The transistor integration process was performed on a freestanding polyethylene terephthalate (PET) substrate. This technique enables a more realistic scenario for a later large-scale production and avails adequate photolithographic resolution and accurate alignment between different mask levels. Additionally, in order to improve the electrical properties of the nanoparticulated semiconducting film, the nanoparticles were deposited using either spin-coating or spray-coating techniques; furthermore, different surface pretreatments were executed.

This paper presents an extensive overview and a comparison of the most popular models used to make an analytic prediction of the thermal conductance of uncooled microbolometers. The concept of an uncooled microbolometer has existed for many decades, along with simple methods to determine the thermal conduction both under vacuum and at atmospheric conditions. However, recent advances and the maturation of the MEMS fabrication technology have sparked a renewed research interest in these devices, including a number of improvements in the analytic modelling of the thermoelectric interaction, notably also improvements in the prediction of the thermal conduction. A comparison is made between a number of recent techniques, adapted for either thin-film metal or semiconductor type detector materials, operating either at vacuum conditions or atmospheric pressure conditions, as well as adjustable pressure conditions. The approach followed in the work is to determine the various parameters by means of the proposed analytic methods, which is then compared to multiphysics FEM simulation results. This comparison provides essential information regarding the shortcomings of the traditional methods. Finally, the results are also compared with experimentally extracted results from manufactured devices. The last set of results offer insight into manufacturing deviation. It is shown that the traditional methods often suffer from a significant error, sometimes in the region of almost 40%, in the prediction of the thermal conductance, which can be largely removed by using the appropriate modified analytic model.

We present a method for the development of paper-based electrochemical sensors for detection of heavy metals in water samples. Contaminated water leads to serious health problems and environmental issues. Paper is ideally suited for point-of-care testing, as it is low cost, disposable, and multi-functional. Initial sensor designs were manufactured on paper substrates using combinations of inkjet printing and screen printing technologies using silver and carbon inks. Bismuth onion-like carbon nanoparticle ink was manufactured and used as the active material of the sensor for both commercial and paper-based sensors, which were compared using standard electrochemical analysis techniques. The results highlight the potential of paper-based sensors to be used effectively for rapid water quality monitoring at the point-of-need.

In this work, glassy carbon electrodes are functionalised with alkynyl substituted phthalocyanines via electrografting and click chemistry as well as with quantum dots (QDs)-phthalocyanine conjugates via adsorption. The use of click chemistry and the addition of QDs is to try observe improvements in the electrocatalytic behaviour of electrocatalyst compared to similar electrocatalysts in literature. The electrografting and click chemistry methods provide greater molecule stability on the substrate surface due to the covalent bonds formed. Results show that these methods of electrode fabrication do improve the functionality of the electrocatalysts.

In this work, we have demonstrated a dual fibre Bragg grating (FBG) sensor for a temperature-insensitive chemical concentration or refractive index sensor by etching the cladding of one of the FBGs. The dual FBG sensor was used to measure different solution concentrations of glycerol in water. The sensor showed sensitivities of 2.13×10^-3 and 2.28×10^-3 at 85% and 0% (pure water) glycerol solution concentrations, respectively. The dual FBG sensors demonstrate that it can be used to detect chemical or biological changes in the surrounding media by measuring the Bragg wavelength and reflectivity differences between the dual FBG’s reflection spectrum peaks.

This paper presents the design of a low-complexity, linear and sub-pF CMOS capacitance-frequency converter for reading out a capacitive bacterial bio/sensors with the endeavour of creating a universal bio/sensor readout module. Therefore the priority design objectives are a high resolution as well as an extensive dynamic range. The circuit is based on a method which outputs a digital frequency signal directly from a differential capacitance by the accumulation of charges produced by repetitive charge integration and charge preservation1. A prototype has been designed for manufacture in the 0.35 μm, 3.3V ams CMOS technology.

At a 1MHz clock speed, the most pertinent results obtained for the designed converter are: (i) power consumption of 1.37mW; (ii) a resolution of at least 5 fF for sensitive capacitive transduction; and (iii) an input dynamic range of at least 43.5 dB from a measurable capacitance value range of 5 – 750 fF (iv) and a Pearson’s coefficient of linearity of 0.99.

The presence of Escherichia coli (E. coli ) is a commonly used indicator micro-organism to determine whether water is safe for human consumption.¹ This paper discusses the design of a micro-incubator that can be applied to concentrate bacteria prior to environmental water quality screening tests. High sensitivity and rapid test time is essential and there is a great need for these tests to be implemented on-site without the use of a laboratory infrastructure. In the light of these requirements, a mobile micro-incubator was designed, manufactured and characterised. A polydimethylsiloxane (PDMS) receptacle has been designed to house the 1-5 ml cell culture sample.² A nano-silver printed electronics micro-heater has been designed to incubate the bacterial sample, with an array of temperature sensors implemented to accurately measure the sample temperature at various locations in the cell culture well. The micro-incubator limits the incubation temperature range to 37±3 °C in order to ensure near optimal growth of the bacteria at all times.³ The incubation time is adjustable between 30 minutes and 9 hours with a maximum rise time of 15 minutes to reach the set-point temperature. The surface area of the printed nano silver heating element is 500 mm². Electrical and COMSOL Multiphysics simulations are included in order to give insight on micro-incubator temperature control. The design and characterization of this micro-incubator allows for further research in biosensing applications.

