For the past 40 years, acoustic sensing has been a major avenue for the growth of interfero- metric fiber-optic sensors. Fiber-optic acoustic sensors have found uses in military, commer- cial, and medical applications. An interferometric fiber-optic acoustic sensor is presented utilizing the Michelson interferometer configuration with Faraday mirrors to eliminate po- larization fading. A 3 × 3 coupler is used as the beamsplitting component, and a symmetric demodulation algorithm is applied to recover the phase signal. This sensor has a theoretical resolution of 5.5 pico-strains and room to improve. Such improvements are discussed in the conclusion. / Master of Science

In this conducted research, optical fiber sensors are used to measure low strength alternating magnetic fields. Various fiber sensor configurations are tested and investigated to demonstrate sensing capabilities at different field magnitudes and frequencies. Distributed acoustic sensing fibers (DAS) have been largely studied and documented across a variety of applications and sensing systems. This research uses the DAS technology in tandem with magnetostrictive materials to create a distributed multi-material optical fiber magnetic sensor. Magnetic sensing has high demand across different fields and often runs into challenges of extreme environments including high temperature, corrosion, and areas with poor accessibility. The robust and distributed nature of optical fiber sensors which can be cheaply produced for long lengths is an attractive option over other single point magnetic sensors. In down hole applications specifically, having a distributed sensor able to be deployed easily and over long distances for magnetic sensing would be a large improvement to bulkier traditional magnetometers. In the conducted study, different magnetostrictive materials are implemented in distributed optical fiber sensors to analyze and compare the effective sensitivity and potential commercial viability. Nickel, galfenol alloy, and MetGlas alloy inclusions are drawn into fused silica optical fibers with Bragg gratings inscribed later on for DAS capability. Each was investigated for its response to varying AC magnetic fields to determine relative sensitivity and resolution for distributed magnetic field sensing. / Master of Science / Magnetic sensing has high demand in biomedical applications as well as within the oil and energy industry. This research proposes a series of optical fiber-based sensors to overcome many of the challenges present amidst traditional magnetic sensors. Materials that respond to magnetic fields by either contracting or expanding are coined magnetostrictive. The proposed fiber-based sensors use magnetostrictive materials to create a change in the optical path length of the light being transmitted through the optical fiber. This path difference can be converted to a strain measurement and when compared with a standardized magnetometer, a calibration curve is established for the fiber sensor. Different magnetostrictive materials are studied for measuring various alternating magnetic field amplitude strengths to look at improved sensitivity and/or resolution. This includes nickel, galfenol alloy, which is made up of iron and gallium, and MetGlas, which is composed of primarily of iron. Small wires of the respective materials are drawn out inside the silica fiber while the optical fiber is made so that continuous lengths run the course of the fiber. Different sizes were experimented with. Another simplified tested setup used a ribbon of the MetGlas while a distributed acoustic fiber sensor was laid on top to pick up the strain response while exposed to an alternating magnetic field. All of the mentioned test setups showed success in measuring alternating magnetic field strengths with a clear positive correlation of strain response to magnetic field amplitude. A calibration curve was established for each sensing system and analyzed to show an effective sensitivity range.

