Abstract-Terahertz Differential Computed Tomography: a Relevant Nondestructive Inspection Application

Alexandre Duhant, Meriam Triki, Olivier Strauss

https://link.springer.com/article/10.1007/s10762-018-0564-5

In recent years, tremendous advances have been made in the choice of materials used in the industry. With weight reduction as the goal, composite and polymer materials are more and more popular but they are almost transparent to X-ray. Because of this, interest has grown in other wavelengths like terahertz (THz). Due to a difference in how X-ray and THz propagate, X-ray CT algorithms cannot be directly used. For example, THz induces refraction making the reconstruction problem nonlinear. In this paper, we present a new algorithm which complies with beam profile intensities, refraction, and reflection. It is based on linearizing the reconstruction process around a computer-aided design (CAD) model of the object to be reconstructed. The method we propose computes the deviation between the object and this model.

Abstract-Quantitative diagnostics of ancient paper using THz time-domain spectroscopy

M. Missori, 

D. Pawcenis, 

J. Bagniuk, 

A. Mosca Conte, 

C. Violante, 

M.S. Maggio, 

M. Peccianti,

O. Pulci,  

J. Łojewska, 

https://www.sciencedirect.com/science/article/pii/S0026265X17308391

In this work we have studied the terahertz spectra of modern artificially aged and ancient paper samples using terahertz time-domain spectroscopy. Hydrothermal artificial aging was performed in closed and open reactors. Ancient paper samples were produced during the 15th century in European countries. The main aim of the work is the quantitative assessment of spectral feature observed by terahertz spectroscopy as a function of degradation. To this goal, the state of degradation of paper samples was characterized by crystallinity measurements obtained by using X-ray diffraction and by the degree of polymerization of cellulose polymers obtained by size exclusion chromatography. The behavior of the terahertz spectra was formerly investigated as a function of the hydration of paper samples. This allowed discriminating between the spectral features induced by the presence of water and those induced by degradation of paper. Results indicate clear dependences of spectral parameters from the evolution of crystallinity and the degree of polymerization. They can be used as a nondestructive analytical method to assess the state of degradation of ancient paper by terahertz spectroscopy.

Abstract-Nondestructive evaluation of GFRP composite including multi-delamination using THz spectroscopy and imaging

Dae-Hyun Han, Lae-Hyong Kang

https://www.sciencedirect.com/science/article/pii/S0263822317323103


We utilize a fiber-coupled terahertz time-domain spectroscopy system (THz-TDS) based on photoconductive antennas to visualize multi-delamination and their thickness in a glass-fiber-reinforced polymer (GFRP) composite plate. We simulate a hidden multi-delamination by inserting a Teflon film in the GFRP composite plate that is fabricated using the vacuum-assisted resin transfer molding (VARTM) process. Reflected or transmitted terahertz (THz) waves are recorded from GFRP samples mounted on the x–y linear motorized stage during the investigation. The x–y linear motorized stage is driven in steps of 0.2 mm, thereby allowing us to scan the sample. We examine and compare the performances of the THz time-domain visualization (TTV) and THz frequency-domain visualization (TFV) algorithms to evaluate their characteristics for the visualization of defects. The thickness of the GFRP sample and multi-delamination is estimated using the reflection geometry method. Finally, we confirm that the hidden multi-delamination of the GFRP sample has been successfully visualized in the B- and C-scans. In addition, the thicknesses of the GFRP sample and the simulated delamination as compared with the experimental values exhibit a close consistency.

Abstract-THz Spectroscopic Identification of Red Mineral Pigments in Ancient Chinese Artworks

Yuping Yang, Dongwei Zhai, Zhenwei Zhang, Cunlin Zhang

https://link.springer.com/article/10.1007%2Fs10762-017-0408-8

Nondestructive analysis of historical objects is of significance for cultural heritage conservation. In this paper, terahertz time-domain spectroscopy (THz-TDS) was used to distinguish seven red mineral pigments used in ancient Chinese artworks. Two absorption features of natural minerals HgS and four highly resolved spectral features of mineral pigment Pb3O4 were observed and identified as their fingerprints in the range 0.2 to 3.0 THz, based on which the spatial distribution of individual chemical substances including cinnabar, vermilion, and red lead were clearly revealed at various frequencies using terahertz spectroscopy imaging. Moreover, a noncontact evaluation of thickness changing and dehydration of a wet painting was monitored by inferring time delay as well as signal amplitude of THz pulses transmitted through the painting. In order to demonstrate the feasibility of THz-TDS and THz imaging for authentic artworks detection, a complete set of THz analysis of two nineteenth century wall paintings discovered in the Fuchen Temple of the Forbidden City, Beijing, was performed and the results indicate that THz measurement techniques provide a noninvasive and nondestructive solution for the care, preservation, and restoration of cultural relics.

Hamamatsu- Nondestructive measurement

http://www.hamamatsu.com/jp/en/technology/lifephotonics/environment/NonDestructiveInspection/index.html

Nondestructive measurement

Developing sustainable systems for the production goods requires that we change our conventional methods of mass consumption and mass disposal. Nondestructive inspection offers us ways to look inside of things without taking them apart, thus opening the possibility of reducing waste and garbage.

Terahertz camera

We envision the terahertz cameras for use not only in manufacturing facilities, but also for outdoor applications of nondestructive testing. For example, by using a terahertz cameras to inspect the inside of a building, internal damage could be discovered early and thus help extend the life of the property.

Features

Terahertz waves can penetrate soft materials such as paper or plastics, while at the same time having strong absorption to water. Therfore, they can discover areas that are prone to corrosion due to heavy moisture as well as areas that are already corroded. Terahertz waves do not penetrate metals, so it can be used to find the positions of nails and other metal parts that are covered by heat-insulating materials, ceramics, and wallpaper. This can help make building maintenance more efficient.

Measurement example

In this example, the sample is worm-eaten wood that is covered in wallpaper. In the image captured with terahertz waves, the holes in the wood under the surface of the wallpaper can be clearly observed.

Soft X-ray 3D microscope

In materials engineering, light element materials such as carbon fiber-reinforced plastics have been gaining attention as an energy-saving and eco-friendly alternative to conventional metallic materials, due to their strength and light weight. For these materials, soft X-rays of a few keV or less are an effective means of observation. By using a compact X-ray source and X-ray reflecting optical elements, Hamamatsu has developed a laboratory-scale soft X-ray 3D microscope for making 3D structural observations at sub-micron resolution.

·                                 This technology uses soft X-rays to visualize the three-dimensional structures inside an object made from light elements.

·                                 Due to the high attenuation coefficient of the light elements for soft X-rays, a high-contrast image of such samples can be obtained.

·                                 In the development of light element materials with low environmental impact, this technology can be useful for the design of such materials or for controlling their microstructure during manufacturing.

Features of the measurement example

Observation of carbon fiber-reinforced plastic

Publications

·                                 S. Ohsuka, A. Ohba, S. Onoda, K. Nakamoto, T. Nakano, M. Miyoshi, K. Soda, and T. Hamakubo, “Laboratory-size three-dimensional x-ray microscope with Wolter type I mirror optics and an electron-impact water window x-ray source”,Review of Scientific Instruments 85, 093701 (2014).

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