Cooling and ventilation systems play an important role in human occupied spaces. However, cooling using reversible air conditioners systems pollutes the environment and consumes a significant amount of energy. With global warming that experiences our environment, the large consumption of electrical energy and the operating instructions for reversible air conditioners, there is a need to find alternatives to those cooling systems. Hence this research project aims to investigate an air storage system, a microsystem reversible ventilation system using natural atmospheric air (renewable energy) for cooling at low consumption of energy. For the variation of the temperature range of comfort due to thermal heat produces by occupants, equipment and environment, an optimal transient automatic regulation of air flow as to be design in order to maintain the temperature of comfort in occupied spaces during peak hours.

Research on affordable point-of-care health diagnostics is rapidly advancing¹. Colorimetric biosensor applications are typically qualitative, but recently the focus has been shifted to quantitative measurements^2,3. Although numerous qualitative point-of-care (POC) health diagnostic devices are available, the challenge exists of developing a quantitative colorimetric array reader system that complies with the ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, Deliverable to end-users) principles of the World Health Organization⁴.

This paper presents a battery powered 8-bit tonal resolution colorimetric sensor circuit for paper microfluidic assays using low cost photo-detection circuitry and a low-power LED light source. A colorimetric 3×3-pixel array reader was developed for rural environments where resources and personnel are limited. The device sports an ultralow-power E-ink paper display. The colorimetric device includes integrated GPS functionality and EEPROM memory to log measurements with geo-tags for possible analysis of regional trends.

The device competes with colour intensity measurement techniques using smartphone cameras, but proves to be a cheaper solution, compensating for the typical performance variations between cameras of different brands of smartphones. Inexpensive methods for quantifying bacterial assays have been shown using desktop scanners, which are not portable, and cameras, which suffer severely from changes in ambient light in different environments. Promising colorimetric detection results have been demonstrated using devices such as video cameras⁵, digital colour analysers⁶, flatbed scanners⁷ or custom portable readers8. The major drawback of most of these methods is the need for specialized instrumentation and for image analysis on a computer.

We present an ultra-high frequency radio frequency identification based wireless communication set-up for paper-based point-of-care diagnostic applications, based on a sensing radio frequency identification chip. Paper provides a low-cost, disposable platform for ease of fluidic handling without bulky instrumentation, and is thus ideally suited for point-ofcare applications; however, result communication – a crucial aspect for healthcare to be implemented effectively – is still lacking. Printing of radio frequency identification antennas and electronic circuitry for sensing on paper are presented, with read out of the results using a radio frequency identification reader illustrated, demonstrating the feasibility of developing integrated, all-printed solutions for point-of-care diagnosis in resource-limited settings.

Key issues for flexible complementary electronics are low temperature processing, sufficient performance of the integrated p- and n-type FET devices, and cheap semiconducting and dielectric materials. Organic semiconductors commonly depict p-type behavior, whereas metal oxide semiconductors show n-type characteristics. This paper presents a new approach for common integration of organic and ZnO transistors on transparent substrates for complementary transistor electronics. The gate dielectric consists of a special high-k resin, the metallization utilizes Au and Al films. The thermal budget for processing of the devices is limited to 120°C to enable foil substrates.

This paper describes the development and optimisation of a paper-based E. coli impedimetric biosensor for water quality monitoring. Impedimetric biosensing is advantageous because it is a highly sensitive, label-free, real-time method for the detection of biological species. An impedimetric biosensor measures the change in impedance caused by specific capture of a target on the sensor surface. Each biosensor consists of a pair of photo paper-based inkjet printed electrodes. An impedance analyser was used to measure the impedance at frequencies ranging from 1 kHz to 1 MHz at 1V.

The parameters that were investigated to achieve enhanced sensor performance were buffer type, antibody attachment method, measurement frequency, electrode layout, and conductive material. A 0.04M PBS (phosphate buffered saline) solution achieves better results compared to a less conductive 0.04M PB (potassium phosphate dibasic) solution. The direct adsorption of anti-E. coli antibodies onto the sensor surface yielded better results than attaching the sensor to a lateral flow test. The resistive component had a greater impact on the detected impedance, therefore an optimal frequency of 1 MHz was identified. Geometrical electrode designs that maximise the resistive change between the electrodes were utilised. Both lower cost silver and bio-compatible gold ink were validated as electrode materials. The impedance change generated by the selective capture of E. coli K-12, ranging in concentration from 10³ to 10⁷ colony forming units per millilitre (cfu/ml), showed a detection limit of 10⁵ cfu/ml.

