Wave-based sensor, actuator and optimizer

Programa doutoral em Sistemas Avançados de Engenharia para a Indústria (AESI)A presente tese explora a utilização de ondas para abordar dois desafios significativos na indústria automóvel. O primeiro desafio consiste no desenvolvimento de um sistema de cancelamento ativo de ruído (ANC) que possa reduzir os ruídos não estacionários no compartimento de passageiros de um veículo. O segundo desafio é criar uma metodologia de conceção ótima para sensores de posição indutivos capazes de medir deslocamentos lineares, rotacionais e angulares. Para abordar o primeiro desafio, foi desenvolvido de um sistema ANC onde wavelets foram combinadas com um banco de filtros adaptativos. O sistema foi implementado em uma FPGA, e testes demonstraram que o sistema pode reduzir o ruído não estacionário em um ambiente acústico aberto e não controlado em 9 dB. O segundo desafio foi abordado através de uma metodologia que combina um algoritmo genético com um método numérico rápido para otimizar um sensor de posição indutivo. O método numérico foi usado para simular o campo eletromagnético associado à geometria do sensor, permitindo a maximização da corrente induzida nas bobinas recetoras e a minimização da não-linearidade no sensor. A minimização da não-linearidade foi conseguida através do desenho (layout) das bobinas que compõem o sensor. Sendo este otimizado no espaço de Fourier através da adição de harmónicos apropriados na geometria. As melhores geometrias otimizadas apresentaram uma não-linearidade inferior a 0,01% e a 0,25% da escala total para os sensores de posição angular e linear, respetivamente, sem calibração por software. O sistema ANC proposto tem o potencial de melhorar o conforto dos ocupantes do veículo, reduzindo o ruído indesejado dentro do compartimento de passageiros. Isso poderia reduzir o uso de materiais de isolamento acústico no veículo, levando a um veículo mais leve e, em última análise, a uma redução no consumo de energia. A metodologia desenvolvida para sensores de posição indutivos contribui para o estado da arte de sensores de posição eficientes e económicos, o que é crucial para os requisitos complexos da indústria automóvel. Essas contribuições têm implicações para o desenho de sistemas automotivos, com requisitos de desempenho e considerações ambientais e económicas.This thesis explores the use of waves to tackle two major engineering challenges in the automotive industry. The first challenge is the development of an Active Noise Cancelling (ANC) system that can effectively reduce non-stationary noise inside a vehicle’s passenger compartment. The second challenge is the optimization of an inductive position sensor design methodology capable of measuring linear, rotational, and angular displacements. To address the first challenge, this work designs an ANC system that employs wavelets combined with a bank of adaptive filters. The system was implemented in an FPGA, and field tests demonstrate its ability to reduce non-stationary noise in an open and uncontrolled acoustic environment by 9 dB. The second challenge was tackled by proposing a new approach that combines a genetic algorithm with a fast and lightweight numerical method to optimize the geometry of an inductive position sensor. The numerical method is used to simulate the sensor’s electromagnetic field, allowing for the maximization of induced current on the receiver coils while minimizing the sensor’s non-linearity. The non-linearity minimization was achieved through its unique sensor’s coils design optimized in the Fourier space by adding the appropriate harmonics to the coils’ geometry. The best optimized geometries exhibited a non-linearity of less than 0.01% and 0.25% of the full scale for the angular and linear position sensors, respectively. Both results were achieved without the need for signal calibration or post-processing manipulation. The proposed ANC system has the potential to enhance the comfort of vehicle occupants by reducing unwanted noise inside the passenger compartment. Moreover, it has the potential to reduce the use of acoustic insulation materials in the vehicle, leading to a lighter vehicle and ultimately reducing energy consumption. The developed methodology for inductive position sensors represents a state-of-the-art contribution to efficient and cost-effective position sensor design, which is crucial for meeting the complex requirements of the automotive industry.I would like to thank the Fundação para a Ciência e Tecnologia (FCT) and Bosch Car Multimedia for funding my PhD (grant PD/BDE/142901/2018)

Evaluation of Pavement Roughness and Vehicle Vibrations for Road Surface Profiling

