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Electrospinning and characterization of fibrous structure for piezoapplications
Svobodová, Anežka ; Kaštyl, Jaroslav (referee) ; Částková, Klára (advisor)
The master’s thesis deals with the preparation and characterization of PVDF-based composite fibrous layers prepared by electrospinning. Ceramic particles TiO2, BaTiO3 and BCZT were used as fillers. The fibers were prepared containing 10, 20, 30, 40 and 50% of these particles and then their morphology, piezoactive phase representation and dielectric characterization were characterized. The effect of the presence of particles on the fiber diameter and on the crystallinity fraction of the polymer was shown. Particle size significantly influenced their distribution in the fibers. Piezoelectric particles further influenced the content of electroactive phases beta and gamma. The highest proportion of electroactive phases was determined in BaTiO3 filled fibers, which reached up to 98%. For the BaTiO3 filled fibers, the dielectric constant values were also measured, which reached lower values than expected due to the high porosity of the prepared fibers The as-prepared fibers can be considered promising not only for piezoapplications, therefore, optimization of their preparation and measurement of electrical characteristics will be further studied.
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Characterization of PVDF material in nanoscale resolution
Pisarenko, Tatiana ; Dallaev, Rashid (referee) ; Sobola, Dinara (advisor)
Tato práce se zabývá charakterizací nanovláken na bázi polyvinylidenfluoridu. Zaměření práce je na piezoelektrické vlastnosti vlákna, které jsou studovány metodou piezoelektrické silové mikroskopie. Takto byly měřeny dva typy odlišných vzorků, které se lišily v parametrech výroby. Odlišnosti vláken v jejich fázovém složení byly také zkoumány za využití Ramanovy spektroskopie a infračervené spektroskopie s Fourierovou transformací. Chemická analýza povrchu a jeho stavu proběhla pomocí rentgenové fotoelektronové spektroskopie. Různé uspořádání nanovláken spolu s jejich průřezem bylo pozorováno rastrovacím elektronovým mikroskopem za využití fokusovaného iontového svazku. Rovněž byla zkoumána smáčivost a kontaktní úhel povrchu vzorků s demineralizovanou vodou. Bylo zjištěno, že vyšší rychlost otáček válce během procesu elektrostatického zvlákňování má velmi významný vliv na jejich uspořádání a tím i na parametry ovlivňující tvorbu piezoelektrického jevu a dalších materiálových vlastností.
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Electrospun fibers based on PVDF and nylon
Černohorský, Petr ; Sobola, Dinara (referee) ; Papež, Nikola (advisor)
Polymer nanofibers used for the construction of triboelectric nanogenerator (TENG) and piezoelectric nanogenerator (PENG) are new and promising technologies for energy recovery. Thanks to the generation of electrical energy based on mechanical movement (deformation), these fibers can find application in the field of self-powered electronic devices. In this work, three nanofibrous structures of materials were prepared by electrostatic spinning: pure polyvinylidene fluoride (PVDF), pure polyamide-6 (PA6) and their mixed combination PVDF / PA6. Non-destructive analyzes such as Raman spectroscopy, FTIR, XPS and electron microscopy were used to study the properties of nanofibers. Analyzes confirmed the positive effect of electrostatic spinning of polymers on the support of the formation of highly polar crystalline -phase in PVDF and , -phase in PA6. The structure arrangement of the nanofibrous material and their defects were observed by scanning electron microscopy (SEM). Furthermore, the contact angle of the wettability of the liquid on the surface was measured for the materials, and the permittivity was measured to monitor the dielectric properties. The described results make the mixed material PVDF / PA6 very promising for further research in the field of nanogenerators and functional textiles.
