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Book ChapterDOI

Terahertz Techniques in NDE

01 Jan 2018-pp 1-20
About: The article was published on 2018-01-01. It has received 3 citations till now. The article focuses on the topics: Terahertz radiation.
Citations
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Journal ArticleDOI
TL;DR: The results showed that THz time-domain spectroscopy enables the discrimination of various inks on different supports, including the application on paper, together with the proper determination of the absorption coefficients and indices of refraction.
Abstract: Dry and wet drawing materials were investigated by THz time-domain spectroscopy in transmission mode. Carbon-based and iron-gall inks have been studied, some prepared following ancient recipes and others using current synthetic materials; a commercial ink was studied as well. We measured the THz signals on thin film of liquid inks deposited on polyethylene pellicles, comparing the results with the thick pellets of dried inks blended with polyethylene powder. This study required the implementation of a new experimental method and data analysis procedure able to provide a reliable extraction of the material transmission parameters from a structured sample composed of thin layers, down to thickness of few tens of micrometers. THz measurements on thin ink layers enabled the determination of both the absorption and the refractive index in an absolute scale in the 0.1 - 3 THz range, as well as the layer thickness. THz spectroscopic features of a paper sheet dyed by one of the iron-gall inks were also investigated. Our results showed that THz time-domain spectroscopy enables to discriminate the various inks on different supports, including the application on paper, together with a proper determination of the absorption coefficients and indices of refraction.

12 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used TPI coupled with a newly designed flow cell to quantify the rate of water ingress into α-alumina pellets with a range of different porosities.
Abstract: Investigating the liquid transport kinetics of solid catalysts is of great importance for gaining a better understanding of the manufacturing and performance of such catalysts during reaction upon contact with the liquid. Terahertz pulsed imaging (TPI) coupled with a newly designed flow cell was used to quantify the rate of water ingress into α-alumina pellets with a range of different porosities. A wide range of compaction forces (cold compaction, 7–58 kN) and sintering conditions (no firing and sintering at 1200 and 1300 °C) was investigated to explore the optimal pellet microstructure, i.e. mechanically strong but sufficiently porous for fast liquid transport kinetics. The results confirm that both the microstructure characteristics, particularly porosity, as well as the surface properties, i.e. wettability, influence the liquid transport kinetics. Fitting the TPI penetration rates with a power law shows that the type of observed mass transport characteristics is consistent with Darcy flow. The Lucas–Washburn equation was used to calculate the hydraulic radius based on the transport data. In summary, the results demonstrate that TPI has great potential to study the liquid transport kinetics of porous ceramic catalysts and catalyst supports and that can comfortably quantify transport processes at rates of 250 μm s−1 and beyond in such substrates for better quality control and optimised design and performance of such materials.

9 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the state-of-the-art technologies on photonics-based terahertz communications are compared with competing technologies based on electronics and free-space optical communications.
Abstract: This Review covers the state-of-the-art technologies on photonics-based terahertz communications, which are compared with competing technologies based on electronics and free-space optical communications. Future prospects and challenges are also discussed. Almost 15 years have passed since the initial demonstrations of terahertz (THz) wireless communications were made using both pulsed and continuous waves. THz technologies are attracting great interest and are expected to meet the ever-increasing demand for high-capacity wireless communications. Here, we review the latest trends in THz communications research, focusing on how photonics technologies have played a key role in the development of first-age THz communication systems. We also provide a comparison with other competitive technologies, such as THz transceivers enabled by electronic devices as well as free-space lightwave communications.

1,238 citations

BookDOI
01 Jan 2003
TL;DR: In this paper, the authors describe the use of photomixers for continuous-wave terahertz radiation and apply them to time domain ranging and scattering in bio-medical applications.
Abstract: Spectroscopy in the Terahertz Spectral Region.- Terahertz Imaging.- Free-Space Electro-Optic Techniques.- Photomixers for Continuous-Wave Terahertz Radiation.- Applications of Optically Generated Terahertz Pulses to Time Domain Ranging and Scattering.- Bio-medical Applications of THz Imaging.- Electronic Sources and Detectors for Wideband Sensing in the Terahertz Regime.

850 citations

Journal ArticleDOI
TL;DR: In this article, the absorption spectrum of the explosive 1, 3,5-trinitro-1,3, 5-triazacyclohexane (RDX) has been measured using a conventional Fourier transform infrared spectroscopy and by terahertz pulsed spectroscopic imaging.
Abstract: The absorption spectrum of the explosive 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) has been measured using a conventional Fourier transform infrared spectroscopy and by terahertz pulsed spectroscopy. Seven absorption features in the spectral range of 5–120cm−1 have been observed and identified as the fingerprint of RDX. Furthermore, the spatial distribution of individual chemical substances including RDX, has been mapped out using reflection terahertz spectroscopic imaging in combination with component spatial pattern analysis. This is the terahertz spectroscopy and chemical mapping of explosives obtained using reflection terahertz measurement, and represents a significant advance toward developing a terahertz pulsed imaging system for security screening of explosives.

699 citations

Journal ArticleDOI
TL;DR: Terahertz time domain spectroscopy was assessed as a nondestructive evaluation technique for aircraft composites and showed that burning did not change the refractive index or absorption coefficient noticeably, but material blistering was detected.
Abstract: Terahertz time domain spectroscopy (TDS) was assessed as a nondestructive evaluation technique for aircraft composites. Damage to glass fiber was studied including voids, delaminations, mechanical damage, and heat damage. Measurement of the material properties on samples with localized heat damage showed that burning did not change the refractive index or absorption coefficient noticeably; however, material blistering was detected. Voids were located by TDS transmissive imaging using amplitude and phase techniques. The depth of delaminations was measured via the timing of Fabry-Perot reflections after the main pulse. Evidence of bending stress damage and simulated hidden cracks was also detected with terahertz imaging.

323 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of shunting in the framework of the Dyakonov-Shur plasma-wave theory was theoretically studied, with the following key results: in the quasistatic limit, the capacitive shunt induces the longitudinal high-frequency field neede...
Abstract: In search of novel detectors of electromagnetic radiation at terahertz frequencies, field-effect transistors (FETs) have recently gained much attention. The current literature studies them with respect to the excitation of plasma waves in the two-dimensional channel. Circuit aspects have been taken into account only to a limited degree. In this paper, we focus on embedding silicon FETs in a proper circuitry to optimize their responsivity to terahertz radiation. This includes impedance-matched antenna coupling and amplification of the rectified signal. Special attention is given to the investigation of high-frequency short-circuiting of the gate and drain contacts by a capacitive shunt, a common approach of high-frequency electronics to induce resistive mixing in transistors. We theoretically study the effect of shunting in the framework of the Dyakonov–Shur plasma-wave theory, with the following key results. In the quasistatic limit, the capacitive shunt induces the longitudinal high-frequency field neede...

315 citations