Disertacijoje sprendžiama lėtinimo sistemų kraštinių ir galinių laidininkų įtakos modelių tikslumui įvertinimo problema. Pagrindiniai tyrimo objektai – daugialaidžių ir meandrinių mikrojuostelinių linijų matematiniai modeliai, skaitiniai analizės metodai. Darbo tikslas – sukūrus modelius, grįstus baigtinių skirtumų laiko srities metodu, ištirti galinių ir kraštinių laidininkų netolygumų įtaką meandrinių mikrojuostelinių vėlinimo linijų laiko ir dažninėms charakteristikoms, pasiūlyti meandrinių vėlinimo linijų konstrukcijų tobulinimo priemones. Darbe sprendžiami uždaviniai: matematinių pavienės, susietųjų ir daugialaidžių mikrojuostelinių linijų modelių sudarymas ir savybių tyrimas, taikant baigtinių skirtumų bei baigtinių skirtumų laiko srities analizės metodus; daugialaidžių mikrojuostelinių linijų sintezės ir meandrinių mikrojuostelinių vėlinimo linijų analizės algoritmų bei jų elektrinių charakteristikų skaičiavimo metodikų sudarymas. Disertaciją sudaro įvadas, keturi skyriai, bendrosios išvados, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai. Įvadiniame skyriuje formuluojama tiriamoji problema, aptariamas darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomi pranešimai konferencijose disertacijos tema bei pateikiama disertacijos struktūra. Pirmajame skyriuje pateikiama literatūros... [toliau žr. visą tekstą] / There are investigated accuracy issues of edges and ends evaluation problems of meander slow-wave systems in the dissertation. Objects of research – mathematical models of multiconductor and meander microstrip delay lines, numerical analysis methods. Aim of the work – after creating mathematical models, based on finite difference time domain method, explore ends and edges discontinuity effects on meander microstrip delay lines time and frequency characteristics, propose structural improvement measures of meander delay line. The dissertation approaches major tasks such as: mathematical individual, coupled, multiconductor microstrip lines models composition for performance and their properties investigation using finite difference and finite difference time domain methods of analysis; synthesis algorithm of multiconductor microstrip lines and analysis algorithm of meander microstrip delay line and methodology of their electrical characteristics calculation creation. The thesis consists of four parts including introduction, 4 chapters, conclusions, references. The introduction reveals investigated problem, importance of the thesis and object of research. It also describes the purpose and tasks of the dissertation, research methodology, scientific novelty and the practical significance of results examined in the thesis and defended statements. The introduction ends in presenting the author’s publications on the subject of the defended dissertation, offering the material of made... [to full text]

There are investigated accuracy issues of edges and ends evaluation problems of meander slow-wave systems in the dissertation. Objects of research – mathematical models of multiconductor and meander microstrip delay lines, numerical analysis methods. Aim of the work – after creating mathematical models, based on finite difference time domain method, explore ends and edges discontinuity effects on meander microstrip delay lines time and frequency characteristics, propose structural improvement measures of meander delay line. The dissertation approaches major tasks such as: mathematical individual, coupled, multiconductor microstrip lines models composition for performance and their properties investigation using finite difference and finite difference time domain methods of analysis; synthesis algorithm of multiconductor microstrip lines and analysis algorithm of meander microstrip delay line and methodology of their electrical characteristics calculation creation. The thesis consists of four parts including introduction, 4 chapters, conclusions, references. The introduction reveals investigated problem, importance of the thesis and object of research. It also describes the purpose and tasks of the dissertation, research methodology, scientific novelty and the practical significance of results examined in the thesis and defended statements. The introduction ends in presenting the author’s publications on the subject of the defended dissertation, offering the material of made... [to full text] / Disertacijoje sprendžiama lėtinimo sistemų kraštinių ir galinių laidininkų įtakos modelių tikslumui įvertinimo problema. Pagrindiniai tyrimo objektai – daugialaidžių ir meandrinių mikrojuostelinių linijų matematiniai modeliai, skaitiniai analizės metodai. Darbo tikslas – sukūrus modelius, grįstus baigtinių skirtumų laiko srities metodu, ištirti galinių ir kraštinių laidininkų netolygumų įtaką meandrinių mikrojuostelinių vėlinimo linijų laiko ir dažninėms charakteristikoms, pasiūlyti meandrinių vėlinimo linijų konstrukcijų tobulinimo priemones. Darbe sprendžiami uždaviniai: matematinių pavienės, susietųjų ir daugialaidžių mikrojuostelinių linijų modelių sudarymas ir savybių tyrimas, taikant baigtinių skirtumų bei baigtinių skirtumų laiko srities analizės metodus; daugialaidžių mikrojuostelinių linijų sintezės ir meandrinių mikrojuostelinių vėlinimo linijų analizės algoritmų bei jų elektrinių charakteristikų skaičiavimo metodikų sudarymas. Disertaciją sudaro įvadas, keturi skyriai, bendrosios išvados, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai. Įvadiniame skyriuje formuluojama tiriamoji problema, aptariamas darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomi pranešimai konferencijose disertacijos tema bei pateikiama disertacijos struktūra. Pirmajame skyriuje pateikiama literatūros... [toliau žr. visą tekstą]

