Electrically Small Dipole Antenna Probe for Quasi-static Electric Field Measurements

The thesis designs, constructs, and tests an electrically small dipole antenna probe for the measurement of electric field distributions induced by a transcranial magnetic stimulation (TMS) coil. Its unique features include high spatial resolution, large frequency band from 100 Hz to 300 kHz, efficient feedline isolation via a printed Dyson balun, and accurate mitigation of noise. Prior work in this area is thoroughly reviewed. The proposed probe design is realized in hardware; implementation details and design tradeoffs are described. Test data is presented for the measurement of a CW capacitor electric field, demonstrating the probe’s ability to properly measure conservative electric fields caused by a charge distribution. Test data is also presented for the measurement of a CW solenoidal electric field, demonstrating the probe’s ability to measure non-conservative solenoidal electric fields caused by Faraday’s law of induction. Those are the primary fields for the transcranial magnetic stimulation. Advantages and disadvantages of this probing system versus those of prior works are discussed. Further refinement steps necessary for the development of this probe as a valuable TMS instrument are discussed

Antennas for wireless sensor network applications

The objective of this thesis is to present an analysis of antennas, which are applicable to wireless sensor networks and, in particular, to the requirements of the Speckled Computing Network Consortium. This was done through a review of the scientific literature on the subject, and the design, computer simulation, and experimental verification, of various suitable designs of antenna The first part of this thesis outlines what an antenna is and how it radiates. An insight is also given to the fundamental limitations of antennas. As antennas investigated in this thesis are planar-printed designs, an insight into the types of feed lines applicable, such as microstrip, CPW and slotline, is given. To help characterise the antennas investigated, the fundamental antenna analysis parameters, such as impedance bandwidth, S-parameters, radiation pattern, directivity, antenna efficiency, gain and polarisation are discussed. Also discussed is the 3D electromagnetic simulation software, HFSS, which was used to simulate the antennas in this thesis. To help illustrate the use of HFSS, a proximity-coupled patch antenna, operating at 5.8 GHz, was used as an example. A range of antennas were designed, manufactured and tested. These used conventional printed circuit boards (PCBs) and Gallium Arsenide (GaAs) substrates, operating at a range of frequencies from 2.4 GHz to 12 GHz. A review was conducted into relevant, suitable radio architectures such as, conventional narrowband systems, Ultra-Wide Band (UWB), and simplified radio architectures such as those based on the diode rectifier method, and Super Regenerative Receivers (SRR). There were several UWB antennas designed, which operate over a 3.1 – 10.16 GHz operational band with a VSWR ≤ 2. All the UWB antennas were required to transmit a UWB pulse with minimal distortion, which placed a requirement of linear phase and low values of group delay to minimise distortion on the pulse. UWB antennas investigated included a Vivaldi antenna, which was large, directional and gave excellent pulse transmission characteristics. A CPW-fed monopole was also investigated, which was small, omni-directional and had poor pulse transmission characteristics. A UWB dipole was designed for use in a UWB channel modelling experiment in collaboration with Strathclyde University. The initial UWB dipole investigated was a microstrip-fed structure that had unpredictable behaviour due to the feed, which excited leakage current down the feed cable and, as a result, distorted both the radiation pattern and the pulse. To minimise the leakage current, three other UWB dipoles were investigated. These were a CPW-fed UWB dipole with slots, a hybrid-feed UWB dipole, and a tapered-feed UWB dipole. Presented for these UWB dipoles are S-parameter results, obtained using a vector network analyser, and radiation pattern results obtained using an anechoic chamber. There were several antennas investigated in this thesis directly related to the Speckled Computing Consortiums objective of designing a 5mm3 ‘Speck’. These antennas were conventional narrowband antenna designs operating at either 2.45 GHz or 5.8 GHz. A Rectaxial antenna was designed at 2.45 GHz, which had excellent matching (S11 = -20dB) at the frequency of operation, and an omni-directional radiation pattern with a maximum gain of 2.69 dBi as measured in a far-field anechoic chamber. Attempts were made to increase the frequency of operation but this proved unsuccessful. Also investigated were antennas that were designed to be integrated with a 5.8 GHz MMIC transceiver. The first antenna investigated was a compact-folded dipole, which provided an insight into miniaturisation of antennas and the effect on antenna efficiency. The second antenna investigated was a ‘patch’ antenna. The ‘patch’ antenna utilised the entire geometry of the transceiver as a radiation mechanism and, as a result, had a much improved gain compared to the compact-folded dipole antenna. As the entire transceiver was an antenna, an investigation was carried into the amount of power flow through the transceiver with respect to the input power