Piezo-acoustic distance tracking sensors have challenges of reporting true distance readings. Challenges include directional anisotropy signal loss in transmission power and in receiver sensitivity, distance-related attenuation of signal and the phase shifts that result in jittery values, some preceding, and others succeeding the expected distance readings. There also exist signal time losses arising from dead time associated with processor latency, with carrier signal pulse length and with voltage rise-time delays in pulse detection. Together these factors cause distance under-reporting, and more critically, makes each reported value uncertain, which is unacceptable in distance-critical applications.

Piezo-inertial accelerometers have equivalent if not more severe challenges in tri-axial configurations, for instance where a rotational tilt may happen under linear accelerative force. In the absence of tensor component adaptation to change of orientation, signal is lost until the next axial sensor detects it.

Study paper focusses on piezo-acoustic transducers UCD1007 and 400SR160 (40kHz), used in a face-to-face configuration over a 600mm range. Within that range 10 successive phase shift wave fronts were identified, but it took 15 reconstructed wave fronts to uniquely identify a continuous end-to-end jitter-free and slippage-free kinematic data stream from the jittery sensor data. The additional 5 degrees of freedom were consumed by the 5-stage filter applied. The technique has remarkable combinatorial and projective geometry implications for digital sensor design. It is possible for the procedure to be applicable in 3-axis accelerometers and adapted into firmware for truly kinematic device driver interfaces so long as the reporting rates are matched with the user interface refresh rates.

It is shown that acoustic transducer sensors require phase loop locking for kinematic continuity whereas gravimetric accelerometers demand better measurement time consistence in sensor values for induced kinematic phase locking.

Near infrared (NIR) spectroscopy has gained extensive use in quality evaluation. It is arguably one of the most advanced spectroscopic tools in non-destructive quality testing of food stuff, from measurement to data analysis and interpretation. NIR spectral data are interpreted through means often involving multivariate statistical analysis, sometimes associated with optimisation techniques for model improvement. The objective of this research was to explore the extent to which genetic algorithms (GA) can be used to enhance model development, for predicting fruit quality.

Apple fruits were used, and NIR spectra in the range from 12000 to 4000 cm^-1 were acquired on both bruised and healthy tissues, with different degrees of mechanical damage. GAs were used in combination with partial least squares regression methods to develop bruise severity prediction models, and compared to PLS models developed using the full NIR spectrum.

A classification model was developed, which clearly separated bruised from unbruised apple tissue. GAs helped improve prediction models by over 10%, in comparison with full spectrum-based models, as evaluated in terms of error of prediction (Root Mean Square Error of Cross-validation). PLS models to predict internal quality, such as sugar content and acidity were developed and compared to the versions optimized by genetic algorithm. Overall, the results highlighted the potential use of GA method to improve speed and accuracy of fruit quality prediction.

This paper covers the design of a complementary metal oxide semiconductor (CMOS) pixel readout circuit with a built-in frequency conversion feature. The pixel contains a CMOS photo sensor along with all signal-to-frequency conversion circuitry. An 8×8 array of these pixels is also designed. Current imaging arrays often use analog-to-digital conversion (ADC) and digital signal processing (DSP) techniques that are off-chip¹. The frequency modulation technique investigated in this paper is preferred over other ADC techniques due to its smaller size, and the possibility of a higher dynamic range. Careful considerations are made regarding the size of the components of the pixel, as various characteristics of CMOS devices are limited by decreasing the scale of the components².

The methodology used was the CMOS design cycle for integrated circuit design. All components of the pixel were designed from first principles to meet necessary requirements of a small pixel size (30×30 μm²) and an output resolution greater than that of an 8-bit ADC. For the photodetector, an n⁺-p⁺/p-substrate diode was designed with a parasitic capacitance of 3 fF. The analog front-end stage was designed around a Schmitt trigger circuit. The photo current is integrated on an integration capacitor of 200 fF, which is reset when the Schmitt trigger output voltage exceeds a preset threshold. The circuit schematic and layout were designed using Cadence Virtuoso and the process used was the AMS CMOS 350 nm process using a power supply of 5V.

The simulation results were confirmed to comply with specifications, and the layout passed all verification checks. The dynamic range achieved is 58.828 dB per pixel, with the output frequencies ranging from 12.341kHz to 10.783 MHz. It is also confirmed that the output frequency has a linear relationship to the photocurrent generated by the photodiode.

