Stable and reliable operation of an optical sensor for pH monitoring is important for many industrial applications. This dissertation reports a series of studies on the development of novel and highly sensitive fibre optic sensors which are based on wavelength, instead of intensity changes and the development of thin film optical fibre working combinations for effectively enhancing the durability and value of the sensor probe. Several novel optical fibre sensors were fabricated and evaluated in this work. In order to measure the pH of a solution using optical methods, the sensor probes were prepared using layer~by-layer deposition techniques, a simple and versatile method to deposit a sensitive thin film i.e. active pH indicators on such optical fibre-based devices. In further work, the selection of a charged and water-soluble. pH indicator which introduces the highest wavelength shift, while varying the pH of the media, was investigated since the wavelength shift was considered as the basis of the sensitivity index. Brilliant yellow (BY) was applied as an indicator because of its greater wavelength shift with pH change compared to the use of other indicators. Poly (allylamine hydrochloride) (P AH) was also used as a crosslinker. To this end, the layers of BYIPAH were deposited on the bare silica core optical fibre using the layer-by-Iayer technique. The research was then developed to optimize the design factors that have an important effect on the sensitivity of the device. Utilizing V-shaped fibre with small radius which coated six bilayers of (BY IP AB) prepared from a polyion solution of low concentration was seen to provide a sensor with wider range of sensitivity which presents a highly sensitive device working over a smaller pH range offering higher resolution.

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This work describes the design, development and testing of a portable charge-coupled device detector system to be used for the simultaneous collection of X-ray diffraction and X-ray fluorescence data from powdered samples. The detector was designed for both terrestrial and extra-terrestrial applications that require in-situ analysis of samples, where access to a laboratory instrument is restricted. The detector system incorporates 4 e2v technologies CCD30-11 devices, employing multi-phase pinned technology for low noise operation. Geometrical calculations and thermal studies concerning the design of the detector are presented, with particular emphasis on motivations for the chosen geometry. Initial characterisation and calibration of the detector was performed in a laboratory environment using a purpose built test facility. The test facility included a high brightness X-ray micro-source from Bede Scientific Instruments, coupled with an XOS polycapillary collimating optic, which was used to deliver a focused beam of low divergent X-rays to the sample. The design of the test facility is discussed and the spectra and flux produced by the X-ray micro-source are investigated. The operational performance of the detector is highlighted and the use of the instrument in different applications is described, namely the planetary sciences and pharmaceuticals sector. Finally, based on the knowledge gained from initial testing of the instrument, improvements to the detector design are outlined, which greatly enhance the combined X-ray diffraction/X-ray fluorescence performance of the instrument.

This thesis considers the design and implementation of passive wireless microwave readable pressure sensors on a single chip. Two novel-all passive devices are considered for wireless pressure operation. The first device consists of a tuned circuit operating at 10 GHz fabricated on SiO2 membrane, supported on a silicon wafer. A pressure difference across the membrane causes it to deflect so that a passive resonant circuit detunes. The circuit is remotely interrogated to read off the sensor data. The chip area is 20 mm2 and the membrane area is 2mm2 with thickness of 4 µm. Two on chip passive resonant circuits were investigated: a meandered dipole and a zigzag antenna. Both have a physical length of 4.25 mm. the sensors show a shift in their resonant frequency in response to changing pressure of 10.28-10.27 GHz for the meandered dipole, and 9.61-9.58 GHz for the zigzag antenna. The sensitivities of the meandered dipole and zigzag sensors are 12.5 kHz and 16 kHz mbar, respectively. The second device is a pressure sensor on CMOS chip. The sensing element is capacitor array covering an area of 2 mm2 on a membrane. This sensor is coupled with a dipole antenna operating at 8.77 GHz. The post processing of the CMOS chip is carried out only in three steps, and the sensor on its own shows a sensitivity of 0.47fF/mbar and wireless sensitivity of 27 kHz/mbar. The MIM capacitors on membrane can be used to detune the resonant frequency of an antenna.