Electromechanics of an Ocean Current Turbine

The development of a numeric simulation for predicting the performance of an Ocean Current Energy Conversion System is presented in this thesis along with a control system development using a PID controller for the achievement of specified rotational velocity set-points. In the beginning, this numeric model is implemented in MATLAB/Simulink® and it is used to predict the performance of a three phase squirrel single-cage type induction motor/generator in two different cases. The first case is a small 3 meter rotor diameter, 20 kW ocean current turbine with fixed pitch blades, and the second case a 20 meter, 720 kW ocean current turbine with variable pitch blades. Furthermore, the second case is also used for the development of a Voltage Source Variable Frequency Drive for the induction motor/generator. Comparison among the Variable Frequency Drive and a simplified model is applied. Finally, the simulation is also used to estimate the average electric power generation from the 720 kW Ocean Current Energy Conversion System which consists of an induction generator and an ocean current turbine connected with a shaft which modeled as a mechanical vibration system

Electromechanics of an Ocean Current Turbine

The development of a numeric simulation for predicting the performance of an Ocean Current Energy Conversion System is presented in this thesis along with a control system development using a PID controller for the achievement of specified rotational velocity set-points. In the beginning, this numeric model is implemented in MATLAB/Simulink® and it is used to predict the performance of a three phase squirrel single-cage type induction motor/generator in two different cases. The first case is a small 3 meter rotor diameter, 20 kW ocean current turbine with fixed pitch blades, and the second case a 20 meter, 720 kW ocean current turbine with variable pitch blades. Furthermore, the second case is also used for the development of a Voltage Source Variable Frequency Drive for the induction motor/generator. Comparison among the Variable Frequency Drive and a simplified model is applied. Finally, the simulation is also used to estimate the average electric power generation from the 720 kW Ocean Current Energy Conversion System which consists of an induction generator and an ocean current turbine connected with a shaft which modeled as a mechanical vibration system

Design and Optimization of Physical Waveform-Diverse and Spatially-Diverse Radar Emissions

With the advancement of arbitrary waveform generation techniques, new radar transmission modes can be designed via precise control of the waveform's time-domain signal structure. The finer degree of emission control for a waveform (or multiple waveforms via a digital array) presents an opportunity to reduce ambiguities in the estimation of parameters within the radar backscatter. While this freedom opens the door to new emission capabilities, one must still consider the practical attributes for radar waveform design. Constraints such as constant amplitude (to maintain sufficient power efficiency) and continuous phase (for spectral containment) are still considered prerequisites for high-powered radar waveforms. These criteria are also applicable to the design of multiple waveforms emitted from an antenna array in a multiple-input multiple-output (MIMO) mode. In this work, three spatially-diverse radar emission design methods are introduced that provide constant amplitude, spectrally-contained waveforms implemented via a digital array radar (DAR). The first design method, denoted as spatial modulation, designs the radar waveforms via a polyphase-coded frequency-modulated (PCFM) framework to steer the coherent mainbeam of the emission within a pulse. The second design method is an iterative scheme to generate waveforms that achieve a desired wideband and/or widebeam radar emission. However, a wideband and widebeam emission can place a portion of the emitted energy into what is known as the `invisible' space of the array, which is related to the storage of reactive power that can damage a radar transmitter. The proposed design method purposefully avoids this space and a quantity denoted as the Fractional Reactive Power (FRP) is defined to assess the quality of the result. The third design method produces simultaneous radar and communications beams in separate spatial directions while maintaining constant modulus by leveraging the orthogonal complement of the emitted directions. This orthogonal energy defines a trade-space between power efficiency gained from constraining waveforms to be constant amplitude and power efficiency lost by emitting energy in undesired directions. The design of FM waveforms via traditional gradient-based optimization methods is also considered. A waveform model is proposed that is a generalization of the PCFM implementation, denoted as coded-FM (CFM), which defines the phase of the waveform via a summation of weighted, predefined basis functions. Therefore, gradient-based methods can be used to minimize a given cost function with respect to a finite set of optimizable parameters. A generalized integrated sidelobe level (GISL) metric is used as the optimization cost function to minimize the correlation range sidelobes of the radar waveform. System specific waveform optimization is explored by incorporating the linear models of three different loopback configurations into the GISL metric to match the optimized waveforms to the particular systems

Електромагнітна сумісність у системах електропостачання

The textbook is devoted to electromagnetic processes connected both with conducted and field electromagnetic interferences. Special attention is paid to interharmonic electromagnetic interference. Questions of electromagnetic compatibility in power networks with wind electric sets, problems of voltage dips and voltage impulses are considered. Active filters are considered as a specific problem of electromagnetic compatibility. Influence of electromagnetic fields on biosphere, of electromagnetic ecology, economic and legal problems of electromagnetic compatibility are presented

Wave Propagation

A wave is one of the basic physics phenomena observed by mankind since ancient time. The wave is also one of the most-studied physics phenomena that can be well described by mathematics. The study may be the best illustration of what is “science”, which approximates the laws of nature by using human defined symbols, operators, and languages. Having a good understanding of waves and wave propagation can help us to improve the quality of life and provide a pathway for future explorations of the nature and universe. This book introduces some exciting applications and theories to those who have general interests in waves and wave propagations, and provides insights and references to those who are specialized in the areas presented in the book

Design of millimetre-wave antennas on low temperature co-fired ceramic substrates

