Gibson, Adam, Kathryn E. Piquette, Uwe Bergmann, William Christens-Barry, Graham Davis, Marco Endrizzi, Shuting Fan et al. "An assessment of multimodal imaging of subsurface text in mummy cartonnage using surrogate papyrus phantoms." Heritage Science 6, no. 1 (2018): 7.
Thursday, 22 March 2018
THz Tomography and image processing: a new tool for polymer and ceramic additive manufacturing quality control
Perraud, J. B., A. F. Obaton, B. Recur, H. Balacey, F. Darracq, J. P. Guillet, and P. Mounaix. "THz Tomography and image processing: a new tool for polymer and ceramic additive manufacturing quality control."
Additive manufacturing (AM) is an essential tool to make 3D objects having very complex shapes and geometries, unachievable with standard manufacturing approaches. Meanwhile, quality controls of such objects become challenging for both industrials and applications in laboratories due to both their complexity and the materials they are made of. Consequently, we demonstrate that terahertz (THz) imaging and THz tomography can be considered as efficient methods for such object inspection in routine applications. Thus, this paper proposes an experimental study of 3D polymer objects obtained by AM techniques. This approach allows us to characterize defects and to control dimensions by volumetric measurements on 3D data reconstructed by tomography.
Molecular Characterization and Theoretical Calculation of Plant Growth Regulators Based on Terahertz Time-Domain Spectroscopy
Qu, Fangfang, Lei Lin, Chengyong Cai, Tao Dong, Yong He, and Pengcheng Nie. "Molecular Characterization and Theoretical Calculation of Plant Growth Regulators Based on Terahertz Time-Domain Spectroscopy." Applied Sciences 8, no. 3 (2018): 420.
Terahertz (THz), as an advanced spectral technology, has unique absorption characteristics for most biological macromolecules. In this work, the theoretical fundamentals for the application of THz time-domain spectroscopy (THz-TDS) to molecular characterization and fingerprint peak detection of three plant growth regulators (PGRs), including 2,4-Dichlorophenoxyacetic acid (2,4-D), forchlorfenuron (CPPU) and indole-3-acetic acid (IAA) were researched. Meanwhile, the effects of eight types of window functions on THz spectra were studied when converting time-domain spectra into frequency-domain spectra by Fourier transform. Based on the optimal window function, the THz absorption coefficient and refractive index of PGRs in frequencies of 0.2–3 THz were extracted. The molecule structure and vibration mode of three PGR samples were simulated by using density functional theory (DFT). The results showed that the three PGRs had different fingerprint peaks. Characteristic absorption and anomalous dispersion of 2,4-D were found at 1.35, 1.57 and 2.67 THz, those of CPPU were found at 1.77 and 2.44 THz, and the absorption peak of IAA was located at 2.5 THz. The absorption peaks obtained from THz spectra were identified according to the theoretical calculation results of DFT. These fingerprint peaks in THz spectra were generated by the interior stretching vibration and external deformation vibration of molecular groups. The experimental results revealed the feasibility of identifying PGRs species and detecting residues using THz-TDS.
for full paper see http://www.mdpi.com/2076-3417/8/3/420/htm
Sun, Jingye, and Stepan Lucyszyn. "Extracting Complex Dielectric Properties From Reflection-Transmission Mode Spectroscopy." IEEE Access 6 (2018): 8302-8321.
Material characterization of homogeneous dielectric slabs using reflection–transmission mode spectroscopy can be problematic due to the ambiguity from a phasor term. A comprehensive analytical review of methods for calculating the normalized power spectra, to extract the effective complex dielectric properties of a sample, is undertaken. Three generic power response models (zero-order, power propagation, and electric-field propagation) are derived; these models act as a consolidated mathematical framework for the whole paper. With our unified engineering approach, the voltage-wave propagation, transmission line, and telegrapher’s equation transmission line models are then independently derived; the first two giving the same mathematical solutions, whereas the third generates the same numerical results, as the exact electric-field propagation model. Mathematically traceable simulation results from the various models are compared and contrasted using an arbitrarily chosen data set (window glass) from 1 to 100 THz. We show how to extract the approximate effective complex dielectric properties using time-gated time-domain spectroscopy and also the exact values with our theoretical graphical techniques from the first-order reflectance and transmittance. Our approach is then taken further by considering all the Fabry–Pérot reflections with the frequency- and space-domain spectroscopy. With the scalar reflection–transmission mode infrared spectroscopy, we model the threshold conditions between the solution space that gives the single (exact) solution for the complex refractive index and the solution space that gives multiple mathematical solutions. By knowing threshold conditions, it is possible to gain a much deeper insight, in terms of the sample constraints and metrology techniques that can be adopted, to determine the single solution. Finally, we propose a simple additional measurement/simulation step to resolve the ambiguity within the multiple solution space. Here, sample thickness is arbitrary and no initial guesses are required. In theory, the result from this paper allows for the exact extraction of complex dielectric properties using simpler and lower cost scalar reflection–transmission mode spectroscopy.
for full paper see http://ieeexplore.ieee.org/abstract/document/8268097/
Truong, Bao CQ, Anthony J. Fitzgerald, Shuting Fan, and Vincent P. Wallace. "Concentration analysis of breast tissue phantoms with terahertz spectroscopy." Biomedical optics express 9, no. 3 (2018): 1334-1349.
for full paper see https://www.osapublishing.org/DirectPDFAccess/05AFAAF3-AAC5-9BF4-273918F849D54E5A_382131/boe-9-3-1334.pdf?da=1&id=382131&seq=0&mobile=no