Within recent years, numerous fields of engineering, like mechanics, optics and electronics, have been influenced and revolutionised by the technique of microand nano-structuring. For example, special optical elements for beam shaping, surface structures for the reduction of friction or modern "lab on chip" devices have been produced. Within this thesis a universal system has been developed facilitating the production of such structured surfaces with dimensions down to 500 nm. This system is not only capable of structuring surfaces by means of lithographic processes; it further allows the inspection of surfaces by scanning their topography. To realise such a system, two different technologies have been evaluated: Scanning Near-field Optical Lithography (SNOL), a very sophisticated technique which uses a thin fibre tip to expose a photo resist-covered surface, and confocal scanning technology. Here, the confocal scanning is accomplished using an adapted optical component, the optical pickup unit (OPU), from a gaming console, which turned out to be the most suitable and cost-efficient solution for the realisation of this system. Several test series have been carried out during this work, to verify the performance of the confocal system, both to structure photo resist surfaces and to characterise unknown surfaces. This present work will show the ability of the developed system to produce structures down to the sub-micron range and to characterise unknown surfaces with sub- micron precision. Various patterns have been written into photo resistcoated substrates to structure their surface. Beginning with diffractive optical elements (DOE) for beam shaping, followed by Dammann gratings for twodimensional beam shaping and optical gratings for light guidance as well as producing technical surfaces imitating the properties of sharkskin or simple micromechanical structures, the developed confocal system has shown itself to be flexible and widely-applicable. IV During the development of the confocal system, a strong need for a beam profiling system analysing the light beam diverging from the OPU, was recognised. Due to the fact that no commercially available system was capable of characterising beam sizes within the range of the diffraction limit, a novel method for beam profiling was invented. This method makes use of the fibre tips already applied within the SNOL system, producing tomographical scans of the beam spot.

In recent years, there has been considerable interest in the use of gas/vapour monitors and electronic nose instruments by the environmental, automotive and medical industries. These applications require low cost and low power sensors with high yield and high reproducibility, with an annual prospective market of 1 million pounds. Present device and sensor technologies suffer a major limitation, their incompatibility with a standard silicon CMOS process. These technologies have either operating/annealing temperatures unsuited for MOSFET operation or an inappropriate sensing mechanism. The aim of this research is the development of CMOS compatible gas/vapour sensors, with a low cost of fabrication, high device repeatability and, in the future, transducer sensor amalgamation. Two novel approaches have been applied, utilising bulk CMOS and SOI BiCMOS. The bulk CMOS designs use a MOSFET sensing structure, with an active polymeric gate material, operating at low temperatures (<100°C), based on an array device of four elements, with channel lengths of 10 μm or 5 μm. The SOI designs exploit a MOSFET heater with a chemoresistive or chemFET sensing structure, on a thin membrane formed by the epi-taxial layer. By applying SOI technology, the first use in gas sensor applications, operating temperatures of up to 300 °C can be achieved at a power cost of only 35 mW (simulated). Full characterisation of the bulk CMOS chemFET sensors has been performed using electrochemically deposited (e.g. poly(pyrrole)/BSA)) and composite polymers (e.g. poly(9-vinylcarbazole)) to ethanol and toluene vapour in air. In addition, environmental factors (humidity and temperature) on the response and baseline were investigated. This was carried out using a newly developed flow injection analysis test station, which conditions the test vapour to precise analyte (<15 PPM of toluene) and water concentrations at a fixed temperature (RT to 105°C +- 0.1), with the sensor characterised by either I-V or constant current instrumentation. N-channel chemFET sensors operated at constant current (10 μA) with electrochemically deposited and composite polymers showed sensitivities of up to 1.1 μV/PPM and 4.0 μV/PPM to toluene vapour and to 1.1 μV/PPM and 0.4 μV/PPM for ethanol vapour, respectively, with detection limits of <20 PPM and <100 PPM to toluene and <20 PPM and 10+ PPM to ethanol vapour (limited by baseline noise), respectively. These responses followed either a power law (composite polymers) or a modified Langmuir isotherm model (electrochemically deposited polymers) with analyte concentration. It is proposed that this reaction-rate limited response is due to an alteration in polymers work function by either a partial charge transfer from the analyte or a swelling effect (polymer expansion). Increasing humidity caused, in nearly all cases a reduction in relative baseline, possible by dipole formation at the gate oxide surface. For the response, increasing humidity had no effect on sensors with composite polymers and an increase for sensors with electrochemically-deposited polymers. Higher temperatures caused a reduction in baseline signal, by a thermal expansion of the polymer, and a reduction in response explained by the analyte boiling point model describing a reduction in the bulk solubility of the polymer. Electrical and thermal characterisation of the SOI heaters, fabricated by the MATRA process, has been performed. I-V measurements show a reduction in drain current for a MOSFET after back-etching, by a degradation of the carrier mobility. Dynamic measurement showed a two stage thermal response (dual exponential), as the membrane reaching equilibrium (100-200 ms) followed by the bulk (1-2 s). A temperature coefficient of 8 mW/°C was measured, this was significantly higher than expected from simulations, explained by the membrane being only partially formed. Diode and resistive temperature sensors showed detection limits under 0.1°C and shown to measure a modulated heater output of less than 1°C at frequencies higher than 10Hz. The principal research objectives have been achieved, although further work on the SOI device is required. The results and theories presented in this study should provide a useful contribution to this research area.

