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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Information-Theoretic Control of Multiple Sensor Platforms

Grocholsky, Ben January 2002 (has links)
This thesis is concerned with the development of a consistent, information-theoretic basis for understanding of coordination and cooperation decentralised multi-sensor multi-platform systems. Autonomous systems composed of multiple sensors and multiple platforms potentially have significant importance in applications such as defence, search and rescue mining or intelligent manufacturing. However, the effective use of multiple autonomous systems requires that an understanding be developed of the mechanisms of coordination and cooperation between component systems in pursuit of a common goal. A fundamental, quantitative, understanding of coordination and cooperation between decentralised autonomous systems is the main goal of this thesis. This thesis focuses on the problem of coordination and cooperation for teams of autonomous systems engaged in information gathering and data fusion tasks. While this is a subset of the general cooperative autonomous systems problem, it still encompasses a range of possible applications in picture compilation, navigation, searching and map building problems. The great advantage of restricting the domain of interest in this way is that an underlying mathematical model for coordination and cooperation can be based on the use of information-theoretic models of platform and sensor abilities. The information theoretic approach builds on the established principles and architecture previously developed for decentralised data fusion systems. In the decentralised control problem addressed in this thesis, each platform and sensor system is considered to be a distinct decision maker with an individual information-theoretic utility measure capturing both local objectives and the inter-dependencies among the decisions made by other members of the team. Together these information-theoretic utilities constitute the team objective. The key contributions of this thesis lie in the quantification and study of cooperative control between sensors and platforms using information as a common utility measure. In particular, * The problem of information gathering is formulated as an optimal control problem by identifying formal measures of information with utility or pay-off. * An information-theoretic utility model of coupling and coordination between decentralised decision makers is elucidated. This is used to describe how the information gathering strategies of a team of autonomous systems are coupled. * Static and dynamic information structures for team members are defined. It is shown that the use of static information structures can lead to efficient, although sub-optimal, decentralised control strategies for the team. * Significant examples in decentralised control of a team of sensors are developed. These include the multi-vehicle multi-target bearings-only tracking problem, and the area coverage or exploration problem for multiple vehicles. These examples demonstrate the range of non-trivial problems to which the theory in this thesis can be employed.
2

Detecting the Presence of a Proximate Cellular User through Distributed Femtocell Sensing

Parag, Pankaj 1988- 14 March 2013 (has links)
The current cellular industry is undergoing a huge paradigm shift from an old homogeneous one-tier network structure to a new heterogeneous two-tier structure with joint deployment of traditional macrocell base stations along with a relatively new small cell base stations, widely known as femtocells. Femtocells are low-powered, low-cost, user-deployed base stations meant to improve poor network coverage and, thereby, increase overall system capacity. As more and more femtocells are deployed, their spectrum usage and resulting interference become non-negligible. While using different operating frequency for femtocells is indeed possible, a co-channel deploy- ment of these will increase spectral efficiency, a much sought design by cellular opera- tors. In this thesis, a femtocell-based scheme is considered as a prospective means to enhance the performance of the current cellular infrastructure. In the adopted frame- work, the femtocell access point is tasked with connecting local femtocell users to the network operator without creating undue interference to cellular users. As such, the femtocell is required to cease communication when a nearby cellular user is present to prevent interference. In the envisioned paradigm, an access point possesses little information about the parent cellular base station. For instance, it may not know the individual channel gains, user locations or frequency allocations. To achieve this goal, femtocell users collectively act as sensing devices and are used to acquire data about local signal strength. This work shows that, despite having little knowledge of the operation of the macro environment, a femtocell can take advantage of the data provided by the acquisition devices and agility of the re-configurable antenna to gain insight about proximate cellular devices. The proposed inference scheme leads to a significant performance gain over oblivious femtocells. Experimental results are provided to support this study and its conclusions.
3

