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Microwave polarimetry based wood scanning
Halmstad University, School of Business and Engineering (SET), Mechanical Engineering and Industrial Design (MTEK).ORCID iD: 0000-0002-4826-019X
2000 (English)In: Proceedings of the 12th International Symposium on Nondestructive Testing of Wood: University of Western Hungary, Sopron, 13-15 September 2000, Sopron: University of Western Hungary , 2000, p. 8-Conference paper, Published paper (Other academic)
Abstract [en]

We describe a method to detect knots and faults in wood logs based on microwave measurements and the depolarising properties of wood. The depolarisation is an effect of the anisotropy in the dielectric properties of wood, which is caused by the fibre structure. The measurements are made in the frequency domain where a discrete reflec-tion spectrum is sampled. By transforming the frequency spectrum into the time domain the spatial distribution of the reflections appear. The wave is transmitted in a pure linear polarisation, tilted to 45° For each discrete frequency all available information is measured for the reflected wave and therefore it is possible to calculate the complex polarisation ratio and the state of polarisation which are the quantities containing the most visible information. The measurements are one dimensional and by combining measurements from different directions we create tomographic slice images of the inner structure of a log. Our measurements has showed the possibility to follow the extension of knots in a log using only a iso-surface visualisation. The used equipment is working at low intensity and is therefore virtually harm-less to human beings, furthermore it is portable and can be operated by one single person.

Place, publisher, year, edition, pages
Sopron: University of Western Hungary , 2000. p. 8-
Keywords [en]
Microwave measurements, Wood logs, Image reconstruction, Tomography
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:hh:diva-1949Local ID: 2082/2344ISBN: 963-7180-88-5 OAI: oai:DiVA.org:hh-1949DiVA, id: diva2:239167
Conference
12th International Symposium on Nondestructive Testing of Wood, University of Western Hungary, Sopron, 13-15 September, 2000
Available from: 2008-09-23 Created: 2008-09-23 Last updated: 2013-11-15Bibliographically approved
In thesis
1. Non-Invasive Multidimensional Imaging Applied on Biological Substances
Open this publication in new window or tab >>Non-Invasive Multidimensional Imaging Applied on Biological Substances
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents the research and development of a microwave in-strument to capture tomographic information from the inner structure ofthe biological sample. The principle of the instrument is based on theanisotropy introduced by the fibres in materials such as wood and musclesin terms of information regarding changes in the fibre structure. The in-formation is presented as images representing the state of polarization us-ing Stokes parameters, the complex polarization ratio, and the ellipticityand the linear tilt angles. The theory of wave propagation in anisotropicmedia is discussed and related to the dielectric properties of wood. Ex-periments have shown that the developed instrument can be utilized invarious applications such as localizing knots and cavities in wood andto detect mechanical contamination of meat. A second instrument hasbeen improved by introducing a new signal analysis step to estimate therelative shrinkage profile of paper. The estimator is based on trackingfrequency variations in the joint time frequency spectrum and follows thelower bound of the problem for the relevant noise levels.

Place, publisher, year, edition, pages
Göteborg: Chalmers university of technology, 2002. p. 154
Series
Doktorsavhandlingar vid Chalmers Tekniska Högskola, Ny serie, ISSN 0346-718X ; 1886
Keywords
Microwave propagation, Tomography, Polarimetry, Frequency estimation, Anisotropic media, Wood, Muscles, Paper
National Category
Natural Sciences
Identifiers
urn:nbn:se:hh:diva-2461 (URN)2082/2863 (Local ID)91-7291-204-9 (ISBN)2082/2863 (Archive number)2082/2863 (OAI)
Public defence
(English)
Note

[Paper A] Kaestner, A.P. & Bååth, L.B., Microwave polarimetry based scanning for internal defects, Submitted to IEEE Transactions on Antennas and Propagation.

Scopus-ID: 2-s2.0-0036389438

Available from: 2009-04-16 Created: 2009-04-16 Last updated: 2018-09-11Bibliographically approved

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Bååth, Lars B.

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