Abstract-Determination of Dielectric Function of Water in THz Region in Wood Cell Wall Result in an Accurate Prediction of Moisture Content

Han Wang, Tetsuya Inagaki, Ian D. Hartley,  Satoru Tsuchikawa, Matthew Reid

https://link.springer.com/article/10.1007/s10762-019-00594-0

This report follows up previous work that presented a model for the simultaneous detection of moisture content and density of wood using Terahertz time-domain spectroscopy. A significant improvement in the prediction accuracy of the model is demonstrated by including a moisture content-dependent dielectric function for the water within the wood samples. Justification for using the dielectric function is presented, the prediction accuracy is quantified, and the results compared with prior work.

Abstract-Terahertz Measurement of the Water Content Distribution in Wood Materials

M. Bensalem, A. Sommier, J. C. Mindeguia, J. C. Batsale, C. Pradere
https://link.springer.com/article/10.1007%2Fs10762-017-0441-7

Recently, THz waves have been shown to be an effective technique for investigating the water diffusion within porous media, such as biomaterial or insulation materials. This applicability is due to the sufficient resolution for such applications and the safe levels of radiation. This study aims to achieve contactless absolute water content measurements at a steady state case in semi-transparent solids (wood) using a transmittance THz wave range setup. First, a calibration method is developed to validate an analytical model based on the Beer-Lambert law, linking the absorption coefficient, the density of the solid, and its water content. Then, an estimation of the water content on a local scale in a transient-state case (drying) is performed. This study shows that THz waves are an effective contactless, safe, and low-cost technique for the measurement of water content in a porous medium, such as wood.

Why Terahertz Technology is Unique for Wood Product Industry?

http://terasense.com/news/terahertz-wood-industry/

A number of various applications like X-ray density scanning, infrared moisture sensors, visible light profilers and microwave kiln drying, employ different parts of electromagnetic spectrum to provide imaging in wood processing industry.

Terahertz part of the spectrum was not in the list until now and not because the THz are not useful to the wood industry, but due to the absence of technology in this frequency range. Every new step in the development of the terahertz technology opens the doors to many applications in  number industries including wood processing.

Why it is so interesting particularly for the wood industry? Transparency, resolution, safety and ability to probe gross fibre structure, all these 4 characteristics make the terahertz unique for the industry, as terahertz is the only part of the spectrum that can access all four characteristics. 

Comparing to X-ray, THz technology is essentially less invasive. Terahertz radiation has no ionising effect, thus absolutely harmless to people and other living beings  therefore allows usage in all public places without strict regulations obligatory for X-ray do when implemented in working environment.

In addition to this, the polarisation state of THz radiation is sensitive to fibrous structures which offers more information about the system being probed than can be obtained with X-rays.

Therefore, the THz technology offers the possibility for transmission imaging that can simultaneously probe internal structure of non-conductive dry material with sub-mm spacial resolution.

To summarise, the ability to image non-conductive dry materials in 'transmission' mode with sub-mm spatial resolution and sensitivity to fibre structure makes terahertz technology ideally suited for applications in the wood processing industry.

For non-destructive test of wood products, TeraSense offers a unique Terahertz High Speed Line Scanner which fits most of conveyors with belt running speed up to 15 m/s. Due to our original patent-protected technology the scanner is a low-cost and compact solution.

 

Have any questions? Please contact us.

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Abstract-Applicability of effective medium theory to wood density measurements using terahertz time-domain spectroscopy

• Soichi Tanaka, 
• Keiichiro Shiraga, 
• Yuichi Ogawa, 
• Yoshihisa Fujii, 
• Shogo 

• Okumura

http://link.springer.com/article/10.1007%2Fs10086-013-1386-7

The use of an effective medium theory is important when accurately measuring wood density using millimeter and terahertz wave techniques. To confirm the applicability of this theory to the evaluation of wood density, the relative permittivity and dielectric loss of oven-dry flat-sawn specimens of 11 different wood species were measured in a frequency range of 0.15–1.2 THz using a transmission measurement system for terahertz time-domain spectroscopy. A mixture model based on the effective medium theory well explained the density dependence of relative permittivity over the entire frequency range, while it did not fully explain that of dielectric loss, especially for higher frequencies. This indicates that wood scatters the terahertz wave with a wavelength close to the transverse sectional dimensions of the pores in wood in the same way as Mie scattering. It was found from the dielectric loss spectrum of wood substance that the frequency around 0.23 THz was preferable for the nondestructive evaluation of wood.