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Institute
For almost a century, active load modulation techniques have been used to increase the backoff efficiency of high frequency power amplifiers. The Doherty architecture, which is based on active load modulation, has become the standard power amplifier architecture in cellular base station transmitters and makes a significant contribution to the energy-efficient operation of cellular mobile radio networks today.
In recent times, the increasing availability of ever more powerful digital signal processing also led to a paradigm shift in the field of transmitter systems. The application of complex digital predistortion algorithms opens up new ways to overcome some of the bandwidth limitations that are inherent to classic power amplifier architectures based on active load modulation and thus allows to exploit the efficiency advantages of active load modulation also for the increasingly important wideband operation.
In this work, a universal and illustrative method of analysis of multi-harmonic load modulation spaces is developed and the possibilities and characteristics of hybrid modes within the ‘Doherty-Outphasing continuum’ with regard to wideband operation are investigated. In the last part of the work, the theoretical findings are verified using a wideband Doherty PA demonstrator with a peak output power of 300 W in the frequency range of 680 to 1020 MHz.
The continuously growing focus on reducing energy onsumption worldwide has infiltrated into the telecommunications domain in its both mobile terminals and base stations. This has led eventually to the introduction of advanced power amplifier (PA) architectures.
This work investigates the suitability of outphasing PAs for use as a high efficiency solution in next generation base station applications. Besides the classical Chireix concept, several newly emerging outphasing variants are analyzed and compared. The effects of the nonlinear output capacitance are considered in detail. It is shown that harmonic isolation is vital for the Chireix PA realization using transistor devices. In addition, the power capability of the Chireix outphasing PA is discussed and a load-pull simulation technique for the complete PA is proposed. The findings are used to develop a method for designing practical Chireix PAs.
A proof of concept 60 W Chireix PA prototype using state of the art GaN HEMTs is presented. Measurements with 5 MHz 1-Carrier and 20 MHz 2-Carrier W-CDMA signals of 7.5 dB PAR resulted in respectively 45% and 44% average drain efficiencies.
Development of a spectrum-efficient OFDM MIMO radar for future urban air mobility applications
(2020)
This thesis presents novel research in the field of OFDM MIMO RadCom
systems for the use in future urban air mobility (UAM) scenarios.
The UAM scenario creates new requirements for sense and avoid as well as
communication systems. Various flying platforms, manned and unmanned,
will soon fly over our cities. Today’s technology and systems cannot provide
means to enable a safe and reliable operation of such air vehicles. Thus, it
is necessary to investigate new technologies, like the OFDM MIMO radar
which enables 3D sense and avoid plus communications in one device.
This thesis presents several new aspects in terms of digital signal processing
and system design including hardware and software.
Concerning the system design, the thesis treats issues like transmit (TX) receive
(RX) antenna crosstalk, and the optimization of the number of virtual
antennas for a larger virtual aperture and thus a higher angular resolution
through real-valued baseband signals. The thesis presents a complete
simulation model including a channel model for OFDM MIMO radar. Furthermore,
it presents a complete hardware, firmware and software design of
an OFDM MIMO radar which was tested indoors and outdoors in various
conditions.
In terms of signal processing, the thesis introduces a novel phase correction
method to improve the dynamic-range of the direction of arrival (DOA) estimation
for OFDM MIMO radars, and it shows the application of Newman
phase sequences to OFDM symbols in order to lower the peak to average
power ratio (PAPR).
Starting from a pure OFDM MIMO radar, the necessary steps towards a
combined RadCom system are explained. Last, a concept for the airspace
integration of several of these systems is presented.
The research presented in this thesis is the result of a cooperation of the Institute
of Microwaves and Photonics Friedrich-Alexander University Erlangen-
N¨urnberg and Airbus Central Research and Technology in Taufkirchen near
Munich, Germany.
This thesis investigates the recognition of human activities from the position of the wrist and the feasibility of occupancy detection based on environmental sensors. In preparation to this thesis, a wrist-worn 10-axis human activity tracker combining a 3-axis accelerometer, a 3-axis gyroscope, a 3-axis magnetometer, and a barometric pressure sensor was developed. Four volunteers participated in collecting a first dataset of 190 measurements by performing ten everyday activities. An approach is introduced by which a person's energy expenditure can be estimated independently of the measurement position. Using the acceleration data obtained at the wrist, various methods for detecting cycling are presented. It is also shown that the barometer allows discriminating activities that involve a vertical displacement, such as climbing stairs or riding an elevator, as well as helps to reduce the false alarm rate of a fall detector. The potential of magnetic field sensing is derived from the signal characteristics of the magnetic interference as experienced during cycling and riding an elevator. It is demonstrated that the examined activity set can be discriminated by fusing the data of either the accelerometer and the barometer or the gyroscope and the barometer.
