Development of a fiber-based shape sensor for navigating flexible medical tools

Robot-assisted minimally invasive surgical procedure (RAMIS) is a subfield of minimally invasive surgeries with enhanced manual dexterity, manipulability, and intraoperative image guidance. In typical robotic surgeries, it is common to use rigid instruments with functional articulating tips. However, in some operations where no adequate and direct access to target anatomies is available, continuum robots can be more practical, as they provide curvilinear and flexible access. However, their inherent deformable design makes it difficult to accurately estimate their 3D shape during the operation in real-time. Despite extensive model-based research that relies on kinematics and mechanics, accurate shape sensing of continuum robots remains challenging. The state-of-the-art tracking technologies, including optical trackers, EM tracking systems, and intraoperative imaging modalities, are also unsuitable for this task, as they all have shortcomings. Optical fiber shape sensing solutions offer various advantages compared to other tracking modalities and can provide high-resolution shape measurements in real-time. However, commercially available fiber shape sensors are expensive and have limited accuracy. In this thesis, we propose two cost-effective fiber shape sensing solutions based on multiple single-mode fibers with FBG (fiber Bragg grating) arrays and eccentric FBGs. First, we present the fabrication and calibration process of two shape sensing prototypes based on multiple single-mode fibers with semi-rigid and super-elastic substrates. Then, we investigate the sensing mechanism of edge-FBGs, which are eccentric Bragg gratings inscribed off-axis in the fiber's core. Finally, we present a deep learning algorithm to model edge-FBG sensors that can directly predict the sensor's shape from its signal and does not require any calibration or shape reconstruction steps. In general, depending on the target application, each of the presented fiber shape sensing solutions can be used as a suitable tracking device. The developed fiber sensor with the semi-rigid substrate has a working channel in the middle and can accurately measure small deflections with an average tip error of 2.7 mm. The super-elastic sensor is suitable for measuring medium to large deflections, where a centimeter range tip error is still acceptable. The tip error in such super-elastic sensors is higher compared to semi-rigid sensors (9.9-16.2 mm in medium and large deflections, respectively), as there is a trade-off between accuracy and flexibility in substrate-based fiber sensors. Edge-FBG sensor, as the best performing sensing mechanism among the investigated fiber shape sensors, can achieve a tip accuracy of around 2 mm in complex shapes, where the fiber is heavily deflected. The developed edge-FBG shape sensing solution can compete with the state-of-the-art distributed fiber shape sensors that cost 30 times more

Clinical evaluation of a new optical fibre method of measuring oxygen saturation using photoplethysmograph signals reflected from internal tissues

MD (Res)Traditional methods of measuring oxygen saturation, e.g. pulse oximetry, depend on an adequate peripheral circulation and have a 20–30 second lag time before readings are obtained. This was a series of evaluations of novel optical probes, designed to measure oxygen saturation using fibreoptic technology directly from internal organs including the brain, oesophagus and organs with splanchnic circulations. A series of pilot studies were proposed and research ethics approval obtained to carry out studies in humans, under general anaesthesia, using these probes. Innovative reflectance probes were designed specifically for each of the four applications, so as to obtain potentially useful signals needed for signal processing, analysis and evaluation. Signals were successfully obtained from the brain, oesophagus and splanchnic region in almost all of the patients recruited. Good quality photoplethysmograph signals were recorded and these were translated into clinically meaningful values of oxygen saturation comparable to traditional methods of pulse oximetry. Overall, the signals were prone to movement artefacts as well as occasional interference from surgical diathermy and other sources. Nonetheless, the probes could prove to be a useful alternative to conventional external transmittance pulse oximetry methods as well as providing useful information regarding regional perfusion and oxygenation. The success of these pilot studies will form the basis of more research in the area and further development of such probes on the medical engineering front

Robotic surface exploration with vision and tactile sensing for cracks detection and characterisation

