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Cited by 27Terahertz technology and applicationsWood Treatment and PropertiesMicrowave and Dielectric Measurement Techniques

Simultaneous detection of density, moisture content and fiber direction of wood by THz time-domain spectroscopy

Open access
Kashima, Moe, Tsuchikawa, Satoru, Inagaki, Tetsuya·2020·Journal of Wood Science
DOI 10.1186/s10086-020-01874-3
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Abstract

In the wood product-manufacturing process, the physical properties of wood must be monitored. The terahertz (THz) radiation has a high potential for sensing and imaging wood with a good spatial resolution. This study demonstrates the simultaneous prediction of the density, moisture content, and fiber direction of wood, which are important in determining the wood quality, using THz time-domain spectroscopy. We measured the spectra of 12 kinds of wood at various moisture contents while rotating the sample against the THz wave polarization. The fiber direction was predicted by observing the birefringence, which is the optical property of a material, in which the refractive index depends on the polarization direction. The density and the moisture content were predicted by multiple linear regression using the refractive indices and absorption coefficients obtained from the THz measurement. In a series of THz measurements, we successfully identified the wood fiber direction with an R2 of 0.90 and a root mean square error (RMSE) of 16.51° (total measured range = 0–170°), the density with an R2 of 0.97 and an RMSE of 0.022 (total measured range = 0.25–0.67 g/cm 3), and the moisture content with an R2 of 0.78 and an RMSE of 4.06 (total measured range = 0.00–30.98%).

AI snapshot

Written from the paper’s full text.

TL;DR

This study used terahertz time-domain spectroscopy to simultaneously predict wood fiber direction, density, and moisture content across 12 wood species and varying moisture contents. It reports strong predictions for density and fiber direction and moderate prediction for moisture content.

Key findings

  • Fiber direction was predicted with an R² of 0.90 and RMSE of 16.51° over a measured range of 0–170°.
  • Density was predicted with an R² of 0.97 and RMSE of 0.022 g/cm³ over a measured range of 0.25–0.67 g/cm³.
  • Moisture content was predicted with an R² of 0.78 and RMSE of 4.06% over a measured range of 0.00–30.98%.
  • For each species, refractive index and absorption coefficient correlated strongly with density and moisture content; determination coefficients ranged from 0.80–0.998 for n vs. density, 0.65–0.97 for n vs. MC, 0.73–0.99 for α vs. density, and 0.59–0.98 for α vs. MC.

Methods

  • Twelve wood species were cut from radial and tangential planes, roughly 3 mm thick and 20 × 20 mm²; samples were oven-dried for 48 h at 103 °C and then conditioned at RH = 65, 85, 95, and 100% to vary moisture content.
  • THz-TDS transmission measurements used a Tera Prospector-Kit with bandwidth approximately 0.01–4.00 THz and a beam spot diameter of about 5 mm; samples were rotated from 0° to 180° in 10° increments relative to THz polarization.
  • Refractive index and absorption coefficient were averaged over 0.30–0.35 THz; fiber direction was estimated by fitting refractive index values at four orientation angles to Eq. (5), and density and moisture content were predicted by multiple linear regression using n∥, n⊥, α∥, and α⊥. The best interval angle was β = 50°.

Limitations

  • Stated: Eq. (5) does not take into account extinction of the THz wave; prediction accuracy was not better than other wavelength ranges; low THz transmission intensity at high moisture content reduced the correlation coefficient and directly affected the absorption coefficient, giving the worst prediction for moisture content; predicted angles were overestimated at low RH.
  • Stated: all samples were mature wood, so microfibril angles were expected to be close to 0°, and the main origin of measured birefringence was expected to be form birefringence.
  • Evident from the text: the study used 12 species and measurements below the fiber saturation point, and the text does not describe a separate validation set; predictions appear based on the same measurements used for model fitting.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1186/s10086-020-01874-3

Cites

26 of 26 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

5 of 23 cited sources checked · 5 supported · 0 flagged

  • Premisecitation

    The complex refractive index of a sample can be obtained by analyzing the amplitude and phase of a THz pulse after Fourier transform.

    “The complex refractive index of the sample can be obtained by analyzing the amplitude and phase [9].”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [9] Reid M, Fedosejevs R (2006) Terahertz birefringence and attenuation properties of wood and paper. Appl Opt 45:2766–2772 source
  • Findingown data

    Wood moisture content was predicted with an R2 of 0.78 and an RMSE of 4.06% over a measured range of 0.00-30.98%.