The research explores aspects of road surface measurement and monitoring, targeting some of the main challenges in the field, including cost and portability of high-speed inertial profilers. These challenges are due to the complexities of modern profilers to integrate various sensors while using advanced algorithms and processes to analyse measured sensor data. Novel techniques were proposed to improve the accuracy of road surface longitudinal profiles using inertial profilers. The thesis presents a Half-Wavelength Peak Matching (HWPM) model, designed for inertial profilers that integrate a laser displacement sensor and an accelerometer to evaluate surface irregularities. The model provides an alternative approach to drift correction in accelerometers, which is a major challenge when evaluating displacement from acceleration. The theory relies on using data from the laser displacement sensor to estimate a correction offset for the derived displacement. The study also proposes an alternative technique to evaluating vibration velocity, which improves on computational factors when compared to commonly used methods. The aim is to explore a different dimension to road roughness evaluation, by investigating the effect of surface irregularities on vehicle vibration. The measured samples show that the drift in the displacement calculated from the accelerometer increased as the vehicle speed at which the road measurement was taken increased. As such, the significance of the HWPM model is more apparent at higher vehicle speeds, where the results obtained show noticeable improvements to current techniques. All results and analysis carried out to validate the model are based on real-time data obtained from an inertial profiler that was designed and developed for the research. The profiler, which is designed for portability, scalability and accuracy, provides a Power Over Ethernet (POE) enabled solution to cope with the demand for high data transmission rates.

Broadband In-plane Relative Permittivity Characterization of Ruddlesden-Popper Sr(n+1)Ti(n)O(3n+1) Thin Films

We present a broadband on-wafer measurement technique for the characterization of the in-plane complex relative permittivity of a thin-film test wafer and a companion substrate test wafer from 100 Hz to 40 GHz, and potentially to 110 GHz. From 100 Hz to 300 MHz, the approach uses an ensemble of interdigitated capacitors with different interdigitated active lengths l = (0.100 mm, 0.325 mm, 0.875 mm, 1.835 mm, 2.9 mm) fabricated on both test wafers. Within this regime, from 100 Hz to 1 MHz, the measurements were performed with an inductance-capacitance-resistance meter. From 1 MHz to 300 MHz, the scattering parameters of the set of interdigitated capacitors were measured with a radio frequency vector network analyzer. In the high frequency regime, 300 MHz to 40 GHz, we measure scattering parameters of a set of coplanar waveguides of active lengths l = (0.420 mm, 1.270 mm, 2.155 mm, 3.22 mm, 3.993 mm, 5.933 mm) fabricated on the test wafers. We extracted the capacitance and conductance of the interdigitated capacitors and coplanar waveguides on the test wafers for the appropriate frequency regimes. We then obtained a mapping function from 2D finite element simulations that relates the change in capacitance of the thin-film test wafer relative to the companion substrate test wafer to the real part of the in-plane relative permittivity. The imaginary part of the in-plane relative permittivity was obtained from the real part of the in-plane relative permittivity and the in-plane loss tangent. We applied this broadband dielectric spectroscopy technique to explore the frequency-dependent relative permittivity of unstrained Ruddlesden-Popper series Srn+1TinO3n+1(n=1, 2, 3) thin films as a function of temperature and dc electric field. At room temperature, the in-plane relative permittivities (K11) obtained for Srn+1TinO3n+1(n=1, 2, 3) were 42 plus/minus 3, 54 plus/minus3, and 77 plus/minus2, respectively, and were independent of frequency. At low temperatures, K11 increased with a behavior consistent with an incipient ferroelectric, and paraelectric behavior developed in Sr4Ti3O10(n=3). In 2004, J. H. Haeni, et al. showed that SrTiO3 (n = infinity) on DyScO3 (110) undergoes a ferroelectric to paraelectric phase transition around room temperature. As a means to understand the origins of the loss and tunability in strained SrTiO3 (n = infinity), we performed our broadband dielectric spectroscopy technique on epitaxial thin-films of Ruddlesden-Popper series Srn+1TinO3n+1(n=2, 3, 4, 5, 6) on the rare-earth scandate substrates, DyScO3 (110) and GdScO3 (110). For these thin films, DyScO3 (110) and GdScO3 (110) corresponded to biaxial tensile strain of approximately 1% and 1.7%, respectively. The thin films were 50 nm thick on DyScO3 (110) and 25 nm thick on GdScO3 (110), which ensured uniform strain throughout the film. We report the dependence of the critical temperature, tunability, and loss tangent on series number and strain at 1 MHz. We also examined the broadband frequency dependent dielectric properties of these thin films as a function of temperature, electric field, series number and strain

