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FEM simulation of interactions between microwaves and wood during thawing
Luleå tekniska universitet.
2006 (English)In: 2nd Conference on Mathematical Modeling of Wave Phenomena / [ed] Nilsson B, Fishman L, New York: American Institute of Physics , 2006, 260-267 p.Chapter in book (Other academic)
Abstract [en]

Dipole polarization of water molecules is an important factor when microwaves interact with moist wood. Hence there will be a considerable change in dielectric properties when the wood changes from frozen to nonfrozen condition. The aim of this study was to develop a model that simulates measurements with a microwave scanner based on a sensor working at 9.4 GHz. Two-dimensional finite element modelling (FEM) was implemented to analyze interactions between microwaves and green wood during thawing of frozen wood at room temperature. A medical computed tomography scanner was used to measure the internal structure of density in a piece of wood in green and dry condition. From these density images the distribution of dry weight moisture content was calculated for a cross section of the piece and used in the model. Images describing the distribution of the electric field and phase shift at different temperatures where obtained from the FEM simulation. The results show that simulated values correspond well to measured values. This confirms that the model presented in this study is a useful tool to describe the interaction between microwaves and wood during microwave scanning at varying conditions.

Place, publisher, year, edition, pages
New York: American Institute of Physics , 2006. 260-267 p.
Identifiers
URN: urn:nbn:se:umu:diva-46082OAI: oai:DiVA.org:umu-46082DiVA: diva2:436945
Available from: 2011-08-25 Created: 2011-08-25 Last updated: 2011-09-08
In thesis
1. Microwave sensors for scanning of sawn timber
Open this publication in new window or tab >>Microwave sensors for scanning of sawn timber
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A microwave imaging sensor that measures the signal transmitted through a board was investigated with respect to the ability to predict the distribution of moisture and density in sawn lumber. Furthermore, the response from the sensor was related to strength properties of the boards. Multivariate statistics was used to relate the measured variables to various properties. A finite element model based on X-ray computed tomography images was developed to describe the interactions between microwaves and wood. The model made it possible to simulate the response from the sensor under varying conditions.

The results show that microwaves can be used for prediction of density and moisture content. They can also be used for prediction of strength properties, mainly from the correlation to density, but also from the influence on microwaves of structural variations in the wood. The finite element model is useful in the evaluation of microwave sensors for wood, drying equipment or other applications where electromagnetic waves interact with wood.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2007. 40 p.
Series
Doctoral thesis / Luleå University of Technology, 2007:9
Keyword
microwave scanning; wood; density; moisture content; strength grading; finite element
National Category
Control Engineering
Identifiers
urn:nbn:se:umu:diva-46102 (URN)1402-1544 (ISBN)
Public defence
2007-04-18, Hörsal A, Forskargatan 1, Skellefteå, 10:00 (English)
Opponent
Supervisors
Available from: 2011-08-29 Created: 2011-08-26 Last updated: 2011-08-29Bibliographically approved

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Citation style
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