Most injuries in football occur in the lower extremities due to high muscle stress. To prevent such injuries, the Dutch Football Association (KNVB) and the Delft University of Technology developed the Smart Sensor Shorts, an inertial sensor-based tracking system measuring the athlete’s lower body kinematics, to improve physical load estimates during training sessions and matches. However, the system currently only has offline data analysis software, which results in poor monitoring capability.

This thesis proposes a near real-time data analysis system for Smart Sensor Shorts, featuring an automatic sensor calibration module, a football-specific activity recognition module, and a user interface, to monitor users' lower limb movement and load during football training. The proposed automatic sensor-to-body calibration algorithm maintains a high calibration accuracy with an 18.92º(±5.74º) calibration error on average and simplifies the calibration process by leveraging detected standing and walking movements to estimate calibration parameters. The proposed gradient-boosting decision trees activity recognition model utilizes hip joint angles and joint angular velocities derived by the system to predict users' football-related activities, achieving an overall accuracy of 93.62%. The designed system processes the data recorded by IMUs in real time with a speed of 21 milliseconds per iteration and displays the calculated results related to the user's physical load on the user interface at a frame rate of 20 Hz. ... Read more

Distributing power and data around a garment is a common problem in sensor enabled e-textiles, as connecting separate electronic subsystems together using connectors and wires has proven to be unreliable and cumbersome. In this work a solution is presented that will eliminate the connectors by using two pairs of short-range wireless inductive links. The proposed system is able carry power from one node to the next, while at the same time facilitating data transfer between the nodes. In this work the double inductive link is analysed, and a novel compensation topology is presented. A modified class-E amplifier is proposed to generate a carrier signal, improving the system settling time. Using a placeholder data protocol the system is able to transmit 62mW of regulated power to an external load at a total efficiency of 7.3%, while simultaneously transmitting data at a rate of 8.5kbit/s. Without data transmission it is able to deliver 185mW of DC power at 6.09V unregulated, at an efficiency of 23%. The system is also shown to be capable of handling a maximum bitstream of 240kbit/s.
... Read more

In football, most of the injuries occur in the lower extremities of the athletes. The leading cause of this is high muscle stress during explosive actions. To be able to prevent injuries, the Dutch Football Association (KNVB) and Dutch Hockey Association (KNHB) are working on smart sensor shorts in collaboration with the Delft University of Technology. The human movement scientists from the VU and RUG use these sensor shorts to develop a model which can predict potential incidents. The product’s goal is for the physical trainer to use it to monitor the team in real-time during a game or training.
The physical trainer will use a computer to analyze all the data. The sensor shorts consist of 3 Inertial Measurement Units (IMUs). Each IMU measures the angular velocity (dps), linear acceleration (g), and magnetic field (µT) with a ampling rate of 250 Hz. The high volume of data due to the high sampling rate induces challenges for wireless communication and design.
The sensor shorts can, at the moment, read out the IMUs and compress the sensor data. Besides, possible antennas for the sensor shorts have already been looked at. This thesis will continue with the communication link between the sensor shorts and the computer used by the physical trainer. The thesis will be focused on designing a reliable system for wireless communication. Multiple challenges must be faced to develop a reliable wireless communication system with minimal size. The challenges are the minimum amount of resources available, high data rate, large area to cover for communication, and obstruction due to the human body.
According to literature about monitoring devices currently described in the literature used for football, eight base stations are needed around the football field. The goal is to minimize the number of base stations so that the system can be easily set up. For the development of the system, first, the different Data Collection Protocols(DCP) are examined. Based on the network topology corresponding to the DCP, we want to choose a DCP that is the most efficient and reliable. The Direct Delivery protocol was chosen as most suited in combination with WiFi operating at 2.4 GHz. WiFi can deal with the high data rates and communicate over large distances.
The number of base stations needed is determined based on tests performed on the football field. The choice was made to place the antenna of the sensor shorts on the back of the athlete because there it has the most negligible chance of obstruction due to the athlete’s limbs. The athlete’s own body could cause attenuation of 10 dBm. Additionally, it was chosen to have the base station at 2.2 m height, to have fewer chances of obstruction due to the athletes on the football field. Multiple tests have been performed to determine how many base stations are needed. First, the possible signal strength values of the sensor shorts around the football field have been measured for a single base station. After that, a relation between the measured signal strength and possible loss and delay has been established. These results made it clear that more than one base station is needed. In tests with two base stations, it became clear that data might get lost when there is no base station in the radiation plane of the patch antenna of the sensor shorts. Therefore the choice was made to have four base stations, one on each corner of the football field, so that there is always a base station in the radiation plane of the patch antenna. Based on the test results, the choice was made to have four base stations, one on each corner of the football field. Assuming that the sensor shorts’ RSSI values are always higher than −80 dBm, the system with four base stations would have a loss of less than 5%. The upper boundary for the delay would be 5 s.
... Read more