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Measuring the Parameters of Piezo Energy Harvesters
Kunz, Jan ; Novák,, Martin (referee) ; Hadaš, Zdeněk (referee) ; Beneš, Petr (advisor)
This dissertation deals with the measurement of piezoenergy harvester parameters, in particular the measurement of their efficiency. The first part of the thesis summarizes important metrics for their comparison and reviews existing measurement systems for measuring harvester performance parameters. The measurement of harvester efficiency is simplified due to the complexity of power measurement and harvester efficiency is calculated from its parameters. However, this method is not accurate because it neglects mechanical losses and has a large measurement uncertainty. For this reason, the main objective of this work is to find a way to directly measure the harvester power input and thus measure its efficiency by definition, i.e. including mechanical losses. By analyzing the power flow in the harvester power chain, a way to achieve this goal has been found. Then, I have created an automated measurement system that allows to measure the harvester power parameters and also its efficiency including the determination of measurement uncertainties. In the last section, the performance, parameters and especially the two types of efficiency for commercially available harvesters are compared. As expected, the efficiency evaluated according to the definition come out smaller than in the case of its simplified version. However, this ratio varies widely for different harvester types, with the new efficiency being approximately one-third for PZT harvesters but only one-hundredth for PVDF harvesters. This significant difference shows that the different types of harvesters have large differences in mechanical losses, this difference could not be measured until now and thus remained neglected.
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Design of tester of piezoelectric PVDF layers
Sijková, Simona ; Rubeš, Ondřej (referee) ; Hadaš, Zdeněk (advisor)
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.
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Development of PVDF nanofibers sensor
Klásek, Matyáš ; Tofel, Pavel (referee) ; Hadaš, Zdeněk (advisor)
This diploma thesis deals with the feasibility of using PVDF nanofibers as an active sensor layer generating electrical signal. PVDF and related electromechanical effects are described. A research study is conducted regarding existing PVDF nanofiber applications and based on it, an event sensor design utilizing triboelectric effect and electrostatic induction is proposed. The electrical response of the layers is experimentally investigated and a pulse detection algorithm is conceived and implemented. Finally, a way of integrating the sensor into a rail track is proposed.
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Measurement of energy harvesters
Kašpárek, Ondřej ; Pikula, Stanislav (referee) ; Kunz, Jan (advisor)
Over recent years the power outputs of piezoelectric energy harvesters have increased to the point where they rival other types of energy harvesting and therefore their sufficient parameterization is necessary. Four piezoelectric PVDF films - DT1-028KL, DT1-052K, DT2-028K a LDT2-028K made by SENZOR SOLUTIONS TE Connectivity were parametrized by two created systems of measurement with force strain. Power outputs of these films when pressed with harmonic force signal with 3 Nrms amplitude are in nW and transferred energies after force impulse with size 300 N are between hundreds and tenths of fJ. Furthermore, values of quality factor, resonance frequency, optimal load resistance and maximal power stability were determined.
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Characterization and preparation of PVDF nanofiber matrices for wearable electronics
Zajacová, Lucia ; Papež, Nikola (referee) ; Macků, Robert (advisor)
The presented bachelor thesis deals with the process of production PVDF nanofiber matrices uising electrospinning and subsequent electrical characterization of the produced material. At the beginning, it introduces nanotechnologies and their undeniable importance in medical applications. It focuses on the influence of process parameters, production enviroment and the very properties of the spinning solution itself, leading to final character of the spun fiber. Various morphological differences obtained by individual process settings then continue to influence their piezoelectric properties, which are the subject of the reaserch in the experimental part of this thesis. The obtained results are applied to devices uising the piezoelectric effect with the potential for application in the biotechnological fields.
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Electrode Materials for Li-S Batteries
Jaššo, Kamil ; Almáši,, Miroslav (referee) ; Syrový,, Tomáš (referee) ; Kazda, Tomáš (advisor)
This thesis is focused on the research of electrode materials for lithium-sulphur (Li-S) batteries, with an emphasis on the optimization of the process of preparation of positive electrodes through the modification of the individual technical steps of the manufacturing process and the selection of a suitable binder. The theoretical part of the thesis is devoted to terminology and battery issues with emphasis on Li-S batteries, their working principle, shortcomings, critical parameters for commercialization and existing research in this field. The practical part of the thesis deals with the influence of the compression pressure used in the production of positive electrodes on the electrochemical properties of the resulting Li-S cells. In the next part of the thesis, the influence of the binder used on the resulting electrochemical properties is investigated. In the following sections, the influence of the thickness of the electrode material layer and the ratio of its individual components (C/S) on the resulting electrochemical properties of the Li-S cell is analyzed. On the basis of the measured results, the optimum conditions for the preparation of the positive electrodes of the Li-S cells have been identified with respect to the individual technical steps of the manufacturing process.
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