Non-Linear Electro-Ultrasonic Spectroscopy of Resistive Materials

Elektro-ultrazvuková spektroskopie je založena na interakci dvou signálů, elektrického střídavého signálu s frekvencí fE a ultrazvukového signálu s frekvencí fU. Ultrazvukový signál mění vzdálenost mezi vodivými zrny ve vzorku a tím mění jeho celkový elektrický odpor R. Změna odporu R je proměnná s frekvencí ultrazvukového signálu fU. Vzorek, který obsahuje mnoho defektů ve své struktuře, vykazuje vysokou změnu odporu R v porovnání se vzorkem bez defektů při stejné hodnotě ultrazvukového a elektrického signálu. V disertační práci je popsána elektro-ultrazvuková metoda na tlustovrstvých rezistorech, hořčíkových slitinách, monokrystalech Si a CdTe, varistorech a také jeden z prvních pokusů aplikace elektro-ultrazvukové spektroskopie na horninové vzorky a tak diagnostikovat jejich stav poškození. V našem případě byl proměřen vzorek žuly. Jelikož se jedná o nedestruktivní metodu testování, tak má tato metoda velmi perspektivní budoucnost. Tato metoda je citlivá na všechny defekty ve vzorku. Její výhodou je, že se měří velikost signálu ne frekvenci danou rozdílem nebo součtem budících frekvencí fE a fU a tím se dá dosáhnout vysoké citlivosti. V mém případě byl vždy měřen signál na rozdílové frekvenci fi = fE-fU.All materials contain cracks and micro-cracks in structure. My aim is to detect these cracks. Electro-Ultrasonic spectroscopy is a non–destructive testing method which describes quality and reliability of a tested sample. Tested sample is excited by the harmonic electrical signal of frequency fE and ultrasonic signal of frequency fU. A new harmonic signal of the frequency fi is created as a result of electrical resistance change due to the variation of the crack effective area by ultrasonic excitation. The intermodulation frequency fi is given by the subtraction of excitation frequencies fE and fU. Amplitude of the intermodulation signal at frequency fi is influenced by the electric current, which flows through the sample structure, and resistance change, which is ultrasonically induced due to the defects and unhomogeneities in a sample structure. High sensitivity of this method comes from the fact that the frequencies of exciting sources and measured signal are on different frequencies. The signal-to-noise ratio and high sensitivity for NDT analyses are based on the application of electrical filters for attenuation of exciting signals in signal preprocessing. Experimental verification of this method was performed on various samples such as magnesium alloy, aluminium and dural plates, both without and with cracks, varisotors, MOS FET transistor, rock samples, monocrystals Si and CdTe. This work presents a new non-destructive testing method of solids with metallic electrical conductivity, monocrystals, resistive materials and electronic devices.

The effects of molecular and processing parameters on energy harvesting capability of PVDF-based nanogenerators

In the research of the alternative vibration sensing systems, the major potential is attributed to piezoelectric materials that can generate the electrical output from the waste vibration sources of the industrial machines. Poly(vinylidene fluoride) (PVDF), mostly in the electroactive β-phase, is a great option due to its excellent piezoelectric properties and good flexibility. The β-phase PVDF can be obtained by simple stretching of the a- phase PVDF films, and the conditions of this process are well documented. Surprisingly, the implications of molecular parameters of the PVDF have not been addressed yet. This study investigates the effect of the molecular weight (Mw) of the PVDF on the β-phase development and consequential vibration sensing capabilities after uniaxial stretching. The successful phase transformation was confirmed using FTIR and XRD. In the FTIR spectra, a typical a-phase peak at 762 cm-1 diminished giving rise to the β-phase peak at 840 cm-1 after the stretching. The results also showed a remarkable impact of the Mw on d33 coefficient making Mw an important parameter that should not be overlooked in designing the PVDF-based sensing elements. The obtained data are highly important for the optimization of the PVDF-based vibration sensors applicable in the efficient structural and health monitoring nanosystems. © 2021 TANGER Ltd., Ostrava.Czech Science FoundationGrant Agency of the Czech Republic [19-17457S]; Ministry of Education, Youth and Sports of the Czech Republic - DKRVO [RP/CPS/2020/003, RP/CPS/2020/006]RP/CPS/2020/003, RP/CPS/2020/006; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Grantová Agentura České Republiky, GA ČR: 19-17457

