| 1. |
- Kotte, Hari Babu, 1979-
(författare)
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High Frequency (MHz) Resonant Converters using GaN HEMTs and Novel Planar Transformer Technology
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increased power consumption and power density demands of moderntechnologies have increased the technical requirements of DC/DC and AC/DC powersupplies. In this regard, the primary objective of the power supply researcher/engineeris to build energy efficient, high power density converters by reducing the losses andincreasing the switching frequency of converters respectively. Operating the convertercircuits at higher switching frequencies reduces the size of the passive componentssuch as transformers, inductors, and capacitors, which results in a compact size,weight, and increased power density of the converter. Therefore, the thesis work isfocussed on the design, analysis and evaluation of isolated converters operating in the1 - 5MHz frequency region with the assistance of the latest semi conductor devices,both coreless and core based planar power transformers designed in Mid SwedenUniversity and which are suitable for consumer applications of varying power levelsranging from 1 – 60W.In high frequency converter circuits, since the MOSFET gate driver plays a prominentrole, different commercially available MOSFET gate drivers were evaluated in thefrequency range of 1 - 5MHz in terms of gate drive power consumption, rise/fall timesand electromagnetic interference (EMI) and a suitable driver was proposed.Initially, the research was focused on the design and evaluation of a quasi resonantflyback converter using a multilayered coreless PCB step down transformer in thefrequency range of 2.7 – 4MHz up to the power level of 10W. The energy efficiency ofthis converter is found to be 72 - 84% under zero voltage switching conditions (ZVS).In order to further improve the energy efficiency of the converter in the MHzfrequency region, the new material device GaN HEMT was considered. Thecomparisons were made on a quasi resonant flyback DC-DC converter using both theSi and GaN technology and it was found that an energy efficiency improvement of 8 –10% was obtained with the GaN device in the frequency range of 3.2 – 5MHz. In orderto minimize the gate drive power consumption, switching losses and to increase thefrequency of the converter in some applications such as laptop adapters, set top box(STB) etc., a cascode flyback converter using a low voltage GaN HEMT and a highvoltage Si MOSFET was designed and evaluated using a multi-layered coreless PCBtransformer in the MHz frequency region. Both the simulation and experimentalresults have shown that, with the assistance of the cascode flyback converter, theswitching speeds of the converter can be increased with the benefit of obtaining asignificant improvement in the energy efficiency as compared to that for the singleswitch flyback converter.In order to further maximize the utilization of the transformer, to reduce the voltagestress on MOSFETs and to obtain the maximum power density from the convertercircuit, double ended topologies were considered. Due to the lack of high voltage highside gate drivers in the MHz frequency region, a gate drive circuitry utilizing themulti-layered coreless PCB signal transformer was designed and evaluated in both ahalf-bridge and series resonant converter (SRC). It was found that the gate drive powerconsumption using this transformer was around 0.66W for the frequency range of 1.5 -v3.75 MHz. In addition, by using this gate drive circuitry, the maximum energyefficiency of the SRC using multilayered coreless PCB power transformer was found tobe 86.5% with an output power of 36.5W in the switching frequency range of 2 –3MHz.In order to further enhance the energy efficiency of the converter to more than 90%,investigations were carried out by using the multiresonant converter topology (LCCand LLC), novel hybrid core high frequency planar power transformer and the GaNHEMTs. The simulated and experimental results of the designed LCC resonantconverter show that it is feasible to obtain higher energy efficiency isolated DC/DCconverters in the MHz frequency region. The peak energy efficiency of the LCCconverter at 3.5MHz is reported to be 92% using synchronous rectification. Differentmodulation techniques were implemented to regulate the converter for both line andload variations using a digital controller.In order to realize an AC/DC converter suitable for a laptop adapter application,consideration was given to the low line of the universal input voltage range due to theGaN switch limitation. The energy efficiency of the regulated converter operating inthe frequency range of 2.8 – 3.5MHz is reported to be more than 90% with a loadpower of 45W and an output voltage of 22Vdc. In order to determine an efficient powerprocessing method on the