To detect and count occupants, an approach using a fusion of environmental sensors from an indoor air quality measurement system is presented. Environmental sensors, as opposed to motion detectors, are nonintrusive, easy to install, low cost, detect nonmoving occupants, do not have dead spots, and can even infer the number of occupants. For this study, measurements of carbon dioxide, volatile organic compounds, air temperature, and relative air humidity were conducted in four student apartments for a total of 49 days. Features were extracted from the environmental sensor data and subsets selected using correlation-based feature selection. In this thesis, a comparison of the supervised learning models RIPPER, Naı̈ve Bayes, C4.5 decision tree, logistic regression, k-nearest neighbours, and random forest is performed. Furthermore, a method is proposed to greatly reduce time and effort of collecting training data in residential buildings. The results indicate that the predictive power of volatile organic compound sensing is comparable to that of carbon dioxide. With a simple Naı̈ve Bayes classifier, the approach detected occupancy and estimated the number of occupants with an accuracy of 81.1% and 64.7%, respectively. In addition, a gas sensor test setup was developed that is capable of characterizing carbon dioxide and volatile organic compound sensors simultaneously.
Inner source (IS) is the use of open source software development practices and the establishment of open source-like communities within an organization. The organization may still develop proprietary software but internally opens up its development. IS promises to resolve problems of traditional software development by easing software reuse and enabling parties within an organization to collaborate across organizational boundaries.
However, it is unclear what elements constitute IS (problem I) and how to measure the presence and magnitude of IS collaboration (problem II). The large majority of research articles on IS to date are limited to qualitative results regarding IS. There are yet no quantitative studies on IS collaboration exploring how much IS collaboration takes place or how IS practices affect it (problem III).
We followed a three-phase research approach to address these problems. First, we performed an extensive literature survey and analyzed 43 IS publications. We found that four key elements constitute IS (shared cultural values, open development environment, communities around software, IS-specific scenarios) but that IS programs and projects differ on at least five dimensions (addressing problem I).
Second, we developed the patch-flow method (and a software tool implementing it) for measuring IS collaboration. Patch-flow is the flow of code contributions across organizational boundaries ("silos") such as organizational unit or cost center boundaries. We evaluated the method using case study research with a non-trivial industry organization and found it to be viable and useful to practitioners (addressing problem II).
Third, we performed a multiple-case case study with three large software organizations running a total of five IS program. We identified the used IS practices and the resulting patch-flow. We found patch-flow to exist in all organizations but that only fraction of all code contributions to IS projects constitute patch-flow. We observed that the number of IS practices implemented correlates with the distance of parties involved in collaboration. This indicates that IS is particularly suited to enable collaboration between parties of high distance in an organization (addressing problem III).
This thesis delivers a holistic definition of IS and the first classification framework for IS programs and projects. Researchers can use such a framework to reason about generalizability of their results more precisely. The patch-flow measurement method is the first of its kind to measure and quantify IS collaboration and can serve as a base for further quantitative analyses of IS collaboration. The exploration of the patch-flow in the three industry cases can serve as example and benchmark for practitioners.
Thanks to the emerging digital technology and fast digital converters, it is possibleto transfer the efforts of designing analog duplex filters into digital numeric algorithms applied to recursive structures, operating on power amplifiers (PAs) in transmitters. The system approach, which was invented during the course of research project cognitive mobile radio (COMORA) supported by the German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung (BMBF)) and Nokia Networks, is highlighted.
In this thesis the design of a novel hybrid digital base-band feedback and feed-forward applied to the analog RF PA called also ” ampli-filter” is presented and verified by measurements. This architecture provides a periodic band-pass filter at the output of the RF PAs as frequency response that allows the transmitter design to relax duplex filter requirements with a potential form factor and weight reduction and cost saving inside BTS. This digital sub-system is placed in the feedback path applied to the RF transmitter and provides high attenuation and filter slope in the transition bandwidth. Both of these requirements are usually reached in the duplex filter with a large number of cavities and a long design process. Moreover the digital subsystem in the ampli-filter is frequency agile and adaptive allowing this structure to be attractive for multi-band and multi-standard scenarios.