Effect of extrusion process and various elongation ratios on the structural and dielectric properties of pvdf-based copolymer containing micro and nano-sized crystallites

In this contribution, the effect of the extrusion process of the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) with the subsequent elongation/poling on its structural and dielectric properties is presented. The extrusion can be understood as continuous processing of polymer melts in the large scale (in comparison to solvent casting), when the thickness of the final product can be varied depending on the final operation conditions. Herein, the PVDF-co-HFP sheets of 5 cm in width were extruded using a single screw extruder. The fabricated sheets were cooled down and then, they were cut to the stripes and subsequently stretched to various elongations (100, 200 and 500 %) using a universal tensile testing machine. Such samples were investigated using FTIR in order to determine the effect of the elongation process on the transformation of the a-phase to the β-crystalline phase. The extend of the electro-active β-phase was quantified and its impact on the dielectric properties was investigated. The results clearly demonstrated that the elongation has a crucial effect on the final dielectric properties of the PVDF-co-HFP. © 2021 TANGER Ltd., Ostrava.Czech Science FoundationGrant Agency of the Czech Republic [19-17457S]; Ministry of Education, Youth and Sports of the Czech Republic DKRVO [RP/CPS/2020/003, RP/CPS/2020/006]RP/CPS/2020/003, RP/CPS/2020/006; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Grantová Agentura České Republiky, GA ČR: 19-17457

PVDF/PVDF-TRFE blends loaded with BaTiO3: from processing to performance testing

Concerns surrounding the limited supply of fossil fuels have been the subject of much debate. As of promising solutions, polymers like poly(vinylidene fluoride) (PVDF) have gained attention due to their ability to generate electrical energy from the waste mechanical vibrations. The energy harvesting and vibration sensing potential of PVDF is however limited due to its low content of electroactive β-phase, which has to be increased by indirect post-processing. Recently, a synergistic effect was found in PVDF directly blended with its trifluoroethylene copolymer (PVDF-TrFE) due to strong interfacial polarization. In this study, we aim to further increment the piezoelectric performance of PVDF/PVDF-TrFE blends by incorporating a small amount of BaTiO3 nanocrystals via a facile and scalable processing route. The β-phase content was monitored using FTIR and XRD. Melt rheology experiments showed that co-blending of PVDF-TrFE as well as the addition of BaTiO3 slightly increased melt viscosity and complex modulus. Despite that, rheological data suggested that developed formulations can be processed by conventional techniques intended for a large-scale production. More importantly, PVDF/PVDF-TrFE binary blends supplemented with BaTiO3 are expected to exhibit superior d33 compared to conventional neat blends, which could make them highly promising for modern energy harvesting and sensor-related applications. © 2021 NANOCON Conference Proceedings - International Conference on Nanomaterials. All rights reserved.RP/CPS/2020/003, RP/CPS/2020/006; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Grantová Agentura České Republiky, GA ČR: 19-17457

Comparative study of pvdf sheets and their sensitivity to mechanical vibrations: The role of dimensions, molecular weight, stretching and poling

This paper is focused on the comparative study of the vibration sensing capabilities of poly(vinylidene fluoride) (PVDF) sheets. The main parameters such as molecular weight, initial sample thickness, stretching and poling were systematically applied, and their impact on sensing behavior was examined. The mechanical properties of prepared sheets were investigated via tensile testing on the samples with various initial thicknesses. The transformation of the α-phase to the electro-active β-phase was analyzed using FTIR after applying stretching and poling procedures as crucial post-processing techniques. As a complementary method, the XRD was applied, and it confirmed the crystallinity data resulting from the FTIR analysis. The highest degree of phase transformation was found in the PVDF sheet with a moderate molecular weight (Mw of 275 kDa) after being subjected to the highest axial elongation (500%); in this case, the β-phase content reached approximately 90%. Finally, the vibration sensing capability was systematically determined, and all the mentioned processing/molecular parameters were taken into consideration. The whole range of the elongations (from 50 to 500%) applied on the PVDF sheets with an Mw of 180 and 275 kDa and an initial thickness of 0.5 mm appeared to be sufficient for vibration sensing purposes, showing a d33 piezoelectric charge coefficient from 7 pC N−1 to 9.9 pC N−1 . In terms of the d33, the PVDF sheets were suitable regardless of their Mw only after applying the elongation of 500%. Among all the investigated samples, those with an initial thickness of 1.0 mm did not seem to be suitable for vibration sensing purposes. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Czech Science FoundationGrant Agency of the Czech Republic [19-17457S]RP/CPS/2020/003; Horizon 2020 Framework Programme, H2020; European Cooperation in Science and Technology, COST: CA18203; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Grantová Agentura České Republiky, GA ČR: 19-17457