secondary side of the converter, a comparison was madebetween diode rectification and synchronous rectification and optimal rectification wasproposed for the converters operating in the MHz frequency range for a given powertransfer application. In order to maintain high energy efficiency for a wide load rangeand to maintain the narrow switching frequency range for the given input voltagespecifications, the LLC resonant converter has been designed and evaluated for theadapter application. From the observed results, the energy efficiency of the LLCresonant converter is maintained at a high level for a wide load range as compared tothat for the LCC resonant converter.Investigations were also carried out on isolated class E resonant DC-DC converter withthe assistance of GaN HEMT and a high performance planar power transformer at theswitching frequency of 5MHz. The simulated energy efficiency of the converter for theoutput power level of 16W is obtained as 88.5% which makes it feasible to utilize thedesigned isolated converter for various applications that require light weight and lowprofile converters.In conclusion, the research in this dissertation has addressed various issues related tohigh frequency isolated converters and has proposed solution by designing highlyenergy efficient converters to meet the current industrial trends by using coreless andcore based planar transformer technologies along with the assistance of GaN HEMTs.With the provided solution, in the near future, it is feasible to realize low profile, highpower density DC/DC and AC/DC converters operating in MHz frequency regionsuitable for various applications.
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| 2. |
- Lundgren, Jan, 1977-
(författare)
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Behavioral Level Simulation Methods for Early Noise Coupling Quantification in Mixed-Signal Systems
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, noise coupling simulation is introduced into the behavioral level. Methods and models for simulating on-chip noise coupling at a behavioral level in a design flow are presented and verified for accuracy and validity. Today, designs of electronic systems are becoming denser and more and more mixed-signal systems such as System-on-Chip (SoC) are being devised. This raises problems when the electronics components start to interfere with each other. Often, digital components disturb analog components, introducing noise into the system causing degradation of the 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, causing large design iterations and increased costs if the designers are required to return and make alterations, 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 models that can be used at a very early design stage such as the behavioral level and then follow the design through the various design stages. To realize this, SystemC is selected as a platform and implementation 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 noise coupling models can also be refined to suit the current design. This new way of thinking in primarily mixed-signal designs is called Behavioral level Noise Coupling (BeNoC) simulation and shows great promise in enabling a reduction in the costs of design iterations due to component cross-talk and simplifies the work for mixed-signal system designers.
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| 3. |
- 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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| 4. |
- Shen, Jue
(författare)
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Interactive RFID for Industrial and Healthcare Applications
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis introduces the circuit and system design of interactive Radio-Frequency Identification (RFID) for Internet of Things (IoT) applications. IoT has the vision of connectivity for anything, at anytime and anywhere. One of the most important characteristics of IoT is the automatic and massive interaction of real physical world (things and human) with the virtual Internet world.RFID tags integrated with sensors have been considered as one suitable technology for realizing the interaction. However, while it is important to have RFID tags with sensors as the input interaction, it is also important to have RFID tags with displays as the output interaction.Display interfaces vary based on the information and application scenarios. On one side, remote and centralized display interface is more suitable for scenarios such as monitoring and localization. On the other side, tag level display interface is more suitable for scenarios such as object identification and online to offline propagation.For tag level display, though a substantial number of researches have focused on introducing sensing functionalities to low power Ultra-High Frequency (UHF) RFID tags, few works address UHF RFID tags