Orthogonalität ist eine besondere Eigenschaft Boolescher Funktionen. Die Orthogonalisierung einer Booleschen Funktion vereinfacht die Transformation in eine andere äquivalente Form. Mit dieser Arbeit werden zwei neue allgemeingültige, logische operative Verknüpfungsmethoden die 'orthogonalisierende Differenzbildung ⊝' und das 'orthogonalisierende Verodern v ' vorgestellt. Die orthogonalisierende Differenzbildung wird zur Ermittlung einer Differenz in orthogonaler Form zweier Produktterme oder zweier Funktionen eingesetzt. Das orthogonalisierendes Verodern wird zum Verodern zweier Produktterme oder zweier orthogonaler Funktionen angewendet, welches auch Ergebnisse in orthogonaler Form darbietet. Darüber hinaus weisen die algorithmischen Implementierung beider Verknüpfungsmethoden geringere Rechenzeiten mit zunehmender Dimension im Vergleich zu den herkömmlichen bekannten Operationen auf. Auch werden die Vorteile im Hinblick auf den Speicherplatzbedarf hierbei besser genutzt, weil kein zusätzlicher Algorithmus zur Orthogonalisierung benötigt wird. Zudem werden Anwendungen der orthogonalisierenden Differenzbildung in weiteren Verfahren gezeigt, wie z.B. die Bildung der orthogonalen Negierten einer Funktion der disjunktiven Normalform. Durch die inhärente Orthogonalisierung werden weitere Verarbeitungsschritte in der TVL-Arithmetik, wie das Boolesche Differentialkalkül, erheblich vereinfacht. Ternär-Vektor-Listen werden als rechnerinterne Darstellung für binäre Funktionen verwendet und sind für die Behandlung Boolescher Probleme vorteilhafter.
Daneben werden in dieser Arbeit zwei neue mathematische Boolesche Gleichungen zur Orthogonalisierung Boolescher Funktionen bzw. Ternär-Vektor-Listen disjunktiver Normalformen hergeleitet, welche jeweils auf den neuen Verknüpfungen ⊝ und _g basieren. Damit wird zum ersten Mal mathematisch die Problematik der Orthogonalisierung behandelt und einfache Gleichungen zur Berechnung der orthogonalen Form vorgestellt. Zudem werden die beiden neuen Methoden in der Bestimmung von Testbelegungen für kombinatorische Schaltnetzwerke zur Verifizierung möglicher logischer Fehler in der TVL-Arithmetik eingesetzt. Ihre implementierten Algorithmen weisen zudem Vorteile bezüglich Rechenzeit und Speicherplatzbedarf auf und ermöglichen damit die Berechnung von minimierterer Menge an Testbelegungen. Im Vergleich zu den Methoden aus der Literatur reduzieren die neuen Algorithmen ORTH[⊝] und ORTH[ v ] die Rechenzeit um einen Faktor von ca. 2,5. Zusätzlich haben die beiden neuen Algorithmen ORTH[⊝] und ORTH[ v ] die Eigenschaft bessere Lösungen zu liefern, das bedeutet, orthogonale TVLen geringerer Anzahl an Termen, d.h. eine Reduzierung um etwa 50%. Damit wird eine Weiterbehandlung der ermittelten orthogonalen TVL mit geringerer Anzahl an Operationen gewährleistet, welche zum einen weitere Rechenzeiten optimiert und zum anderen die Anzahl an Terme in den nachfolgenden Verfahrensschritten niedriger ausfallen lässt. Mit dieser Verminderung wird die Reduzierung an Termen bis zur Ermittlung der Testbelegungen fortgesetzt, so dass minimierte Testsätze zur Verifizierung von kombinatorischen Schaltungen am Ende der Berechnungslinie erhalten werden können. Mit der geringeren Rechenzeit der Algorithmen und der minimal ermittelten Menge an Testsätzen wird eine Einsparung in Testzeit und die damit verbundenen Testkosten erreicht werden können.
The digitization of the analog radio frequency (RF) domain, carried out to realize flexible, low-cost software-defined radio transmitters, has reached the power amplifier (PA).
Switched mode operation is used to implement a digital input interface and optimize the efficiency of RF amplifiers by minimizing the current-voltage overlap at the transistor. Differential (push-pull) operation is used to enhance the bandwidth of an amplifier by taking advantage of the symmetry to match even harmonics.
This work discusses differential switched mode operation to design simultaneously efficient and wideband PAs. Using the example of the current mode class-D (CMCD) amplifier, the required harmonic output impedances in differential and common mode are derived from the ideal waveforms. In order to implement the output impedances with a large bandwidth, this thesis presents optimized designs of wideband output filters and planar baluns.
