Analysis of Current Ripples in Electromagnetic Actuators with Application to Inductance Estimation Techniques for Sensorless Monitoring

Techniques for estimating the plunger position have successfully proven to support operation and monitoring of electromagnetic actuators without the necessity of additional sensors. Sophisticated techniques in this field make use of an oversampled measurement of the rippled driving current in order to reconstruct the position. However, oversampling algorithms place high demands on AD converters and require significant computational effort which are not desirable in low-cost actuation systems. Moreover, such low-cost actuators are affected by eddy currents and parasitic capacitances, which influence the current ripple significantly. Therefore, in this work, those current ripples are modeled and analyzed extensively taking into account those effects. The Integrator-Based Direct Inductance Measurement (IDIM) technique, used for processing the current ripples, is presented and compared experimentally to an oversampling technique in terms of noise robustness and implementation effort. A practical use case scenario in terms of a sensorless end-position detection for a switching solenoid is discussed and evaluated. The obtained results prove that the IDIM technique outperforms oversampling algorithms under certain conditions in terms of noise robustness, thereby requiring less sampling and calculation effort. The IDIM technique is shown to provide a robust position estimation in low-cost applications as in the presented example involving a end-position detection

The Sensitivity of the Parkes Pulsar Timing Array to Individual Sources of Gravitational Waves

We present the sensitivity of the Parkes Pulsar Timing Array to gravitational waves emitted by individual super-massive black-hole binary systems in the early phases of coalescing at the cores of merged galaxies. Our analysis includes a detailed study of the effects of fitting a pulsar timing model to non-white timing residuals. Pulsar timing is sensitive at nanoHertz frequencies and hence complementary to LIGO and LISA. We place a sky-averaged constraint on the merger rate of nearby ($z < 0.6$) black-hole binaries in the early phases of coalescence with a chirp mass of 10^{10}\,\rmn{M}_\odot of less than one merger every seven years. The prospects for future gravitational-wave astronomy of this type with the proposed Square Kilometre Array telescope are discussed.Comment: fixed error in equation (4). [13 pages, 6 figures, 1 table, published in MNRAS

Ultra-low noise, high-frame rate readout design for a 3D-stacked CMOS image sensor

Due to the switch from CCD to CMOS technology, CMOS based image sensors have become smaller, cheaper, faster, and have recently outclassed CCDs in terms of image quality. Apart from the extensive set of applications requiring image sensors, the next technological breakthrough in imaging would be to consolidate and completely shift the conventional CMOS image sensor technology to the 3D-stacked technology. Stacking is recent and an innovative technology in the imaging field, allowing multiple silicon tiers with different functions to be stacked on top of each other. The technology allows for an extreme parallelism of the pixel readout circuitry. Furthermore, the readout is placed underneath the pixel array on a 3D-stacked image sensor, and the parallelism of the readout can remain constant at any spatial resolution of the sensors, allowing extreme low noise and a high-frame rate (design) at virtually any sensor array resolution. The objective of this work is the design of ultra-low noise readout circuits meant for 3D-stacked image sensors, structured with parallel readout circuitries. The readout circuit’s key requirements are low noise, speed, low-area (for higher parallelism), and low power. A CMOS imaging review is presented through a short historical background, followed by the description of the motivation, the research goals, and the work contributions. The fundamentals of CMOS image sensors are addressed, as a part of highlighting the typical image sensor features, the essential building blocks, types of operation, as well as their physical characteristics and their evaluation metrics. Following up on this, the document pays attention to the readout circuit’s noise theory and the column converters theory, to identify possible pitfalls to obtain sub-electron noise imagers. Lastly, the fabricated test CIS device performances are reported along with conjectures and conclusions, ending this thesis with the 3D-stacked subject issues and the future work. A part of the developed research work is located in the Appendices.Devido à mudança da tecnologia CCD para CMOS, os sensores de imagem em CMOS tornam se mais pequenos, mais baratos, mais rápidos, e mais recentemente, ultrapassaram os sensores CCD no que respeita à qualidade de imagem. Para além do vasto conjunto de aplicações que requerem sensores de imagem, o próximo salto tecnológico no ramo dos sensores de imagem é o de mudar completamente da tecnologia de sensores de imagem CMOS convencional para a tecnologia “3D-stacked”. O empilhamento de chips é relativamente recente e é uma tecnologia inovadora no campo dos sensores de imagem, permitindo vários planos de silício com diferentes funções poderem ser empilhados uns sobre os outros. Esta tecnologia permite portanto, um paralelismo extremo na leitura dos sinais vindos da matriz de píxeis. Além disso, num sensor de imagem de planos de silício empilhados, os circuitos de leitura estão posicionados debaixo da matriz de píxeis, sendo que dessa forma, o paralelismo pode manter-se constante para qualquer resolução espacial, permitindo assim atingir um extremo baixo ruído e um alto debito de imagens, virtualmente para qualquer resolução desejada. O objetivo deste trabalho é o de desenhar circuitos de leitura de coluna de muito baixo ruído, planeados para serem empregues em sensores de imagem “3D-stacked” com estruturas altamente paralelizadas. Os requisitos chave para os circuitos de leitura são de baixo ruído, rapidez e pouca área utilizada, de forma a obter-se o melhor rácio. Uma breve revisão histórica dos sensores de imagem CMOS é apresentada, seguida da motivação, dos objetivos e das contribuições feitas. Os fundamentos dos sensores de imagem CMOS são também abordados para expor as suas características, os blocos essenciais, os tipos de operação, assim como as suas características físicas e suas métricas de avaliação. No seguimento disto, especial atenção é dada à teoria subjacente ao ruído inerente dos circuitos de leitura e dos conversores de coluna, servindo para identificar os possíveis aspetos que dificultem atingir a tão desejada performance de muito baixo ruído. Por fim, os resultados experimentais do sensor desenvolvido são apresentados junto com possíveis conjeturas e respetivas conclusões, terminando o documento com o assunto de empilhamento vertical de camadas de silício, junto com o possível trabalho futuro

