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| 3. |
- Aranda, Jesus Javier Lechuga
(författare)
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Towards Self-Powered Devices Via Pressure Fluctuation Energy Harvesters
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The growing interest in the Internet of Things has created a need for wireless sensing systems for industrial and consumer applications. In hydraulic systems, a widely used method of power transmission in industry, wireless condition monitoring can lead to reduced maintenance costs and increase the capacity for sensor deployment. A major problem with the adoption of wireless sensors is the battery dependence of current technologies. Energy harvesting from pressure fluctuations in hydraulic systems can serve as an alternative power supply and enable self-powered devices. Energy harvesting from pressure fluctuations is the process of converting small pressure fluctuations in hydraulic fluid into a regulated energy supply to power low power electronics. Previous studies have shown the feasibility of pressure fluctuation harvesting. However, for the development of self-powered sensor systems, the methods and techniques for converting pressure fluctuations into electrical energy should be further investigated.This thesis explores the methods, limitations, opportunities and trade-offs involved in the development of pressure fluctuation energy harvesters in the context of self-powered wireless devices. The focus is on exploring and characterizing the various mechanisms required to convert pressure fluctuations into electrical energy. In this work, an energy harvesting device consisting of a fluid-to-mechanical interface, an acoustic resonator, a piezoelectric stack, and an interface circuit is proposed and evaluated. Simulations and experimental analysis were used to analyse these different components for excitation relevant to hydraulic motors.The results of this work provide new insights into the development of power supplies for self-powered sensors for hydraulic systems using pressure fluctuation energy harvesters. It is shown that with the introduction of the space coiling resonator for pressure fluctuation amplification and a detailed analysis of the fluid interface and power conditioning circuits, the understanding of the design and optimization of efficient pressure fluctuation energy harvesters is further advanced.
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- Bader, Sebastian
(författare)
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On the lifetime and usability of environmental monitoring wireless sensor networks
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless sensor networks have been demonstrated, at an early stage in their development, to be a useful measurement technology for environmental monitoring applications. Based on their independence from existing infrastructures, wireless sensor networks can be deployed in virtually any location and provide sensor samples in a spatial and temporal resolution, which otherwise would only be achievable at high cost or involve significant work by humans.The feasibility of the usage of wireless sensor networks in real-world applications, however, is only maintained if certain technological challenges are overcome. Amongst these challenges, are the limited lifetime of the distributed sensor nodes, and user interfaces, which allow for the technology to be utilized in an efficient manner. Contributions to the solution of these challenges have been the objective of this thesis.After an analysis of the contributions wireless sensor networks can provideto the application domain of environmental monitoring, and the introductionto the restrictions, which are posed by a limited operational lifetime and lowsystem usability, these issues are addressed at the system level of sensor nodedevices.The lifetime of sensor nodes, which is closely linked to the lifetime of thecomplete wireless sensor network, is addressed with regards to the energyefficiency of nodes, as well as the utilization of solar energy harvesting inorder to increase the available energy resources. With respect to energyefficiency, an analysis has been performed of the contributions to the energyconsumption of environmental monitoring sensor nodes, which leads to thedesire to minimize the nodes' duty cycles and quiescent currents. A sensornode design is presented, which features energy efficiency as a key attribute by utilizingmodern semiconductor architectures. Moreover, an argument for the usage of synchronization-based, contention-free communication is madein order to reduce active communication periods and, thus, the duty cycleof a sensor node. A synchronization method with its focus on low protocoloverhead is introduced as a basis for such communication forms. After an initial feasibility study in relation to using battery-less solar energyharvesting architectures in locations with limited solar irradiation, multiplearchitectural implementations are analyzed in a comparative manner.Among these comparisons is an analysis of short-termenergy storage devices in the form of double-layer capacitors and thin-film batteries, which provide prolonged component lifetimes than those for conventional secondary batteries, but which can only buffer for short periods of time due to their limited energy capacity. In order to be able to dimension such energy harvesting systems with respect to the individual application constraints at hand, state of charge simulations are proposed. Amethod for such simulations is presented and demonstrated for the implementation of an energy harvester model on a component basis. While the modeling in this manner is time consuming, the model can predict the state of charge of the energy buffer in the architecture with a high level of accuracy. Finally, a method for the systematic evaluation of solar energy harvesting architectures is presented. The presented method can be summarized as a solar energy harvesting testbed, which utilizes configurable energy harvesting circuits in order to create a deploy-once-test-many type of system. The output results of this testbed can significantly improvethe efficiency of architecture comparisons and system modeling.Contributions to the improvement of the usability of wireless sensor nodesare made on two separate levels, namely, developer usability and end userusability. A method for the programming of sensor nodes based on hierarchical finite state machines is presented, which improves the usability of software development by creating familiarity for technically experiencedusers. Moreover, the utilization of finite state machine principles allowsfor the software to be developed in a systematic andmodular manner. Asimplemented applications typically require to be verified, which, in the environmental monitoring domain, usually results in outdoor deployments,usability considerations for sensor nodes are presented, which can simplifythis process. Special attention has been paid in order for these improvements to be achieved with low overheads. While software development is a familiar concept for most system developers, this is not the case for the end users of these systems, who are typically domain experts. In order to allow for wireless sensor nodes to be operatedby domain experts, a method for the configuration of sensor nodes has been proposed.The method uses a combination of graphical specification of the node behavior and a configurable sensor node. Theevaluation of this method, which has been based on a proof-of-concept implementation, demonstrated that the performance can remain high, while end users, without technical experience, are enabled to configure sensor nodes without prior training.In summary, the contributions, presented in this thesis, address systemlifetime and usability with regards to the sensor node level. The results haveled to the implementation of an energy efficient sensor node, which allows for the operation frombattery-less solar energy harvesting sources. Furthermore, support tools for the implementation of these nodes, both on the hardware and software level, have been proposed.