The thesis describes development and application of coupled resonant coil sensors, which is of growing interest for remote monitoring applications. An interrogation technique, which improves the accuracy and interrogation range of coupled resonant coil sensors, is introduced. The method uses time-domain gating to produce measurements that are dominated by the response of the sensor coil and are immune to surrounding object interference. For application in structural health monitoring a low cost embeddable coupled coil sensor, which is able to monitor the corrosion potential of reinforcement steel is presented. Results of an accelerated corrosion test using the sensor indicate that corrosion potential can be monitored with a resolution less than 10 mV and a sensitivity of 0.76 kHz/mV. The last part describes a coupled-coil pH sensor based on pH electrode potential measurement. A linear response over a 4 to 10 pH dynamic range and 50 kHz/pH sensitivity are achieved with a 0.1 pH resolution and 30 s response time.

Ultrasparčių puslaidininkinių komponentų kūrimas reikalauja gilesnio supratimo apie tai, kaip puslaidininkiuose vyksta fizikiniai procesai, trunkantys kelias pikosekundes ar net mažiau nei vieną pikosekundę. Tokie reiškiniai, kaip elektronų impulso ir energijos relaksacija bei nepusiausvyrųjų krūvininkų pagavimas yra labai svarbūs puslaidininkinių fotonikos ir terahercinio diapazono prietaisų veikimui. Iki pastarojo meto pagrindinis ultrasparčiųjų procesų puslaidininkiuose tyrimo įrankis buvo optiniai metodai, kuriuose elektronų dinamikai stebėti buvo pasitelkiami pikosekundinių ar femtosekundinių lazerių impulsai. Nepaisant išskirtinai didelės šių metodų laikinės skyros, optinio kaupinimo-zondavimo matavimų rezultatus yra palyginti sudėtinga interpretuoti. Šie rezultatai dažniausiai yra įtakojami kelių sistemos parametrų kitimo ir įvairių fizikinių reiškinių tarpusavio sąveikos, todėl sunkiai susiejamas su kuria nors elektronų laikine charakteristika. Disertacijos darbo tikslas – naudojant terahercinės spinduliuotės impulsus išmatuoti elektronų impulso ir energijos relaksacijos trukmes keliuose siauratarpiuose puslaidininkiuose bei jų gyvavimo trukmes medžiagose, skirtose fotolaidžių terahercinės spinduliuotės emiterių ir detektorių gamybai. Šioje disertacijoje yra pateikiami įvairių charakteringų elektroninius procesus puslaidininkiuose apibūdinančių trukmių matavimų naudojant terahercinės spinduliuotės impulsus rezultatai. Tokie tyrimai atlikti ir optinio žadinimo –... [toliau žr. visą tekstą] / Creation of ultrafast semiconductor components is inconceivable without understanding various processes of picoscond duration in semiconductors. These processes, as electron energy relaxation time or nonequiriblium carrier capture are very important for semiconductor photonics and terahertz range devices. Since now, the most popular tool of measuring ultrafast processes in semiconductors was picosecond or femtosecond laser pulses. In spite of excellent time resolution, optical pump – probe methods have a significant imperfection. Interpretation of the results can be very complicate. Also, the measured result can be affected by few variable parameters or interaction of various physical phenomenon. Therefore determinate results can be hardly related with electron time dependent characteristic. The aim of this dissertation was to measure electron energy relaxation times and electron life times by using terahertz pulses in narrow – gap semiconductors used for photoconductive terahertz emitters or detectors. In this dissertation, electron characteristic times witch describe various processes in semiconductor, were studied. These measurements were performed by optical pump – terahertz probe technique and time domain terahertz spectroscopy. The emission of terahertz pulses from the semiconductor surface, illuminated by femtosecond laser pulses, was investigated.