Electrochemical biosensing is used to detect specific analytes in fluids, such as bacterial and chemical contaminants. A common implementation of an electrochemical readout is a potentiostat, which usually includes potentiometric, amperometric, and impedimetric detection. Recently several researchers have developed small, low-cost, single-chip silicon-based potentiostats. With the advances in heterogeneous integration technology, low-power potentiostats can be implemented on paper and similar low cost substrates. This paper deals with the design of a low-power paper-based amperometric front-end for a low-cost and rapid detection environment. In amperometric detection a voltage signal is provided to a sensor system, while a small current value generated by an electrochemical redox reaction in the system is measured. In order to measure low current values, the noise of the circuit must be minimized, which is accomplished with a pre-amplification front-end stage, typically designed around an operational amplifier core. An appropriate circuit design for a low-power and low-cost amperometric front-end is identified, taking the heterogeneous integration of various components into account. The operational amplifier core is on a bare custom CMOS chip, which will be integrated onto the paper substrate alongside commercial off-the-shelf electronic components.

A general-purpose low-power two-stage CMOS amplifier circuit is designed and simulated for the ams 350 nm 5 V process. After the layout design and verification, the IC was submitted for a multi-project wafer manufacturing run. The simulated results are a bandwidth of 2.4 MHz, a common-mode rejection ratio of 70.04 dB, and power dissipation of 0.154 mW, which are comparable with the analytical values.

Applications for diagnostic and environmental point-of-need require processes and building blocks to add smart features to disposable biosensors on low-cost substrates. A novel method for producing such biosensors is printing electronics using additive technologies. This work contributes to the toolbox of processes, materials and components for printed electronics manufacturing - as well as rapid prototyping - of circuits.

Printing protocols were developed to facilitate successful inkjet printing of nanosilver ink (Harima NPS-JL) onto different microsystem substrates using a functional printer (Dimatix DMP-3281). Photo paper is a standard inkjet substrate, which were compared with glass, polycarbonate (PC), plastic projector transparency foil, and polydimethylsiloxane (PDMS). Comparison attributes include physical and electrical properties. The layout design comprised dogbone elements of 8 mm length, and widths varying between 100 μm and 2 mm. All printed features were thermally cured for 1 hour at 120 °C.

The physical characteristics were measured with a laser scanning microscope (Zeiss LSM-5) to determine the width, thickness and surface roughness of the printed features. An LCR meter (GW-Instek 8110) was used to measure the printed structures’ electrical characteristics (resistance, capacitance and inductance). A lumped element model and layout design rules were extracted to assist in standardized design procedures. The model incorporates prediction of the bandwidth attainable with these structures.

The layer thickness on all substrates is larger than the 1 μm on photo paper, and varies between 1.6 μm (PC) and 7 μm (PDMS). The spreading for PDMS is similar to photo paper, but since for the other substrates it is between 5 (glass) and 10 (PC) times larger than for photo paper, the layout design rules require large spacing, leading to larger area networks. Electrical probing on the PDMS is not consistent and results are inconclusive. For the other substrates, the comparative dogbone resistance (100 μm width) is significantly larger than the 2 Ω standard, varying from 12.6 Ω (PC) to 19.3 Ω (glass). The bandwidth relative to photo paper is smaller by a factor of between 6 (PC) and 9.5 (glass).

Low-cost and non-invasive diabetes diagnosis is increasingly important [1], and this paper presents a handheld readout system for chemiresistive gas sensors in a breath acetone diagnostic application.

The sensor contains reference and detection devices, used for the detection of gas concentration. Fabrication is by dropcasting a metaloxide nanowire solution onto gold interdigitated electrodes, which had been manufactured on silicon. The resulting layer is a wide bandgap n-type semiconductor material sensitive to acetone, producing a change in resistance between the electrode terminals [2]. Chemiresistive sensors typically require temperatures of 300-500 °C, while variation of sensing temperature is also employed for selective gas detection. The nano-structured functional material requires low temperatures due to large surface area, but heating is still required for acceptable recovery kinetics. Furthermore, UV illumination improves the sensor recovery [3], and is implemented in this system. Sensor resistances range from 100 Ω to 50 MΩ, while the sensor response time require a sampling frequency of 10Hz.

Sensor resistance depends on temperature, humidity, and barometric pressure. The GE CC2A23 temperature sensor is used over a range of -10°C to 60°C, the Honeywell HIH5031 humidity sensor operates up to 85% over this temperature range, and the LPS331AP barometric pressure sensor measures up to 1.25 bar. Honeywell AWM43300V air flow sensors monitor the flow rate up to 1000 sccm. An LCD screen displays all the sensor data, as well as real time date and time, while all measurements are also logged in CSV-format. The system operates from a rechargeable battery.

