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-THz spectroscopy application for analyzes of internal structure damage due to moisture influence

Magdalena Mieloszyk,  Katarzyna Majewska,  Wieslaw Ostachowicz

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10972/109720Z/THz-spectroscopy-application-for-analyzes-of-internal-structure-damage-due/10.1117/12.2513265.short?SSO=1

Glass composite structures are recently very popular in many branches of industry, such as marine (e.g. ship hull), civil engineering (e.g. composite bridge deck) or energy (e.g. wind turbine blades). Due to high safety requirements related to the objects structural health monitoring systems based on fiber optics techniques are recently widely applied. One of problems that can influence on material durability is moisture introduced into element structure during its manufacturing or exploitation processes. Moisture changes material characteristics, affect element durability and can be a damage origin especially during exposure on negative temperature influence. One of the non-destructive techniques that can be applied for evaluation of internal structure of non- conductive materials (like glass fiber reinforced polymers) is THz spectroscopy. This method can be used for identification of material structural disintegrations that results in changes of absorption coefficient, refractive index or scattering of THz waves propagating throughout analyzed material. The paper presents an application of THz spectroscopy for inspection of glass composite samples internal structure. The method was used for evaluation of internal material structure as well as detection, localization and determination of size of internal damage due to influence of moisture and exposure on negative temperature. During analysis the limitations of proposed method will be determined.

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Abstract-Effect of Moisture Content and Particle Size on Extinction Coefficients of Soils Using Terahertz Time-Domain Spectroscopy

 Gi-Jun Lee,  Seungchul Kim,   Tae-Hyuk Kwon,

http://ieeexplore.ieee.org/document/8002624/

Use of ultrafast terahertz (THz) laser spectroscopy as a nondestructive way to characterize the physicochemical properties of natural soils is still immature because how and to what extent the soil type, particle size, porosity, and moisture contents affect the THz spectroscopic responses of natural soils remains poorly identified. Herein, we explored the effect of moisture content and particle size on extinction coefficients of soils at a frequency range of 0.2–2 THz using ultrafast THz time-domain spectroscopy (THz-TDS) for three representative natural soils at different moisture contents. In the absence of water, the porosity and particle size distribution were found to mainly affect the THz transmission and scattering. Particularly, the Mie scattering appeared to have a pronounced effect on extinction coefficients of sand. In the presence of water, the moisture content played the governing role in absorption over the other factors. It was found that the effective medium modeling using Lambert–Beer model well predicted the extinction coefficients of silt and clay for a frequency range of 0.1–1 THz. Whereas, the experimentally determined extinction coefficients of sand were significantly greater than our model over the tested frequency range, owing to severe Mie scattering. These results provide complied test data that support the feasibility of using THz-TDS to remotely identify the physical characteristics of soils.

Abstract-Moisture detection in composites by terahertz spectroscopy

Paweł Malinowski1, Norbert Pałka2, Szymon Opoka1, Tomasz Wandowski1 and Wiesław Ostachowicz1,3

http://iopscience.iop.org/1742-6596/628/1/012100

The application of Glass Fibre Reinforced Polymers (GFRP) in many branches of industry has been increasing steadily. Many research works focus on damage identification for structures made out of such materials. However, not only delaminations, cracks or other damage can have a negative influence of GFRP parts performance. Previous research proved that fluid absorption influences the mechanical performance of composites. GFRP parts can be contaminated by moisture or release agent during manufacturing, while fuel, hydraulic fluid and moisture ingression into the composite can be the in-service treats. In the reported research authors focus on moisture detection. There are numerous sources of moisture such as post manufacturing NDT inspection with ultrasonics coupled by water or exposition to moisture during transportation and in service. An NDT tool used for the research is a terahertz (THz) spectrometer. The device uses an electromagnetic radiation in the terahertz range (0.1-3 THz) and allows for reflection and transmission measurements. The spectrometer is equipped with moving table that allows for XY scanning of large objects such as GFRP panels. In the conducted research refractive indices were experimentally extracted from the materials of interest (water and GFRP). Time signals as well as C-scans were analysed for samples with moisture contamination. In order to be sure that the observed effects are related to moisture contamination reference measurements were conducted. The obtained results showed that the THz NDT technique can detect moisture hidden under a GFRP with multiple layers.