ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / In this paper we will present a new fiber sensor integrated monitor (FSIM) to be used in an embedded instrumentation system (EIS). The proposed system consists of a super luminescent diode (SLD) as a broadband source, a novel high speed tunable MEMS filter with built in photodetector, and an integrated microprocessor for data aggregation, processing, and transmission. As an example, the system has been calibrated with an array of surface relief fiber Bragg gratings (SR-FBG) for high speed, high temperature monitoring. The entire system was built on a single breadboard less than 50 cm² in area.

<p>Human motion monitoring is an important function in numerous applications. In this dissertation, two systems for monitoring motions of multiple human targets in wide-area indoor environments are discussed, both of which use radio frequency (RF) signals to detect, localize, and classify different types of human motion. In the first system, a coherent monostatic multiple-input multiple-output (MIMO) array is used, and a joint spatial-temporal adaptive processing method is developed to resolve micro-Doppler signatures at each location in a wide-area for motion mapping. The downranges are obtained by estimating time-delays from the targets, and the crossranges are obtained by coherently filtering array spatial signals. Motion classification is then applied to each target based on micro-Doppler analysis. In the second system, multiple noncoherent multistatic transmitters (Tx's) and receivers (Rx's) are distributed in a wide-area, and motion mapping is achieved by noncoherently combining bistatic range profiles from multiple Tx-Rx pairs. Also, motion classification is applied to each target by noncoherently combining bistatic micro-Doppler signatures from multiple Tx-Rx pairs. For both systems, simulation and real data results are shown to demonstrate the ability of the proposed methods for monitoring patient repositioning activities for pressure ulcer prevention.</p> / Dissertation

Neste trabalho é proposto um método de interrogação de fibra óptica com arquitetura reduzida, que pode ser empregado em sistemas distribuídos de detecção de intrusão de médias e longas distâncias, como para proteção de perímetros, divisas, faixa de dutos, plantas industriais, ou outras instalações, usando uma fibra óptica comum como elemento sensor. O método é baseado na técnica Brillouin Optical Time Domain Analysis (BOTDA), porém dispensando-se a varredura sequencial com diferentes frequências, o que simplifica o sistema, reduz custos e melhora o tempo de resposta. O trabalho consiste de uma abordagem geral sobre o tema, sendo apresentada a teoria básica dos fenômenos de espalhamento não linear em fibras ópticas, o detalhamento do método de interrogação proposto e a descrição dos experimentos realizados em laboratório, seguida de uma analise e comentários quanto ao desempenho alcançado, bem como de algumas de sugestões para melhor explorar o potencial do método. / In this research work is proposed an optic fiber interrogation method with reduced architecture, that can be applied in distributed intrusion detection systems of medium and long distances, such as for the protection of pipeline\'s right of way, perimeters, boundaries, industrial plants or others installations, using a standard optic fiber as a sensor. The proposed method is based on a Brillouin Time Domain Analysis (BOTDA), however dispensing the sequential frequency sweeping, what simplifies the system, reduce its costs and improve the response time. The work comprehends a general discussion of the subject, being presented the basic theory of the nonlinear scattering phenomena in optic fibers, the description of the proposed interrogation method and the conducted in lab experiments, followed by an analysis and comments on the achieved performance, as well as a few suggestions to better explore the potential of the method.

Neste trabalho é proposto um método de interrogação de fibra óptica com arquitetura reduzida, que pode ser empregado em sistemas distribuídos de detecção de intrusão de médias e longas distâncias, como para proteção de perímetros, divisas, faixa de dutos, plantas industriais, ou outras instalações, usando uma fibra óptica comum como elemento sensor. O método é baseado na técnica Brillouin Optical Time Domain Analysis (BOTDA), porém dispensando-se a varredura sequencial com diferentes frequências, o que simplifica o sistema, reduz custos e melhora o tempo de resposta. O trabalho consiste de uma abordagem geral sobre o tema, sendo apresentada a teoria básica dos fenômenos de espalhamento não linear em fibras ópticas, o detalhamento do método de interrogação proposto e a descrição dos experimentos realizados em laboratório, seguida de uma analise e comentários quanto ao desempenho alcançado, bem como de algumas de sugestões para melhor explorar o potencial do método. / In this research work is proposed an optic fiber interrogation method with reduced architecture, that can be applied in distributed intrusion detection systems of medium and long distances, such as for the protection of pipeline\'s right of way, perimeters, boundaries, industrial plants or others installations, using a standard optic fiber as a sensor. The proposed method is based on a Brillouin Time Domain Analysis (BOTDA), however dispensing the sequential frequency sweeping, what simplifies the system, reduce its costs and improve the response time. The work comprehends a general discussion of the subject, being presented the basic theory of the nonlinear scattering phenomena in optic fibers, the description of the proposed interrogation method and the conducted in lab experiments, followed by an analysis and comments on the achieved performance, as well as a few suggestions to better explore the potential of the method.