This research describes a method of using distributed acoustic sensing to noninvasively measure volumetric flow rate via multiple unique sensor styles. This work modifies previously used methods of flow detection via fiber optic acoustic sensors affixed onto the exterior body of a flow apparatus. Flow rate measurement methods for two unique sensor styles are described. Weak trends are additionally observed as a function of flow temperature that may represent opportunity for future optimization. A discussion of current noninvasive flow rate measurement methods is given as well as their limitations. A background of distributed acoustic sensing is presented along with a summary of its fundamentals as well as its functionality in noninvasive flow rate measurement. A description of previous techniques that utilized distributed acoustic sensing in conjunction with fiber optic acoustic sensing is shown. The acoustic properties of the fluid-induced vibrations are measured as a function of flow rate and flow temperature utilizing a special type of fiber optic sensor. Numerically smoothed frequency domain acoustic peaks are evaluated by intensity, area, central frequency, and full width at half maximum as flow conditions vary. All tested sensors were found to yield a strong dependence between peak intensity and flow rate. A dependence between central frequency and flow temperature was observed in some cases. The sensor system developed was able to measure fluid-induced vibration intensity and vibrational central frequency and offers potential uses in a myriad of vibrational applications. / Master of Science / This research provides a method of measuring fluid-induced vibrations caused by internal pressure fluctuations stemming from a variety of flow conditions. In this case, a specially fabricated optical fiber is applied to the external surface of the pipe. As water flows at a known volumetric flow rate and temperature, the acoustic signal generated is detected by the optical sensor signal demodulation system. The fiber used is a silicate material designed to transmit optical signals over long distances with minimal loss. Modifications to the fiber can be made to differentiate the measured optical signal loss by frequency band, as well as to designate the spatial position on a fiber sensor to locate where loss is occurring. By measuring optical loss of distinct fiber spatial positions at high sampling frequencies, an abundance of sensing opportunities become available. In knowing optical signal travel time of select wavelengths to corresponding strain characteristics amongst a section of fiber, optoelectronic devices with strong computing power called interrogators can powerfully measure the intensity and rate of fiber strain at a significantly high sampling frequency. Fiber optic sensors have been used in many areas where monitoring of changes in positional microstrain is desired. Such sensors are embedded in-ground for seismic monitoring, as well as on the ocean floor for submarine structural characterization with long singular fibers. Flow rate measurement is performed with fiber coils and various other geometries for active oil wells, fission reactors, and other areas. Improving the performance and applicational flexibility of these sensors allows for greater opportunity for scientific advancement in an array of fields. This research was completed to offer a new method of flow rate measurement while also gauging if flow temperature was able to be measured via a single fiber optic sensor. Fiber strain was observed to be strongly dependent on flow rate, whereas the rate at which strain occurred suggests simultaneous flow and temperature measurement is possible in certain types of fiber arrangements. The work produced in this research is a step towards singular-fiber flow rate and temperature sensing.

A dynamically dexterous legged robot platform generates specific acoustic signals during the interaction with the ground and the environment. These acoustic signals are expected to contain rich information that is related to the interaction surface as a function of the position of the legs and the overall contact process mixed with the actuator sounds that initiate the movement. As the robot platform walks or runs in any environment, this convolved acoustic signal created can be processed and analyzed in real time operation and the interaction surface can be identified. Such an utilization of acoustic data can be possible for various indoor and outdoor surfaces and with this can be useful in adjusting gait parameters that play an essential role in dynamic dexterity. In this work, surface type identification is achieved with using the several popular signal processing and pattern classification methods not on the robot platform but off-line. The performances of the selected features and the algorithms are evaluated for the collected data sets and these outputs are compared with the expectations. Depending on the off-line training and experiment results, the applicability of the study to an embedded robot platform as a future application is found quite feasible and the surface type as an input to the robot sensing is expected to improve the mobility of the robot in both indoor and outdoor environment.

<p dir="ltr">The Alpine Fault, located in the South Island, New Zealand, is a subject of intense geological study due to its potential to trigger large earthquakes. It encompasses a complex system with the interplay of mechanics, thermodynamics, and fluid. Gaining insights into these systems not only enhances our understanding of the fault but also holds the potential to guide risk mitigation efforts.</p><p dir="ltr">The damage extent and fracture networks within the metamorphic rock mass adjacent to the fault can be effectively characterized by seismic anisotropy, an elastic property of rock, where seismic waves travel at different speeds with variation directions. This thesis presents a comprehensive exploration of seismic anisotropy in the hanging wall immediately adjacent to the principal slip zone of the Alpine Fault in New Zealand. Leveraging the borehole seismic data from a unique scientific drilling project and advanced numerical modeling techniques, the ultimate goal is to invert and parameterize the bulk seismic anisotropy.</p><p dir="ltr">Motivated by these challenges, the thesis undertakes several key initiatives: The first effort focuses on gaining a comprehensive understanding of an innovative method for seismic measurement: Distributed Acoustic Sensing (DAS) – examining its operational principles, factors influencing observed wavelets, and how it contrasts with traditional point sensors for accurate interpretation. Subsequently, the research introduces the implementation of an open-source seismic wave solver designed for modeling elastic wave propagation in complicated anisotropic media. This solver is further optimized for computational efficiency with its performance rigorously benchmarked.</p><p dir="ltr">With this preparedness, the inversion is further facilitated by high-performance computing (HPC) and a deep-learning algorithm specifically designed for automatically picking transit times. The inverted bulk elastic constants, compared to the intact rock, reveal 28% to 35% reductions in qP-wave velocity, characterizing the damage due to mesoscale fracture. Further analysis sheds light on the existence of orthogonal fracture sets and an intricate geometrical arrangement that agree with the previous borehole image log. This represents an advancement in our ability to characterize and understand the geologic processes with seismic anisotropy.</p>