with display interfaces. Power consumption and integration with display of rigid substrate are two main challenges.With the recent emerging of Electronic Paper Display (EPD) technologies, it becomes possible to overcome the two challenges. EPD resembles ordinary ink on paper by characteristics of substrate flexibility, pattern printability and material bi-stability. Average power consumption of display is significantly reduced due to bi-stability, the ability to hold color for certain periods without power supplies. Among different EPD types, Electrochromic (EC) display shows advantage of low driving voltage compatible to chip supply voltage.Therefore this thesis designs a low power UHF RFID tag integrated in 180 nm CMOS process with inkjet-printed EC polyimide display. For applications where refresh rate is ultra-low (such as electronic label in retailing and warehouse), the wireless display tag is passive and supplied by the energy harvested from UHF RF wave. For applications where refresh rate is not ultra-low (such as object identification label in mass customized manufacturing), the wireless display tag is semi-passive and supplied by soft battery. It works at low average power consumption and with out-of-battery alert.For remote and centralized display, the limitations of uplink (from tags to reader) capacity and massive-tag information feedback in IoT scenarios is the main challenge. Compared to conventional UHF RFID backscattering whose data rate is limited within hundreds of kb/s, Ultra-wideband (UWB) transmission have been verified with the performance of Mb/s data rate with several tens of pJ/pulse energy consumption.Therefore, a circuit prototype of UHF/UWB RFID tag replacing UHF backscattering with UWB transmitter is implemented. It also consists of Analog-to-Digital Converter (ADC) and Electrocardiogram (ECG) electrodes for healthcare applications of real-time remote monitoring of multiple patients ECG signals. The ECG electrodes are fabricated on paper substrate by inkjet printing to improve patient comfort.Key contribution of the thesis includes: 1) the power management scheme and circuit design of passive UHF/UWB RFID display tag. The tag sensitivity (the input RF power) is -10.5 dBm for EC display driving, comparable to the performance of conventional passive UHF RFID tags without display functions, and -18.5 dBm for UWB transmission, comparable to the state-of-the-art performance of passive UHF RFID tag. 2) communication flow and circuit design of UHF/UWB RFID tag with ECG sensing. The optimum system throughout is 400 tags/second with 1.5 KHz ECG sampling rate and 10 Mb/s UWB pulse rate.
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| 5. |
- Unander, Tomas
(författare)
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Characterization of Low Cost Printed Sensors for Smart Packaging
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Currently there are very significant interests in printed electronics in the world. The possibility to produce electronics in a roll to roll printing process will considerably reduce the cost of the electronic devices. However, these new devices will most probably not replace the traditional silicon based electronics, but will be a complement in low cost applications such as in intelligent packages and other printable media. One interesting area is printable low cost sensors that add value to packages. In this thesis a study of the performance of low cost sensors is presented. The sensors were fabricated using commercial printing processes used in the graphical printing business. The sensors were characterized and evaluated for the intended application. The evaluated sensors were moisture sensing sensor solutions and touch sensitive sensor solutions. A printable touch sensitive sensor solution is presented where the sensor is incorporated into a high quality image such as in point of sales displays. The sensor solution showed good touch sensitivity at a variety of humidity levels. Four printed moisture sensor concepts are presented and characterized. Firstly, a moisture sensor that shows good correlation to the moisture content of cellulose based substrates. Secondly, a sensor that measures the relative humidity in the air, the sensor has a measuring accuracy of 0.22% at high relative humidity levels. Thirdly, a moisture sensor that utilizes unsintered silver nano-particles to measure the relative humidity in the air, the sensor has a linear response at very low relative humidity levels. And fourth, an action activated energy cell that provides power when activated by moisture. A concept of remote moisture sensing that utilizes ordinary low cost RFID tags has also been presented and characterized. The remote sensor solution works both with passive and semi-passive RFID systems. The study shows that it is possible to manufacture low cost sensors in commercial printing processes.