Nodal sampling: a new image reconstruction algorithm for SMOS

Soil moisture and ocean salinity (SMOS) brightness temperature (TB) images and calibrated visibilities are related by the so-called G -matrix. Due to the incomplete sampling at some spatial frequencies, sharp transitions in the TB scenes generate a Gibbs-like contamination ringing and spread sidelobes. In the current SMOS image reconstruction strategy, a Blackman window is applied to the Fourier components of the TBs to diminish the amplitude of artifacts such as ripples, as well as other Gibbs -like effects. In this paper, a novel image reconstruction algorithm focused on the reduction of Gibbs -like contamination in TB images is proposed. It is based on sampling the TB images at the nodal points, that is, at those points at which the oscillating interference causes the minimum distortion to the geophysical signal. Results show a significant reduction of ripples and sidelobes in strongly radio-frequency interference contaminated images. This technique has been thoroughly validated using snapshots over the ocean, by comparing TBs reconstructed in the standard way or using the nodal sampling (NS) with modeled TBs. Tests have revealed that the standard deviation of the difference between the measurement and the model is reduced around 1 K over clean and stable zones when using NS technique with respect to the SMOS image reconstruction baseline. The reduction is approximately 0.7 K when considering the global ocean. This represents a crucial improvement in TB quality, which will translate in an enhancement of the retrieved geophysical parameters, particularly the sea surface salinity.Peer ReviewedPostprint (author's final draft

HIGH RESOLUTION TIME-OF-ARRIVAL RANGING OF WIRELESS SENSOR NODES IN NON-HOMOGENOUS ENVIRONMENTS

Wireless Sensor Networks (WSN) have emerging applications in homogeneous environments such as free space. In addition, WSNs are finding new applications in non-homogeneous (NH) media. All referred applications entail location information of measured data or observed event. Localization in WSNs is considered as the leading remedy, which refers to the procedure of obtaining the sensor nodes relative location utilizing range measurements. Localization via Time-of-Arrival (ToA) estimation has received considerable attention because of high precision and low complexity implementation, however, the traditional techniques are not feasible in NH media due to frequency dispersion of transmitted ranging waveform. In this work, a novel and effective ToA-based ranging technique for localization in NH media consisting of frequency dispersive sub-media is proposed. First challenges of ToA estimation in NH media regarding frequency dispersion is investigated. Here, a novel technique which improves ToA estimation resolution at fixed bandwidth via maximum rising level detector (MRLD) technique is discussed. The MRLD receiver utilizes oversampling and multiple correlation paths to evaluate with high resolution the path corresponding to the maximum rising level of matched filters output. In order to achieve higher resolution, a novel and effective ToA estimation is introduced that incorporates orthogonal frequency division multiple access (OFDMA) subcarriers. In the proposed technique, pre-allocated orthogonal subcarriers are utilized to construct a ranging waveform which enables high performance ToA estimation in dispersive NH media in frequency domain. Here, we show that each frequency component of propagated waveform is received with different time delay and phase which dramatically increases the number of unknowns in the received signal system model. Then, we propose a novel idea based on frequency domain analysis of the transmitted OFDMA subcarriers to reduce the number of unknowns exploiting feasible approximations. Finally, the proposed ToA technique is applied multiple times at different carrier frequencies to create a system of linear equations which can be solved to compute the available sub-mediums thickness and range. Simulation results prove that the proposed technique offers high resolution range measurements given simulated ToA estimation error at different signal to noise ratio regimes in NH media

Review and Analysis of Peak Tracking Techniques for Fiber Bragg Grating Sensors

Fiber Bragg Grating (FBG) sensors are among the most popular elements for fiber optic sensor networks used for the direct measurement of temperature and strain. Modern FBG interrogation setups measure the FBG spectrum in real-time, and determine the shift of the Bragg wavelength of the FBG in order to estimate the physical parameters. The problem of determining the peak wavelength of the FBG from a spectral measurement limited in resolution and noise, is referred as the peak-tracking problem. In this work, the several peak-tracking approaches are reviewed and classified, outlining their algorithmic implementations: the methods based on direct estimation, interpolation, correlation, resampling, transforms, and optimization are discussed in all their proposed implementations. Then, a simulation based on coupled-mode theory compares the performance of the main peak-tracking methods, in terms of accuracy and signal to noise ratio resilience