La quantité d'énergie disponible dans les batteries et le nombre limité de cycles de recharge compliquent singulièrement la conception de réseaux de capteurs sans fil (WSN) autonomes. La récupération d'énergie dans l'environnement direct des nœuds et un stockage d'énergie à base de supercondensateurs sont aujourd'hui considérés comme solutions potentielles pour atteindre une durée de vie du réseau théoriquement infinie. Un gestionnaire d'énergie (PM pour ''Power Manager'') est embarqué dans chaque nœud afin de permettre un fonctionnement en neutralité énergétique (ENO), ce qui veut dire que les énergies récupérées et consommées par un nœud sont équivalentes sur le long terme. Dans cette thèse, nous proposons de nouveaux PMs qui adaptent dynamiquement l'intervalle de réveil des nœuds en fonction de l'énergie récupérée. La faible complexité de nos PMs, leur indépendance vis-à-vis du type de source d'énergie récupérée et leur faible empreinte mémoire facilitent leur implantation sur une plate-forme réelle de réseaux de capteurs sans fil. Par ailleurs, lorsque l'on considère un réseau multi-sauts, une variation trop fréquente de l'intervalle de réveil peut s'avérer pénalisante pour l'établissement de rendez-vous entre les nœuds et risque de fortement dégrader la qualité de services globale. Nous proposons donc un gestionnaire d'énergie (WVR-PM) qui limite autant que possible ces variations et qui permet d'améliorer le débit de près de 60% par rapport aux PMs de l'état de l'art tout en diminuant de 45% l'énergie consommée par une communication réussie. / The limited energy and recharge cycles of batteries are crippling the design of autonomous Wireless Sensor Networks (WSNs). To overcome this issue, everlasting harvested energy and supercapacitor-based energy storage are considered as potential solutions to achieve a theoretically infinite lifetime. A Power Manager (PM) is embedded in each WSN node to respect the Energy Neutral Operation condition (ENO), which means harvested energy is equal to consumed energy for a long period. In this thesis, a set of PMs are proposed for energy harvesting WSN nodes to adapt their average consumed energy by changing the wake-up interval according to the available harvested energy. Our PMs are low complexity, independent of energy sources, small memory footprint and therefore, can be easily implemented on a real EH-WSN node. Another issue addressed in this thesis when considering a multi-hop EH-WSN is the effect of wake-up interval variations to the global QoS. Due to its low harvested energy, a relay node is impractical to synchronize with a transmitter if its wake-up interval regularly changes, therefore degrading the global QoS. A new power manager, named Wake-up Variation Reduction power manager (WVR-PM) is proposed to reduce the variations of the wake-up interval. By using WVR-PM, the throughput of a multi-hop EH-WSN can be improved up to 59% compare to state-of-the-art PMs while the average consumed energy for one successful communication is reduced by 45%.

abstract: The structural and electronic properties of compositionally complex semiconductors have long been of both theoretical interest and engineering importance. As a new class of materials with an intrinsic compositional complexity, medium entropy alloys (MEAs) are immensely studied mainly for their excellent mechanical properties. The electronic properties of MEAs, however, are less well investigated. In this thesis, various properties such as electronic, spin, and thermal properties of two three-dimensional (3D) and two two-dimensional (2D) compositionally complex semiconductors are demonstrated to have promising various applications in photovoltaic, thermoelectric, and spin quantum bits (qubits).3D semiconducting Si-Ge-Sn and C3BN alloys is firstly introduced. Density functional theory (DFT) calculations and Monte Carlo simulations show that the Si1/3Ge1/3Sn1/3 MEA exhibits a large local distortion effect yet no chemical short-range order. Single vacancies in this MEA can be stabilized by bond reformations while the alloy retains semiconducting. DFT and molecular dynamics calculations predict that increasing the compositional disorder in SiyGeySnx MEAs enhances their electrical conductivity while weakens the thermal conductivity at room temperature, making the SiyGeySnx MEAs promising functional materials for thermoelectric devices. Furthermore, the nitrogen-vacancy (NV) center analog in C3BN (NV-C3BN) is studied to explore its applications in quantum computers. This analog possesses similar properties to the NV center in diamond such as a highly localized spin density and strong hyperfine interactions, making C3BN suitable for hosting spin qubits. The analog also displays two zero-phonon-line energies corresponding to wavelengths close to the ideal telecommunication band width, useful for quantum communications. 2D semiconducting transition metal chalcogenides (TMCs) and PtPN are also investigated. The quaternary compositionally complex TMCs show tunable properties such as in-plane lattice constants, band gaps, and band alignment, using a high through-put workflow from DFT calculations in conjunction with the virtual crystal approximation. A novel 2D semiconductor PtPN of direct bandgap is also predicted, based on pentagonal tessellation. The work in the thesis offers guidance to the experimental realization of these novel semiconductors, which serve as valuable prototypes of other compositionally complex systems from other elements. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

The diploma thesis deals with a design of a tester device, a selection and verification of a suitable method for comparing the piezoelectric properties of tested PVDF samples. In the introduction, a basic overview of the theory is important to understand the issue and the various branches of use of PVDF in the field of energy harvesting. The tester device includes a unimorph piezoelectric cantilever beam with tip mass, whose properties are described by three models: a model with N degrees of freedom reduced to one degree of freedom (NDOF), a single degree of freedom model (SDOF), both created in Matlab and a model for verifying results in FEM ANSYS Workbench program. The voltage time response and the voltage frequency response of the models is compared with each other. For two different PVDF samples, the voltage response to harmonic excitation is measured using a tester device, and the piezoelectric properties of one of them are determined using the NDOF and SDOF models.