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| 6. |
- Unander, Tomas
(författare)
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System integration of electronic functionality in packaging application
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sensor applications are becoming increasingly important as products are now being requested to be more and more intelligent and safe. As the costs involved in sensor technology decrease its usage will spread to new market segments including new areas with products that have never previously used such functionalities, including, wood fibre based products for packaging, hygiene or graphical use. Currently there is a significant interest in developing technology that will allow packages to become interactive and be integrated with digital services accessible on the Internet. In this thesis, the system integration of a hybrid RFID based sensor platform is presented. This proposed platform provides a trade-off between the communication performance and its compatibility with international standards and also includes flexibility in on‐package customization, including the type and number of sensors. In addition it combines the use of traditional silicon based electronics with printed electronics directly onto wood fibre based materials so as to enable the possibility of creating smart packages. Together with the system integration of the sensor platform, five printed moisture sensor concepts that are designed to work with the sensor platform are presented and characterized. Firstly, there is a moisture sensor that shows a good correlation to the moisture content of wood fibre based substrates. The second one involves a sensor that detects high relative humidity levels in the air and the third is an action activated energy cell that provides power when activated by moisture. The fourth one deals with two types of moisture sensors that utilize silver nano-particles in order to measure the relative humidity in the air. The final one is a printable touch sensitive sensor that is sensitive to the moisture contained in the hand. A concept of remote moisture sensing that utilizes ordinary low cost RFID tags has also been presented and characterized.The main focus is thus on system integration to, by combining silicon based electronics with printed electronics, find the most low cost solution with regards to flexibility, sensor functions and still meet the communication standards.
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| 7. |
- Ahmad, Naeem
(författare)
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Modelling and optimization of sky surveillance visual sensor network
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A Visual Sensor Network (VSN) is a distributed system of a largenumber of camera sensor nodes. The main components of a camera sensornode are image sensor, embedded processor, wireless transceiver and energysupply. The major difference between a VSN and an ordinary sensor networkis that a VSN generates two dimensional data in the form of an image, whichcan be exploited in many useful applications. Some of the potentialapplication examples of VSNs include environment monitoring, surveillance,structural monitoring, traffic monitoring, and industrial automation.However, the VSNs also raise new challenges. They generate large amount ofdata which require higher processing powers, large bandwidth requirementsand more energy resources but the main constraint is that the VSN nodes arelimited in these resources.This research focuses on the development of a VSN model to track thelarge birds such as Golden Eagle in the sky. The model explores a number ofcamera sensors along with optics such as lens of suitable focal length whichensures a minimum required resolution of a bird, flying at the highestaltitude. The combination of a camera sensor and a lens formulate amonitoring node. The camera node model is used to optimize the placementof the nodes for full coverage of a given area above a required lower altitude.The model also presents the solution to minimize the cost (number of sensornodes) to fully cover a given area between the two required extremes, higherand lower altitudes, in terms of camera sensor, lens focal length, camera nodeplacement and actual number of nodes for sky surveillance.The area covered by a VSN can be increased by increasing the highermonitoring altitude and/or decreasing the lower monitoring altitude.However, it also increases the cost of the VSN. The desirable objective is toincrease the covered area but decrease the cost. This objective is achieved byusing optimization techniques to design a heterogeneous VSN. The core ideais to divide a given monitoring range of altitudes into a number of sub-rangesof altitudes. The sub-ranges of monitoring altitudes are covered by individualsub VSNs, the VSN1 covers the lower sub-range of altitudes, the VSN2 coversthe next higher sub-range of altitudes and so on, such that a minimum cost isused to monitor a given area.To verify the concepts, developed to design the VSN model, and theoptimization techniques to decrease the VSN cost, the measurements areperformed with actual cameras and optics. The laptop machines are used withthe camera nodes as data storage and analysis platforms. The area coverage ismeasured at the desired lower altitude limits of homogeneous as well asheterogeneous VSNs and verified for 100% coverage. Similarly, the minimumresolution is measured at the desired higher altitude limits of homogeneous aswell as heterogeneous VSNs to ensure that the models are able to track thebird at these highest altitudes.