This thesis presents a novel algorithm for crack localisation and detection based on visual and tactile analysis via fibre-optics. A finger-shaped sensor based on fibre-optics is employed for the data acquisition to collect data for the analysis and the experiments. Three pairs of fibre optics are used to measure the sensor's soft part deformation via changes in the reflected light intensity. A fourth pair of optical fibre cables is positioned at the tip of the finger and it is used to sense the proximity to external objects. To detect the possible locations of cracks a camera is used to scan an environment while running an object detection algorithm. Once the crack is detected, a fully-connected graph is created from a skeletonised version of the crack. Minimum spanning tree is then employed for calculating the shortest path to explore the crack which is then used to develop the motion planner for the robotic manipulator. The motion planner divides the crack into multiple nodes which are then explored one by one. Then, the manipulator starts the exploration and performs the tactile data classification to confirm if there is indeed a crack in that location or just a false positive from the vision algorithm. This is repeated until all the nodes of the crack are explored. If a crack is not detected from vision, then it won't be further explored in the tactile step. Because of this, false negative have the biggest weight and recall is the most import metric in this study. I perform experiments to investigate the improvements for the time required during exploration when using visual and tactile modalities together. The experimental studies demonstrate that exploring a fractured surface with a combination of visual and tactile modalities is four times faster than using solely the tactile mode. The accuracy of detection is also improved when the two modalities were combined. Experiments are also performed in order to develop a robust machine learning model to analyse and classify the tactile data acquired during exploration via the fibre-optics sensor. Frequency domain features are explored to investigate the spectrum of the signal. Results show that when training machine learning models and deep learning networks using these features, the resulting models are more robust when tested across different databases, on which they are not trained. Thus, when computer vision techniques may fail because of light conditions or extreme environments, fibre-optics sensors can be employed to analyse the presence of cracks on explored surfaces via machine learning and deep neural network algorithms. Still, when introducing tactile in extreme environments, caution must be used when making contact with possible fragile surfaces which may break because of the friction produced by the tactile sensor. Proximity may be used in this case to calculate the distance between the sensor and the object and to reduce speed when getting closer to the object. In conclusion, the thesis has contributed to advances in crack detection by introducing a multi-modal algorithm that is used to detect cracks in the environment via computer vision and then confirming the presence of a crack via tactile exploration and machine learning classification of the data acquired from a fibre-optic-based sensor. Few methods currently use tactile sensing for crack characterisation and detection and this is the first study which shows the reliability of tactile-based methodologies for crack detection via machine learning analysis. Furthermore, this is the first method which combines both tactile and vision for crack analysis

Li-ion batteries monitoring for electrified vehicles applications

L'abstract è presente nell'allegato / the abstract is in the attachmen

An Investigation of Untapered and Tapered Fibre Transmission Properties

This thesis is about investigation of untapered and tapered fibre transmission properties by experimentation and simulation. Tapered fibre fabricated from commercial products and custom fibre from Bath University was investigated including different fibre type, taper length, and taper ratios. Simulations of untapered and tapered fibre by consideration of geometrical optics using Zemax are presented and compared to electromagnetic waveguide simulations using COMSOL. In addition, the impact of modal noise in tapered fibre is investigated, especially graded-index tapers, by quantifying macro- and micro-bending loss. Moreover, the fabrication of build-inhouse connector tapered fibre is introduced as a robust and cost-saving tool for spectrograph link. Lastly, a tapered fibre is tested with a compact EXOplanet high-resolution SPECtrograph (EXOhSPEC) of the University of Hertfordshire using Tungsten and ThAr lamps. Although the cladding light is detected clearly in custom graded-index taper, the light throughput in EXOhSPEC is improved. Overall these results indicate the potential for reasonable fibre-fed spectrograph performance using a ’single tapered fibre’

