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Merilni sistem za samodejno visokotemperaturno in nizkofrekvenčno karakterizacijo dielektričnih materialov
KOS, TOMAŽ (Author), Klančar, Gregor (Mentor) More about this mentor... This link opens in a new window, Rojac, Tadej (Co-mentor)

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Abstract
Piezoelektrični materiali se kot senzorji, aktuatorji in pretvorniki mehanskih signalov v električne veličine in obratno uporabljajo v širokem območju industrijskih in znanstvenih področij. Trenutno se nekateri najbolj uporabljeni piezoelektrični materiali z visokim piezoelektričnim odzivom depolarizirajo oziroma izgubijo piezoelektrično aktivnost že pri relativno nizkih temperaturah (~ 200 °C), kar onemogoča njihovo uporabo v visokotemperaturnih aplikacijah. Nedavno so različni industrijski sektorji izrazili potrebo po uporabi piezoelektričnih materialov z visoko učinkovitostjo v višjem temperaturnem območju (> 200 °C). Pri razvoju takih piezoelektričnih materialov je potreben vpogled v dinamične električne lastnosti, ki jih je mogoče spremljati z meritvami dielektričnega odziva pri nizkih frekvencah (< 1 kHz). Zaradi visokih cen merilnih sistemov, ki omogočajo vpogled v dielektrični odziv pri nizkih frekvencah, poskušamo v magistrskem delu razviti merilni sistem, ki omogoča samodejno visokotemperaturno in nizkofrekvenčno dielektrično karakterizacijo materialov v frekvenčnem razponu 2 mHz–1 kHz in temperaturnem razponu 25 °C–450 °C. Istočasno mora biti izdelani merilni sistem cenovno ugoden, kvaliteten, omogočati mora vpogled v zahtevane dinamične dielektrične lastnosti materialov, hkrati pa natančen, fleksibilen in z možnostjo karakterizacije velikega obsega merjenih vzorcev. Na osnovi temeljite preučitve prednosti in slabosti poznanih metod dielektrične spektroskopije smo najprej določili primerno metodo nizkofrekvenčne dielektrične karakterizacije. V osrednjem delu prikažemo realizacijo merilnega sistema iz obstoječih elektronskih naprav in sestavnih delov. Ob tem pojasnimo princip delovanja posameznih elektronskih naprav in sestavnih delov, njihove prednosti in slabosti ter njihov namen v izdelanem merilnem sistemu. Nadalje predstavimo izdelano programsko opremo, ki v namen samodejne izvedbe dielektrične karakterizacije v odvisnosti od temperature in amplitude ter frekvence vsiljene napetosti upravlja s strojno opremo realiziranega merilnega sistema. Pri tem so predstavljene izvirne rešitve, ki omogočajo natančno karakterizacijo dielektričnih materialov kljub nekaterim slabostim uporabljenih elektronskih naprav. Nazadnje predstavimo karakterizacijo in testiranje izdelanega merilnega sistema, s čimer so bile preverjene ustreznost delovanja, kvaliteta izdelave in natančnost ter možne izboljšave izdelanega merilnega sistema. V ta namen je bila izvedena meritev dielektričnih vzorcev pri sobni in povišani temperaturi ter primerjava merilnih rezultatov z referenčnim merilnim sistemom in podatki iz strokovne literature. V sklopu tega dela smo pokazali, da so pri karakterizaciji kondenzatorja za profesionalno uporabo z izdelanim merilnim sistemom izmerjene vrednosti faznega zamika (v frekvenčnem območju 2 mHz–100 Hz) v območju vrednosti, ki jo je definiral proizvajalec, in izmerjene vrednosti kapacitivnosti znotraj definirane tolerance kondenzatorja 1 %.

Language:Slovenian
Keywords:dielektrična spektroskopija, dielektričnost, dielektrične izgube, lock-in ojačevalnik, ojačevalnik električnega naboja, PID-regulator, LabVIEW
Work type:Master's thesis/paper (mb22)
Organization:FE - Faculty of Electrical Engineering
Year:2016
Views:766
Downloads:211
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Secondary language

Language:English
Title:Measurement system for automated low-frequency and high-temperature characterization of dielectric materials
Abstract:
As sensors, actuators and interconverters of mechanical signals into electrical quantities, piezoelectric materials are used in a wide range of industrial and laboratory settings. Currently, some of the most widely used piezoelectric materials are those with high piezoelectric responses, but their usefulness only extends over a relatively small temperature range, as at temperatures as low as ~ 200°C such materials depole or lose their piezoelectric activity. Recently, various industrial sectors have expressed the need for the use of piezoelectric devices in high temperature environments (> 200°C), where the piezoelectric materials are also required to have a high piezoelectric response. For the development of such piezoelectric materials insight into their dynamic electrical properties is required, which can be monitored, for example, by measuring the dielectric response at low frequencies (< 1 kHz). Such measurements can be performed by dedicated, commercially available measurement systems, however, efforts to identify high temperature piezoelectric materials sweep a broad range of chemical compositions, structures and properties, thus a novel measurement device was envisaged that could cater to the diverse range of materials properties that need to be explored. This master’s thesis presents the development of a measurement system that enables an automated high-temperature and low-frequency characterization of dielectric materials in the frequency range between 2 mHz and 1 kHz and in the temperature range from room temperature and 450 °C. The following requirements have been defined for the system: i) affordability, ii) high accuracy and iii) flexibility in terms of characterization of various dielectric samples of different dimensions and shape. Based on a thorough examination of the advantages and disadvantages of the available methods of dielectric spectroscopy, in the first part of the thesis we determined the appropriate method for the low-frequency dielectric characterization. In the central part of the thesis, we explain the development of the measurement system, from the existing electronic devices and components, their working principles the related advantages and disadvantages, and their purposes in the developed measurement system. Furthermore, we present a computer software, that was designed within the scope of this thesis to cater to the unique requirements of the equipment and its operation. The software allows for fully automated measurements of the dielectric permittivity as a function of temperature, frequency and amplitude, and incorporates innovative design features that assist with minimizing experimental error and increase the overall accuracy of the measurements. In the final part of the thesis, we present the characterization and testing of the developed measurement system, which allowed us to verify the quality and the accuracy of the system as well as possible improvements. For this purpose, we have measured various dielectric samples at ambient and elevated temperatures and compared the measurement results with a reference measurement system and literature data. Within this work we characterized a standard capacitor (for professional use) using the developed measurement system. We have confirmed that the measured values of the phase shift (frequency range of 2 mHz–100 Hz) are within the range defined by the capacitor manufacturer and that the measured values of the capacitance are within the defined tolerance of 1 %.

Keywords:dielectric spectroscopy, dielectric permittivity, dielectric losses, lock-in amplifier, charge amplifier, PID controller, LabVIEW

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