Thickness characterization of multi-layer coated steel by terahertz time-of-flight tomography

Zhai, Min; Locquet, Alexandre; Roquelet, Cyrielle; Ronqueti, L. Agrizzi; Citrin, D. S.

doi:10.1016/j.ndteint.2020.102358

Cited by 25 publications

(7 citation statements)

References 38 publications

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“…The terahertz wave generated by the photoconductivity is a transient pulse signal, and the typical pulse width of terahertz is approximately 1ps, therefore the terahertz pulse can be used for timeof-flight tomography [4,5]. For opaque multi-layer structures in the visible-light range, the penetration of terahertz waves can be used for non-destructive thickness detection, to achieve the transversal resolution of tens of microns (Figure 2).…”

Section: Terahertz Window Materialsmentioning

confidence: 99%

Design and Application of Optical System Based on Terahertz Time-of-Flight Imaging

Wang¹,

Liu²,

Wang³

et al. 2021

Int J Opt Photonic Eng

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Using the penetration and transientness of Terahertz pulses and the photoconductive delayed detection method, the tomographic imaging of the interior of the object based on the time of flight can be realized. By comparing the transmittance of several crystals and polymers in the Terahertz band, Polymethylpentene (TPX) was selected as the material of Terahertz lens, and High Resistivity Float Zone Silicon (HRFZ-Si) as the material of beam splitter; By comparing the focal depth of normal incidence and oblique incidence optics system, the normal incidence optical system was used to realize time-of-flight imaging; Using the idea of optical-mechanical integration, the corresponding optical camera is designed according to the normal incidence optical system, and the peak-to-valley map and thickness map of the Lithium cobaltate coating of aluminum foil were obtained by time-of-flight imaging, and the defects such as complete shedding of the coating and uneven thickness were observed. The results show that the normal incidence optical system can realize Terahertz time-of-flight imaging and is applicable in the industrial nondestructive testing field.

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Section: Terahertz Window Materialsmentioning

confidence: 99%

Design and Application of Optical System Based on Terahertz Time-of-Flight Imaging

Wang¹,

Liu²,

Wang³

et al. 2021

Int J Opt Photonic Eng

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“…To overcome these problems, various algorithms have been developed [ 13 ]. Recently, Chen et al used the Wiener deconvolution method to process the terahertz echo signal to improve the signal time resolution, but the method is less effective for the thin layer [ 14 ].…”

Section: Introductionmentioning

confidence: 99%

Accurate Characterization of the Adhesive Layer Thickness of Ceramic Bonding Structures Using Terahertz Time-Domain Spectroscopy

Yang

Zhang

et al. 2022

Materials

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Ceramic adhesive structures have been increasingly used in aerospace applications. However, the peaks of the signal on the upper and lower surface of the adhesive layer are difficult to measure directly due to the thin thickness of the adhesive layer and the effect of the attenuation dispersion of the ceramic layer. Thus, the existing non-destructive testing techniques have been ineffective in detecting adhesive quality. In this paper, the thickness of the adhesive layer is measured using terahertz time-domain spectroscopy. A sparse deconvolution method is proposed for the terahertz time-domain spectral signal of ceramic adhesive structures with different adhesive layer thicknesses. The results show that the methods proposed in this paper can realize the separation of reflection signals for glue layers with a thickness of 0.20 mm. By comparing with a wavelet denoising method and a modified covariance method (AR/MCM), the effectiveness of the sparse deconvolution method in estimating the thickness of the glue layer is demonstrated. This work will provide the theoretical and experimental basis for using terahertz time-domain spectroscopy to detect the homogeneity of ceramic adhesive structures.

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“…Moreover, as non-ionizing radiation, in contrast to ultraviolet light and x-rays, THz waves at the relevant powers present no known health risks to biological tissue. Due to these advantages, THz-based techniques have achieved success in a variety of fields, such as heritage science [1][2][3][4][5], steel industry [6][7][8][9], as well as biomedical applications [10][11].…”

Section: Introductionmentioning

confidence: 99%

“…Let us consider how these conflicting demands have been met. For the former case of optically thin layers, vast effort has been exerted to separate overlapping echoes, such as frequency wavelet-domain deconvolution (FWDD) [1,6,12], sparse deconvolution (SD) based on iterative shrinkage/thresholding (SD/IST) algorithm [2,13,14], autoregressive spectral extrapolation [8,15,16], numerical fitting combined with a rigorous one-dimensional electromagnetic model [17], advanced regression with a self-calibration model [18], and Hilbert transform together with multiple-signal spectrum estimation [19]. The second case, viz.…”

Section: Introductionmentioning

confidence: 99%

Terahertz Nondestructive Stratigraphic Analysis of Complex Layered Structures: Reconstruction Techniques

Zhai

Citrin

Locquet

2021

J Infrared Milli Terahz Waves

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Terahertz (THz) time-of-flight tomography (TOFT), a nondestructive-evaluation technique for the stratigraphic characterization of structures with layers on the micron-to-millimeter scales, has proven to be challenging to apply to samples containing both micron-scale and millimeterscale layers. In THz TOFT, echoes reflected from distant interfaces and defects are often obscured as they may be immersed in a noisy background as such features in the reflected signal may be weak due to attenuation and dispersion, leading to the loss of valuable information. Moreover, overlapping echoes from any optically thin layers, such as thin coatings on thick specimens, are likely to be mistaken for a single interface in reconstructing the stratigraphy. Thus, layered structures containing both thick and thin layers have proven problematic for THz TOFT characterization. In this paper, a sparse-deconvolution (SD) technique, based on an interior-point method, and including a propagation model accounting for dispersion is demonstrated. The method is shown to be successful in extracting the impulse response of samples that combine the challenges of both thick and thin layers. The robustness and effectiveness of this method are verified numerically and experimentally. While the SD approach does not perform quite as well as cross-correlation (CC) techniques in terms of maximum thickness, it can provide a clearer and more accurate reconstruction of moderately thick samples incorporating thin layers.

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Thickness characterization of multi-layer coated steel by terahertz time-of-flight tomography

Cited by 25 publications

References 38 publications

Design and Application of Optical System Based on Terahertz Time-of-Flight Imaging

Design and Application of Optical System Based on Terahertz Time-of-Flight Imaging

Accurate Characterization of the Adhesive Layer Thickness of Ceramic Bonding Structures Using Terahertz Time-Domain Spectroscopy

Terahertz Nondestructive Stratigraphic Analysis of Complex Layered Structures: Reconstruction Techniques

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