This report presents a proof-of-concept for a sensor measuring the ionic concentrations in sweat using cyclic voltammetry. Development is focused on feasibility of the sensor. Theoretical evaluations of voltammetry as a working principle and its physical and electrochemical foundations are guiding principles of the design. The sensor is then implemented using commercial components. Experiments show that the sensor has good sensitivity and linearity for single ions in the physiological range. For the measurement of multiple ions the voltammogram is characterized in-depth. A matrix of different ionic fluids with multiple ions is prepared and two independent parameters for the concentration of two ions (sodium and potassium) are found, proving the concept of the sensor for more complex solutions. The usability of the sensor is verified using a sweat sample. Different influencing factors are researched and their impact characterized. Varying electrode materials are evaluated considering durability and sensitivity. Conclusions are drawn and an outlook for future research on this type of sensor is given. The concept of the sensor is proven to work within certain limitations. ... Read more

Cochlear implants (CIs) are the most effective solution to treat severe-to-profound hearing loss. These medical devices mimic and replace the function of the damaged structures of the cochlea. To this date, more than 700,000 individuals worldwide have benefited from CIs. However, state-of-the-art CIs do not provide a natural and high-quality sound perception to their recipients, who poorly appreciate music and hardly understand speech in crowded or noisy atmospheres. Furthermore, CIs are expensive and unaffordable for poorer portions of society. The CI electrode array is the component that presents the most margin of improvement as it is still composed of classic materials and is fabricated via a tailored manual manufacturing process that does not maximize the potential of the system. Concretely, commercial CI electrode arrays contain from 12 to 24 individual stimulating channels that cannot optimally substitute the role of the 3000 neural stimulation sites of a normal-functioning cochlea. Moreover, most of the commercial CI electrode arrays cannot fit in the narrow deep areas of the cochlea to completely cover the low-frequency audible spectrum. Hence, to overcome these limitations, novel strategies and materials to optimize CI electrode arrays ought to be investigated. Chapter 1 of this work starts with an introduction to the auditory system and the different types of hearing loss. Chapter 2 goes through the history and research that led to the development of cochlear implants and presents their main components and current limitations. Chapter 3 discusses in detail the state-of-the-art of CI electrode arrays and Chapter 4 reviews novel materials to enhance them. In Chapter 5, PEDOT:PSS is suggested for the development of all-polymeric cochlear implant micro-electrode arrays. Initial experiments provide a proof-of-concept that demonstrates that by patterning PEDOT:PSS layers with conductive and non-conductive areas, it is possible to create electric circuits with superior electrodes and leads that give rise to all-polymeric CI micro-electrode arrays. Future work will be directed towards developing an actual prototype using this strategy. Furthermore, a study of the long-term stability of the material will be necessary. ... Read more

Moisture absorbed by the hygroscopic polymers like molding compound and die-attach vaporizes during reflow lead to a high vapor pressure inside the electrical components lead to failure in the electrical device, named as popcorn failure. Popcorn failure in plastic encapsulated microcircuits has been a critical issue for electronic device reliability. Researches have been conducted on investigating the failure mechanism. Among all the factors that contributed to the failure, vapor pressure is one of the primary sources of stress that causes crack of the molding compound and delamination between critical interfaces. Numerous publications demonstrate the vapor pressure evolution and contributing factors with mathematical models, simulations, and tests. However, direct measurement of vapor pressure is not yet reported. This thesis presents the design and fabrication verification of a pressure sensor to measure the vapor pressure evolution in moisture-containing polymers at reflow temperatures. The specifications and requirements are extracted from the failure mechanism reported in the literature. A touch-mode capacitive pressure sensor with in-situ doped poly-SiC is designed to measure vapor pressure from atmospheric pressure to 8 MPa under reflow temperature up to 300 °C. Simulation on touch mode capacitive readout is performed to verify the design parameters and provide an estimation of device performance. The fabrication process is designed and conducted with several methods for crucial steps along with different structure dimensions to investigate an optimal solution. A complete fabricated device is achieved with measured initial capacitance from 12.3 to 26.7 pF for different sizes of diaphragms. The deviation between the measured results and simulation results due to fabrication problems is analyzed. Possible causes and solutions of problems that occurred in fabrication and measurement, such as unexpected upward bending of the diaphragm, leakage current between the capacitor electrode plate, and uniformity of SiC layer fabrication, are discussed. Problem correction, device optimization, complete characterization, and experiments for vapor pressure measurement in molding compound remain as future work. ... Read more