Information-Theoretic Control of Multiple Sensor Platforms

Grocholsky, Ben January 2002 (has links)
This thesis is concerned with the development of a consistent, information-theoretic basis for understanding of coordination and cooperation decentralised multi-sensor multi-platform systems. Autonomous systems composed of multiple sensors and multiple platforms potentially have significant importance in applications such as defence, search and rescue mining or intelligent manufacturing. However, the effective use of multiple autonomous systems requires that an understanding be developed of the mechanisms of coordination and cooperation between component systems in pursuit of a common goal. A fundamental, quantitative, understanding of coordination and cooperation between decentralised autonomous systems is the main goal of this thesis. This thesis focuses on the problem of coordination and cooperation for teams of autonomous systems engaged in information gathering and data fusion tasks. While this is a subset of the general cooperative autonomous systems problem, it still encompasses a range of possible applications in picture compilation, navigation, searching and map building problems. The great advantage of restricting the domain of interest in this way is that an underlying mathematical model for coordination and cooperation can be based on the use of information-theoretic models of platform and sensor abilities. The information theoretic approach builds on the established principles and architecture previously developed for decentralised data fusion systems. In the decentralised control problem addressed in this thesis, each platform and sensor system is considered to be a distinct decision maker with an individual information-theoretic utility measure capturing both local objectives and the inter-dependencies among the decisions made by other members of the team. Together these information-theoretic utilities constitute the team objective. The key contributions of this thesis lie in the quantification and study of cooperative control between sensors and platforms using information as a common utility measure. In particular, * The problem of information gathering is formulated as an optimal control problem by identifying formal measures of information with utility or pay-off. * An information-theoretic utility model of coupling and coordination between decentralised decision makers is elucidated. This is used to describe how the information gathering strategies of a team of autonomous systems are coupled. * Static and dynamic information structures for team members are defined. It is shown that the use of static information structures can lead to efficient, although sub-optimal, decentralised control strategies for the team. * Significant examples in decentralised control of a team of sensors are developed. These include the multi-vehicle multi-target bearings-only tracking problem, and the area coverage or exploration problem for multiple vehicles. These examples demonstrate the range of non-trivial problems to which the theory in this thesis can be employed.
4

Fully Distributed Multi-parameter Sensors Based on Acoustic Fiber Bragg Gratings

Hu, Di 31 March 2017 (has links)
A fully distributed multi-parameter acoustic sensing technology is proposed. Current fully distributed sensing techniques are exclusively based on intrinsic scatterings in optical fibers. They demonstrate long sensing span, but their limited applicable parameters (temperature and strain) and costly interrogation systems have prevented their widespread applications. A novel concept of acoustic fiber Bragg grating (AFBG) is conceived with inspiration from optical fiber Bragg grating (FBG). This AFBG structure exploits periodic spatial perturbations on an elongated waveguide to sense variations in the spectrum of an acoustic wave. It achieves ten times higher sensitivity than the traditional time-of-flight measurement system using acoustic pulses. A fast interrogation method is developed to avoid frequency scan, reducing both the system response time (from 3min to <1ms) and total cost. Since acoustic wave propagates with low attenuation along varieties of solid materials (metal, silica, sapphire, etc.), AFBG can be fabricated on a number of waveguides and to sense multiple parameters. Sub-millimeter metal wire and optical fiber based AFBGs have been demonstrated experimentally for effective temperature (25~700 degC) and corrosion sensing. A hollow borosilicate tube is demonstrated for simultaneous temperature (25~200 degC) and pressure (15~75 psi) sensing using two types of acoustic modes. Furthermore, a continuous 0.6 m AFBG is employed for distributed temperature sensing up to 500 degC and to accurately locate the 0.18 m long heated section. Sensing parameters, sensitivity and range of an AFBG can be tuned to fit a specific application by selecting acoustic waveguides with different materials and/or geometries. Therefore, AFBG is a fully distributed sensing technology with tremendous potentiality. / Ph. D.
5

Fiber-Optic Sensors for Fully-Distributed Physical, Chemical and Biological Measurement

Wang, Yunjing 21 January 2013 (has links)
Distributed sensing is highly desirable in a wide range of civil, industrial and military applications. The current technologies for distributed sensing are mainly based on the detection of optical signals resulted from different elastic or non-elastic light-matter interactions including Rayleigh, Raman and Brillouin scattering. However, they can measure temperature or strain only to date. Therefore, there is a need for technologies that can further expand measurement parameters even to chemical and biological stimuli to fulfill different application needs. This dissertation presents a fully-distributed fiber-optic sensing technique based on a traveling long-period grating (T-LPG) in a single-mode fiber. The T-LPG is generated by pulsed acoustic waves that propagate along the fiber. When there are changes in the fiber surrounding medium or in the fiber surface coating, induced by various physical, chemical or biological stimuli, the optical transmission spectrum of the T-LPG may shift. Therefore, by measuring the T-LPG resonance wavelength at different locations along the fiber, distributed measurement can be realized for a number of parameters beyond temperature and strain. Based on this platform, fully-distributed temperature measurement in a 2.5m fiber was demonstrated. Then by coating the fiber with functional coatings, fully-distributed biological and chemical sensing was also demonstrated. In the biological sensing experiment, immunoglobulin G (IgG) was immobilized onto the fiber surface, and the experimental results show that only specific antigen-antibody binding can introduce a measurable shift in the transmission optical spectrum of the T-LPG when it passes through the pretreated fiber segment. In the hydrogen sensing experiment, the fiber was coated with a platinum (Pt) catalyst layer, which is heated by the thermal energy released from Pt-assisted combustion of H2 and O2, and the resulted temperature change gives rise to a measurable T-LPG wavelength shift when the T-LPG passes through. Hydrogen concentration from 1% to 3.8% was detected in the experiment. This technique may also permit measurement of other quantities by changing the functional coating on the fiber; therefore it is expected to be capable of other fully-distributed sensing applications. / Ph. D.
6