Les capteurs distribués à fibre optique (aussi nommés DAS) sont une nouvelle technologie d'acquisition sismique qui utilise des câbles traditionnels à fibre optique pour fournir une mesure de la déformation le long du câble. Ce système d'acquisition est largement utilisé dans les profils sismiques verticaux (PSV). Le couplage est un facteur clé qui a une grande influence sur la qualité des données. Alors que, pour les acquisitions PSV, les géophones sont attachés à la paroi du puits, le câble de fibre optique est soit cimenté derrière le tubage, soit attaché avec des pinces rigides au tubage ou simplement descendu dans le puits. Cette dernière stratégie de déploiement donne généralement le plus petit rapport signal sur bruit, mais est considérée comme la plus rentable en particulier pour les installations dans des puits existants. Cette thèse porte sur la problématique du couplage du DAS quand le câble est simplement descendu dans le puits. Nous développons des modèles numériques pour analyser les données réelles. L'interprétation de ces résultats nous permet de conclure qu'un contact immédiat du câble avec la paroi du puits avec une force de contact calculée est nécessaire pour fournir des bonnes conditions de couplage. Sur la base de ces résultats, nous proposons des solutions pour optimiser davantage les acquisitions avec le système DAS. Nous modifions numériquement la force de contact et les propriétés élastiques du câble DAS et démontrons comment ces modifications peuvent améliorer mais aussi détériorer la qualité des données. Enfin, nous proposons un algorithme de détection du couplage qui permet d'assurer l'acquisition de données réelles avec un rapport signal / bruit élevé. / Distributed Acoustic Sensing (DAS) is a new technology of seismic acquisition that relies on traditional fibre-optic cables to provide inline strain measurement. This acquisition system is largely used in vertical seismic profiling (VSP) surveys. Coupling is a key factor influencing data quality. While geophones and accelerometers are clamped to the borehole wall during VSP surveys, the fibre cable is either clamped and then cemented behind the casing, or attached with rigid clamps to the tubing, or loosely lowered into the borehole. The latter deployment strategy, also called wireline deployment, usually acquires the lowest level of signal but is regarded as the most cost-effective in particular for existing well installations. This PhD thesis addresses the problematic of coupling of DAS using wireline deployment. We develop numerical models that are used to analyse real data. The interpretation of these results allows us concluding that an immediate contact of the cable with the borehole wall with a computed contact force is required to provide good coupling conditions. Based on those findings, we propose solutions to further optimise DAS acquisitions. We numerically modify the contact force and the elastic properties of the DAS cable and show how these modifications can improve but also deteriorate data quality. Finally, we propose a coupling detection algorithm that is applied to real datasets and allows ensuring the acquisition of data with a high signal-to-noise ratio.