A comprehensive model for staring array simulation is described. The model covers all effects from photon signal generation through to detection and processing in the staring array sensor. The model follows the signal flow from photon generation, through a staring focal plane array (FPA) from the detector, through several conversions in the read out integrated circuit (ROIC) and finally conversion to a digital signal. Spatial nonuniformity modeling for photoresponse, dark current generation and source follower offset is included. The list of noise sources includes: photon noise, quantum conversion uncertainty, dark noise, kTC noise, source follower noise and quantization noise. Several components with (simplified) nonlinear responses are also modeled: sense node capacitance variation with charge, source follower nonlinearity and nonlinearity in the digital conversion. The code implementations take images as input, applying the various processes independently on individual pixels (e.g., shot noise) or on complete images (e.g., spatial nonuniformity). Some noise sources vary temporally across frames (shot, thermal, kTC) while other noise sources are fixed across frames (fixed pattern noises). The application of the model is demonstrated by tracing the signal path from source to sensor output, with intermediate results along the path. The model is implemented in Python (as part of the pyradi open source computational radiometry module) and in a C++ image simulation. The purpose with this work is to predict what the performance of a given sensor will be in terms of image appearance, given the devices specifications and key design parameters. The execution of this work lead to the important recommendation that nonuniformity correction for infrared sensors should be performed at well fill levels corresponding to the minimum and maximum in the scene, not to fixed percentage levels in the charge well.

The objective with this work is to provide a `generic' model that can be adapted by adjusting model parameters. For more accurate modeling of specific sensors, dedicated models should be developed, but for all but the most demanding requirement, this model should be adequate in scope of detail and freedom of characteristics.

A distributed temperature fiber sensor based on the ratio of the Raman anti-Stokes to Rayleigh backscattered light components was investigated. The aim of the study was to propose a method of quantifying the interferometric noise exhibited in the Rayleigh backscattered signal and use correlation coding techniques to increase the signal-to-noise ratio noise in the Raman-Rayleigh backscattered signal.

Optical pulse correlation codes, namely uniform amplitude random duty cycle and random amplitude random duty cycle, were implemented to quantify the interferometric noise. Both correlating coding techniques were compared and evaluated in a Raman-Rayleigh distributed temperature fiber sensor. The uniform amplitude random duty cycle correlation code technique showed better performance in terms of signal to noise ratio compared to the random amplitude random duty cycle technique as well as increasing the number of averaged traces for each technique.

Materials with combined ferroelectric and ferromagnetic properties or magneto-electric coupling effects are promising candidates for information technology, photosensoring, and device fabrication. Preparation and characterization of multiferroic materials in which ferroelectricity and ferromagnetism coexist attracted much interest in research for functionalized materials and devices. They present a possibility to electrically control magnetic memory devices and, conversely, magnetically manipulate electric devices. In this work we considered Fe₃O₄ magnetic nanoparticles with and without a protective SiO₂/TiO₂ double-layer coating embedded into the carbazole-based, namely, polyepoxypropylcarbazole (PEPC) thin (500 nm) film. Optical characterization of the PEPC films was performed using light irradiation in the UV/VIS and NIR ranges. A shift in the optical absorption edge toward a higher wavelength region of the spectrum took place for all irradiated samples: the polymer film, as well as for the samples with Fe₃O₄ and Fe₃O₄/SiO₂/TiO₂ nanoparticles inside of the polymer matrix. We suggest that changes in the UV/VIS/NIR spectra took place as a function of the degree of structural changes and stabilizing of the atomic matrix, as well as due to change in the values of the refractive index following irradiation, calculated from the spectral data. In such a way photo-structural modifications induced by the UV irradiation and the implantation of the magnetic nanoparticles make these materials perspective for optical recording media. We conclude, therefore, that Fe₃O₄ and Fe₃O₄/SiO₂/TiO₂ nanoparticles considerably affect the optical properties of the PEPC thin film, and result in the enhancement of the photodarkening effect following the UV irradiation.

We investigate the selection of a flat-top beam and a Gaussian beam inside a laser cavity on opposing mirrors. The concept is tested external to the laser cavity in a single pass and double pass regime where the latter mimics a single round trip in the laser. We implement this intra-cavity selection through the use of two 16 level diffractive optical elements. We consider a solid-state diode side-pumped laser resonator in a typical commercial laser configuration that consists of two planar mirrors where the DOEs are positioned at the mirrors. We out couple the Gaussian and flat-top distributions and we show that we improve the brightness of the laser with active mode control. We also demonstrate that the quality of the beam transformations determine the brightness improvement.

We show how one can determine the various properties of light, from the modal content of laser beams to decoding the information stored in optical fields carrying orbital angular momentum, by performing a modal decomposition. Although the modal decomposition of light has been known for a long time, applied mostly to pattern recognition, we illustrate how this technique can be implemented with the use of liquid-crystal displays. We show experimentally how liquid crystal displays can be used to infer the intensity, phase, wavefront, Poynting vector, and orbital angular momentum density of unknown optical fields. This measurement technique makes use of a single spatial light modulator (liquid crystal display), a Fourier transforming lens and detector (CCD or photo-diode). Such a diagnostic tool is extremely relevant to the real-time analysis of solid-state and fibre laser systems as well as mode division multiplexing as an emerging technology in optical communication.

