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Mapping of mechanical properties of the surface by utilization of torsional oscillation of the cantilever in atomic force microscopy

100%
Sikora A., Bednarz L.
Open Physics
|
2011
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vol. 9
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issue 2
372-379
EN
The measurement of the surface topography in dynamic mode (intermittent contact mode) is one of the most popular ways of imaging surfaces at nanoscale with atomic force microscopy. It also allows obtaining so called phase images which reveal the viscous-elastic non-homogeneities of the surface, therefore can be used for detecting the presence of different materials. It is, however, very difficult to interpret the phase map due to the origin of phenomena, method of signal detection and processing. Therefore one cannot determine whether the observed feature is caused by increase or decrease of any of specific mechanical properties of the surface. In this article we present the modified setup of commercially available AFM, where detection of torsional oscillation of the cantilever is used for the determination of mechanical properties such as: elasticity, adhesion, peak force and energy dissipation. By advanced signal processing, the reconstruction of the force spectroscopy curve and the calculation of mentioned parameters are performed. All the operations are done in real time regime. The developed method allows one to obtain much more complex information about measured surface. Test measurement results are also presented.
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Equivalent circuits used in the diagnostics of insulation in power transformers

81%
Glinka T., Decner A., Polak A., Sikora A.
Czasopismo Techniczne
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-
PL
An equivalent circuit of the insulation system in power transformers comes in many forms. In tests for the dielectric loss tangent (tgδ) of the main insulation, the equivalent circuit has been simplified to two-terminal RC series connected or parallel connected circuits. For direct current tests of groundwall insulation modelling, two two-terminals circuits are required – one for charging and shorting, the other for the voltage recovering after shorting. The model turn-to-turn insulation may also be presented by two-terminal circuits. The parameters of the two-terminal circuit can be determined by direct current. The tested winding is energized by DC voltage, the current is interrupted and the voltage waveform on the terminals of the winding is recorded. The parameters of turn-to-turn insulation (equivalent circuit parameters) are calculated from the voltage waveform and they can be used for diagnostic purposes.
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