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- Englisch (6) (entfernen)
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- Anisotropy (1)
- Complex resistivity tomography (1)
- Daedalea Quercina (1)
- Electrical measurements (1)
- Fungi (1)
- Geoelectrics (1)
- Geophysics (1)
- Granite landmarks (1)
- Ground penetrating radar (1)
- Ground penetrating radar (GPR) (1)
Complex resistivity (CR) has been used to investigate the properties and the extent of damage in wood and standing trees. Our laboratory experiments have proved that wood´s anisotropy influences its electrical behaviour. It is a well-established fact that wood exhibits the lowest resistivity amplitudes in the axial direction compared to that in tangential and radial directions. It has been shown that anisotropy affects not only the amplitude but also the phase. Phase values are the highest in the axial direction, particularly in the lower frequency range. The changes in resistivity due to fungi-induced damage were investigated in a long-term laboratory test. With progressing damage, both resistivity and phase decrease. The phase also shows sensitivity to the changes in the structure of wood cell. CR Tomography (CRT) has been employed in the field to detect fungi-infected zones in fallen trees. A number of factors such as the type and age of the tree, and the season seem to influence the CRT results. Among those, the effect of seasonal changes has been demonstrated here. Furthermore CRT can be used to characterise fungi-infected zones in the tree.
In this paper complex electrical resistivity measurements
on oak samples are described. They were performed
to study the effect of anisotropy, moisture content
and fungi-infection. The laboratory results indicate that anisotropy
of wood affects not only the electrical resistivity
but also the phase shift. The results can be explained by the
macro- and microstructure of wood. The moisture experiment
showed that resistivity and phase behave differently.
As expected, resistivity decreases with increasing moisture.
In contrast, phase and the imaginary part of conductivity
first increase with rising moisture content but then start to
decrease again at higher moisture level.
The experiment involving fungi-infected wood proved
particularly important. Its results suggest that phase can be
used as an indicator for the structural damage of wood cells.-----------------------------------------------------------------------------------------------------------------------------------------------------------In diesem Artikel werden die Ergebnisse
von Messungen des komplexen elektrischen Widerstands
an Eichenholz gezeigt. Mit dem Verfahren der Spektral
Induzierten Polarisation (SIP) wurden Untersuchungen
zur Anisotropie, zum Wassersättigungsverhalten und zum
Pilzbefall an Eichenkernholzproben durchgeführt. Diese Laborergebnisse
zeigen, dass die Anisotropie des Holzes nicht
nur Einfluss auf den elektrischen spezifischen Widerstand
hat, sondern auch auf die Phasenverschiebung zwischen
Strom- und Spannungssignal. Beim hier gezeigten Sättigungsversuch
zeigte sich auch, dass sich Phase und spezifischer
Widerstand verschieden verhalten. Während der Widerstand mit zunehmender Holzfeuchte kontinuierlich
abnimmt, steigt die Phase bis zu einem bestimmten Holzfeuchtegehalt
an und nimmt danach erst ab. Weitreichende
Konsequenzen hatten die Experimente, bei denen gesundes
Eichenkernholz mit dem braunfäuleerregenden Pilz Daedalea
Quercina infiziert wurde. Aus diesen Ergebnissen lässt
sich schließen, dass sich der komplexe elektrische Widerstand
als Diagnosemethode für Pilzbefall eignen kann.
One of the main problems in the assessment of the operability, stability and contamination potential of tailings facilities is the lack of data on subsurface materials, properties and structures. One key task in the use of geophysics is the selection of the proper methods for a given site/problem combination. Interpretation of the acquired and processed physical data (e.g. electrical resistivity distribution) into something useful for site assessment (e.g. contamination distribution) is another. In the TAILSAFE project (funded by the European Commission) we have worked with partners on the use of geophysics for tailings facilities inspection. DC and complex resistivity, ground penetrating radar, and spectral analysis of surface waves and multichannel analysis of surface waves have been used on dams and beaches. In most cases, our methods provided useful information on the subsurface structure, but the translation of geophysical values into geotechnical or other parameters is still challenging.
The method of low-frequency impedance spectroscopy has been successfully applied in Earth sciences to characterize soils and rocks. The method uses the diagnosing power of complex electrical resistivity in a frequency range between 1 mHz and 1 kHz. In our study, the potential of this method has been explored for the investigation of wood. We observed remarkable differences in the resulting spectra of complex resistivity for different European and Tropical tree species. The data processing of the acquired low-frequency impedance spectra yields integrating parameters. The comparison of the integrating parameters with the mean pore diameter that has been separately determined for the tropical tree species indicates clear correlations. An additional investigation has revealed remarkable difference in the complex resistivity spectra between oil bearing and non-oil bearing sandal wood. This result and the relations between electrical parameters and structural parameters of wood indicate the prospective potential of low-frequency impedance spectroscopy.