Tässä työssä tutkitaan millimetriaaltoalueella toimivien, LTCC- monikerroskeraamitekniikalla valmistettujen, antennien toteutusmahdollisuuksia. Erityisesti keskitytään 60 GHz taajuudella toimivien mikroliuska-antennien suunnitteluun, mallintamiseen, valmistukseen ja testaamiseen. LTCC-tekniikka on nykyaikainen pakkaustekniikka, jolla voidaan valmistaa laadukkaita monikerroksisia komponentteja ja moduuleja jopa millimetriaaltotaajuuksille asti. LTCC-tekniikan hyötyjä ovat suuri pakkaustiheys, matalat eriste- ja johdinhäviöt, luotettavuus ja vakaus. LTCC-tekniikan suurimpia haasteita on valmistusepätarkkuus, joka muodostuu ratkaisevaksi tekijäksi 60 GHz taajuudella toimivien antennien suorituskyvylle. Kirjallisuuskatsauksessa esitellään antenniteorian perusteet ja yleisiä antennien ominaissuureita. Myös antenniryhmän käsitteet esitellään. Tämän jälkeen tarkastellaan mikroliuska-antennien ominaisuuksia, jonka jälkeen perehdytään LTCC-tekniikkaan. Työssä suunnitellaan usean tyyppisiä mikroliuska-antenneja ja antennit mallinnetaan käyttäen kaupallisia ohjelmia. Antenneja simuloidaan myös käyttäen itse kirjoitettua ohjelmakoodia. Antennien toimivuus varmistetaan käytännössä suorittamalla sirontaparametri- ja säteilykuviomittaukset. Mittaus- ja simulointitulokset ovat melko yhteneviä. Pienet poikkeavuudet tuloksissa johtuvat antennien toteutuneiden ja suunniteltujen mittojen eroavaisuuksista. Kuitenkin, paluuvaimennuksen arvoksi saadaan helposti -10 dB tai parempi. Impedanssikaistanleveys vaihtelee välillä 3...6 % ja antennien maksimivahvistus välillä 3...4 dB. Tulosten perusteella voidaan todeta, että perinteisen LTCC-tekniikan avulla voidaan toteuttaa toimivia antenneja jopa 60 GHz taajuudelle.In this work, implementation possibilities of millimetre-wave antennas fabricated with low temperature co-fired ceramic (LTCC) technology are investigated. Especially, microstrip antennas operating at 60 GHz frequency band are designed, modeled, manufactured and tested. LTCC is a modern packaging technology which enables manufacturing of multilayer components and modules with high performance up to millimetre-wave region. Benefits of the LTCC technology are high packaging density, low dielectric and conductor losses, reliability and stability. The challenges of the LTCC technology are related to the manufacturing tolerances which become critical for operation of the antennas at 60 GHz frequency band. In the literature review, the basics of antenna theory are presented and common antenna parameters are introduced. Issues related to antenna arrays are also introduced. Then, basic characteristics of microstrip antennas are presented, followed by the introduction of the LTCC technology. Several types of microstrip antennas are designed and modeled with numerical simulation software. Two types of antennas are also modeled with simulation code implemented by the author. The functionality of fabricated antennas is validated by conducting scattering parameter and radiation pattern measurements. Measurement results agree quite well with the simulated ones. Small deviations between simulated and measured results are caused by the differences in designed and realised dimensions of the antennas. Return loss of -10 dB or better is easily achieved. Impedance bandwidth of the antennas is in the order of 3...6 %. Maximum absolute gains vary between 3...4 dB. It is clearly seen from the results that functional antennas can be fabricated with standard LTCC process and materials even for the 60 GHz frequency band

High Frequency Permanent Magnet Generator for Pulse Density Modulating Converters

This thesis describes an investigation of high frequency permanent magnet generators for use in a novel power generation system for aerospace applications. The system consists of a high frequency generator (in the 10s of kHz range) which feeds a full-wave rectifier to produce to a high frequency pulse train as input to a pulse-density modulated soft-switched converter. Various topologies of flux-switching, flux-reversal and Vernier machines are investigated using electric-circuit coupled finite element analysis. Having demonstrated the limitations of these topologies, a comprehensive design study into a single-phase, surface mounted permanent magnet machine based on a single turn serpentine winding is described. This study covers both internal and external rotor machines with pole numbers of 192 and 96 which correspond to generator fundamental frequencies of 32kHz and 16kHz at the rated speed of 20,000rpm. Several aspects of the machine design are optimised through extensive use of finite element modelling, including mechanical analysis of the rotor containment. This study includes a detailed consideration of iron loss, including consideration of iron powder based cores. This study has resulted in a down-selected design based on a low permeability but high resistivity powdered iron core. The manufacture of a demonstrator is described including the need to re-design the machine to employ ultra-thin Nickel Iron laminations because of the difficulties encountered in the machining of a powdered iron core. The performance of this Nickel Iron variant is investigated and a final design established. The numerous challenges involved in manufacturing this novel machine are described