For the first time, we demonstrate, VCSEL-to-VCSEL wavelength conversion within the low attenuation 1550 nm window, including transmission over fibre and bit error rate (BER) performance characterization. We experimentally demonstrate a low injection power optical wavelength conversion by injecting an optical beam from a signal carrier master vertical cavity surface-emitting laser (VCSEL) into the side-mode of the slave VCSEL. This technique solves the challenge of wavelength collisions and also provides wavelength re-use in typical wavelength division multiplexed (WDM) systems. This paper, for the first time, uses two 1550 nm VCSELs with tunability range of 3 nm for a 5-9.8 mA bias current. The master VCSEL is modulated with a non-return-to-zero (NRZ) pseudo-random binary sequence (PRBS_2⁷-1) 8.5 Gb/s data. A data conversion penalty of 1.1 dB is realized when a 15 dBm injection beam is used. The transmission performance of the converted wavelength from the slave VCSEL is evaluated using BER measurement at a 10^-9 threshold. A 0.5 dB transmission penalty of the converted wavelength data is realized in an 8.5 Gb/s transmission over 24.7 km. This work is vital for optical fibre systems that may require wavelength switching for transmission of data signals.

Laser frequency stabilisation in the telecommunications band was realised using the Pound-Drever-Hall (PDH) error signal. The transmission spectrum of the Fabry-Perot cavity was used as opposed to the traditionally used reflected spectrum. A comparison was done using an analogue as well as a digitally implemented system. This study forms part of an initial step towards developing a portable optical time and frequency standard.

The frequency discriminator used in the experimental setup was a fibre-based Fabry-Perot etalon. The phase sensitive system made use of the optical heterodyne technique to detect changes in the phase of the system. A lock-in amplifier was used to filter and mix the input signals to generate the error signal. This error signal may then be used to generate a control signal via a PID controller. An error signal was realised at a wavelength of 1556 nm which correlates to an optical frequency of 1.926 THz. An implementation of the analogue PDH technique yielded an error signal with a bandwidth of 6.134 GHz, while a digital implementation yielded a bandwidth of 5.774 GHz.

In this work, the frequency response of a single-element, direct band gap indium gallium arsenide (In0.53Ga0.47As) infrared photo-detector on a lattice matched indium phosphide (InP) substrate is investigated by varying the intrinsic layer doping concentration. The intrinsic device operation and transport physics are theoretically determined and simulated. The epitaxial layer structure, physical dimensions, doping profiles and carrier concentrations are modelled for a complete PIN photodetector with cut-off wavelength of 1680 nm at 295 K. The calculated and simulated device performance parameters are based on the responsivity, quantum efficiency, dark-current in reverse-biased operation, frequency bandwidth and intrinsic junction capacitance. These parameters are also measured and the frequency response is determined by a low-power 1064 nm neodymium-doped yttrium aluminium garnet (Nd:YAG) pulsed laser at the output of a high-gain transimpedance amplifier. The shortest measurable pulse rise-time for this configuration is 12.4 ns. The dark-current, frequency response and intrinsic junction capacitance results are used to represent the equivalent circuit model of the photodetector at the input of the transimpedance amplifier. The primary goal is to identify the variations in performance based on the intrinsic layer composition, manufacturing considerations and epitaxial enhancements to improve the bandwidth of such a device.

An optical fiber based laser radar time transfer system has been developed for the 64-dish MeerKAT radiointerferometer telescope project to provide accurate atomic time to the receivers of the telescope system. This time transfer system is called the Karoo Array Timing System (KATS). Calibration of the time transfer system is essential to ensure that time is accurately transferred to the digitisers that form part of the receivers. Frequency domain reflectometry via vector network analysers is also used to verify measurements taken using time interval counters. This paper details the progress that is made in the verification measurements of the system in order to ensure that time, accurate to within a few nanoseconds of the Universal Coordinated Time (UTC, is available at the point where radio signals from astronomical sources are received. This capability enables world class transient and timing studies with a compact radio interferometer, which has inherent advantages over large single dish radio-telescopes, in observing the transient sky.

Wildland fires are a widespread, seasonal and largely man-made hazard which have a broad range of negative effects. These wildfires cause not only the destruction of homes, infrastructure, cultivated forests and natural habitats but also contribute to climate change through greenhouse gas emissions and aerosol particle production. Global satellite-based monitoring of biomass burning using thermal infrared sensors is currently a powerful tool to assist in finding ways to establish suppression strategies and to understand the role that fires play in global climate change. Advances in silicon-based camera technology present opportunities to resolve the challenge of ubiquitous wildfire early detection in a cost-effective manner. This study investigated several feasibility aspects of detecting wildland fires using near-infrared (NIR) spectral line emissions from electronically excited potassium (K) atoms at wavelengths of 766.5 and 769.9 nm, during biomass burning.