Distributed Vibration Sensing using Rayleigh Backscatter in Optical Fibers

Sang, Alexander Kipkosgei 22 December 2011 (has links)
Sensing has been essential for the investigation, understanding, exploitation, and utilization of physical phenomena. Traditional single-point sensing methods are being challenged by the multi-point or distributed sensing capabilities afforded by optical fiber sensors. A powerful technique available for distributed sensing involves the use of the Optical Frequency Domain Reflectometry (OFDR). This work focuses on using OFDR as a means of obtaining distributed vibration measurements using the Rayleigh scatter along a single-mode optical fiber. The effort begins by discussing various distributed measurement techniques currently in use before discussing the OFDR technique. Next, a thorough discussion on how high spatially resolved Rayleigh measurements are acquired and how such measurements can be used to make static strain measurements is presented. A new algorithm to resolve strain at regions of high spatial gradient is developed. This results in enhanced measurement performance of systems using the Rayleigh scatter to determine static strain or temperature measurements by improving measurement fidelity at the high gradient locations. Next, discussions on how dynamic strain (vibration) couples to optical fiber in a single point and in a distributed setting are presented. Lessons learned are then used to develop a new and unique distributed vibration measurement algorithm. Various consequential benefits are then reviewed before concluding remarks are stated. A simulation model was developed and used to supplement this investigation in every step of the discussion. The model was used to gain insight on how various physical phenomena interact with the optical fiber. The simulation was also used to develop and optimize the high gradient and vibration algorithms developed herein. Simple experiments were then used to validate the theory and the simulation models. / Ph. D.
7

Diode Laser Spectroscopy for Measurements of Gas Parameters in Harsh Environments

Behera, Amiya Ranjan 06 March 2017 (has links)
The detection and measurement of gas properties has become essential to meet rigorous criteria of environmental unfriendly emissions and to increase the energy production efficiency. Although low cost devices such as pellistors, semiconductor gas sensors or electrochemical gas sensors can be used for these applications, they offer a very limited lifetime and suffer from cross-response and drift. On the contrary, gas sensors based on optical absorption offer fast response, zero drift, and high sensitivity with zero cross response to other gases. Hence, over the last forty years, diode laser spectroscopy (DLS) has become an established method for non-intrusive measurement of gas properties in scientific as well as industrial applications. Wavelength modulation spectroscopy (WMS) is derivative form of DLS that has been increasingly applied for making self-calibrated measurements in harsh environments due to its improved sensitivity and noise rejection capability compared to direct absorption detection. But, the complexity in signal processing and higher scope of error (when certain restrictions on operating conditions are not met), have inhibited the widespread use of the technique. This dissertation presents a simple and novel strategy for practical implementation of WMS with commercial diode lasers. It eliminates the need for pre-characterization of laser intensity parameters or making any design changes to the conventional WMS system. Consequently, sensitivity and signal strength remain the same as that obtained from traditional WMS setup at low modulation amplitude. Like previously proposed calibration-free approaches, this new method also yields absolute gas absorption line shape or absorbance function. Residual Amplitude Modulation (RAM) contributions present in the first and second harmonic signals of WMS are recovered by exploiting their even or odd symmetric nature. These isolated RAM signals are then used to estimate the absolute line shape function and thus removing the impact of optical intensity fluctuations on measurement. Uncertainties and noises associated with the estimated absolute line shape function, and the applicability of this new method for detecting several important gases in the near infrared region are also discussed. Absorbance measurements from 1% and 8% methane-air mixtures in 60 to 100 kPa pressure range are used to demonstrate simultaneous recovery of gas concentration and pressure. The system is also proved to be self-calibrated by measuring the gas absorbance for 1% methane-air mixture while optical transmission loss changes by 12 dB. In addition to this, a novel method for diode laser absorption spectroscopy has been proposed to accomplish spatially distributed monitoring of gases. Emission frequency chirp exhibited by semiconductor diode lasers operating in pulsed current mode, is exploited to capture full absorption response spectrum from a target gas. This new technique is referred to as frequency chirped diode laser spectroscopy (FC-DLS). By applying an injection current pulse of nanosecond duration to the diode laser, both spectroscopic properties of the gas and spatial location of sensing probe can be recovered following traditional Optical Time Domain Reflectometry (OTDR) approach. Based on FC-DLS principle, calibration-free measurement of gas absorbance is experimentally demonstrated for two separate sets of gas mixtures of approximately 5% to 20% methane-air and 0.5% to 20% acetylene-air. Finally, distributed gas monitoring is shown by measuring acetylene absorbance from two sensor probes connected in series along a single mode fiber. Optical pulse width being 10 nanosecond or smaller in the sensing optical fiber, a spatial resolution better than 1 meter has been realized by this technique. These demonstrations prove that accurate, non-intrusive, single point, and spatially distributed measurements can be made in harsh environments using the diode laser spectroscopy technology. Consequently, it opens the door to practical implementation of optical gas sensors in a variety of new environments that were previously too difficult. / Ph. D.
8

