Single-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection

Defects and cracks in dried natural timber (relative permittivity 2–5) may cause structural weakness and enhanced warping in structural beams. For a pine wood beam (1200 mm × 70 mm × 70 mm), microwave reflection (S<sub>11</sub>) and transmission (S<sub>21</sub>) measurements...

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Autores principales:	Mohamed Radwan, David V. Thiel, Hugo G. Espinosa
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	non-destructive testing near-field cavity-backed slot antenna microwaves Plant ecology QK900-989
Acceso en línea:	https://doaj.org/article/e5bde2e9f1bb46ff8e54f2481ccdd2ff
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spelling	oai:doaj.org-article:e5bde2e9f1bb46ff8e54f2481ccdd2ff2021-11-25T17:37:48ZSingle-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection10.3390/f121114861999-4907https://doaj.org/article/e5bde2e9f1bb46ff8e54f2481ccdd2ff2021-10-01T00:00:00Zhttps://www.mdpi.com/1999-4907/12/11/1486https://doaj.org/toc/1999-4907Defects and cracks in dried natural timber (relative permittivity 2–5) may cause structural weakness and enhanced warping in structural beams. For a pine wood beam (1200 mm × 70 mm × 70 mm), microwave reflection (S<sub>11</sub>) and transmission (S<sub>21</sub>) measurements using a cavity-backed slot antenna on the wood surface showed the variations caused by imperfections and defects in the wood. Reflection measurements at 4.4 GHz increased (>5 dB) above a major knot evident on the wood surface when the E-field was parallel to the wood grain. Similar results were observed for air cavities, independent of depth from the wood surface. The presence of a metal bolt in an air hole increased S<sub>11</sub> by 2 dB. In comparison, transmission measurements (S<sub>21</sub>) were increased by 6 dB for a metal screw centered in the cavity. A kiln-dried pine wood sample was saturated with water to increase its moisture content from 17% to 138%. Both parallel and perpendicular E-field measurements showed a difference of more than 15 dB above an open saw-cut slot in the water-saturated beam. The insertion of a brass plate in the open slot created a 7 dB rise in the S<sub>11</sub> measurement (<i>p</i> < 0.0003), while there was no significant variation for perpendicular orientation. By measuring the reflection coefficient, it was possible to detect the location of a crack through a change in its magnitude without a noticeable change (<0.01 GHz) in resonant frequency. These microwave measurements offer a simple, single-frequency non-destructive testing method of structural timber in situ, when one or more plane faces are accessible for direct antenna contact.Mohamed RadwanDavid V. ThielHugo G. EspinosaMDPI AGarticlenon-destructive testingnear-fieldcavity-backed slot antennamicrowavesPlant ecologyQK900-989ENForests, Vol 12, Iss 1486, p 1486 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	non-destructive testing near-field cavity-backed slot antenna microwaves Plant ecology QK900-989
spellingShingle	non-destructive testing near-field cavity-backed slot antenna microwaves Plant ecology QK900-989 Mohamed Radwan David V. Thiel Hugo G. Espinosa Single-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection
description	Defects and cracks in dried natural timber (relative permittivity 2–5) may cause structural weakness and enhanced warping in structural beams. For a pine wood beam (1200 mm × 70 mm × 70 mm), microwave reflection (S<sub>11</sub>) and transmission (S<sub>21</sub>) measurements using a cavity-backed slot antenna on the wood surface showed the variations caused by imperfections and defects in the wood. Reflection measurements at 4.4 GHz increased (>5 dB) above a major knot evident on the wood surface when the E-field was parallel to the wood grain. Similar results were observed for air cavities, independent of depth from the wood surface. The presence of a metal bolt in an air hole increased S<sub>11</sub> by 2 dB. In comparison, transmission measurements (S<sub>21</sub>) were increased by 6 dB for a metal screw centered in the cavity. A kiln-dried pine wood sample was saturated with water to increase its moisture content from 17% to 138%. Both parallel and perpendicular E-field measurements showed a difference of more than 15 dB above an open saw-cut slot in the water-saturated beam. The insertion of a brass plate in the open slot created a 7 dB rise in the S<sub>11</sub> measurement (<i>p</i> < 0.0003), while there was no significant variation for perpendicular orientation. By measuring the reflection coefficient, it was possible to detect the location of a crack through a change in its magnitude without a noticeable change (<0.01 GHz) in resonant frequency. These microwave measurements offer a simple, single-frequency non-destructive testing method of structural timber in situ, when one or more plane faces are accessible for direct antenna contact.
format	article
author	Mohamed Radwan David V. Thiel Hugo G. Espinosa
author_facet	Mohamed Radwan David V. Thiel Hugo G. Espinosa
author_sort	Mohamed Radwan
title	Single-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection
title_short	Single-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection
title_full	Single-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection
title_fullStr	Single-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection
title_full_unstemmed	Single-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection
title_sort	single-sided microwave near-field scanning of pine wood lumber for defect detection
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/e5bde2e9f1bb46ff8e54f2481ccdd2ff
work_keys_str_mv	AT mohamedradwan singlesidedmicrowavenearfieldscanningofpinewoodlumberfordefectdetection AT davidvthiel singlesidedmicrowavenearfieldscanningofpinewoodlumberfordefectdetection AT hugogespinosa singlesidedmicrowavenearfieldscanningofpinewoodlumberfordefectdetection
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Single-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection

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