No description available.

Brillouin scattering has been verified to be an effective mechanism in temperature and strain sensing. This kind of sensors can be applied to civil structural monitoring of pipelines, railroads, and other industries for disaster prevention. This thesis first presents a novel fiber sensing scheme for long-span fully-distributed pressure measurement based on Brillouin scattering in a side-hole fiber. After that, it demonstrates that Brillouin frequency keeps linear relation with temperature up to 1000°C; Brillouin scattering is a promising mechanism in high temperature distributed sensing. A side-hole fiber has two longitudinal air holes in the fiber cladding. When a pressure is applied on the fiber, the two principal axes of the fiber birefringence yield different Brillouin frequency shifts in the Brillouin scattering. The differential Brillouin scattering continuously along the fiber thus permits distributed pressure measurement. Our sensor system was designed to analyze the Brillouin scattering in the two principal axes of a side-hole fiber in time domain. The developed system was tested under pressure from 0 to 10,000 psi for 100m and 600m side-hole fibers, respectively. Experimental results show fibers with side holes of different sizes possess different pressure sensitivities. The highest sensitivity of the measured pressure induced differential Brillouin frequency shift is 0.0012MHz/psi. The demonstrated spatial resolution is 2m, which maybe further improved by using shorter light pulses. / Master of Science

Distributed temperature and strain sensing is demanded for a wide range of applications including real-time monitoring of industrial processes, health monitoring of civil infrastructures, etc. Optical fiber distributed sensors have attracted tremendous research interests in the past decade to meet the requirements of such applications. This research presents a multiplexed sensor array for distributed temperature and strain sensing that can multiplex a large number of UV-induced sensors along a single fiber. The objective of this research is to develop a quasi-distributed sensing technology that will greatly increase the multiplexing capacity of a sensor network and can measure temperature and strain with a high accuracy and high resolution. UV-induced intrinsic Fabry-Perot interferometric (IFPI) optical fiber sensors, which have low reflectance and low power loss, are good candidates for multiplexed sensors networks. Partial reflectors are constructed by irradiating photosensitive fiber with a UV laser beam. A pair of reflectors will form a Fabry-Perot interferometer that can be used for temperature and strain sensing. A sensor fabrication system based on a pulsed excimer laser and a shadow mask is developed. A spectrum-based measurement system is presented to measure the interference fringes of IFPI sensors. A swept coherent light source is used as the light source. The spectral responses of the IFPI sensors at different wavelengths are measured. A frequency division multiplexing (FDM) scheme is proposed. Multiple sensors with different optical path differences (OPD) have different sub-carrier frequencies in the measured spectrum of the IFPI sensors. The multiplexing capacity of the sensor system and the crosstalk between sensors are analyzed. Frequency estimation based digital signal processing algorithms are developed to determine the absolute OPDs of the IFPI sensors. Digital filters are used to select individual frequency components and filter out the noise. The frequency and phase of the filtered signal are estimated by means of peak finding and phase linear regression methods. The performance of the signal processing algorithms is analyzed. Experimental results for temperature and strain measurement are demonstrated. The discrimination of the temperature and strain cross sensitivity is investigated. Experimental results show that UV-induced IFPI sensors in a FDM scheme have good measurement accuracy for temperature and strain sensing and potentially have a large multiplexing capacity. / Ph. D.