The thesis describes development and application of coupled resonant coil sensors, which is of growing interest for remote monitoring applications. An interrogation technique, which improves the accuracy and interrogation range of coupled resonant coil sensors, is introduced. The method uses time-domain gating to produce measurements that are dominated by the response of the sensor coil and are immune to surrounding object interference. For application in structural health monitoring a low cost embeddable coupled coil sensor, which is able to monitor the corrosion potential of reinforcement steel is presented. Results of an accelerated corrosion test using the sensor indicate that corrosion potential can be monitored with a resolution less than 10 mV and a sensitivity of 0.76 kHz/mV. The last part describes a coupled-coil pH sensor based on pH electrode potential measurement. A linear response over a 4 to 10 pH dynamic range and 50 kHz/pH sensitivity are achieved with a 0.1 pH resolution and 30 s response time.

The interaction of light and matter at nanoscale is the subject of study of this dissertation. Particularly, the coupling of light to surface plasmons and their applications in the fields of spectroscopy and sensing is the focus of this work. In terms of spectroscopy, the simple reason of using light to study the chemical structures of different materials is the fact that the energy of light lies in the range of vibrational and electronic transitions of matter. Further, the ability to squeeze light to subwavelength dimensions opens up new possibilities of designing nano-optical devices. In this work we explore surface plasmons for two major applications: (i) Directivity enhanced Raman spectroscopy and (ii) Chemical/biological sensing. Here a new enhancement phenomenon has been demonstrated experimentally in regards to Raman spectroscopy. Typically, Raman enhancement is considered in terms of local fields only. Here we show the use of directive nanoantennas to provide additional enhancement of two orders of magnitude. The nanoantenna design is optimal in the sense that almost all of the scattered light is coupled into the numerical aperture of the collecting lens. It is shown that the additional enhancement from directivity pushes the sensitivity to single molecule regime. Further, the out of plane radiation and simplicity of the design makes it an ideal candidate for use with typical commercial microscope setups. Extra ordinary transmission through nanohole arrays in metallic films is studied for refractive index sensing. Bulk resolution of 6×10-7 is demonstrated by optimizing array dimensions, wavelength of operation, noise reduction and consideration of sensitivity of the detecting CCD camera. Self-assembled nanostructures are investigated for spectroscopic applications. Time dependent studies of nanorods assembled in end-to-end and side-by-side configurations are conducted. The end-to-end configuration results in higher local field enhancements whereas; the side-by-side configuration shows a reduction in local fields because of the cancellation of radial field components between the neighbouring nanorods. It should be noted that higher fields are desirable for Raman spectroscopy. Grating structures have been analysed using reduced coupled mode theory. In most cases, only three lowest order modes prove to be sufficient for accurate description of the system response. Here we present design guidelines for broadband operation and optimization of high quality factor resonators. Finally the complex reflection coefficient from arbitrary terminated nanorods has been investigated. Phase of reflection plays an important role in the determination of resonance wavelength of nanoantennas. It is shown that the localized surface plasmon resonance of nanoparticles can be considered in terms of propagating surface plasmons along a nanorod of similar geometry where the length of the nanorod approaches zero accompanied with π degrees of phase of reflection. The contributions made in this work can prove useful in the fields of analytical chemistry and biomedical sensing. The directive nanoantenna can find applications in a number of areas such as light emitting devices, photovoltaics, single photon sources and high resolution microscopy. Our work related to EOT based sensing is already approaching the resolution of commercially available refractive index sensors with the added advantage of multiplexed detection. / Graduate