    “the moisture content with an R 2 of 0.78 and an RMSE of 4.06 (total measured range = 0.00-30.98%).”
    • Also stated in: § Results and discussion · plain
      “It exhibited good prediction, with determination coefficient values of R 2 = 0.97 and 0.78 and RMSE values of 0.022 g/ cm 3 and 4.06% for density and MC, respectively.”
    Quote in the paperSubstantial claim
  • Findingown data

    The wood fiber direction was identified with an R2 of 0.90 and an RMSE of 16.51° over a measured range of 0-170°.

    “we successfully identified the wood fiber direction with an R 2 of 0.90 and a root mean square error (RMSE) of 16.51° (total measured range = 0-170°)”
    • Also stated in: § Results and discussion · plain
      “The relationship between the measured and predicted angles θ for all species at all the MC was good with a determination coefficient value of R 2 = 0.90 and a root mean square error (RMSE) value of 16.51° (Table 2).”
    Quote in the paperSubstantial claim
  • Findingown data

    Wood density was predicted with an R2 of 0.97 and an RMSE of 0.022 g/cm3 over a measured range of 0.25-0.67 g/cm3.

    “the density with an R 2 of 0.97 and an RMSE of 0.022 (total measured range = 0.25-0.67g/cm 3 )”
    • Also stated in: § Results and discussion · plain
      “It exhibited good prediction, with determination coefficient values of R 2 = 0.97 and 0.78 and RMSE values of 0.022 g/ cm 3 and 4.06% for density and MC, respectively.”
    Quote in the paperSubstantial claim
  • Findingown data

    Measuring under four differing rotation angles of the sample enables determination of fiber direction with an R2 of 0.90 and an RMSE of 16.51°.

    “Measuring under four differing rotation angles of the sample enables us to determine the fiber direction with an R 2 of 0.90 and an RMSE of 16.51°.”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim. 18
  • May combine two claims. 22

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    THz-TDS has already been shown to be a suitable tool for investigating wood, including wood identification, imaging defects in building blocks, and dendrochronology.

    “In fact, it has already been shown as a suitable tool for investigating wood (e.g., wood identification [10], imaging of defects in building blocks [11], and dendrochronology [12]).”
    Quote in the paperNot a substantial claim2 of 3 sources checked
    • cites [10] Wang Y, She S, Zhou N, Zhang J, Yan H, Li W (2019) Wood species identification using terahertz time-domain spectroscopy. BioResources 14:1033–1048 source
    • cites [11] Oyama Y, Zhen L, Tanabe T, Kagaya M (2009) Sub-terahertz imaging of defects in building blocks. Ndt E Int 42:28–33 source
    • cites [12] Jackson JB, Mourou M, Labaune J, Whitaker JF, Duling IN, Williamson SL, Lavier C, Menu M, Mourou GA (2009) Terahertz pulse imaging for tree-ring analysis: a preliminary study for dendrochronology applications. Meas Sci Technol 20:075502 source

  • May combine two claims.

    Premisecitation

    Solid wood exhibits both strong birefringence and diattenuation in THz regions.

    “Reid et al. [9] found that solid wood is shown to exhibit both strong birefringence and diattenuation in THz regions.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [9] Reid M, Fedosejevs R (2006) Terahertz birefringence and attenuation properties of wood and paper. Appl Opt 45:2766–2772 source

  • Classified as probably not a substantial claim.

    Interpretationcitation

    Wood fiber direction can be determined by observing the change of refractive index as a function of the angle between THz polarization and wood grain angle.

    “It is expected that one can determine the wood fiber direction by observing the change of index refraction value as a function of angle between THz polarization and wood grain angle as Reid et al. [9] predicted the fiber direction of lens paper.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [9] Reid M, Fedosejevs R (2006) Terahertz birefringence and attenuation properties of wood and paper. Appl Opt 45:2766–2772 source

  • May combine two claims.

    Findingown data

    For each species, both the refractive index and the absorption coefficient had strong correlations with both density and moisture content.

    “For each species, both the refractive index and the absorption coefficient had strong correlations with both the density and the MC.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning

    The intercept value of the regression between reference and predicted fiber angle tends to be high at low relative humidity, meaning predicted values are overestimated at low relative humidity.

    “The intercept value tends to be high at low RH (i.e., the predicted values are overestimated at low RH).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The range of determination coefficients between n and density, n and MC, α and density, and α and MC for each species was 0.80-0.998, 0.65-0.97, 0.73-0.99, and 0.59-0.98, respectively.