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| 8. |
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| 9. |
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| 10. |
- Ambatipudi, Radhika, 1982-
(författare)
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High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing the power density of power electronic converters while reducing or maintaining the same cost, offers a higher potential to meet the current trend inrelation to various power electronic applications. High power density converters can be achieved by increasing the switching frequency, due to which the bulkiest parts, such as transformer, inductors and the capacitor's size in the convertercircuit can be drastically reduced. In this regard, highly integrated planar magnetics are considered as an effective approach compared to the conventional wire wound transformers in modern switch mode power supplies (SMPS). However, as the operating frequency of the transformers increase from several hundred kHz to MHz, numerous problems arise such as skin and proximity effects due to the induced eddy currents in the windings, leakage inductance and unbalanced magnetic flux distribution. In addition to this, the core losses whichare functional dependent on frequency gets elevated as the operating frequency increases. Therefore, this thesis provides an insight towards the problems related to the high frequency magnetics and proposes a solution with regards to different aspects in relation to designing high power density, energy efficient transformers.The first part of the thesis concentrates on the investigation of high power density and highly energy efficient coreless printed circuit board (PCB) step-down transformers useful for stringent height DC-DC converter applications, where the core losses are being completely eliminated. These transformers also maintain the advantages offered by existing core based transformers such as, high coupling coefficient, sufficient input impedance, high energy efficiency and wide frequencyband width with the assistance of a resonant technique. In this regard, several coreless PCB step down transformers of different turn’s ratio for power transfer applications have been designed and evaluated. The designed multilayered coreless PCB transformers for telecom and PoE applications of 8,15 and 30W show that the volume reduction of approximately 40 - 90% is possible when compared to its existing core based counterparts while maintaining the energy efficiency of the transformers in the range of 90 - 97%. The estimation of EMI emissions from the designed transformers for the given power transfer application proves that the amount of radiated EMI from a multilayered transformer is lessthan that of the two layered transformer because of the decreased radius for thesame amount of inductance.The design guidelines for the multilayered coreless PCB step-down transformer for the given power transfer application has been proposed. The designed transformer of 10mm radius has been characterized up to the power level of 50Wand possesses a record power density of 107W/cm3 with a peak energy efficiency of 96%. In addition to this, the design guidelines of the signal transformer fordriving the high side MOSFET in double ended converter topologies have been proposed. The measured power consumption of the high side gate drive circuitvitogether with the designed signal transformer is 0.37W. Both these signal andpower transformers have been successfully implemented in a resonant converter topology in the switching frequency range of 2.4 – 2.75MHz for the maximum load power of 34.5W resulting in the peak energy efficiency of converter as 86.5%.This thesis also investigates the indirect effect of the dielectric laminate on the magnetic field intensity and current density distribution in the planar power transformers with the assistance of finite element analysis (FEA). The significanceof the high frequency dielectric laminate compared to FR-4 laminate in terms of energy efficiency of planar power transformers in MHz frequency region is also explored.The investigations were also conducted on different winding strategies such as conventional solid winding and the parallel winding strategies, which play an important role in the design and development of a high frequency transformer and suggested a better choice in the case of transformers operating in the MHz frequency region.In the second part of the thesis, a novel planar power transformer with hybrid core structure has been designed and evaluated in the MHz frequency region. The design guidelines of the energy efficient high frequency planar power transformerfor the given power transfer application have been proposed. The designed corebased planar transformer has been characterized up to the power level of 50W and possess a power density of 47W/cm3 with maximum energy efficiency of 97%. This transformer has been evaluated successfully in the resonant converter topology within the switching frequency range of 3 – 4.5MHz. The peak energy efficiency ofthe converter is reported to be 92% and the converter has been tested for the maximum power level of 45W, which is suitable for consumer applications such as laptop adapters. In addition to this, a record power density transformer has been designed with a custom made pot core and has been characterized in thefrequency range of 1 - 10MHz. The power density of this custom core transformer operating at 6.78MHz frequency is 67W/cm3 and with the peak energy efficiency of 98%.In conclusion, the research in this dissertation proposed a solution for obtaining high power density converters by designing the highly integrated, high frequency(1 - 10MHz) coreless and core based planar magnetics with energy efficiencies inthe range of 92 - 97%. This solution together with the latest semiconductor GaN/SiC switching devices provides an excellent choice to meet the requirements of the next generation ultra flat low profile switch mode power supplies (SMPS).