Decreasing injuries in football is a topic of interest for the KNVB and KNHB. To reach this goal, the use of smart sensor pants is researched. The data will be used to develop models for finding injury risk factors that are related to movements. Currently, the system is capable of reading out the IMUs and storing the data on an SD-card, for post-analysis of the data. As next step, the communication link should be implemented, for real time feedback to the football players. The design of an efficient communication system in terms of power, size, and reliability, is quite a big task. By looking at similar research to body-worn devices, it is noted, that most devices deal with a 10 times lower data rate than the current device. On top of that, it is noted that the absorption of the body is causing problems on the link reliability. Based on these observations, it is decided to focus the research of this Thesis on the reduction of the data load, and the optimization of the transmission part of the smart sensor pants. The Thesis is split into two parts, the first part will show the use of lossless data compression. The second part will start with showing the benefit of using a patch antenna over a dipole antenna and continues by showing the benefit of using a dual antenna configuration over a single antenna configuration. To be more specific, the first part of this Thesis starts by comparing different lossless data compression algorithms, from which the FELACS algorithm is chosen as most suited. This algorithm is then implemented on the current hardware and tested on data from the smart sensor pants in a realistic football scenario. These results show an average compression ratio of 43 %-45 % in the most intensive 5-minutes of a football game, with a minimum of 38 % in an interval of 10 s. To improve the compression algorithm, an adjustment to the FELACS algorithm is proposed. This adjustment is theoretically tested and shown to outperform the FELACS algorithm with a higher compression ratio. In the second part, the use of a dual antenna configuration is discussed, whereby the use of a patch antenna is compared to a dipole antenna. It will be shown, that a dual antenna configuration can significantly improve the signal strength around the player, resulting in an almost isotropic radiation pattern, using pattern diversity. On top of that, this form of pattern diversity is observed to increase the reliability of the link, using switched combining. Moreover, it will be shown that a patch antenna will be more suited for this application, due to the higher gain in the front, and the robustness against interference when placed close to a conducting material. In summary, the two main contributions of this Thesis, are the reductions in data load, and the testing and verification of the dual patch antenna configuration. These contributions provide the basis for the communication part of the smart sensor pants. ... Read more

In the last 4 decades, surface electromyography (sEMG) signal processing has been applied to detect local muscle fatigue, this non-invasive approach is suitable for detecting EMG signals generated by athletes in motion. Also, EMG could directly reveal the muscle’s performance like endurance and recruitment of motor units, which is hard to be obtained by other methods. With the sEMG system, we can research whether EMG signals can be used to measure muscle fatigue and how this relates to injury risk. This thesis aims to build a sensor node for sEMG to detect local muscle fatigue. An sEMG system is built for this purpose, and a physiological experiment is designed to collect sEMG signals from human muscle (Vastus Medialis) using the sEMG system. Both isometric and isotonic exercises are studied. The data analyzing method is calculating mean power spectrum frequency (MNF), median power spectrum frequency (MDF), and muscle fiber propagation velocity (MFPV) of the collected sEMG signals, because local muscle fatigue is related to MNF/MDF decrease and MFPV decrease. 5 groups of isometric exercise, wall-sit and 2 groups of isotonic exercise, cycling, are recorded. All the athletes are healthy males, around 25. The data analyzing result shows that MNF/MDF decrease is related to muscle fatigue, and MFPV changes similarly with MNF/MDF. ... Read more

This report details the design of an instrumentation system to be used on a skeleton sled. The system will measure data during the run on a skeleton track using several sensors and process and visualise the data afterwards in order to shorten the learning curve of the athlete and give quantitative feedback. The subsystem discussed in this report concerns the measurement of the forces between the body and the sled in order to analyse the steering behaviour of the athlete. This is accomplished via thin film resistive force transducers. The g-forces on the athlete and the sled and the orientation of the sled are measured as well in order to give a better insight how this influences steering and is measured using an IMU (Inertial Measurement Unit). The data is collected using an ESP32 microprocessor. ... Read more