Distributed Optical Sensing in Adhesively Bonded Joints and Polymer Matrix Composite Laminates

Meadows, Leeanna 06 May 2017 (has links)
As the use of polymer matrix composites for structures increases, there is a growing need for monitoring these structures. Distributed strain sensing using optical fibers shows promise for monitoring composite structures due to optical fiber's small size, light weight, and ability to obtain continuously distributed strain data. This study investigates the feasibility of using embedded optical fibers using two case studies: embedding the fibers in the adhesive layer of double lap shear composite specimens, and within composite end-notched flexure specimens to locate a growing crack front. To establish a repeatable fabrication methodology, manufacturing techniques for embedding the optical fibers were investigated. The measured strain distribution from the optical fibers compares well with data obtained from finite element analyses for both the double lap shear and end-notch flexure specimens. Additionally, the embedded optical fibers do not seem to impact the failure loads or fracture behavior of the specimens.
9

Numerical Analysis of Optically-induced Long-period Fiber Gratings for Sensing Applications

Wang, Chaofan 25 September 2014 (has links)
Long-period fiber gratings (LPGs) with a period ranging from several hundred micrometers to a few millimeters can couple a core mode to discrete co-propagating cladding modes when the phase matching condition is satisfied. The rapid attenuation of cladding modes results in loss bands in the transmission spectrum. As the attenuation bands are sensitive to the LPG period and the fiber surrounding environment such as temperature, strain and ambient refractive index, LPGs can be used for sensing. However, traditional LPGs with gratings inscribed in the fibers can only sense a single point and cannot be used for distributed sensing. Although new ideas were proposed to use traveling LPG formed by a pulsed acoustic wave, the large attenuation of the acoustic wave in the fiber greatly limits the sensing range to only several meters. In this thesis, we proposed to use a traveling LPG formed by the interference of two high power co-propagating core modes, usually LP01 and LP11. The beating of the two modes will induce a refractive index grating due to the optical Kerr effect, and the grating is called optically induced long-period fiber grating (OLPG). Compared to the grating induced by acoustic waves, OLPG is able to travel for a long distance due to the small attenuation of the guided core modes. Mode conversion in the OLPG is numerically simulated and analyzed using the finite-difference beam propagation method (FD-BPM). The result shows full conversion for both core-core and core-cladding mode coupling under phase matching condition. Moreover, the sensitivity of OLPG to temperature, axial strain and ambient refractive index is investigated and analyzed. It is seen that the sensitivities of temperature and axial strain with OLPG are different from the traditional LPGs since the period variation in OLPG is caused by the effective index difference of the two core modes at the writing wavelength, while in the traditional LPGs it is directly induced by temperature or strain. For the refractive index sensitivity with a large cladding, OLPG behaves the same as a traditional LPG with only material contributions since the grating period remains unchanged. / Master of Science
10