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| 11. |
- 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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| 12. |
- Imran, Muhammad
(författare)
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Investigation of Architectures for Wireless Visual Sensor Nodes
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless visual sensor network is an emerging field which has proveduseful in many applications, including industrial control and monitoring,surveillance, environmental monitoring, personal care and the virtual world.Traditional imaging systems used a wired link, centralized network, highprocessing capabilities, unlimited storage and power source. In manyapplications, the wired solution results in high installation and maintenancecosts. However, a wireless solution is the preferred choice as it offers lessmaintenance, infrastructure costs and greater scalability.The technological developments in image sensors, wirelesscommunication and processing platforms have paved the way for smartcamera networks usually referred to as Wireless Visual Sensor Networks(WVSNs). WVSNs consist of a number of Visual Sensor Nodes (VSNs)deployed over a large geographical area. The smart cameras can performcomplex vision tasks using limited resources such as batteries or alternativeenergy sources, embedded platforms, a wireless link and a small memory.Current research in WVSNs is focused on reducing the energyconsumption of the node so as to maximise the life of the VSN. To meet thischallenge, different software and hardware solutions are presented in theliterature for the implementation of VSNs.The focus in this thesis is on the exploration of energy efficientreconfigurable architectures for VSNs by partitioning vision tasks on software,hardware platforms and locality. For any application, some of the vision taskscan be performed on the sensor node after which data is sent over the wirelesslink to the server where the remaining vision tasks are performed. Similarly,at the VSN, vision tasks can be partitioned on software and the hardwareplatforms.In the thesis, all possible strategies are explored, by partitioning visiontasks on the sensor node and on the server. The energy consumption of thesensor node is evaluated for different strategies on software platform. It isobserved that performing some of the vision tasks on the sensor node andsending compressed images to the server where the remaining vision tasks areperformed, will have lower energy consumption.In order to achieve better performance and low power consumption,Field Programmable Gate Arrays (FPGAs) are introduced for theimplementation of the sensor node. The strategies with reasonable designtimes and costs are implemented on hardware-software platform. Based onthe implementation of the VSN on the FPGA together with micro-controller,the lifetime of the VSN is predicted using the measured energy values of theplatforms for different processing strategies. The implementation resultsprove our analysis that a VSN with such characteristics will result in a longerlife time.
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| 13. |
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| 14. |
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| 15. |
- Shahzad, Khurram
(författare)
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Energy Efficient Wireless Sensor Node Architecture for Data and Computation Intensive Applications
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless Sensor Networks (WSNs), in addition to enabling monitoring solutions for numerous new applications areas, have gained huge popularity as a cost-effective, dynamically scalable, easy to deploy and maintainable alternatives to conventional infrastructure-based monitoring solutions.A WSN consists of spatially distributed autonomous wireless sensor nodes that measure desired physical phenomena and operate in a collaborative manner to relay the acquired information wirelessly to a central location. A wireless sensor node, integrating the required resources to enable infrastructure-less distributed monitoring, is constrained by its size, cost and energy. In order to address these constraints, a typical wireless sensor node is designed based on low-power and low-cost modules that in turn provide limited communication and processing performances. Data and computation intensive wireless monitoring applications, on the other hand, not only demand higher communication bandwidth and computational performance but also require practically feasible operational lifetimes so as to reduce the maintenance cost associated with the replacement of batteries. In relation to the communication and processing requirements of such applications and the constraints associated with a typical wireless sensor node, this thesis explores energy efficient wireless sensor node architecture that enables realization of data and computation intensive applications.Architectures enabling raw data transmission and in-sensor processing with various technological alternatives are explored. The potential architectural alternatives are evaluated both analytically and