    “The range of determination coefficients between n and density, n and MC, α and density, and α and MC for each species was 0.80-0.998,0.65-0.97,0.73-0.99,and 0.59-0.98,respectively.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The THz field polarized perpendicular to the visible grain arrived first, while that polarized parallel arrived last.

    “The THz field polarized perpendicular (⊥) with respect to the visible grain arrived first, while that polarized parallel (ǁ) arrived last.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisereasoning

    THz measurements have sub-millimeter spatial resolution, whereas microwave measurements have spatial resolution on the order of several centimeters.

    “First, the spatial resolution is in sub-millimeter, while the microwave, which has a longer wavelength, is in the order of several centimeters.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Bound water strongly affects the properties of wood below the fiber saturation point, so moisture content must be controlled and monitored.

    “Bound water strongly affects the properties of wood below the FSP; hence, the MC must be controlled and monitored [7].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [7] Hartley ID, Kamke FA, Peemoeller H (1992) Cluster theory for water sorption in wood. Wood Sci Technol 26:83–99 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Higher-density wood generally has higher modulus of elasticity and strength.

    “A higher-density wood generally has higher MOE and strength [2].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [2] Shmulsky R, Jones PD (2011) Forest products and wood science; an introduction, 6th edn. Wiley-Blackwell, Hoboken source

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    Wood quality is evaluated by density, moisture content, and fiber direction, which greatly influence wood properties.

    “The wood quality is evaluated by various factors, including density, moisture content (MC), and fiber direction, which greatly influence the wood properties [1].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [1] Beall FC (2000) Subsurface sensing of properties and defects in wood and wood products. Subsurf Sens Technol Appl 1:181–204 source

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

    Premisenone given

    THz radiation is non-ionizing and poses no significant health concerns, unlike X-rays.

    “Third, the THz radiation is non-ionizing, and poses no significant health concerns, unlike X-rays.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    The large birefringence observed in wood may be due to either intrinsic or form birefringence, with contributions from both types varying by species.

    “Todoruk et al. [18] concluded that the large birefringence observed may be due to either intrinsic or form birefringence, although the source of birefringence varies according to species, the trend shows contributions from both types of birefringence.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [18] Todoruk TM, Hartley ID, Reid ME (2012) Origin of birefringence in wood at terahertz frequencies. IEEE Trans Terahertz Sci Technol 2:123–130 source

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Interpretationreasoning

    Because refractive index is determined by the physical properties of a material, physical properties can be predicted by examining the relationship between refractive index and physical property values.

    “The refractive index is determined by the physical properties of the material; therefore, the physical properties can be predicted by examining the relationship between the refractive index and the physical property values.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisereasoning

    THz waves are relatively transparent to wood because their longer wavelength causes less scattering and allows penetration into the material.

    “Second, it is relatively transparent to wood.THz waves have a longer wavelength than visible and infrared rays; thus, the THz wave scattering is less, and it penetrates into the material.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisereasoning

    THz-TDS can obtain complex refractive index values, whereas visible, near infrared, infrared, or X-ray spectroscopy can obtain only absorbance information.

    “Fourth, the complex refractive index values can be obtained by THz-TDS although only the absorbance information can be obtained for visible, near infrared (NIR), infrared (IR) or X-ray spectroscopy because of high frequency.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Reference THz measurements without the sample were taken before and after each THz measurement set, and the average values were used for analysis.

    “The reference measurements without the sample were taken before and after each THz measurement set and the average values were used for analysis.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    Inagaki et al. successfully performed simultaneous prediction of density and moisture content.

    “Inagaki et al. [17] successfully performed a simultaneous prediction of density and MC.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [17] Inagaki T, Ahmed B, Hartley ID, Tsuchikawa S, Reid M (2014) Simultaneous prediction of density and moisture content of wood by terahertz time domain spectroscopy. J Infrared Millim Terahertz Waves 35:949–961 source

  • May combine two claims.

    Interpretationown data

    The prediction was bad with three different direction angles because the variations in refractive index and absorption coefficient acquired in this study were significantly bigger than in the prior result due to large variations of moisture content and density.

    “The reason why the prediction was bad when using three different direction angles is that the variations in the refractive index and absorption coefficient acquired in this study were significantly bigger compared to their result due to big variations of MC and density.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [19] Jordens C, Scheller M, Wietzke S, Romeike D, Jansen CP, Zentgraf T, Wiesauer K, Reisecker V, Koch M (2010) Terahertz spectroscopy to study the orientation of glass fibres in reinforced plastics. Compos Sci Technol 70:472–477 source

  • Classified as probably not a substantial claim.