Exploration of Radar Cross Section Models and Distributed Sensing Techniques in JCAS Cell-free Massive MIMO / Exploration av radar tvärsektionsmodeller och distribuerade avkänningstekniker i JCAS Cellfri Massive MIMO

Zou, Qinglin January 2023 (has links)
Joint Communication and Sensing (JCAS) technology enables the sharing of infrastructure, resources, and signals between communication and sensing. However, studying the performance and algorithms using appropriate target reflectivity models for detection poses a significant challenge. Moreover, the increasing demand for efficient sensing systems in large-scale environments necessitates the study of distributed sensing for handling extensive data collection and processing. This study investigates the impact of target mobility on the choice between the Swerling-I and Swerling-II models for target reflectivity and proposes a brief method for reflectivity models in multi-static sensing. This method constructed a dedicated decorrelation area for a single radar detector using its decorrelation angle. Multiple radar system constructs an intersection of these areas. For targets expected to remain in this area, the Swerling-I model is preferred, while for targets likely to move to the outside intersection, the Swerling-II model is more suitable. Additionally, this thesis proposes and derives the test statistics for the distributed sensing in JCAS cell-free massive MIMO (multiple-input multiple-output) systems, where only the statistical distribution of transmitted signals is known at the receiver access points for the sensing purpose. This thesis compares the sensing performance of the proposed distributed processing with the centralized processing. Moreover, the results of a power allocation algorithm that maximizes sensing performance are compared against a baseline algorithm that minimizes total power consumption. In terms of sensing performance via guaranteeing the quality of service of the communication, the results indicate that the sensing algorithm consistently outperforms the power-minimizing algorithm, regardless of the selected reflectivity model. Furthermore, the Swerling-II model performs relatively worse when the reflectivity of the target is low, but exhibits improved performance on a relatively high reflectivity target. Regarding distributed sensing, its implementation may lead to a deterioration in sensing performance. However, the results show that distributed sensing can approach the performance of centralized sensing when the target has high reflectivity. The major advantage of distributed sensing is the reduced fronthaul signaling load in a JCAS cell-free massive MIMO system. / Joint Communication and Sensing (JCAS) teknologi möjliggör delning av infrastruktur, resurser och signaler mellan kommunikation och sensorik. Studier av prestanda och algoritmer med lämpliga modeller för detektering av målets reflektivitet utgör emellertid en betydande utmaning. Dessutom kräver den ökande efterfrågan på effektiva sensorsystem i storskaliga miljöer studier av distribuerad sensorik för att hantera omfattande datainsamling och -bearbetning. Detta studie undersöker påverkan av målets rörlighet på valet mellan SwerlingI och Swerling-II modellerna för målets reflektivitet och föreslår en kort metod för reflektivitetsmodeller i multi-statisk avkänning. Denna metod konstruerar ett dedikerat dekorrelationsområde för en enskild radardetektor med hjälp av dess dekorrelationsvinkel. Ett flertal radarsystem konstruerar en skärningspunkt av dessa områden. För mål som förväntas förbli i detta område föredras Swerling-I-modellen, medan för mål som troligen rör sig till den yttre skärningspunkten är Swerling-II-modellen mer lämplig. Dessutom föreslår och härleder denna avhandling teststatistik för distribuerad avkänning i JCAS cellfri massiv MIMO (multiple-input multiple-output) system, där endast den statistiska fördelningen av överförda signaler är känd vid mottagarens åtkomstpunkter för avkänningsändamål. Denna avhandling jämför avkänningsprestanda för föreslagen distribuerad bearbetning med centraliserad bearbetning. Dessutom jämförs resultaten av en effekttilldelningsalgoritm som maximerar avkänningsprestanda mot en baslinjealgoritm som minimerar total effektförbrukning. När det gäller avkänningsprestanda genom att garantera kommunikationens tjänstekvalitet indikerar resultaten att avkänningsalgoritmen konsekvent presterar bättre än effektminimeringsalgoritmen, oavsett vald reflektivitetsmodell. Dessutom presterar Swerling-II-modellen relativt sämre när målets reflektivitet är låg, men uppvisar förbättrad prestanda på ett relativt högreflekterande mål. När det gäller distribuerad avkänning kan dess implementering leda till försämrad avkänningsprestanda. Resultaten visar dock att distribuerad avkänning kan närma sig prestandan hos centraliserad avkänning när målet har hög reflektivitet. Den största fördelen med distribuerad avkänning är den minskade signalbelastningen i en JCAS cellfri massiv MIMO-system.

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