quantitatively with regards to different design parameters, in particular, the performance and the energy consumption. For quantitative evaluation purposes, the experiments are conducted on vibration and image-based industrial condition monitoring applications that are not only data and computation intensive but also are of practical importance.Regarding the choice of an appropriate wireless technology in an architecture enabling raw data transmission, standard based communication technologies including infrared, mobile broadband, WiMax, LAN, Bluetooth, and ZigBee are investigated. With regards to in-sensor processing, different architectures comprising of sequential processors and FPGAs are realized to evaluate different design parameters, especially the performance and energy efficiency. Afterwards, the architectures enabling raw data transmission only and those involving in-sensor processing are evaluated so as to find an energy efficient solution. The results of this investigation show that in-sensor processing architecture, comprising of an FPGA for computation purposes, is more energy efficient when compared with other alternatives in relation to the data and computation intensive applications.Based on the results obtained and the experiences learned in the architectural evaluation study, an FPGA-based high-performance wireless sensor platform, the SENTIOF, is designed and developed. In addition to performance, the SETNIOF is designed to enable dynamic optimization of energy consumption. This includes enabling integrated modules to be completely switched-off and providing a fast configuration support to the FPGA. In order to validate the results of the evaluation studies, and to assess the performance and energy consumption of real implementations, both the vibration and image-based industrial monitoring applications are realized using the SENTIOF. In terms of computational performance for both of these applications, the real-time processing goals are achieved. For example, in the case of vibration-based monitoring, real-time processing performance for tri-axes (horizontal, vertical and axial) vibration data are achieved for sampling rates of more than 100 kHz.With regards to energy consumption, based on the measured power consumption that also includes the power consumed during the FPGA’s configuration process, the operational lifetimes are estimated using a single cell battery (similar to an AA battery in terms of shape and size) with a typical capacity of 2600 mA. In the case of vibration-based condition monitoring, an operational lifetime of more than two years can be achieved for duty-cycle interval of 10 minutes or more. The achievable operational lifetime of image-based monitoring is more than 3 years for a duty-cycle interval of 5 minutes or more.
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| 16. |
- 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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| 17. |
- 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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| 18. |
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| 19. |
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| 20. |
- 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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| 21. |
- 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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| 22. |
- Nazar Ul Islam, Muhammad
(författare)
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Reference setup for characterization and calibration of low-range differential pressure sensors
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, a reference setup for the characterization and calibration of low range differential pressure sensors is presented. The setup utilizes the principle of ideal gas law and actuates on the volume for accurate reference pressure inputs for the calibration process. The error sources for the proposed setup are analysed and an error propagation modelis presented. The range of the setup is ±320 Pa, with the resolution of 0.001% of full scale. The verified sensitivity of the setup is 0.032 Pa. A complete characterization of a high performance differential pressure transducer is conducted as a test case study for the performance analysis of the proposed setup. During these experiments the sensitivity of the calibration setup to the thermal gradient is observed. To this end, the effects of thermal gradient on the transient response of the setup are also studied, utilizing a comparative experimental study. From the presented experimental study it is concluded that the thermal gradient can cause the system to remain in transient state for at least 96 hours. To reduce this effect, a mechanical design optimization is proposed and a finite element model is presented to be studied in comparison to its preceding design for its thermal performance. From the results it is concluded that the optimized design can reduce the transient time of the measurement system due to thermal gradient, by 11 times. Future work is also proposed to further investigate the optimized model for implementation purposes.