    Premisecitation

    Inagaki et al. reported the use of effective medium theory for the prediction of density and moisture content from the complex permittivity values of wood in THz regions.

    “Inagaki et al. [17] reported the use of effective medium theory for the prediction of density and MC from the complex permittivity values of wood in THz regions.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [17] Inagaki T, Ahmed B, Hartley ID, Tsuchikawa S, Reid M (2014) Simultaneous prediction of density and moisture content of wood by terahertz time domain spectroscopy. J Infrared Millim Terahertz Waves 35:949–961 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Inagaki et al. extracted the volume fraction of each component from measured permittivity of wood after deciding the permittivity of each component in advance.

    “They extracted the volume fraction of each component from measured permittivity of wood after they decided the permittivity of each of the components in advance.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [17] Inagaki T, Ahmed B, Hartley ID, Tsuchikawa S, Reid M (2014) Simultaneous prediction of density and moisture content of wood by terahertz time domain spectroscopy. J Infrared Millim Terahertz Waves 35:949–961 source

  • Classified as probably not a substantial claim.

    Premisecitation

    Todoruk showed that birefringence increases with moisture content of wood.

    “Todoruk [18] shows the birefringence increase with MC of wood.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [18] Todoruk TM, Hartley ID, Reid ME (2012) Origin of birefringence in wood at terahertz frequencies. IEEE Trans Terahertz Sci Technol 2:123–130 source

  • May combine two claims.

    Study design and conductown data

    Four different direction angles were employed to predict fiber direction because prediction of fiber orientation, moisture content, and density was not stable with only three different direction angles.

    “However, we employed four different direction angles to predict the fiber direction of the wood samples, because the prediction of fiber orientation and MC and density was not stable when we employed only three different direction angles for the fitting like Jorderns et al.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [19] Jordens C, Scheller M, Wietzke S, Romeike D, Jansen CP, Zentgraf T, Wiesauer K, Reisecker V, Koch M (2010) Terahertz spectroscopy to study the orientation of glass fibres in reinforced plastics. Compos Sci Technol 70:472–477 source

  • May combine two claims.

    Study design and conductown data

    The frequency range 0.30-0.35 THz was used because THz intensity is high in this range, calculated refractive index values are identical with frequency, and water vapor absorption is minimized.

    “We used the frequency range of 0.30-0.35THz because (1) THz intensity acquired with the measurement system is high in this range; (2) calculated index refraction values in this range were identical with frequency; (3) in order to minimize the effect of absorption of water vapor found at 0.56, 0.75 and 0.99 THz.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Density prediction was good even at high relative humidity because the effect of low THz intensity, i.e., signal-to-noise ratio, on the real part of refractive index, which is strongly related to wood density, is not significant.

    “The density prediction was good even in the high RH because the effect of low intensity of THz wave (i.e., signal-to-noise ratio) on the real part of refractive index value, which is strongly related to the density of wood, is not the significant.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisenone given

    Wood is a composite material of air, cell wall material, and water.

    “Wood is a composite material of air, cell wall material, and water.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Wood is a composite material of air, cell wall material, and water.

  • May combine two claims.

    Interpretationnone given

    Considering all wood species, both the amount of water and the volume fraction of the cell wall material were different for each species.

    “However, considering all wood species, both the amount of water and the volume fraction of the cell wall material were different for each species.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The three parameters, fiber direction, density, and moisture content, can also be simultaneously determined at microwave frequencies.

    “The three parameters (i.e., fiber direction, density, and MC) can also be simultaneously determined at microwave frequencies.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [19] Jordens C, Scheller M, Wietzke S, Romeike D, Jansen CP, Zentgraf T, Wiesauer K, Reisecker V, Koch M (2010) Terahertz spectroscopy to study the orientation of glass fibres in reinforced plastics. Compos Sci Technol 70:472–477 source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Schajer and Orhan successfully predicted grain angles for hemlock and Douglas fir with standard errors of 0.9° and 2.5°, moisture content of 1.2 and 1.9%, and dry density of 0.16 and 0.30 g/cm3.