The book concludes with several examples of differential switched mode RF PAs. Furthermore, the integration of antennas as differential loads for differential PAs is examined and an implementation of a so-called "amplitenna" is presented.
The power amplifier (PA) is the key component of the transmit chain in a mobile telecommunication system. It allows the coverage of a wide service area but it’s non-linear effects need to be compensated in order to obtain high linearity and efficiency without introducing interference on the adjacent channels. Digital Pre-Distortion (DPD) is the commonly used solution to overcome these problems. The The LTE system makes use of OFDM modulation used in modern systems, provides signals with wide bandwidth, but low average power, thus common PA designs achieve low average efficiency.
Dual-input Doherty power amplifiers with digital steering introduce new degrees of freedom in terms of linearization and reconfiguration.
This work analyzes the tradeoffs between linearity, efficiency and linearization bandwidth, when digitally driving the DPA inputs separately. The knowledge of the physics of the devices allows to design a workflow to linearize the dual-input DPA obtaining high efficiency and reconfigurability.
In this work an application of a bio inspired optimization algorithm show how to calibrate the DPD directly at the base-station.
Cyber-physical systems (CPS) security, as a prevalent concern in all
digital industries, must be implemented on different levels of
abstraction. For example, the development of top-down approaches,
e.g., security models and software architectures is equivalent in
importance to the development of bottom-up solutions like the design
of new protocols and languages. This thesis combines research in the
field of CPS security from both approaches and contributes to the
security models of the two lighthouse examples automotive software
engineering and general password security.
Most existing countermeasures against cyberattacks, e.g., the use of message
cryptography, concentrate on concrete attacks and do not consider the
complexity of the various access options offered by modern cyber-physical systems. This is
mainly due to a solution-oriented approach to security problems. The
model-based technique SAM (Security Abstraction Model) adds to the early
phases of (automotive) software architecture development by explicitly
documenting attacks and managing them with the appropriate security
countermeasures. It additionally establishes the basis for comprehensive
security analysis techniques, e.g., already available attack assessment
methods. SAM thus contributes to an early, problem-oriented and
solution-ignorant understanding combining key stakeholder knowledge. This
thesis provides a detailed overview of SAM and the resulting analyses of our
evaluation show that SAM puts the security-by-design principle into practice
by enabling collaboration between automotive system engineers, system
architects and security experts. The application of SAM aims to reduce costs,
improve overall quality and gain competitive advantages. Based on our
evaluation results, SAM is highly suitable, comprehensible and complete to be
used in the industry.
The bottom-up approach focuses on the area of password hardening encryption
(PHE) services as introduced by Lai et al.~at USENIX 2018. PHE is a password-based
key derivation protocol that involves an oblivious external crypto service
for key derivation. The security of PHE protects against offline brute-force
attacks, even when the attacker has full access to the data server.
The obvious evolution of PHE is the extension of the protocol to use multiple
rate-limiters (guardians) to mitigate the single point of failure introduced by
the original scheme.
In the second part of this thesis, a general overview of the motivation and
use cases of PHE is given, along with a new formalization of the protocol to
help the mentioned scalability and availability issues. Moreover, an implementation
of the resulting threshold-based protocol is briefly explained and evaluated. Our
implementation is furthermore tested and evaluated in a novel use case featuring
password hardened encrypted email.
In this thesis, a simulation platform with multi-functions was developed by the software Comsol and Matlab. This platform can be compatible with a variety of physics research, including static heat transfer or electromagnetics, and a variety of physical field coupling; it can be compatible with a variety of materials and a variety of geometric forms, orientations and distributions of fillers or component in a multiphase system. This platform also includes the functions of automatic generation, screening and checking of initial conditions, automatic storage and analysis of simulation results, time control, meshing strategy analysis, etc.
This work analyses potentials of signal integrity metrics to measure the amount of hardware imperfections in a base station transmitter that constitutes RF fingerprints. The wireless radio interface between legitimated regular base station (RBS) and user equipment (UE) in a mobile network is vulnerable to fake base station (FBS) attacks. The FBS masquerades as a legitimate network and establishes an adversary against UE for various security threats in all cellular standards. The practical realization of FBS is feasible with the availability of a variety of software defined radio (SDR) and open-source software platforms.