The dissertation investigates the optical time domain reflectometer (OTDR) systems. The main object of research is an optical receiver for OTDR. The aim of the work is to create an optical receiver design method-ology to achieve optimal dynamic range of the system for a given band-width, design and investigate integrated fully differential variable gain tran-simpedance amplifier for OTDR optical receiver. Main tasks solved in this work are: perform analysis of OTDR struc-tures, main specifications and suggest possible improvement approaches; analyze main optical receiver noise sources and noise minimization and create generalized noise model; create optical receiver for an OTDR design methodology, that allow calculating avalanche photodiode multiplication factor, transimpedance amplifier feedback resistance and voltage amplifier input transistor dimensions that achieves optimal OTDR dynamic range; design and perform simulations of transimpedance amplifier integrated cir-cuit using AMS 0.35 µm CMOS technology and calculate optical receiver parameters in 0.1–100 MHz range of bandwidths The dissertation consists of four parts including Introduction, 4 chap-ters, Conclusions, References and 1 Annex. The introduction reveals the investigated problem, importance of the thesis and the object of research. It also describes the purpose and tasks, research methodology, scientific novelty, the practical significance of re-sults examined in the paper and defended statements. The... [to full text] / Disertacijoje nagrinėjamos laiko srities optinės reflektometrinės (OTDR) sistemos. Pagrindinis tyrimo objektas yra OTDR įėjimo pakopa – optinis imtuvas (OI). Disertacijos tikslas – sukurti OI projektavimo metodiką, lei-džiančią pasiekti optimalų dinaminį diapazoną, suprojektuoti ir ištirti integ-rinį diferencinį pereinamos varžos stiprintuvą (PVS) su kintamu stiprinimo koeficientu. Darbe sprendžiami šie uždaviniai: atliekama OTDR ir jų pagrindinių charakteristikų analizė ir formuluojamos tobulinimo kryptys; analizuojami pagrindiniai optinio imtuvo triukšmų šaltiniai, jų mažinimo galimybės ir su-daromas apibendrintas optinio imtuvo triukšmų modelis; sukuriama OI pro-jektavimo metodika, leidžianti apskaičiuoti griūtinio fotodiodo dauginimo faktorių, pereinamosios varžos stiprintuvo grįžtamojo ryšio varžą ir įėjimo tranzistoriaus fizinius matmenis, kuriems esant gaunamas optimalus dina-minis diapazonas; projektuojamas optinio imtuvo maketas iš diskrečiųjų elementų ir tiriami jo parametrai; atliekamas integrinio PVS projektavimas ir modeliavimas, taikant 0,35 µm KMOP technologiją bei optinio imtuvo pa-rametrų skaičiavimas 0,1–100 MHz dažnių juostų diapazone. Disertaciją sudaro įvadas ir keturi skyriai. Pabaigoje pateikiami naudo-tos literatūros ir autoriaus publikacijų disertacijos tema sąrašai ir 1 priedas. Įvadiniame skyriuje aptariama: tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, suformuluotas darbo tikslas bei uždaviniai, ap-rašoma tyrimų metodika... [toliau žr. visą tekstą]

