Optical Current Sensors for High Power Systems: A Review

The intrinsic advantages of optical sensor technology are very appealing for high voltage applications and can become a valuable asset in a new generation of smart grids. In this paper the authors present a review of optical sensors technologies for electrical current metering in high voltage applications. A brief historical overview is given together with a more detailed focus on recent developments. Technologies addressed include all fiber sensors, bulk magneto-optical sensors, piezoelectric transducers, magnetic force sensors and hybrid sensors. The physical principles and main advantages and disadvantages are discussed. Configurations and strategies to overcome common problems, such as interference from external currents and magnetic fields induced linear birefringence and others are discussed. The state-of-the-art is presented including commercial available systems.info:eu-repo/semantics/publishedVersio

Hybrid Optical Fiber Sensors for Smart Materials and Structures

There has been a rapid growth in the use of advanced composite materials in a variety of load-bearing structures, for example in aviation for structures such as rotor blades, aircraft fuselage and wing structures. Composite materials embedded with fiber-optic sensors (FOS) have been recognized as one of the prominent enabling technologies for smart materials and structures. The rapid increase in the interest in composite materials embedded with FOS has been driven by numerous applications, such as intelligent composite manufacturing/processing, and safety-related areas in aircrafts. Research has been focused recently on using several optical sensor types working together to form so called “hybrid optical fiber sensors” in order to overcome the limitations of the individual sensor technologies. The main aim of the research described in this thesis is to investigate a hybrid sensing scheme that utilizes polarimetric sensors and FBG sensors working in a complimentary fashion to measure multiple physical parameters in a composite material, with a particular focus on measuring the complex indirect parameters thermal expansion and vibration. The research described in this thesis investigates the performance of a hybrid sensing scheme based on polarimetric sensors and FBG sensors after embedding in a composite material. It is shown that the influence of thermal expansion within a composite material on embedded polarimetric sensors is the main source of errors for embedded fiber sensor strain measurements and that for practical strain sensing applications buffer coated PM-PCF are more suitable for embedding in composite. Further, using a buffer stripped PM-PCF polarimetric sensor, a measurement scheme to measure a composite material\u27s thermal elongation induced strain is proposed. A novel hybrid sensor for simultaneous measurement of strain, temperature and thermal strain is demonstrated by integrating polarimetric sensors based on acrylate coated high bi-refringent polarization maintaining photonic crystal fiber (HB-PM-PCF), and a coating stripped HB-PM-PCF sensor together with an FBG sensor. Flexible demodulation modules that can be embedded or surface attached is a challenge for composite materials containing fiber-optic sensors. In this thesis an interrogation method that allows intensity domain operation of hybrid sensor is demonstrated. Further focusing towards the miniaturization of the hybrid sensor interrogator, a miniaturized flexible interrogator for the demonstrated hybrid sensing scheme embedded in a composite material is also designed. Low frequency vibration measurements are performed for glass fibre-reinforced composite material samples with two different strain-sensitive polarimetric sensor types embedded. It is shown that the strain sensitivity of polarimetric sensors limits the vibration measurements to a certain range of vibration amplitudes. A polarimetric sensor based buffer stripped HB-PM-PCF is demonstrated for monitoring the different stages of the curing process for a Mageneto-Rheological composite material. By providing information about multiple parameters such as strain, temperature, thermal strain, vibration amplitude and vibration frequency the proposed and demonstrated hybrid sensing approach has a high potential to change the paradigm for smart material design in the future

Eksperimentalna karakterizacija magneto-optičkih osobina Faradejevog kristala namenjenog za konstrukciju senzora magnetskog polja

The thesis explores preparation and magneto properties of bismuth germanium oxide single crystal (B12GeO20) which is irradiated by pulsed femtosecond laser of increasing power. Analyses performed on irradiated and un irradiated samples showed significant changes in transmittance, transmission spectra, sample color, Raman spectra (RS), X-ray diffraction (XRD) pattern, Verdet constant (VC), magneto-optical property and absorption coefficient. After irradiation, the transmission spectra values increased whereas anisotropy detected in the transmission spectra of unirradiated samples disappeared. The change of color caused by irradiation was noticeable to the naked eye. The XRD measurements confirmed structural changes induced by laser irradiation, i.e., the laser- beam-incident side of the sample became almost amorphous, whereas the side opposite to the incident can be indexed to the Bi12 Ge O20 compound. Irradiation caused increase of Raman spectra peaks with the exception of crystal peaks of type E, which disappeared. The femtosecond pulsed laser irradiation can be used to improve bismuth germanium oxide single crystal optical properties. Femtosecond pulsed laser irradiation can improve optical properties of Bi12 GeO20 single crystals.Disertacija razmatra pripremu za proizvodnju i magneto optička svojstva Bizmut germanijum oksidnih kristala (B12GeO20) koje se ozračuju femtosekundnim laserskim impulsima zracima sa rastućom snagom. Analize izvršene nad ozračenim i neozračenim uzorcima kristala pokazale su značajne promene u transmitansi, transmisionom spektru, boji, Ramanovom spektru, rezultatima difrakcije X zraka, Verdeovoj konstanti, magneto-optičkim svojstvima i koeficijentu apsorpcije. Posle ozračivanja došlo je do porasta transmitivnosti i izostanka anizotropije u transmisionom spektru u odnosu na neozračene uzorke. Izmena boje uzoraka primetna je čak i golim okom. XRD merenja pokazala su strukturne promene indukovane laserskim zracima tako da je npr. strana uzorka neposredno ozračena laserom postala skoro potpuno amorfna dok se suprotna strana uzorka indeksira na B12GeO20 jedinjenje. Ozračivanje je izazvalo porast vrhova u Ramanovom spektru sa izuzetkom vrhova za tip E koji se nisu pojavili. Femtosekundni laserski impulsi mogu se iskoristiti da unaprede optička svojstva kristala..