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| 23. |
- Thörnberg, Benny
(författare)
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Memory modeling and synthesis for real-time video processing systems
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, a new design methodology and new tools for modeling and synthesis of real-time video processing systems are presented. A real-time video processing system is a system that performs computations on a continuous sequence of images. Image processing is a memory intensive application. This, in turn, leads to the design challenge of bridging the classical gap of speed between memories and computational units. Several techniques exist for building memory hierarchies that exploit data- locality and reuse in order to overcome this memory gap. However, the support from tools to aid the designer in dataflow analysis and memory design is very modest. Additional constructs for modeling electronic systems enable well-known sequential programming languages such as C/C++ to be used for system modeling. Ocapi and SystemC, two object-oriented specification methods are compared in a case study. In this study, SystemC is found to be the most suitable specification method for video processing systems. Most operations invoked in video processing are neighborhood oriented. For a video system designer, this spatio-temporal collection of pixels represents a natural abstraction. In addition, the same pixel neighborhood reflects data dependencies that are crucial to system synthesis. An extended SystemC modeling methodology, called IMEM is presented. IMEM can be used to capture memory transactions and stream interfaces based on the pixel neighborhood as an abstraction. Two important steps towards synthesis of video systems onto Field Programmable Gate Arrays (FPGAs) are presented. These two steps are parts of a decomposition of the complete synthesis task. Firstly, the optimal sizes and placements of all FIFO-buffers in the memory system are optimized. Bit-widths, pipelining and possible sharing of FIFO-buffers among several data flow dependencies are considered at this step. Secondly, the set of FIFO-buffers are allocated onto a set of dual-ported fined grained memories. Both synthesis steps are formally modeled using network flow techniques and linear programming. In addition, a synthesis method that can automatically transform an IMEM model of a single spatial neighborhood into a multimedia processor implementation is presented. The cache and the instruction scheduler performance are both optimized by the tool. IMEM is an application specific methodology that provides the nonhardware skilled video designer with an easy programming model and an FPGA synthesis tool. Memory usage is modeled separately from computation. This is a key feature since memory usage is accepted as being the biggest design bottleneck for video processing.
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| 24. |
- Zhang, Yuxuan
(författare)
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Tiny Machine Learning for Structural Health Monitoring with Acoustic Emissions
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Acoustic Emission (AE) technology, as one of the non-destructive Structural Health Monitoring (SHM) methods, is increasingly utilized for the damage prediction, classification, maintenance, and real-time monitoring of infrastructure. Addressing the need for low latency, power consumption and high portability, a novel approach has been adopted where processing algorithms are embedded close to the sensors on these devices. Continuous data monitoring and collection, coupled with data processing and interpretation comparable to human experts, are anticipated from the next generation of the Internet of Things and smart sensing systems. While Machine Learning (ML) and Deep Learning (DL) has been successfully applied in a number of domains including SHM, resource-constrained, low-power devices pose a challenge for computationally complex ML algorithm execution.To explore the feasibility of deploying ML and DL algorithms on edge devices, this study first proposes a lightweight CNN model based on raw AE signals for concrete damage classification and evaluates its performance on an ultra-low-power microcontroller unit (MCU). Subsequently, to further simplify the algorithm and explore the adaptability across various MCU platforms, a raw AE signal-based Artificial Neural Network (ANN) model is proposed, and its deployment performance on multiple MCUs is assessed. Additionally, the study assesses the impact of feature extraction on ANN performance with raw AE signals on MCUs, finding that using raw data directly is more resource and time-efficient. Lastly, the study investigates the generalization ability of the aforementioned CNN on a carbon fiber panel AE dataset, as well as the performance of 13 traditional ML algorithms on this dataset and their final deployment performance on MCUs. Due to the small size of the dataset, various data augmentation methods were also introduced and their impact on model robustness and accuracy was evaluated.This thesis demonstrates for the first time that real-time inference on edge devices using AE signals for SHM is feasible. It also effectively demonstrates how to balance the critical trade-offs between accuracy, resource demands, and power consumption. Different MCUs and signal preprocessing methods are evaluated, and the impact of various data augmentation techniques on the accuracy of different ML algorithms and their inference robustness is explored in response to the challenge of collecting AE data, which is crucial for the next generation of SHM devices.
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