Energy harvesting technologies for structural health monitoring of airplane components - a review

With the aim of increasing the efficiency of maintenance and fuel usage in airplanes, structural health monitoring (SHM) of critical composite structures is increasingly expected and required. The optimized usage of this concept is subject of intensive work in the framework of the EU COST Action CA18203 "Optimising Design for Inspection" (ODIN). In this context, a thorough review of a broad range of energy harvesting (EH) technologies to be potentially used as power sources for the acoustic emission and guided wave propagation sensors of the considered SHM systems, as well as for the respective data elaboration and wireless communication modules, is provided in this work. EH devices based on the usage of kinetic energy, thermal gradients, solar radiation, airflow, and other viable energy sources, proposed so far in the literature, are thus described with a critical review of the respective specific power levels, of their potential placement on airplanes, as well as the consequently necessary power management architectures. The guidelines provided for the selection of the most appropriate EH and power management technologies create the preconditions to develop a new class of autonomous sensor nodes for the in-process, non-destructive SHM of airplane components.The work of S. Zelenika, P. Gljušcic, E. Kamenar and Ž. Vrcan is partly enabled by using the equipment funded via the EU European Regional Development Fund (ERDF) project no. RC.2.2.06-0001: “Research Infrastructure for Campus-based Laboratories at the University of Rijeka (RISK)” and partly supported by the University of Rijeka, Croatia, project uniri-tehnic-18-32 „Advanced mechatronics devices for smart technological solutions“. Z. Hadas, P. Tofel and O. Ševecek acknowledge the support provided via the Czech Science Foundation project GA19-17457S „Manufacturing and analysis of flexible piezoelectric layers for smart engineering”. J. Hlinka, F. Ksica and O. Rubes gratefully acknowledge the financial support provided by the ESIF, EU Operational Programme Research, Development and Education within the research project Center of Advanced Aerospace Technology (Reg. No.: CZ.02.1.01/0.0/0.0/16_019/0000826) at the Faculty of Mechanical Engineering, Brno University of Technology. V. Pakrashi would like to acknowledge UCD Energy Institute, Marine and Renewable Energy Ireland (MaREI) centre Ireland, Strengthening Infrastructure Risk Assessment in the Atlantic Area (SIRMA) Grant No. EAPA\826/2018, EU INTERREG Atlantic Area and Aquaculture Operations with Reliable Flexible Shielding Technologies for Prevention of Infestation in Offshore and Coastal Areas (FLEXAQUA), MarTera Era-Net cofund PBA/BIO/18/02 projects. The work of J.P.B. Silva is partially supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/FIS/04650/2020. M. Mrlik gratefully acknowledges the support of the Ministry of Education, Youth and Sports of the Czech Republic-DKRVO (RP/CPS/2020/003

Ultrasonic transducer peak-to-peak optical measurement

Possible optical setups for measurement of the peak-to-peak value of an ultrasonic transducer are described in this work. The Michelson interferometer with the calibrated nanopositioner in reference path and laser Doppler vibrometer were used for the basic measurement of vibration displacement. Langevin type of ultrasonic transducer is used for the purposes of Electro-Ultrasonic Nonlinear Spectroscopy (EUNS). Parameters of produced mechanical vibration have to been well known for EUNS. Moreover, a monitoring of mechanical vibration frequency shift with a mass load and sample-transducer coupling is important for EUNS measurement