Aerosol attenuation in the atmosphere has a relatively weak spectral variation compared to molecular absorption. However, the solar spectral irradiance differs considerably for the sun at high zenith angles versus the sun at low zenith angles. The perceived color of a sunlit object depends on the object's spectral reflectivity as well as the irradiance spectrum. The color coordinates of the sunlit object, hence also the color balance in a scene, shift with changes in the solar zenith angle. The work reported here does not claim accurate color measurement. With proper calibration mobile phones may provide reasonably accurate color measurement, but the mobile phones used for taking these pictures and videos are not scientific instruments and were not calibrated. The focus here is on the relative shift of the observed colors, rather than absolute color. The work in this paper entails the theoretical analysis of color coordinates of surfaces and how they change for different colored surfaces. Then follows three separate investigations: (1) Analysis of a number of detailed atmospheric radiative transfer code (Modtran) runs to show from the theory how color coordinates should change. (2) Analysis of a still image showing how the colors of two sample surfaces vary between sunlit and shaded areas. (3) Time lapse video recordings showing how the color coordinates of a few surfaces change as a function of time of day. Both the theoretical and experimental work shows distinct shifts in color as function of atmospheric conditions. The Modtran simulations demonstrate the effect from clear atmospheric conditions (no aerosol) to low visibility conditions (5 km visibility). Even under moderate atmospheric conditions the effect was surprisingly large. The experimental work indicated significant shifts during the diurnal cycle.

Silicon-germanium (SiGe) bipolar complementary metal-oxide semiconductor (BiCMOS) transistors have vertical doping profiles reaching deeper into the substrate when compared to lateral CMOS transistors. Apart from benefiting from high-speed, high current gain and low-output resistance due to its vertical profile, BiCMOS technology is increasingly becoming a preferred technology for researchers to realise next-generation space-based optoelectronic applications. BiCMOS transistors have inherent radiation hardening, to an extent predictable cryogenic performance and monolithic integration potential.

SiGe BiCMOS transistors and p-n junction diodes have been researched and used as a primary active component for over the last two decades. However, further research can be conducted with diode-connected heterojunction bipolar transistors (HBTs) operating at cryogenic temperatures. This work investigates these characteristics and models devices by adapting standard fabrication technology components.

This work focuses on measurements of the current-voltage relationship (I-V curves) and capacitance-voltage relationships (C-V curves) of diode-connected HBTs. One configuration is proposed and measured, which is emitterbase shorted. The I-V curves are measured for various temperature points ranging from room temperature (300 K) to the temperature of liquid nitrogen (77 K). The measured datasets are used to extract a model of the formed diode operating at cryogenic temperatures and used as a standard library component in computer aided software designs.

The advantage of having broad-range temperature models of SiGe transistors becomes apparent when considering implementation of application-specific integrated circuits and silicon-based infrared radiation photodetectors on a single wafer, thus shortening interconnects and lowering parasitic interference, decreasing the overall die size and improving on overall cost-effectiveness. Primary applications include space-based geothermal radiation sensing and cryogenic terahertz radiation sensing.

To synchronise the elements of a radio interferometer array, a phase stable reference frequency from a central clock is disseminated to the different elements of array. The reference frequency is modulated onto an optical carrier and transported over optical fibre over a distance of up to 12 km. For radio interferometric efficiency, the propagation delay of the transferred reference frequency is required to be stable to less than 3 picoseconds (ps) over 20 minutes. To enable this, the optical fibre transmission line is thermally shielded to minimise length changes due to thermal expansion and contraction on the optical fibre. A test setup and procedure, that measures propagation delay changes to the required accuracy and precision, is required to verify the efficiency of the thermal shielding on the installed optical fibre. This paper describes a method using photonic and radio frequency (RF) components together with an RF vector network analyser (VNA) and post-processing to measure changes in propagation delay on the optical fibre link to sub-picosecond levels. The measurement system has been tested to a stability of < 200 femtoseconds (fs) and a resolution of < 10 fs.

For the infrared detection in the 3-5 μm range, p-GaAs/Al_xGa_1-xAs heterojunction is an attractive material system due to light hole/heavy hole and spin-orbit split-off intra-valance band transitions in this wavelength range. Varying the Al mole fraction (x) provides the tuning for the wavelength threshold, while graded Al_xGa_1-xAs potential barriers create an asymmetry to allow a photovoltaic operation. The photovoltaic mode of operation offers the advantage of thermal noise limited performance. In our preliminary work, a 2 – 6 μm photovoltaic detector was studied. Implementation of an additional current blocking barrier improved the specific detectivity (D*) by two orders of magnitude, to 1.9×10¹¹ Jones at 2.7 μm, at 77K. At zero bias, the resistance-area product (R₀A) had a value of ~ 7.2×10⁸ Ω cm², which is five orders higher in magnitude (with a corresponding reduction of the responsivity by only a factor of ~ 1.5), compared to the R₀A value without the blocking barrier. A photoresponse was observed up to 130K.