The absorption coefficient is a fundamental parameter in understanding the underwater light field, for solving the Radiative Tranfer Equation and understanding/interpreting remotely sensed data from the ocean. Measuring the absorption coefficient is particularly complicated in coastal areas where the optical properties of the water body are the result of a complex mixture of dissolved and particulate components, but mainly because of the interfering effect that scattering has upon the measurements. A great variety of in situ instruments and laboratory techniques have been developed to measure total absorption or the absorption by the various fractions that constitute the total absorption. They are, however, all affected by scattering and empirical corrections need to be applied. Among the instruments to measure absorption, a promising one appeared to be one based on an integrating cavity. Kirk (1995, 1997) outlined the principle and theory of an absorption meter based on an integrating sphere: a Point Source Integrating Cavity Absorption Meter (PSICAM). He argued that owing to its design, a PSICAM would be insensitive to scattering. A novel Monte Carlo code was written to simulate the behaviour of a PSICAM of various cavity radiuses. The results of the simulations carried out with this code showed that such an absorption meter should indeed be unaffected by scattering even with high levels of scatterers. One important disadvantage deduced from numerical modelling for a PSICAM is its sensitivity to the reflectivity of the integrating cavity. Several prototype PSICAMs of increasing quality were built and tested with scattering-free standard solutions. A major difficulty in the development of the prototype was found to be the calibration of the integrating sphere reflectivity. A final laboratory instrument made of a Spectralon sphere was built and tested with artificial and natural water samples containing different levels of scattering particles and compared with existing in situ and laboratory techniques: the ac-9 transmissometer and the filter paper technique for particulate absorption as well as measurement of Coloured Dissolved Organic Matter. Compared with the ac-9 transmissometer, the PSICAM showed remarkable agreement even for water with very high content of Suspended Particulate Matter. Very good correlations were obtained when compared with traditional CDOM measurement. In some cases, significant discrepancies occurred with filter paper measurements of particulate absorption. From laboratory to in situ experiments the PSICAM proved to be a reliable instrument assuming that the instrument was regularly and carefully calibrated. Finally, the PSICAM was deployed during a cruise around the Antarctic Peninsula where total and dissolved absorption measurements were carried out together with chlorophyll absorption measurements after extraction in acetone.