To identify such non-legitimate FBS, this work provides a signal integrity processing model for the UE to inspect the base station based on its unique fingerprints. The first proposed detection scheme inculcates phase noise signatures that can identify low and medium performing SDR transmitters through characterization of decision threshold. A highly effective clock-based carrier frequency offset (CFO) detection scheme is proposed that is based on the synchronization of legitimate network by a central precision clock. The CFO signatures reveal that multiple surrounding RBS exhibits identical CFO values, whereas FBS that runs in a separate clock domain shows relatively large deviations. Additionally, a robust CFO stability analysis identifies all levels of adversaries, even if the FBS is locked to a precision clock.
This work also contains a higher order statistical analysis on error vector in both symbol and sample domain. The symbol-based error vector magnitude (EVM) approach is based on second order moment and detects low performing FBS by specifying a region of RBS (RoRBS) in proximity of the reference constellation points. The higher order kurtosis approach in symbol domain, based on 4th order moment, determines how noise is shaped. This approach outperforms EVM and phase noise signatures and reveals nonlinearities of the transmitter. However, this method grows computationally complex with the modulation order and additionally error signal is suppressed due to equalization in the receiver. Due to this, high-end transmitters used as FBS may escape from being identified as they lie near the boundary line of the determined threshold.
This work is also aimed at investigating a reliable, computationally efficient, and early detection of FBS. The applicability should be generic for all mobile communication standards. This leads to sample-based higher order kurtosis analysis in which parametric estimation of noise is carried out and it is then compared with the reference noise distribution to enable strong and highly robust fingerprints for the identification of low, medium, and high-end SDRs. The detection threshold is first characterized by measurement campaign through a setup involving a smartphone UE and data from the FBS and RBS. Afterwards, this is optimized by Neyman-Pearson lemma. The kurtosis approach is highly time efficient as it requires only 10ms of observation samples to reliably inspect the given base station.
The reliability of higher-order statistical approach is also presented as probability of true detections and false alarms. The overall accuracy of up to 97.8% is recorded at specified observation time, which is scalable to higher accuracy in proportion to the inspection time that can be managed at the receiver. Moreover, the proposed signal integrity model provides a scalable security based on the standard needs, required level of security, and receiver capabilities. The receiver complexity doing inspection and a general comparison of various detection schemes is also assessed in this work. Moreover, decision fusion that incorporates all the local decisions is also presented. Finally, the signal integrity analysis is proposed for various applications in other domains including IoT, V2X, GNSS and Radar adversary detections.
In dieser Dissertation, basierend auf dem Molecular Communication (MC)-System, wird ein wasserbasiertes Testbed im Makromaßstab verwendet, um die Ausbreitung von biokompatiblen, wirkstoffbeladenen superparamagnetischen Eisenoxid-Nanopartikeln (SPIONs) durch ein menschliches Gefäß für Anwendungen zur Arzneimittelabgabe zu imitieren. Im Testbed wird Partikelsuspension mit unterschiedlichen Fließgeschwindigkeiten in einen mit Wasser gefüllten Kanal gepumpt und von einem Suszeptometer detektiert. Alle Grundlagen, die zum Verständnis der Physik des Testbeds erforderlich sind, werden besprochen. In einer Vorstudie wird das Testbed zu einem mathematisch beschriebenen 2D-rotationssymmetrischen Modell vereinfacht und sein Strömungsregime analytisch hergeleitet. Eine vollständige numerische Untersuchung des vereinfachten Modells wird durchgeführt. Um die Rechenkomplexität der 3D-Multiphysik-Simulationen zu vermeiden, werden die magnetischen und fluidischen Simulationen entkoppelt und separat simuliert, woraus die Systemantwort effizient geschätzt wird. Andere Detektoren, einschließlich Helmholtz-, Maxwell- und Planarspulen, werden ebenfalls in Betracht gezogen. Es zeigt sich, dass das detektierte Signal der Spulen direkt proportional zur Volumensuszeptibilität und damit zur Dichte der Partikel in ihren Detektionsbereichen ist. Eine Änderung der Partikelverteilung im Sender vor der Injektion in den Kanal führt zu verschiedenen Verteilungen im Detektor, was die Systemreaktion erheblich beeinflusst.
Due to the progress in communication technologies and the ever-shrinking form-factors of electronic devices, sensors are becoming increasingly ubiquitous in daily life. In smart-home applications especially, detecting the number of humans present and determining their positions allows for intelligent controls of heating, ventilation, lighting, and entertainment systems, potentially saving significant amounts of energy and CO2 emissions in the process. However, while recent progress through deep learning in computer vision enables cameras to detect human targets accurately, privacy concerns and their dependency on good sight conditions prevent their adoption. Contrary to that, radar sensors are privacy-preserving, work independent of sight conditions, and allow for the estimation of range, velocity, and angle information of targets.