Detailed radiometric analysis has shown that 3-5 µm medium wave infrared (MWIR) staring array well fill quickly reaches very high percentages, once hot optics, path radiance and inefficient f-number matching are taken into account. Well fill values of 90% plus are not unheard of. Likewise, the sensor noise eats away at the sensitivity. Therefore, it would appear that the very small signals often sought might not get sufficient dynamic bit-range to describe small signal flux propagating through poor atmospheres. This work presents a very detailed real-world model that includes all known factors that might compete for the bit resolution in a digitized sensor signal. The effect of different scene temperatures, atmospheric conditions and sensor design characteristics are briefly investigated. The effect of the various well fill contributors are shown in relation to each other in order to build an understanding of the nature of the total well fill. Finally, some mitigation measures are described to limit the negative effects of undue large well fill.

Fast scintillators are necessary for electron microscopes, as well as in many other application fields like medical diagnostics and therapy and fundamental science. InGaN/GaN multiple quantum well structures (QW) are perspective candidates due to strong exciton binding energy, high quantum efficiency, short decay time in order of ns and good radiation resistance. The aim of our work is to prepare scintillator structure with fast luminescence response and high intensity of light.

InGaN/GaN multiple QW structures described here were prepared by metal-organic vapour phase epitaxy and characterized by high resolution X-ray diffraction measurements. We demonstrate structure suitability for scintillator application including a unique measurement of wavelength-resolved scintillation response under nanosecond pulse soft X-ray source in extended dynamical and time scales. The photo-, radio- and cathodo-luminescence (PL, RL, CL) were measured. We observed double peak luminescence governed by different recombination mechanisms: i) exciton in QW and ii) related to defects. We have shown that for obtaining fast and intensive luminescence response proper structure design is required. The radioluminescence decay time of QW exciton maximum decreased 4 times from 16 ns to 4 ns when the QW thickness was decreased from 2.4 nm to 2 nm. We have proved suitability of InGaN/GaN structures for fast scintillator application for electron or other particle radiation detection. For x-ray detection the fast scintillation response would be hard to achieve due to the dominant slow defect luminescence maximum.

The results of combined IR absorption and photoconductivity studies on hydrogen donors in ZnO and TiO2 are presented. It is shown that hydrogen donors in ZnO and rutile TiO₂ can be detected as Fano resonances in the photoconductivity spectra at the frequencies corresponding to the vibrational modes of these defects. In the case of anatase TiO₂ IR absorption lines at 3412 and 3417 cm⁻¹ are assigned to the stretching local vibrational modes of a donor in the neutral and the positive charge states, respectively. Interstitial hydrogen is suggested as a tentative model for the defect giving rise to these vibrational modes.

Opto-mechanical tolerancing is a complex art, which is often reduced to inadequate tabled data of allowable tilts and decentres. During the process the respective roles of optical- and mechanical designers can become entangled and a source of conflict. A framework of principles is introduced to guide the design team through these murky waters. From these principles the development of a catalogue of models, practices and past precedents are proposed. An example is presented to serve as illustration. The final result is a model, of opto-mechanical tolerances, which allows a structured flow of tolerances into optical performance prediction.

The conventional directional sound sensing systems employ an array of spatially separated microphones to achieve directional sensing. However, there are insects such as Ormia ochracea fly that can determine the direction of sound using a miniature hearing organ much smaller than the wavelength of sound it detects. The MEMS based sensors mimicking the fly’s hearing system was fabricated using SOI substrate with 25 micrometer device layer. The sensor was designed to operate around 1.7 kHz, consists of two 1.2 mm × 1.2 mm wings connected in the middle by a 3 mm × 30 micrometer bridge. The entire structure is connected to the substrate by two torsional legs at the center. The sensor operates at its bending resonance frequency and has cosine directional characteristics similar to that of a pressure gradient microphone. For unambiguously determining the direction of sound, two sensors were assembled with a canted angle and outputs of the two sensors were processed to uniquely locate the bearing. At the bending resonant frequency (1.7 kHz) an output voltage of about 25 V/Pa was measured. The uncertainty of the bearing of sound ranged from less than 0.3 degrees close to the normal axis (0 degree) to 3 degrees at the limits of coverage (± 60 degrees) based on the 30 degree canted angle used. These findings indicate the potential use of a dual MEMS direction finding sensor assembly to locate sound sources with high accuracy.

Thermoelectric generators (TEGs) can be used as robust and maintenance-free power supplies. The power density of currently available TEGs is about 1 W/cm² and sufficient for many low power sensor/microelectromechanical systems. By changing the sintering atmosphere and using a special set-up a standard industry process used for insulating or metallic materials was transferred to thermoelectric FeSi₂-, Mg₂Si- and SiGe-material. Thereby, separated compact- and sintering steps allows a mass producible process in contrast to the almost exclusively used SPS- and FAST-processes. All three materials have been further processed to functional TEG-modules by sawing, bonding and electrically contacting with TiSi₂. Thereby, the mechanical bond as well as the electrical contacts are thermally stable up to 800 °C. The general functionality and the characteristics of the final TEG-modules were confirmed by analysis in a measurement setup that simulates an application in a realistic environment.