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- Cheng, Peng
(författare)
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Applications of embedded sensors in loader crane positioning and rotor RPM measurement
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, two novel applications involving embedded sensors arestudied, one dealing with loader crane positioning and the other involving rotorRevolutions Per Minute (RPM) measurement. The thesis presents a generalintroduction to the embedded sensor, its architecture and its use in mechanicalindustry, and provides the reader with an overview of conventional sensortechnologies within the fields of angle sensors and angular speed sensors, coveringtheir working principles, features, advantages and disadvantages and typicalapplications. The particular problems associated with the use of conventionalsensors in both loader crane positioning and rotor RPM measurement aredescribed and these problems provided the motivation for the designs of theembedded sensor systems developed in this thesis.In the case of the loader crane positioning, the origins of the project and thespecial requirements of the application are described in detail. In addition, apreliminary study is conducted in relation to the idea of a contactless joint angularsensor using MEMS inertial sensors in which four different methods, namely, theCommon-Mode-Rejection with Gyro Integration (CMRGI), Common-Mode-Rejection (CMR), Common-Mode-Rejection with Gyro Differentiation (CMRGD)and Distributed Common-Mode-Rejection (DCMR), are conceived, modeled andtested on a custom-designed prototype experimental setup. The results gatheredfrom these four methods are compared and analyzed in order to identify thedifferences in their performances. The methods, which proved to be suitable, arethen further tested using the prototype sensor setup on a loader crane and theperformance results are analyzed in order to make a decision in relation to the twomost suitable methods for the application of the loader crane positioning. Theresults suggested that the two most suitable were the CMRGD and the DCMR. Thepractical design issues relating to this sensor system are highlighted andsuggestions are made in the study. Additionally, possible future work for thisproject is also covered.In the first case for the rotor RPM measurement, the thesis presents themodeling and simulation of the stator-free RPM sensor idea using the Monte Carlomethod, which demonstrated the special features and performance of this sensor.The design aspects of the prototype sensor are described in detail and theprototype is tested on an experimental setup. The conclusions for the stator-freeRPM sensor are then made from the analysis of the experimental results and futurework in relation to this sensor is also proposed.In the second case of the rotor RPM measurement, the thesis presentsanother idea involving the laser mouse RPM sensor and the main focus of thestudy is on the performance characterization of the laser mouse sensor and theverification of the RPM sensor idea. Experiments are conducted using the test setup and results are gathered and analyzed and conclusions are drawn.Possibilities in relation to future work for this laser mouse RPM sensor are alsoprovided.The summary and the conclusion form the final chapter of the thesis andseveral important aspects of the designs relating to both the loader cranepositioning project and the rotor RPM measurement project are discussed.