[by] John Van Maanen. / This work is to be published as a chapter in Herbert Jacobs (Ed.) Volume III of the Annals of Criminal Justice (Beverly Hills, California: Sage Publishing Co.) / Bibliography: leaves 90-92.

Industrial flow measurement is a challenging area and in high demand. Tremendous research has been carried out to improve and solve problems in the flow measurement system. Thus, new techniques are produced and a wider range of flow measurement solutions have become available in market. This study has introduced a new technique that is useful and proves to be applicable in industrial flow measurement system. Microwave Doppler radar sensor was used to extract useful information of the solid flow characteristics. The amplitude level of the Doppler signal is analysed instead of the frequency shift that is normally used in conventional Doppler radar sensor. The relation between the amplitude level and the characteristic of the flow was determined to define the characteristics of the flow. The solids weight and dimension are among the characteristics that are investigated in this study. Microwave sensor circuits based on Doppler radar technique operating at 2.45GHz and 10.58GHz were designed, constructed and tested. The 2.45GHz system was built in the initial study and pre-testing of the Doppler radar sensor system prior to the construction of the 10.58GHz system that was later used for the measurement purposes. The antennas and circuit analyses were carried out in building an optimum sensor system. Two-antenna and two-antenna with copper plate are two new antenna configurations that are applied in single solid flow measurement analysis. The flow measurements were carried out using different types of solids ranges from 4mm to 20mm sizes and 0.02g to 0.63g of weight for single and multiple solids flow. The linear relations of the reflected power and the solids characteristics determined from the analyses are found to be useful in differentiating the type of solids and measuring the total weight of solids flowing.

The continued trends of product miniaturisation and increased part complexity have led to a requirement for highly accurate coordinate metrology, suitable for small parts. Coordinate metrology of such parts is performed on a micro-coordinate measurement machine (micro-CMMs), for which a specialised micro-scale probing system is required. These probing systems consist of a probe onto which a stylus is mounted. The probe provides significant flexibility allowing the stylus tip to be easily deflected during contact with a surface. Achieving an optimum stiffness for the probe represents a significant design challenge, and often leads to undesirable compromises. For example, as stylus tip size reduces the contact pressure for a given load increases, requiring the probe stiffness to be kept as low as possible to prevent damage to the part surface; however, for a more robust probing system the stiffness should be increased. This thesis presents an improved tactile micro-probing system that makes use of an active suspension structure that can be tuned to have either low or high stiffness as required for each phase of a measurement. Development of the probe includes analytical and numerical modelling for a range of solutions as well as empirical investigations into the manufacture of a smart suspension structure for a prototype probing system. Modelling results demonstrate significant stiffness reduction is possible by using the concept of adjusting the internal strain of suspension beam elements. In principle stiffness may be reduced down to zero at the point of beam buckling. It is also shown that such a probing system can provide isotropic stiffness for a range of different styli lengths. A prototype of the suspension structure was fabricated using a chemical etching process and 6.6 mm long stylus. The stiffness of the structure was assessed by measuring the modal frequencies of the suspension structure that correspond to vertical and lateral probe motion. Using this method, results show it is possible to reduce the frequency of the vertical mode and the torsional mode by 70 % and 33 %, respectively. Using finite element analysis it is shown that this equates to a reduction in vertical and lateral stiffness to 12 % and 46 % of their initial value, respectively, representing a ratio of the vertical to lateral stiffness of 1.7, which is close to the isotropic stiffness. A novel control system is presented that monitors and controls stiffness, allowing easy switching between “stiff” and “flexible” modes. During switching, the stylus tip undergoes a displacement or approximately 18 μm, however, the control system is able ensure a consistent flexible mode tip deflection to within 12 nm in the vertical axis. Combining stage errors with the probing system linearity error, the stylus tip zero offset position error and the probing system measurement repeatability, gives an estimate of a combined uncertainty for the probing system or of 58 nm (coverage factor, k = 2), which demonstrates the potential of this innovative variable stiffness micro-scale probe system.