Clean drinking water is still not widely available around the globe and therefore remains an unsolved issue. In fact, 1 in 9 people lack daily access to safe water and sanitation. Groundwater is a water supply source that needs minor treatment and thereby presents itself as a good solution to this global issue. Especially in development countries for example in East Africa this would be a viable solution. One interesting exploration method to detect groundwater in an area is airborne Frequency Domain Electromagnetic (FDEM) survey. However, most airborne EM survey instruments are expensive and bulky. Even though that this exploration technique has been around since the 50s, a commercial inexpensive airborne FDEM instrument has still not penetrated the market. This thesis describes the investigation of a novel portable FDEM survey instrument that will be employed by an Unmanned Aerial Vehicle (UAV). The system architecture for the measurement instrument is presented and the functionality, design considerations and requirements of each system block is given. To check the feasibility of the proposed architecture, a handheld Proof-of-Concept is implemented, which can carry out measurements between 100 - 12.000 Hz. The experimental measurement results of the Proof-of-Concept at operating frequencies of 925, 2175, 5025 Hz are presented and compared against measurements of GEM-2A instrument, which is employed as a reference. ... Read more

Large scale industries like automobile, agriculture and poultry etc.. are in the need of a reliable technology for gas sensors. Till date various types of sensors have been developed for gas applications but the SiC gas sensing has been a recent trend. With increase study in MEMS technology, the SiC material is gaining importance for sensor applications. Although, Silicon Carbide has been the epitome of research in the field of semiconductors in past couple of years due to its commendable properties and resilience. And being one of most used semiconductor in the field of sensor applications lately, an extensive research is being done and proved that Silicon Carbide is one the best suited sensor material. But very little is known about the possibilities of porous silicon carbide and its applications. Since there is no extensive research available on porous Silicon carbide, this thesis aims at it to show how silicon carbide can be made porous, and the role of it in the gas sensor application. An in-depth study of the silicon carbide including its features, issues, and possible advantages and disadvantages. A detailed procedure on design and fabrication is presented along with various models and its parameters used to fabricate the sensor device. The design parameters, technical and economic feasibility of the device are discussed using the results from the experiments. ... Read more

Miniature ultrasound probes, such as intravascular ultrasound (IVUS) probes, are valuable diagnostic tools and provide image guidance during minimallyinvasive interventions. As more ultrasound transducer elements are built into such probes to improve image quality and frame rate, it becomes increasingly difficult to accommodate the cables needed to connect these elements to an imaging system. Among several reported cable-count reduction approaches, in-probe digitization of the received echo signals is a promising solution, as it allows digital data-link techniques to be leveraged to minimize cable count. This work takes a previously-developed application-specific integrated circuit (ASIC) for an IVUS probe as a starting point. This ASIC employs a load-modulation datalink to transmit digitized echo signals of one element via a single micro-coaxial cable at 0.6 Gb/s. This thesis extends this work to multi-bit per-symbol signalling to increase the data rate, allowing the echo signals of multiple elements to be combined into one cable. First, the measured performance of the existing ASIC is compared to simulation results, showing the need for an S-parameter based cable model to faithfully reproduce the measured performance. Based on this simulation model, load modulation with a maximum of three bits per symbol and a maximum symbol rate of 600 MHz is investigated. The trade-off between data-transmission conditions and bit-error rate is investigated and gives a general idea about how fast the data rate can be. An experimental setup is proposed to experimentally validate the performance of multi-bit load-modulation data links. For this, a prototype chip has been designed that includes a multi-bit load-modulation circuit and interfaces with an FPGA that provides test data. The chip has been taped out in a TSMC 0.18 um HV CMOS technology. Post-layout simulation shows that the prototype is able to generate a data rate of 1.6 Gb/s when there are two bits per symbol at the symbol rate of 800 MHz. Compared to the 0.6 Gb/s of the previous design, this is a substantially higher data rate. ... Read more

ECG signals captured almost always have motion artefact noise. This noise arises due to relative motion between the ECG electrode and skin. To remove this noise a reference signal is required that correlates to the noise. This thesis presents the design and test results of a prototype system that incorporates various motion sensors into an ECG electrode and finds correlation between the motion artefacts and motion sensors. ... Read more

The goal of this project is to identify the most promising measurement method and strategy for measuring the thickness of grease and to design a sensor module with electronic read-out and communication module. This project has been split into two parts: a sensor implementation and a communication system. This report describes the design and implementation of the communication module and power supply. The communication module has been designed to work conform a master-slave principle using MODBUS over an RS-485 databus. The used hardware for the communication module is rated to work within a desired 1 to 100m range. Furthermore the master node is connected to the internet to present the data on a small webserver. The power supply design depends on the implementation of the sensor, and contains the use of linear voltage regulators and inverters. The results show that the communication module works properly, whereas the power supply requires some further work. ... Read more