Multimode fibre broadband access and self-referencing sensor networks

Future Internet Access technologies are supposed to bring us a very performing connection to the main door of our homes. At the same time, new services and devices and their increase use will require data transfers at speeds exceeding 1Gbps inside the building or home at the horizon 2012. Both drivers lead to the deployment of a high-quality, futureproof network inside buildings and homes. This environment may end up taking advantage of optical cabling solutions as an alternative to more traditional copper or pure wireless approaches. Related to this latter fact, the objectives of this work are: • The achievement of a full convergence scenario between optical networks from the telecommunication services providers to the end users underscores the necessity of accurate and realistic fibre models in assessing the performance of broadband access networks with the premises of high-capacity and total compatibility. Silicabased MMFs and PF GIPOFs are the most promising candidates for such a convergence within the in-building/home scenario. Contributions to a better understanding of the possibilities of signal transmission outside the baseband of such fibres are investigated, in order to extend their capabilities, together with the evaluation of current fibre frequency response theoretical models by means of an extensive set of measurements. • The achievement of a full convergence scenario between optical networks from the telecommunication services providers to the end users is also contingent on research and development in the field of optical fibre sensors, mainly driven by the growing demand of fully building/home and industry automation, leading to a reliable integration of the optical networks. Related to this, development of multiplexing and measurement techniques for fibre-optic intensity-based sensors are analyzed and experimentally investigated. In the sensor network topology proposed, by replacing the fibre delay line with an electronic delay in the reception stage, it is possible to avoid long fibre delay coils in the remote sensing points and achieving a compact, flexible and re-configurable self-referencing technique. Applications in both scenarios can be considered, on the one hand the in-building/home network and on the other hand the WDM-PON access network topology through which operators provision the different services. -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------La demanda e incursión en la sociedad de nuevos servicios multimedia, tales como televisión por Internet (IPTV, Internet Protocol Television) o video-bajo-demanda (VoD, Video on Demand) junto con el incremento del tráfico de datos requerido para nuevas aplicaciones como la televisión por alta definición (HDTV, High-Definition Television) y transferencias P2P (Peer-to-Peer) exigen un aumento de la capacidad de las redes de datos desplegadas hoy en día. Para hacer frente a este aumento de la demanda de capacidad de las redes de acceso, los proveedores de estos servicios multimedia están reemplazando las infraestructuras de las redes de acceso basadas en cable coaxial, tales como xDSL (x- Digital Subscriber Line), por otras nuevas de mayor capacidad desplegadas en fibra óptica, permitiendo la interconexión de los nodos de red con los múltiples hogares y negocios de los abonados, constituyendo el núcleo de lo que es conocido como “fibra hasta el hogar/nodo/edificio” o redes FTTx. Tradicionalmente el despliegue de las redes ópticas se ha realizado mediante fibra óptica monomodo de sílice (SMF, Singlemode Fibre). Ello es debido a su gran ancho de banda que permite una gran capacidad de transporte de servicios y datos. Es por ello que en base a este tipo de fibra se ha realizado el despliegue de redes de distribución y metropolitanas y, de un tiempo a esta parte, incluso penetrando su instalación en las redes de acceso. Junto con lo anteriormente expuesto, existe una necesidad de convergencia de servicios e infraestructuras dentro de las redes de acceso. Actualmente, cables coaxiales, par trenzado de cobre e incluso señales inalámbricas se encuentran entremezcladas dentro del hogar proporcionando servicios diferentes con apenas cooperación entre ellos. Una infraestructura común dentro del hogar en el que una gran cantidad de servicios pudieran ser integrados y soportados por la misma sería un aspecto deseable. Y es más, frente a las desventajas de infraestructuras basadas en cable de cobre (cable coaxial y par trenzado) como son susceptibilidad a interferencias electromagnéticas, presencia de crosstalk y relativa baja capacidad de transporte de datos, las fibras ópticas (tanto en su versión monomodo como multimodo) presentan las ventajas de un menor volumen, mayor flexibilidad y menor peso junto con una capacidad mayor de transmisión de datos sobre distancias mayores. Es por esto que éstas últimas constituyen la base para las futuras redes de acceso en el hogar

Writing of holographic diffraction gratings of unrestricted length.

Available from British Library Document Supply Centre-DSC:DXN049851 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

The glottalic consonants of Hausa.

This thesis is concerned with the examination of the glottalic consonants of Hausa, a Chadic language spoken in northern Nigeria, Niger, Cameroon, Togo and Ghana. The glottalic consonants constitute a set of phonemes in the language whose historical and phonetic properties merit further investigation. The study is laid out in three parts. Part one (Chapters 1, 2 and 3) is the historical section. Here, a general overview of the Hausa language is given. Also discussed are several specific points made by pioneers of the genetic classification of Chadic within Afroasiatic and the reconstruction of glottalic consonants in both Chadic and Afroasiatic. The discussion here is not new but presents a summary of the literature. Hausa native words that have glottalic consonants are compared with possible cognates from other related Chadic languages from West, Central and East branches of Chadic and also from other Afroasiatic languages. Part two (Chapters 4 and 5) of the study concerns the investigation of phonation types in general. Chapter 4 gives a short account of the larynx, the mechanism of the vocal fold vibration and classification of phonation types. Chapter 5 is devoted to a review of instrumental techniques used in voice measurement. Part three (Chapter 6, the instrumental section) presents and discusses the results of a detailed electro- laryngographic analysis of the activity of the behaviour of the vocal folds in the production of the glottalic consonants and their non-glottalic counterparts as observed in the speech of educated native speakers of the language. The chapter begins with a review of the literature reporting early instrumental and non-instrumental studies of the segmental phonemes of the language. This is followed by a description of the techniques used to record, display and annotate both speech pressure and laryngographic waveforms. Both qualitative and quantitative analysis of the waveforms are presented. The most important parameter in the quantitative analysis is estimated open quotient (OQ) derived from the Lx waveforms measurements of Fundamental Frequency, duration and Voice Onset Time are also given. The chapter concludes by presenting the results of the experiment: 1 OQ increases in anticipation of plain voiceless consonants, and is relatively high at the consonantal release; 2 OQ decreases in anticipation of laryngealized consonants including the glottal stop (for most speakers) and less sharply for the ejectives; 3 OQ remains approximately at the speaker's modal value for the plain voiced consonants; 4 The laryngealized segments tend to lower pitch at the left of the consonant; and 5 They also tend to be longer than their plain counterparts