This master thesis deals with design and numerical modelling of piezoceramic sensor, which is placed on a rail, in order to generate electrical energy, which can be used for wireless monitoring of railway traffic and to monitor the condition of the railway. The thesis is divided into three parts. Theoretically background of piezoelectric energy harvesting is described in first part, where some previous application of piezoelectric generator in railway area are shown. In the second part, parametric analysis of numerical model is performed, which directly leads to finding best location on a rail, where piezoelectric generator should be placed. For this analysis the homogenized model of MFC sensor was used. Results of the numerical model were then compared with the results of the conducted experiment. The third part presented own design of piezoceramic sensor, which is placed onto most suitable location on a rail. Results from numerical analysis shown eligibility of using piezoceramic sensor to monitor the railway traffic.

Masters thesis deals with design and practical implementation of wireless sensor module. The primary requirement for this module is its energy self-sufficiency. In this context, the work gets to the subject of "energy harvesting". Then, in terms of energy requirements, several wireless communication platforms which are favorable for the selected application, are compared. From mentioned technologies was chosen communication platform IQRF. The next parts deals with initial prototype of sensor module, which will be demonstrated as the application of measuring wind direction. This paper describes the hardware and software solution. Followed by a detailed analysis of its properties in terms of energy requirements. Based on the obtained measurements resource parameters are set.

Master’s Thesis deals with obtaining electricity from the vibrations of the surrounding environment through piezoelectric vibration generator. To simulation piezoceramics and design mechanical parts of the generator was used simulation program ANSYS 10.0. First, parameters of the designed piezoelectric generator were numerically calculated, and then these values were compared with the real sample. Further work is in the description of material properties of piezo materials.

This work deals with the power supply of wireless sensors. When using a wireless sensor is desirable application of alternative energy sources, because the primary cells or batteries may reduce the extent or length of service of the sensor itself. Ambient energy can be used as a suitable alternative source. This energy must be in an appropriate form, which allows its conversion to electric energy. These appropriate, already used types include: solar en., temperature gradient en., en. of flowing liquids, vibration, etc. The advantage of vibrations is its presence in almost all mechanical systems. One of the possibilities for using the vibration of machine systems for power supply wireless sensors is using the vibration power generator with oscillating component. The generator must be designed so that its resonance frequency coincides with the frequency of vibration in the machine system. This method can be used only if the machinery system vibrations at least partially constant. Another option is to use the vibrations caused by, for example, transit transport, or different step acting factor. In this case, it is desirable that the generator is designed with variable resonant frequency, which can partly be achieved, for example, integrating several oscillating component in the body of generator. After the general analysis of the problem, graduation theses will be concerned with the possibility of use of energy from the short damped oscillation and step impulse. Focusing on a proposal of multi-element structures.

This work is focusing on analysis of current development in energy harvesting projects in aerospace industry field, and on analysis of current development in vibration generator field. It is also concentrating on establishment of a complex simulation model of vibration generator. It deals with modeling of magnetic field of generator and its cross connection with a mechanic and an electronic model.

Tato diplomová práce se zabývá vývojem autonomního zdroje elektrické energie založeného na MEMS termoelektrickém generátoru. Uvažovaný generátor bude následně použit pro napájení autonomní senzorické jednotky pro letecké aplikace. Systémový pohled na autonomní senzorickou jednotku zahrnuje senzor se zpracováním a přenosem dat, energy harvester (termoelektrický generátor), power management, akumulační prvek a autodiagnostiku. Všechny výše uvedené komponenty jsou v práci podrobně popsány. V úvodu práce je provedena široká rešerše existujících termoelektrických generátorů pro letecké aplikace. Následně jsou popsány základní teoretické poznatky z oblasti DC/DC měničů pro energy harvesting. Zvláštní pozornost je věnována metodám MPPT (Maximum Power Point Tracking). Jako základ pro vývoj napájení autonomní senzorické jednotky bylo provedeno množství simulací za pomoci nástroje MATLAB/Simulink Simscape. Pro identifikaci prametrů modelu posloužilo měření na speciálním přípravku. Praktická implementace teoreticky popsaných problémů je provedena na k tomuto účelu navrženém technologickém demonstrátoru. Závěrem je zhodnocena reálná využitelnost navržené technologie pro finální aplikaci v leteckém průmyslu.

This master's thesis deals with the development and verification of the model of the piezoelectric generator, incl. determination of its parameters. This mathematical model should be used as a tool for development of new devices, especially for analysis of applicability of available energy source (vibration) and for design of device itself. At first the review of energy harvesting is described deeply. Subsequently piezoelectric generators and the ways how we can model them, are depicted in details. The methodology of parameters estimation and model development is presented in state space or in MATLAB/Simulink environment and applied on the commercial generator Midé V21BL. A device has been made within the scope of the thesis, which can be used as an universal tool in experiments with generator. Finally the model is applied on the analysis of energy yield from man's walk and there is also brief introduction to model modifications.