An extraction channel cleaning company wanted a grease thickness sensor to be developed that would send the data via the internet so that information on the thickness could be accessed remotely. This system consists of two parts: the sensor part and a communications part. This report is on the sensor part, which uses a change in capacitance of an interdigital capacitor, which in turn will change the frequency of the oscillator readout circuit. Initially research was done on the properties of grease to see if it would be a good method to measure the thickness. The results showed that it is possible to use capacitance, but that the permittivity of grease depends on the temperature, so the final design needs a temperature sensor. The prototype that was built was used to measure thicknesses and had quite reasonable results. ... Read more

The cleaning company "VETkanaal" requested a sensor system that measures the thickness of a grease layer within kitchen extraction ducts independently and is able to send this to an online platform. The goal of this project is to find an acoustic implementation of the sensor and be able to apply it. It appeared that measuring a shift in resonance frequencies of a plate with varying amounts of grease is the best solution for estimating the thickness of a grease layer. Afterwards, a hardware implementation was made. The conclusion of this report is that an acoustic measuring principle is certainly possible. The first tests of trying to implement such a system were moderately successful. ... Read more

Since the 1960s, the semiconductor industry’s rate of progress has followed by what is commonly known as Moore’s law. In recent years, the traditional approach of downscaling the feature size and increasing the operating frequency of the devices to improve the performance is slowing down due to the reaching of physical limits. Different solutions have been proposed to increase the performance such as using multi-core platforms, able to work in parallel. However, this introduced other issues such as a high latency and power dissipation due to the long communication distances. To overcome this, 3D Stacked ICs have been proposed, allowing for shorter vertical interconnects and higher transistor density. With the introduction of 3D stacked ICs (3D-SIC), the manufacturing processes and its test flow become more complex. As each chip requires to be tested prior to deployment, its crucial to find optimal test flows.
Developing an effective test strategy for 3D SICs is a complex task. During a 2D process, there are typically two test moments (i.e., wafer test and packaging test). However, for a 3D process, the number of possible moments grows based on the number of dies in the stack as many partial stacks test can be performed. In addition, also the interconnects between the stacked dies can be tested, as they play a crucial role in determining the correct functioning of the device. Testing such a partial stack may reduce the cost as it prevents good dies being stacked on them, but on the other hand may increase the total cost due to extra test costs. To help making such decisions, appropriate cost models are required. They are tools used to estimate the cost of a test flow typically applied at an early design stage. The information obtained from them can then be used to optimize the process in question and reduce the cost.
In this thesis, the functionality of 3D COSTAR is extended. 3D COSTAR is a tool developed with the goal of modeling the complete 3D SIC supply chain, including design, manufacturing, test, packaging and logistics. This thesis first presents a test flow optimization algorithm. It is used to evaluate and find the best test strategy, i.e., the highest fault coverage at the lowest cost. Second, a stacking order analysis is performed in which the impact of different stacking orders is evaluated. The goal is to evaluate whether a different stacking order reduces the overall cost. We evaluated both extensions using three case studies. Overall, lower cost solutions were found across all three cases. With respect to test flow optimization, cost reductions of 4%, 6% and 27% were obtained for the three case studies. With respect to stacking order analysis, a cost improvement up to 16% was realized.

... Read more

Batteries are vital sources in many wireless embedded systems applications like the Tire Pressure Management System (TPMS) in the automobile industry. Also, the growth of electric cars will result in an increasing demand for batteries. Although batteries do not directly pollute the environment during their active life, the production phase and decomposition phase will contribute to pollution. The limited lifetime of batteries also emphasizes the need for a change to new technologies.
Replacing batteries becomes difficult in applications on desolated places. Energy harvesting can be an attractive alternative solution. Techniques like electrostatic, electromagnetic and piezoelectric energy harvesting can convert the energy in the ambiance to an useful electrical energy. Piezoelectric energy harvesting can be useful as they have been proven vital in converting vibration energy to the required form. This research focuses on powering wireless systems like a TPMS in a car by piezoelectric energy harvesting. It provides the requirements and decisions involved in designing a circuit capable of transferring input energy to output in an efficient manner. The circuit rectifies the output of a piezoelectric material and provides an output of 3.3 V. Result showed that the circuit was able to power an LED for 5.8 s. By adjusting the circuit according to the power requirements, the circuit can be the source to low power wireless embedded systems. ... Read more