<p dir="ltr">The design of hardware platform in acoustic sensing is critical. The number and the spatial arrangement of microphones play a huge role in sensing performance. All microphones should be properly processed for simultaneous recording. This work introduces an FPGA-based acoustic transceiver system supporting acoustic sensing with custom acoustic signals. The system contains 16 microphones and a speaker synchronized during sensing processes. The microphones were arranged into an ‘L’ shape with eight microphones on each line for a better resolution of angle estimation on two dimensions. The microphones were placed on a specifically designed PCB to achieve an optimal distance of the half-wavelength of acoustic signals for optimized sensing performance. A microphone interface was implemented on Ultra96-V2 FPGA for handling the simultaneous high-speed data streams. The system features an implementation of full-level data transmission up to the top-level Python program. To evaluate the sensing performance of the system, we conducted an experiment used Frequency Modulated Continuous Wave (FMCW) as the transmitted acoustic signal. The result of evaluation shown the accurate sensing of range, velocity and relative angle of a moving hand on the two dimensions corresponding to the microphone groups.</p>

This paper investigates how audio monitoring systems should be designed, in the context of smart cities and in accordance with Swedish legislation. Audio monitoring for smart cities is promising and have previously shown great potential. However its opportunities are still relatively unexplored. ShotSpotter is one of several examples of audio monitoring in the context of smart cities. In the US only, the system has successfully been used to alert and locate shootings in over 90 cities. However, the technology is surrounded by controversies and there has been debate whether audio monitoring systems are compatible with law. Compatibility is critical since incompatibility could result in severe sanctions. Research related to this paper has been conducted according to the Design Science research strategy. The research resulted in design guidelines for audio monitoring systems, for law enforcement purposes, in accordance with Swedish law. The design guidelines are based upon existing audio monitoring systems, previous research and empirical data. The empirical data consists of 12 interviews with experts in law, phonetics and digital forensics. Additionally, the design guidelines have been evaluated by an expert in a criteria-based evaluation interview. Results of the research shows that it is, in fact, possible to design audio monitoring systems, in the context of smart cities, in accordance with Swedish legislation. The design guidelines can be applied in the development of audio monitoring systems with law enforcement purposes. With some modification, they can also be used for audio monitoring systems with other purposes. / Uppsatsen syftar till att undersöka hur ljudövervakningssystem inom ramen för smarta städer- konceptet bör utformas i enlighet med svensk lagstiftning. Ljudövervakning för smarta städer har visat på stor potential och ännu är dess möjligheter outforskade. ShotSpotter är ett av flera exempel på ljudövervakning inom ramen för smarta städer. Systemet har med framgång använts för att uppmärksamma och lokalisera skottlossningar i över 90 amerikanska städer. Det råder dock debatt huruvida ljudövervakningssystemet är kompatibelt med lagstiftning. Denna kompatibilitet är kritisk då det motsatta kan resultera i stränga påföljder och därmed utgöra direkta hinder för implementation. Forskning i relation till uppsatsen har genomförts inom ramen för forskningsstrategin Design Science. Forskningsprocessen har mynnat ut i designriktlinjer för hur ett ljudövervakningssystem med brottsbekämpande syfte bör utformas i enlighet med svensk lagstiftning. Designriktlinjerna baseras på befintliga ljudövervakningssystem, tidigare forskning och omfattande empiriskt underlag. Det empiriska underlaget utgörs av 12 intervjuer med olika typer av experter inom juridik, fonetik och IT- forensik. Designriktlinjerna har med framgång utvärderats i en kriteriebaserad expertintervju. Av forskningsresultatet att döma är det möjligt att utforma ljudövervakningssystem för smarta städer i enlighet med svensk lagstiftning. De framtagna designriktlinjerna kan användas vid utveckling av ljudövervakningssystem med brottsbekämpande syfte. Med viss modifikation kan de även användas för ljudövervakningssystem med andra syften.

Im vorliegenden Bericht wurde untersucht, wie Spanndrahtbrüche in einem Brückenträger sowohl mittels Schallemissionsanalyse (SEA) als auch mit (eingebetteter) verteilter faseroptischer akustischer Sensorik (DAS) zu erkennen sind. Die Ergebnisse zeigen, dass die Bruchsignale anhand beider Messverfahren detektiert werden können. Die jeweils detektierten Drahtbrüche werden miteinander verglichen. Durch eine Gegenüberstellung werden SEA und DAS detailliert dargestellt.