Strontium Barium Niobate Thin Films for Dielectric and Electro-Optic Applications

SBN exhibits excellent dielectric non linear properties and one of the largest known Pockels electro-optic coefficient. Thin films of SBN are therefore particularly attractive for their potential use as low voltage electro-optic waveguides or for the realization of electrically-tunable photonic crystals. This chapter proposes an overview of the questions relative to the preparation, dielectric and electro-optic properties of SBN thin films, with a special focus on epitaxial growth in view of electro-optic applications. Experimental results obtained with films prepared by RF magnetron sputtering are presented

Electrooptic electric field sensor for dc and extra-low-frequency measurement

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The thesis reports the results of the research carried out towards the development of an electrooptic sensor for DC and extra low frequency electric field measurement. Available cubic electrooptic crystals were compared from the sensor sensitivity point of view. A new figure of merit was used taking into account the attenuation of the electric field in the dielectric crystal and its shape. The effect of optical activity in 23 cubic crystals was analyzed using the concept of Poincare sphere. The cubic crystals were further characterised for the charge relaxation time constant to estimate their performance in DC field measurements. Crystals of Bismuth Germanate and Lithium Niobate were identified as suitable materials for the DC field sensor. The selected crystals were found suitable at extra-low-frequencies. DC field measurements, without the rotation of the crystal, were possible only with Lithium Niobate. However, its performance was influenced to a great extent by the effect of stimulated conductivity. The quarter-wave plate and the crystal of Lithium Niobate were identified as the main sources of temperature instability. A new method of temperature compensation of the quarter-wave plate is proposed. Due to the temperature instability of Lithium Niobate, mainly attributed to the pyroelectric effect and natural birefringence, it is difficult to use the sensor in practical applications. The performance of the sensor is significantly affected by the presence of an external space charge. The proposed method of its elimination using an artificial extension of the sensing element did not reduce the space charge effect adequately. The response of the sensor in a space charge environment was found to be linear and independent of the space charge density. This enabled measurements of static fields in a unipolar environment. The direct field measurements in bipolar environment suffered from a drift which is intolerable in practical measurements. The minimum detectable electric field of this sensor in the frequency range from 1 to 200Hz was 1V/m, with a signal to noise ratio equal to 0dB and a resolution of 1V/m. The static field measurements were limited to measurements of pulses with a duration of 200s, due to a long term drift of photodetectors. The minimum detectable level of DC electric field was 2.4kV/m.EPSR

Polarized Light Applications towards Biomedical Diagnosis and Monitoring

Utilization of polarized light for improved specificity and sensitivity in disease diagnosis is occurring more often in fields of sensing, measurement, and medical diagnostics. This dissertation focuses on two distinct areas where polarized light is applied in biomedical sensing/monitoring: The first portion of worked reported in this dissertation focuses on addressing several major obstacles that exist prohibiting the use of polarized light as a means of developing an optical based non-invasive polarimetric glucose sensor to improve the quality of life and disease monitoring for millions of people currently afflicted by diabetes mellitus. In this work there are two key areas, which were focused on that require further technical advances for the technology to be realized as a viable solution. First, in vivo studies performed on New Zealand White (NZW) rabbits using a dual-wavelength polarimeter were conducted to allow for performance validation and modeling for predictive glucose measurements accounting for the time delay associated with blood aqueous humor glucose concentrations in addition to overcoming motion induced birefringence utilizing multiple linear regression analysis. Further, feasibility of non-matched index of refraction eye coupling between the system and corneal surface was evaluated using modeling and verified with in vitro testing validation. The system was initially modeled followed by construction of the non-matched coupling configuration for testing in vitro. The second half of the dissertation focuses on the use of polarized light microscopy designed, built, and tested as a low-cost high quality cellphone based polarimetric imaging system to aid medical health professionals in improved diagnosis of disease in the clinic and in low-resource settings. Malaria remains a major global health burden and new methods for, low-cost, high-sensitivity diagnosis of malaria are needed particularly in remote low-resource areas throughout the world. Here, a cost effective optical cell-phone based transmission polarized light microscope system is presented utilized for imaging the malaria pigment known as hemozoin. Validation testing of the optical resolution required to provide diagnosis similar to commercial polarized imaging systems will be conducted and the optimal design will be utilized in addition to image processing to improve the diagnostic capability