Spin-orbit torques and photocurrents in 2D materials

While conventional electronics rely on the electron charge as information carrier, using another intrinsic property of the electron, its spin, offers promising ways to further improve information storage technologies. However, the key hurdle lies in gaining precise control over the electron spin. Currently, both electrical and optical methods are being explored to achieve this control.This thesis delves into the realm of spintronics and optoelectronics, focusing on the effects observed in layered two-dimensional (2D) materials called transition metal dichalcogenides (TMDs). These materials are particularly well-suited for this purpose due to their direct bandgap in atomically thin layers and strong spin-orbit coupling, which is advantageous for spintronic and optospintronic effects.The initial section of the thesis addresses spintronic effects, specifically the spin-orbit torque (SOT) in TMD/ferromagnetic bilayers. Notably, our study on WSe2/permalloy devices reveals a lack of clear dependence on WSe2 thickness for SOTs, suggesting an interfacial origin. Additionally, we observe the presence of SOTs in a device with a single ferromagnetic layer, highlighting the importance of studying reference samples for accurate determination of the SOT strength.Turning to the optoelectronic aspect of TMDs, our exploration uncovers that the Schottky barrier at the MoSe2-metallic contacts interface induces additional polarization-dependent photocurrents. Furthermore, we demonstrate that modifying the crystal structure of MoTe2 locally enhances the optoelectronic performance of TMDs based devices.This thesis provides important steps for the integration of 2D materials in future spintronic and optoelectronic devices

Spin-orbit torques and photocurrents in 2D materials

While conventional electronics rely on the electron charge as information carrier, using another intrinsic property of the electron, its spin, offers promising ways to further improve information storage technologies. However, the key hurdle lies in gaining precise control over the electron spin. Currently, both electrical and optical methods are being explored to achieve this control.This thesis delves into the realm of spintronics and optoelectronics, focusing on the effects observed in layered two-dimensional (2D) materials called transition metal dichalcogenides (TMDs). These materials are particularly well-suited for this purpose due to their direct bandgap in atomically thin layers and strong spin-orbit coupling, which is advantageous for spintronic and optospintronic effects.The initial section of the thesis addresses spintronic effects, specifically the spin-orbit torque (SOT) in TMD/ferromagnetic bilayers. Notably, our study on WSe2/permalloy devices reveals a lack of clear dependence on WSe2 thickness for SOTs, suggesting an interfacial origin. Additionally, we observe the presence of SOTs in a device with a single ferromagnetic layer, highlighting the importance of studying reference samples for accurate determination of the SOT strength.Turning to the optoelectronic aspect of TMDs, our exploration uncovers that the Schottky barrier at the MoSe2-metallic contacts interface induces additional polarization-dependent photocurrents. Furthermore, we demonstrate that modifying the crystal structure of MoTe2 locally enhances the optoelectronic performance of TMDs based devices.This thesis provides important steps for the integration of 2D materials in future spintronic and optoelectronic devices

Bowdoin Orient v.133, no.1-24 (2003-2004)

https://digitalcommons.bowdoin.edu/bowdoinorient-2000s/1004/thumbnail.jp

Bowdoin Orient v.115, no.1-27 (1985-1986)

https://digitalcommons.bowdoin.edu/bowdoinorient-1980s/1006/thumbnail.jp

Bowdoin Orient v.114, no.1-24 (1984-1985)

https://digitalcommons.bowdoin.edu/bowdoinorient-1980s/1005/thumbnail.jp