This work explores the use of millimeter-wave frequency continuous wave radar sensors for estimating the number of human targets and detecting their positions in indoor environments.
To this date, most methods in literature on radar-based tracking, detection, and counting, focus on automotive applications and are mostly based on traditional signal processing-based methods.
The work presented in this thesis shows that deep learning enables a low-cost radar sensor to succeed in said tasks in complex multi-target indoor environments, where signal-processing-based methods reach their limits due to multi-path reflections, clutter, and ghost targets.
To this end, new training schemes, network architectures, and loss functions were developed to enable performance gains similar to what was seen with the advent of deep learning in computer vision.
Korrelation von Materialqualität und Ausfallmechanismen leistungselektronischer SiC-Bauelemente
(2023)
Ziel dieser Arbeit war es, eine Korrelation der Siliciumcarbid (SiC) Materialqualität mit Ausfallmechanismen leistungselektronischer 4H-SiC Trench-MOSFET Bauelemente herzustellen. Dafür wurden homo-epitaktische, n-leitende SiC-Schichten abgeschieden. Diese Schichten wurden anschließend mit konfokaler DIC-Mikroskopie und UV-PL Methoden hinsichtlich ihrer Defekte charakterisiert. Die so charakterisierten Epitaxie-Wafer wurden zur Herstellung von leistungselektronischen Trench-MOSFET Bauelementen verwendet. Nach der Prozessierung wurden die Bauelemente elektrisch charakterisiert. Elektrische Ausbeute-Maps wurden anschließend mit den während der Prozessierung aufgenommenen Defektdaten überlagert und mit entsprechenden Defektklassen abgeglichen. Abschließende Untersuchungen an diesen charakterisierten Bauelementen dienten zur Analyse der Langzeitstabilität und Zuverlässigkeit.
Mobile communication is rapidly growing. Increasing demands on capacity and bandwidth have to be addressed by future developments. This means higher signal requirements and bandwidth for transceivers in mobile basestations. Transceivers are the component with highest power consumption in a basestation. Especially analog components show different impairments and nonideal behavior with negative effects on energy efficiency and signal integrity. These effects can be analyzed and mathematically described to build a specific digital signal processing algorithm, which mitigates certain effects. This work treats impairments from machine learning perspective. IQ Imbalance of modulators as well as power amplifier nonlinearities are representive impairments with significant influence on the signal quality. These effects are trained to artificial neural networks (ANNs) for digital impairment mitigation. Furthermore it is shown that the ANNs are able to model different impairment effects with a single network and can be simply enhanced by further input parameters to mitigate dynamic effects. Physically inspired modeling of long term memory effects like thermal memory and charge trapping are a special focus of this work.
This thesis is a comprehensive study of piezoelectric energy harvesting circuits in response to human gait. The main goal of this work is to take advantage of ambient mechanical vibration to power a gait based wearable device integrated in a shoe.
Most wearable devices are battery operated,which is followed by unsustainable course of action as the battery life expires. To meet the growing demand of
wearable devices with environment friendly approaches, walking is one of
the ways. The stress generated from walking has the potential to convert mechanical energy into electrical energy via piezoelectric elements. In this work, the piezoelectric element is used not only as an energy harvester but also
as a sensor. We take advantage of the foot-strike to collect gait information
and obtain electrical energy simultaneously. This brings a paradigm shift from
wrist-based wearables to foot-based wearables.
There are several energy harvesting circuits discussed in this work to under
stand their response to a gait signal. The circuits studied were standard energy harvesting circuit (SEH), Self-powered Parallel Synchronous Switch Harvesting on Inductor (sp-p-SSHI), Self-powered Synchronous Electric
Charge Extraction (sp-SECE), Self-powered Optimized Synchronous Electric
Charge Extraction (sp-OSCE) and Full wave Voltage Doubler (VD), and then
implemented in the proposed shoe application. Their working principles are
assessed and rated against the used case of gait-excited piezoelectric elements.
The advantages and disadvantages of these circuit topologies incorporating
non-linear techniques are also discussed.
Thesystem based-investigation is presented discussing the power consumption of each stage from sensor data collection to data transmission. Athorough
analysis of the extent to which piezoelectric elements can contribute to the
application with and without battery is presented in this thesis. The role
of battery as back-up in simultaneous sensing and energy harvesting is also
investigated.