Modular, reconfigurable approach for a commercial space spacecraft programme

This thesis presents the work performed in producing a system-level design for a modular, multipurpose small satellite platform. A multipurpose platform may be applied to a wide range of missions, and, to be commercially viable, the envelope of missions for which it is suitable should be as large as possible. The research therefore addresses the particular requirements that are specific to different mission types, and produces characteristic requirement sets for each. General design requirements are also derived, such as those for enabling modularity and allowing compatibility with different launch vehicles. The commercial requirements arising from the different market and customer sectors are also examined. Industry analysis allows identification of general market trends, and predictions are made regarding the likely size and characteristics of the market in which the proposed platform would compete. It is anticipated there could be a worldwide demand for more than twenty small satellites each year, for which a flexible small spacecraft platform could potentially compete. After derivation of the necessary requirements has been performed, a system-level design of the spacecraft platform is undertaken. The resulting design is based on a multi-module, reconfigurable concept, which can be adapted to fit the different launch envelopes of Pegasus-XL, Taurus, ASAP-5 and larger launchers, and also to accommodate a wide range of payloads. The subsystems are offered in different capability variants, which may be interchanged in response to different mission requirements. The platform equipment and structure forms a 'standard parts lisf', from which the appropriate configuration can be built up. Schedule reductions are obtained due to the modular design allowing more of the integration and testing of the platform to be performed in parallel. The proposed programme for development of the platform uses up-front investment to conduct much of the detailed design of the platform in advance of any actual project. This allows the design effort to be shared across many subsequent projects, and the design phase of each new project to be minimised. The key benefits of the proposed platform and programme are adaptability, ability to rapidly reconfigure to mission requirements, suitability for future upgrading, and reduction of the project schedule.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Modular, reconfigurable approach for a commercial space spacecraft programme

This thesis presents the work performed in producing a system-level design for a modular, multipurpose small satellite platform. A multipurpose platform may be applied to a wide range of missions, and, to be commercially viable, the envelope of missions for which it is suitable should be as large as possible. The research therefore addresses the particular requirements that are specific to different mission types, and produces characteristic requirement sets for each. General design requirements are also derived, such as those for enabling modularity and allowing compatibility with different launch vehicles. The commercial requirements arising from the different market and customer sectors are also examined. Industry analysis allows identification of general market trends, and predictions are made regarding the likely size and characteristics of the market in which the proposed platform would compete. It is anticipated there could be a worldwide demand for more than twenty small satellites each year, for which a flexible small spacecraft platform could potentially compete. After derivation of the necessary requirements has been performed, a system-level design of the spacecraft platform is undertaken. The resulting design is based on a multi-module, reconfigurable concept, which can be adapted to fit the different launch envelopes of Pegasus-XL, Taurus, ASAP-5 and larger launchers, and also to accommodate a wide range of payloads. The subsystems are offered in different capability variants, which may be interchanged in response to different mission requirements. The platform equipment and structure forms a 'standard parts lisf', from which the appropriate configuration can be built up. Schedule reductions are obtained due to the modular design allowing more of the integration and testing of the platform to be performed in parallel. The proposed programme for development of the platform uses up-front investment to conduct much of the detailed design of the platform in advance of any actual project. This allows the design effort to be shared across many subsequent projects, and the design phase of each new project to be minimised. The key benefits of the proposed platform and programme are adaptability, ability to rapidly reconfigure to mission requirements, suitability for future upgrading, and reduction of the project schedule.EThOS - Electronic Theses Online ServiceGBUnited Kingdo