Structural health monitoring (SHM) has become a strong national interest because of the need of reliable and accurate damage detection methods for aerospace, civil and mechanical engineering infrastructure. Health monitoring of these structures usually requires the sensors to have such features as large area coverage, maintenance free or minimum maintenance, ultra-low cost per measurement point, and capability of operation in harsh environments. Fiber Bragg grating (FBG) has attracted considerable interest for this application because of its compactness, electromagnetic immunity, and excellent multiplexing capability. Several FBG multiplexing techniques have been developed to increase the multiplexing number and further reduce the unit cost. To the author's best knowledge, the current demonstrated maximum multiplexing number are 800 FBG sensors in a single array using optical frequency domain reflectometry (OFDR), whose maximum fiber span is limited by the coherence length of light source. In this work, we proposed and demonstrated a wavelength-scanning time-division multiplexing (WSTDM) of 1000 ultra-weak FBGs for distributed temperature sensing. In comparison with the OFDR method, the WSTDM method distinguishes the sensors by different time delays, and its maximum operation distance, which is limited by the transmission loss of the fiber, can be as high as tens of kilometers. The strong multiplexing capability and low crosstalk of the ultra-weak FBG sensors was investigated through both theoretical analysis and experiment. An automated FBG fabrication system was developed for fast FBG fabrication. With this WSTDM method, we multiplexed 1000 ultra-weak FBGs for distributed temperature sensing. Besides the demonstrated temperature measurement, the reported method can also be applied to measure other parameters, such as strain, pressure. / Ph. D.

All-optical signal processing has grown over the last decade due to the demand for high-speed and high-bandwidth data processing. The main objective of all-optical signal processing is to avoid signal conversions from the optical domain to electrical domain and then back to optical, which introduces noise and bottlenecks data transmission speeds. These conversions can be avoided by manipulating light using an optical medium, e.g. an optical fiber, and taking advantage of the nonlinear response of the medium's dipoles to an external electric field. Nonlinear effects arising from the third-order nonlinearities, such as the Kerr effect, allow for an intense light beam to modify the refractive index of a medium through which it propagates. As a consequence, the phase of the light beam changes as it propagates and new frequencies are generated; this phenomenon is referred to as self-phase modulation (SPM). Light's ability to modify not only its own properties but also the properties of other co-propagating beams has been widely applied in telecommunications to create integrated all-optical data regenerators. While optical fibers are mainly utilized to transmit data at extreme speeds, they can also act as sensors when considering the reflected signal as opposed to the transmitted signal. Surprisingly, most of the fiber sensing field relies on electrically-driven components for manipulating light and does not take advantage of all-optical signal processing capabilities. In this thesis, we demonstrate the use of the nonlinear Kerr effect to improve aspects of both fiber point and distributed sensing. These sensing scenarios respectively refer to the use of a fiber as a single sensing element, and to the detection of external perturbations continuously along the entire length of the fiber. The sensing improvement are obtained by first inducing a sinusoidal modulation on the light before it experiences self-phase modulation in a nonlinear medium, leading to the generation of optical sidebands. By judiciously adjusting the peak power of the light and extracting a specific sideband, multiple all-optical signal processing functions are achieved. First, high extinction ratio pulses can be generated by extracting a higher-order sideband, which allows for extending the sensing distance of distributed fiber-based sensors. The extinction ratio refers to the ratio between the pulse peak and pedestal powers. To quantify the generated extinction ratios, we develop a measurement technique based on a single-photon counter and measure a pulse exhibiting a 120 dB extinction ratio, which was originally created by an electro-optic modulator with a 20-dB extinction ratio. Second, all-optical peak power stabilization can be achieved by extracting the first-order SPM-generated sideband. We utilize this technique to stabilize the peak power of an optical pulse sent to a distributed fiber sensor. We demonstrate that this stabilization technique allows for the detection of applied vibrations that would otherwise remain buried in the background noise. Third, we demonstrate an all-optical scheme, based on sinusoidally-modulated light experiencing SPM, that enables the magnification of fluctuations in the peak power intensity of a pulsed signal. The light's peak power at the entrance of the nonlinear medium is adjusted to reach a power regime yielding a magnification factor of 2m+1, when extracting the mth-order SPM-generated sideband. Finally, we propose a new sensing scheme composed of two all-optical signal processing steps to allow for the detection of environmental perturbations previously too small to be detected by a given intensity-based fiber sensor.