Power distribution networks (PDNs) are conducting structures employed in semiconductor systems with the aim of providing circuits with reliable and constant operating voltage. This network has non-neglible electrical parasitics. Consequently, when digital circuits inside the chip switch, the supply voltage delivered to them does not remain ideal and exhibits spatial and temporal voltage fluctuations. These fluctuations in the supply voltage, known as the power-supply noise (PSN), can affect the functionality and the performance of modern microprocessors. The design of this PDN in the chip is an important part in ensuring power integrity. Modeling and simulation of the PSN in on-chip PDNs is important to reduce the cost of processors. These PDNs have irregular geometries, which affect the PSN. As a result, they have to be modeled. The problem sizes encountered in this simulation are usually large (on the order of millions), necessitating computationally efficient simulation approaches. Existing approaches for this simulation do not guarantee at least one of the following three required properties: computationally efficiency, accuracy, and numerically robustness. Therefore, there is a need to develop accurate, numerically robust, and efficient algorithms for this simulation. For many interconnects (e.g., transmission lines, board connectors, package PDNs), only their frequency responses and SPICE circuits (e.g., nonlinear switching drivers, equivalent circuits of interconnects) terminating them are known. These frequency responses are usually available only up to a certain maximum frequency. Simulating the electrical behavior of these systems is important for the reliable design of microprocessors and for their faster time-to-market. Because terminations can be nonlinear, a transient simulation is required. There is a need for a transient simulation of band-limited frequency-domain data characterizing a multiport passive system with SPICE circuits. The number of ports can be large (greater than or equal to 100 ports). In this simulation, unlike in traditional circuit simulators, normal properties like stability and causality of transient results are not automatically met and have to be ensured. Existing techniques for this simulation do not guarantee at least one of the following three required properties: computationally efficiency for a large number of ports, causality, and accuracy. Therefore, there is a need to develop accurate and efficient time-domain techniques for this simulation that also ensure causality. The objectives of this Ph.D. research are twofold: 1) To develop accurate, numerically robust, and computationally efficient time-domain algorithms to compute PSN in on-chip PDNs with irregular geometries. 2) To develop accurate and computationally efficient time-domain algorithms for the causal cosimulation of band-limited frequency-domain data with SPICE circuits.

One of the most significant goals in coal mining technology research is the automation of underground coal mining machinery. A current challenge with automating underground coal mining machinery is measuring and maintaining a coal mining horizon. The coal mining horizon is the horizontal path the machinery follows through the undulating coal seam during the mining operation. A typical mining practice is to leave a thin remnant of coal unmined in order to maintain geological stability of the cutting face. If the remnant layer is too thick, resources are wasted as the unmined coal is permanently unrecoverable. If the remnant layer is too thin, the product is diluted by mining into the overburden and there is an increased risk of premature roof fall which increases danger. The main challenge therefore is to develop a robust sensing method to estimate the thickness of thin remant coal layers. This dissertation addresses this challenge by presenting a pattern recognition methodology to estimate thin remnant coal layer thickness using ground penetrating radar (GPR). The approach is based upon a novel feature vector, derived from the bispectrum, that is used to characterise the early-time segment of 1D GPR data. The early-time segment is dominated by clutter inherent in GPR systems such as antenna crosstalk, ringdown and ground-bounce. It is common practice to either time-gate the signal, disregard the clutter by rendering the early-time segment unusable, or configure the GPR equipment to minimise the clutter effects which in turn reduces probing range. Disregarding the early-time signal essentially imposes a lower thickness limit on traditional GPR layer thickness estimators. The challenges of estimating thin layer thickness is primarily due to these inherent clutter components. Traditional processing strategies attempt to minimise the clutter using pre-processing techniques such as the subtraction of a calibration signal. The proposed method, however, treats the clutter as a deterministic but unknown signal with additive noise. Hence the proposed approach utilises the energy from the clutter and monitors change in media from subtle changes in the signal shape. Two complementary processing methods important to horizon sensing have been also proposed. These methods, near-surface interface detection and antenna height estimation, may be used as pre-validation tools to increase the robustness of the thickness estimation technique. The proposed methods have been tested with synthetic data and validated with real data obtained using a low power 1.4 GHz GPR system and a testbed with known conditions. With the given test system, it is shown that the proposed thin layer thickness estimator and near-surface interface detector outperform the traditional matched filter based processing methods for layers less than 5 cm in thickness. It is also shown that the proposed antenna height estimator outperforms the traditional height estimator for heights less than 7 cm. These new methods provide a means for reliably extending layer thickness estimation to the thin layer case where traditional approaches are known to fail.

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