    “Schajer and Orhan [19] successfully predicted the grain angles for hemlock and Douglas fir with standard errors of 0.9° and 2.5° (measured range from -90 to + 90°), MC of 1.2 and 1.9% (measured range from 7 to 28%), and dry density of 0.16 and 0.30 g/cm 3 (measured range from 0.325 to 0.625 g/cm 3 ) [20].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [19] Jordens C, Scheller M, Wietzke S, Romeike D, Jansen CP, Zentgraf T, Wiesauer K, Reisecker V, Koch M (2010) Terahertz spectroscopy to study the orientation of glass fibres in reinforced plastics. Compos Sci Technol 70:472–477 source
    • cites [20] Schajer GS, Orhan FB (2006) Measurement of wood grain angle, moisture content and density using microwaves. Holz Als Roh-Und Werkst 64:483–490 source

  • May combine two claims.

    Interpretationreasoning

    Not only the birefringence value but also properties such as the axial direction of birefringence would change with moisture content, resulting in overestimation of angle at lower relative humidity values.

    “We consider that not only the birefringence value, but also properties like axial direction of birefringence would change with MC result overestimation of angle at lower RH values.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Premisenone given

    In actual wood product factory measurement, wood samples have a wide range of complex refractive index values that change with density and moisture content.

    “In the actual measurement in wood product factory, wood samples have wide range of complex refractive index values changing with the density and the MC of wood.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationnone given

    Although prediction accuracy was not better than other wavelength ranges, the THz region has an advantage in spatial resolution compared to the microwave region and in transparency compared to the NIR region.

    “Although the prediction accuracy was not better than the other wavelength ranges, the THz region has an advantage for the spatial resolution compared to the microwave region and transparency compared to the NIR regions.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductown data

    Although Eq. (5) does not take into account the effect of extinction of THz wave, the procedure to estimate n∥, n⊥, α⊥, α∥, and θ from n and THz transmission intensity at four direction angles was employed because the estimated values were almost the same as the actually measured values.

    “Although it should be pointed out that Eq. ( 5) does not take into account the effect of extinction of THz wave, we employed the procedure to estimate n , n ⊥ , α ⊥ , α and θ from n and THz transmission intensity meas- ured at four difference direction angles, because the estimated n , n ⊥ , α ⊥ , α were almost the same as the actually measured values.”
    Quote in the paperSubstantial claim
33 of 33

  • The paper relies on this without support.

    Wood is an anisotropic material with independent mechanical properties in the longitudinal, radial, and tangential directions.

    “Wood is an anisotropic material, with independent mechanical properties in the three directions: longitudinal, radial, and tangential.”

  • The paper relies on this without support.

    The difference in Young's modulus depending on wood direction is roughly longitudinal:radial:tangential = 10:1-2:0.5.

    “The difference in the Young's modulus depending on the wood direction is roughly in the L direction:R direction:T direction = 10:1-2:0.5.”

  • The paper relies on this without support.

    All samples in this study were matured wood, so their microfibril angles are close to 0°.

    “All the samples in this study were matured wood; hence, their microfibril angles are expected to be close to 0°”

  • The paper relies on this without support.

    The volume fraction of the cell wall in the same species is identical.

    “The volume fraction of the cell wall in the same species is thought to be identical”

  • The paper relies on this without support.

    Wood is a composite material of air, cell wall material, and water.

    “Wood is a composite material of air, cell wall material, and water.”
5 of 5

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Reference [19] is attributed to two different studies

    Minor

    The text cites [19] for a result by Jordens et al. and later for a result by Schajer and Orhan. The reference list identifies entry 19 as Schajer and Orhan.

1 of 1

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Authors
Kashima, M., Tsuchikawa, S., & Inagaki, T.
Affiliations
Nagoya University (JP)
Corresponding author
Inagaki, Tetsuya
ORCID
Venue
Journal of Wood Science
Publisher
Springer Science and Business Media LLC
Published
2020-04-10
Volume
66
Issue
1
ISSN
  • 1435-0211 (ISSN-L)
  • 1611-4663
DOI
10.1186/s10086-020-01874-3
OpenAlex
W3030869551
Cited by
27
References
24
Citations by year
2026: 3 · 2025: 9 · 2024: 6 · 2023: 4 · 2022: 2 · 2021: 3
FWCI
0.76
Type
journal article
Language
en
Open access
Licence
Locations
  • Journal of Wood Science (publishedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
Japan Society for the Promotion of Science (16H02559)
Topics
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Terahertz technology and applications
  • Physical Sciences › Engineering › Building and Construction › Wood Treatment and Properties
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Microwave and Dielectric Measurement Techniques
Keywords
wood, terahertz time-domain spectroscopy, wood density, moisture content, fiber orientation, birefringence, refractive index, absorption coefficient, polarization rotation

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