This dissertation demonstrates the first of its kind distributed magnetic field sensor based on a fiber optic distributed acoustic sensing (DAS) scheme. Ferromagnetic nickel and Metglas® were dispersed internally within a fiber optic preform and then drawn on an in-house fiber optic draw tower to lengths in the kilometers. Due to the close proximity of the ferromagnetic metals and fiber optic core, the magnetostrictive strain response of the ferromagnetic materials when exposed to a magnetic field would perturbate within the fiber cladding and transfer that strain, internally, to the fiber optic core. Strain resulting from the magnetostrictive effect allows the DAS based sensor to accurately translate strain into readable magnetic field data. Due to the high sensitivity seen in this sensor design, multiparameter sources, acoustic and magnetic fields, were tested and validated and a three dimensional magnetic-field vector sensor was proposed. Numerical analysis of the novel sensor design was first implemented using COMSOL Multiphysics, where inputs such as magnetostrictive element shape, size, distance, and number were first investigated. Upon optimizing system constraints, the sensor design was further modified such that single mode operation was consistent across multiple fiber draws while retaining high strain transfer from the ferromagnetic elements to the fiber optic core. Ferromagnetic material selection was evaluated as a function of the saturation magnetostriction constants and a total of 4 modules were used to fully characterize the complex physics involved in this sensor design. All fabrication and testing were performed in-house using a full scale 3-story fiber draw tower and custom environmental testing stations to imitate naturally occurring events such as magnetic or acoustic point sources. A unique stacking method was used to embed ferromagnetic nickel and Metglas® into a fiber optic preform which when combined with a custom fiber draw process resulted in consistent multi-material fibers drawn to lengths of 1-km. In-house testing facilities included different types of electromagnetic generators, in addition to a soil test bed, and an outdoor test bed which allowed 100 meters of fiber to be tested simultaneously. All tested sensors demonstrated high strain transfer capabilities on the order of 0.01-10 μϵ depending on the materials used, ferromagnetic rod number, and core to metal spacing. Due to the sensitivity of the system the difference between AC and DC was distinct, and directional magnetostriction was studied. Transverse and longitudinal magnetic wave propagation was controlled through a solenoid and rectangular Helmholtz coil, both built in-house. A three-dimensional magnetic field vector sensor was proposed due to the success of the magnetic field sensor, and a design was proposed and initially tested to validate direction as a function of field strength and distance. To summarize, this dissertation explores the first fully distributed magnetic field sensor using DAS based techniques and one of the first multi-material fiber draw processes which can produce consistent single mode fiber up to 1-km. Due to extensive FEA modeling, multiple iterations of the magnetic sensor were fully characterized and an equation describing the relationship between sensor design and strain transfer has been created and validated experimentally. Multi-parameter tests including acoustic and magnetic fields were implemented and an algorithm was developed to separate the mixed signals. Finally, a test was performed to demonstrate the feasibility of sensing magnetic fields directionally. Cumulative results demonstrate a high-quality sensor alternative to current designs which may surpass other magnetic sensors due to innate multi-parameter capabilities, in addition to the inexpensive production cost and extremely long operating lengths. / Doctor of Philosophy / This dissertation demonstrates the first of its kind distributed magnetic field sensor based on a fiber optic distributed acoustic sensing (DAS) scheme. Ferromagnetic nickel and Metglas® were dispersed internally within a fiber optic preform and then drawn on an in-house fiber optic draw tower to lengths in the kilometers. Due to the close proximity of the ferromagnetic metals and fiber optic core, the magnetostrictive strain response of the ferromagnetic materials when exposed to a magnetic field would perturbate within the fiber cladding and transfer that strain, internally, to the fiber optic core. Strain resulting from the magnetostrictive effect allows the DAS based sensor to accurately translate strain into readable magnetic field data. Due to the high sensitivity seen in this sensor design, multiparameter sources, acoustic and magnetic fields, were tested and validated and a three dimensional magnetic-field vector sensor was proposed. Numerical evaluation of the sensing structure was perused before experimental testing using COMSOL Multiphysics. Experimental and numerical evaluations were compared and showed a high degree of certainty which allowed expedited design modifications. Sensor characterization included scanning electron microscopy, and electron diffraction spectroscopy, which provided insight into material composition and fiber polishing quality. Due to the high-quality results attained in the combined acoustic and magnetic field tests, a final design was proposed to gather magnetic field data as a vector, showing both magnitude and direction. The 3D magnetic field vector sensor was partially validated based on a test which compared intensity with distance and a design and methodology was proposed to fully test and characterize this design. To summarize, a novel magnetic field sensor, capable of multi-parameter sensing, was proposed and tested experimentally and numerically resulting in a robust and highly sensitive design. The work presented here provides some of the first insights into multi-material fiber fabrication, an equation which provides an estimated relationship between magnetostrictive strain transfer onto a fiber optic core and the perceived DAS based sensor results, as well as a first of its kind multi-parameter distributed acoustic and magnetic field sensor.