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| 7. |
- Haller, Stefan, 1982-
(författare)
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Towards Low-Voltage, High-Current : A pioneering drive concept for battery electric vehicles
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The first electric low-voltage vehicles were constructed in the mid-19th century, but by the early 20th century they were progressively replacedby successors with internal combustion engines. As the consequences ofusing fossil fuels are better understood, our society is now transitioning back. The strong driving force towards electric transportation can be traced to several events and trends. The foremost of these is perhaps the rising awareness of climate change and the necessary reduction of the environmental footprint, as well associated political will for change. Alongside this, the pioneering automotive company Tesla, Inc. showed what electric cars are capable of and how to easily charge them along the road. The diesel gate unearthed in 2015, also played a major role. This transition is not without challenges, however. An electric car is expected to be reasonable priced, sustainable, environmentally friendly and electrically safe, even in case of an accident. Overnight charging at home should be possible, as well as the ability to quickly charge while in transit. While the industry has long experience with high-voltage electrical machines, the required battery technology is quite new and low-voltage in nature. Currently, the battery is the most costly part of an electric drivetrain and it has the highest environmental impact. Efficient battery use is therefore key for sustainability and a responsible consumption of the resources available. Nonetheless, most electric vehicles today use lethal high-voltage traction drives which require a considerable isolation effort and complex battery pack. Previous research results showed that a 48 V drivetrain compared to a high-voltage one, increases the drive-cycle efficiency. Hence, similar driving range can be reached with a smaller battery. This thesis provides an introduction to low-voltage, high-current, battery-powered traction drives. With the aim of increasing efficiency, safety and redundancy while reducing cost, a solution that breaks with century-old electric machine design principles is proposed and investigated. An overview and motivation to further investigate 48 V drivetrains with intrinsically safe and redundant machines is provided. The main focus of this work is the practical implementation of multi-phase low-voltage but high-current machines with integrated power electronics as well as components for a 48 V drivetrain. With this work, it is confirmed that today’s MOSFETs are not the limiting factor towards low-voltage, high-current drives. In the first part of this work, two small-scale prototype machines were constructed and tested. The air-cooled, small-scale 1.2 kW proto-type reached a copper fill-factor of 0.84. The machine’s low terminal-to-terminal resistance of 0.23 mΩ, including the MOSFET-based power electronics, allowed continuous driving currents up to 600 A. The resistive MOSFET losses stayed below 21 W. The second part focuses on the key components for a 48 V high-power drivetrain. A W-shaped coil for a multiphase 48 V machine with direct in-conductor cooling was designed and tested. With glycolwater, it reached a current density of 49.5 A/mm2 with 0.312 l/min flowrate. Furthermore, a reconfigurable battery pack for 48 V driving andhigh-voltage charging was investigated.
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| 9. |
- Lundgren, Jan, 1977-
(författare)
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Simulating Behavioral Level On-Chip Noise Coupling
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, noise coupling simulation is introduced into the behavioral level. Methods andmodels for simulating on-chip noise coupling at the behavioral level in a design flow are presentedand verified for accuracy and validity. Today, designs of electronic systems are becoming denserand more and more mixed-signal systems such as System-on-Chip (SoC) are being devised. Thisraises problems when the electronics components start to interfere with each other. Often, digitalcomponents disturb analog components, introducing noise into the system causing degradation ofthe performance or even introducing errors into the functionality of the system.Today, these effects can only be simulated at a very late stage in the design process, causinglarge design iterations and increased costs if the designers are required to return and makealterations, which may have occurred at a very early stage in the process.This is why the focus of this work is centered on extracting noise coupling simulation modelsthat can be used at a very early design stage, such as at the behavioral level and then follow thedesign through the various design stages. To achieve this, SystemC is selected as a platform andimplementation example for the behavioral level models. SystemC supports design refinement,which means that when designs are being refined and are crossing the design levels, the noisecoupling models can also be refined to suit the current design.This new method of thinking in primarily mixed-signal designs is called Behavioral levelNoise Coupling (BeNoC) simulation and shows great promise in enabling a reduction in the costsof design iterations due to component cross-talk and simplifies the work for mixed-signal systemdesigners.
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| 10. |
- Ma, Xinyu
(författare)
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Power Estimation for Indoor Light Energy Harvesting
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The growing popularity of indoor light energy harvesting for wireless sensor systems and low-power electronics has created a demand for systematic power estimation methods for different lighting conditions. Although existing research has recognized the critical role played by the spectral information on the output power of a photovoltaic cell, power estimation methods have rarely considered it. The vast majority of studies on the power estimation method in the past few years have focused on the conventional diode model, and even though scaling the parameters to other light conditions seems plausible, it is sometimes problematic to interpret the physical meanings of some parameters from theory. Therefore, a systematic investigation of the light condition characterization and PV cell modeling is fundamental to appropriately estimate the available light energy of an indoor environment. The power estimation method proposed in this thesis takes both spectral and intensity information into account and provides a data-driven approach to solve the scaling problem. We use low-cost sensors to measure spectral information and select an appropriate device model based on the classification of the light source. The evaluation results for both lab and real-world light conditions show that the proposed method achieves sufficient accuracy. This study provides new insights into the indoor light energy harvesting system design and makes a contribution to research on available energy estimation of the ambient environment.
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