Non-destructive detection of pigments in oil painting by using terahertz tomography

Zhang, Zhenwei; Wang, Kejia; Lei, Yong; Zhang, ZhuoYong; Zhao, Yang; Li, ChenYu; Gu, An; Shi, Ningchang; Zhao, Kun; Zhan, Honglei; Zhang, Cunlin

doi:10.1007/s11433-015-5744-x

Cited by 17 publications

(7 citation statements)

References 6 publications

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“…It should be mentioned that, to help estimate the transmitted nonlinearity, we use two references in our method, which is hard to achieve for some cases, like FMCW automotive radar detection [40]. However, most of the ultrawideband THz FMCW radars, which are more vulnerable to the nonlinearity problem, are often used in the specific scenarios, like in the nondestructive testing [1,6,7,[14][15][16] and standoff personnel screening [10][11][12]26], where testing the two references beforehand is easy to achieve [10,12,15,25,26].…”

Section: ) Nonlinear Phase Compensation For the Beat Signalmentioning

confidence: 99%

“…Terahertz (THz) testing is a novel and promising measurement technique which offers new solutions for artworks conservation [1][2][3], products quality control [4][5][6][7][8][9], and standoff personnel screening [10][11][12][13], etc. This technique allows for the contactless and high-resolution inspection of both the object's surface and inner structure at any production stage and even in field use [2,3,6,7,10,14,15]. With the demanding requirement of achieving highresolution range profiles, the linear frequency modulated continuous wave (LFMCW) chirp is extensively exploited to transmit large bandwidth signal [6,7,[10][11][12]16], and the deramping technique is adopted for range processing to dramatically reduce the sampling frequency [6,[10][11][12]16].…”

Section: Introductionmentioning

confidence: 99%

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A Non-Linear Correction Method for Terahertz LFMCW Radar

Zhang

et al. 2020

IEEE Access

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The nonlinearity in terahertz (THz) linear frequency modulated continuous wave (LFMCW) radar usually blurs the range profile and decreases the signal to noise ratio, hampering applications where high range-resolution is particularly emphasized. A software correction method, which comprises of transmitted nonlinearity estimation and nonlinear phase compensation for the beat signal, is proposed in this paper to drastically reduce the nonlinearity in THz LFMCW radar. Besides the commonly considered nonlinearity caused by voltage-controlled oscillator (VCO), the nonlinearity from other broadband hardware devices have also been included in our modified correction model, which gives the advantage of preciser compensation. Moreover, utilizing the phase gradient autofocus (PGA) method to estimate the transmitted nonlinear term and the residual video phase (RVP) removal method to remove the range dependency of the received nonlinearity, our method can uniformly compensate the nonlinearity in the whole range profile. In addition, no presupposed parametric model for the nonlinearity waveform is needed, which further strengthens the effectiveness of the proposed method in practical use. Both the simulated data and the real tested data, acquired by a 190 GHz radar with 60 GHz bandwidth, has been used to demonstrate the validity and the effectiveness of the method. INDEX TERMS linear frequency modulated continuous wave (LFMCW), nonlinearity correction, phase gradient autofocus (PGA), residual video phase (RVP) removal, range profile, terahertz (THz) radar.

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Section: ) Nonlinear Phase Compensation For the Beat Signalmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Non-Linear Correction Method for Terahertz LFMCW Radar

Zhang

et al. 2020

IEEE Access

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“…As one of the last mastered frequency ranges of the electromagnetic spectrum, the THz band provides great potential for modern imaging methods which have been widely applied in other spectral regions [6][7][8][9][10][11][12][13][14][15]. Notably, THz imaging techniques can be applied in various fields, such as security screening [16,17], non-destructive testing [18][19][20], biological detection [1,21], and data-rata communications [22,23]. The implementation of such imaging techniques is influenced by various source types with fundamental generation differences [24].…”

Section: Introductionmentioning

confidence: 99%

Terahertz Spiral Spatial Filtering Imaging

Liu

Zhao

et al. 2021

Applied Sciences

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In this paper, we propose a terahertz (THz) spiral spatial filtering (SSF) imaging method that can enable image contrast enhancement. The related theory includes three main steps: (1) the THz image of the target is Fourier transformed to the spatial spectrum distribution; (2) the spatial spectrum is modulated by a spiral phase at the Fourier plane; (3) the filtered spatial spectrum is inverse Fourier transformed to the desired THz image. Meanwhile, analytic expression of the final THz image is derived. Due to the unique nature of the spiral phase, THz image contrast enhancement can be achieved and verified by various simulated target images with different contrasts. In our designed THz SSF imaging system, Fourier transform is carried out by the lens, and the spiral phase is acquired by the spiral phase plate (SPP). Proof-of-principle experiments with three different types of targets (carved metal letters, a high-density polyethylene (HDPE) piece with a scratch, and a leaf) were carried out, and the effectiveness of contrast enhancement and edge extraction on the THz reconstruction images was validated.

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“…Terahertz time-domain spectroscopy (THz-TDS) is a new THz spectrum measurement technique based on ultra-short pulse technology developed in recent years, which has been widely applied in the fields of physics, chemistry, biology, etc. [22][23][24][25][26][27]. The physical and chemical parameters of tested objects, such as the complex dielectric constant, dispersion coefficient, transmission, and absorption, are usually obtained by THz-TDS, and the material composition and structure of the tested objects can then be studied.…”

Section: Introductionmentioning

confidence: 99%

Nondestructive Testing of Hollowing Deterioration of the Yungang Grottoes Based on THz-TDS

Feng

Meng

et al. 2020

Electronics

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Terahertz (THz) spectroscopy is an important method in noninvasive detection and diagnosis for historic relics. A new nondestructive testing (NDT) method based on terahertz time-domain spectroscopy (THz-TDS) technology was developed to measure the hollowing deterioration of the Yungang Grottoes in this paper. Hollowing deterioration samples were strictly prepared, and a series of experiments were conducted to ensure the representativeness of the experimental results. A hollowing thickness model was established by the relationship between the thickness of the hollowing deterioration sample and the time difference of the front flaked stone surface and the stone wall surface of the hollowing deterioration samples. The results show that the R-squared value of the model equation reached 0.99795, which implies that this model is reliable. Therefore, the actual hollowing thickness of the Yungang Grottoes can be obtained by substituting the time difference in the proposed thickness hollowing model, where the time difference is obtained from measured THz spectra. The detection method of stone relic hollowing deterioration is easy to apply, which can not only realize qualitative NDT but also quantitative hollowing deterioration thickness determination. This method has crucial practical significance for the repair and strengthening of stone relics similar to the Yungang Grottoes.

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Non-destructive detection of pigments in oil painting by using terahertz tomography

Cited by 17 publications

References 6 publications

A Non-Linear Correction Method for Terahertz LFMCW Radar

A Non-Linear Correction Method for Terahertz LFMCW Radar

Terahertz Spiral Spatial Filtering Imaging

Nondestructive Testing of Hollowing Deterioration of the Yungang Grottoes Based on THz-TDS

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